Problem with inverted flight?
 

The above quote was taken from another post by Montague. This is what happens to my plane when I try to fly inverted. Can someone tell me what "wing-stab relitive incidences" are so that I can fix the problem?
Thanks,

Troy.

Problem with inverted flight?
 

What was the context for the original post? What plane are you flying? Some planes, like high wings that use flat bottom wings will show this behavior to a certain extent... it is normal.

Incidence is the angle of the wing or stab with respect to a datum or centerline on the plane. You typically need an incidence meter to properly measure these angles. The relative incidence would be how the incidence of the wing relates to the stab, i.e. wing might be -2 degrees while the stab might be +1 degree.

Problem with inverted flight?
 

I suppose what I am trying to ask then is...When I fly inverted my plane wants to dive and I have to give almost full elevator down to keep it level. Is there anything that I can do to fix this problem? I have a 40 size high wing trainer (with dihedral).

Problem with inverted flight?
 

that's kinda normal

Problem with inverted flight?
 

For a flat bottom wing trainer thats normal, another thing is quite often planes are set up to climb slightly (safty blanket) i found that seting the plane to decend slightly at about 1/2 throttle realy helped with inverted flight, probably due to elevator deflection.

i've found an easier way to practice inverted (rather than roll in) is to pull a loop and 1/2 way round (ie. inverted) start to push the elevator stick, you can also practise doing rolls and push elevator as you roll to try and get nice axial rolls.

Problem with inverted flight?
 

troyp,
The biggest problem flying inverted with most trainers is the dihedral.

Trainers have a lot of dihedral in order to make the plane more stable in flight. The problem is, once inverted that dihedral becomes anhedral, which means the plane will constantly try to roll out of inverted to upright.

Add a flat bottom wing, and incidences set to maximize stable, upright flight, and inverted (or most aerobatics) become a real problem.

The good thing? If you become fairly proficient at inverted flight, and other aerobatics with your trainer, once you get that second plane you'll be thrilled with how much easier it is!
Dennis-

reply
 

One thing that you might want to try is to slightly raise up both ailerons( i.e. move them equally together about a 1/32 of an inch up) this will slightly decrease lift and may help with this problem. There was a post from another member who said that if your plane tends to need a lot of down elevator when inverted, then try raising both ailerons......especially if you notice that when you fly normally, and hit the throttle if the plane "balloons" upward that is it starts to climb, than turn the aileron adjustments equally to raise up the ailerons, try a tiny amount and see how it goes.

Problem with inverted flight?
 

What you are describing is a clear tendency of a high wing trainer with dihedral. There isn't a problem with your airplane if this assumption is correct. I would'nt make any control surface mechanical adjustments because this can cause a reverse reaction when flying upright. Just learn to apply forward stick when inverted and make sure you have plenty of power. Many trainers don't fly well inverted for reasons already stated. I find that most trainers require all the power you can get for inverted flight.

DBCherry is right when he says that if you can fly a trainer and proficiently perform aerobatic maneuvers then you are about ready for an upgrade to your 2nd. airplane. You will love the difference. Good luck........

Problem with inverted flight?
 

Wow thats good to hear. I wondered when I would be ready to move on to my second plane as I am currently building a coro spitfire with a 61 size engine in it. I was a little bit aprehensive about trying to fly it as I wasnt sure if I had enough flying skill to move on.

Problem with inverted flight?
 

Have the exact same thing on my trainer. it's a flat bottom with quiet a lot dehidral.

Take it inverted, and I have to give it full elevator to keep it level. It's due to the flat bottom as already mentioned. Keeping it level is a great challenge, since the dehidral is then anhidral, and the wings constantly want to drop the either side. thus required constant aileron feedback. However, if you can fly inverted with a trainer, you'll have a blast on a more aerobatic plane when flying inverted !

I've flown my friends plane once (a high wing aero trainer with semi-symm airfoil and no dehidral) and inverted flight was easy!

Problem with inverted flight?
 

I'm surprised I didn't see more reference to c.g. of the plane if the trainer is very nose heavy (which most trainers are) then your problem probably lies there check it out and try adjusting the c.g. further back but do it slowly and test frequently a nose heavy plane will fly much better than one that is tail heavy

Problem with inverted flight?
 

The nose dropping when inverted has nothing to do with dihedral. The strong tendancy to roll out from inverted is, but that wasn't the question. Flying a hi-dihedral plane inverted does take more attention on the aileron stick to keep it level, but that doesn't affect the elevator.

The plane having a flat bottomed airfoil will increase the amount of down elevator necessary to keep the nose up. So, if you have a radio that has fancy end point adjustments, you can set it up to give more throw down than up. But I'd do this after other adjustments.

Most likely, the CG is too far forward. Move your CG back about a 1/4" and give it a try. Be careful, but most trainers have a very broad "safe" CG range, and the instructions usually put the CG way at the front of that range. Some trainers can fly with the CG back as far as 2" from what is given by the instructions. So, if you see a slight improvement, and the plane isn't too twitchy, move it back another 1/4", repeat as necessary, but keep in mind that the elevator will become more sensitive, and there is a point where the plane will become very very hard to control.

