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I have been looking at various engine configuration in jet powered aircraft. Most have 2 jet engines mounted either side of the fuselage, there are trijet models (e.g. B-727, MD-11) there are also 4-engine aircraft (A380, B-747) and there were even 6-engine (e.g. A-225 Mriya). Yet when looking for a single engine jet powered aircraft, the only one I could find is the Cirrus Vision SF50, which is a fairly new model.

There are, of course, various military/fighter models - but I am more interested in civilian aircraft at this point.

Is there a particular reason why there aren't (almost) any single-engine jet powered aircraft?

EarlGrey
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Aleks G
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  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed. – DeltaLima Oct 25 '23 at 09:25

4 Answers4

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I'm not sure why most of the answers/comments talk about airliners as the question did not specifically asked about them, but about civil aircraft in general.

Is there a particular reason why there aren't (almost) any single-engine jet powered aircraft?

I'm going to assume that the term "jet powered aircraft" refer to turbojet or turbofan engines and not to turboprops as there are plenty of single-engined turboprop aircraft.

Structurally

Having a single jet engine is challenging as there are very few feasible locations for engine placement, each comes with its own issues.

If you put the engine inside the fuselage, it means it needs to be in the rear.

This means the entire central fuselage must be entirely or almost entirely hollow to allow for the air intake/s. This of course does not leave a lot of room for passengers nor cargo.

If you put the engine above the fuselage:

  • The front part of the fuselage might block/shadow the air flow to the engine in higher angles of attacks.

  • It is probably going to be a maintenance challenge to reach the engine.

  • Cabin noise insulation needs to be very good when you have a jet engine a few inches above your head.

  • Most likely requires a V-tail (or H-tail) if you don't want the vertical stabilizer inside the engine exhaust.

Financially

Turboprop engines are much more efficient in the flight regimes applicable for a small civil single-engined aircraft than "pure" jet engines.

DeepSpace
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    Good information. But with respect to engine location the SF50's engine is above the fuselage. –  Oct 24 '23 at 18:18
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    @RTO Indeed it is. Not sure which part of my comment your comment contradicts – DeepSpace Oct 24 '23 at 18:19
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    "Much more efficient:" a recent flight report of a BD-5J, from the point of view of a prop pilot, said as soon as it's running, you're out of fuel and on fire. – Camille Goudeseune Oct 24 '23 at 18:23
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    I'm not intending to contradict your answer. Just pointing out that, as a limiting issue as to why there are not more civil single-engine jets, engine location may not be much of a detrimental issue as demonstrated by the apparent demand for the SF 50. –  Oct 24 '23 at 18:23
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    Counterexamples abound. The 727, Tristar, Falcon 900EX, 7X/8X, and Yak-40 all put the engine "in" the fuselage, i'd say the fuselage wasn't hollow. The HS-121 put 1 engine in the fuselage, and half an engine in the shadow of the fuselage. The DC-10/MD-11 put the engine above the fuselage, and it's not a V- or H-tail. If you can't the obvious answer is a T-tail, but you got the Falcons with the cruciform tail, or a canard. – user71659 Oct 24 '23 at 18:56
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    Some others I missed: Tu-154, Yak-42 are all s-ducted "in" fuselage. Falcon 50 belongs with the other Falcons. With single-engine prototypes, the PiperJet did it DC-10 style. The Diamond D-Jet was the most unique by mounting the engine under the fuselage and had a split duct. – user71659 Oct 24 '23 at 19:25
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With respect to operations conducted under U.S. 14 CFR Part 121 - Operating Requirements: Domestic, Flag, and Supplemental Operations (Airline type operations), they are subject to the regulation below:

§ 121.159 Single-engine airplanes prohibited.

No certificate holder may operate a single-engine airplane under this part.

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    While this applies to air carriers, I don't see how this is applicable to private operators. There are plenty of single-engine propeller airplanes. – Aleks G Oct 24 '23 at 15:37
  • @AleksG My answer does only apply to operations under FAR Part 121. Since you mentioned the type of airplanes typically, but not always, used in Part 121 operations I was attempting to help you understand that a single-engine airplane could not be operated under that part. Perhaps you could re-word your question to limit answers to "private" operations only. –  Oct 24 '23 at 15:50
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    @AleksG The question specifically asks about civilian operations, in which category commercial airlines fall. Your examples include commercial aircraft so unless you change your question, this answer is applicable. You only exclude military aircraft. – Pilothead Oct 24 '23 at 19:07
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To be legally operated by a passenger airline, its airplanes need to comply with certain regulations. One of those stipulates what should happen in case of an engine failure:

§ 25.121 Climb: One-engine-inoperative.

(a) Takeoff; landing gear extended. In the critical takeoff configuration existing along the flight path (between the points at which the airplane reaches VLOF and at which the landing gear is fully retracted) and in the configuration used in § 25.111 but without ground effect, the steady gradient of climb must be positive for two-engine airplanes, and not less than 0.3 percent for three-engine airplanes or 0.5 percent for four-engine airplanes, at VLOF and with—

(1) The critical engine inoperative and the remaining engines at the power or thrust available when retraction of the landing gear is begun in accordance with § 25.111 unless there is a more critical power operating condition existing later along the flight path but before the point at which the landing gear is fully retracted; ...

This obviously cannot be achieved with a single engine. The engine failure case is considered too likely and its consequences too severe to allow single engine airplanes to legally carry more than a handful of paying passengers. In other words: Redundancy. This philosophy can be seen in many aspects of passenger airplane design.

Peter Kämpf
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There are two reasons to want to power your aircraft with a jet engine: either "haha cool jet engine" (which is a super valid reason) or you want to go well over 300 knots in order to shorten travel time. Going 350 knots instead of 300 knots only really makes a difference in travel time if you are going far, far enough that a big fraction of trips will cross oceans. Crossing a body of water on a single engine is spooky.

(The PT6 turboprop engine is so reliable that people are comfortable flying them across the atlantic on single engine planes- in fact, this is how TBMs are delivered to the states. Jet engines of a suitable size for a single engine airplane, with that level of reliability, don't really exist)

QuadmasterXLII
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  • Why would a turbofan engine be less reliable than a turboprop? You've deleted the gearbox and variable pitch propeller parts. The rest of the engine runs on the same concept. – user71659 Oct 25 '23 at 20:17
  • There's no reason for turbofans in general to be less reliable than turboprops in general. The PT6 turboprop engine specifically is extremely reliable – QuadmasterXLII Oct 25 '23 at 21:08