Hi Folks
Quick question for all you hardened Aerobatic flyers.
I am new to this and I am in the process of trimming an airplane. According to the test ( ie the pull straight up vertical and see which way the plane deviates ) the plane I am working with needs more right thrust than the plane was originally built for. If I increase the side thrust it will leave an unsightly gap.
My question is what do people do about this.
Do they just ignore it
or do they modify the nose of the plane once the correct right thrust has been achieved so that the airplanes clean lines are restored.

Mike

I tried re-mounting the engine mount. Takes the longest time because of work involving the original firewall, blind nuts etc.

Just shimming one side of the mount and forget about the clean lines. Fastest.

Replacing the engine mount with a slightly wider (adjustable) mount so that the engine can be turned a little bit.

If you really want to preserve the clean line matching and you are 100% sure that the side thrust adjustment is 100% correct., you may have to mix and match above.

I suggest you to go with the simplest and fastest way, because you may have to re-adjust the thrust.

This is why I use smaller diameter screws to mount some of the engines.

3mm screws on 4mm mounting lug holes etc.

Hope this helps,

Hummmm. Why's that? Badly built or over powered?
I say that because this is a typical down side of overpowering. You could also be using the wrong prop? Different pitches and dyameters effect the engines trust/torque ratio which will effect the amount of right thrust needed.

As will your pull up to vertical... which unless done correctly (pretty difficult for a beginner as any pattern flyer will tell you) will give you a false inpression of which way the aeroplanes tracking. As is an of set fin, and not forgetting the horizontal balanse... if you left wing is heavier than your right and you've trimmed it out with aileron you'll be flying under a false impression that'll only show up in a vertical plane.

The enlinement of the horizontal stab is also critical ...as are elevator halfs that have exactly the same ammount of movement If it's not 100% straight in both planes and identical in motion... your pull up will be a F-up!

I'd start with the obivious:
Check the aeroplanes built 100% straight.
If the fin is off you'll need to correct this will rudder trim.

Check the stab. Straight when you measure it from the top (Wing tip to Stab tip) and parralle to the wing and 90 deg to the fin when you look down the body.If thats all 100%, check the horizontal balanse and correct as necessary.

Next your power. Is it more than specified? if it you have some options. Add more right trust but remember, anything over 3 deg' is getting negative. Change to a different prop. Change to a different engine or try flying the verticals at a lower throttle setting. You have a rudder remember, all aeroplanes will eventually start drifting left and this need to be corrected with a little right rudder stick.

If all the above is in good shape, have a look at how you're entering the verticals, the wing must be absolute paralell to the ground. If not the vertical transition will be off.

Time to experiment.

Gents
Thanks for the advice. The plane I am flying is a 1970s design called the Tornado. It has no side or downthrust but I am using a modern 60 in it. Everything else does check out.
Basically what you are telling me is that if I build a modern pattern design ( which I am currently doing) it should require no engine offset other than that already built in.
For your info I am currently building a MK Skystar which was built for a YS90 but I am putting a Webra 80 long stroke into it.

Mike

Well yes and then again no.
A good well sorted design sould have all the trust angles built/designed in. This depends on just how many hours the producer/designer invested in testing. With a company link MK you are pretty well sure that you're getting something worth while.

But think about this... It was as you say, designed around a YS .91. Thats what the designer used probably with a 14x10/12 APC prop etc etc...and he was happy! Now when you come along with a Webra .80 long stroke, quite a different kind of engine/power delivery I wouldn't expect it to match 100%. You'll very likely have to do a little tweeking here and there. Thats got to be excepted. Again, prop choice can make a great difference. I have a YS.91 powered G-Trick. 14x12 it tracks left. 14x8 it tracks right, 14x10, spot on.

Different designs have diffent ammounts. I have one 2x2 with 1deg down and 1.5 deg right and another 2x2 (with the same wing and stab) that has 1.5deg down and 3.5deg right. Hummmmmm. It goes without saying the former (the expensive design) flys far better then the latter(the cheap design).

By the way, with regards to the original post, if you have no down and right thrust, no wonder its going all over the place. Make the corrections PatternFlyer suggested.

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

These might help.