The incidence I was talking about was, as mentioned, the relitive angles of the engine thrust line, wing, and horizontal tail. I'm taking all measurements from a referance point of the fuse center line here. If the wing is at, say, a positive 2degrees, and the stab is at a negitive 1, the engine will likely have some downthrust, say a negitive 2. (I'm making these numbers up, btw). In that kind of arrangement, if the plane picks up airspeed due to a dive, the plane will naturally start to pull out.

But if you increase the power, the engine pulling downwards will offset some of the lift of the wing, and the plane won't climb quite so quickly. This kind of arrangements is typical of trainers, lots of positive on the wing, lots of downthrust. When you roll inverted, the downthrust will help you keep the nose up, since it's now upthrust. But the positive angle on the wing and the negitive on the stab are now really working against you. To get a flat bottom wing to produce lift inverted, you have to get the AOA up there fairly high. If the wing is at 2 degrees positive, when you roll inverted, you have to pitch the wing past those 2 degrees, then far enough to get enough lift to maintain level flight. The AOA is controlled by the elevator, so that means you need a lot of down, and the more positive incidence you have on the wing, the more down elevator you will need.

The suggestion above to reflex the ailerons is a good one. Why? Because reflexing the ailerons has the effect of lowering the wing incidence! Drooping the ailerons increased the wing incidence.

So, in summary, to reduce the down elevator needed to fly inverted, do the following:
- move the CG back
- reflex the ailerons or shim up the TE of the wing
- increase down elevator travel

If you are having problems keeping the plane from "falling off" to one side or the other, you can't keep it straight and level while inverted, then you need to look at your dihedral.

With my beater-trainer that I keep around, I can fly full circuits of the field inverted with no problem. I can't quite ouside loop, but I can climb gently inverted. It's a Hobico AirVista, the CG is back a bit, and the elevator is turned up. I'd move the CG back a bit more, but I do instruct on the plane once in a while (when a students plane becomes disabled).

Problem with inverted flight?
 

Montague,
If you'll re-read my post you'll see that I never said the nose dropping was a result of dihedral. I DID say that the biggest "problem" flying inverted with a trainer was dihedral, which caused the tendency to roll out of inverted.
Dennis-

Problem with inverted flight?
 

Dennis,
You are correct on both points. I wasn't trying to contridict or disagree with you, I was just re-pointing the thread back to the origional question, about the nose dropping. After your post, the thread didn't address the nose drop at all, everyone was talking about the trainer rolling out and dihedral. I still stand by my assertion that messing with the dihedral won't fix the nose dropping, and that the dihedral isn't causing the nose drop. :D

Personally, and this might just be me, I really don't find the rolling-out tendancy of trainers hard to deal with when inverted. In fact, I don't notice it at all. It's the nose dropping that is the biggest PITA for me. I can't say if it feels the same for a newbie though. I've flown enough very twitchy airplanes that staying on top of the trainer to keep the wings level is second nature. And Tuesday I had a (rather advanced) student trying inverted flight, and he also seemed to have no trouble with the roll, but the "full down" elevator was hard on him.

Ok, so maybe I will disagree with what the "biggest" problem is with flying a trainer inverted after all :D. Minor point though. Both the nose drop and the rolling tendancy make it a lot harder to fly a trainer inverted for any length of time compared to an intermediate sport plane, as was pointed out.

Problem with inverted flight?
 

It sounds like everyone has a handle on the problem but I'm not sure I agree with everyone's solution. Keeping in mind that this is a trainer and won't fly inverted with the ease of a sport plane, I think adjusting wing incidence is not the right move. This is a flat-bottomed wing and inherently will be more difficult to fly inverted. I fear that adjusting the incidence for better inverted flight will serve to create a more unstable plane while flying right-side-up. So you adjust the incidence and what happens? Now you have a plane which only flies half-way decent inverted and crappy right-side-up! In my opinion, the best solution is to slowly adjust the C.G. rearward to a point you are comfortable with and dial in as much elevator throw as possible. Good luck!

Problem with inverted flight?
 

Pauly,
I totally agree. Moving the CG is absolutly the best way to go.

I was just pointing out that some trainers have way more incidence than is actually needed for stable upright flight. Just reflexing the ailerons usually has minimal effect on the upright flight charastics (we are talking SMALL changes here), but can really show up inverted, so on SOME airplanes, SOMETIMES adjusting the incidence helps overall. On ALL airplanes, getting the CG set "right" helps a lot. I gotta be more clear :). Certainly, messing up the upright flight handling to make it fly better inverted is just stupid :D. If you change the wing incidence, and the plane flys poorly, change it back :).

Btw, when you do move the CG back, it's not a bad idea to lower the elevator rate a hair. You're going to find the plane is much more responsive in pitch upright or inverted with a more rearwards CG, so it's normal to reduce throws a bit as the CG goes back. And just because the elevator become more sensitive doesn't mean the CG is too far back.

When I trim out a new combat plane, I am going to for the absolute tightest turning radius I can get, both upright and inverted. I move the CG around, adjust the elevator travel, and change the aileron reflex, all a little at a time to get the best balance. Sometimes less elevator + a more rearwards CG gives a tighter turn, somtimes moving the CG forward and increasing the elevator works better. They are all very closely related. Fortunatly, with most planes, you aren't trying to push to the absolute edge of the flight envelope.