Design > Stunt design

Walker Patent: is it better to have the up line to the rear?

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Leonard Duke:
I was reading Jim Walkers 1942 patent 2,292,416 and he felt that the up line should be the one toward the rear of the plane. His argument was that when pulling the plane up the plane would slow down and be at a higher elevation and that pulling on the line would cause the plane to yaw outward, increasing the line tension when you need it. At first I thought that both lines would always have equal tension (barring friction) unless you pulled to the bellcrank stops, but then I realized that the force necessary to push the elevator against the air would be sent down the pushrod and the rear line would indeed have more tension, causing the plane to yaw outward.

My question is: do any of you feel that it is important to have the up line to the rear? Was Walker right, or is this an insignificant consideration?

Another part of his patent claimed that the prop should have conventional rotation as then the p-force would cause the plane to yaw outward when transitioning to up elevator.

Any comments?

doug coursey:
 IF YOU HAVE ADUSTABLE LEADOUTS YOU CAN MAKE THE LEADOUTS CLOSER TOGETHER ABOUT AN INCH APART SO I DONT THINK IT WOULD MAKE THAT MUCH DIFFERENCE...ON THE TBIRD II THE LEADOUTS WERE OVER AND UNDER BUT THAT REALLY DIDNT CATCH ON

Ken Culbertson:
This is an interesting subject.  I had always, or at least till the late 70's, put the up line in the rear simply because that is the way it is easiest to mount the bellcrank with flaps.  Then I was told by someone who knew a lot more that me that the up line should be in front so I started doing that and have ever since until Endgame.  I needed to exit the wing on the bottom to connect to the "Mr Gadget" flap horn I was testing.  I flipped the bellcrank accordingly, but as it turned out the horn reversed the direction of the elevator once more.  So, quite by accident I have the up line back in the rear.  So my profile Trifecta has it in the front and Endgame in the back.  You know, once I got them both trimmed, I cannot tell the difference.  I simply think that the 3/4" separation between lines pretty much moots the issue.  BUT, there is still a major difference between the two.  The Trifecta uses a normal 3 bladed 11-6.  Endgame uses a pusher 2 blade 12-6.  Could prop rotation be the determining factor in which line goes in front?  If it is, then I probably have them both backwards! LL~

Ken

Tim Wescott:
This has been discussed before.  If you have the energy to do a search, do take a look.

I can give you the highlights that I remember:


* The old-timey airplanes had quite a bit of separation between up and down lines, which accentuates any effects compared to typical leadout arrangements of today.
* From the discussions I recall that there is a subtle difference when you swap up- and down-lines
* If you set the plane up with the up line in front, then as soon as you're inverted the "goes away from the ground" line will be in back.  In other words, whatever effect the leadout placement has on inside maneuvers will be flipped on outside maneuvers.
* If your construction is typical, with most adjustable leadouts you can flip the leadouts.  Yes, they'll cross one another inside the wing, but as long as you make sure to uncross them if you change your mind there's no harm there
I have a policy of not worrying too much about differences that I can't discern when I'm flying, unless I'm getting coached from someone who can.  I suspect I'll never be a good enough pilot to be able to tell the difference, so I'm not too worried about it.  From what I remember about reading what really good pilots have to say about this, it's like the whole clockwise vs. anti-clockwise prop rotation: it'll improve some maneuvers at the expense of others.  For both prop rotation and leadout position, I often hear it justified specifically because it makes the third corner of the hourglass better -- even though it has a slight negative impact on your inside corners.

Post-COVID I've judged a lot of really crappy hourglasses -- I'd say that when you're flying good enough so that you're doing an hourglass that's actually intersecting at 45 degrees above ground, with lines that are 60 degrees off from each other, with a second corner that's as tight as the first -- then you can start worrying about whether you should refine the third corner of the hourglass at a slight cost to every single inside corner in your pattern.  We're literally talking about bumping a 34-ish point hourglass up to a 36-ish point hourglass, or maybe 38-ish points to 39-ish points -- if you're doing 30-point or lower hourglasses stop worrying about it and go practice more.

Ken Culbertson:
 
--- Quote from: Tim Wescott on July 08, 2023, 02:52:14 PM --- if you're doing 30-point or lower hourglasses stop worrying about it and go practice more.

--- End quote ---
y1  LL~  y1

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