High lift airfoils compatible with fabric construction?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Nov 23, 2019.

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  1. Nov 23, 2019 #1

    cluttonfred

    cluttonfred

    cluttonfred

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    Is there any benefit to using something like the GA(W)-1 or similar high lift airfoil with the inherent roughness and irregularity of a fabric-covered wing? Are there are other good high lift airfoils (Cl 1.7 or more) suitable for a relatively thick, fabric-covered wing at general aviation Reynolds numbers? Cheers, Matthew
     
  2. Nov 23, 2019 #2

    Topaz

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    With a traditional fabric-covered wing, you might as well use a traditional airfoil, as well. Even the old Clark Y has decent lift and drag, all things considered, for this kind of application.

    Not to mention that the GA(W)-1 has an absolutely horrific pitching moment.

    In general, the obsession with "high lift" is misplaced with very light aircraft, such as those that tend to be fabric-covered. Remember that stall speed and cruising speed are not the only performance parameters that matter in a light airplane. Perhaps even more important are climb and glide performance, and the safety that comes with them. It's entirely possible to "over-do" the quest for high lift and a small wing, such that climb and glide performance become dangerous. By "glide performance" I don't mean soaring or that you should build a motorglider. I mean how long and how far you can stay up if the noisemaker goes silent, and so how many options you have for a safe out-landing spot.
     
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  3. Nov 23, 2019 #3

    blane.c

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    I have been considering Riblett GA-30 series. I would like to understand more about such a decision.
     
  4. Nov 23, 2019 #4

    cluttonfred

    cluttonfred

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    Thanks, Topaz. In my case, the quest for high lift is related more to limiting wing area for reduced workshop and hangar size and easier removable or folding wings.
     
  5. Nov 23, 2019 #5

    BBerson

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    You can get any CL you want just by bending down the trailing edge of any airfoil. See figure 100 of Theory Of Wing Sections to see the effect of a sealed flap at 5° or 10° (like the GAW-1 appears). More flap equals more pitching moment.
     
  6. Nov 24, 2019 #6

    TFF

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    I would not be using any fancy airfoil on a fabric covered wing. You are not going to get the performance out of it. Clark Y, USA35B, 23012, M-6, the staples. How much span are you trying to lose?
     
  7. Nov 24, 2019 #7

    cluttonfred

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    No specific target in mind, just playing with design spreadsheets and finding that a move from 1.5 to 1.7 or more in CL provided significant reductions in span and area. Some classic glider airfoils like the Goe 535 from the old Slingsby glider trainers that Eric Clutton chose for FRED come pretty close.
     
  8. Nov 24, 2019 #8

    Starflight

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    Hi Matthew. I also was enamoured of "thick" , high lift airfoils for light aircraft. Learned a bit later in life that efficiency comes hand-in-hand with more attention to 'unnecessary drag'. There was a thread involving high lift thick airfoils which was prompted by confusion about the Zenair 701's 65017 airfoil. One of the airfoils mentioned was the NACA 6317, which showed a 1.90 CL max. Please try not to compromise the performance of your selected design of aircraft by limiting it's span. Span loading is crucial and consultation with copies of Prandtl's lift/power ratio/time-to-climb curves might be educational. *hugs*
     
  9. Nov 24, 2019 #9

    lr27

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    For short span, there's always the biplane configuration with a relatively large gap, but that's draggy. I suppose winglets are possible, but that's another can of worms, I think.

    The Ara D, 20 percent, shows good results with Xfoil, including both high lift and a relatively modest pitching moment. Presumably, since it was developed for wind turbines, it would be relatively insensitive to bugs and things like that on it. I don't know if that would extend to distortions from fabric. Plus I don't know if anyone has used it on an aircraft.

    There's an airfoil called the Icarus V, which I think was supposed to have been used on a hang glider. Profili/Xfoil thinks it has high lift, though it may be a little draggier than some. It's supposed to have a modest pitching moment also, and is just less than 15 percent thick.

    I mention the thickness because of course it helps with structural issues. Ditto modest pitching moments, which will help with trim drag as well. As Starflight mentions, using a short span will cost you some low speed performance.

    You could use Junkers flaps, which can also be used as ailerons, but of course that has structural issues. Still, it's a popular approach.

    Seems to me that a three piece wing might address your problem, and a thick airfoil probably makes the wing joining lighter and easier. I suppose the aileron control linkage might be a challenge, unless you take the Skypup approach and use only elevator and rudder for your aerodynamic controls. The Skypup uses something close to the NACA 23018, but that's not especially high lift. It starts as a 23018, but then as the spar narrows, a chunk is taken out of the middle, and in the center section it gets thicker.
     
