Paul, I am sure you are aware of the method that Paul McCready used
 to make the carbon fiber spars for the Gossemer Albatross:

 He used Aluminum irrigation tubing (~3-4" D) and laid the carbon
 fiber up on the tubing, then dissolved the Aluminum out with KOH.
 Bill Schertz

 I was called in as an aerodynamic consultant on the one that
 eventually won the Kremer prize by Jack Lambie around about 1976 or
 1977. My girl friend Rhonda and I drove up to the valley to have a
 look. I was surprise to see a propeller about 4 or 5 feet in
 diameter made from two model airplane wings and wire braced. I
 suggested a larger diameter prop not wire braced and further geared
 down. They did that and went on to win the $50,000 prize :-)

 I was not aware he built the spar that way. I was thinking of using
 a metal or plastic tube covered with several layers of garbage bag
 or other thin plastic material cut in long strips. After the epoxy
 is cured the spar can be slipped off the tube. I have done that many
 times on shorter composite tubes. Sometimes the strips can just be
 pulled out from between the surfaces. That gives enough clearance to
 remove the spar from the tube.

 How's the Kiss Cruiser doing? Do you like living up there in the US
 bush? :-)

 Paul Lamar


 Paul you can also use braided carbon fiber. You get it in a flat
 role with different diameters. This way the "braided fibers" are in a
 more or less 45 bias in the weave to the span of the spar. Do 2
 layers then dremel cut out of the male plug ( split the carbon pipe)
 to get off the male plug. Then do several layers braided over the
 "first split mold" to the different stations according to the bending
 loads and specs Vacuum bag each layer as you progress and scuff
 between layers to get nice finished surface between layers

 Le Roux Breytenbach ZA


 One needs some unidirectional fibers on top and bottom of the tube
 to take the high bending stresses. These should be layered with the
 thickest layers near the center of the wing.

 Paul Lamar


 Spar caps can use pultruded carbonfibre rods
 http://www.marskeaircraft.com/carbon-rod.html


 Carbon Rod - Marske Aircraft Corporation

 www.marskeaircraft.com  Learn more
 about Graphlite Carbon Rod, Pricing, and how place an order with
 Marske Aircraft Corp

 Le Roux Breytenbach


 Hi Paul, Round tube spars are usually an inefficient use of
 materials for a spar! The only bits taking the loads are the upper
 and lower one eights. Why not a box spar or an I beam?

Ray Tolhurst

 Aw so that is assuming the wall thickness is constant around the
 circumference :-)

 The I beam is hard to layup. The round tube is the cheapest male
 mold.

 However I am leaning toward a tapered box tube sections made from
 .032 thick  5052 ten feet long then tig welded together to make a 20
 foot long male mold. The welded joints are then sanded.

 It is hard to find 20 foot look press brakes and 20 foot long sheets
 of aluminum.

 If you seal the small end with a tig welded cap. The aluminum male
 mold will pop out of the cured spar when water pressure is applied
 to the small end.

 Patent pending :-)

 BTW Another reason for rectangular or square tube spar is it
 transmits the torsional load from the ribs into the spar better. It
 is a simple matter to layup angle reinforcement layers to do this as
 they are linear and not curved. In fact one may find pultruded angles
 that can be cut in short pieces..

 http://dragonplate.com/ecart/categories.asp?cID=34

 Check out Pitching Moment  Characteristic in Von Doenhoff page 179.
 Also page 214 for Fowler flaps. I am looking for a C sub L of over
 2. My C182 is fantastic in that regard.

 BTW I am thinking of offering plans if you have Solid Works or
 Rhino.

 Paul Lamar


 Paul


 I do have an idea to built  by using a big pvc pipe which the inside
 diameter meet your requirement

 Cut it in half and install over a long steel angle or steel channel
 to keep it straight,

 Wax it inside and  lay down the carbon fiber and trim each side with
 a knife before full cure,

 Sand each inside edges and rejoin both sides with several carbon
 fiber ribbon

 By placing it with a long rod and attaching the wet ribbon who have
 prewet over polyethylene plastic strip.

 When in place  use a special  made curved roll as same radius of the
 inside tube and attached to the long rod ,

 Before removing the  polyethylene strip  to prevent the roller to
 stick on pre wet ribbon,run it several time over the wet ribbon to
 make sure it lay down perfectly and bubbles removed.

 Let it cure and when done remove the plastic  polyethylene strip
 over the jointing ribbons

 You will have a perfect outer diameter and strong spar to built your
 wing the spar .


 JEAN PRUDHOMME

 Hi Paul

 Have you considered fiber reinforced tubes for the spar

 These are relatively cheap and light weight

 I happened to have a tube in the shop 110 mm OD, 3.2 mm wall as
 shown in picture It weighs 4.9 lbs for a 4 ft section or about 1.25
 per linear foot

 In spite of the thin wall this tube is tough and stiff (maybe not a
 desirable feature but I am not an expert). I would estimate this
 would easily carry a ton of side pressure mid span. Unfortunately I
 don't have a strain gage or would run some tests with the engine
 hoist I don't remember what I paid but it was pretty cheap maybe $25
 per foot ballpark

 Also, years ago I was doing some experiments while trying to make
 the worlds lightest bike frame and the process I came up with is
 applicable for making wing ribs. Each rib would be approx 200 grams
 for a 4 ft wide rib section and strong as heck. Scales linearly. Not
 sure how competitive weight-wise with foam ribs. Can you let me
 know?

