Register here

Author Topic: Jet Engine Assisted Takeoff and Mixed Propulsion Differences  (Read 2693 times)

Offline Stuka_Hunter

  • CLEARANCE: Confidential
  • *
  • Posts: 38
Re: Jet Engine Assisted Takeoff - Examples
« Reply #15 on: August 01, 2018, 04:11:47 am »
Quote
The following statement will cause confusion and worse because your definition is different to mine.

It indeed confused me, yes haha.

What about I-250, Soviet airplane with one V engine in the nose, connected by a disconectable shaft to a motorjet? It sure isnt a case of JATO use, but is this the true mixed propulsion, since motorjet cannot operate by itself?

Offline CJGibson

  • Top Contributor
  • CLEARANCE: Top Secret
  • ***
  • Posts: 1139
  • Shoot him, you fool!
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #16 on: August 01, 2018, 07:04:58 am »
Chemical rocket assistance - RATO - B-47, Fat Albert
Piston/turbomachinery connected - compound engine - Nomad, I-250
Piston/turbomachinery unconnected - boost engines - B-36, Fireball, Savage
Turbomachinery/ramjet sharing same intake but separate nozzles - combination engine - APD.1019, P.1134
Turbomachinery/ramjet sharing same intake and nozzles - turboramjet (but that is a big can o' worms) - XF-103

Discuss

Chris


Offline martinbayer

  • CLEARANCE: Secret
  • **
  • Posts: 440
Re: Jet Engine Assisted Takeoff - Examples
« Reply #17 on: August 01, 2018, 07:14:36 am »
Quote
However, one question remains: How would you by definition separate the aircraft with mixed propulsion (example: Ryan Fireball) from the airplanes with auxiliary engines (example: C-123J), or does both mean the same thing?
The following statement will cause confusion and worse because your definition is different to mine.  The Skyhawk, Shackleton Mk3 and Gannet had thrust augmentation.
It's better if I say:
The thrust on the Skyhawk was insufficient to get it off the deck so it was augmented with a steam catapult.

I would not classify a catapult as thrust augmentation. To me (admittedly not being a native English speaker) thrust augmentation implies some sort of an additional propulsive system on board an aircraft (even if it may be separated after use), whereas a surface based launch aid such as a catapult in my view falls into a larger class of acceleration augmentation, which includes off board devices as well.

Martin
Would be marching to the beat of his own drum, if he didn't detest marching to any drumbeat at all so much.

Offline CJGibson

  • Top Contributor
  • CLEARANCE: Top Secret
  • ***
  • Posts: 1139
  • Shoot him, you fool!
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #18 on: August 01, 2018, 09:12:25 am »
Catapult isn't thrust. it's pull not push.

Chris.

Offline Stuka_Hunter

  • CLEARANCE: Confidential
  • *
  • Posts: 38
Re: Jet Engine Assisted Takeoff - Examples
« Reply #19 on: August 01, 2018, 09:48:13 am »
Quote
However, one question remains: How would you by definition separate the aircraft with mixed propulsion (example: Ryan Fireball) from the airplanes with auxiliary engines (example: C-123J), or does both mean the same thing?
The following statement will cause confusion and worse because your definition is different to mine.  The Skyhawk, Shackleton Mk3 and Gannet had thrust augmentation.
It's better if I say:
The thrust on the Skyhawk was insufficient to get it off the deck so it was augmented with a steam catapult.

I would not classify a catapult as thrust augmentation. To me (admittedly not being a native English speaker) thrust augmentation implies some sort of an additional propulsive system on board an aircraft (even if it may be separated after use), whereas a surface based launch aid such as a catapult in my view falls into a larger class of acceleration augmentation, which includes off board devices as well.

Martin

Which off board devices exist besides catapults though?  ???

