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What is the smallest (by operating empty mass) quad-engine aircraft that satisfies these conditions?

  • Current or past airplane
  • aircraft with fixed wings, not a rotorcraft, not a lighter than air, etc
  • 4 engines, pistons or turbines
  • fuel as a main source for propulsion
  • actual aircraft, not scaled model
  • piloted by a pilot or a crew
  • used for an actual military or scientific goal or business (not for design tests only).

Added to prevent flying suits to be proposed:

  • Need to takeoff and land under its own power.
  • Not a worn wing (flying suit), the aircraft must have a flight deck where the pilot can be.

If this one had been piston or turbine, it would be a good candidate:

enter image description here

... but it's an electric-powered aircraft.

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    $\begingroup$ smallest or lightest? $\endgroup$ – ymb1 Sep 22 '17 at 10:45
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    $\begingroup$ The little twin is a Cri Cri homebuilt originally from France. It is not electric. The initial design had 2 very small gas engines. There have been several builders that used very small turbines (jet) engines. $\endgroup$ – Curt Sep 22 '17 at 13:36
  • $\begingroup$ Why limit to military/scientific/business? How about just personal use? And how exactly do you differentiate "wear"? Does it have to have landing gear? That'd leave out some ultralights. Not to mention that I've owned a few cars, most recently a Miata, which some people might think of as wearable :-) $\endgroup$ – jamesqf Sep 22 '17 at 17:42
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    $\begingroup$ "How about just personal use?", not excluded, but the ones you can buy. I'm trying to exclude experimental overpowered planes which could also fly with only 2 engines. $\endgroup$ – mins Sep 22 '17 at 19:11
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The Short Scion Senior flying boat was powered by four 88 hp radial engines and its weight, empty, was 3,650 lb (1,637 kg).

enter image description here

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I present you Yves Rossy's Jet wingpack, which satisfies your conditions (I know I'm pushing it, but couldn't resist).

Jetpack

Yves Rossy's Jet wingpack, By Rama - Own work, CC BY-SA 2.0 fr, Link

It is certified by FAA as an aircraft, powered by four Jetcat P400 turbojets, piloted by an individual, not a rotorcraft and used in show business.

According to the official site, it weighs 150 kg.


@ymb1's logic is correct. To get to lightweight four engined aircraft with, you have to go back when the engines were not powerful enough for large aircraft. So, I present you the Sikorsky Ilya Muromets, the World's first four engined bomber.

Ilya Muromets

Sikorsky Ilya Muromets, By www.cultinfo.ru, Public Domain, Link

The Ilya Muromets Type S-23 V is reported to have an OEW of around 3700 kg, powered by four Sunbeam Crusader engines. Its predecessor, the Sikorsky Russky Vityaz, was still lighter, though it never saw service in numbers, sadly.

Of course they are not autonomous as per your requirement. Why would you want a manned autonomous aircraft anyway?

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  • $\begingroup$ Ok, good try and +1 for that. I've added the constrains to be autonomous, not requiring being launched from another aircraft. $\endgroup$ – mins Sep 22 '17 at 14:41
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    $\begingroup$ @mins: It might be good to specify in your question that you mean the aircraft must launch and land without assistance from other aircraft, since the term usually refers to the ability of a vehicle to operate without assistance from a human operator. $\endgroup$ – supercat Sep 22 '17 at 16:20
  • $\begingroup$ I've always wondered why they didn't go to 4-engine craft pretty much the moment it was possible to build a wing long enough. Especially given the reliability of early engines. $\endgroup$ – Harper - Reinstate Monica Sep 22 '17 at 17:46
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    $\begingroup$ Why would you want a manned autonomous aircraft anyway? - for the same reason I want a manned autonomous car... so I can fly places without being a pilot. $\endgroup$ – Johnny Sep 22 '17 at 22:17
  • $\begingroup$ It's an entirely different kind of flying, altogether! $\endgroup$ – Columbia says Reinstate Monica Sep 24 '17 at 11:52
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I present to you a light giant (you asked for OEW).

