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5 Answers

RPM ADJUSTMENT

Asked by: 949 views Aerodynamics, Aircraft Systems, Student Pilot

Hello everyone

Plz guide me regarding rpm adjustmnt in case of engine flameout in normally aspirated engine.

Suppose  I was flying at 3000 feet AGL. I have adjusted 25 inch boost and 2500 RPM. engine FLAMES OUT. What should I do with RPM LEVER, IF IT is constant pitch propeller. Should I adjust it to fine or coarse position to get best glide ratio.

5 Answers



  1. Jim F. on Mar 13, 2013

    First off, a minor technicality: The term flame-out is only used with regard to jet engines. It’s literally when the flame in the combustion chamber goes out.

    But when you have an engine failure in a single recip with a CS prop, you loose oil pressure. That oil pressure is what changes the blade angle. Singles in this configuration are made to automatically go to fine-pitch condition upon loss of oil pressure. This is because if you still have engine power, you can still produce the most HP and be able to climb if needed.

    So relating directly to your scenario: noting. When the engine quits, you loose oil pressure, and the prop will go directly to fine-pitch. No need to adjust it manually, as moving the lever will do nothing.

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  2. khoda bakhsh on Mar 13, 2013

    @ Jim.F
    Thanks sir for helpful tip.

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  3. John D. Collins on Mar 13, 2013

    If the engine stops running, but is still turning, there will normally be oil pressure, unless you have had a catastrophic engine failure and lost the oil pressure thru a massive leak. In the latter case, the engine will seize within a minute if it hasn’t already done so, and the prop is very likely to stop.

    But if you just lost engine power because of running out of fuel, mismanaged your fuel, magneto’s failed, engine driven fuel pump failed, or the induction system iced over, the oil pressure will remain and the prop will be fully governable. In my Bonanza, without power, the engine RPM will remain at around 1800 RPM in the glide. The descent rate will be close to 1400 FPM. If I retard the prop control to the full rear stop, the RPM will reduce to 1100 to 1200 RPM and the descent rate will drop dramatically to about 800 FPM.

    My point is that a CS prop will still be governed by the prop control and not go to fine pitch and that you can use the prop control to reduce drag substantially.

    In a working engine, you need three things, fuel, fire, and air. If you able to supply all three, it will run. Normal troubleshooting to determine the reason the engine is not running involves all three being checked in your emergency procedures. Fuel tank selection, boost pump, mixture setting , throttle position, alternate air selection or carburetor heat activation, magneto setting are usually part of the emergency procedure found in your POH. To stretch your glide if you are unable to get your engine running, but it is still rotating, it is normally best in a single engine aircraft to retard the prop control to the full rear stop to provide the lowest drag.

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  4. David Brown on Mar 15, 2013

    John is correct. you need to feather. In a twin it should feather for you.

    Just as a side note, and unrelated you are not providing 25″ of boost. If you were you would have someing in the rode of 51-52″ MP, as all you have done is remove pressure from ambient.

    On that topic I would say why on earth would you do that? Would you fly around with a clogged air cleaner restricting around 3″ of MP? No way!.

    These engine are meant to run Wide Open Throttle. Unless you want only a small amount of power for some other reason, why would you make a negative effect on volumetric efficiency?

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  5. khoda bakhsh on Mar 15, 2013

    Sir John D. Collins thankz so much for such value able comments..

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