MH32 for a 2m glider

[macr]

It is going to be a long summer holidays for me. 2 months to be exact and I was thinking of making a 2m glider, to keep me busy. What I was wondering is if a MH32 section would be good for a 2m glider? I am thinking at the moment of making a polyhedral wing with a flat centre panel, so I can bolt it down, but later on a plank wing could be in order. Any thoughts on this idea? Would it be to thin of a section, that I would need flaps and ailerons?

[Ollie]

Thin, low camber sections like the M32 do best with light wing loadings. A very light wing loading together with ballasting provisions will allow such airfoils to work well under a wider variety of conditions. Flaps extend the narrow low drag range of such airfoils. Ailerons coupled to flaps for a trimmable trailing edge are even better. Thin airfoils also put greater demands on the spar design to achieve the necessary stiffness and strength.

[macr]

Originally posted by Ollie
Thin, low camber sections like the M32 do best with light wing loadings. A very light wing loading together with ballasting provisions will allow such airfoils to work well under a wider variety of conditions. Flaps extend the narrow low drag range of such airfoils. Ailerons coupled to flaps for a trimmable trailing edge are even better.
So, maybe not the best for a 2 channel polyhedral glider then? :( So what would be a better section? MH32 sounds like it would be a go for a plank wing though.

Thin airfoils also put greater demands on the spar design to achieve the necessary stiffness and strength.
That was something I haven't thought about. If I make the spars out of CF, then there should be enough strength. Can you buy CF spars?

[Jack Hyde]

I have 2m planes with SD7037 airfoil. I have had 3m planes with SD7037 and MH32. All flew fine. The 32 will fly fast at a slightly better L/D than the 7037. The 7037 generates a little higher max lift. They aren't a lot different.
SD7037 max thickness = 9.2% chamber =3.0%
MH32 max thickness = 8.7% chamber = 2.4%
The 7037 is said to be easier to fly well, the 32 has a little higher potential if you are good. So they say. If your 2m is going to weigh more than 30 ozs the 7037 may be best.

[Ollie]

Airfoil selection depends on the priorities you place on various aspects of performance like penetration versus float and stall considerations. It also depends on how the airfoil is integrated with planform and twist for the desired lift distribution. How much you should concern yourself with airfoil selection depends on the accuracy with which you intend to reproduce the true airfoil contour. If you are going to use widely spaced ribs, then the covering sag will change the contour and the benefits of a certain airfoil selection will be thwarted. If you are not going to use templates to insure the leading edge contour then airfoil selection is likely to be a mental exercise in self deception. Airfoils like the SD7037 and MH32 are extremely difficult to build accurately using conventional balsa built up construction because of the thin trailing edges. For this type construction an E205 or S3021 might be a better choice.

In other words, accuracy and smoothness of contour from the leading edge back to beyond the thickest part of the wing is at least as important as which airfoil you choose.

I suggest that you order a set of Allegro Lite wing ribs from Laser Arts. They come with shear webs for the spar. Download the wing plans for the Allegro Lite. You will get a wing design where the airfoils are integrated with the planform and twist. The airfoils are designed to avoid covering sag and the spar is stiff and strong enough to withstand a full pedal winch launch. The wing structure is also one of the lightest around. You just can't do better. See:
http://groups.yahoo.com/group/Allegro-Lite/?yguid=108420033
Join the group for access to the plans in the files section and much additional information.

[macr]

Funny you should mention that. I have all the plans for that. But you don't need to join to get them.
http://www.charlesriverrc.org/articles/allegrolite2m/markdrela_allegrolite2m.htm
Although there is benefits to being a member.
I might consider getting the wing ribs cut, but will still be missing the CF spar capping. The other problem would be the fact that I do not want to make such a tiny fuse. I was planning on modifying a Aeroflyte Brolga box fuse, to something with a smaller profile and a bit more nose (I was not happy with the ammount of lead I had to put up front to balance it).

[Ollie]

The S3021 has much to recommend it. It has one of the most forgiving stall characteristyics of any airfoil. As a result it is somewhat less dependent on integrating the airfoil with the planform and twist to avoid tip stalls. It has a flat bottom from the spar aft for ease of accurate construction. If the top sheeting is carried well past the middle of the chord the covering sag will be minimized. If you were building a vacuum bagged, foam cored wing then the SD7037 or MH32 might be better choices.

[macr]

Originally posted by Ollie
The S3021 has much to recommend it. It has one of the most forgiving stall characteristyics of any airfoil. As a result it is somewhat less dependent on integrating the airfoil with the planform and twist to avoid tip stalls. It has a flat bottom from the spar aft for ease of accurate construction. If the top sheeting is carried well past the middle of the chord the covering sag will be minimized.

That sounds like what I want to play with. Will have to look into designing a wing around that.

[BMatthews]

If you go for the 3021 then consider extending the top sheeting back to about the 50 to 60% point. Non other than Selig himself talked about the problems of bubble separation at the edge of the sheeting on the usual D tube type wings when using the 3021 and 205 which were both popular when Soartech 8 came out with Selig's 3021 work in it.

If you go for the Laserarts rib kit of the Allegro Lite there's nothing that say you HAVE to make the AL fuselage. But to keep things up to snuff you'll want to keep the tail moment arm and areas the same.

I think it was Tall Paul that made his own non carbon boom fuselage for the AL... Or was it you Ollie? I remember pics of this a while back.