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  #11  
Old 01-20-2016, 03:06 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,574
Default design goals and specs

I appreciate the interest on the wings.

The basic design goal is to improve cross-country performance without sacrificing access to short fields, and maintain as much as possible the sporty handling.

With the cross country wingtips, wing span will be 25'4" Aspect ratio about 6.4.
Wing area just under 100 sq ft, with a mild laminar flow airfoil.

With the short tips, span will be 24', wing area 96 sq ft, same aerobatic weight, same or better sustained roll rate.

A slotted flap covers 6 ft of each wing, so the hope is that the approach and landing speeds will be the same, despite the reduced wing area.

One challenge in getting a laminar flow airfoil fitted to an existing airplane is that the spar wants to be farther aft in the wing, so that means that the wing needs to shift forward some with respect to the fuselage. Its a pretty mild, conservative airfoil, max thickness at 40% chord. Spar is at 35% chord. It worked out that the 25% MAC point moved forward 1.25 inches.

For the RV-8, this is no problem, since -8's tend to be slightly nose heavy. I will probably move my battery to the front, but don't expect much else to change. For the Rocket-6, this shift is a really good thing, with the IO-540 on the front, it is rather nose heavy too, and shifting the wing is all to the good.
In principle, the -8 wing would fit on a -7, and the Rocket-6 wing would fit on a standard 6. But both those designs tend to have the c.g. a bit aft to begin with, and shifting the wing forward is going to be a challenge. For a new-construction airplane, there are lots of things one could do, like use the O-320 motor mount with the O-360, shifting the engine forward a bit. For a retro-fit, it would probably mean a new engine mount and new cowl. Putting a Hartzell prop on the nose will obviously help.

One poster asked about ribs. Those come next. They are carbon-foam sandwich, with a solid fiberglass strip that allows through-bolting to aluminum angles attached to the spar.

Thanks for the interest, we'll post updates periodically. Once we see how well they work, we might consider pulling hard tooling off the wings and making more. But for now, we are just committed to two sets.

Oh, and someone asked about a link to the HP-24 project....Bob uses Facebook, so the old website is pretty much not maintained. But he keeps the Facebook page up to date. Just go to Facebook and search for HP-24 Sailplane Project
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
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Last edited by scsmith : 01-20-2016 at 03:12 PM.
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  #12  
Old 01-20-2016, 07:06 PM
Evolution10 Evolution10 is offline
 
Join Date: Jun 2014
Location: oregon
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Are you using a wet wing like Lancair does?
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  #13  
Old 01-21-2016, 01:18 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default Wet wing

Quote:
Originally Posted by Evolution10 View Post
Are you using a wet wing like Lancair does?
Yes. Although with the aluminum spar, that means there is an extra web that forms the aft tank close-out. Also we use a web as a forward tank close-out so the fuel does not go right to the leading edge. I felt it might be too difficult to get a complete seal on the leading edge closure, and I wanted a little bit of buffer so if you ding the leading edge, you don't make a leak.
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Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Jan 2020
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  #14  
Old 01-21-2016, 01:29 PM
BonitaRV8 BonitaRV8 is offline
 
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Location: Bonita, Ca
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Are you fastening the skins to the spars as well as bonding? Fiberglass or carbon fiber skins? You don?t have any CTE concerns with bonding aluminum to composite over that length? Why not fabricate composite spars?
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  #15  
Old 01-21-2016, 05:03 PM
Bob Kuykendall's Avatar
Bob Kuykendall Bob Kuykendall is offline
 
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Location: Douglas Flat, CA
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I don't presume to speak for Steve, but so far as I know:

Quote:
Originally Posted by BonitaRV8 View Post
Are you fastening the skins to the spars as well as bonding?
The bonding is the fastening. So far as I know, Steve does not plan any discrete fasteners such as screws.

Quote:
Originally Posted by BonitaRV8 View Post
...Fiberglass or carbon fiber skins?
Carbon, carbon carbon!

Quote:
Originally Posted by BonitaRV8 View Post
...You don’t have any CTE concerns with bonding aluminum to composite over that length?
What is CTE?

Edit Add: Ah, thermal coefficient of expansion. Yes, Steve considered that, and factored it into the lamination schedules for the wing skins. The fiber orientations in the areas where the spars bond on are such that the spar and skin stiffnesses are matched well enough that the thermal stresses anticipated are well within the capacity of the Hysol structural adhesive we'll use.

Quote:
Originally Posted by BonitaRV8 View Post
...Why not fabricate composite spars?
Believe me, we've gone back and forward over this issue dozens of times. Here's the Cliff's Notes version:

In a word, productization.

If it were up to me I would have gone with a carbon pultrusion based spar like I use in my gliders. It would be one piece tip-to-tip, and I'd be taking a sawzall to the belly of your RV to get the spar to go across your fuselage. But as much as I like chopping up airplanes with power tools, sanity has prevailed.

