Jim,

The down leadout in the forward position is a result of attempting to moderate gyroscopic procession. In this case, the tendency of the plane to yaw in (toward the pilot) on down control. Not sure how effective this method is, but some at least. A lot of stuff effects this trim consideration and the down line forward is just one way to help counteract the effects.

Which leadout is in front doesn't effect it's stature as a classic plane. In theory, having the down leadout in front is the preferred position, depending on how you look at things. I doubt you'll notice much difference either way.

Which leadout is in front doesn't effect it's stature as a classic plane. In theory, having the down leadout in front is the preferred position, depending on how you look at things. I doubt you'll notice much difference either way.

OOPS; to counteract precession the preferred installation is UP line forward, DOWN line in back, per the church of "Reverend Al" Rabe.  Maybe he'll check in here and affirm???

Jim:
I'll bet I've really confused the issue for ya now!  I routinely make the front line UP, even modified a couple ARF's that way.  However, it is NOT a deal breaker either way.  More important that the controls work freely, and I really like to see the leadouts spread no more than 1" or so at the tips - further minimizing any impact.

Never flown the SAME airplane both ways.. From airplane to airplane can't tell ya that I ever noticed a difference - there are other things that matter more.

However, talking to Al Rabe WAAAAY back in i the early 1970's he made a convincing argument for putting the UP line in front.  Al was (and still is) flying airplanes with BIG propellors and precession effects.  He links the rudder to the elevator so the rudder turns IN on up manuvers annd OUT on down manuvers  Thus the front line UP is marginally making a contribution to controlling the precession effect.  I bought into the line set-up because it seemed the "right" thing to do, NOT because of any trim problems that I could trace back to.

The only other thing to watch for is whether the bellcrank is straight across the arms or offset, like the Sig 4".  That bellcrank should ONLY be used with the front line up and the pushrod arm pointing at the inboard wingtip.

Build the JD whichever way works the best for you.  As you noted if the pushrod arm points toward the outboard tip there are fewer issues with interference.

Finally, as for the weather report, I'll have you know its a balmy 38degrees as I write this.  I'm thinking about breaking out the sun screen as my long lohns only are rated a 4 in UV protection.   

jeez guys, sounds like lawn chair weather over there, weve been in the mid 20 degrees, with some brisk breezes to help stir up the snow, only about 4 or 5 inchs, but its hard to tell exactly, every time I go measure it, the wind moves it around!

Al Rabe first pointed out the possibility of countering gyroscopic precession in a magazine article the 1970's.

The principle is that gyro precession from propellor rotation tends to yaw the model's nose out on UP control inputs, and in on DOWN inputs. (Normal rotation engine, CCW upright flight direction.)

The leadouts split the pull load and aim it through the leadout guides at the model's CG. One leadout is usually ahead of the mid-line of the pull force, and the other behind it. When there's UP input, there's an increase of the load on the UP line (to overcome the airloads on flap and elevator.) If the UP line is behind the mid-line to the CG between the leadouts, it ADDS to the nose-out on UP tendency from precession. Same happens the other way, on DOWN inputs, the load shifts forward, ADDING to the nose-in tendency.

Al R's idea was to flip the bellcrank over, pushrod connected inboard of the pivot, so that the UP line leadout is forward. When the nose tries to swing right on UP, the pull force shift aims ahead of the CG, tending to pull the nose left. And, of course, vice versa. The slight complication of having the pushrod on the same side as the lines has been no problem for about the past 30 years.

I have seen a definite difference, and have tried it both ways on the same model. (Moved the elevator horn to the top surface of the elevator, on an unflapped profile.) With 'traditional' bellcrank set-up - pushrod on the side away from the leadouts, elev horn underneath - the model was very twitchy in yaw. When I moved the elevator horn to the top surface, the UP line became the forward line. Much less yaw twitch on sharp UP and DOWN inputs.

So, the simplest way to say it is UP line forward to reduce yaw twitch on sharp control inputs. It really appears to work!

I've also flown models with reverse rotation engines, and the 'traditional' (pushrod outboard of pivot) set-up works. The prop gyro precession with the engine going CW is the opposite of the effect with a CCW turning engine.

Ever notice that the HOT Carrier fliers are using reverse rotation engines??? A bigger part of that is the engine torque reaction rolls the model when they jazz the throttle, just like a muscle car did. With normal rotation engines, that reaction tends to roll the model into the center. In the "low" speed segment of the flight, it would be much nicer to have the model try to roll away from the center when you punch the throttle...

Igor wrote a convincing argument in a "Hunting" thread on the SS forum that the front line up configuration exacerbates this problem in a plane with the tendency to hunt.

I'm not sure with narrow line spacing that it really matters much which is up.

I beleive in the early days the leadouts were spaced out to as much or more than two inches.  Would make a difference on yaw of plane.  Now leadouts are 1 inch or less.  I think that is why Palmer had the vertical leadouts on his Thunderbird II.  MERRY CHRISTMAS,  DOC Holliday

OK.  My answer is that it doesn't make much difference, but I have always thought that a front UP line would offer a slight advantage with regard to gyroscopic precession.  The front down line may have a slight negative effect.  Since there isn't enough difference to worry about, why not go for the slight possible improvement?

Al