Engineering – Why did they do it that way?
Let’s talk about engineering. Engineering is that necessary evil where you take a good idea, wring it out, and are left with something that vaguely resembles the stellar idea that started it all. When you are talking about airplanes, you have two very distinct aspects to bringing new things to market. The first is the "make something work" side of engineering where all of the design requirements are outlined. How much can it weigh? How much does it need to carry? How much can it cost? Does it do the job? The second aspect to engineering for certified aircraft is the "does this meet certification requirements" portion. While certainly not mutually exclusive, there are some areas where those two aspects do not align very well. Let"s talk about one such instance.
The flat nose gear spring that Wipaire founder Ben Wiplinger pioneered is one such design item that provides quite a challenge to fit both the real world and FAA certification requirements. One of our current new design projects is the Wipline 1450 float for light-sport aircraft, which is very near to TSO certification. This is the smallest and most weight-sensitive float project that Wipaire has ever undertaken. Due to the weight sensitivity of this installation extra effort was taken to ensure the design was both as light and robust as possible.
To start this specific design effort, a nose spring geometry was selected that would provide a gentle ride over the lumps and bumps of standard airports. This nose gear just felt right. It had the resilience to provide support, but didn’t feel like riding a shopping cart downhill over a rough parking lot. Preliminary nose gear drop tests also indicated that this gear spring would provide proper shock absorption. This effort was off to a great start so far . . . but would it meet certification criteria?
One of the trials of aircraft certification is the need to meet prescribed test criteria. This can make it very difficult to optimize for anything other than the prescribed test conditions. In a perfect world, your design would be able to meet both criteria simultaneously. Unfortunately, that often comes with a complexity premium which is impractical on small aircraft for both weight and expense reasons. The FAA’s test condition is for a landing where someone slams the aircraft into the ground and causes the nose spring to flex back so far that it touches the keel of the floats. This condition forces the design of the nose gear spring to be very stiff so that it can absorb that very high load. Unfortunately, this very stiff nose spring means that the amphibious float plane taxies around the airport like a lightly loaded pickup truck.
The benefit to this design is that it is very difficult to damage the nose spring or nose gear of a Wipline float since it is sized to withstand slamming an aircraft into the ground during a 4-point landing.
The moral of the story is that engineering is a compromise. You have to take the good with the bad. The good is that you have a reliable product that will withstand significant abuse for years to come. The bad is that when taxiing your airplane around you may just feel like you are riding in a shopping cart downhill on a rough parking lot. Since the purpose of an airplane is to remain on the ground as little as possible we hope that you will forgive our engineered compromise. Happy flying!