Why no CAS turboprops?

wrote:

What aircraft would use that setup Rick? I can't imagine how you
could drive a prop directly from a turbine engine with no
reduction gearing? (or did I misread you?)

I think you misread. A turboshaft engine can be used for
anything but driving a propeller directly. They are used to
power everything from generators and air compressors to
ships and water pumps. Some of them, like the GE LM2500
drive the output shaft directly from the power turbine at
3600 rpm so they can be direct coupled to a generator. They
do not use a gearbox.

Rick

Rick wrote:

wrote:

What aircraft would use that setup Rick? I can't imagine how you
could drive a prop directly from a turbine engine with no
reduction gearing? (or did I misread you?)

I think you misread. A turboshaft engine can be used for
anything but driving a propeller directly. They are used to
power everything from generators and air compressors to
ships and water pumps. Some of them, like the GE LM2500
drive the output shaft directly from the power turbine at
3600 rpm so they can be direct coupled to a generator. They
do not use a gearbox.

Rick

Ok, that makes sense as far as it goes...I'm a little surprised
at the low speed of that turbine though but then, I'm used to
aircraft turbines that rotate much faster, could be something to
do with weight requirements though. The other part of your post
seems to say that you 'can' drive a prop directly and that's what
I was querying actually. Most aircraft turbines driving props
rotate at 13,000 - 14,000 RPM and that's much too fast for props
so you need reduction gearing.
--

-Gord.

wrote:


Ok, that makes sense as far as it goes...I'm a little surprised
at the low speed of that turbine though but then, I'm used to
aircraft turbines that rotate much faster,

The LM2500 is an aeroderivative engine, that is it was born
to fly as the TF39 that powers the C5 transports. It was
adapted to stationary and marine use.

The power turbine sits behind the turbine that drives the
compressor. Just like the fan was driven in the aircraft
version the gases leaving the turbine drive the power
turbine at a much lower speed.

Take a google at a turbofan engine and you will see what I
mean.


Most aircraft turbines driving props
rotate at 13,000 - 14,000 RPM and that's much too fast for props
so you need reduction gearing.

You are a bit slow, the smaller engines turn around 40,000 rpm.

Rick

On a modern battlefield, I wouldn't give the A-10 much of a life span.
It might armoured like a tank, but it's sitting duck.

How would the A-10 survive in a theatre full of modern vehicle-mounted
SAMs, I wonder?

Thank goodness you don't fly them then. You wouldn't be able to employ your
weapons system effectively with an attitude like that.

A-10s don't work alone. HARM shooters abound, and even enough A-10s can
overwhelm a SAM site to cause mayhem and allow one to sneak through and
schwack it.

ATTACK!

However, how many aircraft were deployed in the CAS role in large
numbers during that conflict? Without anything to compare those numbers
to, they're meaningless. Who's to say that a similar, faster aircraft
would not have had even fewer losses?

You take a look at the results of the failed A-16 experiment, son?

When you're talking CAS, you can't beat a Hawg.

ATTACK!

But doesn't it sort of defeat the very idea of "survivable combat
aircraft"
when you need a SEAD package et al to keep it alive?

No. Idiots who think that one airplane can do every job might believe that
to be so, but when it comes to CAS, the A-10 is combat proven (against more
threats than you might think).

Sure, passive protection will increase your survival chances in case of
hit
but does it really help if you're so slow that you get hit much more
often?

A-10s normally will operate in conditions where F-16s or F-15Es wouldn't
dare to. It's the nature of true CAS operations that you stick your neck
out for the guy on the ground, and take hits to support him. When you have
that type of mindset going into the game, it's nice to have an aircraft that
can take hits and make it home. Speed isn't always better when it comes to
CAS.

It should also be noted that During Desert Storm, A-10's did very
well:

Actually, A-10 operations to some well-defended areas were restricted
after
some were shot down. Against something like Crotale or SA-15, I'd rate
A-10's survival odds as very low. Or gun systems like Marksman,
Tunguska...those have _very high_ hit probabilities. A turboprop CAS plane
would be even more vulnerable.

Again, the A-10 doesn't operate solely in such environments (SA-15, etc.),
for good reason.

The SA-19/Tunguska and Marksman can be overflown even by the A-10, and with
Precision Engagement coming online with A-10 squadrons (some Guard units
already possess the capability) it will turn into a LGB plink-fest.

Of course, if you're content about bombing some hapless natives, then
maybe
you don't have to worry about such threats and slow attack planes are
viable.

As long as they're hapless natives waving AK-47s in the air vs. helpless
natives, bomb 'em and strafe 'em 'till they are no more.

ATTACK!

In article ,
says...
However, how many aircraft were deployed in the CAS role in large
numbers during that conflict? Without anything to compare those numbers
to, they're meaningless. Who's to say that a similar, faster aircraft
would not have had even fewer losses?

You take a look at the results of the failed A-16 experiment, son?

No I didn't, "dad".

When you're talking CAS, you can't beat a Hawg.

I'm not saying the A-10 is a bad aircraft, I'm saying that a faster, but
otherwise similar aircraft, would be better, which was the thrust (if
you'll pardon the expression) of the original question.

