Why no tri or quad jet fighters?

Unread postPosted: 08 Jun 2018, 21:51
by michaelemouse
Fighters with 2 engines are generally higher performing than single-engined fighters of the same generation. Has anyone tried making fighters with more than 2 jet engines in the last 50 years? Wouldn't more engines allow a large plane with more speed, range, payload, perhaps altitude? Engines do cost a high amount but looking at, say, the F-35, it doesn't seem like adding a second engine would have increased the cost by more than 10% while it would have definitely improved many performance metrics by more than that.



Relatedly, how much can fighters be scaled up? If we compare fighters like the F-15 with the F-22 or the F-16 with the F-35, fighters have been getting bigger and heavier. How much can they be scaled up and at what point would returns on size and weight diminish into the negative? Could 6th generation fighters have 40, 50 ton loaded weight and 50, 60 ton max. takeoff weight?

Re: Why no tri or quad jet fighters?

Unread postPosted: 08 Jun 2018, 21:57
by sprstdlyscottsmn
$$$$$$$

To have a 50 ton aircraft that could pull 9G would be ridiculously expensive to pull off. There is no need for 3 or 4 engine fighters.

Re: Why no tri or quad jet fighters?

Unread postPosted: 08 Jun 2018, 22:32
by basher54321
michaelemouse wrote:Fighters with 2 engines are generally higher performing than single-engined fighters of the same generation. Has anyone tried making fighters with more than 2 jet engines in the last 50 years? Wouldn't more engines allow a large plane with more speed, range, payload, perhaps altitude? Engines do cost a high amount but looking at, say, the F-35, it doesn't seem like adding a second engine would have increased the cost by more than 10% while it would have definitely improved many performance metrics by more than that.



Adding a second engine to F-35 (assuming 2 x F-135s) could be a Rocket ship however for that extra performance could mean having to make the airframe a lot bigger for the extra fuel needed to maintain the required range - which also means your performance gain might not be as expected. If you didn't make the airframe bigger it would have to either carry a lot less fuel or lose space for avionics, weapons etc.

You could also have a higher heat signature to deal with and potentially more issues getting the Radar signature down.

At a basic level performance depends on thrust and lift Vs drag and weight, not the amount of engines and you still want to have some fuel left after the take off run. 8)

Re: Why no tri or quad jet fighters?

Unread postPosted: 08 Jun 2018, 23:30
by outlaw162
North American toyed with the idea of putting a third engine in the nuke bombay tube of the original A-5 Vigilante and proposing it as an interceptor. :shock:

Could be the drawback was the lack of room on the instrument panel for a third set of engine instruments and the extra time on quick reaction alert to start the third engine. :D (just having fun)

(Although the 727 armed with beaucoup slammers might have fit the bill.)

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 00:11
by wrightwing
For a fighter aircraft, there would be no advantage to 3 or 4 engines. It would be too large, to have fighter performance, and too expensive. As for a 2 engine F-35, the performance gains wouldn't outweigh the cost increase. That would add over $20 million to the unit cost (that's just for the engine.)

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 02:05
by madrat
Actually, I believe redundancy is its own reward. Lighter engines that take fewer man hours to maintain would certainly be better. However, front line fighters utilize as few of engines possible because as fighters become heavier and more complex, you have to look for areas to simplify. Your engine efficiency also seems to scale with diameter, which is why one F135 trumps two F414, although they produce similar thrust levels. As F135 matures, the performance gap between the two options will narrow to an insignificant margin. But one engine has been proving with FADEC technology involved to be not significantly less survivable in an emergency. But the man hours saved on one engine versus two will add a significant cost savings.

If the more modern engines are using multiple air streams, then it seems like the one engine is actually multiple types sharing one common core.

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 05:15
by FlightDreamz
Makes little to no sense for a fighter to have more than two engines. More weight, cost, complexity (IE: maintenance) there's just too many downsides to having three (or more) engines in a jet fighter. Any many fighters are going with ONE jet engine these days.
Don't forget Northrop-Grumman/McDonnell-Douglas lost the competition for the Joint Strike Fighter partially due to their lift-plus-lift/cruise engine setup. IE: A forward gas-turbine engine, mounted behind the cockpit, offers vertical lift, while the main power plant provides rear lift and conventional forward thrust. See https://www.flightglobal.com/news/articles/mcdonnell-douglas-loses-jsf-contest-10148/ D.O.D. wanted a single engine to help minimize costs.
I don't see a tri or quad jet fighter serving in anyone's air force anytime soon.

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 10:00
by madrat
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. The most powerful TWR ever installed on a fighter I believe was 20:1 TWR lift jets for the Yak-141 project. Extreme performance in its case require 200 hour swaps, which wouldn't have been exactly constant since the Yak-141 was STOVL like F-35B. But that also meant the majority of the time you carried an extra 1,800 pounds around of ballast.

If jet engines that were 20:1 could be quick-swapped in an automated way, and the costs of the engines was drastically less in comparison, you could also make it work. Aircraft cross section isn't exactly critical, in comparison to the shaping necessary for stealth, otherwise you might just see something have been done before now. The F404 pushes several thousand hours between full overhauls. A smaller engine with 20:1 TWR would require several complete overhauls in the same time period. Your engines would need to be simplified to where robotics did all inspections and parts overhauling. And you'd have to somehow make these magic engines one-quarter of the cost. I don't see that happening with fuel-based engines. And with energy-density being so low in electrics, the only thing you could hope to get in a similar performance ballpark would require hybrid technology, something not mature or even truly demonstrated at jet fighter performance levels.

