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Author Topic: Walker Patent: is it better to have the up line to the rear?  (Read 1904 times)

Offline Leonard Duke

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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?

Online doug coursey

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #1 on: July 08, 2023, 09:54:47 AM »
 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

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Offline Ken Culbertson

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #2 on: July 08, 2023, 02:14:30 PM »
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~

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Offline Tim Wescott

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #3 on: July 08, 2023, 02:52:14 PM »
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.
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Offline Ken Culbertson

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #4 on: July 08, 2023, 03:28:07 PM »
 
if you're doing 30-point or lower hourglasses stop worrying about it and go practice more.
y1  LL~  y1

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Offline Dennis Toth

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #5 on: July 08, 2023, 08:29:50 PM »
The main reason for the back line to down is for a normal IC engine (or motor) turning counterclockwise is to offset the inward nose yaw (gyro presession force of the spinning prop) on outside maneuvers, on inside maneuvers the nose yaw is to the outside. If you use a clockwise rotating motor (pusher prop) the effects are the opposite. If the leadout lines are close to each other or you have a very light prop. the little extra outward yaw that this gives is small, but in stronger winds can help keep the ship out a little.

Best,   DennisT

Offline Dan McEntee

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #6 on: July 08, 2023, 10:59:00 PM »
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?

     Well, one thing to keep in mind is that Jim Walker had the patent on the bell crank and push rod, but the patent ( and two others ) was successfully challenged in court Cox Thimbledrome and proven that he stole the idea from Oba St. Clair. Other examples of other people developing and using the bell crank and push rod independently and at the same time and with out knowledge of Walkers efforts were presented also. Given the state of control line model airplanes at that time, I don't think Walker gave two minutes thought about which lead out was where. If the major accomplishments at flying stunt at that time were a few loops, wing overs and some climbing and diving,  The wording in the patent also fits why some came to put the down line in the rear. If the model is in generally good trim, other adjustments tend to keep the model tight on the lines. it's the outside corners of the squares, square eights, and the hour glass where a little tug on the back of the bell crank would help with better line tension. Al Rabe came along with his Rabe Rudder system and and addressed the problem also. Having the down line in the back in itself isn't that big of a deal, but when combined with all the other little tidbits and adjustments that go into making a stunt model do what we want, it can help make a model feel better in certain maneuvers.

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Offline L0U CRANE

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #7 on: July 11, 2023, 11:49:27 AM »
... then there's also clockwise or CCW flight...

Many (most?) published or kitted designs back then  flew upright from left to right.Torque effects were reverse of our 'accepted standard' of CCW. With conventional prop rotation (CCW as seen from the front) torque on takeoff tries to roll left wing down. i.e., left roll.

The original AA Sr large wing area offset benefitted from torque with conventional rotation engines - no dragging wingtip at takeoff. Flown left to right -CCW- quite the opposite. And less or no outboard tip weight needed. Flew one with CCW AND CW rotation Fox 35s - it is noticeable!

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Online Paul Smith

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #8 on: September 23, 2023, 07:00:57 AM »
I've built many models BOTH ways and it only matters if and when you hang the model on one line.  Otherwise the bellcrank equalizes line pull and it doesn't matter.

Hanging on one line is bad practice and must be avoided.  It can and should be prevented by rigging handle and bellcrank sizes to make it impossible.  You should be able to get full travel of the flipper while keeping both lines in tension.
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Offline Ken Culbertson

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #9 on: September 23, 2023, 07:56:03 AM »
It can and should be prevented by rigging handle and bellcrank sizes to make it impossible.  You should be able to get full travel of the flipper while keeping both lines in tension.
Not as simple as it sounds.  It wasn't till I started using yellow Spectra lines that I found out how easy it was to go to 1 line.  I use stops to limit me to what the controls will do.  Keeps them from the stress of going past their design travel.  In most cases, I hit the famous "wall" well before I hit the stops and my lines tell me because I can SEE them starting to bow more on the slack line.  My only conclusion is that pull is evenly distributed in level flight and to some degree in rounds but definitely not in the corners even if you do not come close to maximum travel.  In my case with my latest ship, having a canard has moved the *wall* back a bit.  In a controlled test I am able to hit both stops (45 elevator, 35 Flaps).  The plane practically flips in it's own length and the opposite line goes really slack.  The point is that there are two points that you lose tension on the opposite line, not just when you hit maximum travel.

Ken
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Online Paul Smith

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #10 on: September 23, 2023, 10:29:24 AM »
If you use end stops on the model you will certainly hang the plane on one line at times.  I think this is bad practice and a cause of failure either to the lines of the model.  The handle and bellcrank geometry can and should be rigged to allow full travel while keeping tension on both lines.
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Offline Ken Culbertson

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #11 on: September 23, 2023, 11:32:40 AM »
If you use end stops on the model you will certainly hang the plane on one line at times.  I think this is bad practice and a cause of failure either to the lines of the model.  The handle and bellcrank geometry can and should be rigged to allow full travel while keeping tension on both lines.
Apparently you have never had a BC over-center.  My stops are well past any reasonable control deflection and if actually reached I would have reached the BC limits as well.  The difference is that I am not putting excess pressure on the flap and elevator horn mounts.  I am sure there are many who disagree, but I will continue to use them.  Fly a pattern on brightly colored lines and you will see that the tension does not remain equal on both lines throughout.  It is not a "one or other" shift but equal, I don't think so. Perhaps in a vacuum.