One of the major reasons to have 4+ engines* is if the engines are weak, and the plane is big. Therefore one of the lightest will be an early 20th century giant. Jets are out of the question since they are inherently heavier and most (if not all) are all-metal.

From the Wikipedia Category:Four-engined_aircraft, the only two planes under push configuration are both experimental. That leaves us with the push/pull configuration if we are after light planes (common nacelle, fewer stress points, etc.).

The lightest (but not smallest) I found and hence nominate is the Gotha WD.27 at an empty weight of 4,500 kg and powered by four 160 h.p. Mercedes D III's driving 4 propellers (each two in push/pull). It weighs as much as 5 Cessna 182's, after all it has 4 (old and heavy) engines.

I doubt we can find any 4-engined fuel powered airplane under 4 tonnes (c. 1913 it was possible, see comment by PK). And piston engines aren't easily miniaturized (dang it, see xxavier's answer).

enter image description here
(Source)

Just look at it, it's nothing but a giant wing with 4 engines and two floats. Reportedly 3 were built for the military for sea patrol. There is not much information about it online. An aircraft encyclopedia I have doesn't say much about it either, only confirms 3 were built. (The smaller cousin, the WD.22, was a prototype at 3,800 kg.)


* I didn't say 3+ because 3 can be a workaround for the era pre-ETOPS.

There's the beautiful Dornier Do 26, but unfortunately it's over 10 tonnes.

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    $\begingroup$ Wasn't Sikorsky's Russky Vityaz even lighter at 2,700 kg empty? Funny fact: Back then it was the largest and heaviest aircraft in the world, by a wide margin. $\endgroup$ – Peter Kämpf Sep 22 '17 at 14:47
  • $\begingroup$ @PeterKämpf - I was eagerly waiting for you to beat my find :D Excellent, but one was built and didn't see service (trying to save face) :D $\endgroup$ – ymb1 Sep 22 '17 at 14:49
  • $\begingroup$ You're right, and the Ilya Muromets production version weighed almost 7000 lbs empty. $\endgroup$ – Peter Kämpf Sep 22 '17 at 14:55
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    $\begingroup$ Another funny fact: The smallest six-engine aircraft was smaller than the smallest four-engine aircraft - but again only built once, for design tests. So it doesn't qualify. $\endgroup$ – Peter Kämpf Sep 22 '17 at 15:02
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    $\begingroup$ Ha! Now I found a four-engined airliner which was produced in (albeit moderate) numbers: The DeHavilland 86 Express which weighed less than 2800 kg empty. But the Short Scion is hard to beat. $\endgroup$ – Peter Kämpf Sep 23 '17 at 13:03
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The 1800 lb “Bally Bomber” is the smallest and lightest 4 engine, manned, conventional aircraft.

It is a 1/3 scale B-17.

enter image description here

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  • $\begingroup$ Hi Mike, nice addition and certainly great engineering, however it doesn't seem to meet the criteria (scaled reproduction, not a true aircraft you can buy, not an aircraft with an actual mission). $\endgroup$ – mins Oct 22 '18 at 14:47
  • $\begingroup$ When you said "actual aircraft, not scaled model" I thought you were talking about RC aircraft. $\endgroup$ – Mike Sowsun Oct 22 '18 at 16:18
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Can I suggest the DH Heron, which first flew in 1950. It was a development of the DH Dove, with a lengthened fuselage and 4 engines. This (according to Wikipedia) weighed in at 3700kg.

DH Heron.

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    $\begingroup$ If you choose DeHavilland, may I suggest an earlier type? The DH 86 Express weighted less than 2800 kg empty. $\endgroup$ – Peter Kämpf Sep 23 '17 at 12:59
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Smallest commercial jet with 4 turbines is probably the BAe 146-100.

https://en.wikipedia.org/wiki/British_Aerospace_146

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