down thrust, right thrust, Whats the best way to do this? - RC Groups
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Feb 07, 2002, 10:28 AM
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hawkeye_abm's Avatar

down thrust, right thrust, Whats the best way to do this?

Howdy all,

I'm new to this only been involved in rc flying for a couple of months now. I currently fly both electric and gas and love both.
I've built 3 planes already and will build several more this year im sure. (cant get enough ). I'm like a sponge when it comes to information but information on setting up down thrust and right thrust of engines(be it electric or gas) is hard to come by. I know why you need and how it works but whats the best way to make sure you have it right? This should be simple enough for you guys. Thanks for any help Ken

( If a kit instructions say 2 degrees down, 2 degrees right I just want to make sure thats where i start.)
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Feb 07, 2002, 10:56 AM
Registered User
Do you mean: How do you build the required amount into a model? or: How do you know when you've got the right amount?

If the first, use a T square and measure the deviation from the fuselage centre line. For every 1 degree offset, the deviation from the centre line 12 inches away from the firewall will be 0.2095 inches.

If the second, the model should have the same trim settings when gliding and when under full power. If it is trimmed for the glide and climbs under power, more downthrust is needed. If it turns left, more right thrust is needed. And vice versa of course.
Feb 07, 2002, 11:05 AM
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U2Steve's Avatar
The best way to see if you've got it right to to fly it!

Enough right thrust and you won't do horrible torque rolls or snap left at full power. Enough down, you won't "balloon" or nose up/stall. Generally, one or two degrees is enough for small slow/park flyers. If a kit designer specifies "x" amount, that's always a good place to start- you'd hope he's done a test flight or two himself! Fly it, get it trimmed for straight and level, and see what it does when you hit the power hard. Adjust from there if needed.

Hope this helps,
Feb 07, 2002, 03:09 PM
Registered User
I machine out a copy of the motor or grearbox mounting surface and bore a hole through the prop shaft line and insert a reasonable length straight rod. I attach this to the motor mount and align the rod with the fuse to give the correct down and side thrust angles. Tack the motor mount with fast glue, remove the alignment fixture and finish glue. If you were doing a direct drive setup and had a junk motor you could remove the existing armature and replace it a long shaft.

Feb 08, 2002, 03:21 AM
ChrisP's Avatar
I hardly ever use side thrust, but often downthrust on the TLAR principle (That Looks About Right).
I am a great fiddler when the model is built. I spend flight after flight tweaking until the model flies how I want it to. Almost more often than not I find that there is a pitch change between power on and power off and sometimes yaw (turning) changes. My Tipsy turns significantly right under power and my Bloody Mary left ! Irrespective of how much side or downthrust you built in you invariably don't get it exactly right.

So most of my models use the mixing capabilities of my Futaba F 28 transmitter. I mix throttle with rudder and throttle with elevator. I also change the shape of the mixing curve to adjust when the mixing kicks in. The only thing you can't do is slam the throttle shut, for obvious reasons. I've seen Graupner (?) transmitters where you can vary the speed of the servo response vs speed of stick which would be nice.

My longest flying model was a QT and I was still fiddling with the CG position when it basically fell apart due to fuel soakage after 650 flights !
Feb 08, 2002, 09:23 AM
Registered User
hawkeye_abm's Avatar
Thanks for the help. I will set them up and try em' out sounds like the best way to go. thanks for the replys. laters