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Multiplex Twin Jet climbs too much????

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Multiplex Twin Jet climbs too much????

Old 05-06-2006, 08:12 PM
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carlrich
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Default Multiplex Twin Jet climbs too much????

I just bought the twin jet and have 3 cell lipo power pulling 25A and really pushing hard on stock motors. Really zips! Problem is that it wont hardly fly level. Wants to climb with throttle. I have the elevons both slightly down to help keep the nose down and have put weight in front that has me nose heavy per CG specs. Still climbs. Anyone else had this problem or advice for it? Could attempt to angle push motors in a fashion that pushes nose down slightly.

Carl
Old 05-07-2006, 07:58 AM
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Larry Dudeck
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Default RE: Multiplex Twin Jet climbs too much????

If you are satisfied with the balance point then you should consider changing the thrust line of the motors. The thrust line should pass through the CoG and when properly adjusted this way, a change in power will not result in a pitch change.

Make small, incremental changes as the effect of ballast in the nose will become more and more pronounced as the thrust line is changed.
Old 05-12-2006, 03:43 PM
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JohnMac
 
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Default RE: Multiplex Twin Jet climbs too much????

Yep, it is definately the trust line. You need downthrust, the more power the more you need. I clamp my motors in with a thin ply plate. This allows me to try different balsa wedges until I get it how I like it.
Regards,

John
Old 05-12-2006, 04:13 PM
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carlrich
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Default RE: Multiplex Twin Jet climbs too much????

John, if you have a picture, I'd like to see it. What you are saying makes sense. The review I read on this twin jet used an 8 cell sub c and listed 17A and 134 Watts which gave 56 W/lb on a 38 oz plane. I am using a 20C 2000mah 3 cell lipo and am reading 25.6 A and 281 Watts (over double) and my all up weight is 30.5 oz. (1/2 pound less) for 147 W/lb. I never thought of it in these terms until you mentioned more power requiring greater down thrust. In this case it is a pusher plane and it flies very smooth and nice (fast) up to about 3/4 throttle or less. Beyond that point it is a rocket but insists on climbing. I am guessing you have this plane and know it is a pusher and therefore I need to tilt the motors in such a way that the back end (near prop) needs to come down to push the back end of the plane up more and thus the front of the plane down. As it is now it is like a boat (motor and prop in back). The more throttle I give it the more the nose wants to come up. If I am thinking this through correctly.
If I change the down thrust such that it flies straight and true at the high throttle end, will it want to nose down at the low to middle throttle area?

I have adjusted this some but it clearly needs more to fly straight at full throttle. I have recently programmed my tx to adjust the down trim proportionally as more throttle is added. This begins at half throttle and increases proportionally with more throttle up to a total of 15% deflection on elevons at full throttle. I've attached this to my flaps switch so I can try it out 2 mistakes high and turn it off if it is not working so well. Have not tried yet. Thanks for the advice!

Carl
Old 03-07-2012, 09:11 PM
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GARY 7
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Default RE: Multiplex Twin Jet climbs too much????



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