Single Engine Drag Configurations
(Vyse Demo)
Objective: To demonstrate the importance of properly configuring a twin engine
aircraft for single engine flight by reducing drag to obtain the best possible performance.
A properly configured light twin operating with one engine shut down and secured will have drag
minimized, thus maximizing performance. The PA-34-220T is required to demonstrate a positive rate
of climb during single engine operations for certification. Keep in mind that this climb
certification is with a minimum drag configuration – as you will see from this demonstration,
an aircraft in takeoff or landing configuration may not climb at all on a single engine! For
this demonstration, one engine will be “shut down” by setting it to a simulated feather power
setting (2300 RPM and 17” MAP). The other engine is brought up to maximum takeoff power.
Begin by completing pre-maneuver checklists. Set power initially to 20” MAP. Open the cowl
flap on the operative engine and close the cowl flap on the engine to be “failed”. Set the
failed engine to simulated feather and set the operative engine to max takeoff power. Roll 3-5
degrees of bank into the good engine. Decelerate to and hold Vyse (92 kts – blue line) and note
climb performance (vertical speed).
Next, go through a series of configuration changes, noting climb performance each time. By the
end of this demonstration, the aircraft will be in landing (or initial go-around) configuration
with the inoperative engine propeller windmilling.
- Slow to 82 kts (10 kts below Vyse) by raising the nose and note climb performance. Since Vy
decreases with altitude, it is possible to note a vertical speed greater than that at 92 knots.
- Accelerate to 102 kts (10 kts above Vyse) by lowering the nose and note climb performance.
It is expected that climb performance will decrease at this speed.
- Return to 92 kts. Extend the landing gear.
- Maintaining 92 kts, lower the flaps one notch at a time.
- Bring the inoperative engine throttle back to idle so that the propeller is windmilling.
Hold 92 kts. On most days, this will result in a descent possibly in excess of 1,000 FPM
even with full power on the operative engine!
To recover, bring the failed engine throttle back up and match the throttles at a cruise setting.
Retract the first notch of flaps. Ensure airspeed is below 108 kts and retract the landing gear.
Retract the remaining flaps and complete a cruise checklist.
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