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Joe Enzminger
Joined: 06 Feb 2006
Posts: 26
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 Posted: Thu Mar 23, 2006 4:34 pm Post subject: ACM - A T-34 Owner's two cents |
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This is my first post to this list - go easy on me. I'd like to provide a little perspective on this issue because we (I also own a CJ-6) are PRIME candidates for ending up in the same boat as we (I'm a T-34 owner, too) did. The bad news is we (the Yak crowd) are actually in a worse position because the FAA's remedy wouldn't be an AD, they simply would stop issuing Experimental/Exhibition Airworthiness Certificates to us. For some background I'm a relatively low time pilot (about 800 hours), aerospace engineer, T-34 Association Board Member, and my sum knowledge of ACM comes from my experience working as a computer programmer on an online game called "Warbirds". Not that it is worth much, but I probably have more time applying Bob Shaw's "Fighter Combat" in a virtual world than most.
I've read the ACM thread and you could go back and read the T-34 group's archive from 1999 and people were making the same points:
1) Any idiot can pull the wings off an airplane
2) Metal has memory
3) Rolling G's are the culprit
4) Ban ACM and next they'll ban aerobatics
5) There are more, but I won't bore you with them...you've read them already anyway. If you haven't go look at the T-34 group's archive.
I'll leave the primer on metal fatigue for another time (although I have learned more about it in the past 4 years than I care to know...I wish I had paid more attention in college). I will say that the fatigue process is at work in any aluminum airplane. When you fly, you are using a limited resource. How you fly determines how fast that resource gets used up. When it is gone, something on your airplane breaks. George Braly (who lurks on this list, I think), has done some interesting studies that indicate that ACM uses up airframe life something like 6-10 times faster than if you just use your airplane for flying around the patch (George will surely correct me if I've missed quoted the figure).
So the central question - should we be using airplanes for ACM? For the Yak owner as an individual I think the answer is clear - as long as you understand that you are using up your airplane faster than if you didn't do ACM, you've convinced yourself that your airplane fits your mission, and you conduct yourself in a safe manner, by all means. It's your choice - it is your life and your airplane.
I would mention, however, that it would be a good idea to know where you stood from a fatigue life perspective. In other words, not all Yaks and CJ's are the same. A high time airplane is not the best for the ACM mission because there just isn't enough data on the airframe for us to know where we stand on the fatigue life spectrum. You wouldn't start a flight knowing you only have enough gas to get airborne (or for that matter not knowing how much gas you have at all!) - you also shouldn't be doing ACM without enough fatigue life to provide a margin of safety. And since fatigue life, unlike gas, is impossible to measure accurately, it is much better to err on the safe side.
Reading this thread, I've seen a lot of traffic about providing "safe" ACM training. The argument is that training is a good thing and that it leaves the trainee with the knowledge required to safely go forth and aviate. The one part of this that I see left out in this argument is the necessity of "training" people to make sure their airplane matches their mission. You wouldn't go train someone to fly aerobatics in their 172 Skyhawk. Along the same lines, no "instructor" in good conscience should train someone in ACM in an airplane that doesn't fit the mission. Does the CJ-6 fit the mission? I won't take a position but I would offer some things to consider when making the determination:
1) Aircraft operational history (known or unknown)
2) Airframe total time
3) Margin of safety (load limits, etc.).
4) Aircraft condition
I would suggest that if you don't know your airplane's operational history, or if you know it's history and the story isn't good, or it is a high time airframe, then you shouldn't be using it for ACM. I would also offer the opinion that there isn't enough data to determine if the CJ-6 has an adequate margin of safety for load limits, but I'm not going to force anyone to agree with me. Just for information, the T-34 has a +6 G load limit, but some studies we have done indicate that you get localized yielding in some high stress areas at just above 6Gs. This means that the metal is permanently deformed and the overall structural strength of the airplane is compromised if you exceed the load limit by as little at 5%. Sure, the airplane will hold together if you do this once (it is required to hold together up to 9Gs), but it is not likely to survive too many excursions to "just above" load limit. So while the airplane has a 1.5 safety factor, the truth of the matter is the "margin of safety" is something much, much less. You can only count on the safety factor ONE TIME. After that, all bets are off from an engineering perspective.
