01/10/03 PLANS vs. HP WINGS

Kevin, I plan on working on the wings components first. In reviewing the price list, the wing wood kit is listed under the HP wing section. I would like to clarify that this kit is interchangeable between the HP and the stock version. Regards, Remi
Remi, The HP wigs can be used on a stock fuselage. Same is true the other way around. Attach points are the same. HP wing require HP struts, wires and ailerons. Stock wings all the same in stock form. So, when considering one set of wings or the other, keep in mind that these are wing "systems" and have to use all the parts of the system. Both styles of wings can be installed on either fuselage without adjustment. We have airplanes flying and being built with various combinations of HP and stock parts.

If you want the HP wing wood kit yet want to make as much of the wing metal as possible, you can do that. Much of the wing metal is the same as stock. There are some parts that are different like drag wires, and pushrods but for the most part, builders are able to figure these out with a bit of guidance from us.

We sell some wing metal parts to scratch builders. Items like cabane fittings and top wing compression members are popular.

As I mentioned to you earlier, you can mix and match between purchased items and scratch built items. We do not force you to make an all or nothing choice. As you get into the project and find a component that seems tough to build, call and get a price on it and see if the trade off of price to labor is worth it to you.

We do offer some stock version specific items for those who are building stock airframes. Items like spar blanks, engine mounts, fitting sets, flying wires, etc are all available. In addition to these items, we offer the items that are common to both versions such as gear, wheels and wheel pants, engine installation components, cowling, etc. KK


What is a safe way to perform flutter tests? Someone once told me to "slap" the stick to the side during cruise flight, but what's the difference between induced flutter and un-expected flutter? - Doug
To perform flutter tests, start at the lower speeds and check all 3 axis. Increase 5 mph at a time until you have checked to Vne + 5. The drill is to trim the airplane for a lower speed, dive thru the check speed then release the pitch. When the aircraft noses up thru the desired speed, excite the control to be checked with a brisk input. The idea is that the airplane is moving towards a slower speed which has already been checked. It is best to do this in smooth air. Also, flutter is a function of True Airspeed, so it is more valid to perform these tests at lower altitudes. Make sure you have a fresh packed 'chute on and aren't afraid to use it. - Monty B
Here's a scan from AC 23.629-1A.   Flutter Curves   These are flutter curves for a control surface, and should help you understand what you're trying to do (or avoid) when you flight test for flutter. You hope your airplane behaves like curves (1) or (2). Curve (3) would be scary, but would probably damp merely by taking a firm grip on the stick. Curve (4) may require a parachute.

When you nose up thru the desired speed and excite the control to be checked, allow the stick to be quite loose in your hand. Note curve (3). Let's suppose the test speed is just past the zero crossing on the velocity line. With the stick loose in your hand you'll feel it nibble, which is your warning that you are reaching possible flutter speeds. If you hold the stick tight and thus damp the surface at this just-barely-into-instablity speed, you may miss the warning. So you preceed to the next faster speed (farther to the right on the velocity line), and when it flutters it will be more violent.

Consider the mass damping effect of control linkages and your hands, and you can see why slack (freeplay) in control linkages and trim surfaces is a Bad Thing.

The steep upslope of curve (4) is what makes it dangerous. No warning at a slower speed, explosive flutter at the next higher speed. - Dan H


Sorry for all the confusion on the weight limits for the Pitts Model 12. Here is the run down on how all these puzzle pieces fit together....

The airplane, both stock and HP have the same ultimate and limit G ratings. This is the case even though the HP airplane is stronger than the stock version which gives the HP wings, for example, greater margins of safety. The airplane was designed at a gross weight of 2300lb. All ultimate and limit load calcs were done at this 2300lb gross weight. Curtis lowered the published weight to 2250lb for an added 50lb fudge factor knowing that many people will fly the airplane at slightly over gross. This is where the 2250lb number comes from.

The ultimate G loads for the model 12 are +9, -7.5g at 2300lb(2250lb published).
The limit G loads for the model 12 are +6, -4.5g at 2300lb(2250lb published).
The acro G loads are the same as the limit loads at the same weight of 2300lb(2250 published).

So, this means the airplane is designed to break at +9 and -7.5g at 2300lb. The airplane is designed to see unlimited number of cycles at +6 and -4.5g at 2300lb without and structural over stress.

Mid America, the previous plans holders, placed the 1900lb figure into the mix. This was intended to be noted as a typical acro weight not a max acro gross weight. Typically, 1 person, fuel, smoke oil, chute etc will weigh in at about 1900lb. Typical for competition or airshow work. 1900lb is not a max acro gross.

You can fly the Pitts model 12 at full gross weight to +6, -4.5 g and not damage the structure. This is the big leap this airplane has over others such as the skybolt or S2B. Acro at full gross weight is not allowed. You must be under the acro gross which in the case of these other aircraft presents the issues you raised of not being able to have 2 people, chutes and gas and be legal.

It is interesting to note that you can place higher than +6, -4.5 gs on the model 12 if you fly at weights of less than 2300lb(2250 published) without hurting the airframe. However, these higher loads are not listed as it may encourage pilots to fly at high Gs while at standard G weights.

The model 12 was designed and flight tested to fly as advertised at the weights above by Curtis Pitts. A skybolt, on the other hand, was originally designed by a high school shop teacher for a max gross of 1650lb and an empty weight of around 850-900lb. It soon was bumped up 1800lb gross and then again to 2000lb gross while maintaining the same non structure. Most 540 skybolts weigh over 1300lb and some as much as 1550lb leaving very little room for people and gas at gross weight. Even if you use the 2000lb currently spec'd gross, the acro gross is still 1650lb as before resulting in 100lb acro useful for many skybolts out there. How do guys fly them if this is the case? Simple. Over gross. A 540 lyc and constant speed prop on a skybolt is like hanging an R985 450hp PW and Hamilton standard prop on a model 12. Too heavy for the airplane.

I hope all of this has eased your concerns on the weights and loads for the Pitts Model 12. When I ran my computer analysis of the structure, I found that the fuselage was a +/-10g structure. The wings were just a tick better than +9 and -7.5.

When I designed the HP wings, I increased strength in them in the areas of designed failure at ultimate loads. This increased the max load capacity of the wings to more closely match the fuselage and tail. The HP wings are +9.8, -8.7 wings at 2300lb. KK


What are the differences between the Kimball HP fuselage & wings versus the plans versions, and how did the changes evolve?
First, let's clear up what it takes to be able to make the changes I will be discussing here. If you are an engineer with design experience in Tube/Wood/Fabric structures, you are qualified to develop and make the type changes we are discussing here. If you do not have these qualifications, you are shooting from the hip without proper knowledge and that can be dangerous. This is why most airplane plans state in them or the related agreements that builders are to follow the plans precisely or use the approved components available for purchase. It keeps the builder from making tragic errors. So, in the case of the model 12, Dad and I were qualified to make the engineering changes in the airplane and went back to Curtis Pitts to have him double check what we did. Pretty safe.

What brought on the changes? In 1995. Curtis gave Dad and I a 3-view of the Model 12. This was before the first part was made and all the design work was not yet completed. At that point, the 3-view was of a short nosed "Cocky" looking biplane and we loved it. As a matter of fact, that original 3-view had the airplane shorter than what we now produce as the HP version. Anyway, we got a picture in our head of what the airplane would look like. In the end, the engine mount had to be quite a bit longer than Curtis had thought in order to get the CG correct. Not that this was a major error on his part, but as the final drawings were being done, he stretched the fuselage, rearranged a few things etc and knew the mount would be longer than the original 3-view. The result was a fine looking, very strong, great flying airplane that all plans holders can build with the data as it is printed. But, for Dad and I, it was NOT the look we had in our heads. This lead us to determine how to get the look the way we wanted and make some creature comfort changes along the way. The result is the HP version of the fuselage and engine mount.

Now the wings are a different story. Ben Morphew test flew the model 12 in acro test for Curtis. He loved the airplane and wanted one RIGHT THEN. We did not know him at the time but later Ben told me that he would have bought the prototype from Curtis if it rolled faster. So, Ben decided to build a model 12 but wanted better wings and ailerons. I designed them to meet his requirements and also be stronger and lighter. Again, I had Curtis as a mentor during this process. The resulting model 12, N69BM, was built by Ben and had the first set of HP wings. It was the first customer 12 to fly and 2nd overall. The wings worked perfectly so, we kitted them. Ben's fuselage was built to full long plans length, engine mount too. Take a look at the photos of the 2 model 12 together in Budd Davisson's EAA article. It is hard to see the difference isn't it?

As for performance between the 2 versions, yes, the HP wings roll faster and work better in hover type figures. Yes, the larger rudder is better in acro than the plans rudder. But, the fuselage/engine mount changes result in such small differences in how the airplane works, that it would take an acro pilot with lots of time in one version to sense the difference when flying the other assuming the wings were the same on both versions. N69BM and N360KJ were flown together quite a bit by two of the world's best pitts drivers, Ben Morphew and Steve Wolf. Both will tell you that the fuse length change does not affect how the airplane flies. I take that as a compliment to me, it means I didn't screw it up!

