Built-in reflex vs built-in camber (AG4x vs HQW3/x)

[rdeis]

I've found two apparently competing theories in wing design- I'd love to hear them compared and contrasted by smarter people than me

The HQW 3/x on the Zenith has plenty of camber built in and expects you to dial in the reflex when you need to cover ground. The idea is thatthe native airfoil (as opposed to the slightly kinked airfoil you get with the flaps deflected) is most efficient and that you want the native efficiency in the thermal.

If I understand correctly, Dr Drela's AG 40-43 (Supra) airfoils have reflex built in for excellent L/D and expect you to dial in camber in thermals. (Perhaps base on the oppositer assumption? Or maybe there is more going on than I realize..)

Perhaps it's just a matter of style, but I'm curious tio hear what you guys think about the different approaches?

[jrerickson]

When you are in reflex you are going fast, so a clean wing is important. You don't want that little gap between the flaps and the center panel. So I side with Dr. Drela on this one.

As a caveat, we are splitting hairs on the issue. I've had planes that you have to reflex and they still cover a lot of ground. Ballasting is more of a factor than the small amount of drag induced by the "flap gap".

JE

[Keith Kindrick]

An MG06 section is designed for massive flaps used for camber changing in flight. Samba's Pike Giant from Skip Miller models when properly set up can fly in the same lift as an Ava and climb with it. It's all in what you want to use for the section. Either approach has its own advantage/dis-advantage.

[OVSS Boss]

Actually, the Supra airfoil when set for a clean airfoil, you have reflex, and then some camber (about 1.5mm) apparent airfoil for cruise and more camber for thermalling. Kieth brings up the mopst radical built reflexed airfoil I have seen, the Pike Giant really is set to go in it's native state, and as you said the Zenith airfoil is just the opposite. Now, the new big Zenith likes camber, and that is in comparison to the smaller Zenith. The tips on the 3.7M has been tweaked compared to the tips of the smallerr one.

Marc

[mlachow]

The built-in reflex is just one of two positions. Reflex has nice bottom surface. And actually for building, it's suitable for building in that position. You're going to cut the top at the kink in that position anyway. If you put it in thermal position you will notice the kink goes away on top.

I would say the real difference is the HQW airfoils were designed as a series of airfoils you can select from. The AG airfoils were designed as part of an overall airframe design.

All a question of how you want to look at things....


If I understand correctly, Dr Drela's AG 40-43 (Supra) airfoils have reflex built in for excellent L/D and expect you to dial in camber in thermals. (Perhaps base on the oppositer assumption? Or maybe there is more going on than I realize..)

[MarkusN]

I would say the real difference is the HQW airfoils were designed as a series of airfoils you can select from. The AG airfoils were designed as part of an overall airframe design.
Yep. If you want "Drela-Philosophy" in your design you can select one of the lower cambered types of the HQW range.

I think it comes down to this: Where do you plan to spend most of your flying? That's where you select your unmodified airfoil. From there you adapt with flap deflections.

What I personally don't understand to well are airfoil designs with lots of aft loading being proposed to be used with camber changing flaps (E.g. Eppler 214, FX 61(?)-131)
I somehow can't imagine how a mean line with lots of camber can positively react to putting a kink in that very section. Yet the FX has been used on many successful full scale designs.