high lift airfoil shapes

[windywestflyer]

I'm trying to build my own scratchbuilt plane and am wondering what kind of airfoil shapes to use.

My design criteria is to have the plane lift as much as possible and be able to travel quite quickly. I am wondering what kind of airfoil shapes I could use for this. Should I go for a high lift high drag wing and keep the speed low or use a lower drag wing so that I can fly faster? Which one will give me more lift in the end?

My fuselage is quite sleek and the engine/prop is tuned for high speed. The engine is a direct drive speed 480 brushed motor connected to a 6X4 prop. Another consideration is the canard configuration which requires the stabilizer to stall before the main wing. Stall isn't much of an issue except in that regard.

thanks

[JetPlaneFlyer]

A Clark-Y or something very similar is hard to beat.. Good Clmax (max coefficient of lift) but also low enough drag to allow the plane to be flown fast. A more cambered airfoil may lift a little more but speed would be limited.

Canards are generally not the best for load lugging because you cant get the main wing near it's Clmax, also flaps can be tricky on a canard due to their down pitching effect. If you are sure its a canard you want then whatever airfoil you use on the wing you should use one with higher coefficient of lift (more camber) on the foreplane.

Steve

[vintage1]

You should get about 50mph plus out of a 480 on a 6x4..more on a 5x5..on 3s LIPO.

It will be hard to get AUW much over 20oz if you want speed though. You need to cut the wing area down for that.


Somewhere I have a picture of my speed machine - started out with a 400 on 7 cells, ended up with a permax 450T on 3s LIPO. Weighed a ton and was too fast to land though.

[Wendi Smol]

Hi

I'm trying to build my own scratch built plane and am wondering what kind of airfoil shapes to use.

My design criteria is to have the plane lift as much as possible and be able to travel quite quickly. I am wondering what kind of airfoil shapes I could use for this. Should I go for a high lift high drag wing and keep the speed low or use a lower drag wing so that I can fly faster? Which one will give me more lift in the end?

As usual you have to make a compromise: would you rather go faster with a lesser load, or carry more load and fly slower. Since the drive is already tuned for high speed, then there is in my view the faster solution the better one. If your fuselage permits you could also go for a canard lay-out – it’s more a matter of taste (fashion) than technical merit. One important criterion is the wing loading; with a model of this size and to keep the landing simple I would aim for WL of around 50 gr/dm^2 (~17 oz/sqft). Clark Y is certainly one of the best choices for the wing section, perhaps thinned to 9%. Anymore specific questions? Just ask.

Have fun

W.

[BMatthews]

You're doing this backwards. You've picked a motor and asked about a plane for it but the info on the load you want to carry be it a camera or whatever is zilch. It doesn't work that way.

If you have a payload in mind you need to identify that load and then set the other factors be it to carry that payload at a fast cruise (keep in mind that a fast cruise for models that must remain in sight to be controllable is perhaps 30 mph) or a slow cruise. Once you set this you can begin on the plane design. Only when that part is all done do you estimate the plane's weight, add the payload and RC gear and battery pack and approximate motor and then determine what level of performance you want to set the watts per lb of overall weight. With that in mind you can finally pick the motor you want.

HOWEVER!.... if you're stuck with the motor then your best option is to make a big old timer built up stick and light covering style of model with a fat'ish fuselage that allows you maximum flexibility to carry a camera or other small lightweight package. And I DO mean lightweight. The old 480 brush motors did not have a lot of excess power to play with.

If you are not locked into the 480 by some sort of event rules you'd be much better off to ditch it and buy one of the various inexpensive brushless motors and ESC combos in the 80 to 100 watt rated range to replace it.

[windywestflyer]

I thought I could have 2 wings and switch them out when I needed them. And I know the weight it is going to be because the parts came from a plane I busted. I can build lighter than that plane and my problem is solved. The ESC and reciever are mixed so I can't upgrade.

