Why no tri or quad jet fighters?

New and old developments in aviation technology.
  • Author
  • Message
Offline

michaelemouse

Enthusiast

Enthusiast

  • Posts: 45
  • Joined: 12 Sep 2017, 10:29

Unread post08 Jun 2018, 21:51

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?
Offline

sprstdlyscottsmn

Elite 3K

Elite 3K

  • Posts: 3611
  • Joined: 10 Mar 2006, 01:24
  • Location: Phoenix, Az

Unread post08 Jun 2018, 21:57

$$$$$$$

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.
"Spurts"

-Pilot
-Aerospace Engineer
-Army Medic
-FMS Systems Engineer
Offline

basher54321

Elite 1K

Elite 1K

  • Posts: 1530
  • Joined: 02 Feb 2014, 15:43

Unread post08 Jun 2018, 22:32

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)
Offline

outlaw162

Elite 1K

Elite 1K

  • Posts: 1156
  • Joined: 28 Feb 2008, 02:33

Unread post08 Jun 2018, 23:30

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.)
Offline

wrightwing

Elite 2K

Elite 2K

  • Posts: 2891
  • Joined: 23 Oct 2008, 15:22

Unread post09 Jun 2018, 00:11

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.)
Offline

madrat

Elite 1K

Elite 1K

  • Posts: 1952
  • Joined: 03 Mar 2010, 03:12

Unread post09 Jun 2018, 02:05

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.
Offline
User avatar

FlightDreamz

Forum Veteran

Forum Veteran

  • Posts: 779
  • Joined: 18 Aug 2007, 17:18
  • Location: Long Island, New York

Unread post09 Jun 2018, 05:15

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.
A fighter without a gun . . . is like an airplane without a wing.— Brigadier General Robin Olds, USAF.
Offline

madrat

Elite 1K

Elite 1K

  • Posts: 1952
  • Joined: 03 Mar 2010, 03:12

Unread post09 Jun 2018, 10:00

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.
Offline

outlaw162

Elite 1K

Elite 1K

  • Posts: 1156
  • Joined: 28 Feb 2008, 02:33

Unread post09 Jun 2018, 15:05

the Retaliator,
Attachments
RockwellNAANR-349IMI02_zpsc93dea75.jpg
Offline
User avatar

FlightDreamz

Forum Veteran

Forum Veteran

  • Posts: 779
  • Joined: 18 Aug 2007, 17:18
  • Location: Long Island, New York

Unread post09 Jun 2018, 17:47

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
A fighter without a gun . . . is like an airplane without a wing.— Brigadier General Robin Olds, USAF.
Offline

outlaw162

Elite 1K

Elite 1K

  • Posts: 1156
  • Joined: 28 Feb 2008, 02:33

Unread post09 Jun 2018, 18:07

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.
Offline

sprstdlyscottsmn

Elite 3K

Elite 3K

  • Posts: 3611
  • Joined: 10 Mar 2006, 01:24
  • Location: Phoenix, Az

Unread post09 Jun 2018, 19:28

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
"Spurts"

-Pilot
-Aerospace Engineer
-Army Medic
-FMS Systems Engineer
Offline
User avatar

sferrin

Elite 3K

Elite 3K

  • Posts: 4741
  • Joined: 22 Jul 2005, 03:23

Unread post09 Jun 2018, 20:13

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
"There I was. . ."
Offline
User avatar

sferrin

Elite 3K

Elite 3K

  • Posts: 4741
  • Joined: 22 Jul 2005, 03:23

Unread post09 Jun 2018, 20:29

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
"There I was. . ."
Offline

outlaw162

Elite 1K

Elite 1K

  • Posts: 1156
  • Joined: 28 Feb 2008, 02:33

Unread post09 Jun 2018, 20:55

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

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

Return to Technology

Who is online

Users browsing this forum: No registered users and 3 guests