Wing types.

[Iglooman]

Hi all,

The wing dihedral thread has really been interesting, and now I'm digging to the back of my brain to remember what I had read about wing types - Symetrical, Semi-symetrical, and the like. I've hunted through my limited magazines, and I can't seem to find the info. Maybe it was a webpage, long lost again... Can anyone help me?

What types of wings are there, and what is the highest lift type, and or benefits of the different types?

Mike.

[Wings]

I'll try to list what I know...

Symmetrical: often used in sport/acro models. I don't know much about its character, since I haven't graduated to any models even close to this category.

Semi-symmetrical: a compromise between symmetrical and flat-bottom, I believe in hopes of increasing acrobatic performance and inverted flight character while reaping some benefit of lift performance.

Flat-bottom: generates lots of lift and acceptable drag. I believe there are even a few flying wings that use this type. Inverted flight performance usually suffers, when possible.

Undercamber: generates the most lift, but also the most drag. Many slow and park flyer trainers use this type. Inverted flight is usually unsustainable (plane loses altitude or attitude quickly), when possible.

Hopefully others will step in to expound upon and correct my comments as necessary. Good luck.

Wings

[Dave Robelen]

Hi Mike,
Wings, you pretty much hit the nail on the head for the basics.
1-Symetrical. Normally only used for aerobatic type machines that need equal upright and inverted lift for manuevering. This type is preety inneficient for cruising performance.
2--Semi symetrical. This family includes most of the really eficient airfoils where a comprimise between speed and lift are the goal. Almost all modern sailplane wings use an airfoil from this family. Many designers of sport aerobatic models choose this type section because the extra lift when upright provides better handling during landings and slow flight.
3- Flat Bottom. A very popular family of airfoils with model designers. A wing with this type airfoil can be built with good accuracy on a flat surface. Used properly, the flat bottom wings are very desirable for trainers that must fly in breezy weather (or sport models). With adequate power a model with a flat battom wing can do any manuver except an ouside loop.
4--Undercamber. This family of airfoils will produce the highest maximum lift, which translates into the slowest speed. These are very popular with the small and/or light indoor and park fliers. This type does have the most drag at higher flight speeds, but it also has the least drag when trimmed for slow flight.
Your turn to ask a more specific question.
Regards, Dave

[Iglooman]

?Inspired? by the foam deli tray article in Backyard Flyer, I want to try and build a seaplane using the deli tray technique. I kept thinking about it, and thought I might be able to build a stronger wing using flat tray on the wing underside, making a flat bottom wing. I thought I'd add a bit of wing attack angle to produce a bit more lift.

Maybe undercambered is what I want, but I really like the flat bottom idea for stength. But maybe it will add too much weight.

Or am I completely off my rocker for trying to make a slowflyer seaplane? Can water's grasp be broken by a slowflyer? I am figuring a 280 motor for power. Is 3 oz of thrust enough?

Hmmm, seem to be running into more vague questions. An insight is appreciated. So far I have a Wingo under my building belt... : )

Liked the look of your Pond Skimmer Dave! (See my other post)

Mike.

[Dave Robelen]

Hi Mike,
Let's get one thing behind us at a time. The wing angle (reffered to as the angle of attack) is the angle the wing meets the oncoming air. Each wing airfoil has a maximum angle where it then stalls. The shape of the airfoil is what determines how much lift the wing generates as it reaches this maximum angle. Going over a range, the symetrical airfoil has the lowest maximum lift, while the undercambered types have the largest maximum lift. Aside from wing loading, it is this contour difference that sets the minimum airspeed for a given wing. Specifically, because the undercambered wing can generate more lift, it can fly slower and still support the airplane.
Now the meat tray wings for a seaplane-- There is a neat comprimise in airfoil design that is seen on the "Roadkill models" from DJAerotech. The top surface of the wing is a continous curved sheet from the leading edge to the trailing edge. This might generate a lot of lift, but it by itself would be too weak. The solution is to fasten a second flat layer to the bottom surface that starts at the leading edge and meets the bottom of the curved sheet about at the 50% chord. The effect is to create an airfoil that is mostly undercambered for the airfoil, but much stiffer.
Now that we have dealt with the next chapter in airfoils, let's tacle the seaplane question. I don't see any reason why a small seaplane made from foam would have a problem. There are a couple of things I would do, such as smoothing/shrinking Reynolds Wrap or similar over the hull to make the bottom slick and help it shed water quickly after liftoff. I would expect a single hull seaplane to do a better job of getting off of the water with modest power, and also have less drag in the air. BTW, thanks for the compliment rearding my little Pond Baby.
Regards, Dave

