I have a Prince America HobbyStar with an OS 46FX. I can't find the right trim to keep it at level flight. I trim it at 1/2 throttle but climbs at full and descends at less than 1/2. What should I do?
Any info is appreciated.

Add some "downthrust". That is, angle the engine down a little with respect to the rest of the plane. A couple of degrees is all it takes.

Make the adjustments by adding small thin washers to the engine mount. This will allow you to experiment to find the correct angle.

thanks, i'll give that a try.

Downthrust will make it worse.....

Take the downthrust out if you want to solve the "Problem" some planes come with up to six degrees of downthrust but two is plenty, the idea is to make the plane climb under power.

You can take the downthrust out by adding washers to the front of the engine, but you might want to check it first to see where it is set in relation to the wing.

Hope this helps.

Downthrust is the solution. As you increase throttle, the downthrust will counteract the increased lift from the wing. At mid throttle you will have a little more up trim than before. So when you decrease throttle it will not sink so fast.

Tracy

Yep! I agree with the downthrust. Try it.

The way it works is the engine is pulling in a straight line, what makes the plane climb under power is the angle of the wing relative to that thrust line. If you have downthrust, as you increase power the engine will try to pull in a straight line increasing the angle of attack and therefore increasing lift.
Downthrust will make you climb under power, thats why you see more downthrust in trainers than regular aircraft.
Just test it and see......

Adding downthrust will pull the nose of the airplane down under power.

Trainers have down thrust for this same reason.

According to your theory, If down thrust mades the airplane climb than right thrust would make it yaw to the left.

Think about it.

Now, now, Boys!
All this stuff about upthrust and downthrust is great to contemplate, but I'm fixin to throw you a little curve. What about wing incidence? Could this man's plane have just a little too much positive main wing incidence or negative horizontal stab incidence or even both. Now what's either one or both going to do to the plane's attitude at different airspeeds? Think about it a little.

Sam

Someone needs to read some pilot training manuals. The engine(power) is used to make a plane climb or descend. Elevator is used to control the speed (angle of attack) of an airplane. Anybody that wants to argue that fact needs to ck up on it first. I had this drilled into my head yrs ago.

Microflight,
My theory does not apply to right thrust as you have removed the lifting area from the equation, the engine will try to pull to the right countering the torque of the engine, but there is not a wing pulling the other way.

Taildragger,
I agree that you climb with power, and you control airspeed with the elevator, anyone with a pilots licence can tell you that.

Thats what I base my oppinion on, When you add power you are causing the thrust of the airplane to increase the angle of attack of the wing, causing it to climb. If you only have 0' to 2' of downthrust this will not happen, as you increase power you will just increase speed with minor other effects I bet if you look at this trainer it has about 6' of downthrust already. I think 2' is the max you should go.

Just my humble opinion.

And I have read all of my flight training manuals

Guys,

i don't know if this will help but here is a link to a trimming chart.

http://www.wtp.net/DBEST/trimchrt.html

Hmmmm---Engine is for climbing and descending. Then why won't my plane go faster if I move the elevator. Just kidding!!!

Granted the elevator controls the wings angle of attack. Downthrust does counter the tendency to pitch up or climb with engine rpm changes.

I have to agree with ChinookPilot. Check the wing incidence and the horizontal stab incidence. Their relationship should be on the same plane. Any negative on the horizontal stab (in relation to the main wing) and the plane will have a tendency to climb. Also make sure no up thrust is there.

I agree with the wing incidence check, positive will make you climb under power, also, not enough negative incidence in the tail will do the same.

Average light plane:
Main wing: positive 1'
Tail: negative 3'
Engine: down 2'
Engine: right 3'

I have a hangar 9 Easy Fly that I bought for my wife and it came with about 6' of downthrust in the engine and It wanted to climb alot under power, so I reduced the downthrust to about 2' and it now flies the way I like it.
this is why I say reduce the downthrust, if it is high to start with...

You are all kind of right,

"climb with power, and you control airspeed with the elevator, anyone with a pilots license can tell you that"

This will in fact happen under certain conditions such as MCA or during a landing when you are on "the back side of the power curve". Like our models, during normal flight conditions, the elevator is the primary control for altitude.

