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Author Topic: "Airfoils" are they really important?  (Read 16011 times)

Offline Gerald Arana

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"Airfoils" are they really important?
« on: January 15, 2016, 06:59:29 PM »
I know everybody has their favorite "airfoil", But, are they really important?

The reason I ask is this: I've seen 1/2 A ships with 1/4" thick wing (combat types) fly and they flew great, or so it seemed. Turned on a dime and did anything the pilot asked it to do. (From a spectator's view)

With this said, why couldn't you (or somebody) blow up one of these planes with a flat plate airfoil, say 1/2" thick and stick a 40-60 size engine in it and fly the pattern?

Just asking, Jerry

Offline Phil Krankowski

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Re: "Airfoils" are they really important?
« Reply #1 on: January 15, 2016, 08:20:50 PM »
It COULD work.  A lot of RC foamies that are scratch built are stiffened 1/4 or 3/8 foam board in a 36 inch span.  (fiberglass or CF battens) Of course these are very light and compared to CL stunt the loading from maneuvers is rather small.  They have a LOT more space to play in.

Solid wings are heavy, but tolerable in certain cases because they are adequately rigid.  A size 40 plane has a more than 1/2 inch thick wing because of rigidity. 

I'm going to argue that rigidity is likely more important than having a perfect airfoil shape.  Look at KFm airfoils.

https://en.wikipedia.org/wiki/Kline%E2%80%93Fogleman_airfoil

I have seen these used on some rather large RC trainers that fly quite well.

Phil

Offline ash

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Re: "Airfoils" are they really important?
« Reply #2 on: January 15, 2016, 08:45:59 PM »
You could, and people have, but they just don't do a very good job of aerobatics. The Yardstick is an all-sheet design capable of flying the pattern, but if you look at the pattern it flies alongside a "proper" stunter, the inadequacy is obvious.
Adrian Hamilton - Auckland, NZ.

Offline Chuck_Smith

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Re: "Airfoils" are they really important?
« Reply #3 on: January 16, 2016, 06:53:11 AM »
If you simply scale an airplane up, it will fly differently.

It has to do with something called "dynamic similarity" in aerodynamics.

Interestingly, in theory any non-cambered airfoil will have the same lift vs angle of attack regardless of thickness or shape. That said, my experience has been that leading edge radius will affect "handling" , but the trailing edge is where it all starts. At the velocities we fly controline stunt at, almost anything can go on in the middle. It's fun to look at stunt airfoils versus time. Early ships had pretty much classic NACA 4-digit "00xx" profiles. The sixties and seventies had a hodge-podge of everything from polliwogs to Al Rabe's' "ellipse with a flap" and all worked well. I still don't perceive any convergence to a "best" configuration.

Also, remember, we don't fly airfoils, we fly airplanes with wings. How the wing responds to changes in pitch is as much a function of its aspect ratio as it is its airfoil.

As always, IMHO and YMMV.

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Offline EddyR

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Re: "Airfoils" are they really important?
« Reply #4 on: January 16, 2016, 07:23:34 AM »
Jerry  In the 1990's some in my club the TBLF in Florida were flying combat models of 350-400 Sq" with 1/4" thick wings made from Coplast. They were very light but did not fly as well as a built up wing model. They were very tough and did not break easily but they were at a big disadvantage.
 I have this model from the early 1950's called the combat kid. A poor flyer with it's 1/4 " thick wing.
Locust NC 40 miles from the Huntersville field

Offline Gerald Arana

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Re: "Airfoils" are they really important?
« Reply #5 on: January 16, 2016, 08:55:41 AM »
Thanks for the replies guys!  H^^

Phil; I was thinking of the foamies....

Thanks for your comment Ash.

Chuck; "Dynamic similarity". I like your explanation. I remember when 2M RC gliders hit the scene and everybody (Myself included) was going for them. It was a good flying size ship but didn't compare to the larger 3M gliders....... I went back to the larger gliders.  ;D

Eddy-R; Kombat Kid. Very interesting. 

I really enjoy this site. Somebody always has an intelligent answer.