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 15:05
by outlaw162
the Retaliator,

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 17:47
by FlightDreamz
Madrat 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.

Fair point, I saw somewhere a U.A.V. design D.A.R.P.A. proposed with several engines on the wing - think it was the XV-24A not sure.. See https://www.darpa.mil/news-events/2017-04-04
And Outlaw thanks for posting that pic of the Rockwell Retaliator model. Interesting design (are those AiM-54 Phoenix's on the belly)? Is that the interceptor version of the A-5 Vigilante you mentioned earlier or something else? Cool pic

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 18:07
by outlaw162
Yes, that's the NR-349 proposed IMI version of the A-5.

Range with 3 J-79s in AB and six external AIM-54s would probably just allow for defending of the airfield perimeter. :lol:

edit: BTW I think Convair proposed an interceptor version of the B-58 at one time.

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 19:28
by sprstdlyscottsmn
outlaw162 wrote:
Range with 3 J-79s in AB and six external AIM-54s would probably just allow for defending of the airfield perimeter. :lol:.

At Mach 3. Hahahahah

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 20:13
by sferrin
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.


jiFfM.jpg

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 20:29
by sferrin
outlaw162 wrote:Yes, that's the NR-349 proposed IMI version of the A-5.

Range with 3 J-79s in AB and six external AIM-54s would probably just allow for defending of the airfield perimeter. :lol:

edit: BTW I think Convair proposed an interceptor version of the B-58 at one time.


With 2 J58s.

Northrop N-167 with 4 J79s, N-176 with 8 J85s

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 20:55
by outlaw162
8 J-85s. :shock: A flight of 4 F-5s.

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

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 21:18
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 09 Jun 2018, 22:16
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 01:40
by edpop
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".

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 02:05
by nutshell
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 11:14
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 16:28
by zhangmdev
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 19:19
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 21:14
by juretrn
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 10 Jun 2018, 22:34
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 11 Jun 2018, 16:54
by zero-one
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

Re: Why no tri or quad jet fighters?

Unread postPosted: 11 Jun 2018, 17:25
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 12 Jun 2018, 01:12
by nutshell
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 12 Jun 2018, 03:59
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 12 Jun 2018, 14:06
by mixelflick
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!

Re: Why no tri or quad jet fighters?

Unread postPosted: 12 Jun 2018, 14:22
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 12 Jun 2018, 14:33
by sferrin
nutshell wrote:Acceleration, lower thermal signature and efficiency; at the cost of an afterburner, maybe altitude, weight..


None of those are "how to". Theoretically, if you made the compressor the rotor in an electric motor, that would give you an air supply. Then use electrical heating elements aft of the compressor to heat (expand) your gas stream. For missiles you could even do a Project Pluto but using an electric heating element in place of the nuclear reactor. (Which should be a clue as to why electric fighter engines will never happen.) The problem is even the best theoretical battery weighs WAYYY too much compared to an equivalent energy content of jet fuel. On top of that you keep that greater weight all the way to landing. No getting lighter as fuel burns off. There was an article in AvWeek a month or two ago about why you'll never see electric airliners. You might see some turbo electric applications for propulsion but then that's not what we're talking about. (And no Madrat, turbo electric won't work for propulsion in a fighter aircraft.)

Re: Why no tri or quad jet fighters?

Unread postPosted: 13 Jun 2018, 01:01
by nutshell
sferrin wrote:
nutshell wrote:Acceleration, lower thermal signature and efficiency; at the cost of an afterburner, maybe altitude, weight..


None of those are "how to". Theoretically, if you made the compressor the rotor in an electric motor, that would give you an air supply. Then use electrical heating elements aft of the compressor to heat (expand) your gas stream. For missiles you could even do a Project Pluto but using an electric heating element in place of the nuclear reactor. (Which should be a clue as to why electric fighter engines will never happen.) The problem is even the best theoretical battery weighs WAYYY too much compared to an equivalent energy content of jet fuel. On top of that you keep that greater weight all the way to landing. No getting lighter as fuel burns off. There was an article in AvWeek a month or two ago about why you'll never see electric airliners. You might see some turbo electric applications for propulsion but then that's not what we're talking about. (And no Madrat, turbo electric won't work for propulsion in a fighter aircraft.)


Yup absolutely not doable.

We can barely make an electric car, let alone a fighter.
I can forsee an ERS in the near future tho.

Re: Why no tri or quad jet fighters?

Unread postPosted: 13 Jun 2018, 21:20
by botsing
Once wireless energy transfer gets efficient enough it will enable a whole new generation of drones with electric engines, airtime would be virtually limitless and with electric engines being relatively simple it will drop maintenance costs as well.

A carrier strike group could use a continuous high flying sensor platform for over the horizon visibility while it's refueling drones could carry more fuel for a longer period of time thereby increasing availability.

Just last year the first continuous maser at room temperature was developed, so there seems to be quite a revolution on the horizon for wireless energy transfer and it's many applications.

Re: Why no tri or quad jet fighters?