Now, I agree it ain't rocket science here and that the stuff we did is not special or really tough to do. But, the simple things can add up to bigger problems down the road. Most do-it-yourselfers or first timers do not see the big picture in a project like this. A change to the fuselage in one plane may seem simple enough and not a big deal either way. But, later you find out that a control component will not work or the specified bearing won't work now because the rod runs into something else. Maybe, you can't get full aileron deflection because the pushrod binds up. These are the little things that can become HUGE whe you shoot from the hip.

There are 2 or 3 model 12 builders out there creating their own version of the short fuselage. In the case of Darin's changes, he asked me what we did. I told him it was about 5" in the fuselage and about 5" in the engine mount for a total of about 10" shorter fuselage/mount. He created his fuselage layout on his own but I gave him a few hints of what not to do. Darin's fuselage is not the same as the HP frame we sell and obviously not the same as on the model 12 plans. I don't think he had an analysis done on the fuselage to see if the changes he made resulted in satisfactory load paths but chances are the paths are OK. When we did our changes, we not only changed the length of the fuselage but rearranged some of the controls, changed some tubing sizes etc to create a complete engineered package. This is what we sell.

So what do we recommend to builders? Simple. If you are gonna scratch build, follow the plans as they are drawn. Buy our fitting package for the fuse and tail which will allow you to make a either a small tailed, rounded version of the long fuselage or a lean looking version with the big tail as Ben's was. It gets you the lean look without the guess work. If you want to buy parts, you will get the HP version as we do not kit the plans version.

Up until now, we have not given out specific dimensions for the HP version parts other than a weight and balance diagram for both versions of the model 12. We have a few reasons why we hold the HP data to ourselves and why we freely sell the stock version of the plans. When we entered into the model 12 biz, we had no intention to sell plans. Curtis told us NOT to do it as the never ending phone calls would drive us crazy with questions like, "can I use these bass boat seats" or " I've got a set of luscombe tail feathers I want to use", etc. He said the backyard "in-guh-nears" can really make a mess of things. So, we went the route of developing tooling and prefab parts.

At that time, we did not own the rights to the model 12. Mid America Aircraft did. They decided to sell plans and maybe supplement that later with parts sales. They looked at several sources for parts manufacture in the US and abroad but never really got that going. We made a deal with them to sell parts only to those who had a serial number and plans from them. This way, they sold plans, we sold parts, the desired activity for both parties. Later, the priciples of Mid America decided to sell the rights to the design and plans. We bought it from them. We thought about what to do with the plans sales and after considering halting the sale of plans, decided to continue selling the Mid Am plans as they had already sold around 100 sets. The plans "horse" was already out of the stable so why not continue selling them. After all, even scratch builders have to buy some parts like gear, wires, canopy etc. We did not want to have 2 sets of data out there for builders to confuse, mix and match. We also wanted to protect the investment we had in both time and money developing the HP versions of the model 12. So, we opted not to distribute plans for the HP version which would minimize the danger of someone mixing and matching the wrong parts. Heck, we made all our tooling so we could build both version of the model 12, stock and HP but have yet to sell a stock fuselage as those who decided to buy a fuselage wanted the HP version anyway. We have built stock tail parts, stock engine mounts etc and sold those to plans builders.

To sum it up, we know there are scratch builders who will copy the HP parts, even directly by copying some from a kit buyer. That is to be expected in this biz. Heck there are those who would rather copy a set of plans from another person instead of spending $300 for a lifetime of support. Silly really. Just keep in mind that YOU need to know what you are doing if you choose to change a design not simply THINK you know. If developing a sound design were easy, the email groups we take part in would all have 1 member........... the designer/biulder/owner/pilot of one of the ump-teen jillion airplanes that would be out there. I know I have spent a lot of time here on this but I felt it was needed to make sure we are all on the same page. Enjoy building, have fun, make the airplane in your style and flair but don't make changes for change sake without proper backup. Smile, build something everyday and always fly safe. KK


If considering aerobatic competition with the Model 12, up to what class would it be effective?
We tried to get the Model 12 accepted as AWAC legal. AWAC is the Advanced World Aerobatic Championships. So, when evaluated by the numbers, the model 12 came out too good for AWAC legal. It ranked as WAC legal. This was determined in 1999 I have the full reports with each of the approximate dozen points that were compared to the other designs. The HP/weight ratio, thrust to weight ratio, Vne speed, etc. etc.

Obviously, the Model 12 is not on par with a Sukhoi or Edge 540. But, it is capable of far more than some of the other sport bipes in the same size class. Keep in mind that there is world class unlimited flying and there is local IAC unlimited flying. I have seen S2As and other smaller or older designs compete in Unlimited. You can complete in whatever you want but that doesn't mean you are competitive. The model 12 is capable of competing and winning locally in unlimited but would not be truly competitive with world class pilots in world class monoplanes. The model 12 is capable of winning in Advanced yet it is too powerful for world level advanced competition at this time. Its Rock >> << Hardplace. KK


Guys, Beware this got long!! I have seen the posts on the subject of the "SS" ailerons. I would like to take this chance to clear up a few details on this subject.

First, the name. These are not actually called "SS" ailerons. That name had come from the Late Hale Wallace and his version of these ailerons for the S1 wing mods he came up with a few years ago. Hale got the rights to the S1C Pitts from Curtis and this may have been a trade for wires or something. I don't know really. But, Hale and now the new guys, have the S1C design rights only. Not all of the S1 versions as it was hinted in one of your posts. The S1S and S1T are still held by the pitts factory, now Aviat Aircraft or its holding company. Hale come up with the SS title to indicate Super Stinker style ailerons and not use a single "S" like the Aviat owned design. He put together a set of drawings for symetrical airfoil wings with the new style ailerons and offered these as an update to the "C" model plans he had for sale. I think he went on to stretch the fuse of the "C" to meet that of the "S" and "T" versions. Not sure on that one though. Oh yeah, back to the name thing............These ailerons are actually, "Aerodynamically Boosted Ailerons". The first design Curtis used them on was the Super Stinker model 11-260. The second design was the Model 12. The 3rd design Curtis used these ailerons on was the new S2C wings for Aviat. I have have used them on 7 designs so far. The redesign of the model 12 wings and ailerons, Steve Wolf's WolfHawk wings, a super cub like bush plane for a friend, Frank Ryder's Cyclone, Sean Tucker's Challenger, Jim LeRoy's Bulldog, and The Mc Cullocoupe. I will use them on other designs as well. As a point of interest in the time line, I designed the alum ailerons for the model 12. Following that, Curtis did the same for the S2C.

Curtis has often done contract design work for others. Doing the design of the ailerons for Aviat, Steen or whoever is no big deal. I too have done work for others in the same industry. It only makes sense to go to the best source for the technology vs. hacking your way through it on your own. When I do design or engineering work for others, a full endorsement of their products is not automatic. I can like what I do for them without liking the entire project. I am sure this is true for some of you and most likely Curtis as well.

I think Randy brought up the old style Fat ailerons from the mid 80's. This design is NOT the same as the ailerons being discussed here. That FAT ailerons were over thickness by 16% at the hinge line, had thick trailing edges and had extra chord length aded to increase total aileron area. This design did improve the roll rate of the airplane but, all the features had to be used as well as good size spades to reduce forces to the point that the pilot liked them. Yes, the over thickness was there to keep the air attached. That was the first step in Symetrical aileron, or round nose aileron design and is exactly what is on the S2B, Husky etc. Over think and round nose. The wing cove is constant gap to the nose of the aileron. When this was first done to the S1S moving away from the freise style ailerons, the stick forces were so high that at speed, the airplane was not fun to fly (I get this info directly from Curtis and others who were in the know at the time). So, the spades were added copying what the Chechs had done on the 526 Zlins for aileron boost(yes spades were someone elses idea). Ben Morphew, a good friend of mine was the person who pointed Herb Anderson of the pitts factory toward the spade idea. So, stick force problem fixed but the ailerons lost center feel which is important for precise acro. This is where the fat trailing edges came into the game. These added some center feel by keeping the 'bleed' from the bottom high pressure side of the wing up and around the trailing edge making the center position of the aileron feel mushy. The added length to the chord simply adds affective area.

Now, back the the aerodynamically boosted aileron as used in the super stinker and model 12, as well as others. This is a system not just an aileron that can be bolted to a given wing as a replacement part. There is a set of formulas to define the thickness, leading edge radius, leading edge camber, hinge location all as a function of the chord length of the aileron and the thickness of the wing airfoil at the chordwise point where the aileron hinges. The upper ailerons are different than the lowers. Another huge key point is the cove shape in the aileron bay. The cove is the area where the aileron fits in the wing and there are critical gaps required between the cove and the leading edge of the aileron. One gap and full deflection. Another at neutral. There is a required radius of curvature of the cove as well as radius of the edges of the cove where it meets the upper and lower wing airfoil surfaces. This is only the requirements. Not the design. With all this in mind, the structure has to be designed to meet all these factors and be strong enough for the required flight loads. My point in writing all this is that the new style ailerons cannot be hap-hazzardly installed in a given wing structure. Rather, the wing structure must be designed to accept the ailerons.

Do I have all the data and formulas to design such aileron systems? Yep. Can I use it on whatever I want? Yep. Can I give it out to everyone who wants it? Nope. Curtis asked me not to. He can but I won't.

