SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Mar 07, 2012, 02:17 PM
Registered User
Joined Nov 2011
63 Posts
Discussion
Clark-Y Airfoil Ordinates

Hi all

I understand that using the Ordinates can be found online/in books. But if you have a delta winged RC-aircraft will it be ok to take and use the coordinates for an airfoil from a reputable book/online.

Thank you all

Charlie
charlie01 is offline Find More Posts by charlie01
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 07, 2012, 02:45 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Socorro, NM
Joined Jul 2004
3,616 Posts
Charlie,

Sure - anything will work on a Delta. I've made lots of them with flat plates. If you google RC Delta you should find examples with section and CG info.

Tom
Tom Harper is offline Find More Posts by Tom Harper
Reply With Quote
Old Mar 07, 2012, 04:23 PM
Registered User
Joined Nov 2011
63 Posts
Hi Tom

I've googled them but I mean they only come up with all other things other than that I'm searching for. I'm just confused because I can't imagine how an aerofoil is fashioned onto a delta wing... I mean in relation to a straight wing you can see how the aerofoil changes over its chord but a delta does not have a straight chord and changes it's shape over chord. Am
I making sense?
charlie01 is offline Find More Posts by charlie01
Reply With Quote
Old Mar 07, 2012, 05:12 PM
Registered User
Joined Oct 2004
2,769 Posts
Generally the thickness %age is adjusted from the root to the tip, so that the tip uses a thicker section. Normally even pure deltas don't end in a pointy tip section, but even if they did I'd expect the section near the tip to have a thicker profile than the section at the root, simply because you can't really make a thin enough wing spar. I also suspect that on most deltas the wing root section will not really be a standard section, but one where the central portion has been stretched more than the leading and trailing portion.
Brandano is online now Find More Posts by Brandano
Reply With Quote
Old Mar 07, 2012, 05:34 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,350 Posts
First off a delta wing is simply a radically tapered and swept flying wing. And a flying wing needs one or two things to fly well. It either has to have a reflexed airfoil or it has to have a lot of washout towards the tip or it has to have some of both.

A proper Clark Y, and not just any old flat bottom/arched top shape airfoil, is not pitch stable when used without a normal tail. So a Delta wing that uses a Clark Y airfoil would need to have a LOT of washout towards the tips. Likely as much as 8 to 10 degrees or so at the tip. On the other hand an airfoil with a neutral or reflexed shape would need much less or even no washout depending on the choice.

Using a "regular" airfoil on a delta wing is often not done since delta wing models have such a wide root chord that the airfoil ends up being crazy thick. For example a proper Clark Y is 11.7% thick if done properly. A delta wing which is 36 inch span by 22 inch root chord would have a root thickness of over 2.5 inches. That's a bit much for most model designs. So often some "educated cheating" is done to make things a little more expected and normal.
BMatthews is offline Find More Posts by BMatthews
Reply With Quote
Old Mar 10, 2012, 05:50 AM
Registered User
Joined Jun 2008
200 Posts
Quote:
Originally Posted by charlie01 View Post
Hi Tom

I've googled them but I mean they only come up with all other things other than that I'm searching for. I'm just confused because I can't imagine how an aerofoil is fashioned onto a delta wing... I mean in relation to a straight wing you can see how the aerofoil changes over its chord but a delta does not have a straight chord and changes it's shape over chord. Am
I making sense?
Hi Charlie,

I think you might be getting your terms a little bit mixed up so you might not be understanding some of the good advice you are getting here. The chord runs from the front of the airfoil to the trailing edge at the rear and is by definition a straight line ( even on a delta). If you lay a wing rib flat and draw a line from the furtherest forward part of the leading edge curve to the trailing edge that is the chord line.

So if you make a set of Clark Y wing ribs each a scaled down version of the last and layed them out with the trailing edges level and the leading edges swept back toward the tips you would have a Delta wing. That's how the airfoil is fashioned into the wing.