Unread postPosted: 13 Jun 2018, 23:00
by collimatrix
michaelemouse wrote:Fighters with 2 engines are generally higher performing than single-engined fighters of the same generation. Has anyone tried making fighters with more than 2 jet engines in the last 50 years? Wouldn't more engines allow a large plane with more speed, range, payload, perhaps altitude? Engines do cost a high amount but looking at, say, the F-35, it doesn't seem like adding a second engine would have increased the cost by more than 10% while it would have definitely improved many performance metrics by more than that.



Relatedly, how much can fighters be scaled up? If we compare fighters like the F-15 with the F-22 or the F-16 with the F-35, fighters have been getting bigger and heavier. How much can they be scaled up and at what point would returns on size and weight diminish into the negative? Could 6th generation fighters have 40, 50 ton loaded weight and 50, 60 ton max. takeoff weight?



Back up a bit, what do you mean by "higher performance?"

If you mean that twin-engine fighters can generally fly faster, then, yes, I agree. If you mean that twin-engine fighters can generally fly further, then, yes, I agree. If you mean that twin-engine fighters generally have better instantaneous and sustained turn rates, then, no, I disagree.

The reason why the above is true has to do with scaling. Imagine that you can just freely scale an aircraft up or down in size. We'll ignore the fact that real engineering doesn't work this way at all, just imagine you could. The entire plane, wings, fuselage, engine are all enlarged or shrunk by some linear factor.

The top level speed of an aircraft is the speed at which the force of drag (which increases with airspeed) matches the force of thrust provided by the engine. Since the forces are equal and in opposite directions, they cancel out and the aircraft cannot accelerate anymore.

What happens if we take a fighter and scale it up? The force of drag is a product of the coefficient of drag (at a given airspeed) and the frontal area of the aircraft. The coefficient of drag is a function of the shape of the aircraft, and we're just scaling the plane up, so the drag coefficient stays exactly the same. So the zero lift drag at any airspeed will increase proportionally to the frontal area of the aircraft, which is a square function of how much the aircraft was scaled up.

But the thrust isn't going to scale like that. Just scaling up the engine and maintaining power density (note: this is not a responsible way to design gas turbines outside of thought experiments) will mean that the thrust the fighter has will increase as a cube function of the scaling factor. Cubes increase faster than squares. Therefore, all else being equal, a bigger fighter is a faster fighter.

But this is a pretty ridiculous level of simplification. You don't just scale planes up and down. For one thing, even if the plane is being scaled up and down, the pilot stays the same size. And it follows that the ejection seat, and the cockpit, and the canopy, and the life support system and everything else that has to do with the pilot ought to stay the same size too. And since we're talking fighters, there are a bunch of other combat systems to consider. A jammer that can protect a seven ton fighter isn't really significantly lighter than the jammer required to protect a twelve ton fighter. A gun that's deemed adequate to kill enemy fighters and strafe ground targets for a seven ton fighter is likewise still adequate on a twelve ton fighter. The navigation, IFF, and a bunch of other avionics don't really need to be scaled up either. So if we make a bigger fighter, there's going to be a lot of weight left over, proportionally speaking, because not everything needed to be scaled up with the airframe.

That means that larger aircraft have more available weight for fuel storage. Therefore, all else being equal, a bigger fighter is a longer ranged fighter.

But what about maneuverability? This is where things stop favoring the heavier aircraft. The amount of Gs an aircraft can pull is a function of its maximum lift divided by its mass. Assuming uniform density as an aircraft is scaled up, the lift will increase as a square function of the scaling factor, since lift is wing area times lift coefficient times a bunch of other garbage. But, assuming uniform density, the mass of the aircraft will go up as a cubic factor. Therefore, all else being equal, a bigger fighter is a less maneuverable fighter.

The performance advantages you're noticing for twin engined fighters aren't a function of them having two engines, they're inherent advantages of larger aircraft. But there are scaling effects that favor big fighters, and there are also ones that hurt them. If a fighter were so large that it required three engines, it would suffer badly in the maneuverability department, and probably have other practical problems as well such as high landing speed.

Now, that said, there are some twin-engine fighters that aren't huge. The F-5 is quite small, for instance. The biggest advantage of having two engines on a small fighter is survivability. If one engine fails or gets shot, the other can keep operating and the fighter can limp back to base. At least, that is, if the engineers did their job right and the firewall that prevents disaster from spreading from one engine to another is up to the task. This argument was especially compelling in the bad old days when jet fighter engines weren't anywhere near as reliable as they are now. The loss rates heavily favored twins.

But that argument only favors twins. A fighter with three engines isn't really any more survivable than a fighter with two engines. If a fighter loses an engine, a single-engine fighter becomes a glider, a twin ceases to be a fighter but can at least still fly back to somewhere safe and a three engine fighter... is in exactly the same situation as the twin. A three engine fighter will have more of its total thrust available if it loses an engine, but no fighter is going to try to fight on two thirds of its design power. It's all the additional cost of another engine, but for no real additional benefit.

