Quote:
Originally Posted by Joekerr
I'm no pilot, and have only the most basic, rudimentary understanding of flying - almost none at all really, so help me to understand this:
I too would have been in the camp that twin engine would be "more safe" - mainly because there is at least another engine in the event one goes wrong. So two questions that I would have:
1. Are you saying it is actually tougher to fly a twin with only one engine, because you have the one side powered and so it is constantly trying to rotate the plane in that direction / no counterbalance of power from the other side? And is it that noticeable where you have to feed that much rudder to correct?
2. If it were that difficult / dangerous, would it be safer then to turn off the second engine and have a lousy glider to work with (or due to the weight of both engines hanging off the wings, do twin engine planes do very little gliding?
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1. Absolutely without a doubt! Twins come in 2 basic flavors - Counter-rotating, or not. If they are counter rotating, the left engine rotates clockwise, and the right enging counter clockwise. That means by turning the prop that direction, the equal and opposite force is trying to tiwst the engine (and thus aircraft they are attached to) in the opposite direction, which means they actually try to lift the fuselage which is a good thing. If they are not counter rotating, they both generally turn clockwise so your left engine becomes your critical engine. If it's working, it is trying to lift the fuselage, however if it's not - the right engine is trying to push the fuselage down. That's one major factor so you will hear twin pilots mention critical engine.
Next factor is the stopped propellor. Until you feather it (turn the blades as far in line with the airflow as possible) it is equivalent to a solid disk sitting in front of that engine - the drag is immense. That's why it's critical to feather the prop fast if you cannot recover the engine to operational.
So, once you have shut down the engine and feathered the prop, you then have to try to maintain at least level flight (and maybe even climb to clear obstacles) with one engine. Because it's off center, it's trying to turn the aircraft, so you're having to apply a lot of rudder to counterract that. But now you have an aircraft flying in a crabbed fashion with a lot of rudder input, which induces a lot of drag (both from the side of the fusalage and the rudder), which slows your airspeed, and you have only half the power available to maintain speed. As your speed drops, rudder authority drops with it meaning you need even more rudder with more drag to keep it straight. There is a speed called Blue Line (there is a blue line on the air speed indicator) which is Vmca - Velocity Minimum Control Asymetric. Basically, Chuck Yeager can hold this aircraft in a straight line down to that speed - most pilots get within about 10 knots of that line before they lose control. So if you start to approach that line, you either need to pitch the nose forward, or try to apply more power if you're not already at 100% on the good engine, which you should be). If you're having to pitch forward to maintain speed, then clearly you cannot maintain altitude nor climb, so now you're on decent, and have to find somewhere to land. And you're landing in a half powered double weight aircraft that's already compromised - it's not a nice place to be.
2. Sadly, I think rather than becoming a glider it becomes a sinker. Proper gliders have a glide ratio of 50:1 - so they can travel 50 feet for every foot they drop. So if you're at 5000 feet when you decide you need to land because you ran out of vodka in your water bottle, you have a range of 250,000 feet (or about 48 miles) to find somewhere to land. Single engine aircraft have a glide ratio of 7.5:1 - so at 5000 feet you have 37,500 feet (or about 7.1 miles) to find somewhere to land. I've struggled to find any data on tiwns (it's as if they don't even glide) but if the point of having a twin is the safety of the second engine, why turn it off?
Don't get me wrong - it's not that difficult to fly a twin on one engine if you're on your game. As part of my training, my instructor pulled the power to one engine just after takeoff, and all I had to do was fly around the circuit and land. Well, as luck would have it, as I came to land the aircraft landing in front of me was too close, so I had to do a go-around, climb back up to circuit height, fly the circuit and come back in to land - at which time someone lined up to take off in front of me, so I had to go-around again, climb back up to circuit height, fly the circuit, and come back in to land. At which point the aircraft landing in front of me was too close again. Instructor asked me "what are you going to do?" to which I replied "if this were a real emergency I would be on the radio calling MAYDAY and telling him to get the F**K out of my way but I can't - we're training" so he called and asked the guy if he could take the grass strip (we could do parallel ops) so on that approach I finally landed. My leg that was on the rudder was visibly shaking because I had not trimmed it out, but it wasn't that hard and I could have gone around again. You just have to be very very aware of your speed at all times regarding blue line. If you get distracted looking at fule pumps and feathering props and looking at maps and don't watch your speed - you're in a death trap. And that's where most twin crashes happen - people not watching. And I believe there's about the same number of tiwn crashes as singles.
Sorry for the long post.