Airfoil Recommendations?

[Jimmy James]

I am designing an electric powered aircraft with a 2M wingspan. This bird will be a pusher with a carbon tube boom (pod & boom) design. It will be designed to carry a camera payload. I am looking for an airfoil that will deliver high lift and fairly slow speed. I would like something akin to the Feisler Storch, comes in somewhat vertical for landing. I am open to the wing design, flaps are an option, I would like the wing to be long and thin, similar to a sailplane wing. I am looking for an airfoil that I can print out for templates to build this bird. I do not want it to be a "dog" in the air, I would like the airfoil to be efficient and not just drag through the air, but the high lift is essential. Big order to fill, I know, but does anyone know of an airfoil that may fit this design? Thanks Much, Jimmy

[Batmanwpg]

Try E392

[BMatthews]

Oddly enough you can't go wrong with the good ol' Clark Y for this application. I've got an older version of the David Fraser Sailplane analysis program that I have not used for years but when I was keen on this sort of thing I was amazed at how close in performance the Clark Y was compared to the "high priced" options. But by "ClarkY" I'm not just saying you put down a flat bottom and trace your shoe sole for a top curve. It needs to be the proper shape AND have the little kick up at the leading edge that so many folks don't bother with.

There's other options like the excellent E392 as mentioned as well as a host of other higher camber airfoils but you mention that you don't want to "drag" through the air. For it's simplicity and close enough performance to some of the fancy stuff the ClarkY wins in this type of flying hands down IMHO. The other options will all have more complex building and covering issues to deal with.

If you don't have it download and install Profili2 from www.profili2.com . The basic freeware version will print out your rib sections complete with sheeting allowances and spar locations.

Beyond that for slow flying just make sure the final weight comes out light. Nothing reduces the flying speed like a light wing loading. A fancy airfoil is just an aid and is far less effective than the loss of a few ounces of weight.

And a note on carbon booms. So many folks these days are using carbon tubes for DLG's that it can easily be forgotten that on larger projects the smaller carbon tubes are far too flexible. I went with a carbon tube of about 1/2 inch diameter on a 2 meter T tail glider and found that the drag off the high mounted tail was enough to bend the tube at higher speeds and force the nose down to an unrecoverable dive. Fortunetley I was high enough that I had the time to realize what was happening and make the drag work for me by pushing the bird into an outside loop and then use the rudder to roll back upright. The moral of the story is that if you are not using at least a 3/4 inch diameter boom that is intended for model flight I would stick with a regular balsa box fuselage. What SEEMED stiff enough in the store proved to be nowhere near stiff enough for flight loads. It onlly takes a few degrees to ruin your whole day.

[Jimmy James]

Thank You for your replies. I am going to download Profili2 and print out the airfoils. Jimmy

[lincoln]

All carbon booms are not the same. A lot depends on the layup. If you know, numerically, the stiffness of the boom, you can look at airfoil pitching moment and so on to see how much it's going to bend. If not, it's just a guess.

The Clark Y is not a bad suggestion. It's fairly deep, which is good structurally, yet it will work at a reasonably low Reynold's number. I assume the high aspect ratio is for looks, as I don't think I see anything else in your list of requirements that justifies it. (Except that at high aspect ratio you can probably get away with a floppier boom!) With a higher aspect ratio, if you want a steep descent you will NEED flaps. If you use a low aspect ratio and an airfoil with a gentle stall (large leading edge radius), then you can mush it in. Not vertical, but not too flat either. Also, with low aspect ratio, you will have less structural problems, apart from the boom. And more benign, less sensitive handling.

I had a 2 meter with a GLASS boom that was probably not over 3/4, and it never tucked.

If you don't have an external aspect ratio constraint, it might be best to leave that open at first, and figure out just how much weight, etc. is required.

I'd like to point out that a Facetmobile has around the same L/D in cruise as a Cessna 152, but I'll bet it can come down a LOT steeper when you pull back on the throttle and the stick. Without flaps. Of course, fitting a Facetmobile model in your car might not be easy.

[avianaut]

I hope it's not rude to stick my nose in here, but I am also looking for an airfoil very much as Jimmy James has outlined. My project is a 2 meter scale model of the Global Hawk. I have calculated my wing loading to be around 11 ozs. / sq.ft.. My concern is that I will have not much thrust to play with and I want really long flights (around 1 hour), so L/D seems important.

Will the same suggested airfoils work for me, too.

Cheers.

[Sparky Paul]

Aerial photography planes ... and everything else about AP
http://www.angelfire.com/indie/aerostuff/AerialPhotos2.htm

[Brandano]

I still have some doubt about high AR wings for slow flight. They surely give you a better LD ratio, but while their drag is lower their stall characteristics tend to be nasty. Gliders aren't meant to fly that close to the stall other than in a strong thermal, and even then it's just to keep more easily in it. A 1/1 AR wing will stall at nearly 45° AOA in some cases!