the proper airfoil

[micro_builder]

hey folks,
i got into DLG gliders last summer and have had a ball with them ever since. recently i built a 20" micro glider and got a few responses with past micro gliders. so far they all quite differant airfoils, i used the AG45 series that were with the plans i built off of on mine, another micro glider used a NACA 6409, and another used an AG03.

seems that all 3 work just fine, but i'm sure there's something out there that is best suited to small winged gliders. is there a consensus as what works best at these lower Re numbers for this type of application?

thanks,
nick

[raptor22]

Its not really important when you get this small; just use something thin without a lot of camber.

It gets to a point where a flat plate is nearly as good as a specifically designed airfoil, and a whole lot better than a profile made for large reynold's numbers.

--Alex

[MarkusN]

If that were true the 6409 should have performed a lot worse than the other two.

I agree about the thin bit. About low camber, not necessarily. It all depends on your design criteria. For DLG, where high speed capability is a must, you are right, though.

[BMatthews]

For that size the weight is important so you probably used built up wings with no sheeting, right? If so the amount of covering sag would make them all about equal with the possible exception of the 6409 one where it would have some extra camber.

The parts between the ribs and spars forms more of a diamond shaped upper surface unless you use things like turbulator spars or foam vacuum bagged or sheeting to support the covering to the shape it should be.


With the super small stuff we have now I've thought about doing a 28 to 36 inch DLG but 20 inches is just amazing! Do you find it's not too small and heavy to catch thermals on a regular basis? What weight did you get it down to?

And pictures... where's the "this thread is useless without pictures smilie.... :D

[micro_builder]

thanks guys. here's a few pics of the glider, i only finished it last week so theres no electronics yet (gotta order them this weekend), AUW should be around 17 grams, wingloading would be below 2oz/sq ft, only 2 channel for now. the wing was done with the D-box construction method, or r-box i suppose, using 1/32 and 1/16th inch balsa and some CF tow, with tissue covering. empty weight is an even 12 grams, and a full flying elevator just for fun.

since i plan on chucking mine pretty hard, i figured the less camber the better, but didnt know if there was something better than flat bottom airfoil. the guy with the 6409 glider got a 45 minute flight with his on a hillside and an evening sea breeze! i'll probably just make a few differant wing types and see if there's any real noticeable change.

either way, i did chuck mine in FF form a number of times to trim it. a few times it ended up coming straight down and it cut through the air like it didnt even have a wing, but when trimmed right it seemed to have a great sink rate. the last picture is when the tree got me. it never fails. i'll probably do another balsa wing, just cause they're fun to build, but will use some .025" foam for the covering, rather than tissue. here's my original thread (http://www.rcgroups.com/forums/showthread.php?t=896669)

thanks,
nick

[BMatthews]

Just for reference in case you hadn't seen this before this is what free flight HLG's in the same size use.