built up wing section suitable for camber change?

[Curare]

Hey all, furhter to my wasting your time on the elliptical tips debate, this new wing is going to flaps and ailerons.

Now I know that the 7037 is a good foil for camber change as it responds well, but is there anything better suited to a built up section that this?

[schrederman]

My Dragonfly Strong is built up, and uses the MH-32. It responds very well to small camber changes. I hope you post a build thread on this.

Jack

[Curare]

I probably will Jack.

I've got a couple of anthem fuselages hovering in the workshop which are simply begging to be built, and to be honest, I can't stand foam wings.

Still tossing up whether I should be butchering an anthem to do this tho.

[schrederman]

You never know... You might make it better!

Jack

[Curare]

It's pretty hard to beat dodgson's designs in my book, they were great for what they were.

I have another fuse which I can still do as a proper anthem, so the purists need not scowl!

[Curare]

okay, new question.

Should I be using an MH 32 for the entire span? It's efficiency drops off dramatically with a change in reynolds numbers.

SHould be looking to thin the section percentage thickess towards the tip?

[kzimmerm]

okay, new question.

Should I be using an MH 32 for the entire span? It's efficiency drops off dramatically with a change in reynolds numbers.

SHould be looking to thin the section percentage thickess towards the tip?


What span are you planning on? You may want to consider the AG series... Drela has done wonders in that area.

Kurt

[Curare]

I'm aware of Drela's airfoils, and really appreciate the design gone into them especially for built up wings.

However the AG 30's used on the BD are for RES, and I'm not sure how they'd rate with camber change, ANd the AG40's are getting really thin for a built up wing.

[Ercoupe Ed]

Hi Curare,
There was a guy here in Indiana that rebuilt a Windsong and used built up wings.It flew quite well. Not sure what airfoil it was, but I see no reason you can't build a set of built up wings for your Anthem.Where there's a will, there's a way!

Ed

[Curare]

Of course it is, you give me a block of balsa and i'll give you a peice of flying art.






...and a bill! hehehe.


Seriously tho, I know the limitations of 7037 airfoil and the construction methods required to get there are a little prohibitive for my style of building.

The 32 works nicely and I should be able to get as close as humanly possible with the techniques available to me..

BUT, we'll see. I'm not afraid of designing my own ships, and have done for nearly 15 years, but airfoil selection is the dark art, and there are alchemists much better than I on RCgroups.

[atjurhs]

Kurt,
You might want to read through this thread. It talks a lot about airfoil selection and the whys.....

[rduder]

Airfoil selection thread & airfoil alchemy explained:

http://www.rcgroups.com/forums/showthread.php?t=750667&highlight=favorite+airfoil

http://www.rcgroups.com/forums/showthread.php?t=751435&highlight=favorite+airfoil

[Curare]

Great for slope, but not much for sailpanes.

:S

[BMatthews]

The key is can you build to the standards and using methods that will gaurantee that the airfoil shape is held closely enough to deliver the performace it promises.

For example all airfoils are quite critical to shape variations around the leading edge. But that's fairly easily dealt with using a LE shaping template and leading edge sheeting.

Then there's the hump at the end of the leading edge sheeting. Tests showed that the edge created by the covering at the usual spot for ending the sheeting at the high point could easily ruin the airfoil's promised performance both for high as well as slow speeds. Hence Mark Drela's airfoil with the sheeting extended back to the 55'ish % point.

On airfoils with a prominent cusp at the trailing edge (7037, E214, etc) the shaping of the upper and lower rear portions of the airfoil are also critical to avoid causing more drag than desired and to ensure the airflow is directed as the airfoil designer intended.

All of which to say is that if you're after an open bay structure then it's generally best to stick to airfoils where the covering between the ribs will at least accurately mimic the desired shape. This means sticking to airfoils without torturous shapes.

Another option that worked quite well for me on one model was to use an extensive number of "turbulator" subspars both ahead and behind the main load carrying spar. The idea of the time was to produce a light "see through" wing but one that the covering is coaxed into sagging as little as possible thanks to the extra support wherever the airfoil shape had any significant curves. While it likely isn't as good as a bagged or all sheeted wing flying the model for almost 20 years on and off has shown that I probably got an 80% solution as it speeds up and flys flat and fast in a most satisfying way and yet it's quite happy to slow down to a loiter speed and sink rate that I'm quite happy with given it's 52 oz weight (early tech electric sailplane) in a 2 meter frame.

[Ercoupe Ed]

I flew class 1/2 a and class A , class B, and class C free flight gas models years ago that had different combinations of turbulator spars .

[Curare]

My plan was in fact to do something similar to the AG BD airfoil, with sheeting to roughly 55% due to the flaps & ailerons being at roughly 75% of chord, using sheeting for this area, this should allow a good overall rendition of the desired section.

My thoughts have gone to fully sheeted centre sections too, and close rib spacing at the tips to get less 'tween rib sag.