Jet Powered Vought F5U-2 "Flying Pancake"

[Derek Hendricks]

I think, FarSight is quite right. A jet powered XF5U would have lost its original
"raison d'etre" as a fighter with very good STOL capabilities. In fact, the conceot
started as a kind of a tailsitter.With jet engines, it probably looks cool, but I don't
know, which aerodynamic advantages it would have had .

The XF5U-2 would have been a large-fighter uniquely well-suited to performing the carrier-borne multi-role job .
Imagine a 600mph F/A with both impressive range and load-out ; unbelievably tough , able to operate from small carriers , yet narrow enough to easily be stored on them in large numbers .

 

[Derek Hendricks]

Even today, a revamped F-5U with 1800 h.p PT-6 turboprops would be an awesome flying vehicle.

So would a jet-engined variant , speed being a prerequisite for a Korean War era fighter .

 

[Archibald]

It is hard to chose between turboprops and jets, for that wonderful flying machine. Turboprops make it VSTOL, jets make it fast (and UFO like !)

 

[Nicknick]

It was Sergei Sikorsky attributed in those Italian language sources, with the jet versions. Is it known for some certainty that it was not the Sergei who worked on the Vought/Zimmerman craft, but coincidentally someone else of that name?

It's a myth that the flappy outward turning props were necessary for either very-low speed STOL performance or for efficiency at cruise.

Those insisting that it is so or that it wouldn't have worked with jets, are unaware of the Arup, the Nemeth, the Eshelman, the Farman 1020, the Little Bird, the Facetmobile, all of which did very well with stall-proof super-STOL performance and were sleek and efficient compared to "normal" higher aspect-ratio planes (the Nemeth and the Farman both being faster than the "normal" planes they were derived from, the Arup, the Eshelman, the Facetmobile and others getting good speed with little power).

They are also unaware of the vortex-driven "Parachute lift" phenomena which the very-low aspect-ratio uses to be stall-proof and fly at super-slow speeds. You can't "counter" the vortices, you wouldn't want to if you could.
The very-low aspect-ratio type is not burdened with always carrying around the excessive drag of the vortices that produce the parachute lift.
The parachute lift effect and the attendant drag of the extreme wrap-around wing-tip vortices are elective and temporary, in order to fly slowly.

None of them worked the same way the Flying pankare did. I guess, the Facetmobile worked the same way like supersonic deltawings with leading edge vortexes at high angle of attac.The Farman 1020 propably had a verly low wing loading which made it a good Stol performer.

If you change the wings of the V-173 to a deltawing and replace the props with a jet you would end up with a totally different airplane. This is no proof at all, that the F-173 would have worked well with jets.

 

[Scott Kenny]

It is hard to chose between turboprops and jets, for that wonderful flying machine. Turboprops make it VSTOL, jets make it fast (and UFO like !)

Remember that the Tu95 is faster than the Nimrod/Comet 4.

Properly designed turboprops can be very fast indeed!

Or "interestingly designed", as IIRC the Bear engines have a LOT of residual thrust so act a lot like turbojets at altitude. Not sure I believe they only deliver ~675lbs residual thrust, but that's what Wiki is claiming. The US engine in the same horsepower class, the XT57, made 15,000hp and 5000lbs residual thrust.

 

[elsiniestro]

It was Sergei Sikorsky attributed in those Italian language sources, with the jet versions. Is it known for some certainty that it was not the Sergei who worked on the Vought/Zimmerman craft, but coincidentally someone else of that name?

It's a myth that the flappy outward turning props were necessary for either very-low speed STOL performance or for efficiency at cruise.

Those insisting that it is so or that it wouldn't have worked with jets, are unaware of the Arup, the Nemeth, the Eshelman, the Farman 1020, the Little Bird, the Facetmobile, all of which did very well with stall-proof super-STOL performance and were sleek and efficient compared to "normal" higher aspect-ratio planes (the Nemeth and the Farman both being faster than the "normal" planes they were derived from, the Arup, the Eshelman, the Facetmobile and others getting good speed with little power).

They are also unaware of the vortex-driven "Parachute lift" phenomena which the very-low aspect-ratio uses to be stall-proof and fly at super-slow speeds. You can't "counter" the vortices, you wouldn't want to if you could.
The very-low aspect-ratio type is not burdened with always carrying around the excessive drag of the vortices that produce the parachute lift.
The parachute lift effect and the attendant drag of the extreme wrap-around wing-tip vortices are elective and temporary, in order to fly slowly.

So, could these aircraft theoretically use jet engines, and could the Vought XF5U-1 be possible with good STOL capabilities? Technically, fighters, space shuttles are lifting fuselage. This one being lifting bodie should be able to be jet powered.

 

[Dilandu]

So, could these aircraft theoretically use jet engines, and could the Vought XF5U-1 be possible with good STOL capabilities? Technically, fighters, space shuttles are lifting fuselage. This one being lifting bodie should be able to be jet powered.

AFAIK no (sorry for late answer). The whole idea was that big propellers would create specific type of airflow around the round body, and with jet engines it simply wouldn't work.

