John Frazer
Airman
- 43
- Apr 21, 2018
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Well, today's your lucky day: I know a person who's a member and they downloaded the file.John Frazer said:Apparently, NASA Langley did studies with a wind-tunnel model and found only changes were slight changes in longitudinal stability at high-"A", with the props spinning in the *same* direction. (not as if to counter the wing-tip vortices).
I can actually agree to that. Short of building a model flight simulator... anybody here got some variation of X-plane?John Frazer said:We still need to see better data on the Arup planes.
Supposedly, the guy who led to the design of it was a podiatrist who somehow figured that a heel lift flew surprisingly well.Only one wikipedia mention of glide ratio, with zero citations...
Yeah it basically seems that if the aspect ratio is high you can get more lift for less wing area, but if the wing area be sufficiently obscene, you can make it fly decently well.And NACA was impressed with the efficiency of the S-2, and Hatfield spoke very highly of their efficiency as well. Models of them are very good at soaring, and the originals were lightly loaded.
Basically it seems to list two things"Radical Wings and Wind Tunnels" is about Langley, and in the section of the V-173 . . . Tests with powered models in tunnels showed little effect from props spinning the other way -inward- at the tips, except more stability that way.
The vibration if I recall was caused at high AoA by span wise airflow. This effect is not dissimilar to advancing/retreating propellers..it's a mystery why they built the silly flappy props
The vibration if I recall was caused at high AoA by span wise airflow. This effect is not dissimilar to advancing/retreating propellers..
Not just US designers, it's been a problem in aeronautics since the Wright brothers, linking a herky jerky reciprocating engine to a smoothly rotating propeller through a crank shaft extension, a driveshaft, or a gearbox light enough for aircraft use. The solutions that work in nautical applications are generally too heavy for aircraft use and are generally aimed at a lower RPM range. Aircraft structures tend to be more flexible than boat hulls and more likely to transmit rather than dampen vibration.All sources say it was the power distribution system to allow either engine to take over and drive either prop, combined with the complexity of the flapping system. It seems US airplane & airplane engine makers were having bad luck designing prop extension shafts or distribution systems; maybe should have asked boat builders for help.
How about asymmetric thrust? The loss of one engine without an interconnect would render a multi engine flapjack uncontrollable. The only thing that keeps a conventional multi engine plane straight with one out is the power of the rudder and the arm through which it is working. This power diminishes abruptly as speed decreases. A flapjack flying slowly at high AOA is not going to be able to handle an asymmetric thrust situation.There was no apparent reason to innovate such extreme measures
The flapping system was designed to deal with the propellers being mounted on the tipsAll sources say it was the power distribution system to allow either engine to take over and drive either prop, combined with the complexity of the flapping system.
Counter-rotating propellers spin in opposing directions, contra-props are coaxial propellers (two rows of props which spin in opposition). While I'm uncertain the exact degree the rotation affected lift since I'm not 100% sure as to what I'm reading, but it seems to be fairly minimal at high-speed and more significant at low speed however significant/insignificant. Low speed would be where it would count so it's a nice touch.V-173 did nothing that the Arup hadn't demonstrated years before, without the consideration of the contra-props.
The Arup planes were designed for considerably lower speeds, and at least the S-2's wings were pretty thick in some areas. The V-173 was a demonstrator, so it had fixed-gears to verify the low speed of the equation (we could already build fast aircraft). The XF5U-1 was built for low and high speed, so a thinner wing would have been arguably more useful, and that could have affected the low-speed side of the equation.There was no apparent reason to innovate such extreme measures, for to counter the vortex which the aspect ratio was specifically designed to maximize at low speed
They had thought of making it able to lift off and rocket vertically, or be able to land vertically if I recall. I don't remember the source so you might not wish to quote meCould they have thought the XF5U could actually be VERTOL
How about asymmetric thrust? The loss of one engine without an interconnect would render a multi engine flapjack uncontrollable. The only thing that keeps a conventional multi engine plane straight with one out is the power of the rudder and the arm through which it is working. This power diminishes abruptly as speed decreases. A flapjack flying slowly at high AOA is not going to be able to handle an asymmetric thrust situation.
The V-173 and XF5U would not have crashed if one engine went out (if one propeller stopped spinning, that would be different): They were designed so that each engine can drive the other shaft. Should you lose an engine, the RPM of both props would slow down a lot, but you'd remain in control.John Frazer said:Only if it uses twin props so far off the cener axis line -'way out at the tips. Many normal twin-prop planes don't suffer too badly, most are fly-able with one engine out.
Isn't that exactly the configuration of the "flapjack"?Only if it uses twin props so far off the cener axis line -'way out at the tips.
