Been a while since I got back to this one....

I'm with Ben on the stab size. That's just way to small. Sure it'll fly since it's a symetrical airfoil and they don't need much stabilizing force but couple the small size with the high drag and possible pitch coupling from a sudden and large rudder deflection and all kinds of mysterious things can happen. Even just going back to my sudden braking action may be enough that the small stab can't provide the proper lift any more and so the nose drops.

It is also an easy thing to check. Glue on some balsa and make the horizontal size something around 25%. Keep the aspect ration similar to the wing. If it is an area effects then being scientific about it trim off the additional area until the nose down effect is noticed again.

The basic thing the larger tail will do is to keep the airplane level long enough to see if the rudder can indeed yaw the airplane. Bigger motors don't let you have the fun of finding out why things happen.

As someone else suggested also check with different amounts of rudder input for both the big and small horizontal tails.

Then try all the above with properly faired canopy and nose areas.

This is an excellent opportunity to do some basic good aerodynamic research. Since you are looking for something causing a nose down pitch with rudder deflection it will be easy to determine if it is there or not.

I would like to encourage you to work on the problem and report the results. It is rare to have something this interesting to investigate that doesn't cost an arm and a leg.

*waits for feedback from the original pilot/poster*

Will be interesting to see what comes of this

Ben, lovely suggestion. Reminds me of when I did something similar with vertical tail area and CG positioning on a 2 meter aileron glider. I learned SO much about the relationship of spiral stibility, vertical tail volume and CG placement in one afternoon that it was like an epiphany.

Qfrc, you'll probably be doing some surgery to replace or otherwise build up the stab and elevator anyway so adding scab pieces onto the exising unit for some research time won't be a big deal. You and we may learn a LOT with some testing.

Add lots to bring it up to about 25% and then cut it back in 5 % steps to the original size and keep some notes about where the biggest change occurs. That would be the critical size that you're looking for.

that plane is a contender?Looks like my contender.but mine has a cowl built on it.they track really nice.I have a os 61FX on it unlimited vertical with it.flies like its on rails.Avery nice windy day plane cut right through it.I made mine very tail heavy plane loves it.Have to use the flap for landing comes in real hot without it.Did you put the strate wing tips on it?It flys better with the angled tips .My friend angled them is much more stable it a flat turn,or i might say it yaws better doesnt yaw to good with straight tips.
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joel

thanks for the input guys.Im going to try what you said.I notice on the full scale planes that are low wing they always have some dihedral in them ill let you all know how i make out
joel

I was thinking about youre posts and was wondering.If i fly the plane inverted and move the rudder I should see some normal yaw in the plane due to the cg being below the wing anding more stability. thiswould prove the need for dihedral in the wing.If it does the same thing stall and drop the nose it needs more tail volume.
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joel

Sorta makes sense to me. But to make it fair I'd trim in the down elevator so it's flying hands off inverted and then snap in the rudder. Or at least brace a couple of your extra fingers on the elevator stick so it stays firmly in place..... this second option might be safer....

------------------- I was thinking about youre posts and was wondering.If i fly the plane inverted and move the rudder I should see some normal yaw in the plane due to the cg being below the wing anding more stability. thiswould prove the need for dihedral in the wing.If it does the same thing stall and drop the nose it needs more tail volume.
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Well you are asking if the airplane needs dihedral? Are you trying to find out
1. why the airplane doesn't roll with rudder input?
2. why the airplane pitches nose down with rudder input??
3. both???

The low wing design you have should be mostly uncoupled in all axes in normal upright flight. The rudder should make only yaw, elevator pitch and ailerons roll. If it is doing that it is working correctly for a full house aerobatic airplane.

When you put the zero dihedral airplane inverted, trim level, put in rudder and observe the airplane roll a little then this is normal. But that has nothing to do with the original question ....... does it.??????

Ben I got the impression he wants to see if the nose drop is due to the tail volume or a pitch couple problem. Not to make it bank.

If it's a pitch couple thing then I can see it trying to lift the inverted nose. But if it's a tail area thing as we suspect then it'll stay consistent and the nose will drop from the overworked stab giving up as the speed suddenly drops.

At least that's how I see it.

And since it's easy to do, may bring up a few more clues and provides material for at LEAST another dozen or so posts here it won't be a waste of time....

qfrc flier is confusing me, a relatively easy thing to do actually :-)

qfrc flier -- have you done the experiments?? Hurry!! Don't let working for a living interfere with serious model stuff. I don't think anyone has ever done this type of thing and it will be worth the reading.

The rudder-pitch coupling on my Ziroli 1/6th scale Stearmann are downright exciting! Makes landings very difficult, knowing the nose will drop when rudder is used.
And it's got dihedral and the upper wing and everything....

I believe they're two seperate problems, pitch coupling and lack of dihedral. I would put dihedral in it, which it needs anyway, and see what it does. I have a Corby Starlet which has enough dihedral in it but has a mean pitch down with rudder,but will do a nice flat turn with enough elevator input.

Time 'n testing will tell but I'd be surprised if it's dihedral problem. I've seen lots of low wingers like qfrc's fly with no dihedral at all just fine. Many of them being old school pattern ships.

But that stab is another thing....

Ben I got the impression he wants to see if the nose drop is due to the tail volume or a pitch couple problem. Not to make it bank.

If it's a pitch couple thing then I can see it trying to lift the inverted nose. But if it's a tail area thing as we suspect then it'll stay consistent and the nose will drop from the overworked stab giving up as the speed suddenly drops.

At least that's how I see it.

And since it's easy to do, may bring up a few more clues and provides material for at LEAST another dozen or so posts here it won't be a waste of time....



That is what im trying to figure out. If the nose drops again ill go right to the tail area.because being inverted will give more stability and yaw it more and not drop the nose.unlees it is tail volume figured that would narrow it down some.

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joel

The dihedral will make it turn in the proper direction as proven in my first post. The Starlet will climb when inverted with rudder input which is roll coupling. I have read where it's caused by downwash off the wing and the only fix is to raise or lower the stab which i'm not about to do since it can be compensated for. The first time I tried it and the nose dropped was a real diaper loader. That was many years ago and I still have it. Q42 powered.

I don't follow full size homebuilt that much and had never seen a Starlet before (sheltered life). The short-fat-cute description fits it pretty well. Thanks for pointing it out.