I'm a big individual rights type of guy, but the "good of the group" should also be considered. If someone does break an airplane in ACM, it will likely ground every airplane who's history is in question. In other words, only the guys with new or single owner airplanes will likely be spared the misery. Not to mention the negative impact that such an accident will have on the reputation of the airplane and it's value. So in some ways we owners are all tied together. When "you" fly ACM, you are actually costing "me" some money. Generally this is true regardless, but it is something to consider when you are looking at this issue from an Association point of view.
ACM, by definition, is a "max performance" flight condition. To "win" you have to operate the airplane at it's limits. You are also putting the airplane in a flight condition that is subject to buffet and vibration (which causes something called high-cycle fatigue) and you put yourself in a position to exceed the load limit of your airplane, which on some airplanes can cause permanent damage to the airframe. This damage may not be apparent immediately, but it will greatly accelerate the fatigue process and dramatically reduce the life of your airframe.
As I write this I am realizing that I could probably write a book on this subject, so I'll shut up now and hope I did so soon enough  . Moral of the story is don't ignore the lesson's of history. I'd hate for us to have to deal with this issue in a non-hypothetical way, but I will also warn that the similarities between where we were with the T-34 7 years ago and where we are with the CJ-6 and Yak community now are strikingly similar.
My two cents, for what it is worth.
Joe Enzminger
700YK (CJ-6)
N520HT (T-34A)
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flushjohnson(at)charter.n
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| Posted: Thu Mar 23, 2006 5:41 pm Post subject: ACM - A T-34 Owner's two cents |
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This is the best info I have seen in a long time.
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YakL1(at)aol.com
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| Posted: Thu Mar 23, 2006 6:05 pm Post subject: ACM - A T-34 Owner's two cents |
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Joe:
You are a good writer and a wise man.
I, as a fellow cj6 owner, agree com with your analysis here completely.
John Zecherle
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wlannon(at)cablerocket.co
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| Posted: Thu Mar 23, 2006 7:16 pm Post subject: ACM - A T-34 Owner's two cents |
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Great post Joe;
Well written and to the point. Your two cents is worth a hell of a lot more
than that. This is information that all owners of CJ/Yak and other types
need to be constantly aware of.
Thank you.
Walt
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dsavarese(at)elmore.rr.co
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| Posted: Fri Mar 24, 2006 4:42 am Post subject: ACM - A T-34 Owner's two cents |
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Thank you Joe for your excellent post. It should make us all think.
Dennis
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dsavarese(at)elmore.rr.co
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| Posted: Fri Mar 24, 2006 4:42 am Post subject: ACM - A T-34 Owner's two cents |
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I agree.
Dennis
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gus.fraser(at)gs.com
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| Posted: Fri Mar 24, 2006 5:40 am Post subject: ACM - A T-34 Owner's two cents |
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Joe,
Great stuff. I agree as George Santayana said "those who ignore history are
destined to repeat it" Joe, you should speak up more often if this is a
taste of the quality you contribute.
Gus
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Valkyre1(at)comcast.net
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| Posted: Fri Mar 24, 2006 7:37 am Post subject: ACM - A T-34 Owner's two cents |
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Good points made Joe. Thank you and welcome to the "Squawk Box hot seat". - Val
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HawkerPilot2015
Joined: 10 Jan 2006
Posts: 503
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| Posted: Fri Mar 24, 2006 8:08 am Post subject: Re: ACM - A T-34 Owner's two cents |
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Joe,
You may have unset the natural balance between quality information and useless jabber that sometimes exist here. The Yak list will now implode.
Good stuff.
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