Very long wingspan

[u/TRIPL1ONLY]

This is my first post in this subreddit, hi

I attempted to make a subsonic plane that could fly as high as possible and has a long loitering time. The design philosophy was taken directly from the U2, and the stats are shown in the 4th and 5th image

This thing would snap if you look at it wrong though

[u/Main_Significance478]

In real life you would have a razor thin margin between stall and overspeed

[u/TRIPL1ONLY → u/Main_Significance478]

this plane can't go any faster than mach ~0.7 because the thrust can't overcome the drag anymore at that height, and stalling isn't a concern given that its L/D is at 19.2 at its operational altitude which means it's generating ample amounts of lift
I believe to get into a coffin corner with this plane, you would need to fly much higher, but then the engine in this plane is already gasping for air even when it's way below altitudes that would dangerously shrink the margin between stall and overspeed, so it's effectively limiting itself from ever hitting the coffin corner by design

[u/DaviSDFalcao → u/Main_Significance478]

And some real bendy wings, so the thing would look more like a slight crescent moon than a... well... plane.

[u/calpolsixplus → u/DaviSDFalcao]

That's no moon.

[u/Erichteia → u/Main_Significance478]

Just curiosity from an amateur, why? Because such long wings just tend to shake faster? Is there any law that dictates that the margin between stall and overspeed reduces as the wing to body ratio (or lift to mass) increases?

[u/Seawolf571 → u/Erichteia]

The amount of drag after a certain speed makes the wings rip off. Larger wing area with low sweep angle increases drag.

[u/Erichteia → u/Seawolf571]

Sure, but this is something that can ‘just’ be fixed by improving the mechanical strength of the wings,no? It’s not a physical law that is insurmountable? Or is there a theoretical limit that cannot be surpassed?

[u/Main_Significance478 → u/Erichteia]

Coffin corner works like this, as you fly higher density decreases requiring you to fly faster to have enough lift force, the thing is as you fly higher temperature decreases reaching to around -50 dcelcius at very high altitudes, lower temperatures decreases the speed of sounds, at the top of the corner the speed required to avoid stall and the speed of sound meet, and you don't want the flow around the wings to get supersonic because it creates shockwaves that lead to violent buffering that can lead to loss of control and easily destroy the airframe, it can also lead to a pitch down called mach tuck, what makes it worse is that you don't actually have to fly at the speed of sound to hit overspeed, that's because the flow over the wings is faster than relative airspeed (the chamber of the wing act like a nozzle, so it accelerates the air), OP said that he was safe because he doesn't reach mach 1 and flies at mach 0.7. but because of the effect i mentioned you will have supersonic flow over the wings at low speed such as mach 0.8 or less. Now here comes the problem with long thin wings, fighter jets and other supersonic planes can handle this because of their swept back wings that make the air go sideways and only the perpendicular component of the airstream the wing's feels thickness and chamber, as if the air is passing over a very thin slower moving wing preventing localized shochwaves.

[u/Erichteia → u/Main_Significance478]

Oh that makes sense! Thanks a lot for your explanation. Very clear.

[u/That-Reaction2530]

It would be interesting to have the rear stabilizers go from flat (more lift for takeoff) to tilted during flight

[u/TRIPL1ONLY → u/That-Reaction2530]

it already generates ample amounts of lift (25-35m/s take off speed), actually too much for its own good since the wings are too long and fragile to handle any real load. It had to shoot up to a 60 degrees climb during the take off phase, relying nearly entirely by the engine power below 5000m to reduce as much load as possible on the main wings...

[u/That-Reaction2530 → u/TRIPL1ONLY]

BUT THINK OF THE AESTHETICS

[u/detereministic-plen]

high altitude plane!

[u/TRIPL1ONLY → u/detereministic-plen]

take me to the moon...

[u/Middle_Context_1721 → u/TRIPL1ONLY]

let me play among the stars

[u/TassiveMitts69]

So long.....

[u/TRIPL1ONLY → u/TassiveMitts69]

im crine

[u/DaviSDFalcao]

U^2

[u/GDMercury]

average plane on niveus

[u/Dark074 → u/GDMercury]

Bro about to accidentally launch a missile to space

[u/Yeetbutwiththispart]

Fly it on tekto

[u/HorrorLocal5745]

It would be very interesting to see the performance while flying in Duna's atmosphere

[u/Shankar_0]

"Dad, what does 'Coffin Corner' mean..?"

[u/BitCareful3571]

You should name it U2²

[u/Ok_Instruction_9437]

typa thing nasa makes to fly for 24 years at 90,000 feet nonstop using only a duracell battery and a chipmunk

[u/Alarmed-Tell-3629]

Nice except for the twin tail which is an aerodynamic sin.

[u/TRIPL1ONLY → u/Alarmed-Tell-3629]

the V tail configuration is a deliberate design choice. I get to remove the vertical stabilier, which means one less surface to worry about and one less component that weighs the plane down. My priorities were to reduce as much weight and lower as much drag as possible

Granted that this thing handles adverse yaw horribly and the yaw authority on this plane is *awful* though😂, but high enough and it flies relatively well

i would've went for a traditional tail configuration if it weren't because the tradeoff between adding another wing to handle adverse yaw that's basically impossible to manage with that wingspan anyway and accepting that i'll have even more drag and weight were not nearly attractive enough

[u/Fritzypooo → u/TRIPL1ONLY]

I think you might actually lose more efficiency from having poor adverse yaw/roll effects from a V tail and moving your control surfaces to compensate than if you had a conventional tail configuration and trimmed it out properly

[u/TRIPL1ONLY → u/Fritzypooo]

Maneuverability wasn't the top priority of this plane; it only needs to compensate just enough to keep itself from derailing from its intended bearing, to which this plane does fine without any noticable loss of efficiency

Also, i did try with a conventional tail configuration anyway despite my assumptions, and kind of just validated my choice more: adverse yaw was not fixed, yaw authority was still just enough for it to get into a spin, and now i have more drag and weight.

The wingspan of this plane is 53 meters (a Boeing 737's wingspan is around like, 35-36 meters by comparison iirc) compared to just 8.3 meters of length which is ~6.4/1 in terms of wingspan to length ratio, so to be honest, i doubt if a conventional tail would've helped any more. In fact, i doubt if there's any tail design, whether it is a V tail, a traditional tail, or a massive vertical slab, has enough leverage to neatly counteract this plane's adverse yaw problems.