sea157

My Feedback: (30)

I have a trainer plane that if you give it any more than ¼ throttle it will go up in a hard 45 degree angle.
I realize that a trainer will rise with more throttle BUT NOT LIKE THIS ONE DOES!
Do I need to put some up thrust or down thrust in the engine mount?
Also I am not sure what direction you need to get the thrust right, is down thrust when the front of the engine is higher than the back of the engine?

Pylonracr

Put in a couple of degrees down thrust and try it again. The engine shousl point down, so the front will be lower that the rear.

ratshooter

You need downthrust. Thats were the nose of the engine is lower than the back of the engine. You may also have too much positive wing incedence. This is where the leading edge of the wing is too high and causes the plane to climb. The only proper way to check this is with an incedence meter.

What plane are you flying? If you don't know the name post a pic and someone will identify the model. This might also help us to help you.

sea157

My Feedback: (30)

The plane is a Hanger 9 EASY 2 ARF Trainer.
So for down thrust I will need to shim the back of the engine up a little, CORRECT?

jester_s1

You shim the top two engine mount bolts so that the nose points more down. That's assuming, of course, that the thrustline is actually the problem. What's also very possible is that the plane is simply out of trim. With a plane that is trimmed wrong for straight and level flight at full throttle, it's possible to glide around at part throttle. I'll make the same suggestion to you that has been made many times on RCU- connect with an instructor so an experienced pilot can trim and inspect your plane and give you pointers on flying it.

FlyWheel

This is a high wing plane. Be careful because adding downthrust on this design can be self defeating as you may end up just adding the prop wash to the underside of your wing increasing it's lift (which will increase with throttle). Look at the incidence angle That's the chord of main wing relative to horizontal stabilizer. If it is very high then reducing it should give better results. Try adding a shim under the TE.

jester_s1

There is no way that moving a thrust line down would increase lift due to prop wash hitting the bottom of the wing. It's not physically possible for that to happen.

The OP probably shouldn't go modifying his plane just yet. Assuming the plane is in the configuration that the factory built it in, it's probably close to being like it needs to be. As I mentioned above, the plane is probably not trimmed right to start with. It's normal for a trainer to rise and fall a bit with speed changes, but not as much as the OP is describing.

The much smarter next step for the OP is to do some measuring. Measure the CG and compare it to where the manual says it should be. Measure the thrust lines, both vertical and horizontal to see where you are. That way we won't be taking a shot in the dark to try and help you. And if you haven't already, do a search for local clubs to try and find an experienced pilot to help you. If I were local to you, I could take your plane up and know within the first 10 seconds of flying what it needed. That's a lot better than taking days to get best guesses from strangers on a forum and possibly making the problem worse.

FlyWheel

Well that's what I was told after I tried increasing DT on a similar design plane and it had little if any effect.

Gray Beard

My Feedback: (-1)

Flywheel, look up the term P-factor, I have a feeling that is what you were thinking about.
Most trainers I have seen these days have the fire wall angled for the thrust as the manufacture decided was needed after a lot of flight testing. When I build a plane I set the thrust at zero and after flight testing/trimming I then decide what is needed, CG, Lateral balancing, incidence and thrust.
With a trainer I usually trim for flight at just a taste over half throttle then make any changes I feel are needed. Engine thrust angle is often the first place I start after balancing but it's often just the balance that needs changing. When it is thrust angle I use washers behind the engine while at the field then when I get home I make up an angled shim to replace the washers.

sea157

My Feedback: (30)

Gray Beard,
I have everything trimmed out right but anything above 1/4 throttle and she will shoot up at about a 45 degree angle.
So in your opinion should I give the motor mount a little down thrust?

buzzard bait

I don't think the problem is the thrust angle.

When you say you have everything trimmed out right, what is your method of determining what is right? If everything is right, you should not need more down thrust than the manufacturer builds in.

You probably just need some down trim on the elevator. For some reason, a lot of models need the elevator to be trimmed down somewhat relative to the stab, i.e., in neutral trim, the elevator might need to angle slightly down. How should the elevator be trimmed? Well, if it is climbing too much, give it some down trim. If you get it trimmed for level flight in a cruise, then it should take off OK.

After you get it trimmed for level flight in a cruise, then how does it behave at other speeds? It should climb with more throttle and descend with less throttle. If it climbs too much with full power and falls too fast at low throttle, then the balance point is too far forward. If the balance point is too far forward then the elevator trim that gives a good cruise will be too far off at other speeds. Check you balance point carefully.

Jim

Gray Beard

My Feedback: (-1)

Hard to say without having the plane in my shop to check the incidence of the wing and stab but I trim the plane at a bit over half throttle so it fly's straight and level then land and with the radio still turned on I look at the control surfaces to see where they are setting while in flight trim. That tells me a lot about the plane set up and is my starting point for everything else. Example of that would be down trim in the elevator would send me into the direction of checking for a plane that is tail heavy. CG is usually the first place to look. From there I would fly and trim the plane again and do the same thing to see how just changing the CG helped or hurt. I use an old pattern plane trim chart to help me with some problems. It just says if the plane does this then check that plus gives you a couple ways to fly the plane and see what it does. Example would be a straight dive and take your hands off the controls and watch what the plane does.
The chart may be posted in the pattern forum.
For your own piece of mind just take some washers with you to the field and change the engine thrust angle, fly it and see what it does. Just go slowly. Some planes require thrust angle and some don't but it is a trimming tool.
If you have any old pattern pilots at the field ask for trim help. In pattern flying trimming is an art form. I had a great one teach me. He also gave me the trim charts!!

jester_s1

You haven't said what your flying experience and skills are, but given the topic I'm guessing you haven't been at this for a long time? To fix your plane, you really need to go through a basic trimming routine. The first task is to get the CG set properly and the control throws at a happy place. For a trainer, I don't bother with the inverted upline that most aerobatic pilots do. I just cut the throttle and watch the plane glide. If the nose drops quickly and I can't hold it up with the elevator without applying the throttle, the plane is too nose heavy to be a good trainer. A similar test is to simply get a feel for how the plane lands. If I can't hold flare with the elevator until the plane is moving pretty slowly, it's too nose heavy. So I move the CG back until it drops smoothly and I am able to flare the plane properly for landing. Too rearward a CG results in a plane that glides shallow and drops out of the sky very suddenly. That CG tuning method will get you in the happy zone to make a good flying trainer.

The second task is to check for thrustline. Trim the plane at WOT for straight and level flight, then chop the throttle. Observe what the nose does. If it IMMEDIATELY drops, you need more downthrust. If it IMMEDIATELY rises, you need less downthrust. Note the bolded "immediately" in both descriptions. A plane the smoothly lowers its nose as it loses airspeed does not have a thrustline problem. Thrustline problems are when the plane changes pitch or yaw due to thrust. It's hard to see that happening when you punch the throttle, so the best test is to look for it when you cut the throttle.

sea157

My Feedback: (30)

As long as the throttle if slightly below 1/2 throttle the plane flies great.
It lands great.
It just will go up at about a 45 degree angle at anything above 1/2 throttle.

buzzard bait

It sounds nose heavy. It might sound contradictory, but here's what happens: You trim it at 1/2 throttle and everything is fine, but in order to achieve that when it is nose heavy, you have to use more up trim than you would use if the CG were further back. Therefore, when you advance the throttle, it pulls up.

In general, a nose heavy airplane will have a less sensitive elevator, but also a bigger trim change in response to throttle.

Jim