Cheers, Jerry

Offline TigreST

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Re: "Airfoils" are they really important?
« Reply #6 on: January 17, 2016, 08:04:13 PM »
Back in the day (1974-1976) we had a large plank wing thing given to us (my brother and I) from a guy named Tim Copley while my family were stationed at RAF Wertherfield in England. I doubt Tim will every see this as he was not a hobby guy in any stretch of the word.  I was in grade 9-10 at the time..my brother grade 11-12.  This thing had a large plank wing of 46inch span or more with a machined flat bottom airfoil carved into it and that may have been 5/8's to 3/4 of a inch thick at the high point.  Wing cord may have been about 6 inches with a large flaps glued solid to the trailing edges that gave it a bit of a swept forward trailing edge look.  There was a "H" shaped hardwood block that was the engine mount that slotted into the front of the 1/2 inch thick fuselage plank and it sandwiched the wire landing gear in place.  There was nothing special about it other than it's total lack of aesthetics qualities.  But it did fly extremely well and would "pull your arm off" as we used to say with the McCoy Series 21 blackhead .35 in the nose.  The dead stick glide was rather unbelievable and you could wip it on 70ft lines to a degree.  As we did nothing but a few loops and wing-overs back then (couldn't fly inverted yet) I can't say how it would have performed attempting the pattern..but it was fun as a big motor trainer. Touch-n-Goes were great fun with the 2 1/2 Veco wheels install. Butt Ugly in it's all black dope finish.  Not sure who kitted this thing but it appeared to be a kit production piece.  It was already built when we got it other than drilling the mounts for the McCoy.  Poor sketch attached.  Yeah, the rudder was tall and ugly too.

Found the actual model I speak of above.  Guillows Profile Basic Trainer III:  Only 36 inch in span.  The mind is the second thing to go

 
« Last Edit: August 23, 2018, 09:55:35 AM by TigreST »
Tony Bagley
Ontario, Canada

Offline Phil Krankowski

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Re: "Airfoils" are they really important?
« Reply #7 on: January 18, 2016, 06:33:42 AM »
I have one of those trainers in my garage.  I have not flow it myself.  It was part of a large lot of planes my parents purchased when I was in middle school.  My older brother claimed it, and flew it some then.   He dropped it off here since I have a place to fly it, and he doesn't.  I had the Enya .09 running a couple years ago and didn't get any further.

I think I need to figure out the line length and get it in the air this summer.

Phil

Offline Steve_Pollock

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Re: "Airfoils" are they really important?
« Reply #8 on: January 18, 2016, 09:24:08 PM »
Some interesting work in sheet-wing stunt models by Broadbent and Prentice in Australia.  Outlines of the Yardstick and Stuntwind models are shown below.

Offline Phil Krankowski

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Re: "Airfoils" are they really important?
« Reply #9 on: January 19, 2016, 08:25:48 AM »
Some interesting work in sheet-wing stunt models by Broadbent and Prentice in Australia.  Outlines of the Yardstick and Stuntwind models are shown below.

They are both flapped which is also rather interesting.

Phil

Offline Chuck_Smith

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Re: "Airfoils" are they really important?
« Reply #10 on: January 20, 2016, 04:20:56 PM »
They aren't bashful about thrustline offset are they?!
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Offline Steve_Pollock

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Re: "Airfoils" are they really important?
« Reply #11 on: January 21, 2016, 05:14:05 PM »
More discussion on plank-wing planes from this forum in 2006: http://stunthanger.com/smf/stunt-design/t-tails/?prev_next=prev

Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #12 on: January 22, 2016, 05:37:14 AM »
They flew VERY well.
I don't know who Broadbent and Prentice are BUT Frank Coombs in South Australia came up with the originals in about 1983 and Leon baird flew the Yardstick at a couple of Nationals. (Placed 8th and 4th.)

They actually do the pattern great and would make the perfect stunt trainer (and some).

(The large motor offset worked on these planes.)

Also it was important to keep them light.
Here is an article done about them back in the late '80s.

« Last Edit: January 22, 2016, 03:01:41 PM by Russell Bond »
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Offline Brent Williams

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Re: "Airfoils" are they really important?
« Reply #13 on: January 22, 2016, 06:00:56 PM »
I got curious about these planes last year and dug up pictures from various forums.  

