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Old Jun 24, 2012, 07:37 PM
Hey was that a Thermal ????
Joined Nov 2009
2,448 Posts
Build Log
The FireFly

The FireFly is an old school style DLG built using new materials and methods. You should have very little issue getting your plane to come in under 8oz.

In order to build your plane you will need;

epoxy, (30 min will work just fine)
Micro balloons, babay powder, or similar filler
Foam Safe CA
electrical tape
straight edge
hobby knife with new blade
tool to drill small hole
power drill or drill press
needle nose pliers
masking tape

The first step is to join the wing halves. Put the wing top down on your bench and tape the two halves together with a couple strips of masking tape running opposite the root and one strip right on the root. Now close the the wing "book" so the bottoms of the wing halves are against each other. Fill the hard point cavities with a mix of epoxy and cabosil or baby powder. Place one wing half back in the beds and carefully weigh it down to the bench. Lift the other wing tip up off the bench 7". That 7" will result in a 6.5" dihedral. This is where I fly my plane, and it seems to be a good comprimise.

When the epoxy has hardened you will want to wrap this joint with fiberglass and then wet it out with thinned epoxy or foam safe CA. I prefer to stick some fiberglass to wax paper using a mist of 3M77 and then cut the wax paper and glass into .75" wide strips. You will need two strips. Mist one of the strips on the glass side with the 3M and apply it to the wing joint. Carefully peel the wax paper and wet it out. when it is dry flip the wing over and do the same to the other side. When both are done trim the trailing edge and and clean up the leading edge with fine sandpaper. !Oh, the fibers of the fabric should run with the wing joint and 90deg to it.!!

Now that the wing is joined you can drill it for your wing posts you will mount on the boom. The posts have an OD of .200" so a 7/32 drill bit is perfect for drilling the wing. I suggest drilling from the bottom of the wing, this way if you are off slightly in angle as you drill the wing will still be pulled down precisely to the fuse. The first hole is drilled at 30MM from the leading edge and the second at 110mm from the leading edge. It helps to drill a small pilot hole first and then you can adjust slightly, if needed, as you work up to the final size of 7/32.

Once you have the wing drilled you can mount the posts to the boom. The front post should be mounted first and it goes 1" from the large end of the boom. To mount the post simply glue it in place with a drop of CA. When the CA is dry enough to handle wrap carbon tow around the boom so it holds the post to the boom. Put 3 layers in front of the post and 3 behind. On the last layer tuck the loose end under the layer and pull snug. A DROP of CA can be added to hold the "knot" .

To do the back post put it through the wing and put a nylon srew into the post. It will not snug up but that is fine. Put the wing on the front post and snug it down with a nylon screw. line the wing up with the boom and without shifting the wing spot glue the rear post to the boom. When this is handlable carefully remove the wing and wrap the rear post just as you did the front post.

When both posts are wrapped and you are happy saturate both wrappings with epoxy. Once it is all wetted out wrap both wrappings with electrical tape. Start the tape and then twist it so the sticky side is out. Once the epoxy is cured carefully peel the tape and you will have two very nice carbon rings holding your posts in place.

There is a small block of wood in your kit and that is used to set your wing angle or longitudinal dihedral. It is glued to the boom right behind and touching the rear post. This can be left very square or it can be shaped so it tapers down to the boom. A little CA does a fine job of locking this in place. I am sure I know a few people who will even color it with a black marker.

I strongly suggest you mount your tails in the following order. Mount the horizontal first and the vertical second. I strongly reconmend putting the stab on the bottom of the boom. This is how we tested it and it seems to fly very well set up like this.

Mounting the Horizontal stab: make two pin holes that line up with the srews for the pylon. Draw two circles the size you want your hard points with the pin holes on the middle. These circle cut outs should be opposite the hinge gap and cut through only the skin on that side. Remove thge foam in the circles with a small flat screw driver. Pour a slurry of epoxy and micro balloons to make your hard points into the two cavities. When the hard points are cured simply drill a clearence hole for the 4-40 screws at the pin marks.


To mount the stab it helps to slide the vertical on the boom and put a piece of tape where the leading edge stops on the boom. To slide the stab onto the boom it may be necessary to pinch the boom slightly. This is so you know where to mount the horizontal. The trailing edge of the horizontal should be just in front of this reference point. You will now want a flat surface like a kitchen table. Place 4 glasses, blocks of wood or what ever you have, of the same height on the table. Set your wing on two of these blocks so that the boom will push down on the stab pylon and the wing is level. Put a drop of CA in the middle of the pylon and set the stab on the two other blocks so the boom contacts the pylon in the correct location. Let the boom drop onto the pylon while making sure the stab is square to the boom. Let the CA cure for a few minutes and then let CA wick under the pylon from the sides. For extra insurance you could do a wrap of light glass from the side of the pylon around the boom and onto the other side of the pylon and wet it out with CA. Very often this is not necessary.
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Last edited by The_Builder; Jul 15, 2012 at 10:36 AM.
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Old Jul 08, 2012, 03:21 PM
ground penetration specialist
Nathan Schmoekel's Avatar
USA, MI, Grand Rapids
Joined Apr 2007
1,818 Posts
Great kit!! Just finishing up the airframe... I built the tails onto the boom first then did the wing posts. BIG MISTAKE Like Paul said... Mount the wing to the boom first that would have been SOOOOO much easier!

Paul, you need to update the name of the plane in the first post.

Also concerning the wing trailing edge to boom gap... With that specific gap, the boom is aligned how, to the center line of the wing? If that gap was derived with the elevator on the bottom, then, due to boom taper, wouldn't mounting elevator on top would require a lot of re-angling to bring the stab into trim with the wing??

Consider posting a reference angle (or range) for the elevator stab alignment to the main wing. Set the main wing with level trailing edge, position an incidence meter and level the plane so the meter reads zero... Now, with that as a zero reference, what what are we looking at for the stab mounting angle?

build log coming soon
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