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VGs/ uncambered airfoils and drag


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Posted

Here is an interesting video circa 1938 about flat , uncambered and streamlined air foils. IF you look at the flat or undercambered airfoil, at high angle of attack the airflow seperated pretty far forward on the wing. This is why it is important to get the VGs up front, if too far back they are in "dead" air and cant do any good. I think Trent said 4% of the airfoil which I think is only 2" aft of the wing leading edge...

Also the undercambered airfoil has more drag than most airfoil even at 0 angle of attack. I guess they work on really slow very low powered airplanes but as kitfoxs amd avids got bigger and bigger engines, it reared its ugly head as a drag producer... one last thing and I am not sure it is talked about here but thin undercamberd airfoils can exhibit nasty stall characteristics without any aerodynamic warning......in fact I have read lots of accident reports , "I was in a 45 degree bank at 50 mph with 2 on board and it stalled"

ANyway I thought the video was of interest to all here. IT also shows how slats work...

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Posted

Nice! And I love the music!

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Posted

I would like to know what wing doesn't stall at 45 degree bank flying  50mph? That is a pretty steep turn in slow flight be careful doing that stuff.

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Posted

Maybe a Quicksilver MX  ???  Although I never had mine in a 45 degree bank, or maybe never got to 50 MPH either.  :lmao:JImChuk

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Posted

in a stall, aerodynamic warning comes in the form of turblent air buffeting the tail... some airplane dont do this. that is they give little or no warning. Thin cambered airfoils are know for this. Believe it or not so is the super cub USA 35B modifield airfoil if the the flaps are up...roll a cum into a 45 degree bank and you are within 1 or 2 degrees of exceeding the critical angle of attack.....flaps down at all wil buffet the tail, the air gap between the fuselage and the flap end cause turblent air and shake the tail but flap up or cubs that are modified to run the flaps all the way intothe fuselage side to get more flap, get little warning....

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Posted

What I remember from flight training was 60deg angle of bank expect the stall speed to increase 40  percent over what it was straight forward stall. At 75 deg. it was 100 percent increase in stall speed. 45 deg. is 18%

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Posted

What I remember from flight training was 60deg angle of bank expect the stall speed to increase 40  percent over what it was straight forward stall. At 75 deg. it was 100 percent increase in stall speed. 45 deg. is 18%

Yes, if the bank is fully trimmed with back stick so it develops the load factor. And no if you do not trim into a zero altitude loss turn.

The better way to say it is that at 2 G's the stall speed increases by 40%.  1.4 x 1.4 = 1.96, so that the V squared portion of the lift equation is satisfied - same wing, twice the lift needs 1.4 times the airspeed.

But if you just bank, and allow altitude loss, no problem and no stall speed increase.

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Posted

Hi all 

i

the video is unavailable to me for some reason, it said the YouTube account associated with video has bin terminated 

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Posted

Nick is right on.  Assuming you won't exceed a 60 degree bank, set your minimum speed for flying the pattern at 1.4 Vs0, and you won't be falling out of the sky.  This is a good number to round up to the nearest 5, and wedge firmly in your noggin.

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Posted

Oops! Got nomenclature wrong!  Vs1 is clean stall speed.  That's what I meant in the above post.  Sqrt(2)*Vs1 rounded up to nearest 5 is more accurate min speed-to-fly in the pattern.

On another note, we all know that CL of the wing sections falls off kinda elliptically going out the span as the wingtip is approached.  So the smart designer chooses an airfoil that is not experiencing drag rise (not climbing the walls of the drag bucket) at zero CL.  This is why the undercambered airfoil is bad.  It's draggy out near the wingtips.

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Posted

After I read Stick and Rudder a few times, things became a lot more clear as far as controlling an aircraft. Its amazing how much we overcontrol and make bad things happen.

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Posted (edited)

FWIW, I found out that the airplane (Avid-C) would flare itself on landing!  Just had to be steely like a fighter pilot, holding 500fpm descent right into the ground!  Trust your airplane, Luke!  Took a while to achieve that level of trust. Playing chicken with Mother Earth, you figure you're gonna lose, a priori, anyway!  

Edited by Turbo

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