This style of aileron with its deep hinge line, airfoil shape, etc is not new. It is on the tail feathers of most jets, on other acro airplanes like sukhois, extras, cap's etc. The big difference is the cove. The cove is the key to what makes Curtis' version work the way it does. I hope you guys have enjoyed this little Aileron 101 course. KK


See http://av-info.faa.gov/dst/amateur/

AC20-27E, Certification and Operation of Amateur-Built Aircraft, This AC provides information and guidance in the building, certification and operation of amateur-built aircraft.

AC20-139, Commercial Assistance During Construction of Amateur-Built Aircraft, Explains FAA regulations and policy regarding commercial assistance during the fabrication and assembly of amateur-built aircraft.

AC21-12B Application for U.S. Airworthiness Certificate, Form 8130-6 (11/2001) word version

AC90-89A, Amateur-Built Aircraft & Ultralight Flight Testing Handbook , This AC sets forth suggestions and safety related recommendations to assist amateur and ultralight builders in developing individualized aircraft flight test plans.

AC65-23A, Certification of Repairpersons (Experimental Aircraft Builders), This AC provides guidance to builders of amateur-built aircraft concerning their certification as repairmen.

AC39-7C, Airworthiness Directives, This AC provides guidance and information to owners and operators of aircraft concerning their responsibility for complying with airworthiness directives (AD) and recording AD compliance in the appropriate maintenance records.

AC103-7 The Ultralight Vehicle, This advisory circular provides guidance to the operators of ultralights in the United States. It discusses the elements which make up the definition of ultralight vehicles for the purposes of operating under Federal Aviation Regulation (14 CFR part 103). It also discusses when an ultralight must be operated as an aircraft under the regulations applicable to certificated aircraft.

FAA Order 8130.2D Airworthiness Certification of Aircraft and Related Products dated 9/30/99 (with Change 1 incorporated 2/15/00 and Change 2 incorporated 12/18/00) establishes procedures for accomplishing original and recurrent airworthiness certification of aircraft and related products, including amateur-built aircraft. The procedures contained in this order apply to both Aircraft Certification Manufacturing and Flight Standards Airworthiness Aviation Safety Inspectors, and to private persons/organizations delegated authority to issue airworthiness certificates and related approvals. Chapter 4, Section 1 provides general guidance material associated with special airworthiness certification. Chapter 4, Section 7 provides specific information for special airworthiness certification of experimental amateur-built aircraft.

Forms: AC Form 8050-88 (PDF) Affidavit of Ownership FAA Form 8130-12 (MS Word) Eligibility Statement: Amateur-Built Aircraft FAA Form 8130-12 (PDF) Eligibility Statement: Amateur-Built Aircraft FAA Form 8130-6 (PDF) Application for Airworthiness Certificate or, electronically completeable word version


A recent email exchange with a model 12 pilot flying off his 40hr test period prompted me to remind you guys of some of the requirements. With acro airplanes in the US (Canada different & rest of world too I am sure), you have to perform all acro figures during phase I (test period) that you want the airplane to be legal to do in Phase II (all flying after test period). So, do all the acro figures you can and list them in the log book after each flight. List the figures once along with entry speeds, etc. If you do a loop, list it but don't list it again if you loop in a later flight. Only the acro you do in phase I is legal to do it phase II. If you (or a test pilot) don't do everything, you will have to go into a new test period to add the acro to you list of approved maneuvers.

Before you sign the airplane into Phase II, you should list all the figures that your actual airplane has flown (not what you know others have done in theirs). For example: take off and landings, xwind TO and landings and wind speeds demonstrated, stalls, loop in and out, roll slow, barrel, point, vertical, snaps L&R pos and neg, spins upright and inverted L&R, knife edge, inverted flight, tumbles (Lumcevak), rolling turns if you do them, hammer heads, stall turns, cuban 8, lazy 8, tailslides, torque rolls, immelmann(sp?) etc etc. List everything.

I have heard that entry speeds are now required to be listed too. It is a good idea anyway as the next guy to fly your plane will know what to do and not do in the thing.

While we are on the subject of logbooks, it is a good idea to list some of the following items in the airframe book: fabric system used, # coats etc, paint used, brand, color code etc. primer type varnish type etc. It sure saves some headaches later............

And don't forget that if you use an aircraft part that has an AD on it, you need to comply with the AD even if your airplane is exp homebuilt. That is, ADs on engines, mags, props, radios, lights, wheels, whatever. If you have an experimental engine that is based on a lyc (modified lyc), you sill have to deal with any lyc ADs on the lyc parts that are in it. It only makes sense. If there is an AD on a type of mag because it is unsafe, the AD should be complied with no matter what airplane it is bolted to so the airplane is safe. Of course, if you have an exp engine (auto, m14petc), exp prop (Whirlwind, exp wood ones etc), you don't have ADs on them. But, you have 40hr test instead of 25hr.KK


Bill, Insurance costs vary with the hull value you pick for the airplane and with the agency you use. As an average, lets say $170k for hull value. You are looking at about $4k per year for insurance. If liability only, you are looking at about $300-$500. If you add open pilot, acro competition, or airshow coverage to the hull costs you can add another 10-10% for each of these.

Some insurance companies will not offer hull coverage until 10hrs are flown off unless the airplane is flown by an EAA flight Advisor who is qualified in that airplane. The trick with one-off airplanes like some of them in this group, how do you find a person with experience in that type of airplane? Any pilot can become a flight advisor if he/she is an EAA member and can fill out a form. Likewise a tech Councsellor, just fill out a form and fax it to EAA and you are one. I had always thought there was more to it but when we finished N80JR, AVEMCO required an EAA flight Advisor do the first 10hrs, so, Dad and Steve Wolf filled out a form off the internet, faxed it in and in a matter of hrs, were flight advisors!!!

A model 12 built by an ameteur is required to have a 40hr test period. This is true for any homebuilt that is in Am Built catagory if either the engine, prop or both are experimental!!! So, ALL airplanes in the US that are Amateur built with an M14P or other variation of it, will have 40hr test periods!!! I have heard that some builders have gotten away with a 25hr period but this was due to the DAR making a mistake. There is NO room for interpretation of this requirement. 40 hrs is the law if a non certified engine or prop is used.

Not in the case of Experimental Exhibition catagory, the test period is at the discretion of the FAA (DAR can't do it) Inspector who can set the test period from zero to infinite # of hrs depending on what he sees and feels.


I'm stuck in enhanced class B, and can only fly with a CFI. With more time on my hands, I took a bunch of pictures of my Pitts 12 yesterday in the sunny weather, and now I'm posting a report on it, for those of you who might be considering building or buying one...

If you were at OSH 2001 you may have seen N80JR; it was the purple and black round-engined bipe by the registration shack in the IAC area. It got a lot of positive comments from various people, both knowledgeable builders and unfamiliar tourists alike. Steve Wolf and I flew it there from Florida and we had a great time with it.

The plane is in the "Exhibition" category as it was built 100% by the Kimballs, who are well known for their restoration work. They sell complete sets of component parts for the Model 12, such as finished fuselages, wings, rib kits, cowlings, gear, etc. They will also sell plans alone for the person who likes to do all the work himself.

Some history on how I ended up with this plane:

In 1979 I built a Quickie, and that experience convinced me that although I like building things, I did not ever want to tackle a 4000 hour project, particularly not one that involved so many different skills, where a shortage of one talent could poison the whole project.

For 25 years I have wanted a Pitts, but a) they were a bit small and b) they had flat engines. Then in 1985 I saw Steve Wolf's SAMSON re-creation in Sport Aviation. *This* was what I wanted, a Pitts with a Great Big Round Engine! I (incorrectly) assumed that having such a plane constructed would be many times the cost of a new S2, so I did nothing more than daydream about it.

Fast forward 10 years, and I see Curtis has designed a new Pitts around the Russian M14P. Looks great, but I'm not going to build it myself.

Then, a year or so later, I see that the Kimballs have negotiated to sell plans and subassemblies. Further, the design has been refined (by the Kimballs and Curtis working together) for more roll rate, a better canopy system, and other improvements. People are building them all over. It is beginning to look more and more like a round-engined Pitts might be in my future. I call Steve Wolf (flying the Kimballs' demo bird in airshows) to ask about how it flies. He tells me it is very close to Samson, and definitely better in roll rate and inverted flight. He says maybe he could build one for me, but to call Jim Kimball first and check his schedule.

I do and am quoted an 18 month delivery date for a turnkey 12, at a price a bit less than a new S2 from Aviat.

This is what I want to hear. I ask Jim how much a smoke system would add to the cost. "Oh, that's standard." I go test-fly the demo plane (purple and yellow, now owned by Keith Campbell in Atlanta) and it is the best airplane I have ever flown. I go ahead with the order.

My plane is finished in July, on time and at the price quoted. It is gorgeous. My own contribution to its construction is limited to helping lay out the panel and designing the paint scheme. Steve Wolf spends 2 days doing the 10-hour fly-off and flight test regime, and the next day we take off for Oshkosh.

Since then, I've put about 40 hours on it. Here are my impressions:

It is a real delight to have an airplane that does exactly what you tell it to do. In order to wring the last few percent "performance" from the unlimited-class monoplanes, designers have made these craft behave in ways I would not tolerate; i.e. let go of the stick and push left rudder in level flight and the nose drops and the plane rolls RIGHT. Pull the stick back and then you have to start pushing because if you let go the elevator will go to full deflection. There is none of this in the Pitts. Controls are light, but you don't have to unlearn normal flying techniques, just refine your smoothness.