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 03:10
by madrat
The big advantage to electric motor technology is it's extreme lightweight for its high torque potential. I did earlier oversimplify it as thrust to weight. While a battery is a horrible weight penalty, it probably is somewhat necessary to stabilize the electric flow through the circuit, making regulation of the current simpler. The bigger picture is that you can rapidly convert electricity into kinetic energy. They may not have the endurance, but don't ever underestimate the benefit of enjoying an advantage to quickly utilize stored energy. You have a very short term anaerobic energy system in the body that makes it possible to lift things that would not be attainable through the glycolic or Kreb,'s cycle. Sferrin, you're mind is stuck in the past. Not only is electric motors perfectly possible for propulsion, they are simpler to engineer in projects such as the NASA project I mentioned earlier. I wouldn't dismiss the idea that other vehicles such as helicopters wouldn't begin to augment their lift and propulsion via electric motors where they could certainly increase control ability of the aircraft while decreasing main rotor drag and all the downside to a large rotor.

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 13:09
by sferrin
botsing wrote:Once wireless energy transfer gets efficient enough it will enable a whole new generation of drones with electric engines, airtime would be virtually limitless and with electric engines being relatively simple it will drop maintenance costs as well.

A carrier strike group could use a continuous high flying sensor platform for over the horizon visibility while it's refueling drones could carry more fuel for a longer period of time thereby increasing availability.

Just last year the first continuous maser at room temperature was developed, so there seems to be quite a revolution on the horizon for wireless energy transfer and it's many applications.


I'm skeptical that this will ever be a thing. Too many down sides.

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 13:11
by sferrin
madrat wrote: Sferrin, you're mind is stuck in the past. Not only is electric motors perfectly possible for propulsion, they are simpler to engineer in projects such as the NASA project I mentioned earlier. I wouldn't dismiss the idea that other vehicles such as helicopters wouldn't begin to augment their lift and propulsion via electric motors where they could certainly increase control ability of the aircraft while decreasing main rotor drag and all the downside to a large rotor.


Except we're not talking about helicopters, we're specifically taking about fighters (you know, the title of the thread). Now tell us, specifically, why and how electric motors would make better fighter engines than turbofans, AS YOU CLAIMED. Go!

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 13:18
by sferrin
collimatrix wrote:Back up a bit, what do you mean by "higher performance?"

If you mean that twin-engine fighters can generally fly faster, then, yes, I agree. If you mean that twin-engine fighters can generally fly further, then, yes, I agree.


This is more a function of design than some inherent physical law. The F-15 and F-14 were designed to carry a big radar and lots of weapons high, fast and a long distance. That took a lot of power which meant two engines. I doubt anybody would argue that the F-104, F-106 weren't fast and had excellent altitude capability. And the F-106 had good range as well. Swap out the J75 for an F119 in the F-106 and that would have been a BEAST. Swap out the radar for an APG-79 and the Falcons and Genie for AIM-120s- carried internally.

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 14:48
by michaelemouse
collimatrix,

Thanks for the great response. How would the square-cube law apply to flight ceiling? If you scaled up a fighter in the way you described, would it be able to fly higher? I suspect it would but I'm wondering about the missing link in the causal chain from: larger volume to surface ratio to higher ceiling.

The SR-71 wasn't a fighter but gives us an example of what could be achieved in the 60s if you wanted an air-breathing aircraft to fly as fast and high as possible. Could a large fighter fly at 30km altitude today? At Mach 4+?

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 16:15
by sferrin
michaelemouse wrote:collimatrix,

Thanks for the great response. How would the square-cube law apply to flight ceiling? If you scaled up a fighter in the way you described, would it be able to fly higher? I suspect it would but I'm wondering about the missing link in the causal chain from: larger volume to surface ratio to higher ceiling.

The SR-71 wasn't a fighter but gives us an example of what could be achieved in the 60s if you wanted an air-breathing aircraft to fly as fast and high as possible. Could a large fighter fly at 30km altitude today? At Mach 4+?


Always thought the original configuration of RASCAL made into a fighter would be awesome. 4 F100s modified with pre-compressor cooling to the degree the engines operated at 100,000 feet as if they were at sea-level. Mach 4. Zoom capability to 200,000 feet. Was roughly fighter sized (XF-108 / B-58-ish).

rascal03.jpg


http://stargazer2006.online.fr/space/pages/rascal.htm



"The Rascal design comprises a high-speed, high-altitude aircraft carrying a two-stage expendable rocket capable of boosting a 150kg (330lb) satellite into low-Earth orbit (LEO). The aircraft, which is designed by Scaled Composites, is powered by four turbojets incorporating mass injection pre-compressor cooling (MIPCC).

This injects liquid oxygen and water into the inlet to cool the compressor and increase massflow, allowing operation to higher speeds and altitudes.

The MPICC turbojets, based on Pratt & Whitney's F100 fighter engine, enable the aircraft to take off conventionally, accelerate to beyond Mach 3 then "zoom climb" to above 200,000ft (61,000m) - essentially outside the atmosphere - to deploy the expendable upper stage from its payload bay, before returning to a runway landing"


Okay, probably not fighter material. :cry:

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 21:20
by collimatrix
sferrin wrote:
This is more a function of design than some inherent physical law. The F-15 and F-14 were designed to carry a big radar and lots of weapons high, fast and a long distance. That took a lot of power which meant two engines. I doubt anybody would argue that the F-104, F-106 weren't fast and had excellent altitude capability. And the F-106 had good range as well. Swap out the J75 for an F119 in the F-106 and that would have been a BEAST. Swap out the radar for an APG-79 and the Falcons and Genie for AIM-120s- carried internally.


