Feb 16, 2012, 10:05 PM I'm a pilot... 100 yrs to late USA, FL, Palm Harbor Joined Jan 2005 3,780 Posts Discussion Installing right thrust and whats the measurement What's the best way to create 2.5 degress right thrust on a firewall.. By sanding the angle into the back of the motor mount or using a shim on the fireweall. Firewall is already in place per instructions / plan. Also how would I know what a 2.5 degree offset would be in terms of the distance offcenter of the shaft? I know the formula has to do with the radius of the circle. For example a 2 inch circle will be quite different from a 2 foot circle where the 2.5 degrees would be a much larger linear measurement. My radius would be the distance from firewall to propeller.
 Feb 16, 2012, 10:18 PM KE your cub. Australia, WA, Perth Joined Jun 2005 4,391 Posts With a pre- positioned firewall, I would be inclined to shim. Also, you say 2.5degrees, this is only a starting measurement, you may find you need more, or less, so if you sand the mount you wont get back what you took off. as for the offset, ask a high-school kid to work it out. It's simple trig
 Feb 16, 2012, 10:42 PM I'm a pilot... 100 yrs to late USA, FL, Palm Harbor Joined Jan 2005 3,780 Posts Good point on the starting point! Shim it is. Yeah, I've foud some formulas but it's a pain in the arse. I just realized I have several plans that show right and down thrust and degress so I'll find one and measure that.
 Feb 16, 2012, 10:47 PM KE your cub. Australia, WA, Perth Joined Jun 2005 4,391 Posts if you give me the distance from the mount to the thrust washer I can knock out a mud map for you. If you give me the width of the mount I can give you the width of the shim too.
 Feb 17, 2012, 01:39 AM Registered User United States, CA, Clovis Joined Mar 2004 3,500 Posts Just put a few washers behind your mount.... with a few good washers.. you can easily change all the angles for right-thrust or down-thrust... and if you want to adjust it.. guess what?.. just add or subtract a few washers.. once you find your angles you might want something permanent..but washers work fine. .. I've actually found it to be that simple.
Feb 17, 2012, 07:07 AM
ARFs Are Me
Traverse City, Michigan
Joined Dec 2005
12,395 Posts
Quote:
 Originally Posted by DGrant Just put a few washers behind your mount.... with a few good washers.. you can easily change all the angles for right-thrust or down-thrust... and if you want to adjust it.. guess what?.. just add or subtract a few washers.. once you find your angles you might want something permanent..but washers work fine. .. I've actually found it to be that simple.
Not that I use right/down thrust that often, but when I do, washers provide the most simple and easy solution.
 Feb 17, 2012, 09:30 AM Visitor from Reality United States, VA, Arlington Joined Dec 1996 12,788 Posts My custom design/build service puts in estimated sidethrust by working out the angle needed for the firewall on the initial plan, then figuring the motor mount offset position to put the prop rear face centre on the model centreline. But any adjustments are done by me with washers, which then puts the prop centre off the model centre a little. Which doesn't ever seem to bother the model all that much. I'd vote for a small drawer with a plentiful supply of washers. Thick and thin per diameter are good if you're real fussy D
Feb 17, 2012, 11:17 AM
Registered User
United States, FL, Edgewater
Joined Nov 2010
167 Posts
Forget equations, Use a simple drawing with your known values to figure out the offset. Draw a T exactly 90deg. set up a protractor at 2.5deg offset of the 90deg. using your known distance from firewall move the protractor left until the arm crosses your measurement on the line. there is your offset. simple and without math. I tried to show on pics but I stink with "MS Paint" Thought that counts, right?
And definitely use shims, that way there is no issues later when you need to readjust. It seems most mounts these days have slotted holes to move the mount around a little bit to adjust this very thing.

# Images

Feb 17, 2012, 12:58 PM
An itch?. Scratch build.
South Wales U.K.
Joined Mar 2003
15,184 Posts
I'll throw another consideration in.

Does it have a cowl and spinner ?, if so, be careful or you could end up with the cowl angled as well.

If you angle the motor from the planes center line, placing the rear of the motor on the center and then angling it, the spinner can end up away from the center line enough to look a little odd.