This rocket was inspired by the X-wing type designs. It just seemed like something fun and different to build. The actual construction proved to be have it's unexpected tricky parts. Getting the wings lined up correct can be a challenge, due to the size and shape of the fins. This picture really doesn't do the paint-job any justice. I'll have to try to get a better picture. Rocksim File : solarhopper.rkt

Parts list

Below is a list of some of the parts you'll need to build your own flying Solar Hopper.

- 3" nose cone (PML)
- 3" airframe (20" long)
- 29mm motor tube (10" long)
- 3 centering rings (3" to 29mm)
- sheet of 1/8" basswood finstock
- Kevlar shock cord
- 1/4" launch lug (3" long)
- kraft/popsicle stick (optional)

Fins And Airframe

The idea was to build this rocket while keeping the weight down, so that it could fly on F motors safely.

The fins, due to their size, will make up a large portion of the overall weight. To keep them light, yet strong enough to fly on G motors, the fins were cut from 1/8" basswood. Once cut, they were stacked and match-sanded. The basswood itself is lighter than plywood, but not quite as strong. Especially for fins that stick out this far from the airframe, strength matters.

Due to this, the fins were fiberglassed and vacuum-bagged. Note that you can probably use 1/8" plywood and not worry about fiberglassing the fins. Do so at your own risk.

The airframe tube is a 3" mailing which I found at Staples. The tube was cut down to 20" and the white layer was removed. Next, the spirals were filled with wood filler and the body tube was marked for fin slots (see below).

The width of the slots will depends on whether or not you fiberglass the fins and what weight cloth you use. I used two layers of 4oz and a veil layer of 1.2 oz. The fins came out 4mm (0.1575") thick.

The fin slots for the wings are 5" long, the one for the fin is 2.5" long. Cut the slots all the back to the back of the body tube.

Providing a traditional fin marking guide wouldn't make much sense, as the tube you use may well have a different outside diameter. For help with fin slot locations, follow the instructions below.

Wrap a sheet of paper around the body tube. Make sure the paper lines up all the way around the tube. Use a piece of masking tape to keep the paper in place and make a mark where the paper overlaps. Remove the paper from the airframe and measure from the beginning of the paper to the mark. This will give you the circumference of the airframe.

Complete the form below and click the button to get exact fin slot locations.

The fins slots were cut out of the tube. A coupler was put into the tube while the slots were cut out with a hobby knife. This makes it so you can apply pressure on the tube without having it buckle as you make the cuts. Cut out slots for the four wings and the back fin.

Motor Mount

Using a 1/8" drill bit, create two holes in one of the centering rings. Do this one for one centering ring. This will be the forward centering ring. These will later be used for shock cord attachment.

Cut the motor tube to be 10" long (if needed). Attach the centering ring with the holes at 1/2" from one end. This is the forward end of the motor mount assembly. Apply an epoxy ring/fillet to both sides of the centering ring. Attach a second centering ring at 5" from the other (aft) end of the motor tube. Apply an epoxy fillet/ring to the forward side of the ring only.

Wings & Fin

Insert the motor mount assembly into the airframe until the aft centering ring is at the end of the fin slots. Tack down the wings and fins with a small amount of epoxy. The picture shows the first set of wings being attached. The top wing is being held in place with some plywood boards while the epoxy cures. As you can see, the wing set lines up.

The second set of wings was quite a bit trickier. I couldn't use my fin jig as the existing wings sit at an angle and were running into the sides of the jig.

This is what I came up with. A box with sections cut out for the wings to protrude through. An Estes fin jig was used to keep the third wing in place while the epoxy cured. The forward end of the tube sticks up a little, which is making the rocket's airframe look crooked it the picture. This is not the case, it is simply sticking up.

The second set of wings required some more cuts into the box to accommodate the fins. The picture shows the final wing tacked in place. As you can see, the second wing set lines up too.

Next is the model rocket's back fin, which is much easier to tack down. Temporarily slide the last centering ring into place. Do not yet glue it in place. This is done to ensure that the back of the fin tab will touch the centering ring. If your fin slot is cut correctly, things should fit perfectly. Once the epoxy cures, the aft centering ring can be removed.

Slide the motor mount assembly out of the rocket's airframe. Next, apply epoxy fillets where the wings and fin meet the rocket's motor tube.

One this fin fillets cure, put a ring of epoxy on the inside of the airframe, 9" from the aft end. Slide the motor mount assembly back into the airframe.

Now apply internal epoxy fillets, where the fins meet the inside of the airframe. Glue the aft centering ring in place. Finally, apply external epoxy fin fillets where the fins meet the outside of the rocket's airframe. Your model rocket should now resemble the one in the picture on the right.

To complete building the rocket, the launch lug is glued 1/4" from the aft end of the model rocket. In an effort to prevent the launch rod from scratching up the paint job, I added a standoff under the launch lug. This is optional. The standoff is a 3" strip of kraft/popsicle stick.

An Aeropack motor retainer was also added to prevent the motor from kicking.

Finishing

After primer, the rocket was painted with silver and blue Rust-Oleum metallic paints. A few layers of clear coat were added after the paint.

First, the silver was applied. Next, the airframe and wing tips were masked off and the inside surface of the wings was painted blue. This was done only for the outward facing fin surfaces.

Flight Data

This model rocket turned out to be a little heavier than expected. It pretty much needed a G79W (on a day without much wind) to lift off safely. When it did lift off, it was amazing to watch. The Solar Hopper flew as straight as an arrow, accompanied by a loud whistle. The delay had been shortened to 6 seconds, which proved perfect for the G79W reload.

The next flight was also on a G79, this is the flight seen in the G79W video below. It didn't whistle this time.

Video(s) : AT G79W RMS