On Thu, 8 Jan 2004 22:18:06 -0500, "Hog Driver"
wrote:

On a modern battlefield, I wouldn't give the A-10 much of a life span.
It might armoured like a tank, but it's sitting duck.

How would the A-10 survive in a theatre full of modern vehicle-mounted
SAMs, I wonder?

Thank goodness you don't fly them then. You wouldn't be able to employ your
weapons system effectively with an attitude like that.

A-10s don't work alone. HARM shooters abound, and even enough A-10s can
overwhelm a SAM site to cause mayhem and allow one to sneak through and
schwack it.

ATTACK!

want there a mission in the 1st Gulf War, where A-10's Teamed up
F-4G's to take out some sam sites. the A-10'w would be the hunter, and
when the radars were turned on to engage them, they inturn were
engaged by the harms. and those that didnt turn their radar on were
then destroyed by the A-10's.

But seriously folks. all these people that say that the A-10 wont
survive in a modern battlefield are not looking at the big picture.

1. An A-10 is designed to operate within the vicinity of or next to
friendly groundforces.

2, if a A-10 can not survive in those conditions then that means that
we do not have air suppieriority(excuse spelling) and that enemy
aircraft are bombing friendly troops.

3. A-10 is going to be shot down, but so would a F-16/F-15 etc. and
it comes to the bottom line. how many tanks etc dose a plane have to
destroy to pay for itself. just look at how many helicopters that were
destroyed sofar in GW2. are we going to get rid of them cause they are
low and slow?


just my opionion.

"Hog Driver" wrote in message
...
But doesn't it sort of defeat the very idea of "survivable combat
aircraft"
when you need a SEAD package et al to keep it alive?

No. Idiots who think that one airplane can do every job might believe
that
to be so, but when it comes to CAS, the A-10 is combat proven (against
more
threats than you might think).

Well, F-16 is also "combat proven" in CAS, then...

Sure, passive protection will increase your survival chances in case of
hit
but does it really help if you're so slow that you get hit much more
often?

A-10s normally will operate in conditions where F-16s or F-15Es wouldn't
dare to. It's the nature of true CAS operations that you stick your neck
out for the guy on the ground, and take hits to support him. When you
have
that type of mindset going into the game, it's nice to have an aircraft
that
can take hits and make it home. Speed isn't always better when it comes
to
CAS.

Having an option of speed is always better than not having it. Sure, flying
too fast over the target won't do any good in CAS, but having speed reserve
increases your chances against missiles etc, plus it makes your plane more
viable to other roles. Hence, highly specialized turboprop plane is a poor
idea in modern battlefield.

Actually, A-10 operations to some well-defended areas were restricted
after
some were shot down. Against something like Crotale or SA-15, I'd rate
A-10's survival odds as very low. Or gun systems like Marksman,
Tunguska...those have _very high_ hit probabilities. A turboprop CAS
plane
would be even more vulnerable.

Again, the A-10 doesn't operate solely in such environments (SA-15, etc.),
for good reason.

And that good reason is that they're too vulnerable, despite all their
passive protection.

The SA-19/Tunguska and Marksman can be overflown even by the A-10, and
with
Precision Engagement coming online with A-10 squadrons (some Guard units
already possess the capability) it will turn into a LGB plink-fest.

Then, you are flying too high to perform effective CAS, plus your odds of
actually detecting those things you are supposed to bomb are very poor. See:
Allied Force.

In article k.net,
Rick writes:
wrote:


Ok, that makes sense as far as it goes...I'm a little surprised
at the low speed of that turbine though but then, I'm used to
aircraft turbines that rotate much faster,

The LM2500 is an aeroderivative engine, that is it was born
to fly as the TF39 that powers the C5 transports. It was
adapted to stationary and marine use.

The power turbine sits behind the turbine that drives the
compressor. Just like the fan was driven in the aircraft
version the gases leaving the turbine drive the power
turbine at a much lower speed.

O.K. That's a Free-Turbine Turboshaft. The output shaft is driven by
its own separate turbine, and, therefore, can be sized to turn at
whaver combination of torque & RPM you want, within certain limits.
The Gas Generator (Compressor/turbinw spools, and the burners) are
then able to turn at whatever speed is best for them. I'll bet it's
quite a bit faster.
Many turboprops are set up the same way - the output shaft is run off
its own turbine, and is separate from the Gas Generator. You can see
this on some commuter airliners - they'll be sitting on the ramp,
whining away, with the props stationary.

As I remember it, Gord was an FE on airplanes with the Allison T56.
That's a bit different - there's only one shaft, and the output to the
gearbox, compressor and turbine are all rigidly connected.
In that case, the whole engine turns at some serious RPM.
(Something like 13,000). A neat deal with teh T56 is that in flight,
it's basically a constant speed engine - the propeller pitch changes
to keep the RPM constant, while the torque varies, and the fuel
control varies the temperature to produce the desired torque.

Take a google at a turbofan engine and you will see what I
mean.


Most aircraft turbines driving props
rotate at 13,000 - 14,000 RPM and that's much too fast for props
so you need reduction gearing.

You are a bit slow, the smaller engines turn around 40,000 rpm.

Rick


--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster