Tail Time
Greetings! We are hard at work getting ready for the load test. The aft fuselage is complete except for a few bolted-on parts we still need to machine. So done in a few days. Then assemble the load testing frame and bolt it all together. I will need to locate a good spot for the test in the parking area at our shop then get a load of gravel bags delivered. The test will be a ton of work - loading and unloading, measuring for permanent deflection, then loading more, etc… Work, but it should be exciting! Pics and video will be posted! I am planning to use the fork lift to make it a less back-breaking effort for the crew.
We built the aft fuselage “box” frame using Cherry stainless pull rivets CCP-42, 43, 46. It went together incredibly well. We are hoping that the end users will enjoy building this part of the airframe. We had to invent a hold down method and fixture on the cnc router table for drilling and profiling the main longeron angle extrusions. That fixture worked exceptionally well and is making kit-ready parts. It validated our decision to go with the Shop Sabre IS 408 instead of a lighter duty (more affordable) option. We are using it for milling and shaping thicker aluminum parts beyond the typical sheet. The sheet metal top, bottom and sides as well as the bulkhead parts were all cut out and pre-drilled. It just cleco’ed together. Not one hole was off location, though we did intentionally leave some holes out of a few mating parts to allow adjustment/fitment of the bulkheads. We did not need to make an alignment fixture for this. We just used a carpenters square for alignment for this first time. We should be able to dial in the exact location and make them matched holes within a few iterations. Very pleased with the results, but always wanting to improve.
Originally, we designed and built the P-36 prototype with an aluminum tubing frame with gussets, riveted and bolted together. This is very similar to the Airdrome Aeroplanes WW1 kits. It worked and was easy to build. However, it took a lot of gussets! This also made for some tricky riveting in places. This aluminum tubing frame was chosen because we thought it would go much faster than our original box design. It really didn’t go any faster and was not any lighter. So we have learned a few things along the way. We are back to the box design and are paying attention to designing it to be easy building and as light as possible. The forward fuselage frame will be welded 4130 steel tubing with welded gussets. The aft aluminum frame will bolt to the forward steel frame. The steel frame up forward is better for crash protection and structural load paths. The aero skins are just for shape and are not considered in the structural calcs - though they do add some strength.
This internal structure method is not weight optimized - taboo in aircraft design. We could save weight and some effort by going semi-monocoque for sure. However, we are on a mission to create more than a single airframe design. The internal structural method allows us to transform this P-40/36 into many models of fighters without the many iterations of structural design and engineering. It also allows us to create some truly unique aircraft models that we hope to bring forward fairly quickly. You will love it! First things first, we are hard at it to complete the P-40 design and kits to our customers.
We have a lot riding on this load test. So much so, we decided to forgo attending Sun ‘n Fun 2025. Too much of a distraction from the effort required right now. Our top priority is making progress on getting to production and delivering. Sun ‘n Fun has always been a fun show to attend - gets us out of the late winter weather up here in CT. But, it is a good week of effort before, the week during and another week after the show. That’s a minimum of a three week investment of time, effort and energy. Love SNF, but just can’t this year. I am hoping we will attend in 2026. With a P-40E and the P-36 on hand.