VMC or Stall in a light twin.

[AAflyer]

Yes Vmc decreases as you climb. Less thrust, less yaw, less rudder = lower Vmc speed.

In a Seminole you will almost ALWAYS STALL before you lose directional control. Why? Because Vs is 57 and VMC is 56. The only way you will lose directional control before you stall is at high negative density altitude.

Remember VMC was determined in basically the worst possible airplane configuration.

Good point, many forget that as DA increases, VMC decreases, however I would not go so far to stand firm on the 56 knots. Remember that airspeed is subject to a host of factors;

AFT CG
MAX POWER
TO COWL FLAPS
TO FLAPS
GEAR RETRACTED
STANDARD ATMOSPHERIC DAY
OUT OF GROUND EFFECT
PROP WINDMILLING
BANK UPTO 3-5 DEGREES
1/2 BALL DEFLECTION

these items in different configurations can lead to more or less rudder effectiveness, basically changing the airspeed at which we can experience VMC.

AA

 

[AAflyer]

Thanks to all who answered. I appreciate your input, and like to see how others view or were taught certain subjects. I think through this we can become better instructors, and many times pick up a better understanding of the subject material.


Cheers,
AA

 

[RefugePilot]

VMC and stalls no problem, unless

I have done power on and off Stalls in an Apaches and Senecas with no problem. We did not use full power in the power on stalls. In a Duchess we recover at the first sign of stall, either buffet or horn.

You do want to be carefull in practicing stalls at the critical density altitude. As a twin gets higher the Vmc speed will get lower while the stall speed will stay the same. At the critical density altitude Vmc=Vs. A Vmc demo at this altitude will bring the worst of both worlds together possibly leading to a non-recoverable spin.

 

[IP076]

Stalling a twin is not a big deal, (with both engines that is). But if you are saying that you take students up and execute a full break stall with one engine inoperative, you are not leaving yourself with any margin for safety. That is why a recovery is made from a Vmc Demo at th FIRST sign of the loss of directional control, stall warning horn, or buffet. Do what you want but you are the only person who I a have ever heard of teach single engine stalls. All the examiners, or any pilot for that matter, that I have ever talked to, don't want to be close to a stall during a Vmc demo because of the possiblity of a flat spin.

You're absolutely right! It was 0530 local when I typed that....musn't have woken up yet! You're right, VMC demos are done to the first indication of a stall or loss of directional control.