I have a World Models P-51 GS that I have removed the mechanical retracs from and replaced with spring air. 1st time to have retracts and I have what will seem to be an easy question. I have a JR retract servo with 160Deg of movement. If I tame the movement down, can I use the servo to actuate the air valve? If I do tame it down and it doesn't make its full turn, will it continue to put a drain on the battery?

The retract servos are designed for a specific application and with what it will cost to repair a P-51 with a gear malfunction I wouldn't even consider taking the chance. Big P-51s usually suffer considerable damage to the fuselage and air scoop when they belly land. Been there done that. A standard servo will work great on the retract control valve and the spring air valve is very reliable. You have taken a Quantum leap forward in landing gear quality. I would take the swap the rest of the way and do it right with all of the right pieces. Good luck!

Jack Devine

Retact servos typically rotate 180 deg and then shut down, unless they can't make the 180 deg cycle then the will sit there and keep trying to continue the cycle.

But if you restrict the servo's ATV to much with a computer radio the servo wont move at all. it wants to rotate 180 deg.

If you set up you linkage to make the full cycle the servo will shut down and not draw current. and will work for you

I usaully just use a standard servo for retract valves. If your linkage is smooth it will draw very little current, just like a throtlle servo does.

Good luck

Thanks for the advice guys. I figured out that the correct approach was to put a standard servo in late last night... and it works fine... now to get the MDS 2.18 running properly or replace it. Bought it on advice from an owner of a local hobby shop. Wish I had gotten better advice!! Thanks again for your help. The retracts operate very smoothly. Will a 1/8th" wheel collar really slow down the operation of the retracts? Is there anyway to incorporate one of the robarts switches with the spring airs?

If you use the Robart adjustable valve it will work with any other brand of retracts.
Those Spring-airs can really slam down

I'd recommend using the adjustable valve. the Wheel collar method can wear the line and cause a hole to develop over time

The adjustable valve I have is the red one with 3 inputs and 2 needle valves. The Spring Airs only have one input....Advice on hookup greatly appreciated. The "slam down" is strong enough that it worries me!! I am sure it sounds worse than it is. Thanks again

I thought the Spring-airs vent back through the retract valve, like all retracts do
The robart valve has one input and two outputs
The input is the middle one
If you seal up one output of the robart valve (so you don't loose all your air preasure in the down position) then the one restrictor will controll the airflow in both directions

Took me all day to think this up

I'm sure someone will correct me if I'm wrong, it's been a long time since I played with spring-airs

I have used the 1/8 inch wheel collar for years and never had any holes or line damage. It does a great job at bringing the gears up and down at a lot slower speed and it is in expensive as well. The up side to Spring Air is that if the wheel collar did put a hole in the tubing, the gear is coming down and is locking. Good Luck, Dave