(Edited picture info)
« Last Edit: January 22, 2016, 07:58:54 PM by Brent Williams »
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Offline Brent Williams

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Re: "Airfoils" are they really important?
« Reply #14 on: January 22, 2016, 06:11:32 PM »
Here are a few more, including the Dick Sarpolus 1/2A Little Brother.
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #15 on: January 22, 2016, 07:11:50 PM »
Hi Brent.
The photo of Leon with the "First sheet stunter" is titled wrong.
The black Nobler was the very first one made by Frank in 1982. (The Black Beast.)
I know because I was the one that test flew it as Frank didn't fly stunt very well because he liked racing etc.
I'll never forget the test flight as I couldn't believe just how well it flew. (I was shocked!)
In fact I did the pattern on the second flight!
Frank designed the Yardstick later and Leon made improvements to it as he went along.
Bandolero

Offline Brent Williams

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Re: "Airfoils" are they really important?
« Reply #16 on: January 22, 2016, 07:59:59 PM »
Thanks Frank...Ooops!!!...Russell, LOL! :-[  ;D I edited the picture title.
« Last Edit: January 22, 2016, 08:34:34 PM by Brent Williams »
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Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #17 on: January 22, 2016, 08:31:09 PM »
I'm Russell, not Frank.  S?P
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Offline Air Ministry .

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Re: "Airfoils" are they really important?
« Reply #18 on: January 22, 2016, 09:20:03 PM »
Quote
I'm Russell, not Frank.  Stir the pot

Roger . :!

Offline David Hoover

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Re: "Airfoils" are they really important?
« Reply #19 on: January 23, 2016, 06:23:45 AM »
Are full-size plans of the Yardstick available anywhere?
Life is simple. Eat. Sleep. Fly!
Best, Hoovie

Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #20 on: January 23, 2016, 06:41:20 AM »
No, but the Mini Nobler and Mini Bandolero are from Airborne plans service.
http://www.airbornemagazine.com.au/planHome.htm

I helped Frank design the Mini Bandolero from my Bandolero II full size model back in 1983.
(I'm now on Bandolero 9.)
Bandolero

Offline Steve_Pollock

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Re: "Airfoils" are they really important?
« Reply #21 on: January 25, 2016, 01:16:18 PM »
The three articles which accompanied these plank-wing designs are included in the attachment.

Offline phil c

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Re: "Airfoils" are they really important?
« Reply #22 on: January 27, 2016, 02:49:31 PM »
While almost any airfoil gives the same lift curve- pretty much a straight line, starting at 0 for a symmetrical wing at zero angle of attack and generally peaking(for an unflapped airfoil) at somewhere near 1.  The main difference is in the shape around peak.  A sheet airfoil will reach stall 8-10 deg AOA.  A really good section will get as high at 15-18 deg with a comparably higher lift.  The sheet airfoil tends to stall very abruptly and requires a noticeable amount of elevator change to get it to unstall and start flying again.  A good airfoil(almost anything but a flat sheet) will stall more gradually and recovers as soon as the elevator is relaxed a bit.

Dick Sarpolus and I did an interesting experiment.  At the time he was building a number of sheet(both foam and balsa) CL and RC planes.  I cut him some cores for an RC design he called the Too Windy.  He brought over an RC version with the foam wing and a CL version with a flat foam sheet wing and another one with the foam wing.  They all flew on the same electric motor and battery so engines weren't an issue.  The RC plane flew just fine.  He'd named it Too Windy because it handled wind much better with the airfoiled wing.  I flew the CL planes.  The sheet wing flew just fine in round maneuvers.  Sharper corners, not so much.  The least little bet of extra elevator and the plane would slow down and threaten to fall out of the sky.  The airfoiled CL plane flew fine.  It did round loops, square loops, triangles without fuss.  Trying to pull full control for 3 loops would cause some major slowing but just opening the maneuver a bit and it was back flying.

The bottom line is a flat wing can work just fine if the wing loading is kept low enough.  Otherwise you get the classic 3 cornered square loop- the first corner is fine, the second corner is a little slow and wobbly, and the third corner blends into the fourth in a 90 deg. corner that's round all the way back to the starting point.
phil Cartier

Offline Ted Fancher

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Re: "Airfoils" are they really important?
« Reply #23 on: February 29, 2016, 05:25:48 PM »
I did note that pretty much all of the "flat plate" airfoil ships pictured were flapped machines (some of the pics it was difficult to tell but none was clearly a simple flat plate wing).  Although probably not the airfoil of choice for most aerial vehicles they clearly fail the flat plate category as soon as there is any pitch input.

I do remember Big Art witnessed some of these several decades ago on a trip down under and was very suitably impressed with their performance.

Curious about the manner in which rigidity was achieved under loads. 

Ted Fancher

Offline Chris Wilson

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Re: "Airfoils" are they really important?
« Reply #24 on: March 03, 2016, 03:32:17 PM »
Spruce spar that doubles as a bell crank support?

