Manufacturer: | Scratch |
Background
Over the past year, the Edinburgh Alliance - a Babylon 5 fan club of which I am
a member - has been working on a CD of songs parodying the show. As it
neared completion, we decided that when the time came to launch the CD, we
really would launch it. Being the clubs rocketeer, I got the job.
Design objectives
High performance was not an objective of this design. The ability to put
the CD in the air and then bring it back safely, possibly in significant wind,
was. Edinburgh Farce 1 is therefore somewhat underpowered, using a pair
of mini-engines. By using two engines in outboard pods, I was able to put
the CD in a pair of slots at the rear of the main tube. In addition, the
nose-cone is a tight fit, sealing the forward end, and inside the tube is the
rolled-up cover of the CD.
Pitch stability is provided partly by the triple-tube configuration and partly by two swept wings. Yaw stability is provided partly by the CD and partly by two large rectangular fins, which hold further CD-related material - copies of the front and back of the cover are stuck to the outer surfaces. The vertical fins also help protect the CD when the rocket lands. The balsa sheet which I used for the vertical fins is only 1/8 thick, and more flexible than I liked, so I fitted three reinforcing strips to the inner surface of each fin; along the top edge, along the bottom edge, and in the middle. The middle one is also the attachment point to the wing.
Recovery is by two small parachutes, cut out of stock Estes 12 chutes. These bring the model down more quickly than a pair of full size chutes, but still gently enough to avoid damage. Theyre now about 8.
Parts
2 x BT-50 1 x BT-5 3 x BNC-50K 2 x 12 parachutes
3/16 balsa 1/8 balsa
2 x Screw eyes Sewing elastic
Spent D casing Spent mini-engine casing Aerotech igniter tube
Edinburgh Alliance Songs from Down Below CD
Outer tubes are all BT-50. The main tube is a whole BT-50; the outboards are each 152mm cut from a second tube. Horizontal fins are 3/16 balsa; vertical fins are 1/8 balsa. Reinforcement strips for the vertical fins are 127mm x 14mm 1/8 balsa. Reinforcement strips for the CD slot are 130mm x 7mm 1/8 balsa.
A launch lug, made from a tube which formerly held an Aerotech igniter, is glued along the joint between the main and starboard outer tubes.
To hold the CD in place, there are two rings cut from a spent D engine casing. Each ring has a pair of diametrically opposed notches which hold the CD in place. The forward ring is glued into the main tube so that its notches are level with the forward ends of the slots in the tube. The aft ring is loose, and is held in place during flight by masking tape.
Engine mounts
The engine mount tubes are cut from stock BT-5. In each one is a blocking
ring cut from a spent mini-engine casing, positioned so that the engine
protrudes 10mm from the rear of the tube. The engine mount tubes
themselves extend 2mm beyond the ends of the outboard BT-50 tubes, and the
centring rings are recessed. This was partly to make the tubes look more
like exhausts for the benefit of observers, and partly so that engines could be
taped to the tubes, rather than relying entirely on friction to hold them in
place.
Launch Report
Edinburgh Farce 1 has flown on two occasions. The first was its test
flight on March 7th. Technical assistance was provided by Bill Gates, in
the form of a free Microsoft Network CD-ROM - the Songs From Down
Below CD was not yet available, and anyway, for this test flight, I
preferred to use an expendable CD! Then on March 21st was the launch of
the Edinburgh Alliance Songs From Down Below CD, the event for
which Edinburgh Farce 1 had been designed. The rocket lived up to its
name as, twice, it failed to fly when only one engine ignited. But the
next two attempts were entirely successful; both engines lit, the rocket went
up straight, then both parachutes deployed. Both photographs shown here
were taken during the March 21st flying session by Dave Willis, another member
of the Edinburgh Alliance.
More Power
You may wish to adapt your version for higher power. If so, use BT-20
instead of BT-5 for the engine mount tubes. You will probably need to
extend the outboard BT-50 tubes to accommodate the longer motors, and you may
need some nose weight to balance the heavier motors. If you really want
to make a higher power version, dont bother with motor mount tubes; stick
a pair of D class engines directly into the outboard BT-50 tubes, and you will
certainly need to add some nose weight.
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