With that whacking big Russian radial hooked to the the 3-blade MTV, thrust is magnificent. I'm not proud; I decided immediately I was always going to go around if I didn't like how I had set up my landing. This plane is the king of the go-arounds. Flare a little high and realize it's dropping in from 4 feet? Full throttle and it stops 3 1/2 feet off the runway and starts climbing like a rocket. There may be other planes that do this equally well but I have never been in one.

Aileron design (now also used on the Super Stinker) is boosted, and adverse yaw is almost undetectable. The elevator is boosted just enough that forces are always modest. The rudder, according to some aeronatical engineers, is much too big. "Yeah, but my planes all come out of spins right away," Curtis has been quoted as saying. He's not kidding. Using the Beggs emergency recovery technique, the spin seems to stop the instant that opposite rudder comes in.

Knife-edge flight is wonderful (much better IMO than a monoplane), and the Model 12 will climb over 1000 FPM at full gross in this attitude(!)

From 240 mph, you get a half-mile of vertical and seven vertical rolls, for those of you who like going straight up.

Cruise 175 mph at 8500 feet and 14.2 gph.

Perhaps the benefit I like best about this plane cannot be quantified, and that is the peace of mind I get flying behind a zero-time (REALLY zero-time) radial. The crankshaft on a 540 Lyc is as long as my arm, while the one on The M14P is as long as...something a lot shorter. Engines with long cranks don't like hard acro, esp. tumbling maneuvers. I don't think a lifetime of aerobatics (by me) is going to shorten the TBO of this engine. I would not say the same of a flat motor.

Other construction benefits are Wolf plywood leading edges instead of aluminum (stronger with smoother fabric adhesion) and cantilever ribs instead of plywood as on the new Aviat S2C. (Will there be a wing rib AD on the S2C a few years hence? Remember what the factory always said about Sparcraft...?)

Last of all, the way it looks! An S2 looks downright homely next to Samson or the M12.

Things I'd change? MAYBE two: Having landed tailwheel-first on a number of occasions, I can't help but wonder what would happen if the tailwheel were 6"-8" higher. Drag on rollout would be greater, requiring less braking. The other is that 99% of my flying is at positive Gs. I'm 44 years old, and Curtis admits he designed the Model 12 as an "old man's airplane." This old man thinks he MIGHT prefer the conventional wing used on Samson (forget the number, same airfoil as a Bonanza IIRC). Better low speed characteristics and even more climb right side up. Wouldn't have the bragging rights, but... Don't know if anyone else would choose a flatwing 12, but Steve Wolf wants to build anotherSamson, and he intends to make it with 4 ailerons but the same conventional wing as the original. That got me thinking. I'd have to fly both and see.

If you're considering ANY 2-place conventional biplane, take a long look at this one. You'll be getting the absolute best biplane technology in existence, and the finished product will probably bring three times the amount on the used market that an equally hard and expensive to build Skybolt or Starduster would fetch.

No, the Kimballs don't pay me. On time, on budget, and flawless workmanship deserve a testimonial. John Ross


Regarding the original 3-view I have for the Model 12 as Curtis first conceived it. This 3 view is what his first thoughts of an M14P powered Pitts biplane were. It has been a while since I looked at it so I pulled it out and found some interesting stuff there. Interestingly, one copy I have of it was given to Dad and I in 1996 at SNF when we had the Gee Bee there. We had Curtis sign it then as a keepsake. This was a year or more before Dad and I ever gave a thought to building an M14P powered biplane. Interesting facts:

Length: 19ft 3in
Height: 7ft 8in
Span Upper: 23ft
Span Lower: 22ft 3in
Total Area: 152.8sq ft
Wing Loading: 13.08 PSF
Gross Weight: 2000lb
Datum: 50 in. aft of firewall
CG Range: 65.624 to 71.712

The wings and tail look pretty much exactly as they do on the stock plans version of the model 12. The fuse is short and maybe even shorter than what we build as the HP short fuse. The engine mount is shorter than can possibly be built, approximately 10" long. The next itteration of sizing thew airplane resulted in a 164" long fuse and a 14" mount. The final version was 169" long fuse and 23.75" mount.

Another feature I see here is that the fin is offset like the super stinker instead of the engine mount having offset thrust in it. The SS has a straight engine mount and offset fin to fix the torque. When the model 12 was fully drawn and designed, the fin was changed to straight ahead and the engine mount was changed to have 2 deg left side thrust, zero down. This works perfectly and is not ugly as heck like the fin to turtle deck joint on the super stinker. The WACO we put the M14P on has a straight mount and straight fin. It takes all the rudder that big WACO has to keep the airplane straight on takeoff just like a Nanchang yak does. The Model 12 with its 2 deg offset takes less left rudder on takeoff than an S2B takes right rudder on takeoff. It works perfectly. Curtis hit it just right. I suggest you M14P powered airplane builders use 2 deg offset left on your mounts.

I'll try to get a digital pic of this 3 view and post it for you to see. It is kinda cool to look at.

This 3-view shows a very short nose and represents the mental picutre Dad and I had for what the model 12 would look like. Then it grew the longer nose for reasons of both equipment location and CG. That's why Dad and I felt the stock airplane had a nose that was too long. We expected this nose. That led us to rework the fuse to get the look we wanted.

The final interesting fact is when this 3-view was drawn by Curtis. It was done on 1-5-1993. That's 8.5yrs ago! Goes to show you that it takes a long time to get from idea to airplane if you take all the required steps to get there (first flew in 1996, a little over 3 yrs after this 3-view). KK


Jim,  I remember the white homebuilt with the R670 but I thought that it was a Starduster Two.   The engine weighs 465 lbs dry without a startor or alternator and that is 100 lbs heavier than an IO 540 and you still have the weight of the oil tank, startor, alternator and that big propto add.   It makes the engine package 200 lbs heavier and that is hard to make up.  You might have noticed that he mounted the engine as far forward as he could and he still had to add a lot of lead to the tail.   That what makes me think that you fellows that are putting the M-14 in your Skybolts are going to be disappointed unless you make many modifications to the airframe.  Power is only one element of a good performing ship.   Wing loading and some other things are there too.  Believe me I am not trying to be a wet blanket.  It is just my opinion as an almost fifty year pilot who has flown about everything from a Midget Mustang to a DC-3.  When we started our Skybolt we gave a lot of thought to a radial engine and the M-14 was one that we considered.   We talked to a lot of people, including the fellow with the R670, and in the end decided that radials were either too heavy, not enough power or both.   If I could have found a 185 hp Warner I might have gone with that.   It is a quite light engine. (about 335lbs but you still need to add all those goodies.   I am officially off my soapbox.  Keenflyer 
The white one was a Skybolt but it did not have the craftsmanship of the red one.  Somewhere I might have a picture of it.  C.G. is definitely a concern and maximum wing loading is mostly a function of gross weight (partly of distribution as well).  I'm analyzing the airframe for a 2000 pound gross weight.  The wing cellule looks marginal.  So far I have a 3% margin of safety on the aft wire for a 9g ultimate low angle of attack condition.  I've not finished looking at the rest of the wing structure.  You're right about major structural modifications to employ an M-14.  As far as CG goes I've moved the pilots aft quite a ways - same relative position as that of Kevin's version of the M-12.  Here's my reasoning.  There's not much difference between the Skybolt and the Model 12 from an aerodynamic perspective - same airfoils, gap, stagger, and tail volumes are close and they have very nearly the same wing area (151 sf for M-12, 159 sf for 'Bolt).  The wings of the Skybolt are of comparable weight, therefore if a Skybolt wing cellule is mounted on a fuselage configured like a M-12 such that it's aerodynamic center is in the same position as that of the M-12 wing cellule the CG should work out and performance should be basically the same.  My airplane is neither a Skybolt nor a M-12.  My fuselage is structurally based on the M-12 and the tail is my own design.  There are structural concerns of course but I'm comfortable addressing them.  The 'Bolt wing will never carry the  2300 pound gross weight capability of the M-12.  That's okay.  I will simply determine a safe acro gross weight and a safe standard category gross weight.  I can't see myself wanting to tear up the sky at full gross weight.  Again, what you say is true, bolting an M-14p to a stock Skybolt airframe without careful modification and consideration is borrowing trouble.  Compromises abound: less useful load, higher landing speed (for increased gross weight), poor visibility, higher operating cost, longer build time (oh man!), untested nature of modifications, etc.  

If I did it again, I would build a M-12 with round surfaces. It's stronger, it's well thought out, and it's made for my engine.  In fact, I would highly recommend the M-12 to anybody interested in a round engined biplane.   From a sportplane standpoint, mods are best kept to aesthetics.

Warner...yeah we considered both a 185 and a 165.  Two problems with this: marginal power for a Skybolt and availability of parts.  I discussed this with Hale at Bartlesville about 5 years ago and he begged us not to mount Warners in the Skybolt.  In fact, he had photos of Culp's airplane and he suggested a similar approach - but only if we could live with it's limitations.  He still thought the fixed pitch 260 hp Skybolt was the best biplane you could build.   Jim Doyle  Stress Analyst
Gentlemen,   Jim's comments are well said.

I've been bugging you guys for accurate weights, examining different plans sets, and digging for Russian engine info.  I've been asked why I'm going with a Skybolt, and I haven't said much.  I guess it's time to spill what I've been cooking.  Comments are welcome.  Please.

