KilroySmith
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- Oct 28, 2015
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So, it's been in the back (and sometimes the front) of my mind for awhile to build a clustered, staged Falcon Heavy. Just read wrad's writeup here for his Soyuz that has a very similar build approach to what I was considering - the core-to-booster hooks even look nearly identical to the ones I fabricated a while back.
At the basics, I'm planning on MPR - an E12 in the core, a pair of D12's for the strap-on boosters (so they separate while the core is still burning), and a D12 engine in the sustainer. This means I don't have to deal with getting three composite motor rockets lit simultaneously, then airstarting a fourth - I've got enough complications in this rocket. The boosters will be attached to the core with hooks that engage while the booster motors are burning, and then slide free under aero drag when the booster motors burn out.
I've acquired sufficient BT-70 tubing (55mm) for the core, sustainer, and boosters, and 3" (76mm) tubing for the payload bay. The boosters/core will be about 2 feet (60 cm) long, and the overall rocket about 3 feet (100 cm). The boosters and sustainer will deploy chutes using the motor ejection charge.
The core is interesting. I could try and do 50 cm gap staging from the core motor to the sustainer motor, but I'm dubious about the likelihood of success - I've read a number of success stories on staging over this big of a gap, but I'm still dubious. Alternatively, I could pull the Missile Works PET2+ out of my other project and use it to stage, whilst allowing the core motor to eject the chute (or letting the PET2 do both). Hmmm.
Rather than angle the boosters through the CG to deal with asymmetric thrust in the case an engine doesn't light, I'm considering using a hold-down to keep the rocket on the pad until all three engines light. After considering a number of over-complicated designs, I'm now thinking of a switch behind a blast deflector under each engine on the launch pad - once all three engines are producing thrust and there's continuity through all three switches, I'll fire one of my remaining, precious fast-acting Q2G2 igniters to blast the hold-down open and release the rocket. With a good battery, this should happen within 10's of milliseconds of the three motors igniting so it shouldn't significantly impact altitude or flight time.
Anyone with thoughts on a hold-down mechanism, please feel free to share. I only need to hold down the center core (the boosters can't leave without it), but I need to withstand three E12's worth of thrust (about 100N / 33Lb peak). I'm thinking of a device with two pivoted arms; each arm has a smooth protrusion that engages the rocket through a hole just above the rear motor mount. The two arms are perhaps 6" (15 cm) long and held together by a pivot at the opposite end from the protrusion. In the middle of, and between the arms is a cylinder with two pistons to push the arms apart. In operation, a very small amount of BP would be in the cylinder, and upon ignition would provide sufficient force to separate the arms, pulling the protrusion out of the rocket and sending it on it's way.
For the sustainer, I'm considering pop-out fins that deploy at separation. That should keep the looks closer to a Falcon Heavy. Saw this thread; maybe I'll build pop-out fins for all four stages so there'll be no visible fins at all on the launch pad! Anyone seen anything closer to the scale I'm building at here?
Anyway, that's kinda where I'm at. Let me know what you think...
At the basics, I'm planning on MPR - an E12 in the core, a pair of D12's for the strap-on boosters (so they separate while the core is still burning), and a D12 engine in the sustainer. This means I don't have to deal with getting three composite motor rockets lit simultaneously, then airstarting a fourth - I've got enough complications in this rocket. The boosters will be attached to the core with hooks that engage while the booster motors are burning, and then slide free under aero drag when the booster motors burn out.
I've acquired sufficient BT-70 tubing (55mm) for the core, sustainer, and boosters, and 3" (76mm) tubing for the payload bay. The boosters/core will be about 2 feet (60 cm) long, and the overall rocket about 3 feet (100 cm). The boosters and sustainer will deploy chutes using the motor ejection charge.
The core is interesting. I could try and do 50 cm gap staging from the core motor to the sustainer motor, but I'm dubious about the likelihood of success - I've read a number of success stories on staging over this big of a gap, but I'm still dubious. Alternatively, I could pull the Missile Works PET2+ out of my other project and use it to stage, whilst allowing the core motor to eject the chute (or letting the PET2 do both). Hmmm.
Rather than angle the boosters through the CG to deal with asymmetric thrust in the case an engine doesn't light, I'm considering using a hold-down to keep the rocket on the pad until all three engines light. After considering a number of over-complicated designs, I'm now thinking of a switch behind a blast deflector under each engine on the launch pad - once all three engines are producing thrust and there's continuity through all three switches, I'll fire one of my remaining, precious fast-acting Q2G2 igniters to blast the hold-down open and release the rocket. With a good battery, this should happen within 10's of milliseconds of the three motors igniting so it shouldn't significantly impact altitude or flight time.
Anyone with thoughts on a hold-down mechanism, please feel free to share. I only need to hold down the center core (the boosters can't leave without it), but I need to withstand three E12's worth of thrust (about 100N / 33Lb peak). I'm thinking of a device with two pivoted arms; each arm has a smooth protrusion that engages the rocket through a hole just above the rear motor mount. The two arms are perhaps 6" (15 cm) long and held together by a pivot at the opposite end from the protrusion. In the middle of, and between the arms is a cylinder with two pistons to push the arms apart. In operation, a very small amount of BP would be in the cylinder, and upon ignition would provide sufficient force to separate the arms, pulling the protrusion out of the rocket and sending it on it's way.
For the sustainer, I'm considering pop-out fins that deploy at separation. That should keep the looks closer to a Falcon Heavy. Saw this thread; maybe I'll build pop-out fins for all four stages so there'll be no visible fins at all on the launch pad! Anyone seen anything closer to the scale I'm building at here?
Anyway, that's kinda where I'm at. Let me know what you think...