Failing that I am sure that some Team Race technologies won't fail to impress.
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Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #25 on: March 06, 2016, 06:06:46 PM »
The wings flex beautifully in square corners but this never caused a problem and they never broke.  ;D
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Offline Chris Wilson

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Re: "Airfoils" are they really important?
« Reply #26 on: March 06, 2016, 06:58:06 PM »
As a side note here, does the inboard wing flex less because it is circulating at a slightly slower speed and has two lines under tension running through it?
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Offline Russell Bond

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Re: "Airfoils" are they really important?
« Reply #27 on: March 08, 2016, 05:15:29 AM »
Not that I noticed............ :o
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Offline proparc

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Re: "Airfoils" are they really important?
« Reply #28 on: March 08, 2016, 02:05:20 PM »
I got curious about these planes last year and dug up pictures from various forums.  

(Edited picture info)

The RC community has the "Foamies" which has proven to be very popular. Maybe, this could have been our equivalent to generate more participants for us.
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Offline Tim Wescott

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Re: "Airfoils" are they really important?
« Reply #29 on: March 08, 2016, 02:11:26 PM »
The RC community has the "Foamies" which has proven to be very popular. Maybe, this could have been our equivalent to generate more participants for us.

I've played a bit with making Dollar Store foam CL planes.  I think that if you made a FliteTest RC "Bloody Wonder" converted to CL that you could have a heck of a nice plane.  Yes, the airfoil is flat-bottomed, but I've seen these things flying RC and I think they'd work pretty well -- and you could always work on making a symmetrical wing.
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Offline Target

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Re: "Airfoils" are they really important?
« Reply #30 on: March 08, 2016, 08:40:29 PM »
You could always do something like this.....
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Offline Chris Wilson

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Re: "Airfoils" are they really important?
« Reply #31 on: March 08, 2016, 10:30:58 PM »
I know everybody has their favorite "airfoil", But, are they really important?

The reason I ask is this: I've seen 1/2 A ships with 1/4" thick wing (combat types) fly and they flew great, or so it seemed. Turned on a dime and did anything the pilot asked it to do. (From a spectator's view)

With this said, why couldn't you (or somebody) blow up one of these planes with a flat plate airfoil, say 1/2" thick and stick a 40-60 size engine in it and fly the pattern?

Just asking, Jerry

Getting back to the OP, Reynolds numbers probably figure heavily here.
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Offline Bootlegger

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Re: "Airfoils" are they really important?
« Reply #32 on: March 09, 2016, 04:46:55 PM »

 I am curious about an airfoil that tapers straight back from the high point to the trailing edge, on the top and the bottom making the airfoil symmetrical.

 How well would this work, and why?
 Thanks a lot
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Offline Target

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Re: "Airfoils" are they really important?
« Reply #33 on: March 09, 2016, 06:37:21 PM »
I can't say how well or why they'd work, but I'm almost certain people have done that very thing, and it worked well enough, and I believe they call that an "ice cream cone" airfoil. If you think about it, it looks like an ice cream cone on its side.
A guy in soaring made a whole series of profiles that had straight to and bottom rear sections, although they were cambered, not "symmetrical" (zero camber is the proper term).
His reason was repeatability, and ease of production. They work as good as the Selig's and European origin RG series of the day, for what they used them for (35oz/sq ft wing loading slope airplanes).
I don't think wing profiles are super critical for u control planes. That being said, that doesn't mean you would never notice any differences between them.
Make your ice cream cone airfoil, I'm sure it will work well. Just make sure the other design parameters are in the ball park.
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Offline Air Ministry .

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Re: "Airfoils" are they really important?
« Reply #34 on: March 11, 2016, 06:32:27 PM »
Beringer uses this .

Gives a bit of incedance ( angle of attack )  free play at the handle , in trck - before the course gets divergent .


Offline Brett Buck

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Re: "Airfoils" are they really important?
« Reply #35 on: March 11, 2016, 07:07:59 PM »
I don't think wing profiles are super critical for u control planes. That being said, that doesn't mean you would never notice any differences between them.
Make your ice cream cone airfoil, I'm sure it will work well. Just make sure the other design parameters are in the ball park.

   You do not want an "ice cream cone" airfoil. For whatever reason, the control loads for any airplane I have had with that type of airfoil were astronomical.

