Large Model Association Forum

Good Evening All,

It's a while since I last fitted retracts in a model - been having an extended rest....

I have a Top Flite Giant scale kitted P51D mustang for which I have bought the recommended 1/5th scale retracts with a rather large air cylinder and the appropriate air valve. Everything has been plumbed in and the retracts work fine without either of the 5 inch main wheels which incidentally weight about 200 grammes each. I charge the cylinder to about 100 psi but with the wheels on it's a bit of an non event in the raising of the retracts - seems that the weight is an issue.

Could I be getting a blockage somewhere ?
I spent hours on the internet looking for light weight 5" wheels but drew a bit of a blank. Years ago when i was foolish i bought a set of three wheels for my 84" B25 Mitchell which cost me a small country's military spend and even these were quite weighty - strangely they work fine on a much smaller air cylinder with successful repeated cycles. Could the cylinder be too big ? sounds strange but until it's resolved progress will cease.

Any Ideas please

Regards Steve

Hi Steve, had same problem with mine, only solved by fitting lighter wheels.
Barrie

Thanks Barrie,

Do you have sources of lightweight wheels ?

Regards Steve

you could always try 2 air bottles, discussed this with a mate of mine, it needs more volume, but my corsair, with robarts, and BIG wheels, lifts easily on the larger air bottle from robart, have you tried all the joints with a soapy water mix?

Thanks Alan - food for thought.

Regards Steve

Hi Steve, I fitted a pair of Dubro pneumatic wheels, not very scale looking but did the trick.
Barrie

I would say the problem is the size of the actuation cylinder, not the resivoir (although more is always better).

More volume at the cylinder will present more 'push'. I run some of my units (one of a similar size to the stang) at 150 psi comfortably.

Mat

many thanks matt

what kind of pump / compressor do you use to achieve 150 psi ?

Regards Steve

Hi Steve,

I use the Aldi equivalent to this http://uk.ebid.net/for-sale/rothenberge ... 272444.htm

I run mine directly from a 12v Battery.

Mat

Thanks Matt,

Regards Steve

I have the T/F 1/5th P47 with these retracts plus the tail wheel. Standard set up, heavy scale wheels from Belair and have no problems, even down to about 75psi.You must have a problem in the installation somewhere,I think.

Just a thought have you tried them out of the airframe, you may have a slight twist on the mounts causing them to bind, I had this problem with one of my ARTF jets.

Dave

Many Thanks.

I bought the model second hand with the Air lines installed - i'm now thinking there must be a kink or twist so they will be tested on the bench next.

Regards Steve

I've run these units fitted with 3/4" dia CJM struts (a lot chunkier and heavier than the Robart versions) and Glennis wheels (also heavy) with no issues at 80 psi.......looks like an installation issue to me. Check for kinked air lines and/or misaligned mount rails.

A 2nd tank will help.....the large tanks are around 30 cu.i......60 cu.i at 100psi will give far more 'uummpphhh' than 30 cu.i at 100, so if you are sure there are no issues and the unit pivots aren't stiff for some reason, a 2nd tank should help.

Phil

many Thanks Phil,

The retracts will be coming out tonite - fresh start from the beginning - will check the piping and go from there.....

Best Regards Steve

Well everything came out and fixed onto temporary bearers on the bench and still no joy. I had a small air leak on one of the T connectors but still not enough to stop them working. Next the air cylinder was pressurised underwater and still no leaks. I left the air compressor on (working off a 12V battery) whilst i manually moved the actuator but still there wasn't enough air pressure to activate the pistons - they work one by one. It was becoming clear that the indicated pressure on the compressor gauge was not a true representation of the pressure being built in the cylinder. Then it became clear that the valve centre of the shrader valve was not being properly 'plunged' by the compreeor cam fitting. The knurled nuts were lowered significantly to allow the fitting to pushed much further on. I charged the cylinder again which showed a much lower pressure reading than had been seen on all previous attempts. I charged to about 80 psi and they rose and lowered like retracts possessed........

It just goes to show that it's often the small things we take for granted are over looked, and that 120 psi isn't always 120 psi just because it's reading that on a gauge. Well now i'm a little wiser than i was this time last night and tomorrow's job is to get them back in the wing. Hope this may be of help to someone else at some time or other.

For those that offered advise - many Thanks.

Regards all - Steve