In article . net,
Robert writes
"John Halliwell" wrote in message

All twins should fly on one engine after a fashion, for conventional
flight this is not too big a problem. The trade off is smaller because
you can trade climb performance, altitude and airspeed (to an extent)
for the extra power needed, so you don't need twice the power needed for
take-off to fly.

You do to be certified for passengers.

That would require the aircraft to take-off fully laden on half the
available engines! Whilst some might be capable of doing it, I'd be very
surprised if it is a certification requirement.

Engine out on takeoff is a definite design issue that everyone has to deal
with.

True, but airlines have more ability to match the aircraft type and
take-off weight to the runways they expect to use them from. As you're
runway length tends towards zero, things become more critical.

Yes, but these are in service decisions (or procurement decisions I
guess).

The design requirement for power is to survive an engine out just after
reaching the "too fast to abort takeoff" speed at maximum weight.

Wouldn't that require V1 and V2 to be the same? How can you calculate
what V1 and V2 should be for certification given you don't know the
runway length and atmospheric conditions?

If you
don't have a big enough engine you have to restrict the plane to lighter
weight and/or longer runways.

Yes.

This relates to ETOPS in that you have to do this without exceeding redline
on the engine. And you have to be able to cruise on one engine in the safe
power range.

One of the "good" features of turbine engines is that if you don't care
about destroying them you can run them at like 150% maximum power for a few
minutes. This can gets you out of "oh ****" flying problems.

The V-22 IIRC is supposed to be able to land vertically on one engine,
and take off empty in an emergency on one engine. I'm not sure this
has been demonstrated yet.

The scenario I'm thinking of is a heavily laden V-22 leaving a carrier
with an engine failure occurring during transition. With very little
height or forward speed to play with (and the possible need to return to
the carrier for safe [vertical?] landing), it needs enough power to
maintain height on a single engine (by definition equal to its weight).

This supposed to be a high performance aircraft. You want to hang a round a
hot LZ while charlie-in-the-treeline or Abdul with an RPG shoots at you?
Having "excess power"
is a good thing. So the combination of "military power" and reduced
performance means you only need 1.5x as much engine as the minimum to hover.

Yes, excess 'power' (engine power) is a good thing, the problem with
VSTOL ops is that it is very expensive as far as extra weight goes to
keep the 1:1 thrust/weight ratio. The bigger the engines the more
power you need to lift the aircraft, the more power to turn them 90
degrees (bigger/heavier mechanisms, more weight, more power etc.). With
a built-in multiplier of 1.5x things are so much harder and weight
elsewhere in the aircraft will always be at a premium.

I don't have the figures to hand, but I guess a 777 has about 100K lbs
thrust to get a 3-400K lbs aircraft off the deck. The engine power
required is much more efficient for conventional aircraft.

Remember these are "prop" planes not rockets so it DOESN'T need
thrust = weight to hover, unlike a Harrier.

Yes, it does. The thrust generated by the 'props' must be greater than
the weight for it to lift off, must be equal for it to hover. The
'props' probably make the engines more efficient at generating that
thrust, but they must do so to lift it. Presumably the engines are rated
in SHP and not lbs thrust?
g
--
John