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Attaching Airfoils to a Bike

  1. Jun 30, 2009 #1
    I know this sounds crazy, but hear me out. My plan is to attach airfoils to my bike. I know it would be very hard to actually take off, but what if I got enough lift to counteract most of gravity? I could then jump my bike or go off a ramp and theoretically fly much farther and longer than usual due to the lessened downwards acceleration. Maybe I'm just crazy, but what are your thoughts?

    Here is what I have:

    Lift = 1/2 * p (air density) * v^2 * A (planar area) * CL (coefficient of lift)

    Air density = 1.2 kg/m^3
    Airspeed = Assuming no wind, I know I can ride my bike at least 50 km/h, but probably up to 60+, especially if I were to use a big hill. Thats 13-17 m/s.
    A = This I am not sure. My bike is just over 5 feet long, and if I were to use up both sides of the street than the wingspan couldn't be more than 14 feet. I am just going to have to make them as big as I need.
    Lift Coefficient = I am going to use a Clark Y airfoil (mostly for simplicity of design), and can probably get the angle of attack pretty set on my bike, so maybe 1.2?

    1/2 * 1.2 kg/m^3 * (60 km/h)^2 * 1.2 (CL) = 200 N/m^2

    My bike and I together weigh about 240 pounds, and assuming I can build the wings light enough, I can probably keep the whole thing under 120 kg, or 1176 N.

    1176 N / 200N/m^2 = 5.88 m^2.

    My data for the Clark Y (where I got the 1.2 CL) was for a wing with an aspect ratio of 6.

    Aspect Ratio = (Wingspan)^2 / (Wing Area)
    6 = (Wingspan)^2 / (5.88 m^2)
    Wingspan = 5.93 meters. Obviously for this to work I am going to need to use a lower Aspect Ratio (I don't know how thats going to affect things), or find a wider runway (Which I could do, but probably not a hill).

    I will probably end up shortening the wings and making them wider. If I have a 14 ft wingspan, for 5.88 square meters I would need them to be 3.78 feet wide.

    Here are some other problems:

    The drag on the wings will make it much harder to go as fast as I can with just the bike. I think it would be too hard to make retractable wings, so I am just going to have to pedal hard. Next, as I pick up speed, I will begin to get lift, which will mean I will get less traction for my tires, making it even harder to speed up. Do you see other potential problems? Any ideas? I am not sure how stable I am going to be. Are
     
    Last edited: Jul 1, 2009
  2. jcsd
  3. Jul 1, 2009 #2
    First of all thank you for the good laugh. I don't mean this in a condescending or obnoxious way, it is just literally humorous to imagine some dude flying by on his bike with 7 foot NACA airfoils attached to either side. Then again, this is basically how the Wright brothers did it on their first prototype, I believe.

    You seem worried about losing traction with the ground as you pick up speed. Actually, this isn't an issue unless your wheels start to slip, which I really doubt will occur for your kinds of speeds. So don't even worry about the traction.

    I think this could be a successful idea for getting more flight across a jump. However, it will depend crucially on minimizing the weight of the wings. Your constructions could easily weigh the bike down more then the lift will bring the bike up. And furthermore, you need to take into account not only the wing weight, but also the weight of the attachments which connect the wings to the bike. Think about it this way. If your wings are seriously going to be lifting the entire combined weight of you and the bike, then those attachments need to be strong enough to carry a pretty significant torque. We're talking about welded or strongly clamped attachments as a necessity. The wings would also need to have a good stiffness.

    The lifting force of the wings depends strongly on the speed of the bike. You might not even notice any difference at all unless you are really going fast as a mad man.

    Also, consider some relevant stability issues. For example if the wings were placed on the front wheel spokes, you might expect the bike to rotate into a back-flip and throw you right off the seat. On the bright side, I expect that the lifting force will be relatively weak enough so that you don't need to worry about anything like this. Probably putting the wings anywhere around the center of the bike would be fine.

    Good luck! To be honest I wouldn't expect a lot of extra lift, but if you can manage to keep the weight of the wings really low, then you might notice something.
     
    Last edited: Jul 1, 2009
  4. Jul 1, 2009 #3
    Well actually I just realized one way you could sort of build up to your idea. You could try mounting strong bars to your front and rear axles, and then attach four smaller wings to these, instead of two big wings in the center. This could be easier, it would have better weight distribution, probably easier to mount, so on and so forth. However, it is true that the flow behind the front wings may become turbulent and interfere with the action of the rear wings. But still, something to consider.
     
