Compared to a twin, a three engined aircraft should have more power, thus better performance AND more safety. EFATO (of a single engine) shouldn’t do anything much at all, compared to a twin, right?
Of course I guess I already know the answer, which is that maintenance cost, fuel consumption and complexity will be higher. So it all comes down to money, as usual, or are there technical/aeronautical reasons as well why three engined aircraft have died out?
There is no need for all that power, performance or safety. The market think it is good enough with one or two engines. :)
(and a couple of older Bizjets)
Alexis wrote:
(and a couple of older Bizjets)
not THAT old ;)
MedEwok, with a 3 engine plane, you get LESS surplus power than with a twin. Probably obvious for most, but I’ll leave it as food for thought
Absolutely. Why do you think that twins like the 757 – 787 go up so fast on two, compared to four engined aircraft on four?
172driver wrote:
Only one I’m aware of is/was the Brittan-Norman Trislander which. More on it here
Noe wrote:
MedEwok, with a 3 engine plane, you get LESS surplus power than with a twin. Probably obvious for most, but I’ll leave it as food for thought
If one were to build a say 1500kg aircraft powered by three Rotax 912 engines at 300 hp, I guess the performance would be worse than a single engine aircraft with a 300 hp engine because of the increased drag?
A twin has more than twice the power it needs to climb because it is designed to climb when one engine fails (>50% excess power). A three engine aircraft does not have 3x the power it needs to climb because it is not designed to climb when 2 engines fail (> 33% excess power).
Aircraft with more than 2 engines were built when engine technology did not allow building them with 2. A few odd exceptions remain such as the Falcon. Maybe also has to do with the fact that you often buy a Falcon to show you have the biggest d*ck and number of engines is easy to identify. The A380 is an example where engine technology did not allow it to be done with 2 engines.
MedEwok wrote:
Is it because of the increased drag?
No.
A twin-engined aircraft needs to meet one engine inoperative (OEI) performance requirement with one engine. A three-engined aircraft needs to meet those requirements with two engines. That means that will all engines operating a twin will have twice the power required for OEI operation while a three-engined aircraft will only have 1.5 times that power.
To put it differently, everything else being equal, each engine on twin needs to be twice as powerful as each engine on a three-engined aircraft.
