Why no tri or quad jet fighters?

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sferrin

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Unread post17 Jun 2018, 05:31

madrat wrote:Actually, I think people abandoned the thread early due to your immediate commentary that devolved into your continued over-aggressive and irrational tone. I understand just fine that the J57 wasn't suitable to for the high speed performance that was desired by the F-106 or F-110 programs.


So basically you're just going to spew bullshit backed up by zero evidence or sources because "you understand"? Based on your record thus far I doubt you "understand" much at all. I think the word we're looking for here is "poser". Have a nice day.
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Unread post17 Jun 2018, 14:03

It's not like you don't have a track record. You're the same guy that debated canards on keypub declaring they were unsuitable for stealth. Even after people clarified what canards were and how even U.S. manufacturers have all explored canard options - including in stealth and LO designs - you resorted to attacks on IQ. Your unpleasant debate style just wouldn't lend itself to a healthy conversation.
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Unread post17 Jun 2018, 14:48

madrat wrote:It's not like you don't have a track record. You're the same guy that debated canards on keypub declaring they were unsuitable for stealth.


Heh, look at that attempt to divert. :lol:

So.
1. let's hear your rational for why electric motors would make a better fighter engine than a turbofan.

2. What is your source for the J57 being a poor performer at high speed?

Are you going to answer those questions or no?
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Unread post17 Jun 2018, 17:21

1. You continue insisting on a lie. I mentioned electric motors in one paragraph. In the following paragraph I mentioned that another way to create a sustainable multi-engine program was to go for extreme performance with automated maintenance, such as engine swaps. The J85 certainly takes fewer crew members to pull a motor. If you could create smaller motors like that, then automate the upkeep of said motors, you can justify the constant motor swaps. The last Yakovlev STOVL program used lift jets with 20:1 TWR that required swaps each 200 hours. Not 200 flight hours, but 200 running hours. That meant every 100-150 landings they needed a swap. Today's motors are reaching 12:1 TWR in western designs, with run times in several thousands of hours. Your 20:1 motor of 1990 may with newer technology run significantly longer than the Soviet project that only ran around 200 hours. So applying newer technology to a motor than can run 20:1 TWR, requires hot sections swaps no more than every 1,000 hours, requires one crew member to complete engine swaps in less time than one large engine with machine aids, and doesn't cost any more overall would be something that would be worth looking into. Spacing between motors was cited as an advantage of YF-23 over YF-22. Maybe its not four motors that is optimal, maybe it's better with 12-16 micro-motors. We'll never know. I suspect as the size of intake drops the resistance scales upwards decreasing efficiency, and as the length of the intake increases it gets worse under Poiseuille's law. One big motors lends itself to efficiency more than 12-16 smaller ones. Without exploring the notion I wouldn't dismiss the possibility.

2. History long since proved J57 was not suitable for the designs that operated in the speeds. You disagreed, so feel free to disprove. Theoretically a J57 could hit Mach 2 with improved intakes. You insisted the nose needed reshaping, which was not supported. The nose needed to be revised and more than likely it had to do with strengthening, not because it had a poor shape. The link mentioned a revision, not redesign.
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Unread post17 Jun 2018, 21:27

Okay, if we are talking electrically driven compressors for a jet engine, there are a couple of ways that might be useful if everything isn’t swamped by the losses of generating, transmitting, and converting that energy.
One would be that you could have different stages driven at different speeds, which means that the RPMs of each stage could be electronically tuned to the conditions of the engine on the fly. Moreover, you could alternate the rotational direction that each stage turns, which might allow you to eliminate the stators.
Second, you could run a fan completely separate from the engine, which could effectively give you a variable bypass ratio. Heck, you could have pop out fans that are stowed at high speed.
Third, you could run an air breathing rocket engine fed by an electrically driven compressor.
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Unread post17 Jun 2018, 21:29

madrat wrote:1. You continue insisting on a lie. I mentioned electric motors in one paragraph.


There is this thing called "context". Once again, here's the conversation:

"I don't see a tri or quad jet fighter serving in anyone's air force anytime soon.

madrat wrote:No, but its not ridiculous to believe it couldn't happen with electric drives. Unlike fuel-based engines, electric motors have an extreme high thrust to weight.


