Mechanical retracts

[andrew wise 2]

A belated Happy New Year to you all. Like a lot of you I suspect, I am hiding away indoors fiddling with models and looking at kits which have been sitting on the bench since I brought them at a swap meet and done nothing with them. Anyway to the problem. I am puting together a 58" ARTF P51 with mechanical retracts. Everything has gone together well I have fitted a HiTec Retract servo. Does anyone have a good tips for setting these up because I am having one hell of a job to make them work well. HELP.

[simon burch]

Move one of the retract legs from one end of the movement to the other. You will need to mark a point on the pushrod against something on the wing which doesn't move (a former or against the servo bay etc) at one extreme, then mark it again when you have moved it through the full movement. This will tell you how far apart the connections will need to be on the retract servo.

 

Keeping things simple, assuming the leg moves 20mm to take it from retracted to fully deployed, then divide this distance by 2. Most retract servos move through 180 degrees, so if the servo connection is set at 10mm out from the centre, when it moves through the circular 180 movement, you will effectively end up with a linear distance moved of 20mm.

 

Not very easy to describe, but I hope that helps. Normally have to kink the pushrods slightly to stop any clashes. Double check the movement of the servo before you connect anything, you'd be amazed how quickly you can strip the gears if you get it wrong !!.

 

Cheers,

 

Simon

[Roger in Dubai]

Good explanation Simon, that is the way I set up the retracts on my aircraft and they always work flawlessly. 

 

A further suggestion on retract mounts in ARTF's - reinforce them as many are weak and maybe just get shown the glue bottle.  I am fortunate in being able to fly off tarmac, but it appears that most sites in the UK do not have this luxury.  An extra piece of MDF mounted underneath the retract rails sometimes does the job quite nicely.  Otherwise a pine strip is also good.  You will need to lengthen the screws as well, but a litle care and attention now can pay dividends in the long run.  Good luck and safe landings.