  5. Jul 1, 2009 #4
    Mordechai9 is right about stability. You would want to locate the wing in the center of gravity. The center of gravity should be about 1/3 of the chord back from the leading edge. Some kind of a vertical stabilizer would be needed. Sounds fun.

    http://en.wikipedia.org/wiki/Chord_(aircraft [Broken])
     
    Last edited by a moderator: May 4, 2017
  6. Jul 1, 2009 #5
    Here are a few to contemplate...
    The Nelson "Glide-O-Bike" http://www.plan59.com/av/av446a.htm
    The Gossamer Albatross http://en.wikipedia.org/wiki/Gossamer_Albatross
    The Para-Cycle (not human-powered) http://www.para-cycle.com/

    My favorite part of the Glide-O-Bike advertisement.. "She goes gliding along, fellows, and that's not all. You can bank, ground-loop, stall and side-slip."

    I wonder how many kids thought, "Oh WOW, I can't wait to try a ground-loop!!" :smile:
     
  7. Jul 1, 2009 #6

    LURCH

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    http://www.youtube.com/watch?v=lLygZUrLv9M&feature=related" of a guy using a dirtbike in a similar fashion. As you might have noticed from this and the albatross, placing the wings at the center of mass may not be such a great idea. Far better to keep the wings above the center of mass as far as possible.

    Also a warning; I watched the same guy in this video experience an aerodynamic stall during a jump. Your wings can turn upward too sharply, giving you enough lift to climb high into the air, then come to a complete stop, after which you fall from that great height onto your backside. Just be aware that that's a possibility, OK?
     
    Last edited by a moderator: Apr 24, 2017
  8. Jul 1, 2009 #7
    This might help. The coefficient of lift of a multi-element wing section is up to about 4.8 --I'm not sure about the Renyold number where this occurs. Such a wing could also come with some adverse effects though, like an abrupt pitch-over stall.

    The penalty of high CL is the unavoidable induced drag. This means your glide ratio (the L/D) could suffer so adversely that you would need a very steep hill.

    Winglets could increase your effective span, but 14 ft?? That's really short. Hang gliders run about a 32 foot span.
     
    Last edited: Jul 1, 2009
  9. Jul 1, 2009 #8
    Last edited by a moderator: Apr 24, 2017
  10. Jul 1, 2009 #9

    DaveC426913

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    Yeah, I guess a confounding factor here is that, once you are airbrone, you are gliding - not like a plane at all. This means your forward motion will very rapidly drop unless you tilt forward to gain speed at the cost of altitude.

    Thus, mostly what you're gonig to encounter is, the moment you lift off, you will simply slow right down and drop back to Earth - not the effect you might have been hoping for.

    What you need is some propulsion.
     
  11. Jul 2, 2009 #10
    That's pretty much it--like a glider, and if you fly down a slop you will get more distance. With a headwind coming up the slop the velocity of the air has a vertical component that will allow you more air-time. With enough updraft you will gain altitude--but you will need a hurricane with a 14 foot wing span.

    Check out the video LURCH linked. I didn't know Bob Wills was such a wild man. He also used a ramp that give him an initial upward velocity component in addition to his horizontal kinetic energy. This has an additional effect. He can accelerate on level ground with the wing at neutra pitch to keep his wheels on the ground, getting traction. He hits the ramp and reorients with some positive pitch-up to get lift.

    How many crashes before he got the center of gravity under the wing, and the ramp angle to all work together, I wonder?

    BTW, the video claims the kite had a 12 foot span (didn't it?). It looks like a 12 foot cord at the root and ~18 foot span.
     
    Last edited: Jul 2, 2009
  12. Jul 4, 2009 #11
    Okay, I built an 8 by 3 foot Clark Y airfoil, and it weighs about 15 pounds. That is kind of heavy but it is sturdy and strong. I know that that is not enough to lift me (unless I was going 90 km/h), but I wanted to test it out. I attached it to a plastic wagon (probably another 15 pounds), and used a rope to connect the wagon handle to the back of my bike. I started riding, and it worked. The foil lifted the front of the wagon off the ground than flipped the wagon vertical so it was riding on its back. I stopped before my airfoil was destroyed, and now need to think of a way to keep it at the right angle of attack (15-20 degrees). I guess it need a tail with a smaller airfoil at the end, which is what I am going to try next.
     