    Brett

Offline Gerald Arana

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Re: "Airfoils" are they really important?
« Reply #36 on: March 12, 2016, 10:13:14 AM »

 They work as good as the Selig's and European origin RG series of the day, for what they used them for (35oz/sq ft wing loading slope airplanes).

Since when has the wing loading been 35oz's/sq.ft.? When I was slope racing it was 24.51 oz's/sq. ft.

And that's why my "Grand Boss" had a 900 sq. in. wing, a 134 sq. in. stab. and weighed 11 lbs, which was the max. weight allowed.  ;D

I've been out of S.R. for several years...........

Jerry

Offline Tim Wescott

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Re: "Airfoils" are they really important?
« Reply #37 on: March 12, 2016, 01:54:00 PM »
You could always do something like this.....

I've made dollar-store foam airplanes with the symmetrical KF airplane, and it worked well.  Rather, it worked well as a quick-built trainer -- I wouldn't try to win any contests with it.
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Offline Target

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Re: "Airfoils" are they really important?
« Reply #38 on: March 12, 2016, 02:13:38 PM »
They work as good as the Selig's and European origin RG series of the day, for what they used them for (35oz/sq ft wing loading slope airplanes).

Since when has the wing loading been 35oz's/sq.ft.? When I was slope racing it was 24.51 oz's/sq. ft.

And that's why my "Grand Boss" had a 900 sq. in. wing, a 134 sq. in. stab. and weighed 11 lbs, which was the max. weight allowed.  ;D

I've been out of S.R. for several years...........

Jerry
Jerry, the Don Ayers A series profiles are made for PSS, planes, not F3F/ slope racing. FAI limits don't apply there. They are flat bottom, 6-7.5% thick, and 1.4-2.0% camber.
I held the USA F3F (slope racing time trials) record for many years, at 31.61 seconds for 10 legs of 100m...
Regards,
Chris Behm
« Last Edit: March 15, 2016, 09:35:02 PM by Chris Behm »
Regards,
Chris
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Re: "Airfoils" are they really important?
« Reply #39 on: March 14, 2016, 07:54:07 AM »
   You do not want an "ice cream cone" airfoil. For whatever reason, the control loads for any airplane I have had with that type of airfoil were astronomical.

    Brett
Hi Brett-
Not to be argumentative, but I'm super curious how you came to the conclusion that the airfoil was the culprit for the high control loads? Is there any way that could be caused by something besides the wing airfoil? Please tell me/us more, when you have time for a detailed explanation. Sounds like you had more than one of these planes by your post.
I'm guessing the only real way to really determine that would be to have two identical planes with everything the same but the wing airfoil. Maybe someone else has the same or similar experience as yours also with regards to the control loads? That would be also a great confirmation.
Thanks in advance for taking the time to explain this further.
Vr,
Chris
Regards,
Chris
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Re: "Airfoils" are they really important?
« Reply #40 on: March 17, 2016, 03:14:11 PM »
Mmmm, ice cream. Sounds good right now, it's about 75f in SoCal currently.
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Chris
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Offline phil c

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Re: "Airfoils" are they really important?
« Reply #41 on: March 27, 2016, 02:12:13 PM »
I am curious about an airfoil that tapers straight back from the high point to the trailing edge, on the top and the bottom making the airfoil symmetrical.

 How well would this work, and why?
 Thanks a lot

The ice cream cone works pretty well for unflapped airplanes.  The Extra 300 appears to use one(http://www.extraaircraft.com/galleries.php).  The first one I saw was on a So.Cal combat plane from Ira Keeler.  Very easy build since it was built flat on the table.  It flew just fine but was VooDoo sized and too small for later generations at 310 squares.  Planes were rapidly getting bigger, my stuff was up to 500 squares.  Ira mentioned that the faster it went, the better it flew.  That seems to be true of quite a few designs, probably due to higher Reynolds number.  Most C/L planes seem to fly in that range of just big enough to start flying well and just not big enough to really fly- Rn=400,000-700,000.

Flaps probably wouldn't work well, although they get by with huge ailerons on full scale planes.  The flat back airfoil and the flap make for a very sharp break in the airfoil as is goes from the wing over the flap.  This can cause a lot of unneeded drag and maybe the heavy control forces Brett mentioned.  There's some evidence, from XFoil graphs, that the basebat leading edge and squaring off the trailing edge to a few percent of the chord actually improve the lift above 7deg or so angle of attack.
phil Cartier


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