VMC DEMO
Vmc Demo Lesson by wifiCFI
Objective
To determine that the applicant exhibits satisfactory knowledge, risk management, and skills associated with a Vmc Demonstration.
Knowledge
The applicant demonstrates understanding of:
Factors affecting VMC and how VMC differs from stall speed (VS).
VMC (red line), VYSE (blue line), and VSSE (safe single-engine speed).
Cause of loss of directional control at airspeeds below VMC.
Proper procedures for maneuver entry and safe recovery.
Risk Management
The applicant demonstrates the ability to identify, assess and mitigate risks, encompassing:
Improper aircraft configuration.
Maneuvering with one engine inoperative.
Distractions, loss of situational awareness, and/or improper task management.
Flying the Maneuver – Set Up
Clear the area.
For a Vmc demonstration, an altitude should be selected that will allow completion of the maneuver at least 3,000 AGL.
With the landing gear retracted and the flaps set to the normal takeoff position, the airplane should be slowed to approximately 10 knots above Vsse or Vyse (whichever is higher) and trimmed for takeoff.
An entry heading should be selected and high RPM set on both propeller controls.
Follow correct configuration settings.
Flying the Maneuver – Performance
Power on the left engine should be throttled back to idle and power on the right engine advanced to the takeoff setting.
The pilot must be alert for the stall warning horn, if the aircraft is so equipped, or watch for the stall warning light.
The left yawing and rolling moment of the asymmetrical thrust is counteracted primarily with right rudder.
A bank angle of 5 degrees should also be established to assist with directional control.
While maintaining entry heading, the pitch attitude is slowly increased to decelerate at a rate of 1 knot per second (no faster).
As the airplane slows and control effectiveness decays, the increasing yawing tendency should be counteracted with additional rudder pressure.
Aileron displacement will also increase to maintain 5 degrees of bank.
An airspeed is soon reached in which full right rudder travel and a 5-degree bank can no longer counteract the asymmetrical thrust, and the airplane will begin to yaw uncontrollably to the left.
Flying the Maneuver – Recovery
The moment the pilot first recognizes the uncontrollable yaw or experiences any symptom associated with a stall, recovery should be initiated by simultaneously reducing power sufficiently on the operating engine while decreasing the pitch attitude as necessary to stop the yaw.
Recovery is made with a minimum loss of altitude to straight flight on the entry heading at Vsse or Vyse, as symmetrical power is set.
The recovery should not be accomplished by increasing power on the windmilling engine.
Flying the Maneuver – Notes
With normally aspirated engines, Vmc decreases with altitude as reduced power available results in less asymmetrical thrust.
Stalling speed (Vs), however, remains the same.
Except for a few models, published Vmc is almost always higher than Vs.
At sea level, there is usually a margin of several knots between Vmc and Vs, but the margin decreases with altitude and, at some altitude, Vmc and Vs are the same.
Where Vs is encountered at or before Vmc, the departure from controlled flight may be quite sudden, with strong yawing and rolling (spinning) tendencies toward the idle engine.
Therefore, during a Vmc demonstration, if there is any indication of an impending stall, such as a stall warning light or horn, airframe or elevator buffet, or rapid decay of control effectiveness, the maneuver should be terminated immediately
Common Errors
Failure to adequately clear the area
Improper starting altitude
Improper aircraft configuration
Losing more than 1 knot/sec in the climb
Slow or improper recovery technique
Not recovering at first indication of stall or loss of directional control
Attempting recovery by increasing power on the operating engine
Improper rudder force to maintain constant heading
Not returning to Vyse during recovery
ACS Standards
Configure the airplane in accordance with the manufacturer’s recommendation, in the absence of the manufacturer’s recommendations, then at VSSE/VYSE, as appropriate:
Landing gear retracted
Flaps set for takeoff
Cowl flaps set for takeoff
Trim set for takeoff
Propellers set for high RPM
Power on critical engine reduced to idle
Power on operating engine set to takeoff or maximum available power
Establish a single-engine climb attitude with the airspeed at approximately 10 knots above VSSE.
Establish a bank angle not to exceed 5° toward the operating engine, as required for best performance and controllability.
Increase the pitch attitude slowly to reduce the airspeed at approximately 1 knot per second while applying rudder pressure to maintain directional control until full rudder is applied.
Recognize indications of loss of directional control, stall warning, or buffet.
Recover promptly by simultaneously reducing power sufficiently on the operating engine while decreasing the angle of attack as necessary to regain airspeed and directional control. Recovery should not be attempted by increasing the power on the simulated failed engine.
Recover within 20° of entry heading.
Advance power smoothly on operating engine and accelerate to VSSE/VYSE, as appropriate, +/-5 knots, during recovery.
FAA Sources Used for This Lesson
Airmen Certification Standards (ACS)
Flying Light Twins Safely