I was a bit surprised about the wing loading. The value mentioned was twice as high as I thought it would be. I'm also glad to see that someone uses metric by the way.

Basically I don't think I can loose cause the parts came off an old hobbyzone supercub. Anything is an improvement over that.

thanks

[JaRaMW]

Canards are generally not the best for load lugging because you cant get the main wing near it's Clmax

Is that because the wing operates in the downwash of the canard? Wouldn't an optimized layout attenuate this at least so much that the additional lift of the canard would offset it? low placement, forward swept canard... air to the fuselage please :)

[JetPlaneFlyer]

Is that because the wing operates in the downwash of the canard?

No, its because the foreplane on a canard must for stability operate at a higher coefficient of lift than the wing and the canard must stall first.

So before the wing gets to it's maximum coefficient of lift the canard stalls, the wing can never reach it's maximum lift. This is both a good thing and bad.. good because the wing should never stall, bad because it can never reach it's maximum lift potential.

If the plane is not designed and ballanced just right then the difference in coefficient of lift between foreplane and wing can be large and then the canard stalls before the wing has even got half way up it's lift slope...

Steve

[JaRaMW]

But wouldn't it be cool to have an acro-transporter that can be pitched up even higher during a stall? Imagine the braking capabilities :eek:
I vote for lower-CL canards and better pilot training :D

[BMatthews]

That may work on some full size canards where the Reynolds numbers will support the canard reaching some mega high lift coefficients. But with models the reduced size of the canard really works against us.

And while I'd like to see a lower CL canard design pulling a Concorde like flare at landing it likely won't be happening any time soon. Why? Because the ability to flare the wing in a post stall maneuver of this sort means the CG is far too far back and the plane would not meet full sized stability requirements. Too bad too. That WOULD be a sight to see... :D

Even in the full size world the only reason canards have found some success over the last few decades is due to the fact that they a) stall nicely and b) in cruise do not operate at Cl's anywhere near the limits for the canard or the main wing. But for load lifting they suck for the reasons JPF gave. In a short field situation the canard on even a full size cargo plane would not be able to drive the main wing to it's best lift coefficient. This and the fact that adding high lift flaps to the main wing produces a strong nose down pitch due to the distance to the CG which further loads the canard means that you're not going to see a cargo canard any time soon other than at the SAE lift competitions where the students, and generally the teachers, just don't know any better. Canards may be all the rage these days but they really are not the best option for most types of tasks. Precious few in fact.

[windywestflyer]

I thought that they'd be a good design for lifting because the canard can be made to operate like a tandem wing. And with my model anyway the canard should stall only slightly before the wing. The engine wouldn't be able to keep the plane at the alpha angle needed for a high lift coefficient.

[biber]

Dr Drela making fun of canards and I guess he is right:

http://www.rcgroups.com/forums/showthread.php?p=3423535&highlight=canard#post3423535

http://www.rcgroups.com/forums/showthread.php?p=5149585&highlight=canard#post5149585

biber

[eflightray]

But wouldn't it be cool to have an acro-transporter that can be pitched up even higher during a stall? Imagine the braking capabilities :eek:
I vote for lower-CL canards and better pilot training :D

If you want a model that will take a high pitch up, (slow it down for landing ?), yet can be quite fast if needed, and have a good wing area for carrying a load, why not consider a delta ?.

[windywestflyer]

I didn't consider a delta initially. Now that you mention it it does sound like a good idea. Delta's seem alot harder to build both from the cutting aspect and the mathematical design aspect. Any I thought that deltas couldn't lift anything heavy.

I just don't have the skills to do it

[biber]

Deltas are exactly the one breed that doesn't require any building skills.
Even a simple flat plate will do fairly well.

And you don't need any math skills for then either.
Just make a small test with cardboard to find the correct CG and off you go.

biber

[JetPlaneFlyer]

But if you want to lift maximum load on limited power a low aspect ratio delta is about the last thing you want, far too draggy.. What's the model for anyway, what's its 'task?