Ken
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Offline pmackenzie

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #12 on: September 23, 2023, 03:22:59 PM »
I've built many models BOTH ways and it only matters if and when you hang the model on one line.  Otherwise the bellcrank equalizes line pull and it doesn't matter.



Not quite. The difference in line tension between the two lines is what provides the force to move the control surfaces.
In some cases you can end up with all the force on one line without hitting any hard stop.
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Offline Mark wood

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #13 on: September 23, 2023, 07:22:48 PM »
That is very much correct. The moments required to deflect the control surfaces can be very high and the slack line "effect" is an indication of that. The 4/4 world is very aware of this and if you look at how they approach removing the control forces you will there is a significant effort to do this. The limitation there is in the pilots ability to push the stick around. Kens observation is relevant. Using the spectra lines gives him some insight. My spades I put on my test ship reduce the control moments and the subsequent models I am planning will do a more finesseful approach at control moment reduction.

What is happening in Kens observation, is that the tension of one line is carrying the force required to generate the moment of the deflected controls. The controls will only deflect as far as the differential tension generated moment in the lines. In other words, regardless of how much deflection is available, the resulting deflection for an input will only be as much the input moment.

Here's a related example. On a torque tube control system of an airplane I flight tested, on the ground the ailerons would deflect 30 degrees. In flight however thing are different. You can go on my Youtube and see some videos. AT 130 knots at full stick deflection you can see the aileron moving to about 27 degrees at full stick deflection. I had no stick force measurements. At 220 knots, the aileron deflection is much less as a result of the torque tube wind up. The deflection is more like 15 degrees.

What this means in model terms is that the maximum deflection won't be achieved and the resulting slack in the non pulling line will be apparent. Even though the pulling line is carrying all of the tension, it may not be enough to fully deflect the controls. The moments are surprisingly high. Igor may have a good idea of the exact levels.
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Offline Dave Hull

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #14 on: September 23, 2023, 10:37:25 PM »
There's a much more complete discussion in this thread regarding differential line tension:

https://stunthanger.com/smf/open-forum/question-on-the-netzeband-wall/

Some very well-reasoned answers and at least one published study that has withstood the test of time.

Online Brett Buck

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #15 on: October 07, 2023, 04:24:31 PM »
I've built many models BOTH ways and it only matters if and when you hang the model on one line.  Otherwise the bellcrank equalizes line pull and it doesn't matter.

    It may or not matter, but as noted, your basic premise is certainly not correct. Any time the controls are deflected, the tension in the lines is different. The bellcrank doesn't "equalize" the tension, you have to have some torque to deflect the bellcrank, that is supplied by differential in the torque on the two arms of the bellcrank, and shows more tension on the line pulling the direction of the turn.

   Also as noted, you do not have to "hit the stops" to have the airplane "hang on one line" (that is, the line tension differential reaches the line tension, so it is all on one line). It is relatively easy to run out of torque before you hit the stop (if any), particularly on Nobler-type airplanes with gigantic flaps. Bill Netzeband recognized this a long time ago, it is called the "Netzeband Wall" in his honor. This is also why 4" bellcranks work better than 3" bellcranks, bigger the better.  Most modern stunt designs are intended to make this a non-factor but it was a serious problem in the good old days.

   I also note that I and most others do not build in "stops" on the bellcrank and with a conventional pivot attached to a spar, it can't go over-center.
 
     Brett

Offline Ken Culbertson

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Re: Walker Patent: is it better to have the up line to the rear?
« Reply #16 on: October 07, 2023, 05:26:23 PM »
   I also note that I and most others do not build in "stops" on the bellcrank and with a conventional pivot attached to a spar, it can't go over-center.
 
Brett:
I am not disagreeing with you for today's normal construction but actually, it can happen and I have had it happen to  me.  Assuming a conventional mount with the upline in the rear and the leadout guide for the upline is in front of the BC center it can over center if your flap has enough range to take the full amount of pushrod movement.  You would probably never notice it since any pulling on the down line would release it immediately.  It happened to me on takeoff when I was in a hurry to get into the air (one last trim) and forgot to center the controls before the motor ramped up.  The plane did a flip and smack before I could process what was happening.  When I picked up the nose-less plane the controls were locked.  I was able to duplicate it in the shop.  I will admit that it is very unlikely with a normal spar since most of us like to but the BC as close to the CG as possible, but this plane had a "Rabe" like airfoil and the spar was a good 4" from the LE at the BC mount and well behind the CG.   And Yes, I had the ribs hollowed out all the way through the wing.  Normally the ribs would prevent over centering until you cut them in half with the leadouts and most flaps don't move enough and become a stop in themselves which is undue stress on the hinges and flap horn mount.

I have put stops at 60 degrees ever since.  Doubt I have ever hit them.  Going to yellow Spectrum lines has given me a field trip classroom demonstration of what you just posted.  You can see the trailing line go slack even in the entry to loops and it is a real heads up as to when you are approaching that very real wall and a bell ringer when you hit it!

Ken

Footnote:  I don't make the stops special either.  I just make the cutout in the spar on the side opposite the pushrod small enough that the bellcrank cannot rotate through the spar before the flaps hit their maximum deflection.  Works for me.
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