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Air Crash Investigation

Why did it crash???

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Paddy Fidling23/06/2010 23:45:03
122 forum posts
6 photos
Well i'm quite sure that the cause was a too powerfull motor as i was rolling at only about a 1/4 throttle and probablly didn't need full throttle but all the controlls were working fine? Any suggestions as to why else this happened?
Tim Mackey23/06/2010 23:50:31
20920 forum posts
304 photos
15 articles
Torque roll....IMO she needed more corrective rudder on the ground run.
Gemma Jane23/06/2010 23:52:03
1349 forum posts
53 photos
Another vote for Torque roll. 
Tim Mackey23/06/2010 23:59:41
20920 forum posts
304 photos
15 articles
Paddy.... bad luck mate, but the damage didnt look too bad. I have "frozen" the film playback several times and can see no sign of right rudder being used. The aeroplane will want to "screw" over clockwise to the left in opposition to the counterclockwise rotating prop and motor, and also from the "screwing" motion of the propwash hitting the fin in a swirl pattern - pushing the tail to the right (as viewed from behind)
Its a perfectly normal trait of many aircraft both model and full size, and gentle and smooth progressive throttle is needed, and as the tail starts to lift on the ground run, use right rudder to counter the forces.
All part of the learning curve mate
Ultymate24/06/2010 08:19:11
1703 forum posts
62 photos
Not sure I'd go with the torque roll theory, I've got and have had many more grossly overpowered models and never any T/R effect at take off. Were you taking off crosswind ?
          The only model I've had do something similar was a Pitt's Special that at take off speed suffered from aileron reversal effect, after several cartwheeling take offs I learned to fly it on rudder until the airspeed was sufficient for the ailerons to work correctly.  
Peter Miller24/06/2010 08:27:31
11222 forum posts
1321 photos
10 articles
I am not completely convinced by the torque roll theory.
If it was just torque the model would start to swing to the left as soon as it started rollling. It does not turn at all until it clears the ground.
 I also note full opposite aileron which is not having any real effect.
I hesitate to ask but have you checked very carefully for warps?
Bruce Richards24/06/2010 08:57:08
1849 forum posts
I see this happen all the time at our patch with this cub type model. It is usually a combination of lifting off the ground with too little speed and application of sudden throttle. Try letting it roll on the ground for longer and slowly opening the throttle. You will need to use the rudder to keep it tracking straight, but be careful as speed builds the rudder becomes much more effective so you will need to ease off the rudder as ground speed increases.
ken anderson.24/06/2010 09:06:38
8714 forum posts
808 photos
paddy-i would say you didn't react in time to the model---i would think you were expecting it to roll...and lift off...and when it went to the left-you didn't catch it in time and it hit the deck-------i would try a combination of longer take off roll and be gentle with the elevator...and get ready to catch it if it go's off to one side........this has happened to us all... ..
Paddy Fidling24/06/2010 11:09:52
122 forum posts
6 photos
Thanks for the replys guy's, i had kinda expected torque as ther was virtualy no wind, and what there was i was flying into. The model itself was fine, just the motor shaft sheared clean off, but i have a spare so no biggie. I will make a note for a longer smoother throttle increase next time, with added rudder, which given the conditions should be in a couple of days.
Always nice to have my suspisions  confirmed by the experts
Thanks Again
Andy Gates24/06/2010 18:12:56
643 forum posts
20 photos
I too would go for premature lift off.
Watching the video, the tail has only just lifted when the mains lifted too.
If you added a bootfull of right aileron at that point, the left hand wing panel is very likely to stall out.
The cure, longer take off, more progression with the throttle, and avoid the up elevator input until you have plenty of speed in the plane.
Rethink the Air Crash Investigation and "Why did it crash?"
Think "What did I do wrong?" since that is where most problems lie.
It is either something you did, or maybe did not do.
Myron Beaumont24/06/2010 21:10:30
5797 forum posts
51 photos
Do you have plenty of diff on the ailerons -A lot more up than down. Especially on a Cub. Don't ask me how I know .With too much "down" then what is a good high wing trainer- type model becomes a nightmare .The Cub seems to suffer more than most IMHO & experience (years ago) Having said that ,I agree with other comments about using right rudder for ground direction control & lift off .It was a bit steep wasn't it ?

Edited By Myron Beaumont on 24/06/2010 21:13:19

kiwi g24/06/2010 21:49:57
1257 forum posts
Paddy I would say not enough ground speed for take off.
It sounds like a nice even application of power, I see you are correcting with the alierons but cannot see the rudder. Although cubs can take off slow at that speed alierons would have less effect. also I see you have full elevator in so once you start to roll to the left the elevator was becoming the rudder and because of the lack of speed the alierons would be struggling to keep up .
Try the run up as you did and release the elevator and let the cub lift off by itself.
Nice plane tho paddy.
good luck  
Kiwi g
Paddy Fidling24/06/2010 22:42:04
122 forum posts
6 photos
Thanks for the inputs everyone, Mental Notes made:
Longer Take off run,
Use Rudder!
Ease off Elevator
Thanks again

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