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Some countries (e.g. Russia) develop fighter aircraft (e.g. Sukhoi) with 2 engines.

Is it for maneuverability, or is it because they can't build an engine that would meet the power requirement?

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  • $\begingroup$ Russia and sukhoi jets $\endgroup$ – kcihtrak May 3 '17 at 18:25
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    $\begingroup$ Also, not all Russian fighters have two engines: MiG-21/23/27, SU-17 (to name a few) have a single engine. $\endgroup$ – DeepSpace May 4 '17 at 11:27
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    $\begingroup$ The edit that added examples (#3) feels weird - it implies that Russian Sukhois are somewhat unusual in their twin engine configuration, which is not true. $\endgroup$ – el.pescado Aug 2 '18 at 8:54
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Taking the Sukhoi Su-35 for example, it has two engines, each capable of producing 86.3 kN of dry thrust, combined they produce 172.6 kN. With afterburner they produce 284 kN (142 kN each).

The jet engine on the American F-22 produces 156 kN with afterburner, close to the 142 kN of the Su-35.

Soviet Union / Russia made the Kuznetsov NK-32 military jet engine, capable of 137 kN (dry) and 245 kN (wet).

So, the ability or technology to make a powerful jet engine is not the reason. It's just powerful engines are much bigger.

The main reasons for selecting a twin engine design are:

  • Slimmer design, two smaller engines make for a slimmer profile than one big engine.
  • Redundancy, in case one fails, especially important for big fighters.
  • Afterburners are easier to make for smaller diameter engines.
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  • $\begingroup$ I believe 180kN out of al-41 is with afterburner. $\endgroup$ – user3528438 May 3 '17 at 18:54
  • $\begingroup$ @user3528438 - added diff engine, thanks for noticing, clear comment? $\endgroup$ – ymb1 May 3 '17 at 19:09
  • $\begingroup$ NK32 has a bypass of 1.4 and AL31 has it 0.59 that pretty much render them different animals for different use cases. I would say F135/F136 is currently as big as it gets for a jet fighter and anything heavier than F35 would need two engines. Only medium and light weight has the luxury of choosing between single or dual engines (F16/FA18/Mig-29/Chengdu J10). $\endgroup$ – user3528438 May 3 '17 at 19:20
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    $\begingroup$ @user3528438 - completely agreed, but what I sense from OP's question is primarily the ability to make a powerful jet engine, country vs country kind of thing. $\endgroup$ – ymb1 May 3 '17 at 19:21
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The general purpose was redundancy. Splitting the power demand of the airframe and payload made for smaller engines and the ability to stay airborne and RTB (return to base) if one engine suffers a failure.

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  • $\begingroup$ too broad. In some cases it's redundancy, in other cases it's the unavailability of a single engine with the required thrust. In yet other cases it's a matter of size (a single engine would be too big for the available space, 2 smaller ones side by side can be made to fit). $\endgroup$ – jwenting May 4 '17 at 10:13
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As pilots, we very often go right for the aerodynamic reasons, but one glaring reason has been omitted from the discussion - price. Governments have to choose between having a smaller number of more expensive, likely more capable, aircraft and having a larger number of smaller, lighter, less expensive aircraft. This applies not only to initial cost, but also to ongoing maintenance, parts and fuel cost to operate the aircraft. The F-16 is a great example of an economically efficient aircraft that can be operated by nations on a budget due to its small size, single engine and availability of parts versus an engineering marvel like the F-22 which is no longer in production due in no small part to the difficulty of obtaining parts, a better explanation of which follows here: https://www.defenceaviation.com/2016/05/why-did-the-united-states-stop-f-22-production-could-lockheed-martin-restart-the-production-line.html

Also, along economic lines, a quick visual price comparison is found here: https://www.popularmechanics.com/military/weapons/news/a25678/the-cost-of-new-fighters-keeps-going-up-up-up/

Price issues aside, from a pilot's perspective I don't think there is a pilot alive who would not want a second engine for many reasons, but we aren't the ones buying the jets.

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  • $\begingroup$ wrong on a lot of grounds. Pilots may not want a second engine because it means a larger, less agile, aircraft that's less survivable in a turning fight. You can see that when comparing the F-16 and F/A-18, the F-16 can turn a lot tighter than its larger brother. $\endgroup$ – jwenting Jul 31 '18 at 4:44
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    $\begingroup$ Actually, correct on all grounds, not "wrong on a lot of grounds". As I clearly stated in my answer, I was discussing the strategic objectives of a government and of a military agency, not the smaller perspective of the individual combatant. And no, you don't have to give up an engine to have a great jet in a turning fight, the F-22 is a great example. I have flown both single-engine and twin-engine supersonic military aircraft, including the F-16, Uncle Sam was kind enough to grant me a pair of silver wings after a lot of hard work. $\endgroup$ – Taurus69 Jul 31 '18 at 14:45
  • $\begingroup$ Regarding the number of pilots that prefer two engines, there is a significant statistical bias: The selection of samples depends on what is measured. One could think it means that most pilots prefer twin engines, but it does not! It is just as possible that most pilots prefer to have one engine, but died because of that before the samples where chosen. (Quite an interesting example for statistical bias!) $\endgroup$ – Volker Siegel Nov 24 '19 at 23:14

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