The designers weren't slaves to scaling laws, but you can still see them tangling with them in the designs. The F-15 has those proportionally enormous bat wings; they're much bigger relative to the size of the airframe than the wings on the F-16. They're like that, in part, because of square/cube scaling. Another reason is that the F-15 is conventionally stable and therefore requires larger control surfaces generally.

The F-14 is swing-wing, which means that with the wings forward it has a better lift slope than its wing loading would suggest. However, it also has the big pancake to help generate lift at high speeds. Again, heavy fighters need help getting lift from somewhere.

The F-104 is fast, kind of (a lot of those earlier jets' top speeds are theoretical as they were actually fuel-limited), but you can see that it has incredibly tiny wings to minimize drag, while the Phantom had more or less the same top speed and was more sanely proportioned. Also, the F-104 had a very austere avionics compliment compared to the Phantom, and quite a lot less range. And these aircraft used variant of the same engine, so comparing them is going to be about as apples-to-apples as real world comparisons are going to get.

Delta-winged fighters like the F-106 usually have above-average range for a reason that isn't square/cube scaling, but is related to it. Delta wings have very long chord length, so for a given chord length to chord thickness ratio (which informs the transonic characteristics of the wing), a delta wing will have absolutely much more chord thickness. This means that delta wings have a better volume to surface area ratio than swept wings or straight wings, which means that they make better fuel tanks than swept wings or straight wings and lead to an aircraft with higher fuel fraction and therefore better range.

michaelemouse wrote:collimatrix,

Thanks for the great response. How would the square-cube law apply to flight ceiling? If you scaled up a fighter in the way you described, would it be able to fly higher? I suspect it would but I'm wondering about the missing link in the causal chain from: larger volume to surface ratio to higher ceiling.

The SR-71 wasn't a fighter but gives us an example of what could be achieved in the 60s if you wanted an air-breathing aircraft to fly as fast and high as possible. Could a large fighter fly at 30km altitude today? At Mach 4+?


I think these days flight ceiling is less a function of lift generation, and more a function of keeping the engines from choking and keeping the pilot alive. So it isn't informed very much by the size of the aircraft.

If you want a plane that's able to fly to high altitude and actually fight up there as well, I think that plane looks a hell of a lot like a Raptor. Huge wings to provide decent lift even in high, thin air, engines with a very low bypass ratio usually work better at altitude, and thrust vectoring to give a little bit of additional control authority.

Re: Why no tri or quad jet fighters?

Unread postPosted: 14 Jun 2018, 23:06
by basher54321
Beside the point but clearly some profiles where the F-4 was the one lacking in range.

Carrying one bomb (guess what kind) with 4 tanks an F-104 will go about half again as far as an F-4 on a Low-Low-Low sortie. And it will do it faster, too.

http://www.916-starfighter.de/Ruminatio ... 0F-104.htm



Although true for a lot of aircraft I remember reading about the Norweigans developing or practising a Mach 2 F-104G intercept profile for intercepting very high altitude targets - will need to find the ref.

Re: Why no tri or quad jet fighters?

Unread postPosted: 15 Jun 2018, 06:45
by sferrin
basher54321 wrote:Beside the point but clearly some profiles where the F-4 was the one lacking in range.

Carrying one bomb (guess what kind) with 4 tanks an F-104 will go about half again as far as an F-4 on a Low-Low-Low sortie. And it will do it faster, too.

http://www.916-starfighter.de/Ruminatio ... 0F-104.htm



Although true for a lot of aircraft I remember reading about the Norweigans developing or practising a Mach 2 F-104G intercept profile for intercepting very high altitude targets - will need to find the ref.


Here's an F-104 launching a Genie from Mach 1.7 and 56,000 feet:



Then there are stories of cruise in min afterburner at Mach 2 and 73,000 feet, doing gun attacks on U-2s at altitude, etc.

Re: Why no tri or quad jet fighters?

Unread postPosted: 15 Jun 2018, 20:34
by basher54321
Great video that :beer:


The Norway intercepts are here http://www.starfighter.no/hi-alt.html - will stick in the F-104 thread as there is one.

Re: Why no tri or quad jet fighters?

Unread postPosted: 15 Jun 2018, 21:39
by madrat
The F-101 was probably the most comparable to F-106. The F-101 did out distance the F-106 nearly as much as F-106 clearly had more top end speed. The frontal area of the two is similar. The J57 didn't have near the high speed performance and probably explains a large amount of the speed difference. Both were about the same length. The F-101 did carry a bigger internal fuel load so no doubt that contributes to the range difference. So two similarly powered jet fighters with drastically different results by design.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 00:57
by sferrin
madrat wrote:The F-101 was probably the most comparable to F-106. The F-101 did out distance the F-106 nearly as much as F-106 clearly had more top end speed. The frontal area of the two is similar. The J57 didn't have near the high speed performance and probably explains a large amount of the speed difference. Both were about the same length. The F-101 did carry a bigger internal fuel load so no doubt that contributes to the range difference. So two similarly powered jet fighters with drastically different results by design.


