Super Decathlon Damage

BruceAir

BruceAir

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BruceAir
Those who fly Citabrias and Decathlons should read the article "Flying the Decathlon to Win" in the June 2005 issue of Sport Aerobatics magazine. The story includes several scary pictures of cracked ribs, popped rivets, damaged fuel tanks, and other problems that the author attributes to agressively flying the Intermediate sequences--albeit, he claims, within the stated limits for the airplane (+6, -3.5 G).

Too bad the article isn't available online (Ken?)
 
I think that guy is lucky to be alive.

Does the SD have a g-meter? How does he "know" that he never exceeded limits?
 
James_Dean said:
Does the SD have a g-meter? How does he "know" that he never exceeded limits?
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Yes it does. I assume he 'knows' because most (all?) G-meters register a min and max load factor that the pilot can reset. At the end of each flight I know how many g's I pushed and pulled for that flight. He would know if he exceeded +6/-5.

Bruce makes a good point. All of us who own AC aircraft need to do some soul searching about the load factors we're willing to put on these aircraft. The Intermediate category introduces snap rolls into the sequence, so that means a lot of practice for someone who wants to place well in Intermediate in a Super D. No telling how many snap rolls the author did in that airplane. I'm glad to read he's decided to stop doing them.
 
You should see the pictures in the Sport Aerobatics article. Scary.

As Gibbons, said, you have to be careful. And understand that many hard-core airshow types effectively rebuild their airplanes each year. For example, Sean Tucker's crew strips the fabric off his airplane, pressurizes the tubing to check for cracks, and does major I&R on the engine, propeller, etc.

That's one reason I eschew maneuvers like tailslides in my Extra. The airplane's more than capable of doing them, but I don't want the expense and hassle of the recurring inspections, etc. that would make them "safe." They're not that much fun.
 
gibbons said:
Yes it does. I assume he 'knows' because most (all?) G-meters register a min and max load factor that the pilot can reset. At the end of each flight I know how many g's I pushed and pulled for that flight. He would know if he exceeded +6/-5.

Bruce makes a good point. All of us who own AC aircraft need to do some soul searching about the load factors we're willing to put on these aircraft. The Intermediate category introduces snap rolls into the sequence, so that means a lot of practice for someone who wants to place well in Intermediate in a Super D. No telling how many snap rolls the author did in that airplane. I'm glad to read he's decided to stop doing them.
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Thanks for the reply, Chip. I can't imagine opening up my aircraft and finding damage as described. It's completely beyond my comprehension to make repairs as described in that article and and then continue doing acro in that aircraft. I admit I know nothing about acro, the SD, or repairs on wood structure aircraft, but that story was nuts.
 
Think about the certification of the aircraft flown. Certification/safety was issued with new materials...tubing, spars,skins,engine etc. I really have to wonder about the condition of 25 year old aircraft that is being subject to someone currently flying aerobatics or learning how to fly aerobatics. Trying to push an aircraft to the edge of its certification limits when it has hours and age on it is a dangerous thing in my opinion. Some years ago I lost a good friend that was flying an older higher time aircraft at the edge of certification limits when a section of the tail departed....fatigue. Were I fly daily in the flight levels between 31.0 and 41.0 its a very unforgiving environment and can kill you quick if you start having aircraft structure problems (anyone remember the emergency rudder cap A.D. on the commanders) I feel the same way about aerobatics ..you place your aircraft in a very harsh unforgiving environment. Definitely need to have a strong progressive maint program and respect for the age of your aircraft.
 
Doug R said:
Think about the certification of the aircraft flown. Certification/safety was issued with new materials...tubing, spars,skins,engine etc. I really have to wonder about the condition of 25 year old aircraft that is being subject to someone currently flying aerobatics or learning how to fly aerobatics.
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A small point ... the airplane in question was a 1995 model and developed problems after only 7 years in service.
 
One point about which I did not editorialize is his strategy of flying the Super D in what he calls a Yak-like manner of crisp, instantaneous moves. Tom or someone else may know more about the dynamics involved here, but I have to think that a load that goes from 1 g to 4 g in .5 seconds has to impose more stress than a similar load over 1.5 seconds.

I like the Super D because it appears more fluid and graceful in aerobatics, while the higher performance birds seem more extreme. To try to fly one it the manner of another seems like asking for trouble.
 
Ken-

I concur that within limits a slower build-up of G's is of less damage than rapid loading and unloading to a similar level. It certainly seems like the author flew the Decathlon very aggressively.

For upright Barnstormer Aero the Citabria and Decathlon series remain fine aircraft, excellent trainers, and great to watch due to their size, AND the fact that, while challenging to perform, high-energy aerobatics aren't very interesting to the uninitiated.

When I received my pre-delivery ACA factory tour I remarked on the differences between the Citabria and Decathlon tanks. Jerry Sr. stated that any Decathlon that was regularly Snap Rolled would eventually develop tank leaks due to the design...........................

Tom-
 
I read the article before I saw this thread. The fact that this kind of damage can happen behind the scenes and remain unknown until tearing off the fabric is pretty scary. It might be possible to buy an airplane from someone who says he's been doing mild aerobatics, and he may be telling the truth or he may believe that the aerobatics he's been doing are mild, and the logbooks are complete and everything looks good, but there could be missing rivets, tears in the metal and all kinds of damage invisible to the eye. This is worrisome.
 
Ken Ibold said:
One point about which I did not editorialize is his strategy of flying the Super D in what he calls a Yak-like manner of crisp, instantaneous moves. Tom or someone else may know more about the dynamics involved here, but I have to think that a load that goes from 1 g to 4 g in .5 seconds has to impose more stress than a similar load over 1.5 seconds.
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The rate of acceleration change is called jerk and AFaIK high jerk doesn't by itself increase mechanical stress. There can be secondary stress issues when the rapid acceleration change causes higher dynamic loading at certain parts of a structure than the structure receives as a whole. OTOH I think this would only occur on an airplane if the there was a lot of compliance (flexing) between the overstressed part and the cabin. Given the author's description of the damaged area this may indeed be the case.

Another more likely issue is that the certification requirements only deal with forces on one axis at a time yet during many acro maneuvers, stresses are the result of combined acceleration about multiple axes. For example full aileron deflection during a hard pullup may develop sigificantly more force on the rising wing spar than either control input individually. I'm not sure, but I would assume that snap rolls involve such combined loads.

I like the Super D because it appears more fluid and graceful in aerobatics, while the higher performance birds seem more extreme. To try to fly one it the manner of another seems like asking for trouble.
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AFaIK the judging methods treat all types similarly in this respect.
 
It's important to note that while this article looks at the Decathlon similar issues will arise with any aircraft used for hard aero, no exceptions, anyone who is convinced a particular aircraft is bulletproof is setting themself up for a surprise, ask Big Ed Mahler, and there are plenty of other similar stories of failures in aircraft used for hard aero. The only difference between a Decathlon and an Extra is how many G's and how many hours, and where the failure will occur.

Tom-
 
Toby said:
I read the article before I saw this thread. The fact that this kind of damage can happen behind the scenes and remain unknown until tearing off the fabric is pretty scary. It might be possible to buy an airplane from someone who says he's been doing mild aerobatics, and he may be telling the truth or he may believe that the aerobatics he's been doing are mild, and the logbooks are complete and everything looks good, but there could be missing rivets, tears in the metal and all kinds of damage invisible to the eye. This is worrisome.
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Yeah, Ken buying a new Citabria suddenly makes a hell of a lot of sense.
 
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