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Old Feb 08, 2012, 11:19 AM
DONT PANIC! :)
out of stock's Avatar
United States, FL, Lehigh Acres
Joined Jan 2012
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Question
motor must be installed at a certain degree/angle. true or false?

im pretty sure this may apply to some planes but i installed my motor as straight as the standoffs are. sbach 342.

is this true?
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Old Feb 08, 2012, 11:27 AM
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elfwreck's Avatar
United States, CA, Oakland
Joined Dec 2002
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Hey now,
Thrust angles are absolutely vital. If you get them wrong the plane will have all kinds of tracking problems. It could dive under power or with cut power or rise like crazy power on or off. Pull left or right or any combination of these.
Of course correct thrust angle depends on the airframe. High wing, low, or inbetween and various other bits will affect the thrust angle needed for good flight. Yes you can compensate by playing with other trims but those are just poor patches compared to proper thrust angle.
RobII
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Old Feb 08, 2012, 11:31 AM
Huckfest or bust!
cryhavoc38's Avatar
United States, WA, Woodinville
Joined Mar 2007
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Quote:
Originally Posted by out of stock View Post
im pretty sure this may apply to some planes but i installed my motor as straight as the standoffs are. sbach 342.

is this true?
its a good bet that your plane's firewall already has a built in right thrust angle
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Old Feb 08, 2012, 11:31 AM
I hate waiting for parts
Mike_Then's Avatar
United States, NC, Garner
Joined Apr 2001
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Quote:
Originally Posted by elfwreck View Post
Hey now,
Thrust angles are absolutely vital. If you get them wrong the plane will have all kinds of tracking problems. It could dive under power or with cut power or rise like crazy power on or off. Pull left or right or any combination of these.
Of course correct thrust angle depends on the airframe. High wing, low, or inbetween and various other bits will affect the thrust angle needed for good flight. Yes you can compensate by playing with other trims but those are just poor patches compared to proper thrust angle.
RobII
Agreed. Thrust angles are vital to almost every airplane. You can get some crazy, hard-to-correct flight problems with a wrong thrust angle.
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Old Feb 08, 2012, 11:48 AM
DONT PANIC! :)
out of stock's Avatar
United States, FL, Lehigh Acres
Joined Jan 2012
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Quote:
Originally Posted by cryhavoc38 View Post
its a good bet that your plane's firewall already has a built in right thrust angle
makes good sense as someone else has also told me the same thing. thanks
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Old Feb 08, 2012, 11:49 AM
DONT PANIC! :)
out of stock's Avatar
United States, FL, Lehigh Acres
Joined Jan 2012
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Quote:
Originally Posted by elfwreck View Post
Hey now,
Thrust angles are absolutely vital. If you get them wrong the plane will have all kinds of tracking problems. It could dive under power or with cut power or rise like crazy power on or off. Pull left or right or any combination of these.
Of course correct thrust angle depends on the airframe. High wing, low, or inbetween and various other bits will affect the thrust angle needed for good flight. Yes you can compensate by playing with other trims but those are just poor patches compared to proper thrust angle.
RobII
very good info. very! thank you!
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Old Feb 08, 2012, 11:53 AM
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srt8madness's Avatar
United States, TX, Houston
Joined Nov 2011
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Now on a twin, you need down thrust, but if you run counter roatating props you can install them straight, correct? Or do you still need to angle to the right?
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Old Feb 08, 2012, 12:09 PM
DONT PANIC! :)
out of stock's Avatar
United States, FL, Lehigh Acres
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Quote:
Originally Posted by srt8madness View Post
Now on a twin, you need down thrust, but if you run counter roatating props you can install them straight, correct? Or do you still need to angle to the right?
good question
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Old Feb 08, 2012, 12:18 PM
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United States, CA, Garden Grove
Joined Oct 2000
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Down thrust counters tendency of model to go nose-up under full power. Right thrust counters tendency of model to yaw left during takeoffs. Just noticeble down and right thrust are usually about right for most models. You can make fine adjustments to thrust angles with washers. Note: It is normal and desirable for models and full size planes to fly level at 1/2 throttle, rise at full throttle and descend at 1/4 throttle. Right rudder stick is also needed with right thrust to keep model from yawing left during takeoffs. Elevator trim can be used used for sustained level high speed flight. Sorry if you knew all this!


With twin counter-rotating motors/engines, both propped and pulling equally, they should cancel each other's torque and other effects.
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Old Feb 08, 2012, 12:28 PM
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United States, CA, Oakland
Joined Dec 2002
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Hey now,
Single or multi, contra or paralle thrust angle still depends on the airframe.
A fun game and fantastic learning experience is to bring a sack of washers out with your favorite model and play with thrust angles. Just try different ones and see how it affects flight. You may be surprised just how much you can alter flight characteristics with tiny changes in thrust angles and/or prop rotation.
This is just one of the games I like to play at the field.
RobII
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Old Feb 08, 2012, 01:41 PM
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Livermore, CA
Joined Sep 2004
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If the motor is mounted directly in line with the cord line, then setting it at "O" "O" angles usually works best.
On a Twin, with counter rotating props, angles would not be needed if the motor shaft lined up with the cord line. If the motor was above the wing cord line or hanging below, it may need just a bit of angle.
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Old Feb 19, 2012, 04:42 AM
I fly bipes
southside's Avatar
United States, OK, Elgin
Joined Dec 2011
101 Posts
down thrust and right thrust

2-3 degrees down and 2-3 degrees right thrust makes for a good flyer....they correct pitch and counterforce from the revolving prop
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Old Feb 19, 2012, 09:38 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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It depends on the model.... and what is its designed intention.

General sport models benefit from down and usually right thrust ... countering climb tendency of lifting wing, torque / yaw effects acting on tail. But move on to full spec pattern models with fully symet wing forms .. zero incidence tails etc. and you may find as I did when I flew pattern - that zero / near zero down and limited right is called for.

Thrust angles are a consequence of design parameters ... wing incidence, wing profile / form, tail incidence, vertical fin offset angle to longitudinal line etc.
Even building a kit can alter the reqt's ....

But lets be honest in most flying conditions and sport models - you'd be hard to tell difference unless a significant adjustment... unlike an pattern machine.
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Old Feb 19, 2012, 09:50 AM
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ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
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For a twin you usually don't need right thrust, simply because the engines don't usually blow air right across the tail (this is different for a P-38, which requires counter rotating props to counteract the vortex flow across the dual rudders.

Down thrust is needed mostly for high wings and not so much for low and mid wings, due to where the lift vector acts on the plane. For pod mounted motors far above the vertical CG where the lift vector tends to pitch the plane down with power application, you need up thrust. (ie seaplanes)
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Old Feb 19, 2012, 09:54 AM
Yea, I fly dusty planes..
zeezee's Avatar
United States, LA, Angie
Joined Apr 2009
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I just rebuilt a Big Stik a buddy gave me and electrified it with a .46. All he told me was that the back of the prop should be 4" from the firewall. It did CG out perfect with the addition of the ESC!!. I made a sub-mount for strength and didn't know if the plane already had offset in it. I have the point of the spinner about a 1/8" off center line on the plane and maybe 2 degrees down thrust. Looks good, according to other planes I have seen. I have enough thread on my bolts to add washers for shims if needed. I think the 1st picture is correct; how it will fly; the 2nd and 3rd are down too much. We'll see! I am anxious about my maiden tomorrow. I am sorta glad for all the rain as my strip is to wet to get on now. Time to reflect. Wish me luck. Dave
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