up thrust & down thrust - RC Groups
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Jul 25, 2004, 02:44 PM
Anything to do with RC
3D4ever's Avatar

up thrust & down thrust

I'm new to this, I build a plane with a brushless motor setup but after build they motor come out with a little up thrust and right thrust? I know that the plane have right thrust but i don't know if the up thrust will make the plabe hard to fly.

I don't get the up thrust and down thrust part. Can anyone tell me anything about it.

Thanks ALL
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Jul 25, 2004, 03:46 PM
Electric since 1990
Foamaholic's Avatar
Depends on the plane.
Don't know the science, but downthrust would keep the plane from climbing too steep under power.
Right thrust helps negate the torque of the spinning propeller which, in a tractor setup, makes the plane want to turn left.
So upthrust would increase the angle of attack when under power. If the plane tends to dive when power is applied, it needs some upthrust. It it tends to pitch up too much or causes a stall then downthrust is called for.
The only way I know to find out if the upthrust is bad on your plane is by flying it.
If the instructions said to add it, then it should be okay.
Jul 25, 2004, 04:21 PM
Anything to do with RC
3D4ever's Avatar
The instruction didn't say anything. The plane come with the motor and the mount but i upgrade to a burshless motor stup so i have to build the mount my self. It does have a right thrust setup but i don't know if the up thrust will hurt the plane fly.

Thanks foamaholic
Jul 25, 2004, 08:27 PM
Electric since 1990
Foamaholic's Avatar
What plane is it, or what type of plane?
Don't think I've ever seen one that calls for upthrust. Maybe something unusual would.
If I had to guess I'd keep the right thrust and get rid of the upthrust.
If you can't do that then I would be very careful with throttle until you see what it does.
Jul 25, 2004, 08:42 PM
Average User
M Ashmore's Avatar
Re-read the post.
The plane didn't come with upthrust. After building a new mount for the brushless motor, it now has upthrust.

3D4ever - Post the name of your model. People can help if they know what you're working with. Off the cuff, I'd say upthrust is not going to be good.
Jul 26, 2004, 01:43 PM
Anything to do with RC
3D4ever's Avatar
it a wattage cap 232 around 25oz with everything RTF.
Jul 26, 2004, 03:29 PM
Electric since 1990
Foamaholic's Avatar
An aerobatic plane probably would want zero offset all around.
Jul 26, 2004, 05:09 PM
Mom says I'm special...
beafraid8's Avatar
I believe my Wattage Cap had some right and down built into the motor mounts, even more so after a few repairs!! I now have it set right at zero (eyeballed) and it's flying better than ever! (Mega 16/15/4, 2.5:1, APC 10x7 E-prop, 3s2p Kokam 1500's)

The downthrust caused some very bad nose-overs during hover attempts, and if you're not too jerky on your throttle control you can keep the torque-effect to a minimum.

I've found that there's no loss in performance during inverted flight or knife-edge with the motor as straight as possible.
Jul 26, 2004, 05:48 PM
Low AltiDude
PGR's Avatar
Originally Posted by Foamaholic
An aerobatic plane probably would want zero offset all around.
Not so, especially for an aerobat.

It's very advantageous that an aerobat fly trimmed and true with all control surfaces neutral. If you trim an aerobat to fly upright and wings-level with your control surfaces, it could have very adverse effect on the inverted and knife-edge flight characteristics of the plane. So if you can't do it with your control surfaces, that pretty much leaves wing and horizontal stab angle of attack and thrust offset.

For example, I was able to trim my Telink Big Bubble (using elevator and aileron trim) to fly true in both upright and inverted attitudes with little to no stick input but trimmed like that, maintaining knife-edge flight was a frustrating 2-thumb ordeal. After dialing in my CG and prop thrust angle(s), I was able to zero all control-surfaces and now, holding a knife-edge attitude only requires rudder input and both upright and inverted flight are now possible thumbs-off.

Every plane is different, but I don't know any that fly the best with centerline prop thrust save for the bug suckers (ducted-fan planes).

Jeez, I bet I'll hear about that crack!

Jul 26, 2004, 06:18 PM
Anything to do with RC
3D4ever's Avatar
I guess i juat have to fly it with the up thrust see what will happend.
Jul 26, 2004, 06:54 PM
Electric since 1990
Foamaholic's Avatar
Just don't let it zoom up and stall when you take off. Get ready with down elevator and back off the throttle if it zooms up. You might have to do it fast.
Jul 26, 2004, 08:34 PM
Anything to do with RC
3D4ever's Avatar
Thanks i will be careful on that. Hope everything work out.
Jul 27, 2004, 04:55 AM
Registered User
djindivik's Avatar
Take out the upthrust !! Start with a couple of degrees of down thrust & a couple of right thrust, or return everything to where it was on the original set up.This is usually a good starting point & should be pretty neutral. You want the plane to climb under power & decend with no power. Aerobatic fliers take months to get it right, but that is extreme. Fly it & see what happens. Ray
Jul 27, 2004, 05:22 AM
Registered User
Fredrik W's Avatar
DONT back off the trottle if the model zooms up. Feed in down elevator to level out, THEN back of the trottle. Or the model will stall and fall out of the sky.

// Fredrik Wergeland
The Great Electric Motor Test
Jul 27, 2004, 05:44 AM
Registered User
Aio_1's Avatar
Right Thrust:
Looking from behind a standard model prop rotates clockwise. In order to spin the prop clockwise the motor also exerts an equal force on the airframe in the opposite direction (rotational force is called torque). This causes a tendency to roll left. Right thrust counteracts this to some extent. Because the torque changes depending on motor speed, prop and flying conditions it would not be possible to trim it out with the ailerons or rudder. However right thrust means the corrective force is dependent on the same criteria so it automatically matches the problem force.
Down thrust:
Stable airplanes are set up so that the CG is in front of the neutral point of the aircraft. When you trim the plane to fly level you set up a pitching force to hold the nose level despite the forward CG position. When you speed up this force increases and the plane pitches upwards beyond level. When you slow down the nose drops.
Sometimes you might want a plane to act like this but usually and especially in the case of an aerobatic plane you want the attitude to remain unchanged when the throttle is adjusted. Down thrust provides downforce proportional to the throttle setting to keep the nose level. A correctly trimmed model should almost always have downthrust and right thrust. There are exceptions of course - for example if the motor is mounted well above the CG it will apply a nose-down pitching effect anyway.

I think that's a bit of a clumsy explanation but I hope it helps.


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