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Main hydraulic system failure


Leviathan667

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As I was about to land, all of a sudden my stick stopped responding (no roll/no pitch) and the plane's nose began dipping.

On the warning panel, the hydraulic pressure light was on. The buster hydraulic system light was not lit.

On the pressure gauge, the main hydraulic system pressure was nil. But. it was  sufficient in the command hydraulic system.

Hydraulic gauge.jpg

According to the manual, p. 67

Quote

image.png

Main hydro system (2) provides hydraulic pressure for nosecone movements, engine compressor anti-surge door operations, landing gear, flaps, airbrakes, engine nozzle, one hydro-booster chamber of the horizontal tail, tyres breaking action during gears retraction, equipment air-conditioning door operations, and – in the case of command hydro system failure – it provides the operation of aileron boosters. The command hydro system (1) provides pressure for one hydro-booster chamber of the horizontal tail and ailerons boosters. If the pressure drops to 160-175kp/cm 2 , a warning light on T-10 (RV70) will warn the pilot to pay attention to that particular hydro system.

 

According to the Emergency procedures for the failure of the hydraulic system, p. 169

Quote

 

3. Failures of hydraulic system


3.1. Failure of Both Hydraulic Systems with Engine Running Symptoms:
- the SORC (CM93) centralized warning system button light is flickering;
- the WATCH MAIN SYST. PRES. and WATCH BSTR SYST. PRES. lights come on in the light panel (RV70);
- the pressure in both hydraulic systems keeps decreasing below 165 kgf/cm 2 (with the НП-27Т PUMP UNIT (RV15) switched on).

Actions to be taken:
- disengage the AFCS (PS4),
- by utilizing the hydraulic pressure still available, provide conditions suitable tor ejection, avoiding vigorous operation of the controls, if practicable,
- disengage the aileron boosters at an indicated airspeed of less than 1000 km/h or at less than 1.4 M;
- it the pressure has not been restored even in one hydraulic system after conditions for safe ejection have been provided, abandon the aircraft immediately.

 

 

So my understanding is roll and pitch should be responding provided one of the two hydraulic systems has sufficient pressure. But, this not what happened in my case. Am I missing something?

 

 

 

Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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Aileron is manual linkage to the pilot's muscles. There are booster systems which are optional by a switch which augment (replace) pilot muscle force with hydraulic actuation. The airplane within certain limits is able to be flown without hydraulic power to the ailerons. Older MiG-21 had no aileron booster at all.

Confirm that extension of flaps in the blowback region (450 km/h+ for 25°, 370 km/h+ for 50°) causes primary hydraulic pressure to plummet uncontrollably. Extension of the flaps outside of the blowback region and then entering it by airspeed change does not cause this issue. Ceasing the condition in which the flaps were set in the blowback region by reducing airspeed below threshold or choosing a flap position that is not in the blowback region causes a recovery. If the hydraulic pressure allowed to progress to less than 0.8kg/cm^2 will cause a rapid decrease in JPT, loss of thrust, jumping RPM needles near 90%, and hydraulic pressure recovery does not occur.

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On 1/5/2022 at 7:24 PM, Frederf said:

Aileron is manual linkage to the pilot's muscles. There are booster systems which are optional by a switch which augment (replace) pilot muscle force with hydraulic actuation. The airplane within certain limits is able to be flown without hydraulic power to the ailerons. Older MiG-21 had no aileron booster at all.

Confirm that extension of flaps in the blowback region (450 km/h+ for 25°, 370 km/h+ for 50°) causes primary hydraulic pressure to plummet uncontrollably. Extension of the flaps outside of the blowback region and then entering it by airspeed change does not cause this issue. Ceasing the condition in which the flaps were set in the blowback region by reducing airspeed below threshold or choosing a flap position that is not in the blowback region causes a recovery. If the hydraulic pressure allowed to progress to less than 0.8kg/cm^2 will cause a rapid decrease in JPT, loss of thrust, jumping RPM needles near 90%, and hydraulic pressure recovery does not occur.

Thank you for your comprehensive answer. Now I know why it happens and what to do.

Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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