Retracts

[Artto Ilmanen]

39 minutes ago, Paul De Tourtoulon said:

Mine is a cheap one, probably £10 at the time running on a 3s 2200 lipo.

 

Thanks Paul,

 

I actually happen to have similar one - I just need to solder a deans connector to run it on a Lipo

 

But I suspect one should have a more reliable air pressure gauge? It's hard to believe you can trust on the gauge on these cheap chines air pumps..

 

I came across this:

 

https://www.lindinger.at/en/AIRPLANES/AIRCRAFT-ACCESSORIES/Landing-Gear/FESTO-PRESSURE-GAUGE-0-10-BAR-4MM-ID-1PCS./91528

 

It seems to be a pretty expensive, though

 

 

 

 

[Artto Ilmanen]

11 hours ago, stu knowles said:

If you connect the two outlets together in the way that you have you will get an apparent leak as one tube would be driving the retract and the other will be open to the air.

Attach two separate tubes, each with one end blocked and try again

 

Thanks Stu,

 

Good remark. In order to get a conclusive test result I actually connected the whole system and submerged the air tank, both cylinders and the control valve. I operated the valve manually and kept the pressure at 80-100psi with a air compressor:

 

The only spot where the system leaked was the air control valve, as expected. But is was nice to notice both cylinders were good and the pistons moved back and forth without any leaks, despite they had been sitting on a shelve for 10+ years..

 

 

[Paul De Tourtoulon]

4 hours ago, Artto Ilmanen said:

 

Thanks Paul,

 

I actually happen to have similar one - I just need to solder a deans connector to run it on a Lipo

 

But I suspect one should have a more reliable air pressure gauge? It's hard to believe you can trust on the gauge on these cheap chines air pumps..

 

I came across this:

 

https://www.lindinger.at/en/AIRPLANES/AIRCRAFT-ACCESSORIES/Landing-Gear/FESTO-PRESSURE-GAUGE-0-10-BAR-4MM-ID-1PCS./91528

 

It seems to be a pretty expensive, though

 Pump it up to maybe 8 kilos and see if it is enough

4 hours ago, Artto Ilmanen said:

 

 Pump it up to maybe 8 kilos on the gauge and see if it is enough for 4/5 retract cycles, the pressure isn't important as long as there is enough for your flight, it isn't like a performance GP motorbike tire for a race,,,

 Mine is only for my Turbine Rafale, air up spring down,,,

4 hours ago, Artto Ilmanen said:

 

 

 

Edited March 26, 2023 by Paul De Tourtoulon
ps

[Ron Gray]

I wouldn’t be too concerned about accuracy of the gauges, as long as you have enough air for, say 3, cycles then that’s OK. Just fill until the gauge says, say 90 psi then operate the retracts until they won’t go up again, that will then give you an idea of what you need to pump the system up to. I tend to do pump up the system before each flight.

Edited March 26, 2023 by Ron Gray

[Frank Skilbeck]

6 hours ago, Paul De Tourtoulon said:

Mine is a cheap one, probably £10 at the time running on a 3s 2200 lipo.

Definitely get an electric pump, the Robart hand pumps are great for small systems but if you have any volume then you'll need a break between pumping up and flying, 😜

 

We use a lipo driven car tyre pump and that works great. We also have the Power box pressure sensor giving telemetry feedback with a low pressure alarm, which is pretty useful on an air up and down system.

[Artto Ilmanen]

1 hour ago, Ron Gray said:

I wouldn’t be too concerned about accuracy of the gauges, as long as you have enough air for, say 3, cycles then that’s OK. Just fill until the gauge says, say 90 psi then operate the retracts until they won’t go up again, that will then give you an idea of what you need to pump the system up to. I tend to do pump up the system before each flight.

 

Yes, this is true. I was more concerned about excessive pressure ruining the seals. But then again, testing with conservative pressure readings should turn out good.

