V-173 / XF5U - Flying Flapjack

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drive330

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Sanman,

The “Holy Grail” of “STOL + High Speed Flight + Range” as you interpret it has been the very same challenge for aircraft designers since the dawn of manned flight. What's then the best way to achieve this combination, in a cost-effective way suitable for personal aircraft? The answer is readily apparent. The market for light aircraft is rife with designs, all of conventional configuration that do a pretty good job meeting all of those conflicting goals.

Aircraft by nature are a collection of design compromises. The gifted designer excels at minimizing and harmonizing compromises. You want to fly real fast; you probably can’t fly relatively slow. I am a retired airline pilot. The A-350 I flew was limited to 350 knots at sea level. Despite all manner of sophistication in wing high lift devices the approach speed was typically 140 knots or more, roughly a 2.5 to one ratio. Desiring long range requires skinny wings; desiring to fly fast requires short stubby wings. What to do?

Zimmerman’s aircraft fall into the broader category of tailless aircraft. Simply put in order to design a tailless aircraft both stable and controllable require numerous compromises invariably resulting in performance inferior to an aircraft with a fuselage and tail surfaces. I will not address the promise of tailless aircraft employing digital flight control and stability systems that open a new world for tailless design…

The “wing body” does not have any performance advantages. In fact, discarding of that pesky fuselage and its internal volume requires overly thick airfoils. A classic example is the Northrop XB-35/YB-49’s thick airfoils (18 percent!) and it’s contemporary the revolutionary Boeing B-47 and it’s thin high-speed airfoils. A direct comparison was the XB-35 and the Convair B-36. Both aircraft were required to meet the same performance demanded by the Army Air Force. The B-36 was clearly superior as a long-range piston powered airplane even without the later addition of four jet engines. When adapted to jet power the B-47 literally blew the doors off the YB-49 by any metric. The closest contemporary to the B-47 in terms of “wing body” was the brilliant Avro Vulcan. Both airplanes had similar performance with the exception of the ability to immediately climb to a higher sustainable operational altitude that favored the Vulcan, a result of its much lower wing loading. That and the Vulcans far lower radar observability or “stealth”.

The Zimmerman planform requires (enabling positive static margins) symmetrical or reflexed airfoils that are terribly less efficient than say the tried-and-true yet ancient Clark Y. This in itself begins to nibble away at range and load carrying capability. If you desire efficiency in range do not choose Zimmerman’s low aspect ratio.

You stated: “But given the ability of the vehicle to change the orientation of its entire body, doesn't that amount to the whole wing-body becoming a "flap"? To me, that seems like the most "flap" you can get."

The short answer is an emphatic no. Respectfully, you apparently do not understand the fundamental difference between merely increasing the angle of attack of an aircraft and its wing and the alteration of a wing and wings airfoil by a flap.

Any winged flying “vehicle” is capable of changing the “orientation” as you are relating to its angle of attack, at least it better be capable of doing so.

Decidedly this is not “the most flap you can get”.

Flaps increase the angle of attack of a wing thus increasing lift while concurrently increasing the maximum coefficient of lift of the airfoil at a lower angle than a “clean” wing or airfoil. By increasing the angle of attack of the wing with flaps and not the “entire vehicle” the aircraft with flaps allows for the pilot better forward visibility looking down to their intended landing site. If you take the time to read Boone Guyton’s experience in flying the V-173 he states that while on approach to landing the high angle of attack of the V-173 (required of the low aspect ratio wing) resulted in lousy forward visibility. The V-173 incorporated windows in the lower leading edge to assist in forward visibility, Guyton found them useless. Guyton barely survived the first flight of the V-173. Luckily for Zimmerman was that Guyton was a very gifted aviator.

Additionally, when fully lowered flaps increase the wings drag. This greater drag allows for steeper approaches to landing, a big advantage to clearing obstacles in the flight path and quicker deceleration in landing roll out.

The history of flight was advanced by theoreticians and designers who thought outside the box. Along the way many ideas and concepts were investigated, some broadly incorporated such as flaps, others discarded for various practical reasons. There is no rational reason attempting to reinvent a flawed design. Despite a gifted designer and the vast resources and practical experience of Vought aircraft the Zimmerman aircraft were discarded for very well-grounded reasons. No pun intended although the V-173 should have remained grounded. Had the turbojet revolution not occurred, the XF5U-1 even with its nearly insurmountable engineering challenges resolved would have been an expensive dud.

