Engine Out Operation

Post by Charles Talleyrand
I'm curious. Can a Blackhawk, Chinook, or other large military
helicopter hover with one engine out? What is the procedure for one-
engine-out operations for large helicopters? I assume no one auto
rotates a 30,000 lbs helicopter???
The obvious internet searches didn't help.
-Much Thanks
-Charles Talleyrand

H-3,H-53 and H-60 can auto rotate. Watching an H-53 recover from auto
rotation is truly impressive. As far as I know all helicopters can auto
rotate. Every helicopter crew I have been around trains to do so.

As for single engine hovering they can do it depending on air density
and load. Above a certain density altitude no helicopter can hover.

An empty H-53 or H-60 can take off on a single engine at sea level.
An H-3 can take off on a single engine, but given the choice I'd prefer
number one engine since the other tends to run a tad weak due to the FOD
shield.

I can't provide citations for any of this since I am only going by
experience.

Dan, U.S. Air Force, retired

Charles Talleyrand

2009-07-16 20:42:05 UTC

I'm curious. Can a Blackhawk, Chinook, or other large military
helicopter hover with one engine out? What is the procedure for one-
engine-out operations for large helicopters? I assume no one auto
rotates a 30,000 lbs helicopter???
The obvious internet searches didn't help.
-Much Thanks
-Charles Talleyrand

H-3,H-53 and H-60 can auto rotate. Watching an H-53 recover from auto
rotation is truly impressive. As far as I know all helicopters can auto
rotate. Every helicopter crew I have been around trains to do so.
As for single engine hovering they can do it depending on air density
and load. Above a certain density altitude no helicopter can hover.
An empty H-53 or H-60 can take off on a single engine at sea level.
An H-3 can take off on a single engine, but given the choice I'd prefer
number one engine since the other tends to run a tad weak due to the FOD
shield.

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

-Curious
-Charles Talleyrand

Paul J. Adam

2009-07-16 20:54:05 UTC

In message

Post by Charles Talleyrand
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 & easier 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
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.

Post by Charles Talleyrand
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*.

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

Paul J. Adam

JohnO

2009-07-16 21:37:49 UTC

On Jul 17, 8:54 am, "Paul J. Adam"

Post by Paul J. Adam
In message

Post by Charles Talleyrand
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?

Post by Paul J. Adam
& easier

Really?

Post by Paul J. Adam
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.

Post by Paul J. Adam
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'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.

Post by Paul J. Adam
--
He thinks too much, such men are dangerous.
Paul J. Adam

Paul J. Adam

2009-07-16 22:32:32 UTC

In message

Post by JohnO
On Jul 17, 8:54 am, "Paul J. Adam"

Post by Charles Talleyrand
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?

Yes, if you have two engines each providing half the horsepower compared
to having to develop a new engine. (Changes if there's an off-the-shelf
turbine that puts out the required power, of course)

Post by Paul J. Adam
& easier

Really?

Yes, depending on dimensions and gearing.

Post by Paul J. Adam
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?

Yes, really.

Post by JohnO
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).

Absolutely so. Now, how often do they get shot at, flown through
brownouts, and so forth?

The flipside argument - why do light twins like the A109 and AS335 ever
sell, if they're so much more expensive for no apparent benefit?

Post by Paul J. Adam
"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.

Which is why many of the later UH-1s went twin-engine and so many
military helos like to have more than one powerplant, even if it's less
strictly efficient than a single engine.

Being able to jettison payload and limp home, or at least to pick a
safer spot to come down, can be quite important to the aircrew.

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

Paul J. Adam

JohnO

2009-07-17 00:05:00 UTC

On Jul 17, 10:32 am, "Paul J. Adam"

Post by Paul J. Adam
In message

Post by JohnO
On Jul 17, 8:54 am, "Paul J. Adam"

Post by Charles Talleyrand
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?

Yes, if you have two engines each providing half the horsepower compared
to having to develop a new engine. (Changes if there's an off-the-shelf
turbine that puts out the required power, of course)

No need to develop a new engine. Just use an existing one.

Post by Paul J. Adam
& easier

Really?

Yes, depending on dimensions and gearing.

Post by Paul J. Adam
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?

Yes, really.

Again, I restrict myself to light twins, and if you look at the
examples I gave the bulgy profiles are always on the twins not the
singles. Two small engines always take more space than one large one.

The gearbox for twins is always bigger than for singles due to the
requirement to combine them.

Absolutely so. Now, how often do they get shot at, flown through
brownouts, and so forth?

Well it would be very difficult to find any helicopter with a track
record for surviving battle damage than a single engined Huey.

Post by Paul J. Adam
The flipside argument - why do light twins like the A109 and AS335 ever
sell, if they're so much more expensive for no apparent benefit?

In large part it's due to regulations mandating their use.

I would like to see statistics showing they are any safer than
singles.

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

Which is why many of the later UH-1s went twin-engine and so many
military helos like to have more than one powerplant, even if it's less
strictly efficient than a single engine.
Being able to jettison payload and limp home, or at least to pick a
safer spot to come down, can be quite important to the aircrew.

Which is exacly what I said.

Post by Paul J. Adam
--
He thinks too much, such men are dangerous.
Paul J. Adam

JohnO

2009-07-16 21:33:19 UTC

Post by Charles Talleyrand

I'm curious. Can a Blackhawk, Chinook, or other large military
helicopter hover with one engine out? What is the procedure for one-
engine-out operations for large helicopters? I assume no one auto
rotates a 30,000 lbs helicopter???
The obvious internet searches didn't help.
-Much Thanks
-Charles Talleyrand

H-3,H-53 and H-60 can auto rotate. Watching an H-53 recover from auto
rotation is truly impressive. As far as I know all helicopters can auto
rotate. Every helicopter crew I have been around trains to do so.
As for single engine hovering they can do it depending on air density
and load. Above a certain density altitude no helicopter can hover.
An empty H-53 or H-60 can take off on a single engine at sea level.
An H-3 can take off on a single engine, but given the choice I'd prefer
number one engine since the other tends to run a tad weak due to the FOD
shield.

If the large helicopters can autorotate, and cannot hover with a
reasonable load on just one engine, why do they have two engines? 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?
-Curious
-Charles Talleyrand- Hide quoted text -
- Show quoted text -

They might not be able to sustain a hover but they are likely to be
able to maintain altitude in level flight.

In other words, the remaining engine will allow them to fly to a more
convenient crash site!

vaughn

2009-07-16 14:10:45 UTC

Post by Charles Talleyrand
I'm curious. Can a Blackhawk, Chinook, or other large military
helicopter hover with one engine out?

Darn! I thought this was going to be a glider question.

Vaughn

Stu Fields

2009-07-16 17:40:46 UTC

Post by vaughn

Post by Charles Talleyrand
I'm curious. Can a Blackhawk, Chinook, or other large military
helicopter hover with one engine out?

Darn! I thought this was going to be a glider question.
Vaughn

It is when you are in a full dead engine autorotation. The SSA doesn't
really recognize them as such, but will accept your membership fee anyway.
However the sink rate is more like 1800'/min @ 60mph.

Linc

2012-07-25 21:32:47 UTC