Those of us who’ve already obtained a multiengine rating likely recall the fact that multiengine airplanes get their superlative performance because of excess power. Even a modestly powered twin such as the Piper Seminole has 360 horsepower to haul around a typical operating weight of 3,100 pounds, which is an excellent power-to-weight ratio of 8.6 pounds per horsepower. That results in a respectable climb rate of around 1,500 feet per minute or more—better if it’s cold out.
But while that spirited performer does quite well with both engines running, it becomes an absolute pig with just 180 horsepower being produced at a point far left or right of the normal center of thrust. Now the power/weight ratio is a pathetic 17.2 pounds/horsepower, exacerbated by the drag of a windmilling propeller and the control surfaces deflected into the slipstream to keep the airplane flying straight. For comparison, a fully loaded Cessna 150 has a power-to-weight ratio of 16 pounds/horsepower.
Therefore, it’s no surprise that most light twins lose 80 percent or more of their climb performance with the loss of an engine. In some cases, such as with high density altitude or a low-powered twin, the result is not a rate of climb but a minimum rate of descent—right to the scene of a forced landing. It’s critical that the pilot maintain control of the airplane while accepting what performance he or she can get out of it. Unfortunately, that’s often not the case and a loss-of-control crash is the result.
All piston twins have a Jekyll-and-Hyde personality of sorts. They are stellar performers on two engines and a dog on one. Pilots who fly hundreds or thousands of hours in an admirable performer may find themselves in that same airplane now unable to climb at more than 200 feet per minute, if at all. It’s that surprise factor that tends to lead pilots to a loss-of-control accident.
Turbine airplanes, especially jets, are a different animal. Turbines possess gobs of excess power that enable them to maintain far better performance on one engine than their piston-powered brethren. Most turbine-powered airplanes can climb at 1,000 feet per minute or better on one engine in standard conditions.
While propellers make airplanes better performers on the runway, they have the opposite effect in an engine-out situation. They are huge drag producers. Most turboprops have autofeathering propellers or negative-torque sensing (NTS) systems to eliminate that problem. Pistons don’t. Jets have an additional advantage because there are no comparatively giant windmilling discs to drag them down in engine-out scenarios.
Most piston twins have wing-mounted engines, aside from the Cessna Skymaster with its push-pull configuration. The engines' location so far from the center is another major disadvantage of piston twins and most turboprops. Many jets and some turboprops, such as the Piaggio Avanti series, have aft-mounted engines relatively close together to reduce asymmetric thrust during engine failure. In addition, modern jets and turboprops have an auto-biasing rudder system that will partially apply proper rudder input in the event of power loss.
Ironically, the farther you progress into your career, the easier the multiengine airplanes are to fly on one engine. The piston twin is the best trainer because it’s the worst-case scenario. If you can fly a piston twin on one engine, you’ll do fine in basically everything else.
When I was a captain at a regional airline I loved having first officers who were former multiengine instructors, with many hours of experience flying piston twins on one engine. The dreaded V1 cut in the simulator of the Jetstream 41 was a relative no-brainer what with the airplane’s NTS system, which brings the propeller to a near-feathered position automatically. Almost inevitably, these guys would say, “That was easier than the Seminole I used to fly.”
To make things challenging for the jets and turboprops, you have to take them to high-elevation airports and load them up. Under these circumstances you’ll be reminded of piston-twin performance. Departing Quito, Ecuador, or La Paz, Bolivia, on a hot day will make you realize that your usually spirited jet quickly can be reduced to Seminole-like performance. In these scenarios, I relish the fact that the failure rate of turbines is extremely low and we have simulators to practice such maneuvers.
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