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Flying Flapjacks

AeroFranz

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AeroFranz said:
Oh, sorry for misunderstanding ;)
The flapping of the blades might have been necessary because at high angles of attack the props are operating in a strong edgewise flow (not unlike a helicopter rotor). The advancing and retreating blades see differing inflow velocity and need to flap to balance thrust across the disc.
Maybe someone else has a better explanation?
I just came across this interesting video of Jack Reeder, longtime engineer and test pilot at Langley
at 48:30, he says there was little practical improvement with turning the props against the direction of the vortices. He also talks about the need to provide flapping motion for the propellers.
https://www.youtube.com/watch?v=HRZu78WozBo&feature=youtu.be
 

Sundog

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AeroFranz said:
AeroFranz said:
Oh, sorry for misunderstanding ;)
The flapping of the blades might have been necessary because at high angles of attack the props are operating in a strong edgewise flow (not unlike a helicopter rotor). The advancing and retreating blades see differing inflow velocity and need to flap to balance thrust across the disc.
Maybe someone else has a better explanation?
I just came across this interesting video of Jack Reeder, longtime engineer and test pilot at Langley
at 48:30, he says there was little practical improvement with turning the props against the direction of the vortices. He also talks about the need to provide flapping motion for the propellers.
https://www.youtube.com/watch?v=HRZu78WozBo&feature=youtu.be
My understanding is that the problems with the flapping propellers is why the XF5U-1 was never flown.
 

AeroFranz

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IIRC, the prototype had F4U props, but there was always an understanding that it would get four-bladed teetering props. I think the decision to ax the program had more to do with the obsolescence of props versus jets.
 

Sundog

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AeroFranz said:
IIRC, the prototype had F4U props, but there was always an understanding that it would get four-bladed teetering props. I think the decision to ax the program had more to do with the obsolescence of props versus jets.
I understand that, but I mean why they didn't just fly it for just the research. Of course, in that regard, I often wondered why they didn't just fly it with the F4U props, from a research standpoint.
 

AeroFranz

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Amen, brother. I'm sure there were some interesting lessons to be had from flying a novel configuration...although to be fair, they had tunnel-tested and flown the V-173.
I checked the references i have on the XF5U. The props were supposed to be Hamilton Standard four bladed teetering, especially designed for the vehicle. They weren't ready by the time the prototype was rolled out, so it was equipped with F4U Hydromatic units. Turns out it was a very poor match and they couldn't fly it like that. While waiting for the props, Zimmerman did some redesign based on lessons learned while ground testing. the cockpit was redesigned, and he added a trailing edge surface between the verticals.
 

riggerrob

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They might have been able to fly it horizontally with F4U props, but could not have demonstrated any high angle of attack flight with conventional propellers. They also had problems with propeller vibration on the (fly able) mock-up.
 

GWrecks

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John Frazer said:
The Vought/Zimmerman/Sikorsky effort might be called "Zimmerman's folly", or how the navy threw away a superior fighter, by not building the Boeing little 390 test plane, as a sincere follow-on to the performance of the Arup.

The Arup S-2 flew for NACA and the Army and CAA. Zimmerman worked for NACA and was on the team that saw the Arup fly. After that, his idea for a VTOL toy with short aspect-ratio and twin screws gelled. (his patents and his participation in that contest followed the successful careers of the Arup plane He plainly was following the interest overseas and here in low-aspect ratio, and the success of Arup gave him what he thought he needed for his VTOL experiments.)
But the Arup nor the V-173 did not need the giggle-factor-inducing silly huge flappy props over the wing-tips.
They were a distraction from the performances the Arup plane put on, they are an un-necessary over-complication, and in the XF5U they killed what could have been a good plane (simple twin-engine & prop plane would have flown, and probably done extraordinarily well if not for the complex power system for those wing-tip things).

Short aspect ratio planes do not suffer abnormally high drag due to wing-tip wash-around while in cruise. In cruise low-A flight, they are sleek, like a little all-wing. Several planforms of low aspect-ratio all-wing and unitary wing/body test planes have flown well.
In low speed high-A flight, the wing-tip vortices wrap around and join the air over the top of the wing, preventing it from separating and stalling. That gives them low aspect-ratio lanes their phenomenal low-speed, high-A performance, typically staying in flight slower than their landing speed, limited by the height of the nose wheel.
You don't want to counter it. You want the vortex-lift at low speeds, and it disappears in normal flight.

So, we might ask why the Navy chose to explore Zimmerman's toy, and ignored the Boeing plane (which appeared more sinister than silly). If followed-up with a flapjack fighter, it would have been like a Bearcat, with more speed, range, payload, and >40 kt landing speed. The planform would have taken over the fleet and pretty soon all military aviation. When the Arup patents expired, all aviation would have been using it.

