Drela DAE 51, doubts.

[Cebola]

Drela DAE 51, doubts.

In my Profili 2, I have the possibility to design and plot this airfoil, in fact I been using on my model Onion, and Hyperbolic Lady, whit a very good results, good glide ratio, and good fly stability.

See on : http://www.rcgroups.com/forums/showthread.php?t=233903&highlight=cebola

and : http://www.rcgroups.com/forums/showthread.php?t=250571&highlight=hyperbolic+lady

The only information about the airfoil is the low Reynolds number that they can fly, or this means low speed for a wing chord about 8”.
In Onion the wing tip chord is 5 ½” and I am using turbulators, near to leading edge, by 2 balsa strips, like spars, reducing the coverage sag.
Onion glides very well, and is a electric motor glider , light whit 20oz.

At this moment I am planing a Onion upgrade, and I am looking for a airfoil that can increase the overall performance.

Has I am a balsa builder, I do not have the ability to use a tiny leading edge for use another airfoil, like the AG series.
So I ask, what is the big difference between DAE 51 and AG 24 , that recommend the specific use????

Tiny leading edge are so critical, or can I make changes in the termination of LE, for some strength , mainly wen I cover whit Oracover, (1/32 tick is good enough) or am I destroying the airfoil characteristics??

Cebola
Brazil

[markdrela]

The DAE51 was designed for a human-powered airplane propeller. It's fairly similar to the Eppler 374, and has a lot of camber. My guess is that it's not the best choice for an RC glider, because it will have a limited speed range.

Since you appear to be using built-up wings, then I would recommend the AG3x series. They have the flat aft bottom surface, thicker trailing edges, and larger LE radii, all intended to make built-up wings easier. I would definitely use the D-tube sheeting if at all possible.

[Cebola]

Mark

Maybe the reason to my model Spirit (man/electric powered plane) fly nicely and slow should be the DAE 51 airfoil, in fact the wing chord is 8” tapered at 5 ½ “, or this airfoil is not adequate for so small wing chord’s

About the AG3x series, where can I found the coordinates??

regards


Cebola
Brazil

[markdrela]

Maybe the reason to my model Spirit (man/electric powered plane) fly nicely and slow should be the DAE 51 airfoil, in fact the wing chord is 8” tapered at 5 ½ “, or this airfoil is not adequate for so small wing chord’s
The objective for an RC glider is not only to fly slow, but to fly slow OR fast as needed. Being able to fly fast is important if you fly in any significant wind. I would switch to a lower-camber airfoil, and reduce the wing loading if you want the same slow flight capability as before. You can just increase the chord by maybe 10% to do this. This new wing will be able to fly faster than the old wing, despite its larger wing area.


About the AG3x series, where can I found the coordinates??

http://www.charlesriverrc.org/articles/drela-airfoilshop/markdrela-ag-ht-airfoils.htm

[gustabmo]

I would switch to a lower-camber airfoil, and reduce the wing loading if you want the same slow flight capability as before. You can just increase the chord by maybe 10% to do this. This new wing will be able to fly faster than the old wing, despite its larger wing area.
Mark,

Would it be possible for you to give us some numbers?

For instance I have a plane designed and built by Cebola with a flat central panel, 2-break poly wing using the DAE51 airfoil, no turbulators and with all spars internal to the wing, not reaching the covering (i.e. no covering sag).

root-chord: 20cm = 7.9in
avg-chord: 18cm = 7.1in
wing-span: 185cm = 72.8in
aspect-ratio: 10.2:1
wing-area: 33.3dm2 = 517sq.in = 3.6sq.ft
AUW: 850g = 29.8oz
wing-loading: 25.5g/dm2 = 8.3oz/sq.ft

(more here: http://www.rcgroups.com/forums/showthread.php?t=216149)

I really don't know what exactly is the speed range I can obtain with this plane but in my humble opinion it works great: it can fly pretty fast, strong winds are no problem (except for wind gusts, of course... poly wing) and can also fly pretty slow to the point that hand catches are very easy with it.

I've measured a 0.64m/s=2.1ft/s motor off vertical speed in still air with it, though I don't have glide ratio numbers.

So... I don't know what is it's speed range, but by how much, percentagewise, do you think the min and max speed could be stretched by going with a different profile, one of the AG3x series for instance ?

Tks,
Gustavo

[Karl B²]

I would switch to a lower-camber airfoil, and reduce the wing loading if you want the same slow flight capability as before. You can just increase the chord by maybe 10% to do this. This new wing will be able to fly faster than the old wing, despite its larger wing area.
So by increasing the chord without increasing the thickness, you effectively reduce camber and increase wing area in one step. Does this work in general for any cambered airfoil, or only for a specific airfoil family? What are the effects of going beyond the 10% increase - I would guess that parasitic drag may offset other gains?

Karl

[gustabmo]

Karl,

I think Mark meant: increase the chord of an already low-camber profile. Read his message again and check if you agree with me...

What I understood is:
- use a low camber profile
- speed will go up
- increase the chord
- wing loading will go down
- speed will go down (hopefully to the same level as before)
- drag will still be less than the original high camber profile
- top speed will be higher than the original profile

:confused: :confused: :confused: :confused:

Gustavo

[Cebola]

Airfoil , what do this in fact means????

They are so different, so exotic, so mysterious .
How to live whit them?????

I REALLY DONT KNOW! :o :o :o :o