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Author Topic: New builder: Is washout required in every wing?  (Read 520 times)
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jaeger820
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« on: July 05, 2019, 10:13:40 AM »

Thanks for any help you can provide.  I am new to building and am enjoying the learning process.  My subjects are all scale because I enjoy the builds about as much as I enjoy the flights.  My question is...
1. Should I be building washout into every wing?
2. Are there some rules of thumb, guidelines, flight dynamics that indicate how much washout is required?

Thanks again for any suggestions.
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ZK-AUD
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« Reply #1 on: July 05, 2019, 12:03:00 PM »

I always do.  But others say you don't need it.  This is one of those questions that invites debate.  You can build without and do just fine but then you'll get a model that persistently likes to drop a wing.  Its generally a good idea with less stable low wing types.  Case in point my Avetek Airsail CT4 Airtrainer.  This is a low wing subject with a lot of top hamper that is inclined to be unstable.  Mine is rock steady with a gentle nodding stall and no wing drop on account of the washout.  You don't need a lot.  You just want the tips to stall after the root and not the other way around!  Give us some examples of your subjects and their wingspans and I'll tell you what I would  do
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lincoln
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« Reply #2 on: July 05, 2019, 01:31:14 PM »

Untapered, unswept wings don't really need it, though a small amount probably doesn't hurt.
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Greg Langelius
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« Reply #3 on: July 05, 2019, 02:15:00 PM »

The aerodynamic purpose of washout is to ensure that the tip portion is the last portion of the wing's span to stall.

By reducing the tip's angle of attack, the washout ensures that the center portion flies at the greater angle of attack and stalls first when the aircraft pitches up and enters the stall regime. This maintains lift at the tips longer, and can assure that tip stall is minimal.

This helps maintain the wing's roll stability.

I generally build in 1/16" of washout per foot of span.

That's an arbitrary personal choice and others may choose to employ another value. My trimming skills originate in Indoor FF.

The sharpness of the leading edge relates directly to stall characteristics. The sharper the leading edge, the more abrupt the stall.

Biplanes can employ more angle of attack in the forward wing. This ensures that the forward wing stalls first, shifting the center of lift rearward at the entry into the stall regime. This imposes a tendency toward a nose down pitch bias, affording some reversal of the stall. This contributes toward pitch stability.

Negative stagger biplanes can make best use of this, since the upper wing (rearmost wing, with less angle of attack) stalls later, and the higher wing aircraft (assume the lift from the lower wing becomes near zero) has better roll stability.

As the stall reverses, the bias in lift across various portions of the lifting surfaces becomes minimal, making the various trim values serve as automatic stabilizing mechanisms. It is better to think of the lift biases that the trim values impose as being relative and comparative, rather than absolute.

Greg
« Last Edit: July 05, 2019, 02:32:25 PM by Greg Langelius » Logged

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jaeger820
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« Reply #4 on: July 05, 2019, 06:04:13 PM »

All,
Thanks for the responses so far...I appreciate your insight and help.

ZK-AUD...in response to your question...I've built three Guillows kits so far, (Spitfire, Typhoon and FW-190).  I am working on my third (Fairchild 24) and have my fourth lined up (Bird Dog).  My intent was to start with the Guillow's kits...learn some lessons and then progress from there.  Of the three I've built, I had the most flying success with the Typhoon...keep in mind, "success" up to this point has been flights under a minute.  The Typhoon lodged itself about 30' up a pine tree here in North Carolina and has been there ever since. 

I've just started the Fairchild (I wanted to attempt something with a high wing) and need to make a decision about the washout soon.

