Design > Stunt design
Walker Patent: is it better to have the up line to the rear?
Dennis Toth:
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
Dan McEntee:
--- Quote from: Leonard Duke on July 08, 2023, 09:18:58 AM ---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?
--- End quote ---
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
L0U CRANE:
... 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!
\LOU
Paul Smith:
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.
Ken Culbertson:
--- Quote from: Paul Smith on September 23, 2023, 07:00:57 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.
--- End quote ---
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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