ggate

My Feedback: (1)

Hello guys.
Pilot yak54 26%
mdl 35 engine.
good flier but needs a few tweaks
problem im having is getting it trimmed correctly.
I have about 3/16 up trim in evelators for level flight.
balance per there dimension-played with that some while flying.
flip inverted and it wants to climb even with the up trim in evelators-weird, you would think it would go down.
What is problem?

mvallyman

My Feedback: (32)

How is the motor, does it have down thrust?

AMA 74894

My Feedback: (1)

yup, that's the FIRST thing I'd check... those symptoms scream "too much down thrust."

ggate

My Feedback: (1)

Thats what i was sort of thinking-just mounted per instructions.Not sure if kit is built with downtrust in it. I will check that. Thanks guys. If weather permits i will tweak this week-end. Will let u no outcome. Very nice plane if i can get the sticks to feel like i want.

speedracerntrixie

My Feedback: (29)

First thing to do with any new airplane is to measure it out. It's impossible to make adjustments without a baseline. This particular airplane should be set engine zero up or down 2.5 degrees right, stab at zero and wing at +.5. Once this is sorted out and it still carries up trim then it's nose heavy.

ggate

My Feedback: (1)

Make sure im hearing you correctlly. 0 degree stab and +5 degrees incidence on wing. I hope this is correct-be hard to change if not.
Engine thrust i can adjust.

ggate

My Feedback: (1)

also, engine spacers are same length-so if down thrust, it had to be built into plane. I will check it out tonight. Thank you

speedracerntrixie

My Feedback: (29)

Yes this is correct, this is done for two reasons. First the wing needs to be at a slight + to generate lift. I set the wing at + so I'm not flying the whole airplane at +. Yes it acts opposite when inverted but most guys are used to forward stick while inverted. The second is that it allows slightly forward CG without up trim. This will help tracking in horizontal flight ( forward CG ) and vertical tracking ( zero elevator trim ). Right thrust is to compensate for torque or P factor or whatever they happen to be calling it this week. The only need to adjust engine up and down thrust is to correct for the airplane pulling or tucking on an up line. With this type of airplane never adjust engine thrust to fix a horizontal flight issue.

speedracerntrixie

My Feedback: (29)

Clamp a strait aluminum bar into the prop hub/washer and set to 90 degrees of the stab. Don't trust it was glued in strait.

ggate

My Feedback: (1)

So you guys are saying i have a problem with stab incidence. Wing is fixed in a pocket,i cant change that. I can possibly pivot the stab around cf tube with mods to locator pin. I dont have any great tools for checking incidence but i can figure it out.

speedracerntrixie

My Feedback: (29)

I have no idea just where you are off, it could be a combination of things. That's what getting baseline measurements is going to tell us. You can use the wing as your fixed reference point and set everything to it as long as it's not too far off.

Bob Pastorello

My Feedback: (198)

Nearly all of these size/style/scale aerobatic planes with hatch-canopies are jigged/designed with the fuse top where the hatch mounts as being "zero", and parallel to the long. axis through the fuse fore-aft....that at least gives a common reference measurement starting place.
To get really precise...set the plane up fully assembled on a flat surface long enough for you to measure the L.E. and T. E. of both wing and stab, as well as the engine shaft. Getting those measurements and doing a little math gets you the "real picture" of how it is.
Then, any changes can be very easily repeated, tweaked, reset to get back to "zero".

Usually those wing and stab setups are very close, being that all the cutting is done by laser CNC....so I'm guessing (and based on personal experience with similar designs) that you have a combination of two issues... ONE - and likely most influential - thrust. You need to tell us if trim changes when you change power settings in level upright flight. That is nearly always the easy way to confirm thrust (or wing incidence issues). TWO - likely the CG is wrong as stated.... and too far forward.

ggate

My Feedback: (1)

I am going to check all that i can. I remember having some problems with stab bolt holes lining up when i put them on. I am almost positive that the problem will be there, but until i do some checking i want know. You may be right also, it could be a combination of things. I have moved cg both way,does not make much difference. Had it more tail heavy once-but didnt like that. The Plane is a nice kit and if your just like to fly on the wing its ok.. I'm getting more into 3d and can tell this plane has a problem somewhere. 4 things that come to mine.
up trim on elevators for level flight. Invert an it climbs. Knife edge rolls bad to canopy. When slowing plane down for landing it wants to flare up taking that elevator up trim. I did not figure on having an issue like this from a new plane. Must have been built on a Monday. lol

ggate

My Feedback: (1)

no trim change in power . Once i set trim for level flight engine doesn"t seem to effect it through power range. Even burning off fuel load does not seem to effect it much.

ggate

My Feedback: (1)

here she is-I will figure it with you guys helping me. A learning curve i guess.

speedracerntrixie

My Feedback: (29)

Ok that sheds a little more light. Everything there except for the pull in knife edge is saying tail heavy. Usually a tail heavy airplane will tuck in knife edge. Having stabs that are out of whack could be causing that pull. The elevator trim becomes more effective when the wing is unloaded. I bet on a vertical upline it pulls too. I am in no way suggesting these are the fixes though, the fist step is to measure it out. As Bob stated, the canopy rail is usually a good zero point. Measure down from there to wing TE and LE then make sure the engine is at 90 degrees to the canopy rail. Lastly see where your stabs are. Trying to fix it before you get all those measurements is like trying to align the front end of your car by sight.

ggate

My Feedback: (1)

trying to tell you guys all i can think of- Right now the cg is perfect with back of wing tube.
but like i said i have moved it both ways an problem still there.

ggate

My Feedback: (1)

vertical up line is fairly straight- but that mdl 35 pulls it to the moon fast. lol stalls from a vertical climb- it fall hard on the nose.

Bob Pastorello

My Feedback: (198)

The good news - based on all you've written, I have to say I think you have both thrust and CG issues....that particular airplane at the flying weight it is at may NEED upthrust at the engine and DOWN elev trim, with the CG moved forward. I can explain why I think that, but it will take a lot of typing. Basically, since you cannot move either the wing angle or stab angle (decalage) with reference to each other, you are forced to "fake it" with moving the only things that can simulate decalage changes...and that's engine thrust, pitch trim, and balance.

PM me w/ your email addr for a comprehensive trimming chart.

speedracerntrixie

My Feedback: (29)

Agreed I have had a couple 40% IMAC airplanes that needed just a tad of up thrust to maintain a strait vertical. He should be able to move the stab incidence by elongating the alignment pin holes and then adding shim material to the top side of the hole. My best guess at this point is the airplane is tail heavy by about 1/2" and the stabs are positive 5+ degrees.

Redback

Have you checked your aileron alignment? If you have both slightly up or down can affect trim.

Terry

Bob Pastorello

My Feedback: (198)

Great suggestion - and that works....sounds like we've battled similar out of trim designs that were not quite what we expected...

speedracerntrixie

My Feedback: (29)

Bob, I was fairly serious about IMAC from '97 to '07 working my way up from sportsman to unlimited. May be mounting a comeback this year if I can get my Extra finished up. Been enjoying pylon racing the past few years.

RCVFR

My Feedback: (7)

Speed recommended +.5 degrees, not +5 degrees.

speedracerntrixie

My Feedback: (29)

Good catch, I missed that. Yes, .5 as in 1/2 degree.