Until a few years ago the NTSB did not recognize kit aircraft as a “type” and would not record them as a common type in accident statistics. That position is technically correct because each amateur-built airplane is certified as an individual with the builder providing at least 51 percent of the total effort to create it. And the builder also technically is responsible for the design of the aircraft.
But the NTSB changed its position because kits are the gigantic majority of all amateur-built airplanes and unless accident data was recorded under the name of the kit, it was impossible to analyze the data and look for trends in accident rates and causes. The NTSB identification of amateur-built aircraft involved in accidents as a type – RV, Lancair, etc. – is not as consistent as we all want, but is much better than it was. The NTSB tracking of kit aircraft as a common type is evidence of how accepted kits are, and how much builders are expected to follow the instructions supplied with the kit.
The fact is that the development of high-quality kits of well-designed airplanes that are straightforward to build has transformed homebuilding. The only part of GA that has shown growth over the past few years is amateur-built, and virtually all of those airplanes are from kits.
Van’s Aircraft alone is most responsible for the success of kit aircraft. Nearly 7,400 RV airplanes have been completed and thousands more are under construction. There are about 30,000 total registered homebuilts so you can see that Van’s with its long list of RV models is driving the boat.
These are the reasons that an article in the August issue of Sport Aviation by Van’s founder Dick VanGrunsven is one of the most important commentaries on amateur-built and kit aircraft in many years.
What triggered Dick’s article and comments was an earlier Sport Aviation story about a builder who made extensive modifications to the design of the four-seat RV-10 that he built. The builder increased the maximum takeoff weight, totally changed the seat belt anchoring system, modified the rudder control cable connections, and apparently doubled the fuel capacity.
None of the changes to the RV-10 design that the builder made violate any rules because as builder he, not Van’s, is responsible for the finished airplane. But as Dick points out, changes to the fundamental structure and design of the airplane sends the builder off into unknown territory. How the airplane will perform and withstand the possible loads of maneuvering and turbulence are unknown to Van’s Aircraft because the alterations have not been tested. Perhaps the builder has the experience and tools to evaluate how the gross weight change, extra fuel, and changed rudder cable connection will alter the proven performance of the RV-10, but maybe not.
There is little question that the change in the shoulder harness anchoring system implemented by the builder does compromise the performance of the belts. Van’s worked with Oregon Aero to create seats and restraints that worked together and the changes made invalidate the testing those companies did. The builder has every right to make the changes, but all of our concern – not just Van’s – should be that those changes were made with full knowledge of a likely compromise in restraint performance.
Read about Greg Hale’s RV-10 in Sport Aviation
Doubling fuel capacity, Dick points out, could cause very unpredictable changes in flutter margins and stall/spin behavior. Adding significant amounts of mass to the wings can alter the natural frequencies of the structure and that can change flutter margins. And extra weight in the wings does add inertia to any wing drop or rotation of the airplane so who knows what the altered RV-10 will do in a stall or spin. The design was tested as specified, but changes become the builder’s responsibility to test.
I am no amateur-built aircraft expert, but pilots I know and trust who have flown the RVs all report that they are well-designed airplanes with conventional flying qualities. In this context the word “conventional” is a high compliment, meaning the airplanes behave the way an experienced pilot expects them to without the flying qualities traps that lurk in some amateur-built airplanes.
The enormous sales success of the RV line proves to me that builders and pilots want an attractive airplane that delivers good performance but requires only basic fundamental building skills to create. The RV designs are sound, the kits are very complete, and the builder has every reason to know what to expect at the end of his efforts. Paint schemes, interior furnishings, and avionics selections give RV builders wide range to express their individuality without altering the tested and proven fundamental design.
View a gallery of Greg Hale’s RV-10
I don’t want to see the amateur-built aircraft rules changed to take away the authority of the builder to create his own airplane whether he starts with a very complete kit or from scratch. But like Dick, I do hope that kit builders understand that when they modify the kit they have launched themselves and their passengers into untested territory. That’s why Dick’s article is so crucial to all who care about amateur-built airplanes. I hope you will read it.