Wednesday, April 14, 2010

Sudden Mach

So, I've finally crossed the Rubicon; I'm going ahead with my latest crazy project, currently named "Sudden Mach". (Like all my Machbusting rockets except one, it's a Dirty Harry pun). It's going to be a 29mm diameter Machbuster, designed to go as fast at 1500 feet per second (Mach 1.38) on I motors. It's designed to meet a number of criteria:

  • Using conventional materials whenever possible - the only exceptions are the two Blue Tube couplers. Unlike the Blackhawk, it needs no expensive carbon fiber, and I intend to do without even glassing it.
  • Able to use LOC 29mm tubing and survive flight. This means, among other things, long couplers to ensure straight tube joints.
  • Capable of dual-deploy, motor ejection, and combinations thereof, with interchangable electronics
  • Easy-to-load payload bay capable of holding one aviatronic board plus a second small payload
  • Capable of flying on smaller 29mm and 24mm motors on small fields
  • Capable of high speeds (Mach 1+) and high altitudes (1 mile +)
  • Cheap. I'm on a limited budget


It's also designed to drag race the Wildman Blackhawk 29. A conventional drag race consists of winning 2 out of 3 of being first off the pad, getting to a lower altitude, and being the first to a (safe) landing. With high power rockets, though, apogee and landing often are out of sight, so the nost important thing is being first off the pad. That means a lightweight rocket... that can still take 1000 mph flight and 50 Gs (i.e, nose-to-tail forces of 50 times its own weight) during liftoff.

To that end, I'm making it out of LOC / Precision tubing. It's 29mm internal diameter, 33mm external diameter, and very strong - it won't even need to be coated with fiberglass. It's also way lighter than the carbon-fiber tubing of the Blackhawk. Fins will be 1/8" plywood or basswood, and the nose cone a cheap Apogee plastic cone. Dry weight (without motor) will be under 10 ounces.

Here's a look at the Openrocket simulation, with design and simulated launches:


The avbay (aviatronics bay) is somewhat unique. The SM is designed to use dual deployment, where a small parachute or streamer is deployed at apogee to slow the rocket to 50-100 feet per second, and another is deployed at lower altitude that slows it to 15-25 fps for landing. This means it can fly to over 1 and a quarter miles, yet land within (hopefully) a quarter mile of the launch pad. The avbay is based around the 9V battery in the center, which supplies power to a specialized mini timer circuit. It's designed to be flexible in size, and even if the rocket suffers a catastrophic failure at 1000mph, the avbay will hold together and protect the timer, which at 50 bucks is the most expensive part of the rocket - even more expensive than most motor cases.

Here's an expanded view of the avbay design. Pictures of the real thing will come eventually.

I can also remove all but one of the blue couplers, tie the shock cords for the drogue and main parachutes together, and fly it like a conventional rocket, with the motor deploying the main parachute at apogee. This will work for smaller motors. It can fly on every 24mm and 29mm motor available, from the C11 (126 feet) to the I200 (6800 feet, Mach 1.35) and beyond. That's a range of 40 times in motor impulse - seven motor classes (C D E F G H I) and 54 times in altitude.

I ordered 29mm tubing, two couplers, 30 feet of kevlar shock cord, the timer, a pair of nose cones, and a pair of rail buttons (to hold it to the launch pad) from Apogee Components on Monday, standard shipping. They arrived today. I need to make a hardware store run for spray paint, allthread and nuts for the avbay, and plywood this weekend, then construction will begin. First flight will be at CATO in May; first Mach flight at NERRF in June.

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