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Author Topic: Jet Engine Assisted Takeoff and Mixed Propulsion Differences  (Read 2694 times)

Offline Stuka_Hunter

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Greetings

I was Googling some stuff about JATO the other day and to my surprise all results were about RATO rockets, not JATO specifically (thats why I stated ˝Jet Engine Assisted Takeoff˝in the title of this topic). I only managed to find one example of JATO being mounted on any aircraft, that being the Avro Shackleton MR.Mk.3 Phase 3. My question is: are there any other examples of JATO being used? ???

Kind regards,
Stuka_Hunter  :)
« Last Edit: August 01, 2018, 04:12:56 am by Stuka_Hunter »

Offline bob225

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #1 on: July 29, 2018, 01:11:28 pm »
Locheed Neptune?
B-36 peacemaker?

Offline Arjen

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #2 on: July 29, 2018, 01:49:28 pm »
I am fairly sure the tail-mounted J33 in the North American Savage helped it to take off from carriers. There's JATO for you.
I may be wrong about this, but I seem to recall JATO and RATO were frequently mixed up. 'JATO bottles' - rocket packs?
« Last Edit: July 29, 2018, 01:54:31 pm by Arjen »

Offline jstar

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #3 on: July 29, 2018, 02:17:50 pm »
« Last Edit: July 29, 2018, 02:25:55 pm by jstar »

Offline CJGibson

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #4 on: July 29, 2018, 06:30:46 pm »
As far as I know JATO and RATO are the same thing. JATO (J refers to a jet of rocket efflux) is old terminology and became RATO when gas turbines i.e. jet engines, became the powerplant of choice in the late 1940s.

Gas turbines on piston-engined aircraft are usually referred to as auxiliary or boost engines.

Chris

Offline Stuka_Hunter

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #5 on: July 30, 2018, 12:11:53 am »
Locheed Neptune?
B-36 peacemaker?
Martin P4M Mercator?

and some of these: https://en.wikipedia.org/wiki/Category:Aircraft_with_auxiliary_jet_engines


I was aware before that these aircraft have auxiliary jet engines, but none of them qualify for JATO in my opinion. That is simply because they can still be used after takeoff on Martin P4M Mercator, Lockheed Neptune, NA Savage and on the Peacemaker, primarily for increased speed over the target (I dont know about Avro Shackleton though).

Comparing that to RATO (I know there might be a slight mixup between both RATO and JATO), which stops working after takeoff, it isnt the same. However, all of the airplanes mentioned above do qualify for mixed propulsion, utilising two different types of engines on one airframe.

Does anyone have info about this one, the Fairchild C-123J. On the wingtips are J44 jet engines.


Offline Zootycoon

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #6 on: July 30, 2018, 01:59:15 am »
DH Trident 3b

A rare example of jet with a take off assist jet.

Online Jemiba

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #7 on: July 30, 2018, 02:03:15 am »
Another example would be the Nord 2508 Noratlas, fitted with two Turbomeca Marboré IIE auxiliary
turbojets at the wing tips.
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Offline PaulMM (Overscan)

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #8 on: July 30, 2018, 02:08:58 am »
Yep, there was no distinction between 'jet' and 'rocket' at that time, JATO was used initially when referring to boosting piston-engined aircraft, and RATO became more popular once you were assisting a jet aircraft to take off.

A true jet engine based disposable/jettisonable "JATO" would not work as the thrust to weight ratio would be far too small especially in those early days and the cost too high. Rockets are simpler, cheaper and lighter, the only downside (high fuel consumption / low endurance) not relevant to a takeoff boost.
« Last Edit: July 30, 2018, 02:10:42 am by PaulMM (Overscan) »
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Offline jstar

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #9 on: July 30, 2018, 03:40:06 am »

"Does anyone have info about this one, the Fairchild C-123J. On the wingtips are J44 jet engines."

