Proficiency: What a drag

After descending through the prescribed 800 feet, Bill yelled, “Recover!” After I slid the mixture control forward, Bill looked from side to side and laughed while he yelled “Clear!” I then pushed the yoke forward and, one by one, began to see the propeller blades begin to turn once again. After reaching 120 knots, the engine roared back to life and we climbed back to altitude for more glides.

My flight test partner that day was William K. Kershner, an aviation author whose books taught generations to fly. Bill took pains to ensure that the information in his books was correct and, whenever possible, verified assertions using tests in his own airplane. That day we were gathering data to demonstrate that a windmilling propeller is a source of considerable drag. Over the course of several flights we conducted 52 glides, half with propeller windmilling and half with it stopped. I analyzed the results (see p. 88) and concluded that, for the Cessna Aerobat, glide distance can be increased by about 8.3 percent by stopping the propeller. That translates to a 17-percent increase in area available after losing the engine.

For airplanes with controllable pitch propellers, slowing or stopping the propeller after engine failure can make an even bigger difference. Multiengine pilots learn early in training that a windmilling propeller generates a lot of drag, and such aircraft are equipped with a mechanism to stop, or feather, the propeller of the inoperative engine. Minimizing that drag makes it easier to maintain positive aircraft control and means that the aircraft can possibly travel farther than if the propeller were left to windmill.

The emergency procedure for an engine failure in a multiengine aircraft (in flight) usually goes something like this:

1. Achieve and maintain at least V_YSE (blue line) airspeed. If the engine failure occurs shortly after takeoff, this will require an authoritative push on the yoke. Increasing to V_YSE improves roll stability and the control effectiveness to counteracts yaw. It also reduces induced drag that is considerable at higher angles of attack (see facing page). Even if the aircraft cannot maintain altitude, the descent angle should be small.
2. While identifying and steering the aircraft gently toward the most favorable terrain, clean it up aerodynamically. This includes retracting the gear, flaps, and cowl flaps as such unnecessary drag has a profound effect on increasing available area in an engine-out situation (see “Overextended,” May 2021 AOPA Pilot). After identifying (and verifying) the inoperative engine, pull the propeller control back to low rpm and into the feather position to stop it. Finally, maintaining coordinated flight usually takes a small bank toward the operating engine and an inclinometer ball slightly deflected toward the good engine.
3. Only if time and altitude permit, one might troubleshoot to diagnose and remedy the problem.

Most of the ingredients for the emergency procedure involve minimizing drag including the first and most important step: push forward to ensure positive aircraft control. Failing to do that first precludes the opportunity to address the others.

While I might typically add the disclaimer that one should always check their operator’s manual and heed that advice, it should also be read with a critical eye. I found it odd that the in-flight engine failure procedure for a Beechcraft Baron B55 involves the same items but airspeed was last on the list. I am a big fan of assembling my own checklist and, were I to do so for this airplane, I would reposition achieving and maintaining VYSE to be the first item of the procedure.

The old joke about multiengine training is that we pay rental fees for two engines but much of that time is spent with only one engine running. With so many loss-of-control accidents because of engine failure in a twin, this training emphasis tries to prevent such events in the future. By the time the candidate gets to the practical exam, she is spring-loaded to push forward on the yoke at the first sign of an engine failure and continue with the emergency checklist.

From what I see on single-engine practical exams, the same can’t be said for single-engine candidates. Often on failing the engine, the candidate immediately looks around at the surrounding terrain while letting the airspeed wander on an airplane that still features all sorts of unnecessary drag. I wonder why we don’t hammer home engine-out procedures the same way for all pilot training. The typical procedure for a single-engine airplane differs slightly from that above:

1. Achieve and maintain best glide airspeed in order to increase control effectiveness and roll stability as well as minimizing the descent angle. Immediately following takeoff, this will require pushing on the yoke.
2. While identifying and steering the aircraft gently toward favorable terrain, clean it up aerodynamically by retracting the gear, flaps, and cowl flaps. With the inoperative engine obvious, pull the propeller control back to allow for minimal rpm and maintain coordinated flight.
3. Only if time and altitude permit, attempt to diagnose and remedy the problem.

Now, stopping a fixed-pitch propeller of a single-engine aircraft is more of an academic exercise than a practical one. But those tests with Bill indelibly impressed the importance of remembering to minimize propeller drag if I am able.

Most of the common items, including the initial push on the yoke, involve eliminating unnecessary drag. Think of any improvements you make in that department as regaining some of the thrust you just lost in the engine failure. I hope flight instructors reading this will take a cue from multiengine training and incorporate more of these engine-out scenarios, along with being spring loaded to push on the yoke and minimize drag, into training.