The F-101 had about 38% more power than the F-106 (33,800lbs thrust vs 24,500lbs), not to mention the F-106 was a WAY cleaner design. (Weapons carried internally instead of semi-recessed in the case of the F-101. and never mind the huge aerodynamic difference of the airframes.) As for frontal area:

Untitled-1.jpg


The F-101's lower speed had less to do with the J57s high speed performance and more to do with the fact that, compared to the F-106, it had the aerodynamics of a brick.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 02:35
by madrat
It's awkward having a stalker.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 13:19
by basher54321
He is pretty much right though the idea that the J-57 itself was some how a top speed limiting factor is a new one on me.

See the last paragraph here - includes inlet and ramp changes that would let the J-57 produce more thrust at high Mach.


F-101B.JPG

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 14:16
by sferrin
madrat wrote:It's awkward having a stalker.


Don't flatter yourself. I responded to your asinine claim (that electric motors could replace turbofans in fighters).

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.


You desperately avoided justifying your claim and here we are.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 15:47
by madrat
The fact you continue to harp on a lie is overly aggressive. Grow up. Never said replace, nor did I say use as the sole motor. Keep pushing that lie. You're obviously following up my posts with an agenda and not with an actual argument. Rather, you're trolling for some kind of response.

Btw - basher64321 actually is arguing we are both wrong. His contention is that J57 wasn't responsible for the speed limitations, nor that F-101 was a flying brick. He posted an argument that demonstrated with changes to the intake it could reach Mach 2.1, which is much less different than the F-106 performance. His argument still comes up short on the argument the J57 has the ability to perform relative to the J75 at high speed. I'm not convinced, but at least he's arguing from a factual basis.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 16:20
by sferrin
madrat wrote:The fact you continue to harp on a lie is overly aggressive. Grow up. Never said replace, nor did I say use as the sole motor. Keep pushing that lie. You're obviously following up my posts with an agenda and not with an actual argument. Rather, you're trolling for some kind of response.


Your own words tell a different story. I've quoted them several times.

madrat wrote:Btw - basher64321 actually is arguing we are both wrong. His contention is that J57 wasn't responsible for the speed limitations, nor that F-101 was a flying brick.


Uh YOU'RE the one that stated the J57 was the problem. And the fact that both the intakes would need to be completely changed AND that the nose would need to be changed supports my statement re. F-101 and bricks.

madrat wrote:He posted an argument that demonstrated with changes to the intake it could reach Mach 2.1, which is much less different than the F-106 performance.


Intake and NOSE, ie aerodynamics.

madrat wrote:His argument still comes up short on the argument the J57 has the ability to perform relative to the J75 at high speed. I'm not convinced, but at least he's arguing from a factual basis.


Where is your evidence to support your claim the J57 lacked high speed ability?

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 17:31
by madrat
The nose in the F-101 wasn't designed for the speed, but there is no evidence that its shape was the issue.

Care to name the J57 equipped production fighter that actually flew the top speeds flown by production F-101? The J75 wasn't a fresh design, it was a successor to J57. Surely you're trying to make an argument that wouldn't quite fit history. We know what the redesigned F-101 became; the F-110 Spectre.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 19:06
by basher54321
madrat wrote:Btw - basher64321 actually is arguing we are both wrong. His contention is that J57 wasn't responsible for the speed limitations, nor that F-101 was a flying brick. He posted an argument that demonstrated with changes to the intake it could reach Mach 2.1, which is much less different than the F-106 performance. His argument still comes up short on the argument the J57 has the ability to perform relative to the J75 at high speed. I'm not convinced, but at least he's arguing from a factual basis.


hmm just posting something that shows exactly what it would take to alter the F-101 to get it to M2.1.

The document proves that the F-101 was speed limited by the fact it did not have the thrust to over come the drag of its airframe thus this was the only speed limit nothing else. (it simply had a lower T/D than the F-106)


So to get to M2.1 they:
1. Increased thrust by altering the airframe inlet/ramps to allow an airflow that will let the J-57 put out more thrust at high Mach.

2. Altered the nose - not known although drag reduction would seem logical.

There is no requirement to swap the engine so the J-57 very likley good for M2.1.

sferrin stated the twin J-57s were already putting out more thrust at top speed than the single J-75 because it has a 38% higher static SL thrust. Don't have the thrust curves to prove it but I don't think it is unreasonable to think that they are and if so that would make the F-101 airframe far more draggy than the F-106s.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 20:54
by madrat
Not many airframes were as optimized for low drag flight as the F-106. But it is reasonable to assume the J75, built on what they learned from J57, was optimized for the very flight regime it was used in the F-106. The F-101 had very good high altitude performance, it just didn't have the sustained thrust at high speeds. I simply demonstrated a single engine design against a twin engine design where the twin actually was under-performing compared to the single in speed, but it certainly had a higher fuel fraction so it outranged the single. I'm pretty sure this parallels the argument collimatrix made earlier that a single engine doesn't mean lesser performing. In this demonstration the aircraft were roughly the same length and similar eras. However, the twin's advantage- even with a large margin of extra thrust - was no indicator it would win in performance.

Re: Why no tri or quad jet fighters?

Unread postPosted: 16 Jun 2018, 23:51
by f-16adf
For information concerning the F-106, you guys need to have a look at Bruce Gordon's Youtube page.
https://www.youtube.com/watch?v=8FQxKkJOvHY

He flew the Six back when Century Series jets ruled the sky. Also, it seems that the 106 not only has a smaller frontal cross section than the 101, its fuselage also appears more finely area ruled (I believe).


