What is the thickest airfoil ever used in an aeroplane wing for lift ?

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challenger_II

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If you're really interested in super-thick sections, the literature to look at would be wind turbines, which go up to 40%+ at the root due to super-high structural loads. Those tend to be at low Re (because the thick sections are limited to the root; thickness taper is highly non-linear), so hard to generalize too far; but there's a whole lot of relatively bizarre mitigations to allow using such a thick section with minimal compromise; e.g. they're often sliced off with a TE thickness of > 10%, which is a massive bluff body, but still less drag than trying and failing to maintain attachment across such a huge adverse pressure gradient.

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Add to your premise that wind turbine blades for anything above 10mw have vortex generators from about 5% of blade span from the root (at the hub) continuing to 20% of blade span, to cut down on turbulence.
 

addaon

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Yep. As comes up often here, vortex-lift-dominated aircraft are a very different design point, and look and act different. The early lifting bodies lacked a sharp chine that we’d normally expect for vortex lift, but they’re AoA was so insanely high that they produced a pair of stabilized vortices over the body anyway.
 

Sraight'nlevel

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I wonder if 50% thick "wing foil" has any less drag than a round one ?

Maybe at very low re-number it might ?
 

bmcj

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I am curious...I recall B-29 had 28% thick airfoil in the root of the wing.

Could 50% thick be possible...would it bring anything...like weight savings ?

I am referring to the good old "tear drop" shape...which is supposed to be the slickest ever.
You might argue apples and oranges, but the Goodyear Blimp has a thickness ratio of over 30%. I say it’s a valid comparison because their blimp can be flown with a much as 800 lbs positive weight by driving it forward with the engines.

Another appropriate example might be the Deltoid Pumpkin Seed.
 

Sraight'nlevel

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I figure this is just 23% thick.
 

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cluttonfred

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I could see using a very thick (~25%) airfoil for a low-powered, low-speed design seeking to maximize the structural efficiency of a cantilever wing and put the fuel inside the spars. Take a look at the Göttingen 435, for example, with a max thickness of 26.1% at 27.8% chord and a max camber of 4.7% at 48% chord. With a 36" chord you'd have a max thickness of over 9" so you could easily fit a spar about 7" x 7" with off-the-shelf 6" diameter spun aluminum fuel tanks in the wing roots.

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geraldmorrissey

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My guess is the B2 has the thickest wing. I spent a lot lf time around them on the assembly line. The wing root was much taller then me at 6 but I would guess nowhere near 50%'. Much bigger airplane then photo's might suggest. As a side note, a B-52 fuselage used to sit outside tucked behind a building at Boeing Wichita. The angle of in incidence at the wing root was laughable.
 
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Norman

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Looking at this the very thick foil still is 10 x less draggy than a 100% round object.
The requirements for wings, struts, and bodies such as fuselages and blimps are entirely different. Struts are simply shaped to reduce their drag relative to a cylinder and aren't expected to produce lift so a fineness ratio of 3:1 is about optimum if the trailing edge is sharp but there's always separation on the last 10% or so, so you can cut the TE off without gaining much drag thereby gaining some structural advantage due to increased thickness but if you try to use that shape for a wing it'll be terribly inefficient because either AoA or camber will increase the adverse pressure gradient and cause separation. Vortex generators could help but then it's just a crappy wing with band-aids. The optimum fineness ratio of bodies is in that range too so blimps and lifting bodies are very fat but the lift to drag ratio of a lifting body is about 4:1. I have no idea what the L/D of a blimp would be but 800 pounds of lift from a few thousand square feet of area doesn't sound like a lot. I design thick airfoils for fun and I hate going over 19% thickness. The maximum lift starts dropping off after 17% for some families but for others it can be as low as 15%. The best L/D is a bit more complicated. If you don't mind sanding a lot before you paint it and then again between layers of paint and then wet sand the clear coat and then wash the wings often during service you can use highly laminar airfoils to get good L/D at fairly large thickness say 18% but if you're like most pilots who don't even wipe the bugs off 13% or lower is what you want for a low drag wing.
 
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Norman

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My guess is the B2 has the thickest wing. I spent a lot lf time around them on the assembly line. The wing root was much taller then me at 6'.
He was asking about percent thickness, not absolute thickness. The XB-35 had a 19% thick airfoil but since the thing was so huge the wing was 7' thick.
 

Sraight'nlevel

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I could see using a very thick (~25%) airfoil for a low-powered, low-speed design seeking to maximize the structural efficiency of a cantilever wing and put the fuel inside the spars. Take a look at the Göttingen 435, for example, with a max thickness of 26.1% at 27.8% chord and a max camber of 4.7% at 48% chord. With a 36" chord you'd have a max thickness of over 9" so you could easily fit a spar about 7" x 7" with off-the-shelf 6" diameter spun aluminum fuel tanks in the wing roots.

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26.1% might be the winner here.
 
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