 Is there a typical rib spacing used on light aircraft or are they
 all over the map depending on specific designs

 Regards,

 Simon Saba

 I was thinking about flaperons and decided it was a bad idea. I am
 sure it takes a lot of flight time to get the handling just right.
 So I decided to copy the C182 wing planform in carbon composites. It
 has known good handling as I have about 3000 hours in one.

 That meant a straight wing out to the ends of the fowler flaps and
 tapered from there on out.

 So a rectangular carbon  tube with reinforced top and bottom would
 be good for the center section. I would need a tapered male mold
 from there on out.

 Here is my latest thinking on the fast bush plane. I lengthened the
 nose and will put a baggage compartment up there. Great for
 adjusting the CG with heavy loads.

 It will also reduce the chance of flipping completely over if it
 encounters an obstruction too large to bounce over.

 How"s your project coming. I'll loan you my 3 rotor TC if you want
 to test it on your dyno.




 Paul Lamar


 I love the big wheels on the Bush Plane looks totally cool in spite
 of the drag. It will go well with a Unimog I like the new concept.
 Duplex Fuselage extra surface area may be offset by the nice
 unobstructed positioning of the engine / prop


 Regards,

 Simon Saba

 Did you see the retracted landing gear version or are you using a
 cell phone ? :-)

 Getting mechanical info on blue Styrofoam is like pulling teeth from
 a chicken. Dow want to sell it as insulation.

 I think it is about 2 pounds per cubic foot with compressive
 strength of 25 PSI. Epoxy does not affect it.

 I tried Jean's idea of the two inch long drywall screw and it works
 great. It is the long length that makes the big difference. 3 inch
 would be even better. It takes at least ten pounds to pull it out I
 am guessing.

 You have a minimum amount  of time to screw the pre cured skin to
 the one inch wide ribs. It might help if all the holes were drilled
 in the skin first. Also more than one person would help as well.

 Way back in the 1960'S I did some research on fiberglass race car
 bodies.

 4 oz glass cloth on both sides of 1/4 inch PVC foam was much stiffer
 than .032 thick T6 aluminum and  much less weight. It was vacuum
 bagged in a female mold. Phil Hill hit the wall with the 2F car and
 it bounced back after bending a 4130 suspension A arm. I was real
 durable and tough.

 For air craft wing skins it would be great if you had a female mold
 and vacuum bag. Screwing the thin skins down with drywall screws
 into one inch thick Styrofoam ribs is far more practical.

 My guess on the rib spacing is about a foot.

 Do the bottom half first and then fill it with water to see if you
 have any leaks.

 If your planning on a wet wing fuel tank.


 Paul Lamar

 Paul, Make your male plug out of 2lb density Styrofoam, round or
 rectangular (I beam is best by far). Lay up your carbon, fibers
 oriented length ways, vacuum bag whilst curing. Hey presto ! done !
 Leave the styro in, it weighs nothing. If you really insist on
 removing it dissolve it out with acetone, done ! Chris. Hoskins.

 That will work.

 We are thinking of kitting this airplane.

 Paul Lamar


 What thickness for the foam insulation? Are you referring to the pink
 or blue stuff in the big box stores?

 Once covered with tyvek will a heat knif or hot wire cut the tyvek
 like it will the foam?

 Thanks! Brad Chubb



  Hi, Styrofoam near fuel is a real bad idea, Gasoline will turn
it into   slime.

  Murry Roszansky

  Here's a more complete website on using pultruded carbon rod for
wing spar:
http://www.ihpa.ie/carbon-dragon/index.php/home-top/articles/83-graphlite-carbon-rod


 I like the above article because it shows how the rod layup
schedule can be adjusted for the load.

 I would think the form or mold for a box or I-beam spar doesn't
need to be made from metal - it could be made from wood cut with a table
saw.  Build the form on a flat tabletop.  The sides of the form could be
doweled and screwed to the tabletop - unscrew them to release the formed
spar.  I might consider using formica counter top laminate to make a
slick finished surface.  The spar pieces would be made in a C-shaped
form and then glued together afterwards.  If an I-beam is desired, glue
the two webs of the Cs together back to back.  If a box is desired, glue
the caps together (lapping - this is probably pickier to get right).

 One thing that's true is that the shorter the wingspan, the less
critical/interesting the weight savings of a carbon spar.  On a
sailplane with a long wing and a thin airfoil, the spar is a massive
structure.  On an RV6A, with thick section airfoil and short wings, the
spar is a much smaller portion of the structure.  Wing skins can only
get so light before being too delicate for a long service life -
considering the normal bumps and dings an airplane gets from having
people walk around it.

 Regards,
 Matt- Prather



You might like to check out an aircraft designed by Nick Jones in the
late '80s - the White Lightning. Only about 12 were ever built. They
utilised a carbon fibre tube as the main spar. It also doubled as the
fuel tank. It is powered by a Continental IO360 and is probably the most efficient
4 seater to ever fly. Looks good as well.
Regards

Mike Arthur

Use Divinycel http://shop.fiberglasssupply.com/Core_Materials-Divinycell_Foam_Core.html.
Cut and form it then overlay the carbon on it. Make your I beam from this, fillet the radii,
lay it up and vacuum form it.

Kevin Alderman

Perter Garrison wrote a good article on tubular spars for May 2017 Aviation History.
Here it is.

The current 10G aerobatic airplanes are using carbon fiber C spars.
The tapered  female mold is bent out of sheet metal and welded together.
Sometimes the C sections are nested in each other back to back to form a box spar.
The Voyager around the world aircraft used this kind of spar.
The advantage is the outside dimension of the spar are closely
controlled and accurate. Also a vacuum bag can be used to insure
a dense laminate.

Paul Lamar

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