I have something that nearly all of those who propose to resurrect the Zimmerman aircraft do not have, practical real-world experience.

There is an effective device for deflecting rocks from tires called a fender.

I recommend you put your precious time and effort in more fruitful endeavors. I have no further opinions to offer and am finished with this discussion.

Chris
 

sanman

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Ah, the good old days - back when we looked forward to flying cars:



This one's narrower, and look at the nifty wide stance of its wheels:




But I just thought of another idea. What if you take an aircraft like the Arup/Flounder/UFO, but you shift your cockpit & canopy farther away from the front of the aircraft?
So that's then helping to shift the Center of Gravity rearward, which can help the aircraft pitch up and maintain high AngleOfAttack during landing & takeoff. You might also enjoy more separation from the engine noise.

Ideally, instead of having your canopy bulging up from the topside of your wing-body, it could instead bulge down from the underside of your wing-body, to give you a better view of the ground.
 
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edwisch

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As for emergency egress -- yes, you would normally enter the aircraft from below. But, in case of a forced landing out in the boonies, why not just open the canopy and walk across the wing?
 

Hephaestus

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And it does this without resorting to the complicated mechanisms of the V-22 Osprey. It's main shortcoming was its other complicated mechanisms of the gears and shafts - which is a more solvable problem, in my opinion.
You need to go back to the initial research.

Gearing and TV is not a 'more solvable problem' for one. @wsimpso1 is a respected member with decades of experience in this field - and has already pointed that out.

Second, the V173 didn't have simple propellers. See the video on the v173's walkaround after restoration. I've never encountered a propeller that has a flapping mechanism before. I think it's safe to say you're not going to get such a prop from any manufacturer today.
 

rotax618

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The CG of any aircraft has to be kept within strict limits to ensure stability, it is not possible to simply move the payload/passenger rearward to increase the angle of attack for landing - control surfaces and undercarriage placement are the controlling factors.
A tricycle undercarriage can provide a higher alpha for landing than a taildragger as the mains are further back.
 

sanman

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Hi Christ/drive330, thanks for your reply, it gave me lots to think about.

So let me then modify the goals/requirements I previously gave, and re-state them as:

Safety + STOL + Speed + Range

So I've added in safety as a goal/requirement, and I'm listing these things in order of priority.

Everyone's different, but for a personal aircraft I'd value these things in the order I've listed them.

So why am I suddenly looking at Low Aspect-Ratio wings?

Because of this:



Bush planes like these are great in so many ways, but they're very vulnerable to cross-winds and turbulence.
That large lateral wingspan creates enough leverage to tip a plane over from the side.

None of Draco's flaps could have saved it, due to its high aspect ratio. Fortunately, Mike Patey is still alive.


You stated: “But given the ability of the vehicle to change the orientation of its entire body, doesn't that amount to the whole wing-body becoming a "flap"? To me, that seems like the most "flap" you can get."

The short answer is an emphatic no. Respectfully, you apparently do not understand the fundamental difference between merely increasing the angle of attack of an aircraft and its wing and the alteration of a wing and wings airfoil by a flap.

Any winged flying “vehicle” is capable of changing the “orientation” as you are relating to its angle of attack, at least it better be capable of doing so.

Decidedly this is not “the most flap you can get”.
Alright, so I wasn't trying to argue the superiority of wingbody over the traditional wing+body.
What I was really focused on was that AngleOfAttack is really about the angle of the wing relative to the oncoming airstream, and how much surface area is effectively deflecting the oncoming airstream to produce both drag+lift. If it's a wingbody aircraft, then changing the orientation of the vehicle does change the AngleOfAttack, since wing and body are one and the same. I wasn't arguing whether it's better to do this with a wingbody vs a traditional wing+body.

You're saying that bending flaps is more convenient than changing the orientation of the entire aircraft for AoA, while also saying that LowAspectRatio wings don't allow for effective flaps. So by your reckoning, the HighAspectRatio wing is the best thing for bush planes, because it allows for the effective use of flaps for changing AoA, while also providing plenty of wing area for low stall speed and good STOL.

Well, the high-aspect-ratio wing on Draco is why it crashed - because that kind of wing is vulnerable to cross-winds and turbulence.