The advent of the Jet Age didn't kill it. The Navy built and operated piston-prop planes for logistics & support and as tactical combat planes until the '70s.
The Vought jet-skimmer or the Sikorsky models would have been built instead of the P-80, and a supersonic version would have followed.
See the Eschelman "Flying Flounder" for a possibility of what such a thing might have looked like.
The Unicraft model kit is the only thing I can find online for this.

The follow on post about William Horton designs was split and merged with the older thread here:

https://www.secretprojects.co.uk/forum/index.php/topic,5996.msg326793.html#msg326793
This seems more than a little fishy to me. For starters that jet F5U image posted is clearly a shooped version of another one. Secondly, there is plenty of evidence that wingtip vortices exist, so unless the implication is that propellers can't do anything about it that's not really saying much. Lastly, it's worth noting that Convair had worked with a similar layout for their GETOL (Ground Effect Take-Off and Landing) proposals, so there's a convergent evolution process there too.

EDIT: Looks like it's not shopped after all, but the landing gear arrangement is clearly nonsensical (The only real changes were the removal of propellers and addition of jet nozzles, and it still uses the same landing gear!) and as a result I have trouble even imagining this was proposed.

Another thing worth mention, the F5U with piston engines would've been faster than most jet aircraft during WWII. There was a turboprop version suggested but I can't find images of it. All of this points (At least to me) in the direction of the propellers existing for a reason. Oh...

John Frazer said:
The planform would have taken over the fleet and pretty soon all military aviation. When the Arup patents expired, all aviation would have been using it.
...This is bait, isn't it?
 

TsrJoe

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You do realise the drawing for the 'jet Vought' is fake, original source is a piece by Bill Rose, UFO Magazine, Vol. 14, No.5 1999 ! and appearing in his subsequent 'saucer' Secret Projects series volume :eek:
 

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hesham

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From Ailes 6/1946,

here is a hypothetical drawing to a Vought Flapjack.
 

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Motocar

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Rare image Skyjacket II from:
http://www.aerotechnews.com/blog/2018/09/07/first-flights-other-sorties-at-mojave-airport-2/

 

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hesham

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From Ai\li Nuove 5/1952,

here is a Zimmerman X.50 ?.
 

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John Frazer

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The fact remains that no appreciable benefit to the Vought 173 or XF5U outward-turning props was found, and the Arups, the Nemeth, the Little Bird, and the Facetmobile all get the same extreme STOL and slow-flight performance without worrying about that myth.
Nemeth had equal or greater speed compared to the biplane. It was not extraordinarily draggy.

The outward turning props of the Vought/Zimmerman experiment didn't stop the extreme wingtip vortices; if they had, it would not have been capable of such slow speeds. That it was capable of slow speeds shows that they didn't effectively counter it. It's nonsensical to even think of trying to do so. That's not what Zimmerman was after.
That other similar-planform planes flew with a normal prop in the center (whether round or delta, whether as parasol wing or integral wing/body) shows that the vortices and the attendant STOL performance are due solely to the "parachute lift" effect, not the outward-turning props.
Jets would have worked just fine if speed was desired, or props for a slower plane. The Navy in '52 built the S-2, followed by the C-1, with piston-props. The advent of the "jet age" didn't stop them or the A1 from being extremely useful. An adaptation of the F5 type planform with the normal S-2 engines and props installed would have been faster, with more payload, and the STOL landing speed if it had suitable landing gear for nose-up attitude.

The Italian language articles show one by Sergei Sikorsky, aircraft engineer, son of Igor, who worked for Vought on the Zimmerman planes. He apparently knew that it didn't need or make any appreciable use of the extravagant and complex Zimmerman props. Suitable landing gear would have allowed it STOL performance and made it a very clean and useful all-wing -plus fins.
According to the Arup and Little Bird and (possibly applicable the Facetmobile) experience, entirely stable and controllable, fast.

In one of the videos of Hatfield and his Little Birds, he congratulates Rutan on the success of the Voyager, and then challenges that if it had been built to the Arup short aspect-ratio all-wing, it would have been lighter, faster, more useful interior room, and made the flight with plenty of fuel to spare.
This doesn't sound like the draggy monster which "conventional wisdom" says low-aspect-ratio to be. Are we here saying that Hatfield was lying/exaggerating/deluded? The Arup 2 was ~900 lbs, 97mph on 37 horsepower (thirty-seven). That also doesn't sound draggy and inefficient.
All discussion of low aspect ratio and the alleged high parasitic or induced drag and "terrible span efficiency" refers to the extreme huge wing-tip vortex drag, as it it follows them around all the time. It simply isn't true.