You could change the airfoil slightly on each rib as you progress from the centre of the wing to the tip that way you can avoid the centre being too thick (top to bottom) or the tip being too thin, or you can change from Clark Y to something else. That's what Brandano and BMatthews are talking about.

I you look at your Clark Y wing rib again and draw another line exactly half way between the top and the bottom that's the camber line. You would notice on a Clark Y rib the camber line is curved. Airfoils with curved camber lines don't work very well on Deltas and require reflex (bent up trailing edges) or washout to fly properly. That's what BMatthews is saying.

Airfoils with a straight camber line (called symmetrical because the top is the same shape as the bottom) work much better on a Delta. Tom Harpers flat Deltas have a symmetrical section.

You could google Peter Russell and Delta 362 or Delta 363 for some ideas. He designed some very successfull Delta models using NACA 00xx series symmetrical sections. Plans are still available in the US and the UK.

Hope this helps,

Dave H
gerryndennis is offline Find More Posts by gerryndennis
Reply With Quote
Old Mar 12, 2012, 04:18 PM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
13,379 Posts
Cambered airfoils have a pitching moment about the 25% chord.
The addition of a horizontal tail controls this pitching moment.
For a tailless airplane, the pitching moment can be worked around a couple ways.
One, is to reflex the trailing edge of the wing, as is done with the Clark YH airfoil.
The reflex changes the direction of the pitching moment from nose-down to nose up.
Placing the center of gravity ahead of the 25% chord line then balances the nose-up pitch.
Interestingly enough, a cambered wing can be stable when inverted with no horizontal.
The pitching moment becomes nose-up... because the plane is inverted..
With sufficient altitude, loss of the horizontal can result in a 1/2 outside loop, with the plane stabilizing inverted.. and steered safely to the ground, inverted.
I watched r/c great Walt Good achieve this many years ago when one of his Multi-Bugs tossed the horizontal..
Another way to get stability with a conventional cambered airfoil is to use inverted. Some flying wings are built this way.. the c.g. ahead of the 25% line.
Pichur...
The usual reflex in a plank wing or swept or delta and a forward c.g. makes these stable.
Sparky Paul is offline Find More Posts by Sparky Paul
Reply With Quote
Old Mar 13, 2012, 01:28 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,350 Posts
Sparky, it's funny that you mention that about the tail coming off. I had the exact same thing happen to my rudder only model I built a few years ago. The rubber bands holding the stab on just plain rotted and snapped due to neglect on my part. The model was high enough to do half an outside. The .049 soon ran dry from being upside down (Black Widow) and the model glided in upside down at a steep but still useable glide angle. No damage other than to my nerves...
BMatthews is offline Find More Posts by BMatthews
Reply With Quote
Old Mar 15, 2012, 02:21 AM
Registered User
Joined Jun 2008
200 Posts
Quote:
Originally Posted by Sparky Paul View Post
The usual reflex in a plank wing or swept or delta and a forward c.g. makes these stable.
And very draggy. A symmetrical section (with no pitch moment) and a slightly further aft balance point and minimal reflex (slight up trim will do) achieves stability with much less drag, at least that's what they found with the delta pylon racers.

Either will work.

I have also seen the practical demonstration of the inverted stability of a cambered section, works even better if you deploy the flaps.

Charlie, have we answered your question?

Dave H
gerryndennis is offline Find More Posts by gerryndennis
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Clark Y airfoil in dxf or dwg format? magic612 The Builders Workshop 22 Mar 18, 2012 10:26 PM
Discussion clark Y airfoil fellwalker The Builders Workshop 2 Feb 04, 2012 03:39 PM
Discussion What is the incidence of a Clark Y airfoil? JIMA Scale Kit/Scratch Built 17 Jan 15, 2012 07:04 PM
Plank With "Clark-Y-ish" Airfoil? Buzz_Man Flying Wings 94 Sep 24, 2004 02:50 PM