New concepts have always been hard do accept. Others will prove it right or wrong. All I can say is that it worked for me.

After reading the entirety of this thread, I'm left with questions. The warped wing could have trim issues that vary with speed but they have to do with roll and I'm slow to want to believe that a roll issue is what is at play causing ground loops (considering that landing gear are not at issue).

I've owned a lot of bibes and like others, have found that power management is important. Some have required slow increases and others needed hammered. Partly I think its a matter of how prop wash or a cross wind hits the stab until the plane has reached flying speed. Mostly however, I think its a matter of torque that requires rudder offset after the tail comes up.

Observe carefully the track of the airplane after takeoff while keeping the wings level. I'm betting it will produce some left turn. If it does, then it tells that right rudder is needed on the takeoff and climb out. Now takeoff and hold right rudder to track straight (again, keeping the wings level). Note the amount of rudder stick movement needed, probably only a slight bit.

Adjust some right rudder mix starting at one third throttle (or the power level at which the tail comes up) and at full throttle the mix is equal to the stick amount experienced. This should provide a good takeoff without the need to time rudder to match the moment the tail starts flying.

Finally...do a loop directly into the wind to see if the rudder mix affects loop tracking. If not adversely... then nail it down.

AA5BY, what I believe is happening is that the left aileron trim (right aileron down) causes the lower right wing to produce enough lift to want to roll the plane to the left but with both wheels still on the ground the plane cannot roll. Also remember that this is happening before the tail comes up. So the plane does a hard left ground loop. As I said before, if I was lucky enough to get the plane into the air it would fly straight and level with the amount of left trim I had dialed in.

So the question is, what causes the plane to fly straight and level in the air with a give trim setting and then do ground loops when on the ground with the same trim settings?? I believe the answer is that GROUND EFFECT is stronger on the lower wing than on the upper wing hence producing more lift on the lower right wing of the plane than on the upper left wing.

The wings are standard balsa/spruce double D-box construction with capped ribs. As such they are very rigid and it would be easer to build a new wing than try to remove the warp in the present wing. The aluminum pop-can trim tab on the upper wing is by far much easer and works surprisingly well.

Applying this theory to my biplane has eliminated all my ground handling problems and the plane flies very well. If you have a squirrelly bipe, try it, you may like it.

Oldbob

I don't think anyone doubts that you have found a way to take off your airplane smoothly. What I think some people are skeptical of (myself included) is that it has anything to do with ground effect. Saying ground effect combined with a warp in the wing was causing ground looping (which is I believe what you have been saying) is roughly analogous to saying that the atmosphere caused your ground looping. I like to use what I know to be true to explain something I don't immediately understand. If holding right aileron (and/or adding a trim tab) helps me take off, then I likely either have a trim problem, a warped wing, or propeller torque is greatly increasing the weight on the left main wheel during the takeoff roll, causing directional problems. These are all well known and understood phenomena - have been for many decades.

Just fly the durn thing and be happy.......you will always find people who over-analyze everyting. Figure it out yourself. It will make you a better person

No sense confusing the matter with facts. Opinions are far more poweful.

Mesae, ground effect is also a well-known and well-understood phenomenon, HighPlains attached a chart with his post #20 that shows how the effect increases as you get closer to the ground. However, as far as I know, no one has ever considered ground effect to be a contributing cause for difficult ground handling of a biplane that has less than perfect wings. I have built a few airplanes and have yet to build a perfect one.

I’m not trying to force my theory on anyone; I just want to share a new concept with those that may benefit from it. I believe that I have presented a valid solution to a long-standing problem with biplanes. If someone should prove the theory wrong, so be it. For now, I will continue to use the ground effect theory as a valid cure for bad ground handling of biplanes.

Oldbob

Actually, the bad ground handling wasn't cured with theory, it was cured with a trim correction. Not theory at all, just practical mechanical adjustment.

Why the adjustment worked is still just opinion. And looks like the opinions are at odds. Let's agree to that.

oldbob,
I just went back through all your posts in this thread trying to find out which side got the pop-can trim tab. I probably just missed it. But I did see where you taped it to one side. Do me a favor and do another experiment.

Move that trim tab to the other wing. Needless to say, you'll have to deflect it in the opposite direction. And let us know what happens. Probably nothing, but it'll be interesting to try. I sorta wish one of my biplanes had shown that bad character just to get to play with fixing it.