In 1955 the prototype C-123B was fitted experimentally with two Fairchild J44 turbojet engines mounted at the wingtips to provide auxiliary power for use in an emergency. As a result ten production aircraft were modified into C-123J with turbojet engines fitted.

http://aviastar.org/air/usa/fair_provider.php

Ten C-123Bs were fitted with two Fairchild J44 turbojets, with about 4.45 kN (450 kgp / 1,000 lbf) thrust each, one mounted on each wingtip; they were also fitted with neat retractable ski landing gear, to be given the new designation of "C-123J", and used for service in Arctic regions. The US Federal Aviation Administration also used two Providers similarly fitted with Continental J69 turbojets on the wingtips, the J69 being derived from the French Turbomeca Marbore turbojet. These two machines were used in Arctic regions as well; it is not clear if they had any special designation.

http://www.airvectors.net/avboxcar.html#m4
 
« Last Edit: July 30, 2018, 03:46:05 am by jstar »

Offline charleybarley

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #10 on: July 30, 2018, 09:15:24 am »
Probably in a category of its own, ie using its cruise missile armament to supplement take-off thrust, the B-52 with Hound Dogs. 2 HD J52 engines used on TO gave 15,000 lb thrust. Ref Jack Connors book. J52 was going to be cheapened as one-use only until pilots started using it to assist TO.
« Last Edit: July 30, 2018, 01:10:36 pm by charleybarley »

Offline Stuka_Hunter

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #11 on: July 31, 2018, 11:47:38 am »
I would like to thank for all the answers on this topic so far.

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?  ???

Offline Dynoman

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #12 on: July 31, 2018, 01:56:50 pm »
Stuka_Hunter, IFAIK the first aircraft in the US to fly with an auxiliary takeoff propulsion system was GALCIT's 1941 Ercoupe, which was called a JATO (Jet Assisted Take Off) despite the fact that it used six small rocket motors. In Beyond the Saga of Rocket Science by Walter Sierra, Von Karman of GALCIT thought that the term 'rocket' had the connotation of being an embryonic technology for a manned aircraft and that the acceptance of the term 'jet' would be more universal. Later the terms JATO and RATO were interchangeable. Of course today, it would probably be more accurate to use the term JATO with those aircraft using a turbine auxiliary propulsion systems and RATO with those aircraft using rocket propulsion for assisted takeoff.   
« Last Edit: July 31, 2018, 02:01:13 pm by Dynoman »

Offline CJGibson

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #13 on: July 31, 2018, 06:25:35 pm »
I'd say JATO is an obsolescent term. RATO or RATOG describes the equipment better in modern literature. However, I note JATO still being used in articles about the Blue Angels Fat Albert.

Chris

Offline charleybarley

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #14 on: July 31, 2018, 07:43:21 pm »
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?

I wouldn't try to do it by definition. I would use a few extra words so there is no ambiguity/ cause for confusion.

The following both have mixed-propulsion and the statements may not be strictly correct and could obviously be improved but are meant to illustrate the value of a few extra words over supposedly "defined" terminology, in this case mixed-propulsion.
The Fireball had a piston engine added  because the early jet engine alone was not considered suitable for operating from a carrier deck. Do we want to come up with a term for this? PATO/PAGA -prop assisted take-off and go-around?
The B36-D had jets added because the pistons alone were too slow over the target.

A further illustration of the shortcomings of definitions, ie are we all using the same?
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.
The prop thrust of the Shackleton was insufficient for take-off so it was augmented with jet engines.
The Gannet's role was looking for submarines for which it needed one Mamba and one propeller. The prop thrust was insufficient to get it off the deck and to its patrol area quick enough so it was augmented with an extra Mamba and propeller.


« Last Edit: July 31, 2018, 08:41:17 pm by charleybarley »

Offline Stuka_Hunter

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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

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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

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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
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Offline CJGibson

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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

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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

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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 »
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Offline Archibald

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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 »
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Offline Archibald

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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.
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Offline Piper106

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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

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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)

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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.
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Offline Archibald

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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 »
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Offline Archibald

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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.

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Offline Zootycoon

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #28 on: August 02, 2018, 12:19:35 pm »
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?

Offline Stuka_Hunter

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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.

Offline Archibald

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #30 on: August 03, 2018, 04:00:09 am »
Quote
. 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?

Well, there was a trade.
Let's suppose a Noratlas transport flying in Algeria, said in 1959. Temperature on the ground is around 45°C.  Yet the Nortlas is heavily loaded - because this is the Algerian war.
At ordinary temperatures- let's say, 22°C - a fully loaded Noratlas is already seriously underpowered.
 Now the hotter the temperature, the longer, and more dangerous, the lift-off, because very hot air degrades both engine power and wing lift.
 By this point, if the Noratlas crew is forced to liftoff fully loaded, and with such temperature, either their risk a crash, or either they light the wingtip jets to help liftoff, even at the expense of range.
in a nutshell: better to have a safe takeoff and a shorter range, rather than risking lives trying to get an overloaded, underpowered aircraft off the ground in a very hot temperature. Same for C-123s in Vietnam.