Thoughts?
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billdennis747
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« Reply #5 on: July 06, 2019, 03:57:38 AM »

I've just started the Fairchild (I wanted to attempt something with a high wing) and need to make a decision about the washout soon.
It absolutely does not need any washout. Build it all flat and straight and it flies like a dream. I´ve done three. Suggest you make a separate balsa noseblock too.
« Last Edit: July 06, 2019, 04:30:31 AM by billdennis747 » Logged
John Webster
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« Reply #6 on: July 06, 2019, 04:05:31 AM »

Peter Fardell is the man to talk to about Guillow's Fairchild 24.
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Pete Fardell
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« Reply #7 on: July 06, 2019, 06:44:50 AM »

I’ve actually only built three too, but would echo what Bill just said. A slightly warped tailplane seems to be the main danger I think. That has crashed one of mine before, and is what wiped out Derek Knight’s at the recent outdoor KS comp. Otherwise though, you can’t go far wrong. Even when it’s old and knackered and held together with Sellotape (as my first one now is) it will still want to fly!
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jaeger820
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« Reply #8 on: July 06, 2019, 08:28:29 AM »

Appreciate the responses.

Pete and Bill...thanks for your advice on the Fairchild build. 

On that bird, my plan indicates no dihedral on the wing.  That seems a little odd to me but I will follow your lead on this one...do you recommend some dihedral or as Bill says..."Build it all flat and straight"?
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Pete Fardell
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« Reply #9 on: July 06, 2019, 08:43:28 AM »

I’m not at home to check, but I’m almost sure the Guillow Fairchild does have some dihedral, as does the real aircraft. Have you got the full plan?
(By flat, I think Bill just meant flat whilst on the board and to end up without warps or added washout.)
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Indoorflyer
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« Reply #10 on: July 06, 2019, 09:27:40 AM »

Seem to recall a part that attaches to the rear lower spar, having an angled edge that sets the root rib dihedral angle.  The wingtips would need to be propped up so the root ribs meet the base ribs on the fuselage.
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flydean1
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« Reply #11 on: July 06, 2019, 09:54:54 AM »

Jaeger820, where do you live?  You may be near some other flyers that can help.
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jaeger820
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« Reply #12 on: July 06, 2019, 11:05:25 AM »

Indoorflyer...you are exactly right on that. That part (E3 on the plan) had me a bit confused since there is no mention of dihedral in the plan and the drawings display a flat surface across the wingspan.  Appreciate your help there!

Flydean1...I live in Robeson County, North Carolina...very near Hoke and Cumberland County.  I'd very much appreciate an intro to any local builders or clubs.  I think there's a local FAC around these parts, but I haven't taken the time to look them up.

Sam
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billdennis747
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« Reply #13 on: July 06, 2019, 11:58:09 AM »


On that bird, my plan indicates no dihedral on the wing.  That seems a little odd to me but I will follow your lead on this one...do you recommend some dihedral or as Bill says..."Build it all flat and straight"?
Sorry - yes, by 'flat and straight' I meant no warps in the wings. It's a very stable structure and does not warp. If you try to build warps in, you may get differential and then all bets are off.
Yes there is dihedral; 3 - 4 degrees, and tail warps can be bad news
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Indoorflyer
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« Reply #14 on: July 06, 2019, 03:20:37 PM »

That part (E3 on the plan) had me a bit confused since there is no mention of dihedral in the plan and the drawings display a flat surface across the wingspan.  Appreciate your help there!

You're welcome!
They also "depend on" the true length of the wing strut "V" assembly to help set the  dihedral angle.  I would carefully shim the tips equally, and have a little excess strut length available for trimming and adjusting after assembly.  You don't want to inadvertently build in a wing warp!
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ILM Tarheel
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« Reply #15 on: July 06, 2019, 10:55:30 PM »

jaeger820,

The Carolina Area Free Flight Association (Raeford NC) is the group you are looking for. Check you Hip Pocket private messages for contact information

Jimmy J, Secretary CAFFA
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C/L Gee Bee
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« Reply #16 on: January 08, 2020, 01:57:20 PM »

Just starting on my Guillows Fairchild 24, thanks very much, Pete and Bill, for the info on wing detail and rudder!
Good point on Wing V strut length, Indoor Flyer...
I'm carving a nose block, using a Gizmo Geezer prop ass'y. Everything else just looks...'elementary'...

I told an inquisitive friend about 'wheels'. He said 'Foam for wheels'? I replied there were all sorts of materials being used, I had experimented with old hardened bread, oven-formed. One flight. He asked how they turned out after that landing... I replied, "Toast..."
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