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  • June 19, 2018, 06:04:13 PM

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Author Topic: Why do parallel chord wings have parallel thickness?  (Read 701 times)

Offline Keith Renecle

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Why do parallel chord wings have parallel thickness?
« on: June 02, 2018, 02:15:31 AM »
Hi All,
I'm just curious to know why parallel or constant chord stunt wings have the same thickness right to the tip? Is this just because it's easier and more practical to make the ribs, or is there some technical reason? The swept leading edge wings have a thinner airfoil at the tip so why do we not do this with the parallel chord wings?

Keith R
Keith R


Offline BillLee

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Re: Why do parallel chord wings have parallel thickness?
« Reply #1 on: June 02, 2018, 05:53:34 AM »
I don't know, Keith, but perhaps it is that both designs you mentioned are built with the percentage wing thickness, center to tip?
Bill Lee
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Offline Jim Mynes

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Re: Why do parallel chord wings have parallel thickness?
« Reply #2 on: June 02, 2018, 06:50:00 AM »
My guess would be ease of construction. Just one rib outline to worry about, and trim a few for the center sheeted section.

Are they all profiles? That would support this theory. Banshee, Twister, Magician, Flite Streak all fit the ‘profile’. Maybe some of the old Midwest series as well.
I have seen the light, and it’s powered by a lipo.

Online Tim Wescott

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Re: Why do parallel chord wings have parallel thickness?
« Reply #3 on: June 02, 2018, 09:19:11 AM »
Two thoughts:  first, if I'm going to build a straight wing, it's because I can cut out a bunch of identical ribs.  Second, tapered wing ribs often have the thickness the same percentage of the chord, at least on models.  I believe the reason that full-scale designs (like the B17) taper thickness from root to tip is structural.
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Online Paul Smith

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Re: Why do parallel chord wings have parallel thickness?
« Reply #4 on: June 03, 2018, 03:35:02 PM »
Control Line stunters just need to do up & down high G maneuvers and not the many other things that real airplanes do, including rolls and efficient long range flight.  Comparisons to B-17's and even Mustangs don't draw much water.

I've never seen a rectangular wing with a tapered thickness.  But if you have a theory that it might work, build one.,
Paul Smith

Offline Keith Renecle

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Re: Why do parallel chord wings have parallel thickness?
« Reply #5 on: June 04, 2018, 12:20:35 AM »
Control Line stunters just need to do up & down high G maneuvers and not the many other things that real airplanes do, including rolls and efficient long range flight.  Comparisons to B-17's and even Mustangs don't draw much water.

I've never seen a rectangular wing with a tapered thickness.  But if you have a theory that it might work, build one.,

Thanks Paul, you sound like me.....a "suck & see" engineer.  #^ I may just do that. I was just curious to hear from the forum experts on whether or not there is some aerodynamic reason for the constant thickness.

Keith R
Keith R

Offline pmackenzie

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Re: Why do parallel chord wings have parallel thickness?
« Reply #6 on: June 04, 2018, 04:41:40 AM »
My 2 cents:

First thing to know is why wings are tapered in the first place.
Main reason is to get a more elliptical lift distribution to reduce induced drag.  Also reduces area at the extremities and moment of inertia to yaw/roll improve handling.
Plus of course it looks better :)


Tapering only thickness will not result in the same change in lift distribution, since CL versus alpha curve is not strongly affected by section thickness.
What is affected by thickness is CL max, so a constant chord wing that is reduced in thickness at the tips will tend to stall from the tips in, exactly the opposite of what you generally want.
If the goal was better snaps then it might be a good idea.

Pat MacKenzie
« Last Edit: June 04, 2018, 05:02:54 AM by pmackenzie »
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Offline Keith Renecle

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Re: Why do parallel chord wings have parallel thickness?
« Reply #7 on: June 04, 2018, 09:20:49 AM »
Thanks Pat,

That makes sense to me, and for sure, the tapered wings look a lot better.

See you shortly in Landres!

