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Are there any, or have there ever been any commercial/military jet bi-planes?
What would be some of the major advantages vs disadvantages if one was built?

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Electric radio controlled ducted fan model.

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University of Tokyo concept model.

AndroidSmoker74
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jwzumwalt
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  • When searching this site for "jet biplane", the second hit is https://aviation.stackexchange.com/questions/33679/ - The answer is the same as the currently highest voted answer to your question. - I'm calling "no research effort"! – I'm with Monica May 03 '19 at 11:29

2 Answers2

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Yes

I present to you, the Belphegor, a jet powered, crop-dusting, biplane. I think I need not say that this is a Soviet Bloc design, from Poland in particular.

M-15 at the Muzeum Lotnictwa Polskiego

Note the braces between the wings acted as tanks for whatever chemical agent it would be dispensing over the kolkhozy. It was not very successful due to a host of disadvantages, including:

  • Jet engines are not efficient at slow speeds, which are in turn required for crop dusting operations. The designers may have hoped to do away with this requirement by using it over the large collectivized farms of the USSR, but the straight wing attests to the top speed being low by design. The jet engine was apparently mandated by soviet planners wanting to simplify the logistics of fuel and maintenance by reusing the AI-25 engine.

  • Biplane configurations are less efficient than monowings of the same total area due to interference between both lifting surfaces.

  • For crop-dusting applications in particular, @Harper points out the fact that the shorter span of biplanes is detrimental to effective spraying, by limiting the width of the spray system, which needs to end short of the wingtips. Otherwise the agent will get picked up by the wingtip vortexes and spread in unintended directions.

On the other hand:

  • One advantage of biplanes is low roll inertia due to the shorter wings, which is mostly useful in dogfights and thus not highly-sought nowadays.

  • Another advantage of biplanes is the lower bending moment at the root of the individual wings, due to them being shorter. This allowed earlier designs to get into the air in spite of poor building materials and QA procedures; this solution was gradually abandoned as aircraft moved away from wood and fabric and towards aluminium alloys.

  • The lower span of biplanes might be useful in application that are span-limited, like modern airliners, which are limited by airport parking and runway restrictions. If you absolutely need to obtain more lift out of an airframe that is already at its maximum span, adding a second wing is not unreasonable.

