Hi,


does anyone know where the CG should be for the airfoil SG6042 ?

Does this change according to aircraft type ? I'm designing a .46 pusher with 80" non-tapered wings.


thanks,
nathan

Hey Nathan, the SG6042 is a wind turbine airfoil. I designed a small DC autogyro recently and used that airfoil on the blades with very good results and was just curious as to why you picked it for a fixed wing a/c. Not saying it's bad choice 'cuz I have no clue about using it in your application.

As far as the CG goes, I think the TVC (tail volume coefficient) would be more important in making your choice than the airfoil section. Check out http://www.aalmps.com/tv.htm for how to calculate the TVC. There's also a nifty free aircraft design file for use in Microsoft Excel here in the aero. forum a few weeks ago. It works great!

Hope this helps ya!

I was told that it was a good alternative to Clark-Y as it offers greater lift.

I'm using it for a camera platform with a .46 pusher and twin booms

Here is the airfoil '.gif':

http://www.aae.uiuc.edu/m-selig/ads/afplots/sg6042.gif

It would appear from the '.gif' that the CG could be set somewhere between 1/3 of the cord and 40% of the cord depending on how you like it to feel while flying and landing. 40% might be the limit and maybe 38% back would be a better maximum if the plane still behaves. However I bet that 1/3 of the cord would handle very well for a stable camera platform.

I would assume the CG for your 'pusher' would be the same as for a 'tractor' arrangement since your horizontal control surface will be behind the wing (typical).

I would start by setting the CG at 1/3 of the cord with no fuel and try small changes in CG over time to see if there is any advantage to moving it back.

Ahhh, camera platform. The SG6042 is only 10% thick which seems pretty thin to me, both from a structural standpoint and it's lifting capabilities. I used in on my gyrocopter rotor because it has less drag but similar lift when compared to the Clark Y and the lower drag caused the rotor rpm to increase and overall performance to be enhanced.

Seems to me that you would want a camera plane to fly very stably and slowly to help get good pics. There are some specialized weight lifting airfoils that may be what you want but just an old reliable NACA 2415 to 2418 should do a great job for you. My opinion only. One of the experts that frequent this venue will probably have a better suggestion for you.

Good luck and post some pics when your finished with it!

Well I'm happy to take advice from anyone - and by the sounds of it I need it!

So what do people reccomend for a heavy lifting airfoil ?

The camera platform has an 80" span, will be powered by a .46 engine and hopefully should be capable of lifting a payload of about 1lb

I originally started with clark-Y and then graduated to SG6042 as I thought that was a better choice. No I have no idea

A one pound payload for an 80 inch span model with a 46 is hardly going to even be noticed.

If you build it up reasonably lightly then it'll be fine with an AUW of up to probably 7 or so pounds with just the plain Clark Y. But I agree with Dickeybird about the speed thing. You may want to use a thicker or more highly cambered or both airfoil to control the speed when you're carrying the "package". Makes for easier aiming.

FWIW, I also recomend some of the old timer models with the big cabins as a camera model. A 72 inc Berkley Brigadeer should come out to about 5 to 5 1/2 lbs ready to fly but with no payload. The wing area and airfols are such that you should have no problem adding a 3 lb payload with only a slight loss of performance and a slightly faster landing speed. I've got a big 84 inch Roger Hammer Flamingo that uses an old loop scavenged OS 35 and at 5 1/2 lbs it climbs like a home sick angel. I can get to around 500 feet in about 60 to 80 seconds from what I remember. I added a 1/2 to 3/4 lb camera to it one time and it didn't even notice it was there.

I wouldn't get bent out of shape about the true heavy lift airfoils until you start wanting to pack up an extra 10 lbs or so. But if you would like to slow it down and add some lift then something like the Goetingen 497 on my Flamingo would help. It's 12.7% thick with 5.3% camber. Slows down really well but has resonable penetration in wind too if you put the nose down a coule of degrees. But it is quite strongley undercambered so it'll require some extra work to cover.

The airfoil doesn't affect the choice of CG location.

Specifically, the CG location needed to get some particular level of pitch stability depends primarily on the top-view planform of the whole airplane (wing+tail). The vertical position of the wing also matters, but much less than the planform. The effect of the wing airfoil is in the noise.

That's great! May I quote you on that one? I love simple answers to seemingly complex questions!

The SG 6042 has 10% thickness and 3.8% camber. The Clark Y has 11.7 % thickness and 3.4% camber. A quick look with Profili says the 6042 produces a max Cl of 1.5 at Reynolds number of 100k. The Y max Cl is about 1.3. So if you can slow the plane down to 20 mph with the 6042, you would "only" be able to slow to about 21 mph with the Y. The slowest speed the plane can fly goes as the square root of lift coefficient, Cl. So a 10% higher Cl with the 6042 gets you a little slower minimum flying speed but not much.
I would make sure the 6042 does not have a nasty slall tendency. The Y is used in lots of models and is reported to be well behaved.