Offline martinbayer

  • CLEARANCE: Secret
  • **
  • Posts: 440
Re: Jet Engine Assisted Takeoff - Examples
« Reply #20 on: August 01, 2018, 10:01:26 am »
Quote
However, one question remains: How would you by definition separate the aircraft with mixed propulsion (example: Ryan Fireball) from the airplanes with auxiliary engines (example: C-123J), or does both mean the same thing?
The following statement will cause confusion and worse because your definition is different to mine.  The Skyhawk, Shackleton Mk3 and Gannet had thrust augmentation.
It's better if I say:
The thrust on the Skyhawk was insufficient to get it off the deck so it was augmented with a steam catapult.

I would not classify a catapult as thrust augmentation. To me (admittedly not being a native English speaker) thrust augmentation implies some sort of an additional propulsive system on board an aircraft (even if it may be separated after use), whereas a surface based launch aid such as a catapult in my view falls into a larger class of acceleration augmentation, which includes off board devices as well.

Martin

Which off board devices exist besides catapults though?  ???

For example downhill rails or ramps for gravity assisted takeoffs, or winches or tow cars for glider launches, see https://en.wikipedia.org/wiki/Assisted_take-off.
« Last Edit: August 01, 2018, 10:02:59 am by martinbayer »
Would be marching to the beat of his own drum, if he didn't detest marching to any drumbeat at all so much.

Offline Archibald

  • Senior Member
  • CLEARANCE: Top Secret
  • **
  • Posts: 2130
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #21 on: August 01, 2018, 10:14:27 am »
Quote
How would you by definition separate the aircraft with mixed propulsion (example: Ryan Fireball) from the airplanes with auxiliary engines (example: C-123J), or does both mean the same thing?

good question. Let me throw my two cents.

There are more or less four reasons / four broad cases why engine pods were added, or why jet engines were mixed with piston-engine.
- the B-36
- the C-123
- the KC-97
...
- the Ryan Fireball

I think a good case could be make that the only difference is that the Fireball was designed, FROM THE DRAWING BOARD, with a jet engine in the tail. When all three others got  jet engines added in wing pods, during their lives. As a cheap-and-dirty expedient to help their performance. But what performance ?

For the B-36 (as said above)  it was a cheap way to get faster over the target.

For the C-123 and Noratlas and many other transports, it was to help at liftoff, not to get faster by any way. Transports don't really care about speed. Piston-powered transport aircrafts were underpowered, and when flying in very hot climates as in Algeria (Noratlas) or Vietnam (C-123) then their performances took a major hit. Jets pods helped getting safer liftoff. The pilots then shut the jets, otherwise they would have cut into the range, being so thirsty.

...and then there is the strange case of the KC-97: that piston engine tanker was too slow to refuel fast jets ! It had to get into a shallow dive to accelerate, and this is no good for in-flight refueling, which is already risky enough. so they put jet pods on KC-97 to get them faster.

and now the Fireball.  Piston + jet. In this case, it was because early jets were awfully unreliable, and guzzled huge amount of fuel. Which was particularly catastrophic for naval fighters. Range was bad, reliability was bad, and veteran WWII pilots had spent their lives flying piston engine fighters.

Also when landing aboard a carrier, if you miss your approach, then you hit full throttle, and climb again to try again. While piston engines, as in the F-4U Corsair, were pretty good at that, early jets had very, very long reaction times. So if you missed a carrier approach with an early jet, then, well, you died. That's the reason why there was no  operational naval Vampire or P-80 variants (I said operational).
 It would have been a slaughter of naval pilots, except of course if you were Eric Winkle Brown, a pilot gifted by God.

So when Ryan got a contract for the Fireball in 1943 the raison d'etre was
a) reassure the pilots with a proven and reliable piston engine that don't explodes or take fire just before landing on the carrier
b) preserve range by flying on the piston engine, light the jet only to accelerate in combat

While the P-80 completely trashed the P-51 with superior speed, and climb and height, its range was abysmal when compared to a Mustang.
For the record, at the end of WWII, Mustangs could fly 10 hours /1500 miles - long missions with small drop tanks: Great Britain to near Polish border and back: Okinawa to Tokyo and back. It took many years for any jet fighter to achieve such range, as late as 1950 or even 1955, the Mustang escort range was still unmatched by any jet. See the Air force many atempts at create a non-piston powered escort fighter: P-81, F-84, F-88...

