PILOT SPIN

Pilot Zone => Pilot Zone => Topic started by: TimRB on January 21, 2020, 11:53:56 AM

Title: Why turboprops for smaller airliners?
Post by: TimRB on January 21, 2020, 11:53:56 AM
It occurred to me that I don't understand the motivation behind turboprop powerplants in smaller airliners typically used by regional operators.  Is there some sort of efficiency line crossed when an airplane is scaled-up to "full-sized" airliner?  If jet engines are the cat's meow, why not use them everywhere?

Tim
Title: Re: Why turboprops for smaller airliners?
Post by: Little Joe on January 21, 2020, 12:02:25 PM
Among other things, jet engines are more efficient at higher altitudes while turboprops are more efficient at lower altitudes.  Since the smaller regional flights don't generally fly at the high altitudes, at least for long, turboprops are more efficient.
Title: Re: Why turboprops for smaller airliners?
Post by: Anthony on January 21, 2020, 12:08:52 PM
It occurred to me that I don't understand the motivation behind turboprop powerplants in smaller airliners typically used by regional operators.  Is there some sort of efficiency line crossed when an airplane is scaled-up to "full-sized" airliner?  If jet engines are the cat's meow, why not use them everywhere?

Tim

A turboprop IS a jet (turbine) engine.  It just uses the prop for thrust.  The economics are better for turboprops in shorter, lower altitude ops.  However, from what I am seeing they are disappearing in the commercial airline world because passengers are AFRAID of anything with a propeller, and small turbine engines have become more efficient.  At least that is my perception. 
Title: Re: Why turboprops for smaller airliners?
Post by: nddons on January 21, 2020, 02:25:59 PM
A turboprop IS a jet (turbine) engine.  It just uses the prop for thrust.  The economics are better for turboprops in shorter, lower altitude ops.  However, from what I am seeing they are disappearing in the commercial airline world because passengers are AFRAID of anything with a propeller, and small turbine engines have become more efficient.  At least that is my perception.
I find that hilarious. When they see a Beech 1900 or something similar, they think you are  asking them to fly over the Atlantic in a Skyhawk.  I love them. Much better than sitting in the Canadian Conspiracy Against Large Americans, otherwise known as the “CRJ.” 
Title: Re: Why turboprops for smaller airliners?
Post by: TimRB on January 21, 2020, 03:29:35 PM
A turboprop IS a jet (turbine) engine.

Yes, I knew that going in--that's why I was confused.  Sounds like greater efficiency for props at the lower altitudes is the key.  Thanks, guys--I didn't want to ask a question at that other place.

Tim
Title: Re: Why turboprops for smaller airliners?
Post by: Lucifer on January 21, 2020, 03:55:18 PM
Here's something to give you an idea on fuel economy  https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft

 Huge advances have been made in turbofans over the past 25 years which has made significant inroads into the turboprop operating regime.  And to be fair, even turboprops have steadily improved.
Title: Re: Why turboprops for smaller airliners?
Post by: EppyGA - White Christian Domestic Terrorist on January 21, 2020, 07:14:16 PM
Yes, I knew that going in--that's why I was confused.  Sounds like greater efficiency for props at the lower altitudes is the key.  Thanks, guys--I didn't want to ask a question at that other place.

Tim
Why not, CapnRon or Brian would have expounded on it for you gladly.
Title: Re: Why turboprops for smaller airliners?
Post by: Lucifer on January 21, 2020, 07:18:10 PM
Why not, CapnRon or Brian would have expounded on it for you gladly.

Does Levy still claim to be a confidant of the FAA?
Title: Re: Why turboprops for smaller airliners?
Post by: EppyGA - White Christian Domestic Terrorist on January 21, 2020, 08:15:23 PM
Does Levy still claim to be a confidant of the FAA?


Don't know, he used to hate it when he talk about being a pilot in the USAF when he actually rode in the backseat.
Title: Re: Why turboprops for smaller airliners?
Post by: Steingar on January 22, 2020, 08:14:48 AM
Suck, Squeeze, Bang, Blow. That's what happens in our piston engines.  Makes lots and lots of vibrations, which is why our engines are life-limited.

Turbines go round and round.  Nowhere near as much vibration, so their duty cycles are far longer.  That, and JetA is more widely available than 100ll.
Title: Re: Why turboprops for smaller airliners?
Post by: Anthony on January 22, 2020, 08:16:56 AM
Suck, Squeeze, Bang, Blow. That's what happens in our piston engines.  Makes lots and lots of vibrations, which is why our engines are life-limited.

Turbines go round and round.  Nowhere near as much vibration, so their duty cycles are far longer.  That, and JetA is more widely available than 100ll.

Turboprops are jet engines that go around, and around and run on Jet A. 
Title: Re: Why turboprops for smaller airliners?
Post by: Lucifer on January 22, 2020, 08:45:31 AM
Suck, Squeeze, Bang, Blow. That's what happens in our piston engines.  Makes lots and lots of vibrations, which is why our engines are life-limited.

