Why no tri or quad jet fighters?

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sferrin

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Unread post09 Jun 2018, 21:18

outlaw162 wrote:8 J-85s. :shock: A flight of 4 F-5s.

Sounds like something that never got past the inter-office memo stage. :D


Yep. I think the "engine" had a different designation. Basically 4 J85s pumping air into a common afterburner. And it had 2 of 'em.
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madrat

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Unread post09 Jun 2018, 22:16

sferrin-

Before you clown, why don't you explain why electric drive isn't capable of supplementing another engine to drive the aircraft? And not only does it not have to drive the entire aircraft in all cases electrics can assist at the intake to help an engine's airflow target. You can get ten times the TWR with electric as you do with comparable fuel burners and it's much less ballast when its not being used unless you try to do something impractical like power them the entire flight via batteries.

Anyone can post a meme, but be a man and explain why it's not feasible before DARPA and private industry wastes any more money on it. Not only is it feasible to utilize electric drives, the modeling industry has been doing it for generations at speeds that scale to what is possible with fuel below the sound barrier. The main reason fuel is preferred is because of energy density, which is why only a hybrid that utilizes a fuel-based engine has any practical chance to be cost effective. Nobody said the electric drives have to propel the aircraft to Mach 3, nor be used solely for cruise or even takeoffs. I've only read about electrics being modeled as supplements except for one NASA product, which IIRC is called Maxwell.
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edpop

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Unread post10 Jun 2018, 01:40

According to blurb under photo which didn't come out in scan starting right after the word interceptor"requirement it was capable of speeds in excess of Mach 2.5 and altitudes of 80,000 feet carrying 6 AIM-54 Phoenix missiles".
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nutshell

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Unread post10 Jun 2018, 02:05

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.


I might be wrong, but long story short, electric engines have higher torque than petrol engine. Not thurst-to-weight(which is just "thrust"), since they won't produce any thrust until a fan and a compressor come into play-


If you really meant t:w, than i'd remind you electric engines need batteries. HUGE batteries. Several tens of tons worth of batteries. An electric jet engines would weight as much as a Saturn's satellite.

I wonder if you could come up with something like F1 cars KERS, altho i really have no idea where/how you could recover energy in a fighter plane just to accelerate both the fan and the rest of the compressor.
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Unread post10 Jun 2018, 11:14

You can buy gas turbines with negligible thrust yet have a high torque. What I mentioned was application of the technology. You're simply playing semantics. And, yes, you need power to drive any motor. If you look at the NASA project, the wing propellers at the tips are for propulsion. The other propellers are for low speeds to boost wing lift. At cruise speed the advantage is less drag. Although the motors are still attached, and are essentially ballast, the propellers fold back against their body to act as vanes and create minor drag in comparison to a larger wing. Motor weight is less than structural weight of a larger wing, which is interesting considering how lightweight wings seem to be.
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Unread post10 Jun 2018, 16:28

There is a functioning electric-driven rocket engine called Rutherford. Instead of a gas turbine, it uses a electric motor to drive the pump. It is simple and cheap to make. The drawback is heavy battery packs. The rocket, named Electron, has to jettison spent battery pack during flight to shed weight. And the engine only works for a few minutes.

Electric propulson in aviation is still limited to small experimental planes like the Solar Impulse 2. The state of art is nowhere near practical use.
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sferrin

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Unread post10 Jun 2018, 19:19

madrat wrote:sferrin-

Before you clown, why don't you explain why electric drive isn't capable of supplementing another engine to drive the aircraft?


If you spent more than ten seconds thinking about it, it would be perfectly obvious why fighter aircraft aren't going to be using electricity to drive them through the air anytime soon (if ever). There was even an article in AvWeek a couple months with Airbus laying out why it's not likely to ever happen even with commercial airliners. And we're talking about pure electricity, not using something like a turboelectric system.

And before you start moving goal posts, how about YOU explain how electric motors would make a fighter aircraft fly better than turbofans do.
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juretrn

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Unread post10 Jun 2018, 21:14

I'm not really sure how an "electric turbine" or the like would work - obviously, you won't be going supersonic using propellers - but the fact is, that batteries have nowhere near the energy density of gasoline (or JP-8), and are more dangerous to boot. You really don't to be anywhere near a Tesla sized, or bigger, Li-ion battery when it's on fire. Maybe some new tech can improve on the energy density, but don't count on it any time soon.
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madrat

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Unread post10 Jun 2018, 22:34

Sferrin-
Please be a gentleman, and quote me where I used the words better or implied anywhere electric motors would be the sole propulsion in anything except one NASA project of which I even provided the name. You did get one thing half right about an attempt at moving goalposts, only you accused the wrong prick.
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Unread post11 Jun 2018, 16:54

When a new fighter program comes along the number of engines is not included in the specification. I always see the weight class and performance requirement for the new fighter program but have never seen the number of engines.

For example.
They want it to weigh around 30,000 lbs empty, have a max take off weight of 60,000 lbs, pull 9Gs when at 60% fuel A-A load etc etc.

The contractor then decides if they can pull it off with 1 engine or if 2 is required. Just like the LWF program, GD went with one while McD went with 2.

I think we need to give props to engine manufacturers for always being able to meet the thrust requirement with the minimum number of engines possible.

Orbital launch platform manufacturers however are more complicated. I still wonder why some would opt to use multiple weaker engines instead of fewer bigger motors
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sferrin

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Unread post11 Jun 2018, 17:25

madrat wrote:Sferrin-
Please be a gentleman, and quote me where I used the words better or implied anywhere electric motors would be the sole propulsion in anything except one NASA project of which I even provided the name. You did get one thing half right about an attempt at moving goalposts, only you accused the wrong prick.


You followed up, "I don't see a tri or quad jet fighter serving in anyone's air force anytime soon." posted by FlightDreamz

with:

"No, but its not ridiculous to believe it couldn't happen with electric drives. "

If you can't even follow your own posts, I can't help you.
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nutshell

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Unread post12 Jun 2018, 01:12

sferrin wrote:
And before you start moving goal posts, how about YOU explain how electric motors would make a fighter aircraft fly better than turbofans do.


Acceleration, lower thermal signature and efficiency; at the cost of an afterburner, maybe altitude, weight.

Honestly i dont know, it's the same as theorycrafting anti gravity engines. It's sci fi stuff like Su57 LO or Rafale active stealth.
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Unread post12 Jun 2018, 03:59

Thank you, sferrin, for proving there was a dick involved and he didn't disappoint, goalposts were moved once again in your last post. Then again your reading comprehension ranks right up there with your pleasant attitude.
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Unread post12 Jun 2018, 14:06

edpop wrote:According to blurb under photo which didn't come out in scan starting right after the word interceptor"requirement it was capable of speeds in excess of Mach 2.5 and altitudes of 80,000 feet carrying 6 AIM-54 Phoenix missiles".


Speed in excess of Mach 2.5 at 80,000 feet while carrying 6 Phoenix?

That's really questionable, especially since said Phoenix don't seem to be semi-recessed!
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sferrin

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Unread post12 Jun 2018, 14:22

madrat wrote:Thank you, sferrin, for proving there was a dick involved and he didn't disappoint, goalposts were moved once again in your last post. Then again your reading comprehension ranks right up there with your pleasant attitude.


Hey, don't whine at me. All I did was point out what you said. If you don't like the words I think we both know who's fault that is. (Well, maybe you don't. You don't seem capable of even following what you said.)

I also note you didn't bother to explain how using electricity would make a better fighter engine than a turbofan. Put up or shut up.
Last edited by sferrin on 12 Jun 2018, 14:35, edited 1 time in total.
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