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
The Glass Goose uses CF-reinforced spar caps in an I-beam configuration
that is easy to build. One side (upper or lower) wing skin is placed in
a jig to control the twist and dihedral, and peel ply/plastic is used as
a separation medium for the spar cap. The spar is created using 1/2"
blue foam covered with eglass for the vertical part, and the spar cap is
laid up onto the peel ply covered wing skin and up the vertical. (The
tapering CF has already been laid up on the wing skin)
Then the final vertical dimension of the spar is approximated with
measurement and a rough fit of the other wing skin using the wing upper
jig. When complete, the other wing skin is tacked on top of the
vertical part of the spar in the jig and allowed to cure. This assures
the shape and size of the wing is accurate. After cure, the first wing
skin is flipped over and separated at the spar cap/peel ply so that the
upper spar is complete and the lower glass can be laid up onto the (now
lower, "tacked") spar and wing skin. This results in a complete I beam
spar in a wing skin which is still in the jig. When all the ribs,
tanks, etc are done the peel ply is removed from the upper spar cap and
the upper skin closed in a conventional manner.
Scott Gettings.
Sounds interesting Scott can you scan some of the instruction diagrams
and attach them?
Paul Lamar
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