Some of you are aware of previous attempts at creating a lighter, direct drive version of the M14 series engine.  The M14P is well known, but there are several other variants.  The common ones seem to be the M14B, which was used on a transport, and the M14V-26, which was used (in pairs) in a helicopter.

The best know previous attempts at direct drive involve taking the nose case from an M-3 (a direct drive 3-cyl radial of 110 hp) and bolting it to an M14 or Huosai core.  This was the original basis of the Culp/Bloomquist Sopwith engine package.  Same main engine case bolt pattern, so it's simple to do.  Ron Bloomquist is flying two of them on WW1 replicas.  They're working fine (at limited hours), but he doesn't flog them very hard.  Not much gyro load, not much HP.  The problem with the M-3 conversion is that it has no front bearing behind the prop flange.  Prop loads are carried by the crankshaft, the front crank roller bearing, and the thrust plate ball bearing.  According to the engineers in the Old Country, none of these parts were ever intended to see this load.

I understand Steve Culp designed (or commissioned) some sort of direct drive front case and shaft that included a proper bearing for the propeller loads.  I know nothing about that setup.  I've asked him about it, but all I get is "Aw, you don't wanna do that, just beef up a Skybolt and bolt on a M14P".  Ok.

Here's the latest news.  George Coy had the engineers in Romania design a direct drive setup.  He will intro the new "M14D" at OSH, complete with a cutaway engine for his display.  Not a giant secret.  I can't be the only one who knows, and George says I can talk about most of it.  The first engines arrive next week.  I've more or less spoken for one.

The base engine is a Romanian overhauled M14V-26.  Same overhaul as the M14P engines from the same source.  They will come with western fluid fittings, the full dress kit, Champions, silicone wires, tool kits, spares and pretty blue paint.  Yeah, blue.

The old right-angle helicopter gearbox gets tossed.  The new drive system includes a proper set of support bearings, and the output shaft matches the standard 20-spline found on round Continentals and similar.  The prop hub is a copy of one typical for wood props on a 220 Continental.  The nice thing about this hub is that the front crush plate is splined to the hub, so driving friction is applied to both the front and the rear face of the wood prop.  Big 'ole hub.

George sent the engineers a custom carved Sensenich for the dyno work.  It's a copy of a Stearman prop but left-hand rotation.  All the dyno work has focused on a 220 hp @2000 RPM application, sort of a 220 Continental replacement package.  It's doing great in that configuration.  I have dyno plots, etc, and the numbers are fine.

Now the plot thickens.  When George told me about it a few weeks ago, he was focused on the above application, not sportplanes.  My thoughts were more performance oriented.  Take a close look at the M14P manual.  It's 360HP for 5 minutes, at least if you do like the Russians say you should.  After that it's the "Nominal 1" power setting, 2400 RPM and 290 HP for continuous operation.

Ok, with one exception, there are no internal differences in the M14P and the M14V cores, at least not that we know about at the moment.  The exception is the cam plate.  The "V" reportedly makes about 260 HP at 2400.  It's perfectly possible to swap the cam plates, something the engineers suggested when asked.  That would bring it up to the 290 HP level.  It's also possible to install the PF-model blower gears <g>.

Here's the important part:  The first engine was weighed at the end of the assembly line.  Weight was reported at 450 lbs with the mount ring, compressor, and all accessories except generator.  We don't think that included the exhaust, but hope springs eternal.  George doesn't have a actual hub weight yet, but I've derived 19 lbs pulling geometric shapes from AutoCAD drawings.  That includes the prop bolts and the shaft nut.  An 80" P-tip hard maple/composite from Prince is (according to Mr. Prince) 15 to 17 lbs.  That totals 486.

If we use the M14P book numbers and the weights supplied by my friends here, the apples-to-apples comparison would be 470 lbs, plus 6.5 (compressor), plus 6.5 (mount ring), plus a little more for the "fine filter".   The V530 prop is 90 lbs with bolts.  Total is 573 lbs.

The difference is 87 lbs, all of it very much firewall forward, with a vast reduction in prop mass moment effects.  Other auxiliary systems (air, oil, etc) woud be the same for both.  The drawback is a fixed pitch prop.  No question a constant speed would be a better performer.  On the other hand, fixed pitch is cheap and almost maintenance free.  No overhaul costs.  There are no significant tip speed issues.  The M14 itself should last a long time when prop-limited to about 2500 RPM.  No planetary gears, no prop governor, no pressure seals.

Nobody seems to have a really accurate direct drive IO-540 weight.  Published weights for base engines start at 402 and run to 476, but I don't know for sure what is included.  For this discussion I'm gonna use the AEIO-540-L1B5D.  Most guys want the heavy case for acro, and it's the only one that includes an inverted oiling system. Published weight is 476 lbs, plus perhaps 15 for a lightweight wood prop, so you have 491 lbs.  Yeah, I know, nobody is gonna put a FP wood prop on an AEIO-540.  It's just an example.  I'd be tickled to death to hear from somebody that has actually hung a 540 on a scale and knows what was included. 

So, there you have it.  My plan is a lightweight, more or less "normal" Skybolt that happens to have a round engine.  Same structural concerns as a fixed pitch IO-540 Bolt, so without "beef-ups", hopefully similar empty weight.  With 290 HP and a light airframe, I won't be very far off the big horsepower guys.  Close enough for this dumbass country boy anyway.  My goal is 1300 lbs max.  Everything will get the "Rutan test", so I hope to do better.  My gram scales have taken a prominent position on the workbench.

My airframe is a very nice unfinished early Skybolt project, complete with wing kits, tanks, fittings, all the wires, wheels, the works.  Not expensive, enough said.  Fuselage was well done, not much to change.  I wanted to build my own wings.   I'm not a trusting soul.

Disclaimers:  George will weigh the package when he gets it in his hands.  Until then, weights are unconfirmed.   If the weight craps out and comes in heavy, all bets are off.  It's pointless.  I'll do something similar to Jim's plan, or sell the project and start over. The engineers have not dynoed the "sportplane" setup described above, only the 220 HP "Continental replacement" package.  They plan to be at OSH, and we'll talk more then.

I'd like to take the opportunity to thank all concerned with this list.  The archives have been a tremendous asset, and the opportunity to be in contact with serious builders is priceless.  It's been quite a learning curve.  Not finished yet, I'm sure.  Sorry to be so long-winded.  Comments?   Dan
...I didn't say it couldn't be done.  It's risky, in my opinion, without some sort of structural assessment. Even mild acro can lead to high g loads.  If he operates at published Skybolt gross weights (1650 acro) he'll probably be okay assuming that the higher "working" loads from the heavier engine don't cause fatigue failures in the engine mount lugs or fuselage longerons.  I say "probably" because he almost certainly had to add weight to the tail to get the airplane to balance properly to get the CG envelope to work out.  A large concentrated weight in the tail would further increase the load on the fuselage longerons during maneuvers.  Anyway, structures are sometimes forgiving, stress guys are usually conservative (and opinionated), and ignorance is always bliss. Jim Doyle  Stress Analyst


The FAA inspection of your homebuilt is quite simple.  The inspector will not look at the airplane until it is completely finished, covered, painted, assembled and test taxied.  They will look at the paperwork, markings and tags as well as the general appearance of the airplane.  The really don't care much about how it is built.  An airplane that exhibits a minimum of fair quality exterior workmanship will not create enough doubt in the mind of the inspector that the workmanship is poor inside.  If you use a DAR to get your A/C, the requirements will, in all likelihood, be even more lax.

My point here is that you, as the manufacturer, must be satisfied that your work is of the required quality.  The inspectors will basically check off that fact that YOU think it is good to go.  To quote a friend of mine with respect to making info avail to the feds......."No need to burden them with that information."  KK
The DAR that did my inspection did just about what Kevin described. He had me mail him copies of the paperwork so he could check all that before he made the trip to see the airplane. I had glue and weld samples, but he never requested them. He spent about 1/2 hr looking over the airplane, had me run-up the engine while he looked at engine gauges. He did take a good look at my weight and balance figures. Charged $300, ate lunch, gave me a temporary certificate and was on his way.  Bill

360 HP vs. 400 HP, M14P vs. M14PF

Jerry Guy asked me about the results of the 360hp M14P vs 400hp M14PF head to head flight tests.  At SNF, we had a chance to fly the 2 model 12s against each other.  The results were quite interesting.  Seems our 360 powered model 12 was able to get a jump on the other one at each start, level or climbing.  The 400 one was never able to catch up and the pilot of the 400 was to one to call the end of each race.  So, unless his airplane is 400lb heavier than he says it is and it is rigged real bad, I'd say the 400 vs 360 thing is a wash if you use the same size prop and same airplane...............

Now, as I see it, almost every time someone has changed to a 400hp engine on a Sukhoi or whatever, they also put the larger diameter prop on.  We put the big prop on Jeff's sukhoi and 360hp engine and it made a huge difference in static thrust and hang time without the added hp.  So, I am not sure what the gains are from the extra $8000 for the PF engine other than to be able to say you have it.  These tests were not formal in any way so the results may vary if someone else does it.  

