July 31, 2009
Here is an update on our aircraft building project. I have been a bit delayed getting this report out because my hard drive on my laptop died last week. Luckily, a local computer tech was able to retrieve (I hope) all my files and pictures!
Flash! My new laptop arrived today! I will miss my trusty old Dell Latitude but it was over 10 years old and couldn’t handle high speed internet very well. I am very relieved that I can now go online without using a dial-up modem.
So here is what has been happening:
I am happy to say that we have been very productive over the past few months. As of last week we have completed the 4 main wing spars for our project.
We made two outer main spars (one for the port wing and one for the starboard wing), and two center main spars. The reason we have two center main spars is because the two spars will be bonded together to make an extra strong double spar for mounting the two wings. These parts have been the most challenging and complex layups of our entire project.
Here is a diagram of what the main outer spar looks like. Note that it has a
“C” shape. The two bent sides facing away from you are the spar caps containing
carbon fiber pultrusions which make the spar extremely stiff and strong.
In this picture, you can see where the port main spar goes in the wing.
We had to make two molds to make these parts. One 12 foot mold was created for making the two outer main spars. This mold was made using two aluminum L-brackets for the sides (spar caps) mounted to a smooth fiberboard base. The mold, and the resulting outer spars are very straight. We used carbon fiber pultrusions in the spar caps to make the resulting spars very stiff and strong. Since the forces become less as you go out towards the wing tip, the carbon pultrusions were cut to various lengths so as to reduce the amount of carbon the farther out you go. Over 6 layers of glass cloth were used on the inner 1/3rd of each outer spar and 3 layers on the outer 2/3rds.
Here is a picture of the mold for the outer spars. Note the aluminum rails which
form the spar caps.
Here I am (Darryl) holding the first outer spar for the whole world to see. (No one noticed)
Here is a picture of the port and starboard spars on the living room floor.
This type of storage requires a very patient wife!
Next we made a mold for the two center main spars. The mold is curved so that the center spars would bend upwards at a three degree angle, producing dihedral wings. Putting dihedral into our wings makes the aircraft more stable. Because of the curve in these parts, we decided to bend and epoxy-coat our carbon pultrusions into bundles before doing the actual spar layup. We used a flat board and inserted nails to make a bend jig.
Here is a picture of the carbon pultrusion bundles in the bending jig.
Unlike the outer spars, the carbon pultrusions in the center spars run the full length of the parts.The top carbon pultrusions were about 1/2″ shorter than the bottom ones however. The bundles turned out great, holding their shape and turning out to be very stiff. After fabricating the 4 bundles, we then used them to make the spar caps for the front and rear main spars. After trimming, Darryl cut out matching holes so that the aileron, elevator and flap linkages can pass through the spars.
Here is a picture of Chuck standing behind the two center main spars. Note the
upward curve which produces the 3 degree dihedral in the wings.
Finally, Chuck has been using a friend’s mill to machine the aluminum brackets that will be used to attach the outer spars to the center spars. This will be the main point for attaching the wings to the airplane.
Here is Chuck at the mill machining a mounting bracket.
Well, that is a quick overview of our progress on the four main wing spars. We hope to make more wing parts in the next few months. I hope to be a bit more timely in my reports since things are beginning to move much more quickly now. Please feel free to comment on our blog.