Turbines go round and round.  Nowhere near as much vibration, so their duty cycles are far longer.  That, and JetA is more widely available than 100ll.

Jet engines operate on the same principal (suck squeeze bang blow) and you are correct, due to the rotation of the engine components results in much less vibration.  The engine oil never touches the combustion process either in a turbine. 

 The enemy of the turbine is the start cycle.  The engine goes through a temperature range from ambient upwards of 800c in a minute.  This is why the use of exotic metallurgy and highly precision tolerances are used.  Once the engine is operating and stabilized it will run as long as the fire doesn't go out (fuel exhaustion).  GE and P&W have turbines running pumps and powerplants that operated for months on end with never shutting down, and need very little maintenance.
Title: Re: Why turboprops for smaller airliners?
Post by: Little Joe on January 22, 2020, 09:26:00 AM
Suck, Squeeze, Bang, Blow. That's what happens in our piston engines.  Makes lots and lots of vibrations, which is why our engines are life-limited.

Turbines go round and round.  Nowhere near as much vibration, so their duty cycles are far longer.  That, and JetA is more widely available than 100ll.
Quite true.  But this discussion isn't about our piston engines.  It is about jet engines that use exhaust for propulsion vs jet engines that use propellers for propulsion. (As Anthony reminded me earlier).
Title: Re: Why turboprops for smaller airliners?
Post by: Username on January 22, 2020, 10:32:31 AM
Turbines scale up really well, but have trouble scaling down.  Once they beat the physics problems with small turbines it will be very, very cool.
Title: Re: Why turboprops for smaller airliners?
Post by: Mr Pou on January 22, 2020, 11:39:41 AM
Quite true.  But this discussion isn't about our piston engines.  It is about jet engines that use exhaust for propulsion vs jet engines that use propellers for propulsion. (As Anthony reminded me earlier).

In a way, high bypass turbofans are more like a propeller aircraft as more thrust comes from the fan than does the exhaust. It's just that the propeller blades are much smaller, there's many more of them, they're direct driven, and they're in a ducted housing.
Title: Re: Why turboprops for smaller airliners?
Post by: nddons on January 24, 2020, 03:21:45 PM

Don't know, he used to hate it when he talk about being a pilot in the USAF when he actually rode in the backseat.
Or right seat. Wasn’t he in an F-111?
Title: Re: Why turboprops for smaller airliners?
Post by: EppyGA - White Christian Domestic Terrorist on January 24, 2020, 04:58:24 PM
Or right seat. Wasn’t he in an F-111?


Don't remember, except he didn’t like people pointing out his lie.
Title: Re: Why turboprops for smaller airliners?
Post by: Anthony on January 24, 2020, 05:25:37 PM
Or right seat. Wasn’t he in an F-111?

He was Navy first, and a right seater (Bombardier/Navigator) in the A-6, then switched to the Air Force, and was essentially the same function in the F-111.  Right seat, Weapons and Radar Officer. 

Ron checked me out in my Tiger, and he does know his stuff, and more about Grummans than I'll ever know.  Still he can be a bit grating at times, but I always got along with him.  Some others did not.  He was very thorough as you can probably imagine.  lol! 
Title: Re: Why turboprops for smaller airliners?
Post by: David on January 27, 2020, 09:05:19 AM
He was Navy first, and a right seater (Bombardier/Navigator) in the A-6, then switched to the Air Force, and was essentially the same function in the F-111.  Right seat, Weapons and Radar Officer. 

Ron checked me out in my Tiger, and he does know his stuff, and more about Grummans than I'll ever know.  Still he can be a bit grating at times, but I always got along with him.  Some others did not.  He was very thorough as you can probably imagine.  lol!
I know his online reputation and posting habits, but I met him for lunch at Williamsburg Airport (great restaurant BTW) and really enjoyed talking to him.
Title: Re: Why turboprops for smaller airliners?
Post by: Lucifer on January 27, 2020, 10:13:25 AM
I know his online reputation and posting habits, but I met him for lunch at Williamsburg Airport (great restaurant BTW) and really enjoyed talking to him.

His propensity to exaggerate himself was really annoying.  It overshadowed anything else about him.
Title: Re: Why turboprops for smaller airliners?
Post by: Rush on February 01, 2020, 07:13:47 PM
Gawd, y’all are talking about him like he died.
Title: Re: Why turboprops for smaller airliners?
Post by: Mr Pou on February 03, 2020, 07:55:41 AM
I know his online reputation and posting habits, but I met him for lunch at Williamsburg Airport (great restaurant BTW) and really enjoyed talking to him.

I've met him several times, he was even nice enough to let me fly left seat in his Cheegar. He's fine in person, a little obnoxious online.
Title: Re: Why turboprops for smaller airliners?
Post by: Anthony on February 03, 2020, 08:00:11 AM
I've met him several times, he was even nice enough to let me fly left seat in his Cheegar. He's fine in person, a little obnoxious online.

That's been my experience as well.  I learned a lot from Ron.  He's a good instructor.