So, why not more of a speed difference gicen that the model 12 easily hits 260mph in a slight dive at cruise power?  I have a theory or 2.  First, lets say the PF makes 400 hp at 41" MP like the book says it does.  What if the rings can't hold back the added cylinder pressure and most of the added squeeze blows past the rings at combusiton?  Or what if the whole thing is a ploy by the russians and the engine dealers to get more $ from us with little invested.....  The 400hp PF engine has been around since the late 80s early 90s and it was not on any russian national world competition team airplane thru the mid 90s.  If it was such a big improvement, why didn't they use it?

I know we have customers that want the 400 engine.  That's ok.  I'll use one because I got a good deal on it and it will add value to the airplane in the eyes of some.  But, the 360 is a good, solid, known quantity that is shown reliable for many years.  The PF is relatively untested thru time. KK


I just got done looking at the skybolt vs. model 12 prices.  Now, this is based on SNF 2001 prices on the Model 12 and SNF2000 prices (the price list avail this year from SAL with a caveat that the prices are not current).  I included the cost of the plans for each too.

If you go thru the SAL list and pick out the items that best add up to a near complete Skybolt kit, you will get $35,307.50.  But this does not include all the items that are in the Model 12 full kit.  This price total of SAL products has more 'kits' and less prefab items like we have.  Like the Canopy for example.  I found several items that we include that they do not.  They are:  Gear Cuffs, all fuse alum skins pre cut and bent, front cockpit headrest bulkhead, fully assy t-deck, fully assy alum ailerons(they hint that they are forth coming), a full cowl instead of a nose bowl only, rudder cables, trim cables and rods, and canopy assembly labor.  If you use the current price for our version of the above items in place of the non published SAL price, the total goes up to $43,434.50.  I find this to be a virtual wash to our $46,388.00 when youfactor in the extreme high quality of our parts in comparision.

Now, lets say a composite 3 blade prop for the 540 bolt and Model 12 each costs $11k.  That's a wash.  The engines to compare have to be both acro engines to be fair and should be of near the same HP.  That means a Barrett or Lycon AEIO 540 Lyc hopped up to a range of 325hp to 375hp.  That'll cost you $45k to $75k depending on what you get.  If you choose a brand new AEIO 540 Lyc of 300hp like in an Extra, that'll cost $55k.  The $15.5k for M14P or or $20k for M14PF is a bargain.

If I total up the complete kit, prop, engine, engine install stuff, covering, instruments, radios, paint, etc I get $100,500.00 for the skybolt with a $45k engine.

The same pile for the Model 12 I get $89,000.00 with the M14P $15.5k engine.

Now, I know that most of those building a bolt will not buy a top drawer engine but rather use a cheaper o/h unit.  Heck, probably a cheap prop too.  But, I wanted a true comparison.  KK


I've decided to obtain a set of those outstanding S1 plans I've heard about to improve my understanding of Pitts designs. Now, there are different choices: As far as I know Aviat sells "S-1S" plans, SAL sells "S-1C" plans, "S-1SS" plans and "symmetrical wings" plans. I'd like to hear about the differences of the above plans sets and would really appreciate some tips which one to get.    -Tom
I've seen the SAL S-1C plans and they look nice and include some full sized non-dimensioned drawings.  In addition, some very useful isometrics are included. I have not bought a set...yet.  As for the Aviat S-1S plans, they are factory plans.  Everything is there, but some of the non-dimensioned drawings are not full size.  They've been ECN'd/updated over the years and they are quite thorough.  In my opinion, they are definitely worth the money.  If I were going to build a Pitts I would get both.  If you just want a reference I'd get the Aviat plans.   - Jim
The S1T is an updated airplane based on the S1S.  S1S was factory built and certified.  S1S has been homebuilt as well yet in many cases until the 80's, a homebuilder was not allowed to call his an S1S by the FAA.  Most opted for S1X or S1SX etc.  The S1T his a 200hp constant speed prop for power vs the 180hp fixed pitch on the S1S.  To fix the added weight of the 200hp/const spd, the top wing on the T was moved forward.  The S1T has symetrical ailerons like on the last 10-15 S2A and all S2B airplanes.

S1C has flat bottom wings with the M-6 airfoil.  The S1C has a shorter fuse that the S or T models.  The C has pin type tail hinges like the skybolt copied rather than the more desirable strap type hinges used on A,B, C, Super stinker, Model 12 etc.

Yes, as far as I know, you are correct that the S1SS drawings from SAL are for the wings only.  These drawings show sym airfoils like on the S1S, super stnker etc as well as a version of the ailerons developed by curtis for the super stinker model 12 S2C etc.  The C had flat bottom airfoils.

$250 is a real bargin!  My copy is of great reprint quality compared to the Super stinker plans I have.  Many of the Super Stinker plans I have a nearly unreadable.  KK<
While I agree with Denis that the Pitts Model 12 plans are nice, they require some understanding of aircraft construction to use them and do not have any info on general systems.  These general systems details are addressed in our kits.  The Super Stinker plans and th efactory S1S plans, both avail from Aviat Aircraft, have lots of system info.  Heck these even show all wiring and labeling. Very detailed.  The Current Skybolt plans are a very weak 14 pages.  Factory S1S, Super Stinker, Model 12 are all over 40 sheets.  I do not know what level of detail or number of pages are avail in the firebolt or S1C plans from SAL.   So, if you are interested in having help with systems, etc. get the S1S or Super stinker plans from Aviat.  KK
S-1C  Flat bottom wing, one set ailerons, 1 seat 180hp fixed pitch
S-1S  Symetrical wing, two sets ailerons, 1 seat 180hp fixed pitch
S-1T  Symetrical wing, two sets ailerons, 1 seat, 200hp, constant speed
S-2A  Symetrical wing, two sets ailerons, 2 seats, 200hp, constant speed
S-2B  Symetrical wing, two sets ailerons, 2 seats, 260hp, constant speed
S-2C  Modernized S-2B, some aerodynamic and ground handling improvements
S-2E  The kit version of the S-2A, AVIAT sold these.
S-2S  I think its like a 1 seat S-2B, i.e. bit lighter


Here is the run down on Model 12 that have flown so far.

1.)  Black Prototype by Curtis Pitts N80XP
2.)  Ben Morphew N69BM Red one (later lost in crash by new owner)
3.)  Ours, the Yellow and Purple one N360KJ now N360KC
4.)  Neil Forsyth of South Africa ZU_BXX
5.)  Phil Bohner yellow and Purple (the one in Darin's poster)
6.)  Phil Bohner Chromalusion with some yellow.

Now, as you can see, Phil has 2 spots on this list.  #5, the one in Darin's poster made several flights the last of which ended in a landing that came in contact with a 2000lb large round hail bail causing the airplane to tumble over.  It was severely damaged but Phil and pax got out unhurt.  The insurance Co. totaled it and Phil was gonna buy it back and rebuild it.  But, the ins. co. was taking too long with it and Phil wanted to fly NOW!  So, he bought a Model 12 project that was already underway with wings etc. covered.  He bought it in September I think and it is finished already!  He plans to buy the wrecked one back from the insurance co. and rebuild it.  He sure LOVES the Model 12!!!!

Other news is that Phil is planning on having his new 12 at SNF and Keith Campbell is planning on flying N360KC to SNF too.  So, we will have 2 there.  I expect 2 or 3 more to be done by Oshkosh this year.  We have one in the shop that will be complete in about 2.5 months.  IT will most likely be # 7 to fly and then I expect, 2 or 3 from Daytona to be done, 2 from Canada to be done, 1 in Mississippi to be done too.  I can't wait to be able to see a line of them at a flyin!  I'll be able to walk amung them like a proud papa!!!    KK


The Model 12 airframe is designed for up to 450hp.  Curtis knew someone would want more hp on it so he planned ahead.  The airframe, as you can see from the drawings, is far more robust than that of most other designs that are of similar size and type. KK


The changes we made to the Model 12 from the original vary in reason.  I'll address the hows and why of each here so others can have the info too.

First, the orignial 3 view of the Model 12 by Curtis showed a very short nosed airplane.  Curtis gave us a copy of this 3 view in 1995 signing it for us and planting the seed of the Model 12 in our heads. He and the 'boys' built the airplane from the firewall aft complete and weighed it and the firewall forward unit separately.  Curtis used these weighed to determine the proper location of the engine for CG reasons.  As it turned our, this was 10" farther forward than the pre design 3 view showed.  So, for everyone who looks at the stock Model 12 who never saw the original 3 view, it looks exactly right. Dad and I had the misfortune of knowing the original snub nose look and then decided to we had to shorten the fuse a bit to try and get closer to the 1995 3view.  We soon realized that there was no way to get the nose as short as it was first drawn and that only about 5" could be taken our of the mount length without having to use bent or curved engine mount tubes like Steve Culp did on the green special.

Next I had to determine how far aft to move the wings to get the balance correct again for the CG.  As it turned out, the fuse is about 5" shorter too.  I say about because both are not exactly 5" change.  When you move the wings aft, the FW and all wing related and gear related stations move with them.  The length of the fuse was done to please us.  WE wanted to improve the look of the side view.  In addition to the length change, we eliminated the pot belly look.

The performance of  a model 12 with  long fuse vs a short one like we sell is virtually unchanged.  I think it would take a supreme being to actually tell the difference between the 2 in flight.  So, fuse length = no performance difference.

