Just finished my TF P40e. I've been reading some cautionary threads on the tip stalling characteristic of the TF model, and moreover several threads on the robustness or otherwise of the Robart twist and turn retracts.
It's all making me rather jittery.

However...
I've noticed a loss of pressure from the air system without exercising the retracts and am concerned even more. The links and attachments have been double checked but it still loses pressure.
Have others encountered this, and at what pressure do you operate your Robrats, oops, Robarts?

If you are losing pressure its time to go through the whole system and find the leak. Most of the time it will be the linkage from the servo through the control valve. If the wire binds on the valve and puts a side load on it it will leak or if it is pushing it too far either way it will leak. Make sure all of the hoses are pushed all of the way on the nipples and that the schraeder valve is tight. Use a couple of drops of Marvel air tool oil in the system to make sure it is lubricated. Hope this helps. Don

Robin-Its also been found that some "tee" fittingBill s are the culprits here....Most of the guys Building the large scale stuff are using BVM "tees" ...I just went thru my Ziroli Corsair which has 168 flts on it and replaced the last few "generic" tees with BVM and each one of them was leaking air....I use a "Q" tip and soak it momentarily in Windex and place it on the questionable fitting and if there is a leak...you'll see the bubbles ...

You didn't say how fast it's leaking down. However small the leak, it should be easy to find with a bottle of "leak check", or the "Q" tip method described above. Be sure and leak check the cylinder rams also.

Vince

Robin, I mentioned lubing the system at the end of my first post but I think that is the most important thing to do even before hooking up all of the air lines. One or two cycles on a dry o-ring will cause a leak almost every time. Just use any good air tool oil and add a couple of drops every other flying session or so. I have a full scale Nanchang CJ6 with pneumatic gear,flaps,and brakes and that is what I do on the real thing weekly. Don

Don,Warbirdz1, Vince,

I'm encouraged, thanks for the advice, I'll get some stuff and check out the T pieces and control valve too.
This site is a boon

Robi, don't over do it with the lubrication, almost any is too much if you know what I mean. Robart lubes the O rings with silicone grease prior to assembly, so they really are not dry.

Vince

Sorry I didn't clarify that. I only use a couple of small drops and only after a couple of flying sessions on my models. Some times the retracts have sat around in a dry climate and can dry out the o-rings on a new set. Once it is all hooked up it is basicly a sealed system except for the exhaust and that is where you will lose the lubrication so it has to be replenished . I have a set of rhoms on an old Platt Spitfire that have worked perfectly for 20 years. Don

No problem Don, It's just that I've seen people really shoot the lube to the retracts, and in no time they are full of dirt.

Vince

Vince, Thats why I like the air tool oil. Good o-ring lube and it doesn't attract dirt as it doesn't dry out and get gooey. Don

The retract units have been sitting around for some years since I bought them. They may be dry, but I'll also experiment with the throw of the valve too, since I've mine set up fairly wide.

Well, I took your advice. I lubricated the valves and I've just changed the T-pieces to metal ones. It's stayed put at 80 lbs pressure for the last two hours. Well pleased.
In addition, at this pressure the system was having trouble lifting the retracts, addmittedly they are heavy. I put restrictors on the tail wheel, and now they're OK.
At the same time I've reground the wire both at oleo attachment points and at the head of the retract with the attachement to the rotating gear. Loctited too, and managed to get a little bit of tow-in.

I hope everyting's fine now for it's maiden flight, just waiting for some good weather here in the UK. Pity since it looks as though our brilliant Indian Summer is just breaking up into the more normal autumnal cold and winds. I'll be patient.

I think that the most significant factor was the metal T-pieces, so thanks Warbirdz1!

What pressure do you guys run your system at? Do any of you run around 100 psi, or do you stick with the 80 psi?

Thanks again

Robin, if you have a metal tank, you do have a metal air tank don't you? You can run 100psi or even a little over. 80 is about the bottom of the preasure range to operate these. If you have a plastic tank get rid of it as I have seen what happens when out in the hot sun. Blows a fuse into very tiny pieces. Don

That's reassuring... I have the metal tank, so up we go to 100 psi
Thanks pittsdriver

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There were quite a few mfgs that had plastic tanks. Some that you could modify a soda bottle. Byron had plastic in his big kits. At the field on a hot day and a guy filled his Byron T-6 with around 105psi and after sitting in the sun for about 45 min it blew the fuselage to smitherines. I think most of the metal tanks will blow an airhose before they would blow. Don

The metal tanks if over pressurized will not blow to pieces, they will split and vent, or blow the hose off.

Vince