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  10. Nov 24, 2019 #10

    cluttonfred

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    Speaking of biplanes, I've always wanted to do a simplified, cartoon interpretation of a DH.87B Hornet Moth complete with the folding wings. About a 3' 6" wing chord should allow the folded mini Hornet Moth to be hangared in a 20' shipping container. And wing area would certainly not be in short supply. ;-)

    DH87B Hornet Moth 8121 ZS-ALA SAAF 2007.jpg dh87b wings folded.jpeg
     
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  11. Nov 25, 2019 #11

    Topaz

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    Ah, okay. You'll still want to be careful about climb and glide performance, regardless of the reason you're doing it.
     
  12. Nov 25, 2019 #12

    Rockiedog2

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    I always heard that the best airfoil wasn't much better than the worst
    especially on the kinda planes most of us here are interested in. well, I don't really know...
     
  13. Nov 25, 2019 #13

    lr27

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    Probably depends on who you ask. I've always heard that much of the reason a Taylorcraft is significantly faster than a Cub is the airfoil. You'd probably need another 15 or 20 hp to make a Cub keep up with a Taylorcraft. (J3 vs BC-12D, say)

    Try a Clark Y on a Pioneer II homebuilt sailplane! (wings are wood and fabric, no horizontal stab)

    How about an SG-38 primary glider with a NACA 009! Or the 009 on a CH-701! Pitts with the RAF-15.

    I think for that adage to be true, you'd have to use very limited values of best and worst.

    ---------------------

    Matt:
    If you use a big gap and minimize the number of wires, you will probably reduce the performance penalty of using a biplane.
     
  14. Nov 25, 2019 #14

    Voidhawk9

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    Yup, that would only be true within a very narrow range - similar airfoils. Airfoil selection is critical to performance. Now, if you are dragging around a lot of wires at limited speed, you might not notice the difference quite so much.
    Notice that when the big iron manufacturers upgrade their designs with a 'new wing', the planform hardly changes. What does? Airfoils.
     
  15. Nov 25, 2019 #15

    lr27

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    Ask an early Long-EZ builder who's flown through a rainstorm if small changes to airfoils matter.
     
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  16. Nov 25, 2019 #16

    henryk

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    =KASPERWING 1-80, 10 kg/m^2, 20 HP.

    Vmin=5 m/s (>18 km/h) Cl >5 !
     
  17. Nov 26, 2019 #17

    pictsidhe

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    Use an airfoil with plenty of camber. Fabric isnt going to reproduce shapes well enough for the highest lift airfoils. They also tend to stall suddenly. I'm another proponent of thick airfoils for our kind of aircraft. 15% is about optimum for L/D, but 18-20% has only a small drag penalty but very useful structural advantages.

    Trying to limit span will increase induced drag. If you halve the span, the induced drag quadruples...
     
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  18. Nov 26, 2019 #18

    Vigilant1

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    FWIW, unless a design is being built to break a record or win a trophy, IMO it makes little sense to take a gamble on some exotic airfoil that is the result of lots of experimenting with software--all in the hopes of an amazing gain in efficiency. If there's an airplane that is similar to the one you are envisioning (stall speed, cruise speed, wing loading, span loading, power loading, etc) and is performing well and has good manners, it makes a lot of sense to use the same airfoil. Some very competent aerodynamicists have been surprised by nasty handling of airfoils they thought were going to be fantastic.
    Regarding high lift airfoils:. Do take a look at the drag numbers that come with the high Cl, and don't forget to make an honest adjustment to a real-world 3d Cl.
     
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  19. Nov 26, 2019 #19

    BJC

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    I wanted my daughter’s first small airplane ride to be in a J-3 on a summer day with the door open. The only one available had a wing leading edge that looked like someone had taken a hammer and dented it from io to tip. (Not sure, but I think that it had landed in a corn field.) I was amazed; it flew just like any other J-3.


    BJC
     
  20. Nov 26, 2019 #20

    Pops

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    Local man had a J-3 that sat in a field at his farm so long a tree grew up through the left wing. Finally cut the tree down and pulled the Cub to the barn and restored it to somewhat flying condition. Painted it with house paint and a brush. One wing had a wood spar and the other a metal spar, the spark plugs on the Cont A65 was 1/2 way rusted into. He would let my buddy and I borrow it. Flew great. Today, its setting back in the field but has a roof over it. Bet it hasn't been touched in close to 20 years.
     

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