I am new at this, my question is how to measure the proper engine thrust angle. Doe's it matter on a 4 stroke VS. 2 stroke? My guess it's the same. So how do you set up the engine with a ruler to get the proper thrust angle? Most ARF's say 1 Degree of right thrust, so what is that in beginners terms? Thanks for your time.

most ARF's will have the offset built in...do you have a cross on the firewall...that will be the where the engine mounts both vertically and horzontally.....if the vertical line is not centered then the thrust angle is already built in

Most ARF's have the thrust angle built in to the firewall. You can usually check this with a square. What model are you working on? Someone here on these forums is bound to know what it should be.

I'd lay a straight edge on the cowling..pointed straight ahead. Then...hold a cheap plastic protractor up to the straight edge to see if you have the correct amount of offset or thrust angle. Might take two people... or at least some tape to hold the ruler/straight edge in the correct position. There is, no doubt, an easier way...but..... I don't know it. Rich

I am working on a Sig 4 star. The engine mounts have predrilled holes with blindnuts. When I mounted the engine I looked at it from the top, and the engine is lined up straight, no thrust angle that I can see. Can I maybe put a small washer behind the left side of the engine mount? Thanks

Hi! I recommend you to use washers on the left side of the mount. And if you wanna be really cool you first put some washers on the upper mounts. This is for some down-thrust. It's a fact that any airplane, high or low winged, WILL pull the nose utt on accelation or down on decelleration. To prevent this you can put washers on the top mounts to tilt the engine a little down. 1 or 2 degrees often helps alot to keep the plane pretty level when throttling. When it comes to sideways thrust the easiest way to measure it is by just trying for example 2 fairly standard washers on the left side and just test taxiing the machine. If it tracks ok without suddenly pulling to one side during throttling(without paying attention to eventual toe-in or out on the gear) then I would test flying the thing.

There's surely a thousand ways of doing this, but this is how I manage.
Good luck!

Thank you Sir, I was about to ask the next question on down thrust, but you answered it. I guess it's a trial and error thing, but I like to make my errors on the ground, not when flying. Testing this will take a few ground tests before it goe's up, I will assure of this. Thank you for helping. We will see what happens.....................

My planes are either scratch built or built from kits, some call for thrust and some don't. I start out with zero thrust and fly the plane to see if it needs it?? I will use washers out at the field as/if needed until I get the plane into trim, I have several planes with zero engine thrust and don't require it. When I get home I measure the washer thickness and make up a tapered hard wood or ply spacer and replace the washers with it. If you don't all the forces and vibration are on that small washer area instead of the complete mount/fire wall. If two degrees are called for on a plane I measure from the fire wall to the front of the thrust washer of the engine, say it's 6 inches. On a sheet of paper I draw one straight line 6 inches long, I then measure 2 degrees from the top of that line and mark it along the side of the first line with a small dot. You can buy rulers with degrees or round degree meters, just draw a line from the bottom of the first line up to the dot then measure the distance between the two lines. This gives you how much off set or how far to the left you have to mount your engine to get the prop to be in the center of a cowl or just be centered in the plane. I'm sure Ken or someone has a drawing of what I just tried to tell you, a picture and that thousand words thing.

If it is a Four Star ARF I would put it together without adding any thrust. If you decide it needs adjustment after flying it you can always add some washers.

Best get it in the air, trim it out and then check for engine side/down thrust. You can't really do this on the ground! Fly a vertical up line, if it pulls left, more right thrust required, if it pulls right less right thrust. On a straight run at full throttle into wind, chop the throttle. If it dives add more down thrust, if it climbs reduce down thrust.

Regards,
Andy

Too much down thrust can really mess things up. Can drive you nuts trying to trim it out