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?

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!

Ken

 

if you're doing 30-point or lower hourglasses stop worrying about it and go practice more.

   

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.

   Type at you later,
    Dan McEntee

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.

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.

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.

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.

   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.