I've only got about 9,000 hours of twin prop time, so maybe I'm not qualified enough to comment, but here goes.Many normal twin-prop planes don't suffer too badly, most are fly-able with one engine out. There's no reason to suspect that a more normal twin arrangement on an extremely low aspect ratio plane would be any different.
His idea was focusing on the fact that part of the massive lift benefit of the V-173 & XF5U came from the massive propeller slipstream itself. Even at low-speeds where AoA is the highest and vortex-strength the most extreme, with the propellers designed to reverse the wrong way, you'd have a loss lift ranging from 33-1/3 to 50%, which is obviously quite substantial, but with no angular momentum (which is a true test of the effect since rotating them the wrong way actually would intensify the vortex, and rotating them the right way will neutralize the vortex), you would see half that loss -- 16-2/3% to 25% produced by vortex cancellation. This would result in 75% to 89-1/3% produced by simply blowing massive quantities of air over the area of the wing.Isn't that exactly the configuration of the "flapjack"?
Sorry about thatAlso, to correct a mistaken idea perpetrated by Zipper, if you lost one engine in a "cross-linked" flapjack, you wouldn't lose prop RPM, (they're governed), but you would lose over half your thrust, and still have a controllable aircraft.
You can't have it both ways. Move the props (rotors?) inward, and you limit their diameter and lose some of your full-span slipstream, for not much improvement in assymetric handling. Leave them out near the wingtips and you get better slipstream/span coverage at the cost of truly impossible single engine handling. Gotta have that propeller interconnect.His contention was if the propellers were mounted further inward, this would reduce the amount of yaw produced by loss of thrust, increase in drag, and roll produced both by yaw and loss of slipstream over the wing affected.
Plus with the existent diameter, you'd only be able to move it in a small ways, and even if you reduced the diameter a skosh, to cover the wing you'd still need a substantial diameter and would have to move the engine further outwards which would be difficult to do, would probably still have poor engine-out performance, and you'd probably need to increase the wingspan to make the cowl and airframe to blend right.You can't have it both ways.
The other possibility that John Frazer proposed was the Boeing 390 (he listed it as the Boeing 396, I couldn't find it in searches, so I just entered "Boeing Flapjack" and got the right answer) which was similar to the Arup S-2 and S-4 arrangement.Move the props (rotors?) inward, and you limit their diameter and lose some of your full-span slipstream, for not much improvement in assymetric handling. Leave them out near the wingtips and you get better slipstream/span coverage at the cost of truly impossible single engine handling. Gotta have that propeller interconnect.
From what the NACA report said, from what I remember, the biggest variable was the slipstream rather than the rotation of the propellers (by that I mean the velocity of the air blowing over the wing, not the direction of rotation) except potentially at low speed, where the result would vary by around 1/3 to 1/2.Not true that it gained the extra lift at very low speed from slip-stream from the outward-rotating props.
I could re-read it, but from what I remember at low speeds the amount would be around 1/3 to 1/2. At higher speeds the amount would likely be less significant.It's stated that 3-4x lift for such a speed, comes from the planform.
I assume you mean the trailing edge of the wing? From what I remember the variables that lead to vortex production are highly swept surfaces, and the trailing edge was more highly swept.It's the same phenomena for the Arup, the Nemeth, the Little Bird, the Facetmobile. (all of which were stall-proof, also due to the "vortex parachute" it creates behind/above it while flying very slow with high A)
But that airplane had a totally different wing-cross section...Wainfan put it into verified science, just as Zimmerman established that the very low aspect-ratio gave it the extra lift at low speed.
He was after something else. The very-slow speed for the clean all-wing-body, was due solely to the planform and type, not the props.
I read the document on the XF5U/V-173. They said the bulk of the performance wasn't due to the direction of the propeller's spinning, but instead, the function of the large slipstream produced by the propellers.None of that's accurate.
As I understand this, the problem would be that it would produce massive amounts of drag unless the wing loading was very very low.The enhanced lift at super-slow speeds is due to the "parachute lift" created by the wing-tip wrap-around vortices of the low aspect ratio.
And that wing loading and aspect ratio are going to produce some bodeacious vortices!Getting to the XF5U on the other hand, the figures are as follows
Note the wing-loading here, it's in the double-digits. It's the only one in the double digits.
- Weight: 16722
- Wing Area: 475
- Aspect Ratio: 1.1462
- Wing Loading: 35.2042
Bodacious vortexes, sure, but the higher the wing-loading the higher the AoA, and that will drive up the drag a lot.And that wing loading and aspect ratio are going to produce some bodeacious vortices!