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Cargo Star with Scorpion Booster
By: Michael W. Hoy
Cargo Star

November entry #1, the Cargo Star by Michael Hoy of Florida

The text file from Michael has this to say:

Dear Jim,

Thank you for having a design contest, it's a great idea. Seeing the other entries on your web site inspired me to enter my own first design and scratch built project. It's a 2 stage model that can be flown as a single stage. Allmost all the parts used to build my entry are either from or available from FlisKits, the only exceptions being the nose cone, 2 transitions and a boat tail, even that can be reduced to just the nose cone and 1 transition if the Cargo Star upper stage is built alone without the Scorpion booster, or maybe you have similar parts by now that can be substituted.  The two transitions, nose cone and boat tail that I used are from Balsa Machining Services.   I designed both stages using the RockSim program from Apogee. The Cargo Star is stable both with and without the Scorpion attached. I would have included the RockSim files but I only have the demo version so I can't save them. Now for some details on the actual models...

The Cargo Star is a "scale like" 18mm standard engine powered model. For the modest size (18.25" tall) of this model it has a generous cargo hold of 2.5" x 1.5" interior space. The cargo section uses BT-60 tubes while the body uses BT-50. One solid balsa transition is used to mate the two tube sizes. When finished it weighed in at 2.03 ounces. I'm sure that weight could be brought down easily since I used two layers of 3/32" balsa glued together, covered with paper and more glue for the fins (nearly indestructible) with lots of epoxy filleting all over as well as ludicrous amounts of paint, clear coat and an (overkill !) 18" parachute. The decal on the body tube is just typing paper glued on then heavily coated with clear wich worked well enough. The fin lettering is self stick stuff I got at the hardware store for something else. All the horizontal black lines are cut from bumper stickers.  Everything else is paint. I wish the picture was better becouse it doesn't do it justice.

I have flown the Cargo Star by itself twice and once with the Scorpion booster underneath so far.  The first flight was on a B6-4. It flew straight as an arrow and probably got to 400' or more. The second flight was on a C6-5, again very straight. RockSim said it would go about 500' but it actually went (I may not be a great judge of altitude) about 750' or more.  The third flight was with the D12-0 powered Scorpion booster attached and a B6-4 in the Cargo Star. RockSim predicted 1000' with a D12-0 and a C6-7 but it totally blew that away probably getting near 2000', hard to tell since I lost sight of it and had to rely on some sharper eyes to track it till I reaquired it again sometime after parachute deployment. I think I would have lost it had I used a C6-7 in the upper stage, it was a long walk to recover it although the booster landed only about 30 yards away.  Now for some details on the Scorpion booster...

The Scorpion booster was not intended to be "scale like", just cool looking and usable on any type of BT-50 based model I might build in the future. Apparently I succeeded in the cool department by the amount of notice it got on the launch pad as well as during flight.  It uses a BT-60 body tube with a 60-50 transition at the top and a V2 boat tail at the bottom.  Inside the boat tail I mounted a 24mm motor tube from a motor mount kit and then a BT-50 tube from the top of the boat tail to the transition as a "gas passer". The transition at top is drilled through to fit a BT-20 into it's upper shoulder wich slides up into the BT-50 upper stage. It's lower shoulder fits into the BT-60 body and is drilled to accept a BT-50 (the "gas passer") tube from the boat tail. The transition also has four 5/8" slots 1/4" down from the BT-50 shoulder at top to vent cold air out when the booster motor blows through and passes gas. Treated the same way as the Cargo Star during construction it weighs in at 2.65 ounces.

On it's only flight so far it performed well on liftoff powering the Cargo Star nearly straight up even though there was a light breeze. On motor burn out it ignited the upper stage motor and seperated (no tape is used) from the Cargo Star flawlessly. It was designed to tumble for recovery and seemed to want too but eventually went into a glide, sailing around in a big lazy circle before hitting the ground a little bit fast. No damage was done to it from the landing but the motor mount had apparently shifted forward 1/4" during blast off. That's not really surprising since I didn't use any glue on it when assembling becouse off what I thought was a really tight fit. The shift may be why it started to glide rather than tumble since it moved it's CG. It got some attention though and I think a couple of people might have thought I wanted it to be a glider. A better method of construction would be to use a single BT-50 as both the motor tube and gas passer, the cut away included in my entry reflects that change.

All in all I'm very happy with both components of the model but especially with the Cargo Star.  I intend to try the Scorpion booster with a scratch designed semi scale IQSY Tomahawk on top next.  If I don't loose it maybe the IQSY will be my next entry.

Sincerly,
Michael W. Hoy

The links below will lead you to Michael's documentation for this design.  These links will open a new window.


 

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