Thanks for sharing your story, btw.

BTW, you might also want to consider moving the trimtab to a lower wing. If it's effect is needed only at ground effect levels, and theory says stuff is more effective in ground effect, then it could be deflected less on a lower wing than on an upper wing. And that detail would help suggest your theory's validity. But more than just backing up the claim, it would also result in a better flying airplane.

You've now got a trim tab on an upper wing that is deflected enough to have the required force in the "ground effect envelope" of the airplane. But it's not in the ground effect as much as the warped surface it's trying to counter. So when the airplane is in ground effect, the trim tab is operating in the less powerful "effect" but the wing is. Also........

When the airplane is not in ground effect, the trim tab should actually be "overpowering". The wing's warp is no longer in the favorable environment (favorable to the warp screwing the aero, that is) when the airplane is at altitude. And now the trim tab is at much greater speed and should be way overtrimming whatever the wing warp can be doing. So your trim tab is set "wrong" almost all the time. And the setting is producing excess roll trim and excess drag.

BTW, did the airplane require any roll trim before and after the trim tab?

Darock, the trim tab was added to the upper left wing curled upward to provide left trim to counteract the right turn built into the upper wing. The lower wing has strip ailerons and adding a trim tab to the lower wing may cause flutter problems with the ailerons. I’ll leave that experiment for you.

Your comment that, “when the airplane is not in ground effect, the trim tab should be “overpowering��, indicates that you do not understand what I am saying.

I will try to post some pictures of the plane and the trim tab arrangement. The weather here has turned bad again so flying is halted for at least a week.

Oldbob

Not at all. I probably should have said that when the airplane is at it's much higher flying speeds, often 2 to 3 times the landing or takeoff speeds, a trim tab that is effective at the slower speeds is going to have even more effect. And if you think about it, a trim tab that's producing enough trim at takeoff speeds is going to cause some appreciably greater trim effect at flying speeds. That probably results in the need to further trim with TX settings. And then what do you have....

BTW, did the airplane require any roll trim before and after the trim tab?

whatever............

If the ground effect is amplifying, then it's going to amplify the lower wing's problems more than the top, right. And if it's ground effect amplification that's the major player, then any solution could employ ground effect amplification and be less obtrusive outside ground effect, right. So wouldn't you want the trim tab to be on the lower wing in order to work in the amplifying ground effect? And if you didn't place the trim tab in the "better" environment, wouldn't it work less at the times it needs to work more? and have too great a negative effect than necessary outside the ground effect envelope?

Embracing your argument would lead me to do the trimming needed, but do it to the lower wing. It after all should be experiencing ground effect sooner and stronger. And since there are strip ailerons there, and it's easy to trim them with the TX, I would expect them to be more than adequate for the required trimming. And that trim, when adequate in the "enhanced environment of ground effect", should be less upsetting outside the ground effect.

You've introduced an interesting "new concept". It's been fun discussing it. Hope we all learn from the discussion.

Well I have been spending a lot of time flying the Bipe, and trying to prove my theory about ground effect. No such luck. I can get the plane into the air on every tack off but the right aileron trim has little to do with it. If ground effect was in fact the cause, than I should be able to lower the left aileron and raise the right and have the bipe turn right at the critical speed. The plane would take off and then roll right, but never did it turn right on the ground. Having proved to myself that I was wrong makes me feel accomplished and bad at the same time. I post this so that others don’t spend time with this flawed idea.

Here is what I think was happening all along. Coupled with a few minor things like GC aft 3/16 too far, tail wheel not perfectly aligned with the rudder, and P-factor, combined to make the bipe crazy on the ground. Added 1.5 oz. to the nose, straighten the tail wheel to be in alignment with the rudder (only about 1/64 off) and during take-off hold full down elevator until the tail comes up. With the tail up P-factor is eliminated and the bipe tracts straight down the runway.

Enough said, I’m out of here.

Oldbob

Just fly the durn thing and stop analyzing the situation......its over...let it go fellas.Now get back to your naps...

If this was written in jest, so be it. But if not, I disagree; otherwise, what is this forum for?

