... We just finished up with the inspection of the entire aircraft last night and am very happy to say this is an extremely well built, bullet proof airplane. We removed all inspection covers, tanks, horizontal stabilizer, vertical stabilizer and all mountings, bulkheads, floor, spars and carry through assembly, all controls and associated parts, engine mount, gear weldments and mountings. Everything looks like new and all damage was confined to the gear, tires, wheels and wheel pants. We are reassembling today with all new undamaged parts and should be back in the air this weekend, (less wheel pants that are in our paint shop). This really speaks volumes to the quality of design and construction of these wonderful little airplanes. Just imagine the nightmare, time involved, paper work, lack of availability of parts and insane costs involved if this were to happen with a factory built spam-can. All I can say is "I LOVE MY RV" and have very little desire to own anything else Thanks, Allan...
OK so the damage is minimal and a visual inspection says that the airframe will soon be ready to go back into service. All good news.
Now the question is did the airframe and crew experience 5-1/5 g's as indicated on the Acceleration instrument or something lower or much higher? Based on the reported damage perhaps it would be prudent to understand the dynamics of the g meter before the information displayed is used in drawing conclusions about the margin. of safety in the design.
I for one do not know the characteristic response of this particular instrument to what was probably a relatively short shock impulse when the landing gear contacted the runway. We typically evaluate the area under a shock envelope (amplitude and period) in order to determine the amount of energy that would have been dissipated into the airframe, or any other structure, in an event such as this. Peak g's as measured by an accelerometer without knowledge of the period over which the acceleration was present do not tell us much. In my business we measure shock impulses with a magnitude of over 1500 g's that have a duration less than two milliseconds that do no damage. On the other hand if we see a sustained impact acceleration over 4 g's for more than a few hundred milliseconds we know that we should scrap the test article as it has probably sustained permanent deformation or structural damage. This may or may not be the case here but using a mechanical g meter to draw any kind of conclusion(s) may lead to problems.
Yes tires were deformed, wheels were distorted, landing gear components may have been permanently deformed. Question is. Is that the extent of the damage?
My point is that if the value indicated on the g meter which is intended to respond over maneuvers lasting many fractions of a second or seconds indicates a value from an event and the actual event from the description was apparently very short in duration should the conclusion that the point be considered in the assessment of the damage to the airframe?
Quote from Alan's original post -
"This 5 1/2 gs translates (With the loading we had) to approximately 9,900 lb on the three gear legs."
I personally believe that this conclusion was at best premature and at worst may lead to returning an airframe to service prematurely. On the other hand perhaps the potential danger lies in the use of this value by others in evaluating the design margins of the RV-9a airframe and potentially making a bad decision down the road. This could include "There is a lot of margin in the design based on Alan's analysis and my aircraft will never be operated at those extremes so it will be OK to lighten up some of the structure."
Not saying that Alan is right or wrong just saying that it may be worthwhile to look at the big picture before jumping to conclusions.