Flaps increase the angle of attack of a wing thus increasing lift while concurrently increasing the maximum coefficient of lift of the airfoil at a lower angle than a “clean” wing or airfoil. By increasing the angle of attack of the wing with flaps and not the “entire vehicle” the aircraft with flaps allows for the pilot better forward visibility looking down to their intended landing site. If you take the time to read Boone Guyton’s experience in flying the V-173 he states that while on approach to landing the high angle of attack of the V-173 (required of the low aspect ratio wing) resulted in lousy forward visibility. The V-173 incorporated windows in the lower leading edge to assist in forward visibility, Guyton found them useless. Guyton barely survived the first flight of the V-173. Luckily for Zimmerman was that Guyton was a very gifted aviator.

Additionally, when fully lowered flaps increase the wings drag. This greater drag allows for steeper approaches to landing, a big advantage to clearing obstacles in the flight path and quicker deceleration in landing roll out.
So your mention of "forward visibility looking down" catches my attention most. That certainly would be difficult with a HighAspectRatio wing where the canopy is on top. But what's wrong with having the canopy below the wing? That can either be done with a high-wing design (which of course is not a wingbody), or else have a wingbody with very long undercarriage (like V-173)

On a low-aspect-ratio aircraft, it would be nice to have a better means of seeing the ground.
Perhaps on the UFO, it would be nice for that hatch to be see-through, so that you could have that better view of the ground.

Maybe a window is a simpler way to get that forward visibility looking down, as compared to depending upon low AngleOfAttack for the entire vehicle fuselage.


There is an effective device for deflecting rocks from tires called a fender.
Okay, fair enough - I do wonder why most bush planes don't seem to have the fender, and instead have the naked tundra tires.
I assume it's because they're afraid of having rocks get stuck between the tire and the fender?
 
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sanman

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As for emergency egress -- yes, you would normally enter the aircraft from below. But, in case of a forced landing out in the boonies, why not just open the canopy and walk across the wing?
Okay, so the underside hatch is the nominal route, but the canopy method would be there as a backup.

Why is it better to have the canopy on top though, when it restricts your view of the ground?
Wouldn't it be better to have the canopy on the underside of your wing, to afford you a better view of the ground?

Or what if your underside hatch was see-through? I'm assuming that the airflow on the underside of the wing would keep it from frosting over, even in very cold weather.
 

edwisch

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Why is it better to have the canopy on top though, when it restricts your view of the ground? Wouldn't it be better to have the canopy on the underside of your wing, to afford you a better view of the ground?

Usually, visibility is optimized for avoiding mid-air collisions.
 

Aesquire

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No, high aspect ratio wings didn't cause the crash of the Draco. The pilot said so. Sailplanes with much higher AR wings don't all flip without pilot oops.

The V-173 did crash, flipped over on it's back on landing in soft soil. The belly hatch allowed the pilot to walk away without injury.... Actually the seat harness did that. But the belly hatch meant he wasn't trapped in an upside down plane... Where's the escape hatch on the RV-?

If you built a flying replica/homage, then it's simple to have the upper canopy disconnect with handles you'd only use in emergency or maintenance. That's a detail worth doing, & no condemnation of the UFO or V-173.

there are multiple reasons to want a low aspect ratio craft. Superiority in range&speed&STOL all at once is advertising hype, not reality.

That's not a hating rebuke of the many clever and cute designs. That's just saying you shouldn't expect a Free Lunch. It doesn't exist.
 

bmcj

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I could imagine a 2-place version as a tandem.

Here's another vid of the high-wing version:



But regarding UFO itself, he's mentioned that he enters and exits from a hatch on the underside of the aircraft.
Watch him sticking his legs out of the bottom of the aircraft at the end of this video, while taxiing to a stop after landing.



He'd improved the UFO-2 with retractable landing gear, which I unfortunately can't find a video of.



I'm not sure how you could do a side-by-side 2-seater, since that might require a smoother, more conformal design.
Fire that cameraman.
 

rotax618

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If your V173 has an underslung fuselarge and a single engine and prop you end up with a high wing Arup, as the model above, given enough power, would be a great bush plane. The high thrust line allows for a big slow turning quiet prop with helicopter like static thrust. The large internal volume of the wings has room to bury the engine and accommodate fuel and baggage.
 