Sooo... if you fly around in MCA (Minimal controllable airspeed) up thrust might work, otherwise add down thrust like all the pattern & IMAC trimming charts will tell you to do for this symptom. Wing to horizontal stabilizer incidence is a good place to start, check that first, and if it's ok add down thrust.

This is bringing back memories of the old downwind turn debate. It seems to me that if he decreases wing incidence it is sure enough gonna come down when he decreases throttle. How about if I just agree that we disagree?

Jeff, How do like the old Cheif? I used to own an old 46 Champ 7AC. It's what I learned to fly in. Wish i still had it. It was a great airplane

Has anybody considered the fact that this is a normal condition in flat bottom airfoil types. Wing lifts more as speed increases. Normal condition,& trains pilot to use his trim, or at least fly the airplane, and not the transmitter.

beat me too it. If the plane trims out at 1/2 throttle, or course it will climb at full throttle, and drop at a throttle setting lower than 1/2. You guys are reading way too much in to the question asked. This is normal flight conditions for the plane in question.


Don't fix it if it ain't broke.

Pug

Upthrust, downthrust, I'm just happy I have thrust........(won't make the obvious wife comment here)

Steve

Well there is always a smart*** in the group so I will take the honors on that one...
I will add one more ingredient to the mix.
TWO LETTERS.........CG
any thoughts from you engineers?

INTERESTING THREAD.
5X5

I am going to go with, just be happy that you have thrust!!!

It is the nature of the airplane, but I always like a good debate.

Taildragger: I love the Chief, its that first airplane that realy tought me how to "Fly" Its alot different from the Cessnas and the such that I used to fly.

TLH101 and Pugsley have it right. This is normal for a flat-bottom wing.

Folks, if this is an established design (been around for a while) the thrust angles and incidences have probably been adequately worked out at the factory. FIVESQUARE, you, I believe, have the right idea.

My belief is that the plane is a tad nose heavy. When trimming out a nose heavy airplane, you must add elevator trim to keep it flying level at 1/3 to 1/2 throttle. As soon as you throw the petal to the metal the trim settings at the lower throttle settings magnify the tail-down forces and the nose will come up.

Technically, it works like this:
If an airplane is balanced perfectly (the center of pressure (CP) and the center of gravity (CG) will in the same spot. In a slightly nose heavy condition the CG will be located slightly forward of the CP. This nose-heavy condition contributes to the pitching moment (desire for the plane to pitch forward about the center of pressure) and must be counteracted by downforce (up elevator trim) on the tail of the airplane. The condition just described is what THE CROW is experiencing at half throttle. As he increases the speed (opens up to full throttle) the main wing lift and tail section down forces increase, but the pitching moment does not (the nose weight does not increase). This imbalance causes the airplane to nose up.

My advice to you (THE CROW) is to recheck the balance. This type of airplane is best flown (for stability reasons) slightly nose heavy (min. of 1/4" ahead of the neutral CG point). The next time you take the plane up, trim it out at full throttle, not half throttle.

I would like to continue, but somebody just threw a frying pan at me. Gotta go...........AHHHHHHHHHHHHHHHHHH

Weldo

OK its obvious that some of you are pilots as am I . Every flat bottom wing I have ever flown, real or RC had a trim change with speed. It is the nature of the beast. Weldo, you are not quite accurate in your statement about C.P. The C.P. is the mid point of the highest velocity with the boundry layer still laminer {yes I know, no boundry layer is truly laminer}. The C.P. changes with angle of attack and velocity. Angle of attack moves the foward most point of the air contact to a different point on the leading edge effectivly changing the shape of the airfoil from the air's point of view, it also causes and earlier seporation of the boundry layer at the rear of the wing. C.G. should always be in front of the C.P. or the result will be pitch induced occilations, or the instability we have all seen when the C.G. is too far aft.

HUH?
Damn I just fly these things......Don't confuse me anymore.......I didn't have the last lesson when I went through pilot training......
5x5