How can modern aircraft fly on just one engine if the other one fails? Shouldn’t the torque produced by the functioning engine make the aircraft yaw?
In: Engineering
The yaw can be compensated with the rudder as the plane moves forward. You couldn’t probably take off with it, but definetely keep it flying straight. This isn’t ideal, but anything that keeps the plane flying in a case of emergency is okay, I guess.
The pilot needs to constantly force the plane to fly level, flying on one engine requires a skilled pilot and landing on one engine without crashing requires an excellent pilot.
The yaw and roll can be countered by adjusting the ailerons and rudder. It would cause some drag and wouldn’t make for a great flight, but one engine will be enough to at least keep you flying level in most planes.
“Shouldn’t the torque produced by the functioning engine make the aircraft yaw”
It does, in fact one of checklist items to do if an engine fails is to trim the rudder by an angle that the aircraft flies straight
The needed power to take off from this small airport strip i more than the one needed to cruise at the speed that lets it glide on air.
Same thing as a car, you need the gas pedal to take off from the street light but barely touch it to keep cruising.
In a similar way to your analogy, some cars have cylinder deactivation technology where it runs on 8 cylinder when accelerating and 4 while cruising.
As long as the airspeed is above a certain minimum, the pilot can keep it straight with application of rudder.
On takeoff, you don’t let the airplane lift off until it’s past that critical speed; if an engine quits before that, you must cut the other and stop. Once you’re airborne, you never let the airspeed get below that minimum (which is substantially less than cruising speed).
You can’t get licensed to fly multiengine airplanes without demonstrating the engine-out condition dozens of times; almost every training flight will involve the instructor shutting down an engine without warning and evaluating how you deal with it.
You’re correct. We refer to this as asymmetric thrust. We compensate for this by using the rudder. Multi-engine aircraft are designed with this exact scenario (loss of one engine) in mind. For this reason, engine placement is a key part of aircraft design. Manufacturers want to place the engines as far out on the wing as possible to reduce cabin noise, but the engineers want to keep the engines as close to the body of the plane as possible to minimize the possible asymmetric thrust during an engine failure. So this leads to finding a happy medium. The engines aren’t right up against the body of the plane, but they’re not out at the wings tips either.
So, when an engine fails, we deflect the rudder in the opposite direction of the failed engine. That is to say if the left engine fails, we deflect the rudder to the right. This deflection allows the plane to continue flying in a straight line. Even with this rudder deflection we can still control the plane fully in all directions. Of course we won’t be able to go as fast, but that’s not a major concern. As long as the plane is kept above a minimum speed then it will fly just fine. A modern airliner can (depending on weight) easily maintain somewhere between 20,000-30,000ft and 200-300 knots of airspeed on one engine. So essentially an engine failure in cruise or in descent is a non-issue for an airliner.
During the take off though, that’s not the case. This is the worst time for an engine failure to occur (low altitude and low airspeed and high thrust setting). This is the reason that pilots practice this manoeuvre over and over again until it becomes muscle memory. The procedure if an engine fails during the take off is essentially to keep the plane flying straight (using the rudder) and fly a certain speed (we call this speed V2). This speed is the most efficient speed that we can climb at with one engine. The plane will keep climbing (even on just the one engine) and then when we get to a safe altitude (typically 1000ft) we’ll lower the nose and pick up some speed and keep climbing away.
Here’s some trivia. You know how when a helicopter rotor is spinning in one direction, the body of the helicopter wants to spin in the opposite direction? This is why they usually have a small tangent propeller on the end of a rear boom that can speed up or slow down to help the craft steer.
Well it’s the same with twin engines aircraft. If the engine that is still spinning a propeller has its inner half moving downwards, then it is also trying to hold the plane up level. If the engine that is still running has its propellers inner half spinning upwards, then it is also trying to make the plane corkscrew around the running engine’s axis.
In WWII, there was at least one plane that had a “reverse spinning” V12 on one side, so no matter what side got shot up, the pilots job was a little easier.
It was a huge logistical pain in the @$s, so they quit doing that, and made both V12s the same.
The Cessna 223 is an orphaned design that had tandem engines. One pulling in front, and one pushing in the rear.
It’s a great design, but the rear propeller is trying to work in turbulent “dirty” air. A conventional twin tractor engine configuration (two engines in front, side by side), will have better fuel efficiency and a higher top speed, even with the same engines as the 223.
Maybe not better by much, but apparently it didn’t take much for customers to prefer the standard configuration.
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