Flap Lengths

Thanks for any replies.

OK, how's this? We use a slightly larger OUTBOARD flap on equal panel wings. So an even larger outboard flap on a plane with a larger inboard wing might be the answer. (Ted put a "wart" on his, but it had the same effect.) It enables you to use more (in my mind the "right" amount) of tip weight which aids in tension. When the plane is flying vertical or overhead, assymetry does nothing while tip weight is still working for you. Too much of anything is bad, but a little more outboard flap seems to help in allowing a proper amount of tip weight without banging in the corners.

Could you elaborate on the part about tip weight still helping overhead or vertical? I thought I had a better handle on this but I can only picture an effect of tip weight (while on top)resulting from any fore and aft displacement from the CG.

I havent even seen mention of the fore and aft location of the tip weight. I try to place mine as close to the CG location as I can.

Thanks

Now, as to tip weight itself.

First, going up. One of the purposes of tip weight is to, at least partially, (hopefully moreso) balance out the weight of the lines on the inside wing. Some people use assymetry to do this. By adding more wing on the inside, we can increase lift there and balance the extra weight of the lines with less, or even no tip weight. Sounds good, right? Now, aim the plane straight up. Where is the affect of assymetry? It is not there. And we not only have the weight of the lines pulling down on the inside wing, but the extra weight of a larger inboard wing helping this along. And one more thing that a lot of people don't consider--drag. When we aim the plane straight up there is the drag of the lines, also, pulling down on that wing.

That's where the bigger outboard flap comes in. More on that later. But you can see where a lot of people lose tension going up. We need tip weight.

Second, overhead: If we are flying with a "typical" 3 g's straight and level and have the plane in trim, we should have about 2 g's directly overhead (gravity, you know). True, some will fly with less tension--and not always purposely--but when we get light on the lines overhead, the hourglass, among others, suffers. I have even seen some people "free flighting" through overhead eights. Not good. We need tension to keep control of the plane.

But if we have tension, we have a tether situation. If we have a rock at the end of a string and whirl it, the rock will stay out at the end of the line. If we put the rock (tip weight) at the end (outboard tip) of the plane, it will help hold the plane out the way we want it. But if we have no weight--or worse, a heavier inboard wing due to too much assymetry)--guess which way the airplane is going to want to fly over head in a tethered situation! Not good.

Now, the larger outboard flap:

When we are flying our plane straight and level, there is drag caused by the lines that we compensate for by raking the leadout guide back some 2 to 3 degrees (it will depend on the size and length of the lines and speed and other trim of the plane). Do a loop and the lines pretty much follow behind the plane--a little off in angle, but not much. Now do a sharp square corner. The plane turns up, but the lines are still pulling back to the right, and this causes the tip to "bang". We often blame it on tip weight and take tip weight out, which causes us to lose out in points one and two as mentioned above. But it is mostly caused by line drag.

This effect is most noticeable on the bottom outside corner. As the plane flies straight down, the lines, trailing behind, are pulling up on the inboard wing and the leadout guide is raked back to compensate. Now turn a sharp bottom corner. The plane turns, but the lines are stilling pulling "up". The pull of the lines lagging behind the plane pull up on the onboard wing, and gravity pulls the outboard wing down. So, do we remove tip weight. NO! We add more outboard flap.

With a larger outboard flap, on a sharp corner as noted above, we suddenly get more lift on the outboard wing to compensate for the "up" pull of the lines on the inboard wing. In level flight the effect of the extra flap is next to nothing, and in loops we have minor deflection of the flap just as we have a minor offset in the pull of the lines. But when we turn the corner and add more deflection, it is there when we need it most.

Adding a couple of inches to the length of the outboard flap, or an eighth to a quarter inch in width to the tip of the outboard flap, will usually be enough to compensate. Some people put "trim tabs" on the outboard flap on an old time or classic ship. To me that is cheating. But it does work.

Oh, by the way, there is the argument that the outboard wing is flying faster and we need that larger inboard wing to compensate. A half inch, at most, will do that. And adding a half inch to the length of the inboard wing may not be all that bad. But I still think a plane is easier to trim with equal size panels and it allows for more tip weight to get more tension all around. And more tension (within reason) gives more confidence to the budding flyer who tends to "lose it" every so often.

That is another argument since the plane is flying tangent to the circle and constantly yawing out. It may well be, which is another argument to build equal panel wings and not use assymetry. I have done mild assymetry (1/2 inch) and equal panels in the past, but lean towards equal panels with a slight increase in size on the outboard flap these days.

Outstanding!

Thank you. THis is the first comprehensive explanation I've seen on these factors. I am continually amazed at the complexity of the problem of this PA environment. It is at least partly responsible for its enduring attraction to many of the "technicians" in the sport I would guess.

Thanks Leonard, this helped alot.

I hope to at least say "HI" in Muncie in a couple of weeks.

Curt

PS: This is also one of those posts that improve with multiple readings.

An adjustable tipweight "box" that allows fore & aft trimming of the tipweight (just in case you feel the need) can be done with a tube with BB's and balsa spacers. A socket head setscrew is the "lid", and it makes a pretty slick installation. My "Humongus" has such a tube, but as I didn't build it, I don't yet know how long it is, how much weight it will hold, or if it is possible to significantly shift the fore & aft location of the required tipweight. But if you want to experiment, this would be an easy way to do it. Looks easy to build, too. I will look into how it was fabricated and post it. Steve