Welcome Guest. Sign in or Signup

7 Answers

Stall recover during Vmc Demo?

Asked by: 6923 views Student Pilot

The standard stall recovery is "Relax, Max, Level, Ball."  Lower the nose to reduce AOA, increase power to increase airspeed and lift, and maintain coordinated flight.

Why then, during an OEI Vmc Demo, do you reduce power to recover from a pending stall if you hear the stall horn prior to reaching Vmc?  I understand why you reduce power to recover from Vmc, but in this common scenario, isn't this a stall recovery and not a Vmc recovery?

Thanks.

 

 

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

7 Answers



  1. lift_vector on Sep 02, 2017

    In the VMC demo, you are simulating the worst case scenario (critical engine out, windmilling propeller, airspeed low and decaying). In this scenario the aircraft could reach VMC or a stall and you recover at either the first indication of the stall or the first indication of VMC.

    In either event the need to lower the nose is given. Lowering the nose will decrease the AOA and give you the needed airspeed to control the direction of the aircraft.

    When flying multi-engine aircraft with one engine inoperative, the left turning tendencies are so great that it could roll the aircraft over and develop into a spin. This is true for both reaching VMC or reaching a stall whichever comes first.

    Remember, a spin is a stall with a rotational moment. When operating OEI, the asymmetrical forces acting on the aircraft are great enough to provide the rotational moment and if you put the aircraft into a stall, you just completed the recipe for a spin. Also, a Spin in a multi engine aircraft could be unrecoverable if insufficient altitude is available.

    So, the recovery in this situation is going to be the same, reduce the power to idle (this takes away that huge asymmetrical moment) lower the nose and gain airspeed, then the power on the operating engine can be brought up and the aircraft can be established in a climb above Vyse.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  2. JDJ on Sep 02, 2017

    I’m going to be that CFI that turns this around into a few questions for you.
    1) If a ME aircraft stalls with OEI and the other at full power, what do you think is going to happen?
    2) Do you really need power to recover from a stall?

    Also, when you get a chance, look up the new recommended stall recovery procedure in the Airplane Flying Handbook, and report back what you find. (Addressing your statement “relax, Max, level, ball”, is incorrect)

    Recommend you do your research in “Flying Light Twins Safely”.

    0 Votes Thumb up 1 Votes Thumb down 1 Votes



  3. heloguy on Sep 02, 2017

    Thank you for the reply, JDJ.

    1. If the aircraft stalls with OEI and the other operative, it would have a yawing moment and possibly enter a spin.

    2. You probably don’t need power per se, but I thought the power provided accelerated slipstream and increased airspeed to lower the AOA and to help recover from the stall.

    I looked at the Airplane Flying Handbook, and I saw that adding power has been moved to the last step. Disregarding autopilot which I don’t have, Recovery is now 1) Pitch nose down, 2) Roll wings level, 3) Add power. So power has been moved to the end.

    I tried to find any articles discussing when and why this change was made, but I didn’t find anything. The interesting thing is that all of the Maneuver Guides I have, all of which I have downloaded from current, well-established schools, still show some form of Relax, Max. If the FAA has made changes to their recommendations, I would have expected these schools to update their guidance and study aides.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  4. jeff on Sep 02, 2017

    when I teach VMC demo, i put my foot on the rudder so that the student will run out of rudder prior to reaching he real VMC. This is specifically to avoid VMC flight so close to stall. In some planes, depending on the configuration, VMC can be very close to stall. If you stall the aircraft with full power on the OE and dont immediately reduce power on the OE, you can flip over before you know it. Im not aware of any production twin certified for spins and this may be unrecoverable if you do enter a spin) You would want to simultaneously lower the nose (technically lower angle of attack) and reduce power. This is not required to be demonstrated on any check ride that I am aware of and not an instructor or examiner I know would even practice such a maneuver with a student. It is way too dangerous in my opinion (practicing stalls in a twin with OEI)

    Its a great question and one should know that power on the good engine must be immdiately reduced. But please do not go out and practice stalling a twin with OEI……..

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  5. JDJ on Sep 02, 2017

    Just remember that directional control is your primary concern in a Vmc situation. As Jeff stated, if you stall in this situation things will progress quickly into a dangerous upset. The ACS states that during execution of this demonstration that the pilot will recognize indications of loss of control, stall warning, or buffett. In most light twin trainers stall speed is very close to Vmc. Typically you will get stall warning horn or buffett before losing directional control. You must remove the asymmetrical thrust to remove the risk of upset if the aircraft were to stall. The accelerated slip stream creates a rolling moment. Remember, you don’t have that on the side with the inoperative engine, which adds one more reason why you don’t want to stall. For that exact reason, the left wing would stall before the right. And there you would be, immediately flipped upside down.
    I believe the reason the FAA made the change in the stall recovery procedure (which I agree with), is to accentuate the point that reducing AOA is the number 1 priority, following by a coordinated roll to wings level. If a pilot were to get a wing drop, adding power too early in recovery could aggravate the situation. (Think left turning tendencies in the event of a left wing drop). Suddenly adding power will cause left yaw, and in an already uncoordinated situation it’s obvious what could happen. It sounds like you have a pretty descent grasp on multi aerodynamics, but continue to study the principles regarding critical engine and factors affecting Vmc.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  6. heloguy on Sep 02, 2017

    Thanks, guys. To be clear, we weren’t practicing stalls with OEI. We were trying to demonstrate Vmc. We just happened to hear the stall horn before we got slow enough to notice a uncontrolled yaw.

    Your two replies have made me understand what could happen using “Relax Max Level Ball” if the stall recovery was not executed correctly or if there was a secondary stall. Thinking about it, it makes sense that the FAA has adjusted their recommended procedures.

    Thanks for the help.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  7. heloguy on Sep 04, 2017

    Thank you, LiftVector. You and the other responders have really cleared this up for me, and the risk all makes sense now.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes


Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.