On Jul 17, 8:54*am, "Paul J. Adam"
wrote:
In message
,
Charles Talleyrand writes

If the large helicopters can autorotate, and cannot hover with a
reasonable load on just one engine, why do they have two engines?

Because it's often cheaper

Really?

& easier

Really?

to use two engines rather than one
for the power needed - you don't end up with an exaggerated hunchback
from one big turbine & gearbox. (Or three engines, as some types - our

Really?

A bit different for the heavies, but light twins such as A109 and
AS355 cost more to purchase, fly and maintain than their single
siblings A119 and AS350, and offer little or no performance benefit
(in fact AS355 has less performance than AS350B3).

In addition to double the engine maintenance, twins have an additional
gearbox element to maintain.

Merlin, the US Sea Stallion - go for.)

Even small helicopters often have two engines, such as our Lynx,
especially if they expect to get shot at.

Now you are talking.


It
would seem that you would have smaller odds of failure with one large
engine rather than two smaller engines. *If you have two engines, and
failure of either leaves you kinda screwed, it is not better to just
have one engine?

Or am I missing something?

"It's better to lose *an* engine than *the* engine." Not being able to
hover doesn't mean you can't sustain flight: if you're in cruise, you
get a lot of lift from the rotor disc and can stay airborne on a lot
less power than you need for a hover. (Landing may be interesting, but
autorotating or a rolling landing are both options).

On the other hand, with one engine, losing it means autorotating in
*now*.

Yep. That second engine will get you out of enemy territory to a
friendly crash location.



--
He thinks too much, such men are dangerous.

Paul J. Adam