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Airfoils that prevent tips from stalling first. - 4/17/2008 11:39:42 PM   
cyclops2


 

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Joined: 12/23/2005
From: Frenchtown, NJ, USA
Status: offline 		I am using the CAP plan # 16 of the Avro Vulcan. 60 inch W.S.
I have cut out the wing outline in pink foam. Have been using the airfoil below. Was in a family of........Flat bottomed Clark Y's...........

If I use it at the root or tip, what areas of it should change for the 4 different sections ? Or can just 2 foils do the job.
I will fly with some UP elevator all the time. O K with me.

A hand pencil sketching over what I posted would be fine. Sport & scale flying only.

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< Message edited by cyclops2 -- 4/17/2008 11:46:49 PM >
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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 12:58:48 AM   
da Rock



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From: western, NC, USA
Status: offline 		Actually, you're not providing near enough info to get good results from.

You need to provide the planform. And some measurements. And don't be surprised if the response isn't too huge. In fact, it's actually true that some wings are going to stall at the tips first no matter what the difference in airfoils is from root to tip. And twisting can't do but so much. It is going to depend on the planform.

It's an unfortunate belief in the flying model hobby that there is a way to stop tip stalls. It's just not universally possible. And in most cases it just doesn't happen.

Depending on your model's planform, it could be helpful to change the airfoil from root to tip. But helpful is the best promise.

Truth is, the advice that's probably going to have as good a chance of working is to simply make the tip airfoil a couple of percentage thicker and build the sucker. BTW, with tapered wings, if you don't reduce the airfoil thickness from root to tip, you get that automatically. (But tapered wings stall at the tips first naturally and aerodynamic twist can't stop that in most cases.)

Whomever helps you will probably need to know the root chord and tip chord to even begin to help.

(in reply to cyclops2)
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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 1:59:00 AM   
Nathan King



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From: Omaha, NE, USA
Status: online 		What are you looking to do with the airplane? I ask because this can be considered a good characteristic to have when doing aerobatics. Remember, there is one way to avoid a stall that causes a wing to drop. Stay in coordinated flight and the airplane can't possibly drop a wing. If it does, correct with rudder and not ailerons.

As da Rock mentioned, we need more information to provide useful advice. Adding a few degrees of washout can work wonders, but won't make the airplane immune. Frankly the Clark Y has pretty tame stall characteristics. I doubt you need much of anything.

P.S. Why the heck do you fly out of trim all the time? I know some people like the feeling of pulling up all the time, but it's a mental issue. A properly trimmed airplane will be much more of a pleasure to fly.


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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 2:23:05 AM   
BMatthews



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From: Burnaby, BC, CANADA
Status: offline 		That airfoil is not a wise choice for a delta shaped flying wing. You'd be far better off with a symetrical airfoil or one that is intended for flying wings. The ClarkY like shape is going to require so much reflex or washout to stabilize it that the wing is going to just look plain odd. On the other hand a symetrical airfoil will only require a few degrees of elevon up for the reflex to stabilize the wing in pitch.

Best of all if you go symetrical it'll even be more scale. The real Vulcan used an airfoil that is almost completley symetrical.


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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 2:46:48 AM   
Nathan King



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From: Omaha, NE, USA
Status: online 		Oh, I didn't notice this was going to be on a Vulcan . What I said still holds true, but BMatthews is right - the Clark Y is not a good choice for a flying wing.

< Message edited by Nathan King -- 4/18/2008 2:47:16 AM >


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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 3:30:37 AM   
cyclops2


 

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Status: offline 		The inner 25% is pretty symetrical. Center 50% is a definate undercamber. Outer 25% is a very slight undercamber. Both wing halves are identical in the large model.

< Message edited by cyclops2 -- 4/18/2008 3:44:33 AM >

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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 3:46:26 AM   
cyclops2


 

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Busy web will not let me post picture of the wing. Do it tomorrow.

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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 4:00:14 AM   
cyclops2


 

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I want to fly it.

Could someone post a picture of a good airfoil to use? I can then enlarge it to what I need.

Many thanks.

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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 4:41:31 AM   
Mike Connor



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Status: offline 		Clark Y on a delta? Yikes! Deltas fly by their own set of rules and tip stalls are usually not a big problem. I would use something like a NACA 0006 up to a NACA 0012 symmetrical airfoil with out wash out or increasing the thickness % towards the tips.

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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 1:37:38 PM   
da Rock



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quote:

ORIGINAL: Mike Connor

Clark Y on a delta? Yikes! Deltas fly by their own set of rules and tip stalls are usually not a big problem. I would use something like a NACA 0006 up to a NACA 0012 symmetrical airfoil with out wash out or increasing the thickness % towards the tips.


You betcha'

It's often said that deltas are almost impossible to stall.

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RE: Airfoils that prevent tips from stalling first. - 4/18/2008 8:53:22 PM   
cyclops2


 

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Deltas are a 2 edged sword.
The SAAB Draken took enough young pilots when they stalled into a flat spin. Apperantly you can not recover from a flat. This is from a Swedish book about the life of the plane.

I know in "Jaynes Fighters Anthology" it is impossible to recover from any height. It is the only plane like that in all of them. Spinning leaf all the way down. Probably would spread your arms all the way down.

Thanks for the safe & easy way to sand my wings into a stabile flier.

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RE: Airfoils that prevent tips from stalling first. - 4/19/2008 3:07:32 AM   
BMatthews



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Status: offline 		I went looking at some Vulcan stuff and found this rather confusing picture...

http://www.spxtraining.com/niactest/images/XM605web3.jpg

It clearly shows that the airfoil of the outer section is anything but symetrical. However for your model I still strongly suggest you just go with a symetrical airfoil.

It would be nice to say to use the scale airfoils but since we don't know the ins and outs of how they chose these options and trimmed the aircraft and at what lift coefficients they typically fly at it's best to stick with the model aerodynamics that we do know.


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RE: Airfoils that prevent tips from stalling first. - 4/19/2008 9:41:01 PM   
cyclops2


 

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There is a neat site with some unbelieviable statement that the Vulcan can beat a F-15 in high altitude mock dogfights.

But when you look at the wing load of the Vulcan it becomes real.

www.users.zetnet.co.uk/mongsoft/vulcan_tech

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RE: Airfoils that prevent tips from stalling first. - 4/21/2008 3:50:16 PM   
Flypaper 2



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Status: offline 		Another good one is the Avro Arrow, where it looks like the wing is in upside down. The top of the wing is flat and the curve is on the bottom. Sort of built in reflex. Where the cut is on the wing, it has leading edge droop from there out.

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RE: Airfoils that prevent tips from stalling first. - 4/21/2008 5:03:17 PM   
combatpigg



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Status: offline 		An ounce of weight control is worth a pound of airfoil "cure" when it comes to stalling. Pink foam is a relatively heavy way to begin just about any .60 and under project. I would use the foam wing panels but slice them up so you can take tracings for balsa ribs and build a conventional built up wing.
The masters of building light with foam cores put way more work into those cores than what meets the eye...in the long run a one of a kind built up balsa wing will be less work if saving weight and maximizing strength is your goal.