I'm putting the finishing touches on my Tiger Trainer 60 and made a slight error when mounting the engine. The instructions call for the thrust line to be angled slightly the left to counter the torque of the engine. However, I must have missed that step and my engine is mounted pretty straight on. Will this be a huge problem or can it be corrected with a little extra rudder (or aileron?) trim.

Re-aligning it really isn't an option due to the fact that the engine mount is pretty firmly epoxied to the firewall and there really isn't enough room on the arms of the mount to re-drill the mounting holes.

Thanks,
Don

You could add some small washers behind the engine mount on the right side to push the engine to the left. This is a cheap and easy fix.

Correct, BUT it should be pointing to the left only if you are looking at it from the front. If you were sitting in the cockpit, it should point to the right

I thought they all pointed to the right (standing behind plane), but thought this plane could be different. I never owned a Tiger trainer.

Not all designers add this feature, but it often helps most planes. Most of the time, the offset is built right into the firewall

I think the OP made a typo, the only way that the engine would be angled to left of the plane would be if he had a bacwards running engine. They are all angled right because of the direction of the engine.

Hey Don,

I'm finishing a Astro Hog and when I mounted the engine
I noticed it's off a bit. I ordered a new engine mount,since
I had already drilled holes for the engine just in case.

I'm planning on using washers on the Left side to correct
the thrust line. The mount came yesterday, but here is a pic
with the mis allignment.


Bob

If your trainer has the traditional tricycle gear then I wouldn't worry about the thrust angle. It will prolly be just fine.

Are you sure the engine is straight? The right thrust angle is usually only 1-2 degrees or so so it might jump right out at you. Typically, a lot of kits have the thrust angle built into the firewall but some don't.

What I would do is fly it as-is and maybe have a really experienced pilot take it up and get his input. If it seems to be in need of right thrust then shim the left side of the mount (left when standing behind the plane) to push the engine slightly to the right. If it flys OK then don't bother, just fly it and have fun.

Umm.. he said the engine was pretty much straight on, not angled right OR left.

And, he could have installed the firewall wrong which could account for the difference in offset. Brett, I don't understand what you mean by backwards running engine. If it's mounted wrong, well, it's mounted wrong. Has nothing do do with the way the prop turns.

But, as you also said, it probably won't make much difference in a trainer. It is probably ok to fly the way it is without making any changes or adjustments. But, if you really gotta get the thrust angle right, insert a washer or two to push it to the right a bit (standing from behind that is.. )

CGr

The angle is there to overcome p factor right? The direction the prop turns is a contributor to p factor. I was just saying that if he had an engine that ran in the opposite direction, and a prop for it, then the thrust angle would be left instead of the traditional right, thats all. Very hypothetical.

Most stunt planes have zero engine thrust and the pilot has to add the thrust angle as he likes it during the trim process. When I am doing the flight trim I do use washers behind the motor mount but as soon as I have it set correctly I go home and measure the thrust angle then make up a shim to go behind the mount so I can remove the washers. Years ago I used to just leave the washers behind the mounts on small engines until I noticed that all the vibration and thrust was pushing the washers into the wooden fire wall. I mentioned this to an engeneering friend and he pointed out that the washers were only giving the mount a small foot print and putting pressure in those two little spots. Buy using a shim you are spreading this area out. I think it was Dubro but some years ago someone made plastic shims with the degree of side thrust stamped into each one and you could gang these together and place them behind your engine mount and it shifted the thrust evenly. I used to have a few bags of these, anyone know if they are still being made?? Much easier to use then me making up my own.

Wphew.. I'll say..

Either way, he said that the mount was pretty much epoxied to the fire wall. Might be difficult to put a washer behind anything at that rate depending on how much epoxy was used. I'd fly it and see how it went.

Then again, that's just me.............

pdm,

You beat me to the punch. Many of us are so used to seeing this question, we stop reading the entire question.

Don,

I'd try flying it and see if there are any bad habits, probably not, just not optimized. You would have difficulty in redrilling, but may be able to egg out a hole, fill with epoxy & filler, then redrill to rotate the engine a bit.

Jack

Grey beard,

I like the idea of using a shim. Thanks for the tip.

Bob

Brett

Have to disagree with you on this one. Down thrust is to eliminate P-factor. The right thrust is used to lessen the degree that the slipstream from the prop hits the fin/rudder, which causes a left turning effect.



Lm

I agree.

I also would fly the model as it is by now and see how much trim does it need to fly a straight path, if you need a lot of rudder trim then try to disassemble the mount and add shims.

My messy shop, I have one build going on plus my wood/golf ball carving and I have stuff getting charged up for flying tomorrow, crap everywhere!! I was able to move some stuff around and find what I was looking for, that just means I was able to open a drawer and get to the bottom of it. I found two of the old shims I was talking about, they are made out of plastic and are marked. I did a scientific measurement and sure enough, using all my high end precision tools I discovered the markings on the shims are correct. KINDASORTA. My thin shim is marked 1 and it is 1/16 thick then tapers, it came out to one degree or close to it. The other well used shim is 5/32 and marked 3 and it came out to about three degrees. I used to use these a lot in years past but for the life of me I can't remember who made them. Anyone know/remember?? These are good little items to have on hand, I have been making them out of ply but the plastic is cheaper and easier!!

Thanks everyone for the replies. I think when I said "angled to the right" I was thinking of myself facing the airplane (sorry, should have referenced it from the plane's perspective). Just to reiterate, removing the mount is not really an option. It could be done but I would have to destroy the mount in the process. If I have to, then I have to but I just wondered if trim alone could overcome it. I hadn't considered that the firewall may be angled. This kit was an ARF so I did not install the firewall. I checked it with a laser pointer laying between the cooling fins on the engine head.

I guess I'll let my instructor take it up and see if it's ok as is...

Don

I asked my instructor about it and he said as long as it's not angled the wrong way it's fine. His exact quote was "Just means you'll have do some pilot stuff to compensate for it..."

I remembered seeing those shims too, but I couldn't recall who made them. Here they are. These are for a .20 size engine, they also list a .40 and .60 size set.

http://www3.towerhobbies.com/cgi-bin...?&I=LXE951&P=7

Chuck, that was them. I have the number for the 60 size so I will order a few packs from my LHS this week. I got mine years ago from my old LHS, didn't know they were a Tower item.