April 26, 2012
OK so I have been shooting rockets where the parachutes get popped out at a pre-determined time by the engine.
Here is how it works:
You set a fuse in the engine that determines how long from ignition a tiny explosion will come out the top of the engine at fire out the chute.
The problem is, you never know how long to set the timer, and the rocket is usually rocketing up or down at the moment the chute deploys, causing the chute to rip apart or it’s cord to rip through the rocket.
It becomes a little game to see how accurately you can set the timer, and I could never get it quite right, consistently.
As well, even if you DO somehow manage to set the timer for the very moment the rocket reaches the top of it’s flight, when the chute pops out at the very top of the flight (apogee) the rocket drifts in the wind FOREVER before it finally touches down.. often coming down in trees, building-tops, etc.
So, there is a solution to both of these problems: It is called the dual-deploy system.
Here is how it works: A computer senses when the barometric pressure is no longer changing on the rocket, and then sends a current through a wire which ignites a little pyrotechnic charge, which pops out a little tiny parachute.. a drogue chute. This chute lets the rocket fall back to Earth at maybe 30 or 40 miles per hour.. pretty darn fast so it cannot drift away in the wind! Then, just as the barometric pressure is getting close to the barometric pressure that existed at the beginning of the launch (meaning the rocket it almost at the ground!) the computer sends a current through a wire hooked to a different pyro charge, which pops out a BIG parachute! THIS chute assures a safe landing.
This is called a dual-deployment system, and should avoid the problems of the fuse not being set quite right for the ejection, and the rocket drifting forever in the wind.
To be really safe, I would fly with a REDUNDANT dual-deploy system! TWO computers, EACH hooked to their own pyros, would fire off at the exact times, basically guaranteeing a safe return with no hassles… right? (If you believe this, then don’t skip ahead to the picture of me on a quad-wheeler with a chain-saw). Below, my workspace, where the rockets are assembled, must be cleared of my wife’s cat Tee-Tee!
So, with both on-board computers charged, one of them sending it’s GPS and voltage status to my laptop on the ground, and four pyros all wired and ready to fire, up went the rocket “Oz-11” onto the pad for launch number one on what I was sure would be an error-free day! (note: This picture taken a few days before the date of this blog, before rocket paint complete)
So wit the area clear of aircraft and a count-down, off wen the Oz-11! The first mystery of the day revealed itself about 12 seconds into the first flight. After a 4-second boost and 8-second coast, at the moment that the drogue chute should have opened, there was only a puff of white smoke! With nothing but a puff of white smoke in it’s wake, the rocket began arcing down to earth.. with no parachute! WHY!?!? As I watched in morbid fascination, the rocket arced into a perfect vertical plummet, and then, just above the ground: POOF! Out came the main chute! It was tangled in the shroud lines, though, and not fully deployed! The rocket hit the ground with a thud, ripping the GPS computer loose inside of the electronics bay. Oops.So, the question becomes: Why didn’t the drogue chute deploy? What went wrong? How could there be a puff of smoke from the pyros OUTSIDE of the rocket, without popping out the chute? The pyros certainly live INSIDE the rocket! How could there be an externally-visible puff of smoke from them?
Well, the rocket on the ground told the story: A hole was punched right through the body of the rocket by the pyro charges. Basically, the pyros seemed to act as a sort of ‘shaped charge’, punching right through the cardboard body of the rocket. Clearly, in the future, it is time for me to switch to fiberglass rockets and pyros that are carefully held in place in the CENTER of the rocket, aiming up and down, so that they do not punch through the body of the rocket itself! SO those are the lessons there: Stronger bodies. Pyro charges held in place. In the CENTER of the body. Aimed up or down, not sideways.
OK lesson learned. But the NEXT launch will surely be cleaner, right? I mean, you know: REDUNDANT dual-deploy? It HAS to work! Right?
So, on to the pad with the smaller rocket, still redundant dual-deploy equipped!
So we hit the button and off goes the rocket like a dream… high into the sky. Then, at what is clearly near the apogee, there is a ‘poof’ of smoke and out comes a chute! Yah! But.. wait.. that chute is ORANGE! I thought the drogue chute on the Oz-12 was RED! And that drogue chute sure does look BIG! What is going on? As we all watched, the rocket drifted.. slowly… away. High in the sky, barely descending, it wafted gently away in the wind. Why? It was supposed to be PLUMMETING down right now under a small red drogue chute.. not a big orange main chute! Was that the MAIN chute that was open? If so, then recovery was surely uncertain… it would be drifting for far too long (and far) in the wind! As I watched, it became apparent that the Oz-12 was sure drifting close to the tree-line. Then, at 500 feet above the ground, a puff of white smoke and out popped… the drogue chute! ARGH!!! The MAIN chute had popped at apogee, and the tiny little drogue right before touch-down!! Then, that heart-sinking moment that follows some launches when the rocket falls down… BEHIND the tree-line and into the woods. AEEIIII!!!!!
Well, luckily one of my friends is an arborist with a quad-wheeler and a chain-saw! So we know what comes next!
In a sudden bit of good judgement, I decided to turn OFF the chain-saw while actually riding ON the quad-wheeler.
Arriving at the scene, I could NOT say that I was optimistic…
But, with a bit of careful cutting (and the arborist’s kids staying at a safe distance), we got-‘er-done!
There is only some minor damage to a fin from the rocket falling from the tree onto a smaller tree we had just cut down beneath it.
So, now for the big question: WHY did the MAIN chute deploy at the top of flight, and the drogue chute down low? The answer: I have no idea.
All of the wires and chutes looked to me to be hooked up correctly. Before the next flight, I will trigger all systems on the ground to test them, and be sure that they all fire at the right time, and fly the rocket to a VERY LOW altitude so I can SEE what is happening throughout the flight. Stay tuned!