Sloppy snap rolls, any suggestions? 8KCAB

A

acronut

New member
I'm not very happy with all the yawing I'm getting during snap rolls, the nose is waggeling all over the place. It's seems especially sloppy during an avalanche (snap near the top of a loop), I'm not sure if that's because there's not much ground to reference or some Newtonian issue with the snap starting with the plane inverted.

I'm entering at 90 MPH, full power, full back stick and rudder simultaneously. After it starts, I push for neutral elevator and add about 20% aileron into the spin to accelerate.

Even the Extras and Pitts wiggle around during snaps, but it just seems like my SD could do them nicer if it only had a better pilot! Any suggestions?
 
You might send an email to Greg Koontz. You can contact him with information from his website: http://www.gkairshows.com. He is the factory sponsored airshow pilot for American Champion with "tons" of model specific experience. I bet he could provide some pointers. If you have time, go to Alabama and fly with him. You would have a blast.
Mike
 
Have you read of the problems with doing snap rolls in the 8KCAB? Some aerobatic schools that teach in them do not even permit snap rolls.
 
Hi acronut, acrodisiac here.

I manage some decent snaps with my 150 Decaf . Here's how.
Your technique sounds good and your entry speed is right on so perhaps it is this little technique that I use that may makes the difference.

Slow to 80 first then lower the nose to accelerate to 90 then snap immediately. Use the momentum to make the snap go smooth. I find right is usually cleaner than left. As for the avalanche the same 'exploit the momentum ' technique works also . Didn't know that Newton could read Aresti!
 
Thanks for the feedback,

I called the factory and spoke with Jody - a guy that's probably done a few hundred snaps for every one of mine! He doesn't like the idea of entering snaps at 90 mph on a down-line ...to much energy; the kind of which can damage the fuel tanks - is that what you've heard about Blackhawk? Jody says it's important to keep fuel at 1/2 tank maximum for snaps; the fuel smashes into the tank's baffles and can tear them out; we've replaced the tank in one wing at 500 hours for this failure (it wasn't catastrophic, but you could smell gas in the cabin - it would leak out of the tanks and run around inside the wing's fabric).

Jody recommends 80-85 mph on down-lines or 90 mph max on level or up-lines. His procedure is a little different than what I've been taught: Pull the stick back in a fluid motion; only start the rudder after the stick is 3/4 back, then press full rudder. After it snaps, feed 1-2" forward stick and 1-2" aileron to accelerate the roll.

Can't wait for some decent weather here in Minnesota to get up there and fly like a REAL pilot again!
 
This is what I've heard. There was actually an article in the IAC magazine about this. A pilot attempted to compete in intermediate in a Super Decathlon and after one season his tanks were trashed. Attached is a link to the article in a news letter.
http://iac35.aerobaticsweb.org/news/Hammerhead-Fall-04.pdf
Scroll to the article "Flying the Decathlon, to win (in Intermediate), Possible, but at what cost?" by Dave Watson.
Also, many if not most flight schools that use Decathlons will no longer permit snap rolls in them. For some reason it seems this problem is confined to those with metal spars.
I will not pretend to be an expert- I've only flown mine for about 1.5 years. But I'd rather not find out first hand that these experts were correct. It would be an expensive lesson.
 
Oh yeah, the article of "I beat the crap out of my airplane, why did it break?" :roll:
I am trying to coax Jody to type up a little paragraph. I assume Bob would nab it for the news letter.

Oh and whats weird about snap rolls is how there is excess pressure inboard (unlike the more symmetrical maneuvers). So you get more damage to areas closer tot he wing root. For meeting the regs, there is nothing that models this behavior. There is a 2/3 limit roll condition, but thats still an outboard center of pressure. The prop effects dont help either. If you are doign a lot of snaps, damage will be in the tank area of the wing....as in the whole section, not just the tank. Typical first victims are the false ribs behind the rear spar. They are more intended to keep an airfoil shape than take any load. Mid-late 90's we beefed up the butt rib (on either side of tank) to help the false ribs survive a little longer. It also helped what happens to the one piece gap seal on the top.
 
Thanks for the replies again and the link to Dave Watson's article.

Now I'm more confused than ever!! The POH says snaps are approved. I just spoke with Jody at the factory and he gave me pointers on doing snaps (he didn't say "don't do snaps"). But now I'm hearing that there's a lot of owners that won't do snaps and Wilson states in his article "Please limit your use of these planes to the normal category limitations (+5g, -3g) and DON”T SNAP them. If the factory warns against it, common sense and perhaps the POH should too." Are we talking to the same factory, American Champion??? I assume Wilson wouldn't just put something in print like that if it wasn't factual. I don't get it. At all.
 
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