Obviously the conversation was about MAIN engines, not lift engines, and now rather than admit you were wrong, or that you misunderstood, you're trying to convince everybody that yes, indeed, you MEANT to face-plant in the mud.

madrat wrote:History long since proved J57 was not suitable for the designs that operated in the speeds.


It proved no such thing. You continuing to repeat nonsense does not turn nonsense into fact.

madrat wrote:Theoretically a J57 could hit Mach 2 with improved intakes.


Proving it wasn't the engine that was the week link. Hell it almost hit Mach 2 without the variable intakes and revised external intake shape.

"The fixed C/D nozzle design of the J57-P-55 engines used in prodcution F-101B aircraft were sufficient to raise the thrust from 16,000 lbs. with the P-53 to 16,900 pounds. Taking some measurements from an F-101B, the exhaust velocity for the P-55 engine works out to about Mach 1.3 assuming ideal gas flow. (For reference, the throat diameter is about 32 inches, the exhaust diameter 34 inches to give an Ae/At ratio of about 1.13.) The same basic afterburner nozzle was used in the later versions of the F-8, equipped with J57-P-16 and J57-P-20 engines. The design was relatively heavy and could only be optimized for one set of conditions, but it was robust, effective, and sufficient to get both the F-101 and F-8 out to very close to Mach 2, and this with non-adjustable inlets."

Ron Easley
Aerospace Museum of California
Sacramento, CA

https://www.secretprojects.co.uk/forum/ ... ic=13929.0


madrat wrote:You insisted the nose needed reshaping, which was not supported. The nose needed to be revised and more than likely it had to do with strengthening, not because it had a poor shape. The link mentioned a revision, not redesign.


Semantics, which does not prove your speculation.
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Unread post17 Jun 2018, 21:34

count_to_10 wrote:Okay, if we are talking electrically driven compressors for a jet engine, there are a couple of ways that might be useful if everything isn’t swamped by the losses of generating, transmitting, and converting that energy.
One would be that you could have different stages driven at different speeds, which means that the RPMs of each stage could be electronically tuned to the conditions of the engine on the fly. Moreover, you could alternate the rotational direction that each stage turns, which might allow you to eliminate the stators.
Second, you could run a fan completely separate from the engine, which could effectively give you a variable bypass ratio. Heck, you could have pop out fans that are stowed at high speed.
Third, you could run an air breathing rocket engine fed by an electrically driven compressor.


An electric engine would be AWESOME if it weren't for the nasty problem of power storage. I read somewhere that the F119 taps 20,000hp from the turbine to drive the compressor. That's almost 15 MW. That's a lot of batteries.
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Unread post18 Jun 2018, 00:12

sferrin wrote:
count_to_10 wrote:Okay, if we are talking electrically driven compressors for a jet engine, there are a couple of ways that might be useful if everything isn’t swamped by the losses of generating, transmitting, and converting that energy.
One would be that you could have different stages driven at different speeds, which means that the RPMs of each stage could be electronically tuned to the conditions of the engine on the fly. Moreover, you could alternate the rotational direction that each stage turns, which might allow you to eliminate the stators.
Second, you could run a fan completely separate from the engine, which could effectively give you a variable bypass ratio. Heck, you could have pop out fans that are stowed at high speed.
Third, you could run an air breathing rocket engine fed by an electrically driven compressor.


An electric engine would be AWESOME if it weren't for the nasty problem of power storage. I read somewhere that the F119 taps 20,000hp from the turbine to drive the compressor. That's almost 15 MW. That's a lot of batteries.


I think you'd be much better off with an APU of some variety providing power to the electric motors, basically a gas-electric system that will take advantage of the strengths of electric motors as well as the energy density of hydrocarbon fuels. The critical variable in that arrangement is the efficiency in the generation and transmission process.
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Unread post18 Jun 2018, 01:26

Battery storage was a problem I never shied away from. But you won't eliminate a battery altogether, just minimize it. And you can redirect mechanical energy into electrical energy. I've never suggested electric only and certainly didn't suggest battery storage compared favorably with chemical storage. If you can redirect energy into a lift fan in F-35B, who is to say something cannot be done to redirect energy the same way to augment flight in a scenario where direct thrust from the engine would be more efficient than what it's forward speed would match.