More generally, mixed piston-jet were a maintenance PITA for a simple reason. The piston engine burned avgas when the jet needed kerosene. So they needed separate tanks. Took me a while to realize this, I thought you could burn avgas into a jet.
« Last Edit: August 01, 2018, 10:33:47 am by Archibald »
Conservatoire de l'Air et de l'Espace d'Aquitaine
http://www.caea.info/en/plan.php

Profanity: weaker mind trying to speak forcefully

Political correctness: just bury your head in the sand for the sake of appeasement and "peace for our time"
- https://fr.wikipedia.org/wiki/Serge_Dassault#Affaires_

Offline Archibald

  • Senior Member
  • CLEARANCE: Top Secret
  • **
  • Posts: 2130
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #22 on: August 01, 2018, 10:38:53 am »
what is really funny with mixed propulsion, is that, while there were four different combinations, all were explored in the span of 15 years, only to be abandonned pretty fast. France tested all of them, one way or another, between 1945 and 1960.
By 1960, jet+reheat ruled supreme.

piston+jet (Fireball)
turboprop + jet (Breguet Vultur)
...
jet+ramjet (Nord Griffon)
jet+rockets (Trident)

Piston+jet or turboprop+jet worked the same: fly on the propeller to get better range, then light the voracious jet for a brief time, to get faster for combat.

Jet+ramjet and jet+rockets were entirely different. Get the jet faster and higher, either through mach 1 or well above mach 2.
Conservatoire de l'Air et de l'Espace d'Aquitaine
http://www.caea.info/en/plan.php

Profanity: weaker mind trying to speak forcefully

Political correctness: just bury your head in the sand for the sake of appeasement and "peace for our time"
- https://fr.wikipedia.org/wiki/Serge_Dassault#Affaires_

Offline Piper106

  • CLEARANCE: Confidential
  • *
  • Posts: 29
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #23 on: August 01, 2018, 06:46:54 pm »
More generally, mixed piston-jet were a maintenance PITA for a simple reason. The piston engine burned avgas when the jet needed kerosene. So they needed separate tanks. Took me awhile to realize this, I thought you could burn avgas into a jet.

Some of the early jet engines were cleared to burn Avgas.  "Aircraft Engines of the World" by P. Wilkinson, 1946 plus 1948 editions lists the I-16/J-31, J-33, J-35, and TG-100/T-31 all as being suitable for 100/130 gasoline.   

Gas wasn't the best for fuel pumps on the jet engines, and the tetraethyl lead in the gas was hard on the hot end parts, but they could burn gasoline.
« Last Edit: August 02, 2018, 04:57:46 am by PaulMM (Overscan) »

Offline Stuka_Hunter

  • CLEARANCE: Confidential
  • *
  • Posts: 38
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #24 on: August 02, 2018, 03:54:25 am »
Some of the early jet engines were cleared to burn Avgas.  "Aircraft Engines of the World" by P. Wilkinson, 1946 plus 1948 editions lists the I-16/J-31, J-33, J-35, and TG-100/T-31 all as being suitable for 100/130 gasoline.   

Gas wasn't the best for fuel pumps on the jet engines, and the tetraethyl lead in the gas was hard on the hot end parts, but they could burn gasoline.

Excuse me, but what does this have to do with this topic?  ???

Offline PaulMM (Overscan)

  • Secret Projects Forum Founder
  • Administrator
  • CLEARANCE: Top Secret
  • *****
  • Posts: 10954
  • Paul Martell-Mead
    • Secret Projects
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #25 on: August 02, 2018, 04:58:29 am »
I edited the post to make it clear what piper106 was responding to.
"They can't see our arses for dust."
 
- Sir Sydney Camm

Offline Archibald

  • Senior Member
  • CLEARANCE: Top Secret
  • **
  • Posts: 2130
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #26 on: August 02, 2018, 08:54:15 am »
Quote
Excuse me, but what does this have to do with this topic?