The wings are a different story.  This was the next thing to get a redesign by me.  In April 1996 right after SNF that year, Ben Morphew did all the hard acro and spin tests in the Black airplane (prototype model 12) for Curtis.  He fell in love with it as at the time he owned the prototype one design, the prototype Super Stinker (model 11, 11-260, S1-11B).  He is one of the world's best airshow pilots according to people like Sean Tucker.  Anyway, Ben would have bought the black airplane if it rolled a bit faster.  It rolled faster than an S2B and bunches faster than an Eagle, S2 A or skybolt but Ben had been flying the other planes mentioned above as well as Sukhois etc.  SO, Curtis said build your own and Ben agreed.

Ben hates wood work and called us to see if we would build him a set of 12 wings as we were already building stuff for ours.  We said yep and He and I became great friends before ever actually meeting face to face.  Ben had a list of requirements for the wings.  Reduce the span from 23' to 22', bigger ailerons, 3 hinges per aileron, square tips.  I combined his desires with mine which were a smooth center section, slave rod aft of I strut and ailerons made of aluminum.  We beefed up the wings in key areas too all the while reducing the weight of the wings and ailerons by over 20lb from the plans version.

With the new wings designed, we had to redesign the tail for 2 reasons.  One to make them look like the wings (square corners).  And two, to get the tail volume coefficients back to the correct #s. You see, the tail size, both horizontal and vertical are a function of many dimensions of the wings.  SO, when the wings change that tail must change if you want the new system to act like the old one.  The end result is the control of the HP vs stock is mathmatically identical.

We went on to clean up or improve many other systems or components for the Model 12 all in an effort to please ourselves.  AS it turns out, many others like what we did and began to buy our parts. Our fuselage jig is designed to build both long and short fuselages yet we have never built a long one.

A few guys like Darin and 3 more in IL have built their own versions of the short frame.  That's ok with us.  Builders can build the entire airplane from scratch or mix and match kit and scratch parts to suit your talents or pocket book.  The fitting set we sell is the same set we use for the HP version and includes the tail ribs etc.  As Bud or Darin and a few others can tell you, it is well worth the price of $500 flat laser cut or $755 fully bent ready to weld.  Some have purchased our ailerons to use in scratch built wings making the mods needed to fit them in. So, as you can see, anything goes in our program.  You decide the cost/benefit of each item as it applies to you then let me know what you need from us.   KK


Just got my Kitplanes Kit issue.  Here is a point by point comparison of the listings for the Culp Special and the Model 12 as printed in the Kitplanes Mag. Top speed of the 12 determined using FAA FARs for certified A/C.  Special not.  Should be the same as the Stock Skybolt. Actual Cruise speed of 12 shown for 15.8gal/hr burn.  Actual cruise speed for Special is 150mph. Stall of 12 calculated and tested to be 64 mph.  70 mph stall of Special seems high. Range of 12 is 525 miles with 30 min reserve on 54gal standard fuel. Range of 600 miles shown in Special listing required 70gal fuel no reserve.   Green Special has 38 gal total fuel.  Blue one more. Rate of climb of 4500 on Special listing is estimated when engine was set to 4000rpm.  ROC at 2950rpm much less.  12 ROC measures  at 3300fpm at gross for several minutes, take off and landing distances are similar. 

Engines same. Fuel Capacity mentioned above. Empty Weight 1470 of Special before cowl, pants, smoke system. Empty Weight of our 12 is 1472 complete with smoke system, all parts as shown in pics.  Number completed and flown 5 Model 12s 3 Specials if you count the single place Russell plane as one of the 3. Rest of list as you see it.

Kit price of special higher than 12 kit if you take out the $3500 canopy, and a few other things to get apple to apple component camparison. Cost to build:  Ours actual number with new engine and new 3 blade MT prop, full instruments and radios, etc.  Can build a 12 for less than $70k with o/h engine, 2 blade prop, few instruments etc. 

Plans for the Model 12 are 44 sheets D size CAD generated plans. Special plans require purchase of Skybolt plans, PLUS purchase of Special supplemental drawings for the mods to the skybolt structure.  Skybolt plans are only 14 hand drawn sheets C size(half size of Model 12 plans).  Supliments are a few hand drawn sheets I think.

Keep in mind that the Culp Special kits Steve now offers are Model 12 fuse, tail, controls modified to accept skybolt wings and gear.  We build the frames for him 3 so far.  He has his fuse kit price the same as we do for the 12.  Steve an I are good friends and we share/team up on many things for the various airplanes we build.  Like finding special items, making parts etc.  He has just found it more efficient to start with the 12 structure and round it up a bit rather than shoehorn the M14P into the bolt structure.

The short of it is this..........The mags will print whatever you give them without verification.  It is up to the kit or plans provider or manufacturer to back up their claims with the builders.  Time and time again, airplanes are listed faster, longer range, lighter than they really are.  We decided years ago NOT to lie or stretch the truth to our customers and this has gained us a reputation of being straight up and honest in the industry.  We continue this with the Model 12 program as it is with our restoration biz.  Expect this with our 2 new offerings, the McCullocoupe and the Raptor A.S. both Non-biplanes......(sorry)  Kevin


Group, take a look at the October 13 issue of The Flyer on the cover and on page 41 for a story on the Model 12 written by Doug Hinton.  Also see the new Custom Planes December 2k issue page 56 for a story on reading blueprints.  Wayne Scraba, a Model 12 builder, wrote this story and uses his Model 12 plans as the subject.  Kevin


Bret, the big rudder does make quite a difference on Pitts type airplanes, S1s S2s (S2C has bigger rudder than S2B).  Granted, for most the stock rudder is OK. INTERMEDIATE!!!  Hmmm.  The Model 12 has competed in Advanced so far and scored well.  Most of the competitor types who are building them are aiming at advanced.  Some for regional unlimited.  The airplanes capabilities are such that is is on the "too good to be allowed list" for Advanced World Aerobatics Contest, AWAC.  The Model12 has aerobatic capabilities beyond that of the Eagle or skybolt.  The Model 12 IS that type of aircraft.  But, like with a high performance car, you don't have to use all of it if you don't want.  A great number of our builders either have had eagles or do have them.  Many have S1s or S2s.  All know the Model 12 outperforms their existing/past airplanes and are moving up.   Kevin


Mike, good to hear from you on the subject of M-14P powered biplanes.  This group has several builders of M-14P powered modified skybolts.  Andy, Bill V. and others.  I noted a few items in your email to me and some of the posts to the group by you and others on this subject.  I'd like to address a few points here if I may. 

Andy pointed out that the gross weight of the Skybolt is 2000lb.  To date, the lightest M-14P powered homebuilt bipe I have heard of is 1472lb empty as you see it in all the photos with smoke system. It is our Yellow and Purple Model 12.  Steve Culp's modified Skybolt called the Culp special is 1477lb empty plus, cowl, wheel pants, ply covered wings added later etc which add up to an empty weight of over 1500lb with no canopy.  I estimate Andy's plane will weight over 1550lb.  So, if you go by the 2000lb gross, you have 500lb useful based on a1500lb empty.  You said you are just under 300lb leaving 200lb for the front seat, fuel and oil.  Min fuel is 30 minutes or about 10gal =60lb.  Oil is 3.5 gal or 21lb leaving 119lb for baggage and front seat person.  Most of the M-14P powered skybolt builders are raising the gross weight to allow for two people and gas.

The Model 12 has a gross weight of 2250lb standard as compared to the 2000lb gross of the 'bolt.  So, you start at 1472 empty, 300lb for you, 200lb front pass,  leaves enough room for 46gal of gas.  Typically, the model 12 can be loaded with two 220lb people, 54gal of gas, 40 lb baggage and be at gross weight.  So, you can  actually fly the airplane at typical loadings and be within the design limits of the structure.  The model 12 is stressed to an ultimate load of +9, -7.5 gs at full gross weight of 2250lb.  I don't know if anyone has done the numbers for a skybolt at 2250lb to see the g limits there.

I think you have the wrong idea of the size of the model 12.  It has larger cockpits than a skybolt.  This ain't no S2A.  The amount of floorspace in a hangar for a model 12 and a skybolt is nearly identical.  We have 6'4" 300lb guys building Model 12s because they fit in much better than a skybolt.  Heck this year at oshkosh, I sat a 6'5" 325lb guy in the 12, closed the canopy with 1.5" to spare over him, he had full range of controls, and his sides didn't hit the longerons.  The 12 is wider than the skybolt at the rear seat.  Curtis Pitts designed the airplane for big guys.

Basically, you can fit into the Model 12 without mods unilke the changes you mention you will need in the bolt.  You should try on a model 12 before you commit to the project.  You will be surprised.  Let me know where you are in the country and I 'll hook you up with a Model 12 builder nearest to you. 

Keep in mind that you will not be able to just bolt the M-14P onto the stock skybolt frame.  The frame will have to be shortened up front, cabanes reworked, firewall moved aft, beefed up, etc. to fit the M-14P in.  The green culp has the oil tank in the aft fuselage to be able to balance the airplane.

The Model 12 has constant chord wings.  It also has the latest in wing and aileron technology.  The bolt and the 12 share the same airfoils as the rest of the symmetrical pitts series wings. 

There are countless times I have heard......."If I hadn't started the skybolt already, I'd be building a Model 12!"  Some in this group have said that.  Heck Steve Culp himself now buys Model 12 fuselages, tails etc from us adding stringers to shape them into Culp Specials.  He doesn't build modified skybolt based Culp specials anymore. 