We need to have Gums chime in about the 101. :D

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 01:29
by sferrin
madrat wrote:The nose in the F-101 wasn't designed for the speed, but there is no evidence that its shape was the issue.


You mean other than the fact that to go faster they would have needed to change it?
madrat wrote:Care to name the J57 equipped production fighter that actually flew the top speeds flown by production F-101?


So no source for your claim. Well, nobody is more shocked than I. :roll:

madrat wrote:The J75 wasn't a fresh design, it was a successor to J57.


And? So what? We're talking about the J57 and it's supposed lack of high speed capability.

madrat wrote: Surely you're trying to make an argument that wouldn't quite fit history. We know what the redesigned F-101 became; the F-110 Spectre.


Well I don't know what YOU know but the rest of us know the F-4 as being a descendant of the F3H-G, which descends from the F3H Demon NOT the F-101.

Capture.JPG


Copy of F3H-GH Brickman.jpg


F3H-GHmockupatMcDonnell-2.jpg


McDonnell_F3H-G_mockup_in_1954.jpg

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 01:35
by sferrin
madrat wrote:But it is reasonable to assume the J75, built on what they learned from J57, was optimized for the very flight regime it was used in the F-106.


That would explain why it was used in the U-2, the SeaMaster (that's a flying boat), 707, and DC-8.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 03:59
by madrat
sferrin wrote:
madrat wrote:But it is reasonable to assume the J75, built on what they learned from J57, was optimized for the very flight regime it was used in the F-106.


That would explain why it was used in the U-2, the SeaMaster (that's a flying boat), 707, and DC-8.


Early U-2 variants were powered by Pratt & Whitney J57 turbojet engines. The U-2C and TR-1A variants used the more powerful Pratt & Whitney J75 turbojet. The U-2S and TU-2S variants incorporated the even more powerful General Electric F118 turbofan engine. So what are you trying to say about the U-2? I'm pretty sure I've read the fuel was more difficult to choose than the engine. And you realize an F-101 was taken to 100,000 feet? Sometimes I just don't get your point you're attempting to make. That's the thing with trolls, they don't often seem to make sense.

The F-101 was a fighter armed with internal Falcon & Genie missiles. The F3H was a Sparrow equipped fighter. Sure looks like the McDonnell team put a little of both into the F-110A Spectre design.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 04:52
by sferrin
madrat wrote:
sferrin wrote:
madrat wrote:But it is reasonable to assume the J75, built on what they learned from J57, was optimized for the very flight regime it was used in the F-106.


That would explain why it was used in the U-2, the SeaMaster (that's a flying boat), 707, and DC-8.


Early U-2 variants were powered by Pratt & Whitney J57 turbojet engines. The U-2C and TR-1A variants used the more powerful Pratt & Whitney J75 turbojet. The U-2S and TU-2S variants incorporated the even more powerful General Electric F118 turbofan engine. So what are you trying to say about the U-2? I'm pretty sure I've read the fuel was more difficult to choose than the engine. And you realize an F-101 was taken to 100,000 feet? Sometimes I just don't get your point you're attempting to make. That's the thing with trolls, they don't often seem to make sense.



I'm 100% certain you're the only one who doesn't understand. So where is your evidence that the J57 had poor performance at high speed? Sources please.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 05:11
by madrat
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. J57 certainly had few issues in the scope it was utilized.

You certainly just want me to say I was wrong and you were correct. It's not going to happen. It's unnecessary considering the lack of honesty if I did. And I quite frankly don't want to encourage your poor behavior.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 05:31
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 14:03
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 14:48
by sferrin
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?

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 17:21
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 21:27
by count_to_10
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 21:29
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 17 Jun 2018, 21:34
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 00:12
by southernphantom
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 01:26
by madrat
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 02:49
by zhangmdev
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 14:42
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 14:45
by sferrin
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 14:48
by sferrin
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"?

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 15:04
by sprstdlyscottsmn
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.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 16:17
by juretrn
Agreed with sprts...

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 16:40
by botsing
Agreed with sprstdlyscottsmn indeed.

Re: Why no tri or quad jet fighters?

Unread postPosted: 18 Jun 2018, 17:12
by sferrin
Sorry guys. I've blocked him so that should be that.

Re: Why no tri or quad jet fighters?

Unread postPosted: 19 Jun 2018, 02:04
by madrat
Wow, the guy that went over dramatic has now saved the day by blocking his victim. Yay. /sardonic tone

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 13:00
by count_to_10
sferrin wrote: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.

As I wrote earlier, there are some interesting things you could do with the ability to independently set the RPMs of each stage or physically disconnect a compressor from any turbine. It would take considerable study to work out if the electrical losses would be worth it. Maybe TEG could give us an idea if it’s feasible, but I don’t think the rest of us can dismiss the idea out of hand with any credibility.

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 15:03
by sferrin
count_to_10 wrote:
sferrin wrote: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.

As I wrote earlier, there are some interesting things you could do with the ability to independently set the RPMs of each stage or physically disconnect a compressor from any turbine. It would take considerable study to work out if the electrical losses would be worth it. Maybe TEG could give us an idea if it’s feasible, but I don’t think the rest of us can dismiss the idea out of hand with any credibility.