[Iglooman]

Thanks Dave,

You are a true wealth of knowledge and experience. We're lucky to have you on this board.

I figured on the Reynolds wrap already, but more because of the desire to protect the electronic equipment and water-tight the hull. I did a test of the wrap over a prototype hull I was playing with and it seemed to work nice (even though it wasn't true Reynolds). The water shredding is the next logical application I guess. My over-excited brain hadn't gotten that far yet. :)

What type of angle should I put on the wing if I use a 5 3/4" chord? I'm assuming not too much since it's a slowflyer type plane. 1/4"-1/2" raised at the front?

Thanks again for the help,

Mike.

[Dave Robelen]

Hi Mike,
Thanks for the nice words.
I would start with the wing at the 1/4" measurement up relative to the centerline of the hull, and set the stab at zero. A good starting point for the CG would be about 1/3 back from the leading edge. This would then give you a location for the hull step, which should be about 1/4" behind the CG. In other words, everything is interrelated.
Regards, Dave

[Iglooman]

Ok, I was getting a good picture of what you were saying, but then I hit a couple terms that threw me... :)

What is the stab? You said start the wing 1/4" up from relative to the centerline of the hull. Is that what I was talking about, with the front (leading edge) of the wing raised 1/4" and the back at a normal postion relative to the centerline? Say 2 1/4" at the front to the center, and 2" at the back for example?

All this interrelation sure makes this confusing... :)

Thanks for your help again. Why do I have this feeling of deja vu - and that this may not be the last time... I sure hope I can send you a picture of a flying foam boat as the fruits of your patience!

Hope your skies are friendly!

Mike.

[Iglooman]

Dave,

I was wondering what the Pond Skimmer uses as an engine - in the lastest issue of Backyard Flyer it looked like a glow engine.

Mike.

[Iglooman]

Could you recommend a prop for the Speed 280 motor? The Hobby Lobby catalogue has a 6x4 prop listed to give 3 oz thrust. Is that what I should be looking for, or is this another interrelated thing? :)

I need to place an order, so I want to get everything at once, rather than incur several shipment charges... (No local hobby shop...) Wish I had the option of swapping multiple props to find the best one.

Would my Wingo direct drive pusher prop work and fit the 280 shaft? (125x110 mm) The real cheap solution... :D

Thanks again!

Mike.

[Dave Robelen]

Hello Mike,
Let's see if I can work my way through the list. A stab is a sloppy way of saying stabilizer, or horizontal tail. To be really picky, the sabilizer is the fixed part, and the elevator the movable.
It sounds like you picked up on my wing relationship. The hull centerline is the primary reference for all of the other angles. When I spoke of the LE being raised 1/4", that did mean 1/4" higher than the TE relative to the centerline.
I thought I was being cute when I made a balsa dummy engine for the Pond Baby, but it sure has given rise to a number of questions. The actual power plant is the DC5-2.4 electric motor.
I would Start with that Gunther 5-4 push on prop for direct drive. You can experiment with the number of cells to get the best results as you bring it together.

[Iglooman]

It's makes more sense now... I think I have it coming around.

I should have a 6 cell 270 mAh pack to test. Should I think about 7 cells? Guess I'm getting ahead of myself again... Should build it first... Yes. Less questions - more build...

That dummy engine was very cute - and probably fooled a lot of people like me! I didn't think that seemed right in BF.

Thanks for the clarification. Started cutting wing pieces. Hope to have Wing assembled by weekend. Then I have to wait for my order.

Mike.