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Sockmonkey

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If your V173 has an underslung fuselarge and a single engine and prop you end up with a high wing Arup, as the model above, given enough power, would be a great bush plane. The high thrust line allows for a big slow turning quiet prop with helicopter like static thrust. The large internal volume of the wings has room to bury the engine and accommodate fuel and baggage.
I've been saying that for a while.
 

edwisch

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C'mon, now, model airplanes have so much thrust they don't need wings!! :)

Here's the video of the retractable gear UFO:
 

cblink.007

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What i like is that those engines at the tip rotate each one i guess to the outside, avoiding the creation of a tip vortex. Possibly the effect is that the plane has in reality a much larger AR than based on the actual planform.
Our proprotors on the Osprey turn opposite the vortices...same with other tiltrotors such as the XV-15, AW-609 and the V-280, for that reason...
 

cblink.007

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Well, the high-aspect-ratio wing on Draco is why it crashed - because that kind of wing is vulnerable to cross-winds and turbulence.
You do know that a fuselage and other vertical surfaces tend to play a factor in crosswind landing events, and not just the wing's aspect ratio, right? It's a phenomena called "weathervaning". Read up on it.

But, since you apparently know the cause of the crash, please post a copy of the investigation report here on this thread. I want to see the part in the report describing the environmental conditions (ie wind direction/velocity and runway heading) at the time of mishap and where the investigation team concluded that wing's aspect ratio was listed as the precipitating factor to the probable cause of the accident. My colleagues and I here in the tiltrotor developmental flight test community would like to understand your rationale. We are just a bunch of seasoned XP's and FTE's, so we are curious.

You seem very new to the aircraft engineering field, which is fine if you are. Welcome to HBA. You are curious and ambitious, which is a trait highly desired at any level in our trade. However, learning the basics before going forward into more nonconventional creations like a reimagined V-173 is absolutely paramount. Aircraft, even the 'simple' ones like a Cessna 152, are complex by nature and are the end result of a complicated game of give and take. Many of us here are highly experienced engineers, mechanics and pilots, while others are just getting started. Heed our feedback. Airplanes, even those that are well-designed, are very indiscriminate and highly efficient killing machines if the right combination of factors line up. So, it has to be done as right as possible coming out the gate. Even at that, problems may still be encountered. I know this as a hard truth- I test fly the V-22 Osprey for a living...and love it.

In the meanwhile, take a look at this Personal Air Vehicle concept from NASA called the "Puffin", and draw some inspiration for your ideas:



Here is a UAS in development from my employer that has drawn upon the Puffin concept:


Word of advice- large props like you may need must flap and feather...necessarily...due to the relatively high aerodynamic and gyroscopic forces in play. If they can't be allowed to do so by way of a smartly-designed hub, there will be some awfully high forces being transmitted throughout the mast-mount-airframe structures. Our drive & rotor folks speak in tongue I can never comprehend, but the Osprey's hub design conceptual heritage goes way back to the V-173. However, prop and hub designs like this won't be found in the Aircraft Spruce catalog...

Best of luck!!
 

Victor Bravo

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So let me then modify the goals/requirements I previously gave, and re-state them as:

Safety + STOL + Speed + Range
OK, I can help you find this combination of features, it's no problem whatsoever.

All it takes is being open to a slightly different way to look at the problem and the solution. For example, let's say you are like me: Overweight, have eaten too much of the wrong things for most of life, and have developed vision problems, kidney problems, and blood pressure problems because of it.

Would you go to one doctor and demand that he or she cures all of your problems? Or would you go to an internal medicine/Endocrinologist doctor, and then an retina specialist/Opthalmologist, and a kidney specialist/Nephrologist?

Fortunately you are much more lucky than I. In your case, the aircraft can address three of your four requirements, and an experienced instructor will allow you to contribute the fourth requirement.

Since we're on an experimental airplanes forum, I'll say that the Bearhawk aircraft excels in STOL, Speed, and Range. You can get all of those features, with fantastic "real world" utility, in one aircraft.

In the types of aircraft that you are discussing in this thread, safety will not be given or taken away by the aircraft; it will be 99+% dependent on the flight instruction that you get. If you watch the Draco video you will see proof of this. Mr. Patey admits that it was his decision to take off at that time, in that wind, pointing in that direction, that caused the aircraft to be damaged. It had nothing to do with the aircraft itself, any more than (most) car accident has anything to do with the design of the car.
 

cblink.007

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Mike Patey NTSB accident narrative here : NTSB Docket - Docket Management System

He said he had full left stick. Must have had full right rudder since he did not let it weathervane. So crossed controls. Crosswind gusts 38 kts.
Did not find any NTSB final report for N123T.
That'll do it to any light aircraft...or even a heavy V/STOL tiltrotor like mine! Here is our crosswind envelope...
20210310_134950.jpg
 
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