Lightning

The Lightning was named after a US clipper ship from the 1800's. It was, like all clipper ships, designed to go fast.  This rocket is an original design, my second one. While this rocket the Lightning wasn't specifically designed for speed only, I incorporated a few design features to enhance the speed of this rocket.

First of all, it has a carved balsa wood boat tail, a taper in the last three inches of the body tube which reduces drag.  I also used a round-tipped nose cone, which also has a slightly lower amount of drag compared to pointy-tipped nose cones. This particular nosecone was hand-made, and has a unique shape that can't be found on stock nose cones. The rounded tip then tapers out into a more parabolic-like shape. It is attached to a three inch payload section and a 11.7 inch body tube, followed by three inches of boattail, so it stands about two feet tall. The fins are swept back, more for looks than anything else.  In theory though, a swept back fin can provide more stability force because that same fin area is further from the center of gravity, so the actual fin area needed would be less and therefore less weight. However, you do need to provide more fin mass just to get that fin area further aft. So I shaped these fins for looks, and to provide three legs to allow the rocket to stand on its own.

The Lightning will use standard 18mm motors, and should just reach over 100 feet on an A8 motor, 300 feet on a B6 motor, and hopefully about 765 feet on an Estes C6 motor, and possibly over 800 feet on a Quest C6 motor. Computer predictions say it could reach a top speed of about 167 mph. It should weigh in at just under 100 grams (about 4 oz.).

Unfortunately, the boattail feaure of this particular design made it difficult to use a spring clip to hold the motor, so I reluctantly accepted that I will need to friction-fit the motor, rather than make a ugly, draggy cutout into the carved balsa boattail. The boattail will also be the only rocket I have built that mates the balsa fin to a balsa body, so we will see how well that particular joint holds up. I'm optomistic.

This being an original or "scratch" model, I don't have the luxury of laser-cut fins. I had to make them old-school style, drawing a template pattern and cutting the balsa by hand, making sure to align the wood grain with the leading edge of the fins.  Like I always do now, the fins were laminated with a thick paper cover to add strength and a smooth surface. The leading edges were rounded and the trailing edges were tapered.

The payload section that holds the altimeter was built in the usual way, by taking advantage of the volume inside a hollow bulkhead made from a tube coupler with a plywood base. While a bit heavier than solid balsa, it saves length and weight of the payload tube.  Another weight saver is using a small loop of Kevlar instead of a steel screw-eye. This time, I just used three small strips of padding to hold the altimeter instead of the usual 100% wrap-around of plastic foam.

Inside the foam padding I used a thin cardboard (or thick paper) tube to hold the altimeter inside. Padding attached to the nosecone will keep the altimeter down in the tube, so I added vent holes in the tube to make sure that the altimeter sees ambient air pressure in flight.  I was pleased to find that this method did save me a few grams of weight, so I may indeed see altitudes approaching 800 feet.


I should show you a few views of the custom nose cone and the boattail next.

The nosecone is sort of a hybrid between a rounded nose which then tails off as though it were a parabolic shape.

The tail section of the Lightning.  The swept fins are attached to the balsa boat tail. Thick fillets have yet to be added.  Just for fun, I also added small dowels to the fin tips, extending about 1/2 inch forward and aft.  I did this partly for looks, and partly to provide a harder "foot" when the rocket is standing on its fins. The tapered balsa tips were fairly soft and would be dog-eared in no time.

Here is a computer rendering showing one possible painting idea of the Lightning.  This was before I decided to add the dowels to the fin tips.

...it should look this good!

By now the Lightning has been primed, sanded, primed and sanded and ready for all the decorative paint. I used a technique I learned from somewhere, priming first with gray and then priming with white.

This allows me to easily see when I sanded off the primer layer so I know when I went too far. More importantly for rockets - which need to be light weight - it allows me to make sure I sand off enough primer. While it doesn't look very good while being finished, it will look good in the end.

In the past I have made some very heavy rockets. Granted, they look good, but flight performance was lacking with all the extra weight of the primer & paint.

With this technique, I have at least one good, thick primer coat, and the second is nearly sanded off, but will remain in the lowest depressions of the finished surfaces.

Next, I painted just the nose cone, payload section and the top part of the body tube with white paint.  The white paint will help make the yellow paint to go on top a bit brighter and look better, since yellow paint does not cover as well as darker colors. You can often still see a little bit of the color underneath the yellow I'm sure.  I learned that lesson with the HD Explorer, where I painted some red over a white base, and glued it to another body tube that was only painted red over the primer. There is a clear difference in the two color hues because of that. I don't want that to happen again with this rocket finish.

The upper part of the tube was painted white also, but in this case it is because I will then mask off a couple of cloud shapes while I paint the rest of the rocket blue and yellow. In the end I should have a cloud shape with yellow lightning bolts - without needing a custom decal.  We will all see how that goes...

Here we have the white painted, then I masked off the cloud shapes and painted yellow. I then masked off the yellow for the lightning flash, and also yellow stripes on the three fins.

With the white and yellow safely behind the masking tape, I can now apply the main blue color to the entire rocket.

Here is a look at the mask for the lightning flash down the sides of the body, with blue paint now being sprayed on.








Now that that is all done, it's time to remove the masking tape and see the results.  It was not pretty.  Sure, the design worked well and the paint was applied and dried well, but I had a lot of trouble peeling off the tape under the paint layers because it was very thin and splitting into tiny shreds.  Finally I had to scrape it off with an X-acto knife, and as a result I gouged out the fins in several places and generally made a mess of the whole thing.  A lot of touch-up painting with a brush and I now have acceptable results if you don't look too close. Next time I will be sure to use THICK tape.

The last step was to apply a few decals, and paint some thin black outlines on the white cloud shape...done!  According to my records (I record everything) it took me a little over a year to complete working off and on. I started it on June 11, 2013.

The final weight of the rocket is 74 grams which does not include the parachute or a motor.  That's not so bad, and I will find out whether I will be able to reach the predicted 788 feet on a C6-5, 329 feet on a B6-4, and 115 feet on an A8-3 motor. At least that is what the Open Rocket software predicted.  My gut says I'll get about 550 on a C6, 210 on a B6, and if it is really that low I will not risk it on an A8 since I think it will be lucky to hit 50 feet.

That will be an interesting contest: Guts vs. computer.  Stay tuned...some weekend with good weather and we will find out!  In the mean time, let's take a closer look at the finished Lightning.

The obligatory "tall" shot:

A closer look at the payload section and nose:

And how about a closer look at those fins, boattail and antenna?

One last big-nose shot:

 SPECIFICATIONS

Length: 24.125 inches, 613mm

Mass (less parachute & motor): 74 grams

Diameter: 1.375inches, 35mm (BT-55)

Number of fins: 3

Altimeter Capable: Yes

Payload Volume: 4.375 cubic inches

Recovery Method: Parachute, 14"

Recovery Protection: Wadding or optional Nomex

Shock Cord Elastic Length: 36"

Shock Cord Mount: Kevlar loop, frayed and glued to body tube.

Fin circular span: 4.075 inches, 103.5 mm

Motor Mount Diameter: 18mm

Motor Length: 70mm

Motor Retention Method: Friction

Motor Power Range: B, C

Nosecone Material: Balsa

Fin Material: Balsa, paper laminated

Special Design Features: Boat tail, Fin-tip antennas

Launch Lug Size: 1/8"

Kit Brand: None, custom design.

 Flight Logs

This model has not been flown yet.