AEhere supports Monica
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  • Wow, I never knew a design like that existed! A jet on a crop-duster makes very little sense as you say, jets take much longer to spool up than props do. – GdD May 01 '19 at 08:22
  • The linked Wikipedia article says that's the world's only biplane. Assuming that's correct it's the only answer (though I wonder about prototypes) – Chris H May 01 '19 at 08:41
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    Yes, laughable. Had seen this design a while ago, but it hadn't occurred to me this thus is actually a conversion from a surplus helicopter frame, which is even less fuel efficient! More a garage project than a design from scratch, but practical if you have a lot of helicopters in your boneyard. Might have been a little better is they somehow got a turboprop on there. – Robert DiGiovanni May 01 '19 at 08:55
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    @RobertDiGiovanni do you have a source on the helicopter conversion bit? Sounds weird because the wikipedia article does point to this being a clean(ish)-slate design. – AEhere supports Monica May 01 '19 at 09:17
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    @ChrisH The question is broad enough to allow for more answers that focus on the biplane pros and cons, and I'd myself appreciate if someone more familiar with this monstrosity would grace us with their knowledge. – AEhere supports Monica May 01 '19 at 09:23
  • No, but it did make me wonder how "spool up" issues were handled in modern jets and turboprops, along the lines of a constant speed, variable pitch jet! (or helicopter ?) Anyways, it may have been a low budget "clean slate" from available parts. So was the original U2, made with a Starfighter fuselage. Could it have gone higher with a turboprop? Just got me thinking about adding fuel/air and increasing pitch of prop at the same time. Not sure if a fan jet (or turbojet) can do that. – Robert DiGiovanni May 01 '19 at 12:03
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    Unless you can identify the reused airframe components, I suggest you take it at face value. After all, this was not a prototype (which was a hodgepodge of parts, just like e.g. the F-117 prototypes), but underwent serial production. The only part that was clearly reused across the serial A/A seems to be the engine. – AEhere supports Monica May 01 '19 at 12:46
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    The short biplane wing works against cropdusters in a way. In America at least, you are only allowed spray nozzles across 2/3 of the wing width, that is to keep chemicals out of the wingtip vortices where they will be kicked up and carried by the wind to places that should not be sprayed. Shortening the wing means more passes needed. – Harper - Reinstate Monica May 01 '19 at 13:05
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    @GdD there are a couple advantages to using a jet engine; one of the biggest (and probably the reason this plane exists) is that turbines can run off of almost any fuel, unlike piston engines which generally run on a rather narrow range of fuels. If you're out in the country and don't know what fuel will be readily available, a jet might be a reasonable choice. – Skyler May 01 '19 at 15:28
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    "Soviet in general, from Poland in particular"??? When and how did Poland get integrated into the USSR? – Vladimir F Героям слава May 01 '19 at 17:17
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    "Soviet", without the "Union" refers to a council of the type that Poland found itself under for nearly half a century. – Jim Horn May 01 '19 at 19:14
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    @ChrisH: The world's only mass-produced jet biplane, technically. – Vikki May 01 '19 at 22:52
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    @Skyler yeah, and on the collective farms the fuel most readily available would be the diesel for the farm machinery, which is very similar to Jet A. – jwenting May 02 '19 at 03:43
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    @VladimirF Poland was integrated economically into the USSR post-WW2. This aircraft was designed and mostly built in Poland using Soviet engines and other equipment, to Soviet requirements, for use in the USSR. – jwenting May 02 '19 at 03:44
  • @JimHorn No, no, just no. Simply no. It was used for such a broad sence (Al the power to the Soviets!) only for a short time after WWI for Germany, Hungary and extremely short lived Slovakian puppet statet ruled by Hungarians. After WWII the communist countries were not called Soviet countries. The adjectives soviet is only used for USSR stuff and that is true on both sides of the Iron courtain. Soviet Germany only refers to the shoet-lived thingaroynd 1919, never the GDR. – Vladimir F Героям слава May 02 '19 at 05:44
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    @Sean that's the suspicion I had, yes. – Chris H May 02 '19 at 05:46
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    @RobertDiGiovanni The closest "related" designs were An-2 and An-14, used for prototyping. With 3000 planned units, conversion was out of the question. Jet was mandated to create fueling and maintenance synergy with other Ivchenko AI-25 powered planes. Helicopter look is merely a result of convergent evolution - when you put a jet/turboshaft on top of the cabin, you're bound to end up with something resembling a helicopter frame. – Agent_L May 02 '19 at 06:34
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    I changed the wording to Soviet Bloc, of which Poland most certainly was a part. I don't know what I expected, honestly, mentioning Poland has a habit of turning things into geopolitical discussions :) – AEhere supports Monica May 02 '19 at 07:22
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    Have to like the reliability and fuel use versatility of the jet. And yes, they can be mounted on anything, including gliders (easier stowing) and biplanes (Screamin' Sasquatch). Centrifugal jets may be a possibility for light sport aircraft, they powered the Mig 15. – Robert DiGiovanni May 02 '19 at 07:55
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    @AEhere We call that period "communism". "soviet" is strictly limited to "USSR proper". Other Comecon countries called themselves "socialist" or "people's republic", but never "soviet". – Agent_L May 02 '19 at 16:35
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A military jet-powered biplane was the I-153DM Chaika, which was adapted by strapping a couple of ramjets underneath each wing. (DM = Dopolnityelnyi Motor – supplementary engine).

I-153DM Chaika picture source

The I-153 was a development of the Polikarpov I-15, an advanced fighter when it debuted in 1933. The I-153 sought various improvements, including retractable undercarriage, but even so by the start of WW2 it was no match for its opposition.

The Russians were pioneers in ramjet technology, and in December 1939 the designer I.A. Merkulov tested the addition of DM-2 and later DM-4 jets to a ski-equipped I-153.

There was little immediate advantage: the jets yielded only an extra 50kph at best. The disadvantage was that in standard flight the extra drag made the little plane rather slower. However, it is notable that this was the first ramjet powered flight.

Over 70 flights were completed with the I-153 variants. It is reported that Merkulov also tested the DM-4 in a similar configuration on the Borovkov-Florov I-207 biplane prototype. source

I-153DM Chaika picture source

I-153DM Chaika picture source

Party Ark
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    This is fascinating! I'd heard of the Belphegor, but not this one - and it is neat to see ramjets combined with a radial propeller engine. – Skyler May 01 '19 at 19:11
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    Technically the chaika could not propel itself on the jets alone, but that's beside the point. I'd heard of this thing but didn't register the fact that it was actually tested and that those were ramjets of all things. Nice one! – AEhere supports Monica May 02 '19 at 07:25