Keith R
Keith R

Offline Matt Spencer

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Re: Why do parallel chord wings have parallel thickness?
« Reply #8 on: June 04, 2018, 11:20:28 PM »
Er Um ,

Some turkeys cut foam wings for APS profile peacemakers , cardboard covered .
Theyed stuff up a few , so the bow bowed and the wings were thinner in the middle .
If you cut them in half & joined them end to end , they were thinner at the tips .

Frightfull .

Particularly covered in cardboard , solid core , 21/22 Oz , with a Yin Yan Silver Swallow 2.5cc .
Whip for 3 laps , hard . Go up to 40 degrees up , keep whipping two laps , Whip & Dive hard ,
Full Up .
50 % chance you might get a loop. Or Crash .
Untill you went to the edge of the field ,
The Bank was near 45 Deg Down ,
So you could crash into the bank if it stalled / staggered etc .
Tho the whipping was easier as you didnt have to go so high .
Worked best loop centered on handle / ground level .
Loading ment it usually was Ground Level .

I dont think consequitive loops were contemplated .

So it has been done , but these were rejects .  LL~  R%%%% R%%%% Tragic but taught momentum , inertia etc .
Probly needed a tuned pipe .  VD~ S?P LL~ :##

The guilty cuprit was Stuart somebody ! . ( Club Chief )

Online Curare

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Re: Why do parallel chord wings have parallel thickness?
« Reply #9 on: June 05, 2018, 07:31:44 PM »
My 2 cents:

First thing to know is why wings are tapered in the first place.
Main reason is to get a more elliptical lift distribution to reduce induced drag.  Also reduces area at the extremities and moment of inertia to yaw/roll improve handling.
Plus of course it looks better :)


Tapering only thickness will not result in the same change in lift distribution, since CL versus alpha curve is not strongly affected by section thickness.
What is affected by thickness is CL max, so a constant chord wing that is reduced in thickness at the tips will tend to stall from the tips in, exactly the opposite of what you generally want.
If the goal was better snaps then it might be a good idea.

Pat MacKenzie

You bring me to an interesting point, that generally while there is a taper in most aerobatic wings, the percentage thickness of the tip is generally thicker than the root, to alleviate tip stalls. Snaps are easy enough to create without having the wing do it for you!
Greg Kowalski
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Online Brett Buck

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Re: Why do parallel chord wings have parallel thickness?
« Reply #10 on: June 05, 2018, 10:55:36 PM »
You bring me to an interesting point, that generally while there is a taper in most aerobatic wings, the percentage thickness of the tip is generally thicker than the root, to alleviate tip stalls. Snaps are easy enough to create without having the wing do it for you!

    They do have that, sometimes, but it doesn't make a lot of sense for stunt. You cannot be running it into a stall, if you do, what it does afterwards is rather a moot point.

     Brett

Online Tim Wescott

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Re: Why do parallel chord wings have parallel thickness?
« Reply #11 on: June 06, 2018, 01:02:50 PM »
You cannot be running it into a stall, ...

You need to fly Ringmasters more often.  Do you think it's signature octagonal "round" loop is done by pilot's choice?
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Online Curare

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Re: Why do parallel chord wings have parallel thickness?
« Reply #12 on: June 06, 2018, 09:40:37 PM »
    They do have that, sometimes, but it doesn't make a lot of sense for stunt. You cannot be running it into a stall, if you do, what it does afterwards is rather a moot point.

     Brett

OK, you have my attention - would we then want to have a geosized root airfoil for the tip airfoil? What ARE we looking for across the planform? Surely it can't just be as simple as elliptical lift distribution?
Greg Kowalski
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Offline Serge_Krauss

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Re: Why do parallel chord wings have parallel thickness?
« Reply #13 on: June 10, 2018, 11:57:36 AM »
Diminishing the chord toward the tip also moves the (Edit: aero Center) toward the root, making the wing less susceptible to gust upsets. The Palmer "Smoothie" was marketed as a windy-weather plane.
« Last Edit: June 11, 2018, 04:29:29 AM by Serge_Krauss »

Offline Matt Spencer

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Re: Why do parallel chord wings have parallel thickness?
« Reply #14 on: June 10, 2018, 12:33:59 PM »
XF 91 .  :-\ :-X



The blokes in the assembly shop mustve been smoking loco weed .  S?P


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