In fact a lot of very large, very heavy transport aircrafts that were piston-powered got jet pods to help liftoff. It is because turboprops were not ready yet.

When ones compare a Noratlas and a Transall, they are pretty similar in weight and overall dimensions and payload, more or less 10 mt. But their engine power is not the same. A Noratlas had two 2200 hp radials, so 4500 hp. A Transall has a pair of Tyne turboprops, 5500 hp each, total 11 000 hp, nearly three times more. The jet pods were there to help those big piston engine transport at lift-off. Then they vanished for the next generation of transports.
« Last Edit: August 03, 2018, 04:05:37 am by Archibald »
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Online Jemiba

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #31 on: August 03, 2018, 07:58:24 am »
... and nevertheless there were even thoughts about fitting auxiliary jet engines to the good old Trall :
https://www.secretprojects.co.uk/forum/index.php/topic,18205.msg173776.html#msg173776
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Offline Stuka_Hunter

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #32 on: August 03, 2018, 08:20:29 am »
Thx for explaining that with Noratlas. I was already aware of the problems with hot and high operations, but with the B727/JATO in particular.

And if anyone is confused right now, your sight isnt messed up. B727 with JATO instalation did exist.

Offline Archibald

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #33 on: August 03, 2018, 09:52:42 am »
didn't knew about that ! Fair enough... according to many pilots Transall hard hard times flying over Afghanistan theater... their anemic rate of climb was not very reassuring when flying over mountains, and in summer, Kabul and other afghan airports had high temperature and high altitude, and Transalls hated that. The A400M should do a better job.
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Offline charleybarley

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #34 on: September 22, 2018, 01:28:02 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 a while to realize this, I thought you could burn avgas into a jet.

You were right the first time. Gas turbines run on avgas.
 All that is required before allowing it is to run an endurance test (50 hours say) and checking the condition of certain components afterwards (eg fuel control) to make sure there is no unusual wear for example.

I've just read (The Handley Page Victor Vol1, Brooks) that the Victor wing structure was designed for the pressure required to stop avgas boiling at high altitude, ie a possible worse case than turbine fuel that could have occurred with engines cleared to run on avgas.

Offline charleybarley

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #35 on: September 22, 2018, 03:57:03 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.


Apologies for repeating, just seen this. Just to add, some of todays engines are cleared for limited running so they can refuel at remote strips where there is no jet fuel. eg small turboprops and business jets.

Offline charleybarley

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Re: Jet Engine Assisted Takeoff and Mixed Propulsion Differences
« Reply #36 on: September 22, 2018, 04:51:47 pm »
Catapult isn't thrust. it's pull not push.

Chris.


Surely what makes the plane go forwards is known as thrust regardless of where it comes from? (Except when going downhill in which case it's usually called weight)

If we say pushing is from behind and pulling is from in front then the catapult deck shuttle pushes the bridle because the steam pressure comes from behind. The bridle, in turn,  pulls the towing hook from in front. So by these conventions the catapult mechanism has both push and pull to give thrust.

Offline charleybarley

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Re: Jet Engine Assisted Takeoff - Examples
« Reply #37 on: September 22, 2018, 06:03:22 pm »
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

Thrust is what urges the plane forwards and augmentation just means making something bigger. The catapult does exactly that, gives more urge, augments the engine thrust.  Traditionally, for gas turbine engines the term has been used for things within the engine that do that. Therein lies the problem. Using just two words, thrust augmentation, because we all like trying to classify things, doesn't work well. You have pointed this out by using a few extra words to make a better job of communicating what you are actually thinking.

Here's an example of trying to use a definition or classification which touches on Chris' turboramjet 'can o' worms'. Kelly Johnson (in his autobiography Kelly More Than My Share of It All) said the J58 'flew as a ramjet". If he had left it at that, as do most other writers on this subject, we would have been left guessing. We would have comments like 'what definition for ramjet is he using?' 'He must mean it is because of this or because of that' It's up to us to guess or assume. The good news is, unlike other writers, he does go on to tell us why he used the term. 'With no machinery obstructing the airflow...' And it turns out to be incorrect as shown in published information, such as YF12 pilots manual, etc.