The spar design that Steve arrived at is probably the best compromise that lets our wings bolt right on to existing RV-8, RV-6, and similar airframes. So somewhere down the road you could buy them, bolt them on, do the wiring and plumbing (that you think is a day's worth but takes a month), paint, and fly.

At issue is that carbon fiber, particularly the very strong unidirectional carbon products we use for wing spars, does not play well with the kind of concentrated loads that prevail where an RV wing bolts onto the fuselage. You can't extract all of the tensile or compressive loads out of the spar caps with the kind of bolted joint the RVs use. With composites like carbon spar, it is much more effective to have wing spars that overlap over a distance of two feet or so, to give you a greater distance over which to react the stresses from one spar cap into the other one. Or, better yet, just use a one-piece spar as I propose above, with a slot in the belly for vertical installation. But the overlapping spars would require a slot in the fuselage that is wider fore-aft than the standard x04 bulkhead, and of course the one piece spar gets into that sawzall territory. Both of those schemes require more airframe modification, and offer less possibility of reversion, than we thought most potential customers would be interested in.

I did propose a couple of design schemes that would have interfaced the airplane's side-of-body wing mount to a two-foot-long aluminum stub spar that in turn interfaces with a carbon fiber spar inside the wing. But when the dust settles, the mass and parts count for that scheme is not much better than the aluminum spars we decided to go with.

Thanks, Bob K.

Last edited by Bob Kuykendall : 01-21-2016 at 05:10 PM.
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  #16  
Old 01-21-2016, 05:13 PM
Mike S's Avatar
Mike S Mike S is offline
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I am guessing he is talking about coefficient of expansion for the alum vs carbon joint.

Also, how are you addressing the electrolysis issue ? I have always heard that alum and carbon do not play well together in the long run.
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  #17  
Old 01-21-2016, 05:27 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default insulate the carbon

Quote:
Originally Posted by Mike S View Post
I am guessing he is talking about coefficient of expansion for the alum vs carbon joint.

Also, how are you addressing the electrolysis issue ? I have always heard that alum and carbon do not play well together in the long run.
Yes, Mike is right. As a kid I made a very light, stiff spinnaker pole for a sailboat by spiral wrapping some old unidirectional carbon tapes around an aluminum tube. Worked great for awhile, until I accidently dropped it in the bay. A few weeks later, it looked like an exploded circus cigar.

So, the solution is insulation. We put a fiberglass tape down where the bond line is, and then of course there is the bond line itself of the structural epoxy.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Jan 2020
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  #18  
Old 01-21-2016, 05:38 PM
1:1 Scale 1:1 Scale is offline
 
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I haven't been hanging around here much lately, but I'm glad to learn about this project

A few years ago another member and I were talking about how cool it would be to have an "upgraded" set of wings available. Get your RV flying with the standard wings, and after a few hundred hours of flying it (and missing the building process), you could order up a new wing kit that offered a higher cruise, lower stall and increased roll rate. You could then sell your completed standard wings to a builder that would normally be interested in the QB wing option. Sounds good to me!
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  #19  
Old 01-21-2016, 06:10 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
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Default Thermal expansion

Quote:
Originally Posted by BonitaRV8 View Post
Are you fastening the skins to the spars as well as bonding? Fiberglass or carbon fiber skins? You don?t have any CTE concerns with bonding aluminum to composite over that length? Why not fabricate composite spars?
The carbon skin is all +/- 45 degree bias cloth. So it has very low modulus, and somewhat higher thermal expansion coefficient. So as the aluminum spar grows or shrinks with temperature change, the skin kind of gets dragged along with it. A temperature change of 75F from assembly temperature uses about a 1/3 of the available bond strength.

Elastic strain at the yield strength of the aluminum spar uses about 1/10 of the available bond strength.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Jan 2020
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  #20  
Old 01-21-2016, 06:21 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,574
Default

Quote:
Originally Posted by 1:1 Scale View Post
I haven't been hanging around here much lately, but I'm glad to learn about this project

A few years ago another member and I were talking about how cool it would be to have an "upgraded" set of wings available. Get your RV flying with the standard wings, and after a few hundred hours of flying it (and missing the building process), you could order up a new wing kit that offered a higher cruise, lower stall and increased roll rate. You could then sell your completed standard wings to a builder that would normally be interested in the QB wing option. Sounds good to me!
This is pretty much the idea. Although it is a tall order to have all those things.
We decided to try to keep the roll rate about the same, try to keep the stall speed as close as possible, and take what we could get in cruise improvement.

The retrofit desire does put pretty severe constraints on the design. You would not want to have to move your F-x04 bulkhead for example. And really, if you can tolerate a high landing speed in exchange for the cruise speed, go get a Lancair or Glasair. But I didn't want a 82 sq ft wing.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Jan 2020
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