Please take a closer look at the Model 12 and you will see that it is 23ft span, near 20ft long purpose built M-14P powered airplane.  Curtis Pitts designed this airplane exactly for the M-14P.  It works Perfectly.  It is 25years newer technology than the skybolt and has a higher resale value compared to a one of a kind, modified skybolt.

We support the Model 12 completely.  You can scratch build from plans, buy some parts or buy all the kits we sell.  Its up to you what level you wish to do or buy. 

You want great cruise performance too.  Then the Model 12 is definitely for you!!  The model 12 cruises a full 20kts faster than  the green Culp special on the same gas burn.  That's 170kts on the GPS on the way home from Oshkosh on 15 gal/hr.  Our bonanza on the same day and 15gal/hr was showing 190kts on the GPS.  That's almost 200mph ground speed in a aerobatic biplane.  Range is 500miles.

I look forward to hearing back from you as you choose your project.  The Model12..........The Best Pitts Yet!!  Kevin
Mike, thanks for the reply. I'm no expert, but I think I have gone through some of the same consideration you are now. When I was considering what to build, I bought 3 sets of plans....Skybolt, McKenzie Firebolt, and Pitts 12, and have decided to build the pitts. By the way I'm 6'-1" and 175lbs.  Here's why I shamelessly recommend the pitts:

Airplane Kimball Pitts 12 Stock Pitts 12 Skybolt McKenzie Firebolt
Length 19' 8" 20' 6" 19' 21' 4"
Wing Area 150 sq. ft. 150 sq. ft. Plans don't say - Same as firebolt? 150 sq. ft. probably same as skybolt
Gross Weight 2300 lbs 2300 lbs 1800lbs 2000 lbs
Aerobatic Gross Wt 2300 lbs (+6 to -4.5 G) 2300 lbs (+6 to -4.5 G) 1650 lbs Plans don't say
Fuel Capacity 54 gal 54 gal 38 gal 39 gal
Distance between longerons at rear pilot shoulders 25.25" 25.25" plans dont say- used autocad to draw it out - 21.28" 21.524"

Finished Airplane Considerations: The skybolt is the slightly smaller airplane from what I can tell from all my plans I just laid out. I have sat in Kevin's Pitts 12 in both seats and it's very roomy, especially the front seat, you could probably put a bench in there and fly 2 kids up there, but they'd only fight over the stick. The canopy system is very well thought out and does give you room to spin your head around with about 2-3 inches of headroom left. I think the skybolt canopies are usually a little tighter. I have only seen skybolts up close, but not sat in one, but they look noticably smaller (of course, the 4 or so extra inches of width in the pitts is a lot, especially if you have to bail out in an emergency!) and the front passenger area seemed kinda tight too, compared to the pitts. 

For cross country flying, I'll bet there wouldn't be much difference in "hands off stability" between them with rigging probably more important, but I'm sure someone in the hangar with more biplane flight time could shed more light on that topic. I would assume with you being 300 lbs your airplane would be at a more rearward CG anyway with some corresponding decrease of pitch stability. The airplanes are all pretty much the same size, the difference between the skybolt and the firebolt being a few inches added to the fuselage of the firebolt. Kevin's Pitts is about 5 inches shorter aft of the cockpit and 5 inches shorter in the engine mount than the plans version, so the cockpit is the same for both. However the pitts carries 15 more gallons of fuel than the skybolt which would be a major consideration for your cross country flying, Also the pitts is designed right from the start to fly at a higher gross weight which would be a nice advantage for you.

Building considerations:  The skybolt plans are difficult for us first time builders. They are very spartan at about 14 pages, and leave many details to be figured out by the builder, in fact the biplane hangar skybolt builders here devote quite a bit of time to this task. Mac McKenzie's plans for the Firebolt are truly works of art with many many pages and every little detail drawn, by hand. He also supplies a full parts list for each sheet. If you still end up building a bolt, I recommend getting his plans too, just for the details.   The pitts plans are very complete also with good detail, and are done on a CAD system.  The parts list is on each page.

The new owners of the skybolt business will have to work hard if they are to eventually provide the kind of support that Kevin already does to pitts builders right now. For example, I have purchased from Kevin a complete set of machine laser cut fuselage weldments that should save a couple hundred hours cutting small parts out of sheet metal.  It looks like the area of the skybolt that you would like to widen is in the taper from the main 30" wide front section back to the tail,  at STA 85. I'm not sure how much hassle it would be, not to mention figuring out the engine swap and all the changes it would cascade. I'm sure Andy and the other guys building radial skybolts have thought most of that stuff through already though. You wouldn't  need to modify the pitts at all.  As far as falling in love with the sig skybolt, I used to fly R/C too and remember them too, they ARE neat airplanes. However, I'd bet your skybolt,  if you built it like you mentioned,  would look more like a pitts 12 than a skybolt though.  If you decide to build a skybolt let me know and I'll sell you my set of plans, they aren't much use to me. I will hang on to the Firebolt plans however, they are too cool!   Darin

06/22/00 INSURANCE

Group, it is my understanding that there are only about 6 aviation insurance underwriters.  The various agencies like Avemco, Forest, Falcon, etc, simply offer your case to the underwriters and mark it up for their own piece of the $ pie.  From our experience, the various underwriters have vastly different policy requirements and guidlines as well as prices.  In the case of our Model 12 in March 99, we used Forest agency.  We got liability, full hull coverage, airshow coverage(add 10%), competition coverage (add 10%), and open pilot coverage(means any pilot with 500TT, 250tailwheel, 50Pitts could fly our Model 12), we could name up to 6 pilots on the policy.  Deductable was $500 Except for the canopy which had a deductible of $2500(lots of S2Bs lose their canopies).  All this was $4200.00 per year. 

Since March 99, their have been several accidents with experimental biplanes of various brand names as well as Factory Pitts accidents.  In December 99 when the new owner of our 12 got his coverage still thru Forest, he saved some $ by dropping the open pilot part but kept the rest as he intends to compete and do airshows.  A different underwriter was used by Forest for the Model 12 which saved some $ for Keith but, he CAN'T have an open pilot clause with them and can only name a MAX of 2 pilots on the policy.   Keith didn't ask how many pilots could be named and the limit of 2 has been a problem for him (and us in moving the plane for shows and giving rides)

So with this example, you can see that knowing what options you want or think you may want in the future is important at the time of getting your insurance.  Also, their is a very small network of underwriters for aviation. They all know what the other offers.  The Agencies, Forest Avemco, AUA are "Dealers" for the underwriters and call all of them shopping a deal for you.  KK


From what I could get from the July 1999 EAA Sport Aviation article, the airplane as shown in the plans had a C.G. problem that required the engine mount to be 11" longer. Do you make two different engine mounts, one for your version and one for the plans version?  Are they 11" different? that sounds like a lot.  Darin
Darin,   The SA article  is slightly misleading.  Curtis designed the model 12 with a 14" engine mount.  The airplane had a very short Samson like nose in the orig 3 view we first saw in 1995.  Because of a lack of hard CG data on the engine, prop, accessories, etc., Curtis decided to build the airplane complete from the firewall back.  I mean everything, belts, cushions, pants etc.  Then they weighed it.  They assembled the engine, prop, cowl oil tank air system, etc on a temp. engine mount and weighed that.  They determined the CG of the FWF unit.  Curtis then did the math and found out that the engine mount needed to be 23.75" long rather than 14" long.  About 10" difference.  The FWF stuff was lighter than he first planned on.  So, the engine mount drawing was updated and very first engine mount built for a Model 12 was 23.75" long.  As it turns out, a 14" mount would not have been long enough to get all the FWF stuff in place anyway. 

So, the plans we sell have an engine mount and fuse length just like the plane Curtis and the Boys built, 23.75" mount, 169" fuselage. 

When we started the wings for our Model 12, the prototype had not yet flown. Dad and I had a copy of the stub nosed 3 view and when we saw the actual airplane after the engine was on, we were shocked as to how long the nose had gotten.  We saw it with the engine on but without a cowl and it didn't seem too bad.  But when the cowl was added, it had gotten real long.  We were disappointed.  So, we determined how short the engine mount could be and stilll get all the FWF stuff in it.  Next we redesigned the fuse to allow for the shorter mount.  The net result is a plane that is about 10 to 11" shorter than the black prototype.  In making these changes, we adjusted the seating, changed the canopy, made the rudder bigger, partly req'd for shorter wing span, partly because it needed more rudder.  Then Ben Morphew test flew the black on some for Curtis doing all the acro tests.  He loved it and decided he wanted one too but didn't want to build the wings.  He contacted us and because the wings were yet to be built, he asked for some changes to them based on flying the stock wings on the black 12.  He wanted 1ft less span, bigger ailerons, 3 hinges, slave rods to behind the I struts. So, with him wanting these things, we decided to add a few wants of our own to the wings. Smooth cross-section, alum ailerons, beefed up spars in spots, tighter rib spacing to help the fabric stay put, and we wanted to keep the same wing area as stock which forced the square-ish tips.  The end result is the wing set we have in kit form now.  Now, this meant the ribs we had built so far from based on the stock wings were not gonna work and we had to start over.

This gives you the basic genesis of the Model 12 as it is today.  The  plans mount is exactly the length of the black 12 prototype.  Our mount is approx, 4.5-5" inches shorter than the stock one.  We have a jig that makes both the stock and our length mounts.  If you build the mount per the plans, it will be the longer stock unit. KK