Since I'm guilty in the first place...  Well, mixed propulsion mean piston engine and jet engine within the same airframe. The fact that they do not burn the same fuel is important because it means separate tanks and fuel systems. Which can be a nuisance.
I wonder how they handled that on, for example, the C-123. I suppose it had avgas tanks in the wings, for its piston engines. Then when they added the engine pods, they evidently need to store the kerosene somewhere in the airframe. I mean, can you fill an avgas tank with kerosene, just like this ? Or does it need some modifications ?
« Last Edit: August 02, 2018, 08:56:08 am by Archibald »
Conservatoire de l'Air et de l'Espace d'Aquitaine
http://www.caea.info/en/plan.php

Profanity: weaker mind trying to speak forcefully

Political correctness: just bury your head in the sand for the sake of appeasement and "peace for our time"
- https://fr.wikipedia.org/wiki/Serge_Dassault#Affaires_

Offline Archibald

  • Senior Member
  • CLEARANCE: Top Secret
  • **
  • Posts: 2130
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #27 on: August 02, 2018, 09:02:29 am »
Quote
What about I-250, Soviet airplane with one V engine in the nose, connected by a disconectable shaft to a motorjet? It sure isnt a case of JATO use, but is this the true mixed propulsion, since motorjet cannot operate by itself?

Ah yes, motorjets. In this case it is a piston engine that drive a compressor. I heard about the Caproni and that I-250 and some others, and as far as my english goes, they are called MOTORJET and not "mixed propulsion". I mean, in this case, mixed propulsion would not be the right term. A motorjet is like a tubojet, that is, it is considered a single unit, and not two separate engines.

Conservatoire de l'Air et de l'Espace d'Aquitaine
http://www.caea.info/en/plan.php

Profanity: weaker mind trying to speak forcefully

Political correctness: just bury your head in the sand for the sake of appeasement and "peace for our time"
- https://fr.wikipedia.org/wiki/Serge_Dassault#Affaires_

Offline Zootycoon

  • CLEARANCE: Confidential
  • *
  • Posts: 93
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #28 on: August 02, 2018, 12:19:35 pm »
So the RB57F;-

Itís two TF33 turbofan engines provide take off/climb/Eco cruise at up to 40k ft but, as is normal for turbofans, rapidly got assmatic and wheezy. So two J60 turbojet, which donít have the same problem, provided the urge up to 100k ft were it was needed over the target.

Question;- are the TF33ís take off assist engines?

Offline Stuka_Hunter

  • CLEARANCE: Confidential
  • *
  • Posts: 38
Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #29 on: August 03, 2018, 12:16:50 am »
Quote
Excuse me, but what does this have to do with this topic?

Since I'm guilty in the first place...  Well, mixed propulsion mean piston engine and jet engine within the same airframe. The fact that they do not burn the same fuel is important because it means separate tanks and fuel systems. Which can be a nuisance.
I wonder how they handled that on, for example, the C-123. I suppose it had avgas tanks in the wings, for its piston engines. Then when they added the engine pods, they evidently need to store the kerosene somewhere in the airframe. I mean, can you fill an avgas tank with kerosene, just like this ? Or does it need some modifications ?

Aha, I understand what you ment now. I doubt that they replaced or modified an avgas tank to kerosene, because it wouldnt make sense to reduce the range of the airplane by, lets say half an hour, to allow those wingtip jets to run maybe 3 minutes?

So the RB57F;-

It’s two TF33 turbofan engines provide take off/climb/Eco cruise at up to 40k ft but, as is normal for turbofans, rapidly got assmatic and wheezy. So two J60 turbojet, which don’t have the same problem, provided the urge up to 100k ft were it was needed over the target.

Question;- are the TF33’s take off assist engines?

Thats a good example, I never knew it existed...  :P

I would render this aircrafts propulsion as mixed more than assisted, for one reason only: like you mentioned, turbofans can be used for eco cruise. What if the aircrafts pilot in one flight never turns on the turbojets, so the whole flight it only uses the turbofans? That means that aircraft would run the entire flight on takeoff engines, should TF 33s classified as ones. It wouldnt make sense.