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Aerospace Creating efficient RC plane

  1. Sep 24, 2008 #1

    djeitnstine

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    Hey all I'm at Embry-Riddle now. I'm in a club called SAE Aero. We are desiging an RC plane that should be as light as possible and lift as much weight as possible - the aim 55 lbs. We have to build it from scratch. However right now we are in the design stage. I was wondering if there was anyone with experience with wings around.

    We are thinking of adding wingtips on our design and I wanted to have a rough idea of what type(s) we should be looking at. Or even the pros/cons of each type we can use.

    Links, sources -anything would be great..thanks!
     
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  3. Sep 24, 2008 #2

    FredGarvin

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    I should hope you have wing tips. Most wings don't work very well without them. Or were you thinking winglets?

    They're not going to help you in the realm of heavy lift. They are a means to more fuel efficient flights. For max lift and stability, you'll probably end up with something along the lines of a flat bottom wing with a decent dihedral. I just can't see what winglets will really do for you in this case.
     
  4. Sep 25, 2008 #3

    djeitnstine

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    Well our last design (which i wasn't a part of) didn't have any wing tips =| we came second, and lifted up to 38 lbs. But thanks for the input. As for the winglets. we came to the conclusion it wasn't feasible for our speeds.

    Also, do dihedrals really increase lift? I'm only asking cus all of my research only showed it increases stability....or does increased stability help with lift? (I'm sure it does...just need confirmation =( )
     
  5. Sep 25, 2008 #4

    FredGarvin

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    Dihedral will give you stability. That's about it. The nice thing is that it will make the airplane more forgiving which can be half the battle in these competitions. What good is a design that can lift a hundred pounds if it's a bugger to fly and stands a greater chance of crashing? Like anything, it's a balancing act. I can't say I have ever seen any reports on the effect of dihedral on drag or lift. You'd have to do the leg work there. My gut feeling is that you'll pay a price in form drag. That's just a hunch.
     
  6. Sep 26, 2008 #5
    A dihedral (or mulithedral, depending how you want to do it... many model gliders have trihedrals) will only increase stability and reduce lift in a straight and level flight. The dihedral increases your stability because of the lift generated by the wing. The dihedral wing will generate a large lift component in the vertical and a small lift component in the horizontal direction (depending on the dihedral angle). Here is an example to give you an idea of how it works: A dihedral wing is producing equal lift on the port and the starboard wing in straight and level flight. If the starboard wing dips, it's vertical lift component will begin to increase and it's horizontal lift component will begin to decrease until the wing is parallel to the flow (trigonometry and the lift force components on your wing) and at the same time the vertical lift component on the port wing will decrease. This makes the starboard wing rise and the port wing dip until it reaches it's equilibrium position (hopefully, level and straight)

    Winglets will help to reduce drag produced by wing tip vortices, but I think you're right that at RC speeds, this probably isn't a very big issue.

    The drag on a dihedral shouldn't really increase, but could increase slightly due to the connection that the wing will have with the fuselage.

    A trihedral will give you a big horizontal centre part of the wing for max lift and a small part at each end that is angled slightly upwards for stability. You'll have to do the maths for the optimal setting for your design requirements.

    attached are some line drawings of dihedrals and trihedrals and the force vectors.

    Hope that helps
     

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  7. Sep 26, 2008 #6

    djeitnstine

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    Thank you both!

    We meet next wednesday so I will post what ideas/solutions come out of that.
     
  8. Sep 28, 2008 #7
    I disagree a bit with the low-wing, dihedral suggestion -- using a high wing instead will give you that added stability without the expense of loss of lift.

    A high wing would be less maneuverable, but may better serve your purpose based on the nature of your competition or goals.

    A few other things to consider: use a high lift airfoil such as a NACA 6 series (keeping in mind that higher lift airfoils produce either higher drag or a larger pitching moment -- if the former, you would need a more powerful propulsion system, and for the latter a larger or longer tail).

    Winglets are useful if your design is limited in wingspan, but not much else.
    Also, consider the area of your propwash -- a larger area of propwash would make a higher portion of your wing ineffective due to turbulence (sometimes a smaller prop with higher rpm is better than a large prop with low rpm)
     
  9. Oct 5, 2008 #8

    djeitnstine

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    Hey all what came out of last week Wednesday's meeting is that we are going with a high wing and either an up swept or down swept wingtips. I found an experiment involving different types of wingtips at about the speeds we will be flying at. It is here http://ojas.ucok.edu/96/T96/Jdavis.htm

    Tell me what you think. I think we should go for the up swept design (#2 in the lift ranking) for simplicity and our skill in design restriction. Building a curved one is a little too complicated for us at this stage.
     
  10. Oct 5, 2008 #9
    I highly suggest you look at current sailplane and wing designs. Some sailplanes have become extremely aerodynamically efficient and the current solar powered aircraft record is held with a sailplane platform.

    I used to have a 48" wing that could get almost 30 minute flights with a 11.1v 1.9mah battery. Wings have the capability of being extremely efficient as well but require a lot of design work to reach those high efficiencies.
     
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