164" Fuselage (5" Shorter Than Plans)

Click Below For Basic Dimensions

Design Considerations

INTRODUCTION: As people look through my website and become more educated about the Pitts Model 12, some eventually want to know more about the short fuselage I've built. So, here's the story behind my efforts. First let me state that my fuselage is not exactly the same as the pre-welded HP fuselages available from Jim Kimball Enterprises.  While my fuselage is very close dimensionally to Kevin's fuselage, his has been optimized for its new size by Finite Element Analysis (FEA), and there are little things that he's done to improve it compared to the plans version. I've tried to incorporate into my fuselage as many of those improvements as I could discover, so that I could utilize as many of the Kimball HP components as possible. Should anyone decide to use the following information, they do so at their own risk! That being said, I did not come up with these changes all by myself. Kevin was kind enough to answer more than a few key questions along the way, and in the beginning it was done on a collaborative basis, with Tom Weinberger and I sending CAD files across the planet every few weeks until late August 2000, when I pretty much settled on the design I have now.

Reasons: I spent a couple days looking at N360KC during Sun-N-Fun 2000, then when I saw pictures and drawings of the plans version it seemed too long. I had been planning to build from scratch all along, but really liked the shorter fuse, which presented a dilemma. I also planned on building Kevin's HP wing kit with its shorter span and bigger ailerons. So, probably like everyone else, I asked Kevin if plans were available for the short version and when he said no, well the wheels kept spinning. I liked the short fuse because it looked more in proportion to the short wings, and probably had slightly better manuverability. I also figured it must have a weight advantage due to 5 inches less fuselage & 5 inches less firewall forward. Also I have the added benefit of being able to use Kimball HP parts  like the turtle deck and laser cut fuselage skins for example.

What Changed: Looking at the side view, my fuselage is basically 5 inches shorter than plans, with the 5 inches coming from between the cockpit and the tail. It's the same as the plans from Fuselage Station (FS) 0.0  to FS 86.0 on the top longeron and back to FS 48.0 on the bottom. The lower cluster at FS 80.75 got moved forward 5 inches to FS 75.75. The fuselage at the tail starting at STA 140 on the top and STA 151.5 on the bottom remains the same except all are at plans-5 inches. The top cluster previously at FS 113 is now at FS 110.5. The two bottom clusters at FS 102.5 & FS 126.5 are now at 98.25 & 122.75 respectively. I'm not planning on doing a FEA on it since I would assume it would be stronger as it gets shorter. My fuselage should be slightly heavier than a Kimball HP fuselage which has been optimized with FEA, because I'm still using the same tube specifications (tube diameter and wall thickness) listed in the plans. To quote Kevin, "By doing a full finite element analysis of the  frame, I was able to optimize the tube sizes while trying to maintain the external appearance of the plans frame.  So, some of my tubes are thinner or smaller or both than the ones you are planning to use.  I changed a few to larger dia tubes for reasons of convenience of assembly or better fit of a fitting etc and reduced the wall thickness to make an equivalent strength member.  But, for the most part, our frame will look like yours and vice versa.  I just have ours tweaked a bit more than you will to save some weight."

Seating Position: The rear seat bottom slides forward 5 inches which changes the recline angle from 13 degrees to 24 degrees measured with the top longeron. Regarding the forward seat, the backrest tubes at the bottom get welded to the seat bottom tubes 2.5 inches forward of the FS 48 cluster. This results in a recline of 19 degrees compared to 13 degrees in the plans.

Building Considerations: Shortening the fuselage made all the nice dimensions on the fuselage side flat pattern layout useless, so I had to figure out another way to do it. The sides of the Pitts 12 fuselage actually twist from firewall to tail, but the top and bottom ladders only bend on one axis. In fact the top ladder is flat except the last crossmember to the tailpost. What I've done is calc the little extra needed in the bottom and top ladders so that they can be built flat on the table, but put the clusters at the proper locations after bending. I just added up the tube intersection to intersection distances with the help of my CAD program. I built the bottom ladder first, then the top ladder. Using the engine mount to help up front, I then jigged the bottom ladder above the top using wood boxes cut to the proper height at each station, and worked my way back to the tail post.

Other Notes: I had to redraw the elevator control system to adjust the lengths of the pushrods and the rear idler, to keep the geometry as close as possible. Per Kevin's advice the Torque tube remains the same, and I used a curved rear stick tube from Kevin to allow more rear seat clearance. The Kimball HP engine mount, cowl, turtle deck, canopy and sheetmetal panels are used. My fuselage is about 1/2" longer than a Kimball HP fuselage and most stations are within 1/4" so I will use the HP weight and balance data.

CONCLUSION: After spending a LOT (understatement) of time making my fuselage and tail parts from scratch, and the numerous visits to the Kimball's hangar documented on this website, I can honestly say that the fuselage and tail feathers they sell have tremendous value. Sure, you can save some money by building your own and trading time for money, but in the end you will probably have paid yourself less than $20 an hour so be forewarned. I mostly wanted to build my fuselage myself for the education, challenge and pride of building something myself instead of just paying for it.  Its been a lot of fun too.