Trim Help!
07-10-2005 | 03:08 PM
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From: Huddersfield, UNITED KINGDOM
Trim Help!
Hi everyone , i was hoping some of you more experienced guys could help me out with this airplane
it flys fairly ok except for.. i have to add down elevator trim if open the throttle too much to prevent the airplane from climbing , and it kindof seems a little.. i dont know like there are counteracting forces for up and down,, i cant really explain it any better than that , sort of like , there is up thrust being counteracted by down elevator ... if that makes sense .. but the other problem i am having also , and this is the one that bothers me the most is look how much aileron trim i need on just to stop it from banking over (gently) during flight...
if there is any other part of the airplane that anyone needs to see in more detial let me know and i will post the pictures
, this is a plane i rebuilt from wreckage, just incase it is anything to do with that. the link to that forum is Here->
[link=http://www.rcuniverse.com/forum/fb.asp?m=3073651&key=trainer%2Ctrash%2Cresurection]Here[/link]
Rick
it flys fairly ok except for.. i have to add down elevator trim if open the throttle too much to prevent the airplane from climbing , and it kindof seems a little.. i dont know like there are counteracting forces for up and down,, i cant really explain it any better than that , sort of like , there is up thrust being counteracted by down elevator ... if that makes sense .. but the other problem i am having also , and this is the one that bothers me the most is look how much aileron trim i need on just to stop it from banking over (gently) during flight...
if there is any other part of the airplane that anyone needs to see in more detial let me know and i will post the pictures
, this is a plane i rebuilt from wreckage, just incase it is anything to do with that. the link to that forum is Here->
[link=http://www.rcuniverse.com/forum/fb.asp?m=3073651&key=trainer%2Ctrash%2Cresurection]Here[/link]
Rick
07-10-2005 | 03:20 PM
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From: La Vergne,
TN
RE: Trim Help!
I can't speak for the elevator trim, since I'm not sure I understand your statement about 'counteracting forces for up and down'. Sounds to me like MAYBE the engine is mounted with too much upthrust, but I'm not sure. Perhaps someone more experienced may better understand what you're describing.
As for the aileron trim, I wouldn't worry a whole lot about it to be honest. My Telemaster 40 that my uncle gave me to learn on had at LEAST that much left aileron in it, and judging from your photos probably more.
It's probably just a slightly uneven wing, or perhaps it doesn't sit level on the saddle. Could also be a a difference between the horizontal axes of the stab and wing.
Here's what I'd suggest for the ailerons:
You don't say what kind of plane this is, but it's clearly a high wing. With the wing mounted, look down the length of the plane from the front. Move your point of view up and down until the horizontal stab JUST disappears under the wing...both sides of the stab should 'meet' the wing at the ame time. if they don't, then one (either the h stab or the wing...or possibly both) are off level. If it's the wing, some foam watherstripping or some other sort of shim between the bottom of the wing and the saddle may take care of it. If it's the stab, you can fix it if you wish by CAREFULLY cutting the stab away from the fuse on the high side, and putting thin balsa shims in, and re-gluing. Just be very careful not to cut into the body of the stab itself, as this will significantly weaken it.
As I say however...if it flies well with that trim in it, then I wouldn't worry too much about it. I WOULD suggest (if you haven't done so already) setting the trim through hardware (adjusting clevises, resetting servo control arms, etc) so that the radio's trim settings are nuetral, and thus you retain complete aileron travel in both directions.
HTH
As for the aileron trim, I wouldn't worry a whole lot about it to be honest. My Telemaster 40 that my uncle gave me to learn on had at LEAST that much left aileron in it, and judging from your photos probably more.
It's probably just a slightly uneven wing, or perhaps it doesn't sit level on the saddle. Could also be a a difference between the horizontal axes of the stab and wing.
Here's what I'd suggest for the ailerons:
You don't say what kind of plane this is, but it's clearly a high wing. With the wing mounted, look down the length of the plane from the front. Move your point of view up and down until the horizontal stab JUST disappears under the wing...both sides of the stab should 'meet' the wing at the ame time. if they don't, then one (either the h stab or the wing...or possibly both) are off level. If it's the wing, some foam watherstripping or some other sort of shim between the bottom of the wing and the saddle may take care of it. If it's the stab, you can fix it if you wish by CAREFULLY cutting the stab away from the fuse on the high side, and putting thin balsa shims in, and re-gluing. Just be very careful not to cut into the body of the stab itself, as this will significantly weaken it.
As I say however...if it flies well with that trim in it, then I wouldn't worry too much about it. I WOULD suggest (if you haven't done so already) setting the trim through hardware (adjusting clevises, resetting servo control arms, etc) so that the radio's trim settings are nuetral, and thus you retain complete aileron travel in both directions.
HTH
07-10-2005 | 03:49 PM
#3
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RE: Trim Help!
It's normal for it to climb with additional throttle, but how much is to much? Dunno. JB has a pretty good theory going there, bu a trim setting is only good for one throttle setting. Add more and it will climb. Remove some and it will descend. Physics and wing loading.
DS.
DS.
07-10-2005 | 08:42 PM
#5
Senior Member
RE: Trim Help!
Rick:
Way to much upthrust in the engine. Shim the motor down a bit at a time till it will not climb when you add throttle. This is called neutral trim. The wing probably has a bit of a warp in it. For a trainer type plane I wouldn't worry about it although a heat gun may take a lot of it out.
Way to much upthrust in the engine. Shim the motor down a bit at a time till it will not climb when you add throttle. This is called neutral trim. The wing probably has a bit of a warp in it. For a trainer type plane I wouldn't worry about it although a heat gun may take a lot of it out.
07-10-2005 | 09:40 PM
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From: N Central,
TX
RE: Trim Help!
Rick..... Nice rebuild... as far as the vertical climb with full throttle the guys are spot on, a tweeking of downthrust will help... but you will have to live with any elevator trim beyond a good flying speed.......
As for the trim (aleron) to fly straight and level, there is a lot of things to consider..... but of course you could live with it ... I noticed on your rebuild photos, the engine had a lot of left thrust, ( the pic with the glow plug removed) Do you have perpendicular thrust or a little right thrust now??? allso I noticed you had wing damage, yes it could be a warped wing, however it looked like you repaired just one side of the wing, the question here is do you have lateral balance??? a quick check is to have a finger under the tail in the center and quickly lifting by the spinner a couple inches off of the table ( with piston in non compression) , ( factoring in any side thrust of the engine) does it allways dip to one side??? and is that the side it allways wants to drift to in flight??? You never did say............ Could be way out of balance left to right, if you know what I am getting at........... possibly adding weight at the wingtip on the cg line might help with that if you are way out of side to side balance...... Just some thoughts, Captain Crash...
As for the trim (aleron) to fly straight and level, there is a lot of things to consider..... but of course you could live with it ... I noticed on your rebuild photos, the engine had a lot of left thrust, ( the pic with the glow plug removed) Do you have perpendicular thrust or a little right thrust now??? allso I noticed you had wing damage, yes it could be a warped wing, however it looked like you repaired just one side of the wing, the question here is do you have lateral balance??? a quick check is to have a finger under the tail in the center and quickly lifting by the spinner a couple inches off of the table ( with piston in non compression) , ( factoring in any side thrust of the engine) does it allways dip to one side??? and is that the side it allways wants to drift to in flight??? You never did say............ Could be way out of balance left to right, if you know what I am getting at........... possibly adding weight at the wingtip on the cg line might help with that if you are way out of side to side balance...... Just some thoughts, Captain Crash...
