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Old 04-04-2011, 07:39 PM   #1
DanWard
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Question Help with new Extreme flight 47" yak - wants to snap to the right all the time?

Hello,

I am pretty new. Flew a lot 20 years ago before kids and am slowly getting back into the hobby. I have a multiplex acromaster, 3DKS 57" ectra 330SC, and a small foam pitts. All are very stable in flight. But just because I mention this I recently have had it proven that I know very little.

I have a new extreme flight 47" yak(yep, one of the last new in box since they were discontinued). Actually I've been trying to make it fly well for a few months now. On 4 cell pack it has good motor performance.

Let me explain, it snaps to the right no matter what I do. For example, hammer head turn, on the down line, try to pull to level flight very gradually and it snaps to the right.

Another example, turning final for landing, nice gradual bank to the left and pull to turn to the left, Pull a little more up to tighten the turn and it snaps to the right.

I could go on with other examples but they all end in snap to the right.

All my other planes are very stable no matter what the flight speed is but it is hard to get comfortable with this one because when you least expect it, when it get critical to pull out, it snaps to the right.

I've checked left right balance and things are spot on as near as I can tell. I've moved CG forward trying to tame it until CG is now well ahead of recommended and it still snaps to the right. Always to the right.

I have checked, elevator perfect alignment with wing. I've check for warped flight surfaces, can't find any problem.

I'm at the end of my knowledge base so I called extreme flight to see if they had any suggestions. Funny when you call or email 3DHS Ben and his team are very supportive. Extreme flight gave me nothing to go on.

I see video's of the extreme flight 47" YAK and they all make me want one that flies like that. Yet...mine...well it is a hand full at all times.

I've played around with throws. I've reduced elevator throw until...well...until there just isn't hardly enough to be safe. Bottom line is it doesn't take much regardless of flight speed and it snaps to the right. Always to the right.

Anyone have any ideas or helpful suggestions?
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Old 04-04-2011, 08:26 PM   #2
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What's the weight like; it's by any chance overweight is it, maybe a large heavy battery? The spec says 38-43oz

Bear in mind that there is only one reason why any plane stalls.. that's because the angle of attack of the wing is too great.. This can only occur if the model is: flying too slow/is too heavy/pulls too many 'G's, or more likely, a combination of all these factors. Fly a bit faster, dont pull back on the stick as much, and lighten the model as much as possible, and you will reduce the chance of stalling.

When the stall comes if it's always the same side then I can only assume there is some slight asymmetry in the model.. Are you sure 100% there isnt a twist in a wing? it can be hard to spot on a symmetrical wing. having said that a model like the yak with quite strongly tapered wing's is likely to snap one way or the other when the stall comes, best option is to avoid the stall in the first place as noted above (yeah, i know it's easier said than done!).


One possible fix that you could try is stall strips: http://en.wikipedia.org/wiki/Stall_strips

Stall strips force the stall to start from the wing root and so prevent 'snap' (tip stall).. bear in mind though they wont stop it stalling, only flying faster, reducing the weight or 'elevator management' can do that, stall strips just make the stall less violent when it occurs and maintain some aileron authority in the stall.

For model purposes you would probably have to make them bigger than typically used on full size planes.. i'd guess something like a piece of 1/4" triangular balsa stock sanded to fit the LE profile and running from wing root to about 1/3rd of the wing panel span.
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Old 04-04-2011, 08:56 PM   #3
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Thanks

Originally Posted by JetPlaneFlyer View Post
What's the weight like; it's by any chance overweight is it, maybe a large heavy battery? The spec says 38-43oz I'll check total weight this evening.

I used the following motor and moved from 2200mAh 3 cell to 2200mAh 4 cell because the motor was whimpy on 3 cell.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8487

Bear in mind that there is only one reason why any plane stalls.. that's because the angle of attack of the wing is too great.. This can only occur if the model is: flying too slow/is too heavy/pulls too many 'G's, or more likely, a combination of all these factors. Fly a bit faster, dont pull back on the stick as much, and lighten the model as much as possible, and you will reduce the chance of stalling.

When the stall comes if it's always the same side then I can only assume there is some slight asymmetry in the model.. Are you sure 100% there isnt a twist in a wing? it can be hard to spot on a symmetrical wing. True, I understand it is hard to see but I've studied it in all ways that I know and beleive it to be straight

Having said that a model like the yak with quite strongly tapered wing's is likely to snap one way or the other when the stall comes, best option is to avoid the stall in the first place as noted above (yeah, i know it's easier said than done!).


One possible fix that you could try is stall strips: http://en.wikipedia.org/wiki/Stall_strips

Stall strips force the stall to start from the wing root and so prevent 'snap' (tip stall).. bear in mind though they wont stop it stalling, only flying faster, reducing the weight or 'elevator management' can do that, stall strips just make the stall less violent when it occurs and maintain some aileron authority in the stall.

For model purposes you would probably have to make them bigger than typically used on full size planes.. i'd guess something like a piece of 1/42 triangular balsa stock sanded to fit the LE profile and running from wing root to about 1/3rd of the wing panel span.
Thanks again
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Old 04-05-2011, 02:38 PM   #4
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Last evening I tried to weigh it. What I found is I probably don't have the right scale. Best I could come up with was to weigh myself on my bathroom scale, 197.6 lb. Then once digital scale had settled I had the wife hand me the plane with flight battery in it as if it was flight ready, 200.6lb. That tells me it is about 3 lbs. If I'm converting right 3 lbs is 48oz so I'm at the upper end of the recommended weight. Right?
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