Secondly, look at NASA's Maxwell program. The motors are to decrease wing size by increasing laminar flow over the wing at lower speeds. Chrysler had a nice looking 'car of future' that prominently used ducted fans to zero out drag. You don't always have to increase thrust to dramatically increase performance.
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Unread post18 Jun 2018, 02:49

madrat wrote:<snip> If you can redirect energy into a lift fan in F-35B, who is to say something cannot be done to redirect energy the same way to augment flight in a scenario where direct thrust from the engine would be more efficient than what it's forward speed would match.

<snip>


There is already such a thing called geared turbofan. Any electric drive system handles that amount of power is limited to maritime applications. There are electic drive systems, getting energy from solar-cells or hydrogen-fuelcells, used on long endurance UAVs, can handle relatively low power like a few hundred horsepowers.
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Unread post18 Jun 2018, 14:42

southernphantom wrote:
sferrin wrote:
count_to_10 wrote:Okay, if we are talking electrically driven compressors for a jet engine, there are a couple of ways that might be useful if everything isn’t swamped by the losses of generating, transmitting, and converting that energy.
One would be that you could have different stages driven at different speeds, which means that the RPMs of each stage could be electronically tuned to the conditions of the engine on the fly. Moreover, you could alternate the rotational direction that each stage turns, which might allow you to eliminate the stators.
Second, you could run a fan completely separate from the engine, which could effectively give you a variable bypass ratio. Heck, you could have pop out fans that are stowed at high speed.
Third, you could run an air breathing rocket engine fed by an electrically driven compressor.


An electric engine would be AWESOME if it weren't for the nasty problem of power storage. I read somewhere that the F119 taps 20,000hp from the turbine to drive the compressor. That's almost 15 MW. That's a lot of batteries.


I think you'd be much better off with an APU of some variety providing power to the electric motors, basically a gas-electric system that will take advantage of the strengths of electric motors as well as the energy density of hydrocarbon fuels. The critical variable in that arrangement is the efficiency in the generation and transmission process.



Why go through all the waste though? What does this get you vs a standard turbofan in increased efficiency, thrust to weight, etc.? I've yet to hear an advantages.
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Unread post18 Jun 2018, 14:45

zhangmdev wrote:
madrat wrote:<snip> If you can redirect energy into a lift fan in F-35B, who is to say something cannot be done to redirect energy the same way to augment flight in a scenario where direct thrust from the engine would be more efficient than what it's forward speed would match.

<snip>


There is already such a thing called geared turbofan. Any electric drive system handles that amount of power is limited to maritime applications. There are electic drive systems, getting energy from solar-cells or hydrogen-fuelcells, used on long endurance UAVs, can handle relatively low power like a few hundred horsepowers.


Not to mention the generator to produce the roughly 20 MW it takes to turn the lift fan is going to be heavy as are the windings/magnets around the lift fan etc.. A drive shaft is a HELL of a lot lighter, compact, and efficient. With electric you're converting mechanical to electrical at Point A, transmitting the electrical to Point B, then converting electrical back to mechanical at Point B. Since it's a straight, short shot best to just use a drive shaft.
Last edited by sferrin on 18 Jun 2018, 14:51, edited 1 time in total.
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Unread post18 Jun 2018, 14:48

madrat wrote:who is to say something cannot be done to redirect energy the same way to augment flight in a scenario where direct thrust from the engine would be more efficient than what it's forward speed would match.


Wut?


madrat wrote:Secondly, look at NASA's Maxwell program. The motors are to decrease wing size by increasing laminar flow over the wing at lower speeds. Chrysler had a nice looking 'car of future' that prominently used ducted fans to zero out drag. You don't always have to increase thrust to dramatically increase performance.


A row of props on the wings of a fighter aircraft to "decrease wing size by increasing laminar flow"?
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Unread post18 Jun 2018, 15:04

Guys, please take this to a PM battle. I don't care to see this argument clogging up page after page of a discussion where I was actually able to learn something earlier on.
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Unread post18 Jun 2018, 16:17

Agreed with sprts...
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