 

And by the way, is there any rule of thumb for the air pressure? I checked the ESM manual but did not see any factory recommendation for the air pressure. I have been thinking of 85-100. I wonder if this is good? Robart recommends 110psi for their gear.

Edited March 26, 2023 by Artto Ilmanen

[Ron Gray]

I used to go to 110 psi but then realised I only needed to go to 60 psi for my tail draggers (Mustang, Hurricane etc). That is more than enough for 3 cycles. On my Tigercat I go to 80 psi.

[Frank Skilbeck]

39 minutes ago, Artto Ilmanen said:

 

Yes, this is true. I was more concerned about excessive pressure ruining the seals. But then again, testing with conservative pressure readings should turn out good.

 

And by the way, is there any rule of thumb for the air pressure? I checked the ESM manual but did not see any factory recommendation for the air pressure. I have been thinking of 85-100. I wonder if this is good? Robart recommends 110psi for their gear.

In some respects it will depend on the volume require to operate the retracts vs the storage volume. Start at say 85 psig and then cycle the undercarriage and see how many times they go up and down. As Jon says you should only need to use them once per flight,  but if you wanted to say do a couple of touch and goes and show off the gear operation on each pass then you'd need more.

 

On my mates 28% scale FW190 with air up/down retracts each cycle takes around 20 psig out of the system.

[Paul De Tourtoulon]

"Show off" come on how many overshoot and then say they were doing a touch and go,,,🤣

[Artto Ilmanen]

Gents,

 

I must confess that I feel embarassed - I started to rethink on what Stu wrote about how the control valve should operate. So, it became obvious that I got fooled by thinking that the control valve was the culprit for the air leak of the system. I was wrong: as I retested the control valve in accordance with Stu's advice: voilà, no issues with the control valve! Instead, after testing the air cylinders individually by submerging them in water it became obvious one of the air cylinders were leaking air through the piston O-ring.

As I dismantled the faulty cylinder I found a small aluminium particle that was sitting on the O-ring (quality control?), maybe causing the leak.

 

This morning I shopped new O-rings of different sizes to test. I will clean out the cylinder throughly and apply new silicone grease. Logically thinking, this should fix the problem as i can not see any scratches on cylinder wall.

 

I was also wondering wether to change the small O-ring that seals the piston axle (how do you call it?) at the same time but I skipped this idea as it is not leaking? How on earth can you even change it? (see picture).

 

Also, I think it might be a good idea to replace the air tubing (which is 10+ years old) although it feens still soft and flexible. But, what size? The manual refers to "1,7mm" inside diameter.  Hobbyking has this size but it's out of stock. Robart is 1,58mm (1/16 inch) and Festo seems to be 2,1mm. (There is also a "pressure reduction inlet" mentioned in the manual - I suspect this is used to reduce the airflow so the gear won't respond too agressively when the valve opens, hence maybe the inside diameter is not that sensitive)

 

But how sensitive is the inside diameter actually is? Can I use any of the ones referred above? 

 

sorry again for many questions - I hope you do not mind

 

 

Edited March 27, 2023 by Artto Ilmanen

[Artto Ilmanen]

Ok, I fixed the faulty air cylinder - I cleaned it out throughly. Then I installed a new 8,9mm X 1,9mm O-ring on the piston and lubed everything with CRC silicon grease. Now everything works as expected - no more leaks.

 

Now that everything works time to learn how to reduce the cycle speed of the gear to have a system that is more realistic.

 

thanks for everyone for great help! This is a great forum!

[stu knowles]

Pleased that the suggestion worked for you.  I don't have to tell you how I became aware that connecting the outlet pipes together gave symptoms of a leaky valve 🙂

[Artto Ilmanen]

4 minutes ago, stu knowles said:

Pleased that the suggestion worked for you.  I don't have to tell you how I became aware that connecting the outlet pipes together gave symptoms of a leaky valve 🙂

😂👍