I AM BUILDING MY FIRST SCALE PROJECT ( A TF GOLD EDITION P-47). I HAVE INSTALLED ROBART RETRACTS, AND WAS WONDERING IF ANYBODY COULD GIVE ME SOME DO'S AND DON'TS. THIS IS MY FIRST SET OF PNUMATIC, I HAVE USED MECHANICAL BEFORE. THANKS, JOSH

In my opinion the main issue is air leaks. I use high quality metal T's and small fuel line clamps on all the lines. Also make sure your gear does not bind anywhere.



FYI... Please do not type your messages in all capitals. In the forum world that is considered screaming. :-)


Good luck!

Air retracts are no more problematical than mechanical.

A couple of points to watch for.

1. the gear may slam up and down very vast, so you might want to restrict the airflow if this is not done by your valve (although I think Robarts are adjustable).

2. If the movement is too slow this may also cause problems, I have one model where a gear door does not fit flush and if the leg moves too slow the drag from the door will stop the leg from going fully up and locking.

Simon.

I'm also in the process of installing my first set of retracts. I'm noticing that my air system leaks approximately 10 psi per hour. I would presume that this is unacceptable. It would probably be worse in flight with all the vibrations.

Should the air system be completely sealed? If I fill the air system to the recommended 100 psi and then leave it alone for a few hours (or days, or weeks, or months), should I still see the 100 psi when I check it again?

I hope I'm not deviating too far from Josh's original question.

Thanks,
Josh

Juice,

You should aim for a completely sealed system, I had one that retained enough pressure to operate the gear three weeks after I pumped it up. Leave it lone enough and the pressure will fade.

10psi per hour does not seem to represent a problem, you will only be airborne about 15 mins between fills so will only loose 2.5psi during the flight at that rate (I don't think vibrations will effect the rate of leak, if it was gonna blow 100psi would do it all by itself!).

For your peace of mind try finding out t what pressure the retracts fail. I have sets that give a max pressure of 100psi, but work anywhere from 75psi up. You will get fewer cycles at a lower pressure, but should only need one per flight.
Simon.

juice,

those are the same kind of questions that i need answered also, so feel free to broaden this subject in any way. and thanks for the rest of the info guys. (sorry about the all caps im a engineer i write everything in all caps.bad habit i guess.)
thanks again,
josh

Hi guys.

This might be a naive question, but I can't help but wonder why electric retracts aren't more prevelant than compressed air in this age of cheap electronics. I can't imagine it would be too difficult to use electric motors with a worm drive gear or some type of gear reduction to raise and lower even the biggest retracts in a smooth, scale manner. If a separate servo on the doors is used in conjunction with an electonic sequencer wouldn't the installation be less complex, and the overall system virtually maintenance free? Granted, the battery system would have to be beefed up there would be more moving parts, but it seems like a good idea. I'm relatively new to the world of retracts and still on the steep part of the learning curve.

Hi David,

I think electric screw jack retracts are used on quite a few large models (out of my league!, so have no direct experience).

I suspect that the lower cost, weight, space requirement and complexity keeps air systems the more popular choice for the smaller model or the 'club' flyer.

Simon.

I am currently in the process of fabricating some electric screw jacks for a 40 size ME 109. The 109's gear retracts out toward the wingtip. I though I could get away with reversing a mechanical retract(hobbico) and that will work but the 109 angle back as well and the mechanical linkage wouldnt work for a scale look.This has been an interesting(and frustrating at times) project in itself. I got the screw part working but when I tried it, it was as quick as the mechanical ones. I tried lowering the voltage and it wasnt enough to get the screw moving, and went up to a second cell and it was to quick. Currently I am working on a gear drive to slow the screw down to scale speeds. I will post some pics whne I finally get it done. I guess I must also mention that I didnt want to spend cash ( reads cheap) on electric retacts and wanted the challenge of engineering them. I am liking my progress so far and will definately consider trying it again on a larger plane next time.

Warren

I'm about to build some jack screw retracts for a 1/5 scale mustang. Lucky for me ill have the help of an electrical engineer, and a machinist, who also happens to fly electrics(those boys like to keep things lite). When they are done i'll try to post some info...

PS if anyone has actually made some for a plane that size let me know. Maybe save a lot of time.

Aerotech has a tail wheel that size.

I am fairly new in the flying, but i like building planes. I just bought a top flight p51 and plan to buy a top flight corsair soon, future building goals and fun. My question is what is the best brand, model number, etc for retracts on these two planes. i have seen various ideas and opinions, and want to see what the newest thoughts are. i figure if i am putting out 7-9 hundred for plane and not counting the labor, i really want the best system that works, fits, and looks good. Can you please help.

thanks

littledjb