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Carbon fiber spars

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Posted

drumming up convo...my wings are naked hanging on the wall, and I keep reading these articles. Not that I have the disposable income, or time, or knowledge, or skill....but if you built our STOL wings exactly yo plans, but instead with carbon fiber spar, I’m curious as to how much you’d save.

http://jameswiebe.blogspot.com/2010/11/building-carbon-fiber-wing-with.html?m=1

https://jameswiebe.wordpress.com/2009/08/09/breaking-a-carbon-fiber-wing/amp/

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Posted (edited)

Carbon Fiber vs. Aluminum you'd save 40-50% in weight and it would be stronger too. Of course, it would be a lot more expensive...

Edited by CSCameron

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Posted

I was thinking you may be able to drop 10-15lbs and have a stronger spar. I talked to James and he said the spars are $400 each

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Posted

2 1/2" x .065" wall aluminum tube weighs about .6 lb per foot.  There are 48' of 2 1/2" tube in  an Avid long wing, or 28.8 lbs.  Cut out half that weight, and you loose almost 15 lbs at that rate.  Not sure how much lighter your wallet would be, but if you fly with it in your pocket, maybe you would figure that in as well... :-)  JImChuk

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Posted

I also thought of Hershey barring the wings which eliminates the fiberglass tips so maybe another 1lb. The juice isn’t worth the squeeze, but I find most aviation things aren’t...just a little bit further in the spectrum than I’d wish. Though $1600 for 4 isn’t the worst misallocation of money, and you are lighter and stronger. Just fun to play with ideas.

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Posted (edited)

There are alloys of aluminum that are much stronger than the 6061-t6 spec'd for these birds.  2024-t3 for one, although it's not as resistant to corrosion, and 7075-t6 which is about 75% stronger than 6061-t6, and has good corrosion resistance.  Heck, there's even a 5000 series alloy, like they use on boats, that's stronger, with outstanding corrosion resistance!  All this points to the possibility of extending the span by lengthening the cantilevered part outboard of the lift strut attachment.  Doing that would also mean getting rid of the underside camber to lower nose-down pitching moment. Just going to a flat undersurface cuts the pitching moment down by almost 40%!  The alternative, of course, is enlarging the H-tail.    Small flap deflections for takeoff could easily buy back any lengthening of takeoff run for the airfoil mod.  Indeed, that's the killer app for these Junkers-style flaperons!  Dean got a lot right on these birds, hats off to him, but the STOL airfoil is over-endowed in the camber department.  This hurts top-end speed by increasing induced drags of both wing and tail, while, like I say,  small flap deflection would have done the trick on takeoff roll.

Edited by Turbo

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Posted

Then of course the next step is to build CF ribs.  BCSC has such a set of wings setting in the loft built for a light sport super cub. I will ask Bruce about the weight and etc when I think of it.  I know the cost could take your breath away.

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Posted

I bet the wooden ribs are lighter. I don’t like the Carbon ribs because it seems the compression will try and delaminate them. Just thinking, no real experience

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Posted (edited)

Kitfox model 1 fiberglass drooptips weigh 3.5lbs each.  I peeled mine off and hung them on the wall. My aluminum plates i made to replace the drooptips weigh 1.5lbs each. Hahahaaaa 

I have some kitfox model 1 wood ribs on shelf i could weigh, and one set of bare wing spars i could weigh also if was of interest. 

Polyfiber says thier covering per wing on a J3 with paint done to thier spec is 21.5lbs 

Edited by Buckchop

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Posted

Could you imagine how light a carbon sparred, wood ribbed, Hershey barred, oratex Wing would weigh, with titanium jury struts.

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Posted

Could you imagine how light a carbon sparred, wood ribbed, Hershey barred, oratex Wing would weigh, with titanium jury struts.

$2.1 million. 

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Posted

 

Polyfiber says thier covering per wing on a J3 with paint done to thier spec is 21.5lbs 

I weighed the fabric after I pealed it off of one of my Avid wings, and had 8 lbs.  That was with ultralight fabric, and minimum poly fiber chemicals on it.  I had done that recover a number of years before.  I think I sprayed 1 less coat of poly brush then recommended by poly fiber.  For poly spray, they say 3 cross coats, I did 2 on top, and 1 on bottom.  Only painted heavy enough to cover completely, and look fairly decent.  It was in fine shape when I removed it to rebuild the plane after an accident.  JImChuk

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Posted (edited)

Kitfox model 1 fiberglass drooptips weigh 3.5lbs each.  I peeled mine off and hung them on the wall. My aluminum plates i made to replace the drooptips weigh 1.5lbs each. Hahahaaaa 

I went out and measured my wings and came up with 112 sq ft of wing area with the fiberglass tips being roughly 5.7 sq ft (included in the 112 total). At max gross weight (850 lbs for a model 1) that's a wing loading of about 7.6 lbs per sq ft of wing area. If you take that area away you bump your wing loading up to 8 lbs per sq ft and you lost about a foot and a half of span both of which might adversely affect your climb performance.  I'm not experienced enough to know if that would actually be a noticeable difference but it's worth thinking about. I have a feeling that us guys that live at higher altitudes would notice the difference more than the ones near sea level. Especially when density altitude goes really high on a hot day here in the desert. 

Also I recall Jim Chuk mentioning that those fiberglass tips might just save your flaperons in the event of a ground loop and would provide some measure of protection from the impact of the wingtip against the ground doing some serious damage to the spars as well. I had planned on getting rid of mine as well but as soon as I read that I decided to keep them. 

Edited by Willja67

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Posted

My avid C speedwing @ 458 empty weight is a rocket off the ground and climbs like a home sick angel, despite the Missing wing area

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Posted

What is your normal stall speed?

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Posted (edited)

Well my tip plates r 2" larger all the way around than the tiprib, plus an extra 1" on back half of top and bottom, i do not like how the wing moves on my blackfox with the drooptip in bad weather or little to hard of a landing, i belive cause of the weight of it out there.  And r u sayin that going from 7.6 to 8 lbs per sq ft of wing is bad? Seems that more wing presser is better, and i dont think ud knotice any difference of lift? Course im nowhere near a plane expert. Ive just never liked drooptips. 

Guess y its experimental, hahahahaaaa

Jim id have to read it again, but mayb that was thier covering and the piper factory wing framework??

Edited by Buckchop

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Posted

Any wing loading under 9-10 PSF is going to be lively in windy/gusting conditions.  My challenger was 4 PSF and it was a terror in anything over 10 MPH.

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Posted

I honestly don't know. Ive got 200 hrs in my logbook only 13 of which are tail wheel hours and none in a kitfox. But it is a 5% difference in wing loading/ area. I guess if you're the type trying to ring every last ounce of performance out of your plane it would make a difference.

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Posted

What is your normal stall speed?

40 ish

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Posted

Buckchop, I wouldn't be surprised that Polyfiber cover on a Cub wing weighs 21 lbs.  If you go with all the coats they use, they have 30 gallons of poly brush, poly spay, and poly tone on the complete cover job.  I probably used 10 or 11.  JImChuk

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