Hooked up the controls on my FJ this morning and came up with a couple questions..

First, does it really matter what direction the throttle moves? I had to put a transfer link in my throttle which reversed it from what a straight link from the bellcrank to the engine would be..

2nd, My bellcrank has more range than the engine. In Paul Smith's Skyrader thread he says..

"The Brodak bellcrank has about 1.15" inches of throttle output, but the OS carb only wants 0.70". To reconcile this, I had to make a new, longer throttle arm for the engine. Otherwise the line pull will be transferred into the throttle.".

I don't think I get it, is this because you will try to move the 3rd line further than it can go?

TIA:

Basically if you have less movement of the arm on the carb than on the bellcrank the controls will "bottom out".  The trigger would be all the way back on the handle for high and when you throttled down instead of hitting idle at full extension of the trigger you would get it at the half way point of trigger movement. 

The direction of movement of the pushrod from the bellcrank to the carb doesnt matter if it pushes or pulls it just matters which way you want your handle to work and the style of bellcrank(inverted or right side up).

David

In a perfect world,

Stunters and combat planes keep equal tension on both lines at all times.

Carrier and Scale jobs keep equal tension on all 3 lines at all times.

But a lot of people recognize that we are not living a perfect world and set up their models accordingly.

Anyhow, I operate under the theory that transmitting LINE PULL to the control horn or the throttle arm is a REALLY BAD TING, and set up my controls accordingly.   In defense of DuBro, In think a lot of abuse aimed at their clevi was unwarrented, but rather the result of grossly overstressing the product.

Thanks guys,

This morning I made a new control arm for the inside of my transfer link 1 inch long and drilled another hole in the engine side arm 1/2 inch from the pivot to give me a 2 to 1 reduction. This made the bellcrank throw match the engine throw.

Still haven't decided about reversing the engine control arm. Easy enough to move it to the top of the carb but then the linkage would (in my eyes) be gaudy, sticking out so far and running under the exhaust. Will probably start out leaving it reversed and change it if I run into any issues. This will be the first 3 line airplane I've ever flown so don't have any habits to unlearn.

Never thought about slot cars did allot of that in the 60's, bet the muscle memory is still ingrained.. kinda like you never forget how to fly or ride a bike. Pull to go fast will probably work out well for me...

Thanks

When you fly a real airplane you push to go, when you drive a car you push to go when you drive a lawnmower you push to go when you drive a boat you push to go but most carrier flyers pull to go fast ?    Mike

Pretty much...

You do pull the trigger to fire a gun.

There is one point about the J. Roberts system that hasn't been mentioned. While it is designed to share the load over all 3 lines, the pull mode does allow the main bellcrank to slide to the hard stop on the mechanism, just in case. That means the up / down lines carry the full flight load.

Pretty much...

You do pull the trigger to fire a gun.

There is one point about the J. Roberts system that hasn't been mentioned. While it is designed to share the load over all 3 lines, the pull mode does allow the main bellcrank to slide to the hard stop on the mechanism, just in case. That means the up / down lines carry the full flight load.

I prefer to set up my handle with the trigger pulled back for high speed. It does prove to be easier to hold the handle in that mode. Moving forward to slow down doesnt give me any issues. Relative to the load, it needs to be on the up and down lines for sure as any load on the throtle line will cause hunting issues.
Wayne

Old DOC here,  All I know is when I pull for high(the trigger) speed the lines all look to be pulling equal tension.  Now if I go to full low sppeed on the ground the lines may not be equal.  Also when I am flying I have never went to full low speed on the handle.  So I say which ever way the trigger is for high speed the lines should be equal tension on all three lines.   This is when the pit boss needs to know which is high speed and not worry about any thing else than line diameters.  We lost a good NATS flyer as a pit boss did not concentrate on his job.

Let me give my preferences on this, too. I pull the trigger for high speed, and my up line is aft. I am pretty pleased with this setup. I also have a cable attached to the leading edge of the wing and ending in a loop that goes around the up line between the line slider and the fuse. The idea of this "corrector line" is to restore neutral elevator to nearly the correct handle position after the slider goes aft, and to minimize the changes to the throttle position. This has been published before, but let me go through the whole deal here.
The idea is to be able to get full throttle in high speed but you don't need to reach minimum throttle during high speed. For low speed you want the full throttle range, or very nearly so. So set your line/leadout lengths so throttle is right in low speed. Neutral elevator is required in high speed, but it is not so important in low: Holding a bit of up in low speed is not a problem, but holding a lot of elevator in low, especially if it is down elevator, makes flying difficult. So my setup procedure would be as follows. First, make all your flying lines the same length, exactly. You might make spares at the same time, so if you break or kink a line and need a replacement, you don't have to go through any setup, just put in a new one you have already made. Then set up your elevation line leadouts so they are the same length when in neutral and slider forward position. This gives you level elevator for high speed. Now, release the slider to the aft position and set the corrector so that you are almost, but not quite, in level elevator position. (Trying to correct this perfectly may be difficult with extreme sliders, and is not needed.) Set the handle trigger in forward (low speed) position and make up the throttle leadout so that the throttle system is at the full low speed end of the bellcrank travel. (All this setup can be done with the throttle linkage disconnected. The idea is to get the travel right from stop-to-stop on the bellcrank. You can hook up the throttle linkage later, without having anyone out on the handle but just using the full travel on the bellcrank.)
Now, when you check things out at the field, you will find that you have the elevator in neutral for high speed, and the throttle uses the full travel in low speed. But the throttle line may be drooping in high speed (slider forward) if you pull the trigger all the way back. This is not a problem for either flight or pull test. For pull test, just leave the trigger alone and the forces on the lines will equalize as the bellcrank automatically moves to a position equalizing the forces. In flight, the forces on the three lines will be equal unless you pull the trigger with a death-grip. Just relax to the tension a bit and the forces are fully distributed. If you really try to pull the trigger hard, you will be fighting the full forces of the flight pull with one finger, which is not a fair match. It doesn't help the flight, and just makes your finger hurt on the trigger, so just relax. When I go to low speed, I might not get full travel using the trigger, but it will slow the airplane down a lot. I set up my slider to release requiring both low throttle and down elevator. This may require me to reach around the handle to pull the throttle line sideways a little while I give a pulse of down elevator. This is pretty easy to do.
I hope I have made this clear enough to be understood by all. It may sound complicated, but it really works well for me.
Pete