I respect Bob for his candidness. He formed a theory, shared it with others for corroboration, then publicly admitted his theory was wrong and revised it. This world needs more people like Bob.

I agree... it is a healthy thing to form a hypothesis of an argument to see if it true or not and Bob did that. It was also very mature to report his conclusions and that was helpful to the process.

Yes, it is important that tail wheel tracking be true.

I have not seen any mention of wheel toe in and toe out. I always thought it helped considerably, if you had a slight amount of toe-in. Can anyone confirm this, or am I off base here?

Toe has an effect for sure. But probably won't cure any other problem unless the other problem is very minor.

And toe out will be a problem if it exists. The severity of the problem will also depend on the amount of the toe out and how much leverage the tires have on the airplane.

This summer, a couple of my flying buddies showed up with new cubs. Well, one was a newly assembled ARF and the other was new to the owner. Both of them had toe out, and both of them showed really nasty ground handling. The newly built suffered through a couple of weeks of trying everything but toe. My buddy was positive that he'd assembled the airplane exactly as the book said, and didn't think toe was the problem. Needless to say, when he finally bent the gear to get toe in the airplane stopped 90% of it's ground looping. (If it hadn't, would I have included it in this? naah) And the other one got it's gear bent when it's owner wasn't looking. Who done it? hehehe..... Danged if I know...... And that airplane cut out about half it's ground looping. It probably would do even better if that guy wasn't a FIREWALLING FOOL!!!! He figures there's less chance of having problems on the takeoff if he can get it over with as fast as possible....... right.......

Toe will have more effect when the gear isn't located properly. Most everything about ground handling is worse when gear is too far from it's optimum location. So toe that's not right will be really bad.

Just make sure you have toe in and you'll be ok.

BTW, there is a normal situation with toe that should be considered always. Whenever you load the tires, the suspension will "comply". It's "compliance" in any suspension system that sometimes changes the toe.

For example, my World Models P40 retracts are not scale in layout. The wheels are actually inboard of the struts. The full scale P40 has it's wheels outboard the struts. When the tires that're outboard a strut encounter resistance they translate that through the strut and slop in the system to cause toe out. A tire that's inboard will twist the system to give toe in.

Keep that in mind and consider rigging the static toe to allow for the compliance in the suspension system. You may think you've got good toe, when in fact, when it's needed most, it's nothing like you think.

BTW, keep in mind that everything in airplane design works in a very complex environment. Toe is just one small detail in gear design. Look at the Me109 for example. I'm sure the Germans considered toe when working out the gear design, but wouldn't you bet they had fits with the camber those two tires were carrying? And consider the range of caster those things went through from taxi to rotation. Jeez what a mess. But the camber would have given some very strong "toe in" effect no matter what angle the airplane was. Amazing what real life lets us get away with.

Why was my post deleted? I was complimenting Bob. There was nothing embarrassing about it.

Oh, never mind. I quoted the embarrassing post.

Anyway, congrats to Bob for being so candid and thorough. Good job, OldBob!


<edited because I was a little slow on the uptake>

When we flew pattern planes with nose gear-and retract setups - it early on became evident that two things needed work
1- the position of main gear relative to center of gravity and
2- relation of rudder to wheel steering motion
Basically the rudder should do the ground steering with little wheel steering involvement - let the wheel scrub.
When th model reached the point where rudder steering forces really hooked up - there should not be any fighting from the nose gear .
On my bipes - same thing - minimized tail wheel steering and correct main wheel placement for easy rotation and a rudder with lots of throw and smooth expo control
again let the tail whel scrub as rudder does the steering -and get off the tail as soon as possible
If the elevator is properly trimmed -
the only controls thet need input before lift off, are power and rudder.
Trying to address all four inputs is usually counter productive.
add power and control track with rudder - let tail come up- increase power then slightly add elevator .
If aileron trim is correct for flying -no input should be needed.
Works for me and is much like full scale practice except for raising the tail with elevator.

this may be a P-factor effect we're seeing here. It's simply impossible to offset if it IS the P-factor though. All planes have their certain traits that you've got to master. That just may be that plane's trait.

While P factor exists at model sizes it really is an extremely minor force. On some of the larger jumbo scale models powered by the gas engines turning rather large and higher pitched props it becomes more of a factor. But at this size of prop and pitch it'll be buried among the other effects.