my plane needs down trim from the neutral position on the elevator to fly level. Does it have too much up thrust or down thrust on the engine?

hulio

Your problem may not be the engine. It could be the the wing incidence or the stabalizer is not mounted correctly. As for the engine, it could be mounted with some up in it, which would cause the plane to climb. You might want to get an incidence meter and check everything. If you are only dialing in a little down trim, you may just want to not worry about it and fly. Good Luck, Dave

Is the CG (Center of Gravity) within the suggested range?

Check it with the plane fully equipped, ready to go...EXCEPT...no fuel/tank empty.

What plane is this?
Many kits, ARFs, etc have the correct thrust angle already built into the design so as the others have mentioned it may not be the engine.

CG is in the center of the recommended range.

astro hog

if everything is correct except for the engine up or down thrust and the engine has up thrust in it, will that make a plane climb or decend is what I really want to know.

hulio

thats where i am confused....i thought someone once told me that an engine with upthrust in it will make it decend, not climb.

sure wish i knew!

hulio

With up in it, it should climb. Dave

If the model has a flat bottom wing, then it will climb under throttle even if you have added down thrust. If the wingplan is symmetrical or semi-symmetrical, it won't do this. If you have a laminar flow airfoil (only Pica used this on their P-51) all bets are off.

I use no down or right thrust on my planes. I use the flight controls, and throttle management to fly the plane, not let the plane fly itself.

Bill, AMA 4720
WACO Brotherhood #1

I figured if i kept it the way it is with the elevator being down about 1/4 inch from the neutral position, in flight, what it is actually doing is putting a load or stress on my elevator servo.

right or wrong?

hulio

Upthrust will make an airplane climb.

Things to consider:

If the airplane's design calls for zero thrust or possibly down thrust, and your plane has up thrust, when we say "the airplane will climb", this "climb" will be fairly drastic whenever full power is applied. Almost like you are beginning to perform a loop.

What thrust does your airplane call for? This is important to know.

Most planes, after properly constructed and trimmed for straight and level flight, will actually climb slightly when you are making a full speed pass. We are talking a very shallow climb here, perhaps only several feet higher in altitude over the entire length of the field. This is normal.

Pattern aircraft, scale, and other special designs can act in different ways also.

I am no expert for sure. This is just what I have found out from sport flying.

Quick basic check:
( The plans will identify if the horizontal stabilizer has any positive or negative incidence, or degrees tilted up or down in respect to the centerline of the fuselage )

With incidence, if any, factored in:

Level your horizontal stabilizer using a small bubble level. Then place the level against your engines mounting flange. What you see...is what it is!

Sure sounds a little tail heavy to me. 1/4 inch of down trim is quite a bit.
Try moving any movable weight such as receiver battery, forward and see if it improves.

upon further inspection the +2 1/2 degress incidence in the wing and +1 1/2 degrees in the stabilizer are correct. the plane calls for 0 degrees on both engine thrust angles. I think I found the problem. it has about 1 inch of up thrust in it. well, the top of the prop is about 1/2 inch back from 0 degrees and the bottom is about 1/2 inch forward of 0 degrees. i guess i forgot to add washers when i changed the engine on it last.

i'll take it off and set it at zero degrees thrust angle. that should do the trick

the CG is in the middle of the recommended range

thanks for all the help everyone

hulio

Good to hear that Hulio!

Let us know how you made out.

The only time this comes into play is when you're checking engine thrust while flying. To do this, you fly WOT in a straight line and then cut throttle to idle and watch if the plane goes up, or down.

If the plane goes down at idle, you have too much up thrust, and vs. if the plane goes up at idle, you have too much down thrust.

This may sound backwards to a lot of folks but what is happening is the engine is the main factor at WOT and the plane has a little up or down trimmed into the elevator to allow for level flight. Once the engine goes to idle, the main control factor shifts to the elevator for flight characteristics. (up and down) If down trim was used to compensate for too much up thrust, you'll see the plane descend at idle due to this down trim. The reverse is true for up trim at WOT.

Hello Stefan........................came across this thread from doing research. I have a Seagull Harrier 46, a nightmare of a plane.
CG recommendation is between 140mm-150mm, I'm mid way 145mm. Climbs when throttle is increased, when throttle is reduced it almost hovers if wind is about 20kmh. down elevator is almost constant. I have not checked the wing and stab incidence. This is an ARF. On another thread, someone said that ARFs hardly have their incidence incorrect. But I'm not betting on that.

I was planning to add some downthrust, about 3 degs.. There is probably too much upthrust, if I understand you correctly. Your help is appreciated.

Charles.

WOT is short for ???????


Thanks.

WOT = Wide Open Throttle

WOT is short for "Wide Open Throttle"

This is something that the car guys use mostly. Why I don't know. I guess they are too lazy to say "Full Throttle", which is what most "plane guys" refer to it as.

Ken

Not cause we're lazy, but cause it sounds cool! WIDE OPEN is the only way to race![sm=shades_smile.gif]

Hmm, sounds like the way I fly!!!!

When I first learned to fly everybody kept telling that there was a throttle on the plane and I could use it. I replied that I was a computer guy, so all I know is binary - on and off. And my flying was the same where. Full throttle or idle!!!! That's it!!!

Ken

RCKEN......................That's how I know it "Full Throttle". I'm a plane guy, I say full throttle, half throttle, quarter throttle so on and so forth [sm=shades_smile.gif] Perhaps it is also cool to say WOT (?) a bit of humour in there. Thanks