Turboprops, on the other hand, might work - but there would be serious engineering challenges.

 

[Dilandu]

Mods, can we remove the 'jet powered' descriptor in the thread heading ? There was NO such creature (other than what-if BS.)

Moreover, jet powered flying pancake would not work - no propellers to cancel tip turbulence.

 

[Archibald]

My gut feeling too. Remove the props and the entire concept falls appart. So turboprops are much preferable.

 

[Dilandu]

My gut feeling too. Remove the props and the entire concept falls appart. So turboprops are much preferable.

Yep, albeit the reduction gear to transform the turbine output into relatively slow rotation of big propellers would be MAJOR headache.

 

[Scott Kenny]

Yep, albeit the reduction gear to transform the turbine output into relatively slow rotation of big propellers would be MAJOR headache.

Not hugely. Steam turbines have some pretty absurd reduction ratios, and there's simple turbine designs that will have a ~2000rpm speed directly.

 

[John Frazer]

None of them worked the same way the Flying pankare did. I guess, the Facetmobile worked the same way like supersonic deltawings with leading edge vortexes at high angle of attac.The Farman 1020 propably had a verly low wing loading which made it a good Stol performer.

If you change the wings of the V-173 to a deltawing and replace the props with a jet you would end up with a totally different airplane. This is no proof at all, that the F-173 would have worked well with jets.

This planform wold not have needed turboprops at the wingtips, it's incorrect to dsay that the jet versions wold have lost their STOL abilities.
It is incorrect to say that they had anything to do with similarity to supersonic delta wings at very slow speeds, with this or with the Facetmobile or the similar Moskalyev SAM-4. Not at all the same effect.
They all worked exactly the same way the V-173 did, as the V-173 did not gain it's stall proof or super-STOL abilities from the props but solely from the very-low aspect-ratio planform.
Most are unaware of the "parachute lift" phenomenon which Zimmerman wrote about for NACA and Wainfan did for NASA.
It's present only at very high "A" at very slow speeds from the huge vortices present only at those slow speeds, and it produces extra lift at such slow speeds and makes it stall-proof.

It remains a myth that the V-173 or the XF5U needed the props outwardly spinning at the tips to make if efficeint or STOL.

 

[John Frazer]

My gut feeling too. Remove the props and the entire concept falls appart. So turboprops are much preferable.

Incorrect, unfortunately, as the Vought nor any other very-low aspect-ratio plane did not need (nor did the Vought plane gain anything from) wing-tip mounted outwardly spinning props either for STOL stall-proof ability or for efficiency at cruise. That is a myth.

 

[John Frazer]

Moreover, jet powered flying pancake would not work - no propellers to cancel tip turbulence.

...
The whole idea was that big propellers would create specific type of airflow around the round body, and with jet engines it simply wouldn't work.

Turboprops, on the other hand, might work

It remains a myth that it needed the props as they were, either for STOL ability or for efficiency at cruise.

 

[Nicknick]

This planform wold not have needed turboprops at the wingtips, it's incorrect to dsay that the jet versions wold have lost their STOL abilities.
It is incorrect to say that they had anything to do with similarity to supersonic delta wings at very slow speeds, with this or with the Facetmobile or the similar Moskalyev SAM-4. Not at all the same effect.
They all worked exactly the same way the V-173 did, as the V-173 did not gain it's stall proof or super-STOL abilities from the props but solely from the very-low aspect-ratio planform.
Most are unaware of the "parachute lift" phenomenon which Zimmerman wrote about for NACA and Wainfan did for NASA.
It's present only at very high "A" at very slow speeds from the huge vortices present only at those slow speeds, and it produces extra lift at such slow speeds and makes it stall-proof.

It remains a myth that the V-173 or the XF5U needed the props outwardly spinning at the tips to make if efficeint or STOL.

Youre wrong, the examples you mentioned are delta wings, which can produce high lift at high angles of attac. This is due to the vortexes generated by the delta wing, which are keeping the flow attached. The flying pancake looked more like a flying half pankake with an almost streight leading edge. Unlike a delta wing, this shape doesn't produce those vortexes and needed the props to archieve a low stall speed. Waifan himself explained the capability of the Facetmobile this way.

 

[Richard N]

At rest, the prop Pancake generates energized airflow over it's wings and control surfaces to enable a controlled STOL takeoff. It's surfaces are partway to flight before it has even moved. It has a blown wing and control surfaces that will allow controlled flight at low speed well below that of a conventional airplane and may even be stall proof as long as the props are turning fast enough.

At rest, the jet Pancake at cannot generate any airflow over the wing and control surfaces until it's jet engines shove the full mass of the airplane down the runway fast enough to reach takeoff speed. In flight, because the jet thrust does not put energized flow over the wing and control surfaces, it will not be able to slow down and be controllable at less than stall speed.

The only jet powered STOL aircraft I know of are the YC-14 and YC-15 and they both used deflected jet thrust to generate energetic flow over their wings. Without deflected jet thrust over the wings and control surfaces, a jet powered STOL is unlikely.