Debris Field

Hi,

I've nearly finished a TF p40E in the colours of a New Zealand Aircraft the Wairarapa Wild Cat (Cowling artwork to come). It will be powered along by a YS 110FZ. That engine should put to rest any issues about power I guess.

The problem I am having is that the Robart Retracts reccomended to be fitted by tower for this kit simply do not have enough power to send the wheels home when standing upright. This isn't even taking into acount the slip stream that might help them when flying, but would work against them when landing. The air pressure on my gauge says 120 Psi. The struts are fitted with robart oleos and lightweight dave brown wheels. The rams simply do not have enough power to bring the wheels past 45 degrees.

Can anyone help? Do I need to add a spring or something?

t_burley

My Feedback: (59)

what size air tank do you have? what PSI do you use with it?
also what kind of air valve as well?

the problem is more than likely air volume to the gear, not the
gear themselves. sometimes getting the gear to rotate, whether
its for this, or another plane is air volume.

on my bigger planes, I am using Sierra gear, and Glennis wheels.
they are heavier then other products. to help with this, I use a larger
air tank, use about 120 PSI, and a large volume air valve from Sierra.

with that valve, I get a big push of air, and it properly helps the
gear retract up/down

Debris Field

I use the Robart air tank supplied with the Robart 188VRX Standard Deluxe Air Control Kit .

I think it's called a small, but it was the one recommended by TF.

I use 120 psi, can they handle more pressure?

rrudytoo

My Feedback: (27)

Debris Field,

Ditto to what Todd said. This is exactly what you are experiencing. The only thing I might add would be to ensure that the gear is moving freely without binding which, I'm sure, you have already done.

Al

t_burley

My Feedback: (59)

Like Al said also, check or binding just to make sure.

The Robart valves are OK, nothing wrong with them. but in some
cases, like what you are seeing, more air volume is the key.

I use this from Sierra "Hi Flow Retract Valve UP-1 $39.00 "

http://www.sierragiant.com/prod17.html

Debris Field

Ok I'll give it a go.

I connected up my hand held compressor, and had them retract correctly but it took in excess of 120 PSI, about 130, so a bigger bottle must be needed as well. They are rotating through with little friction, so I guess they must be working allright in their mounts.

It seems dissapointing that the reccomended valve created by robart are not enough to finish the job once fitted with robart accessories. The wheels I am using are not unreasonable for this job either. But I will give them a go.

That UP1 retract valve seems to be for spring retracts as it doesn't have a return valve that I can see if it's the one on the left of the photo??

t_burley

My Feedback: (59)

the UP valve I use isnt shown. it does have 2 ports for air up, and air down

viper1

In the case it is an airvalve problem, this might be helpfull; http://www.bvmjets.com/tips/ret_valve_mod.htm

Debris Field

Oooohhh that ones interesting, I have the valve in my hand and there is a die grinder nearby.....hmmmmm...

If I have to replace it, why not have a go....

I did notice however that the exhaust ports on my robart valve have a whisker width of a porting hole, maybe if I open that out, the it might help?

Debris Field

Hold the phone! I opened out the ports with a small drill bit and VOILA! the retracts work much more smartly.



I will however still need to get a larger bottle for the air as I only get one decent rotation with a retractable tailwheel soaking up air as well.



The red robart valve has changed a little from this one. It has three O-rings instead of two, and there is an ample amount of room for the air to get through by reducing the diameter of the metal in between the o-rings. so no filing was required I did notice that the exhaust ports through to the outside of the valve body have a whisker size hole to let air out. So I opened out the exhaust ports with a larger drill hole(The outer two of the three nipples side by side). On the red robart valve the nipples have been replaced by variable exhaust needle valves so the job is simple.

viper1

functioning ok now?

Debris Field

Yeah that seemed to be the trick Viper, your tip got me thinking about what I could do to mine to make it better.

I still need a larger bottle like t_burley said, I only get one and a half rotations before the bottle drops below the threshold and she don't push no more.

viper1

An aluminium empty spraycan is easy to convert to airtank

Debris Field

Yeah, I'm hunting about the house now looking for one that will fit....

greenboot

My Feedback: (1)

Any chance you could tell us how to do this???

Tom

Stew99

I think you have some other problem. I have the Robart retracts in a TF P-40E with the heavier Robart wheels on the mains and a retractable tail wheel. I can get 8-10 retract cycles with the small tank at 100 psi.

When I was setting mine up it behaved like you are describing and the problem turned out to be binding in the gear teeth that make the strut rotate. After fixing that, the struts now will flop open and closed on their own weight with no air pressure in the system.

viper1

Take an empty aluminium spraycan, punch a hole in it, glue a nipple or brass tube in?

viper1

Take an empty aluminium spraycan, punch a hole in it, glue a nipple or brass tube in?

Debris Field

I emptied a can and soldered in a small brass tube where the nozzle used to go through, easy peasy.

My own retracts flop in and out under their own weight when there is no air in the system as well, I do have a retractable tailwheel fitted, could that soak up the extra air? The air can I am using is 16cm long and about 4 or 5 cm wide.

viper1

That is a small can yeah.

Tail retract shouldn't make that much difference
One more thing you can check;

Some (and specially Robart) retracts, and I used many trough the years.. have a bad finish on the piston shafts, a bit rough
sometimes, check this with a magnifying glass. Also the inside of the cylinder could have a small scratch.
This could result in an air leak that only occurs during the stroke and not at the endpoints. In other words, the system is perfectly
able to hold pressure when not in use, but leaks during transit.
during a cycle, hold the wheels or legs, and let 'm slowly go , check for leaks halfway
Shafts are easy to recondition, in a mini drill, some 2500 grit (very fine) sandpaper over it, done.

But again, that tank is small. May I ask what's the I.D. & length & shaft dia. of your cylinders?


Hope this helps,
Gert

Debris Field

Hey Gert,

I'm not sure I'll have to have a look this weekend and get back to you.

Do they tend to polish up in use or will I need to linish them myself?


Mick

viper1

If there's a leak it won't fix itself,

Take the cylinder apart and put the shaft in a drill chuck, like described above