Tuesday, December 21, 2010

Review - Art Applewhite 18", 38mm and 54mm Delta Flying Saucer

This is a review of a pre-production version of Art Applewhite's 18", 38mm and 54mm Delta Flying Saucer.  Its construction varied somewhat from the production model. Nonetheless, it is representative of the performance you should expect. I have tried to indicate where the production model varies, however, these notes may not be all-inclusive.

This rocket is a huge, 18" diameter, Level 2 capable version of Art's Delta saucer. It is built primarily from Gatorboard® and includes both 38mm and 54mm motor adapters.

Main saucer parts list:
* 3/16" Gatorflex®, however, the production version will use standard foamboard
* 1/2" Gatorboard ®
* 3" paper tube
* Fiberboard
* Fiberglass cloth
* 1/4" launch lug

54mm and 38mm Motor Adaptors parts list:
* Mount tubes
* 3" thrust ring
* 3/32" Basswood strips

Materials and tools required: utility knife, X-Acto knife with new blade, spatula or other spreading tool, Elmer's Glue-All®, Easy release masking tape (the blue kind), sandpaper, slow setting epoxy, and Devcon 5 minute Epoxy.

This build is very similar to the smaller delta saucers, only bigger. The top and bottom shrouds were made from pre-marked Gatorflex® and the center plate was made from the thicker and denser Gatorboard®. These materials are both multi-layer laminates of dense polystyrene foam, laminated with plastic and paper. The Gatorboard® is laminated on both sides while the Gatorflex® is laminated on only one side, allowing it to be flexible. Cutting these components was much harder than standard foamboard, so new blades, patience, and a good work surface are musts. Unfortunately, the Gatorflex® is no longer available, so in the production model, the top and bottom shrouds are made from standard foamboard. To make it flexible, you make numerous cuts using a provided tool, which holds a hobby-knife blade. Minus this step, the rest of the construction should be almost identical.

You first prepare the top shroud by wrapping it around and connecting the seams with 5-minute epoxy and the supplied fiberboard strip. Once dry, you sand the hole to fit the 3" host body tube. The bottom is prepared similarly.

The center plate really takes some effort and should be cut in short sections. As with the smaller deltas, the edge is beveled. I didn't have the recommended knife so I used a very sharp kitchen knife, which seemed to work quite well.

In short, you glue the mount to the top, coat the inside of the top with slow setting epoxy, attach the center to the top, and finally the bottom to the center. In this beta version, the main trick was to align the holes for the launch rod. In the production model, a ¼" launch lug is glued to the inside of the 3" host tube, thus avoiding having to cut additional holes in any of the components. The removable adapters slide past this lug. After the first flight, I retrofitted a 1/2" lug.

The last step is to glass the top with the provided fiberglass sheet. This too is pre-marked. I won't go into the details here, but make sure you use slow setting epoxy as there is a lot of surface area to cover.

For both size motor mounts, you cut the thin fins from the basswood using the provided pattern, glue them to the tube, and install the thrust ring. On the 38mm mount, I used wood glue and added epoxy fillets. On the 54mm mount, I used only epoxy.

I chose not to paint my saucer.  I may yet change my mind.

This saucer will fly well on a wide variety of motors:
54mm: Pro54, 2 & 3 Grain motors, Aerotech J90W, J180T, J275W, J135W, J315R, K185W
38mm: Pro38, 4, 5 & 6 grain motors, Aerotech I154J, I161W, I195J, I211W, I218R, I284W, I285R, I300T, I355R, J350W

I first flew the big Delta Saucer on an Ellis J228 at the 3rd Annual TRF Reunion at the Whitakers field in NC. The saucer tore off the pad with lots of smoke and noise. It was a fantastic flight. The second flight was at a NOVAAR launch. This was a very interesting flight. The J110 had a nice long 7 second burn. Because of the low average thrust and regressive thrust profile, the saucer arced over and was still under power after apogee.

Big? No problem! In both cases, aerobraking brought it down softly without damage. With the longer J228, the motor and adapter unseated from the main tube upon impact. This is a feature, not a bug and may help to absorb some of the shock from the landing.

On the J110 flight, the saucer aerobraked down and continued to spew large amounts of smoke, causing some concern with the LCO. It landed in an outcrop of brush but that part of the field was damp and thus there was no risk of fire. The ensuing smoke cloud was described as a "mushroom cloud on the horizon". Cool! (But I was really happy the grass was moist!) I'd recommend the J228 over J110, but both are out of production.  I also have my doubts about the J90, although I have no first hand experience.

One final comment about relying on aerobraking on this size saucer.  No, I wouldn't want it to land on me or my car.  As for me, it comes down slowly enough that dodging it wouldn't be a problem.  I seemed about the same an any other high power rocket under 'chute. As for the car, I would certainly do less damage than your typical level-3 rocket under 'chute and a lot less than any high power rocket coming in ballistic.