  13. Jul 4, 2009 #12

    DaveC426913

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    Yes but note that this is fundamentally different than what you are OP proposing in your OP. Your propulsion (your bicycle wheels) remained engaged. You were able to drive the airfoil forward even while its lift changed to drag and stall. No so with the bicycle airfoil. Once the lift takes it off the ground, propulsion is gone, and the bike immediately stalls.
     
  14. Jul 6, 2009 #13
    I realize that but I want to make sure it is balanced. If I jumped off a ramp I think I would still go quite far even though I would have no more thrust. I added stabilizers, and tried again, but it still has a problem. It lifts 6-8 feet high than swerves left and right before swerving into the ground after a few seconds of flight. The airfoil (although with stabilizers it looks like a plane), weighs about 25-30 pounds, and I could go twice as fast on my bike then it took to get it to take off, so I guess I could potentially lift 110 pounds.
     
  15. Jul 6, 2009 #14

    LURCH

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    Perhaps you've not built in enough positive stability? Is your airfoil a single piece that's flat all the way across (left to right)? If so, perhaps it needs to be anled up slightly at the tips (like a very shallow "V"). Or perhaps your center of gravity needs to be further ahead of your center of lift. Is the wagon still trying to climb when it begins to oscillate left to right? If so, you could try mounting the wing a little farther back.

    But before you try either of these, it might be best to explore Dave's statement about thrust. What you're making the wing do is quite different from what you want the bike to do, and this may render the results of your test flights meaningless. It seems to me you could get more useful data by only towing the wagon until it leaves the ground, then stop peddling and let the tow rope go slack. See what the wagon does when it's in the air and not being propelled, you know?

    It also sounds like a angle of attack may not be right. If I understand you correctly, you want a wing that will not lift you off the ground when you're riding straight and level, but will extend your distance when jumping from a ramp, correct? In that case, you will want an angle of attack that is zero, and lines up with your direction of travel when riding. Once airborne, you will have to maintain that 15-20o AoA manually, by shifting your body weight.
     
  16. Jul 6, 2009 #15
    The Wright's tested their wing designs tethered, and flown as a kit. The tether will tell you the center of lift, and will gain you information on stability.

    You need enough wind, of course. Begin with a 3 or 4 point briddle If you can reduce this in area until the tether ties to one point you have a self correcting, stable design.
     
    Last edited: Jul 6, 2009
  17. Jul 6, 2009 #16
    I like this idea. Because of headtube angle, you might actually be able to stear with your front wings!!. Notice the angle of the headset. If you were to have wings mounted on your fork, turning your bars to the right would increase the angle of attack on the left wing and increase the lift on that wing, banking you to the right!!
     
  18. Jul 6, 2009 #17
    It is a novel idea. I've been trying to figure it out. For it to work would require dihedral in the wings (assuming it's not a canard, and all). Assuming the bike and rider mass significantly more than the wing, the leading wing would present a greater angle of attach, and tend to roll the plane into a turn. Even with a zero degree rake on the fork this would work.

    Edit: and I didn't see it at first. Without dihedral, but with fork rake it would also work--assuming you would want to fly a bicycle, or course.
     
  19. Jul 7, 2009 #18

    DaveC426913

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    I still don't see how your flight is going to last more than one second. The moment you leave the ground, your vehicle will stall. The only way for it not to stall is to provide thrust or to dive to maintain speed.
     
  20. Jul 7, 2009 #19
    I'm not sure what you mean. Initially this glider whould have some initial kinetic energy, (1/2)mv2 and zero potential energy with respect to a level surface.

    When it lands it will have lost ∫F·dr, energy due to drag. The kinetic energy will be less, but large enough so that v is over stall speed (hopefully). This is, after all, how a hand launch toy glider works.

    α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω Γ Δ Θ Λ Ξ Π Σ Φ Ψ Ω
    ∂ ∫ ∏ ∑ ← → ↓ ↑ ↔ ± − · × ÷ √ . . . . . ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞
    ∞ ° ² ³ ⁿ Å ~ ≈ ≠ ≡ ≤ ≥ « » †
    .
     
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