There are two different issues. One is would an electric turbofan have advantages over a JP-4 powered engine. (Setting aside the energy source for the moment.) Sure, there are a lot. The problem is an electric turbofan doesn't exist without a source of electricity and that's where it all falls apart. There is no kind of battery, real or theoretical, that has the energy density of jet fuel. It's not even close.

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 17:38
by sprstdlyscottsmn
sferrin wrote:
count_to_10 wrote:
sferrin wrote: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.

As I wrote earlier, there are some interesting things you could do with the ability to independently set the RPMs of each stage or physically disconnect a compressor from any turbine. It would take considerable study to work out if the electrical losses would be worth it. Maybe TEG could give us an idea if it’s feasible, but I don’t think the rest of us can dismiss the idea out of hand with any credibility.


There are two different issues. One is would an electric turbofan have advantages over a JP-4 powered engine. (Setting aside the energy source for the moment.) Sure, there are a lot. The problem is an electric turbofan doesn't exist without a source of electricity and that's where it all falls apart. There is no kind of battery, real or theoretical, that has the energy density of jet fuel. It's not even close.

I think you may be missing something, or I am. As I understand it Count to 10 isn't saying to get rid of the jet engine or jet fuel, just the mechanical linkage between the turbine and the Compressor. There would be losses in converting turbine power to electrical and back to compressor, but Ct10 is wondering if it might be worth it to have "customized" RPMs in the compressor state. Much like how a super charger may take 100hp to tun but it is providing 300hp net gain. It's not a FREE lunch, but it is a bigger lunch.

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 18:01
by botsing
count_to_10 wrote: Maybe TEG could give us an idea if it’s feasible, but I don’t think the rest of us can dismiss the idea out of hand with any credibility.

I agree, we should be prudent with basing any conclusions on the limited dataset we have.

sferrin wrote:The problem is an electric turbofan doesn't exist without a source of electricity and that's where it all falls apart. There is no kind of battery, real or theoretical, that has the energy density of jet fuel. It's not even close.

Lithium–air batteries already have a theoretical specific energy very close to that of jet fuel:

* Specific energy of Lithium–air battery: https://en.wikipedia.org/wiki/Lithium%E ... ir_battery (43.2 MJ/kg)
* Typical energy content of Aviation Fuel: https://www.cgabusinessdesk.com/documen ... review.pdf (~43.54 MJ/kg)

However, significant advances in science are needed to be able to reach those theoretical limits (for both batteries and liquid fuels).

Another advantage of electric engines is that directed energy can give them a (limited) wireless fuel line.

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 19:03
by sferrin
botsing wrote:
count_to_10 wrote: Maybe TEG could give us an idea if it’s feasible, but I don’t think the rest of us can dismiss the idea out of hand with any credibility.

I agree, we should be prudent with basing any conclusions on the limited dataset we have.

sferrin wrote:The problem is an electric turbofan doesn't exist without a source of electricity and that's where it all falls apart. There is no kind of battery, real or theoretical, that has the energy density of jet fuel. It's not even close.

Lithium–air batteries already have a theoretical specific energy very close to that of jet fuel:

* Specific energy of Lithium–air battery: https://en.wikipedia.org/wiki/Lithium%E ... ir_battery (43.2 MJ/kg)
* Typical energy content of Aviation Fuel: https://www.cgabusinessdesk.com/documen ... review.pdf (~43.54 MJ/kg)

However, significant advances in science are needed to be able to reach those theoretical limits (for both batteries and liquid fuels).

Another advantage of electric engines is that directed energy can give them a (limited) wireless fuel line.


I'll see if I can dig up the AvWeek article discussing this. It was within the last couple months if anybody else wants to look. Airbus said it would take something like 340 tons of batteries for an A320 or somesuch. You also have the disadvantage that the batteries don't get lighter as the flight progresses.

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 19:27
by sferrin
sprstdlyscottsmn wrote:I think you may be missing something, or I am. As I understand it Count to 10 isn't saying to get rid of the jet engine or jet fuel, just the mechanical linkage between the turbine and the Compressor. There would be losses in converting turbine power to electrical and back to compressor, but Ct10 is wondering if it might be worth it to have "customized" RPMs in the compressor state. Much like how a super charger may take 100hp to tun but it is providing 300hp net gain. It's not a FREE lunch, but it is a bigger lunch.



I did miss that. 3-shaft engines were an attempt to accomplish some of that but they don't seem to have caught on. Most are still 2-shaft. Now if there were such a thing as room-temperature super conductors. . .

Re: Why no tri or quad jet fighters?

Unread postPosted: 21 Jun 2018, 22:21
by count_to_10
sprstdlyscottsmn wrote:I think you may be missing something, or I am. As I understand it Count to 10 isn't saying to get rid of the jet engine or jet fuel, just the mechanical linkage between the turbine and the Compressor. There would be losses in converting turbine power to electrical and back to compressor, but Ct10 is wondering if it might be worth it to have "customized" RPMs in the compressor state. Much like how a super charger may take 100hp to tun but it is providing 300hp net gain. It's not a FREE lunch, but it is a bigger lunch.

That’s it exactly. You might have some battery storage to raven things out, but otherwise the electrical energy should be generated by a turbine as fast as it is being used up in the fan/compressor. It all comes down to how efficient the electrical system can be made, and yes, room temperature superconductors would help that a lot.
Also, you might only disconnect the “outer” stages, leaving a core compressor and turbine system that share a shaft.