Feel free to consider it bait, to say that a sensible evolution of the Arup as a navy plane, whether as a escort-carrier fighter or the up and coming A1 or A2d Skyshark, or the S-2/C1 series, would have benefitted. Would the evolution of planes after the war have been different without the various persistent myths and misconceptions surrounding the round wing extremely short aspect ratio?
 

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steelpillow

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The fact remains that no appreciable benefit to the Vought 173 or XF5U outward-turning props was found, and the Arups, the Nemeth, the Little Bird, and the Facetmobile all get the same extreme STOL and slow-flight performance without worrying about that myth.
My understanding of the counter-vortex props at low speeds was primarily to improve l/d by reducing vortex drag. Vortices may be great lifters at high AoA but they carry a high induced drag penalty. For cruise where the tip vortices reduce the net lift and add drag. Simple washout drastically reduces net lift during cruise, so a much bigger wing with higher weight is needed to lift the same payload.
In lo-V hi-A flight, the XF5U props were designed to provide a net sidethrust in a vertical direction, aka lift. They achieved this through cyclic pitch variation. In a simple scheme, the angle of the rotation axis to the airstream provides the pitch variation, in a more complex scheme the blades are variable rather like a helicopter's are. As I recall, the 173 relied on the AoA while the XF5U had the full monty: in engineering terms its props were more like rotors than conventional props, however they acted as a variant known as a radial-lift rotor. For more about lifting rotors in general, I recommend Foshag, W.F. and Boehler, G.D.; "Review and Preliminary Evaluation of Lifting Horizontal-Axis Rotating-Wing Aeronautical Systems (HARWAS)", Aerophysics Co., 1969, http://www.dtic.mil/dtic/tr/fulltext/u2/857462.pdf
I speculate that Zimmerman may have calculated that any loss of vortex lift would have been compensated by the lifting props, with the reduction in vortex drag outweighing the additional power needed to drive the hard-working props.
But the truth is always in the testing. Failing to fly the XF5U as a pure research craft once all that money had been spent building it was an incredible wasted opportunity.
 

edwest

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Cutaway Flying Saucer ???, author unknow an retouched by Motocar

This is not a circular aircraft. This is said to be an A.V. Roe of Canada design. A version of their Project Y which was abandoned to build a circular aircraft.
 

John Frazer

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Again, trying to reduce the vortices is nonsensical. Under any circumstances. The understanding of it that says this was an intention is mistaken.
They're the specific design feature sought after by the low aspect ratio. They give it the super-slow ability. You wouldn't want to reduce it.
As its slow speed performance shows it didn't reduce the vortices anyway. By definition, it used them, not reduced them.
The extreme vortices and attendant drag goes away during cruise; there's no point in such complexity to reduce something that isn't there. If the complexity of the aledged lifting props was making it not work, and they were virtually certain to get a plane like the S-2 with more speed & payload and 35kts landing speed.
They ignored it in search of VTOL and the completely new theory of his.
It still makes poor sense to not just stick a couple of engines like the S-2 on it.
 

steelpillow

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trying to reduce the vortices is nonsensical. Under any circumstances.
It is interesting to compare this unsupported opinion with a quote from Aeroplane Monthly posted earlier in this thread; "...full-scale wind tunnel tests at Langley Field indicated that the high induced drag of the low aspect ratio wing would be partially compensated for by the interaction of the large props rotating in opposite directions ahead of the wing. Wing tip vortices which cause loss of lift on conventional wings were nullified by having each propeller rotating counter to the vortices." As far back as 1905 John William Dunne abandoned the stable delta wing in favour of a more effificent high-aspect-ratio swept planform (source: Dunne Archive in the Science Museum. Also, letter to the President of the Aeronautical Society of Great Britain, 1905, Baden-Powell collection, National Aerospace Library). It is only those who seek high manoeuvrability or low supersonic form drag who must resort to lower aspect ratios. Eight years later Dunne also famously lectured to the Aeronautical Society of Great Britain; "But the aeroplane does these things, and if the theory does not give warranty to the practice, then it is the theory that is wrong" (Journal of the AeS, 1913). I am sure that the designers of modern jumbo jets would be fascinated to learn that their long-span, heavy and expensive wings with their vortex-reducing winglets are doubly unnecessary. But some supporting literature might help give credence to John's overturning of a hundred years of aerodynamic belief.
One might note that where designs such as Concorde do adopt a low aspect ratio with vortex lift at low speeds, the drag penalty of the vortices is enormous and requires supersonic-class thrust to maintain flight. Hence Concorde's noise problem during takeoff and landing. This was all exhaustively studied. By contrast, a few personal opinions to the contrary on the capabilities of some poorly-documented private experiments must face an uphill struggle to be taken seriously. It is hard to accept that supporting numbers exist.
 
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