Patriot

My Dad used to do this and showed me how. Wasn't sure if this is how everyone does it, as I hear most using washers to set thrust angle but in additon to that, this is what I do.
Let me know what you guys think of my way for setting thrust on my new plane.
I know using washers is common, which I plan to use on the engine mount against the firewall. But what has always concerned me, is that with larger engines (more vibration), the gap between the firewall and the mount provides less contact support for the mount. So I am used to tracing the mount footprint on the firewall then removing it. Install the washers, and before reinstalling the firewall, add a layer of wax paper to back of the mount. Then run a bead of 30 min epoxy along the traced area of the firewall to fill in the gap when the mount is installed. Install the mount, with engine on the mount, and check alignment and thrust angle just to be sure. When fully cured, remove the mount and peel away the wax paper, sand or file as necessary. Now you have a nice formed footprint for the entire mount against the firewall. Any thoughts?

Patriot

Patriot

Of course do this after the first test flight using only washers so that you know your thrust is correct for actual flight.

Patriot

MinnFlyer

My Feedback: (4)

Sounds like a pretty good idea.

Richard L.

My Feedback: (24)

I usually cut a strip of either brass or aluminum 1/16" or 1/8" thick to the proper length and drill two holes in it for engine mount bolts to go through. I then sandwich it between the firewall and the mount. Plenty of contact surface.

vinnie

My Feedback: (1)

I just buy these.

http://www2.towerhobbies.com/cgi-bin...?&I=LXE953&P=7

Patriot

Those Ernst thrust plates are sure nice, and make it very easy to set up a very precise thrust. However, I have looked for these in the larger sizes for 1.50 and up and they don't seem to exist, or maybe I just haven't found any. The Ernst says it fits .60 size mounts and a few smaller ones, but that's it.
Wish these came in a broader range of sizes and shapes.

Patriot

CafeenMan

Go to a shop that sells auto paints and supplies. They have plastic squeeges that can be cut to any size needed. The only problem is that the wedge may be the wrong angle.

aimmaintenance

Is this mainly needed on 90 size or bigger planes.
I've never done it.
Am I missing something that will make my 40 size stuff fly better.

CafeenMan

You need to look at a trim chart. I know there's one at the Futaba web site. The only way to determine if your aircraft needs a thrust adjustment is to go through the trimming sequence.

There's a lot more to trimming an R/C aircraft than straight and level flight.

I & C Tech

My friend and I are both building UCD 60's. I used the Ernst plates successfully. My friend sanded his motor mount to achieve his desired angle. He hasn't flown it yet but we hope he got it right.

J_R

You sure got that right. Here is a good trim chart: http://www.wtp.net/DBEST/trimchrt.html

I have used ply strips for shims for years. I usually cut them about 1/2" wide and fit them under the firewall and hold them with the bolts, lilke the brass idea already suggested. Since ply is between 1/64 thick, up, you can normally find some that is just the right thickness for what your doing.

Triming the plane right takes a while, and when the chart reaches the point where you are supposed to cut the wing in half and change the dihedral... I quit.

JR

Patriot

Cut the wing in half, AUUGGGHHHH!!!!!!!!!!!!!!!!!![:@]

Not a chance, I would rather learn to fly with it as is. [&:]

The reason I mention my method in the beginning of his thread is because when you use a thin shim plate or a peice of ply, the thickness of the shim is the same for its whole length. So, when you need a right and down thrust, your mount will need a shim that is tapered, which is why I like to use small washers under each mounting bolt, fly it to make sure it is right, then run a bead of epoxy onder the areas where it is open between the mount and firewall to fill in the tapered area between bolts. If you use a flat shim, then it could, and I say "COULD" cause the mount to give a slightly differant thrust when the bolts are tightened, mainly because it will essentially warp the mount a little. Seems to make sense to me. Your thoughts?

Patriot