Touch and Go's = loss of air pressure (no brakes)?

I'm a little befuddled by this one. I took off, raised the gear, set gear lever to neutral. Flew around for 30 minutes to burn some fuel, did five or six circuits around the airbase to practice landing. Procedure:

Gear down flaps down on base. Normal approach, add power about 10-20m over the runway instead of touching down, raise gear, return gear lever to neutral. Rinse, repeat.

Now here comes the fun part. When I decided to do a full stop, I had no air pressure for my brakes or drogue chute, and ran off the end of the runway. I made sure to return the gear lever to neutral after every takeoff, so I don't understand why I ran out of air.

to save weight (its an interceptor)

they left out a compressor for high pressure air.

so you only have a finite amount of pressure stored in the system.

you should never do touch and goes in a mig 21:)

if you forget to put the gear lever into neutral you will bleed air and not have enough to deploy the chute or use the brakes when you land.

basically doing touch and goes you bleed off all your air raising and lowering the gear. and using the brakes.

Even if I do put the lever in neutral, the simple action of raising the gear so many times will also deplete the system? I was trying to do real-world touch and go's like this (12:16 and 12:58 ):

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yep every time you use pressure to provide force you cannot return it to the bottle.

its bled off to remove the force.

so without a compressor the pressure bottle cannot be refilled.

so it will eventually empty.

brakes, landing gear and chute all use pressure.

migs in private hands may have compressors added for safety.

and there is a margin for error.

you can handle more than one take off and landing.

I guess I'll have to keep an eye on my gauge and see how many TGLs I can do. I've done 3-4 before no problems, but this time I did 5-6 (maybe 7).

Plus in the video those are also 2 seater (trainers?) - Someone knows, if they have a compressor vs. the normal 1 seater?

One of them was single seater. I think the big thing we don't know is how many circuits they did.

 

migs in private hands may have compressors added for safety.

It's probably a good bet that a lot of current MiG-21 operators have them added, as well. Croatia's BisDs have some nice new NavAIDs and radios. And, of course, the Romainian LanceRs are kitted. Adding an onboard air compressor is probably well in the cards for these "higher end" MiG operators.

to save weight (its an interceptor)

they left out a compressor for high pressure air.

so you only have a finite amount of pressure stored in the system.

 

 

you should never do touch and goes in a mig 21:)

 

if you forget to put the gear lever into neutral you will bleed air and not have enough to deploy the chute or use the brakes when you land.

 

basically doing touch and goes you bleed off all your air raising and lowering the gear. and using the brakes.

So it's necessary to get the landing gear back to neutral as quickly as possible to save pressure. Did not know that, thx fella as I just used to do it when I remembered :lol:

Even if I do put the lever in neutral, the simple action of raising the gear so many times will also deplete the system? I was trying to do real-world touch and go's like this (12:16 and 12:58 ):

For an airshow plane so many systems are likely not in a functioning state and possibly removed that more compressed air could be stored.

I don't know the number but say the original system had enough air for 3 LG cycles, it might be determined this is insufficient safety factor and larger air capacity was mandated.

So it's necessary to get the landing gear back to neutral as quickly as possible to save pressure. Did not know that, thx fella as I just used to do it when I remembered :lol:

If you're going off of real world flight experience with retractable gear in GA, don't. In jets, the moment you establish a positive rate of climb, retract that gear. So, in practice, you basically pull up the gear within moments of reaching rotational speed.

Don't be waiting until you've run out of usable runway, just pull up those wheels as soon as you're climbing out.

brakes, landing gear and chute all use pressure.

Do you have anything to back this up? My Mig-21 manual states raising and lowering gear use the main hydraulic system.

The pneumatic system is for brakes, jettisoning the RATO units, drag chute and doors, sealing canopy, and control over anti-icing, liquid cooling systems and pressurizing the radar.

Note that wheel brakes are applied when the gear handle is in the up position. Perhaps you bled all your air from repeated gear up during practice?

 

Note that wheel brakes are applied when the gear handle is in the up position. Perhaps you bled all your air from repeated gear up during practice?

That's what I'm thinking. If I only do three circuits I'm fine. If I do five or six I run out of air.

Now the thing that confuses me is, why does the air get depleted when brakes are applied with gear up, but air does not get depleted when using brakes during taxi?

Air is depleted during taxi. Check your gauge to the right of the stick. One reason for the nose gear break, to save air.

Refueling on the ground should replenish your air if your low just like radar coolant

I recently got in the habit of checking the gauge prior to takeoff and prior to landing. The needles are always at the 12 and 6 o'clock positions.

It’s the gauge on the right closest to to you, turn on English cockpit of that’s better than cryllic for you. During taxi you will see it depletes as you use your brakes. Taxi slow for minimal brakes in turns, taxi fast enough in straight lines to use rudder. It depletes fast which might be why you only see full or completely empty. Whatch it closely during taxi during every time you hit breaks

Now the thing that confuses me is, why does the air get depleted when brakes are applied with gear up, but air does not get depleted when using brakes during taxi?

Its just about quantity. You taxi at no more than 20-30 km/h I presume, and make small corrections with the brake. When gear up the system has to immediately stop the wheels from 300-350 km/h. As for touch and go's they are permitted but only using the full circuit to give the brakes time to cool. Still we need a technical manual verification on compressed air use and expense. Maybe its ok, maybe not quite.

It’s the gauge on the right closest to to you, turn on English cockpit of that’s better than cryllic for you. During taxi you will see it depletes as you use your brakes. Taxi slow for minimal brakes in turns, taxi fast enough in straight lines to use rudder. It depletes fast which might be why you only see full or completely empty. Whatch it closely during taxi during every time you hit breaks

The brake pressure gauge, or the main/aux pressure gauge?

It really shouldn't be a problem, you can use the brakes all you want on taxi and do a touch and go whilst still having ample air to brake and deploy the chute on the second attempt.

More landing attempts than that and you came in with too much fuel anyway.

For practicing pattern work keep your gear down if you simply must do so many consecutive passes.

Also the emergency brake uses a back up air supply in case you are caught short