I am working on the design of the carbon fiber six inch diameter tube spar.

The spar is the heaviest part of the aircraft structure so it pays to make it out of expensive carbon. The skins of course can be glass or carbon depending how much money you want to spend.


Paul Lamar

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 round 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

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