How can I use multiple parachutes which eject at different times on one rocket. I've heard some references to this being done, but as much as I've searched for answers I can't find any. I can't even think of a logical way to do this. Well, thank you for your time.

Usually used on larger HPR birds, and not on our smaller models...

It requires the use of electronics, either a dual-firing altimeter (one that triggers at two altitudes -- the apogee for a drogue chute, and at a pre-selected altitude for the main), or a timer that gets triggered by the first deployment (drogue) and waits for a pre-determined time before firing the main.

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As Craig notes, this usually applies to bigger rockets using altimeters or timers.

In model rocketry virtually anything which would go high enough to need dual deploy is generally light enough to land safely with a streamer or undersized parachute.

It is possible to do multiple deploy on smaller models using clusters with different delays, but the utility is somewhat limited.

Sandman and I used differing delays in the clusters in our Pad Abort models, both as a method to ensure redundancy of deployment and to avoid overpressurising the body tube with 4 simultneous ejections.

Well I am building a large rocket so I will definitely have room to case this. I found this online http://info-central.org/recovery_dualdeploy.shtml which pretty much answers my question of how exactly the rocket will fit together. Now I'm just wondering about a few other things:

1. What altimeter will do this and send a charge which will fire out the second parachute.
2. How does the altimeter know how to fire when going up and not down.

...and for a timer version

1. When does the timer start ticking?

mufflerster,

Just do a web search on model rocket altimeters or go to site like Apogeerockets.com that sells altimeters for more info. The two event altimeters are pre-programed to fire once at apogee and then a second time at low altitude (several hundred feet or so). This allows you to deploy a streamer at apogee for a fast controlled descent with a parachute deployment at very low altitude for safe recovery. The engines you use would NOT have their own ejection charge. These would need to be rigged seperately and hooked up to the altimeter. this is pretty advanced stuff for most rocketeers.

Well I did some research, and it seems the only method of ejection is with a capsule containing black-powder. Is there a safer way to do this? Do companies like estes make pure ejection charges?

It does seem unsafe though to use an ejection charge similar to the kind used at lift off. I often get misfires and have to reconfigure the wires until I get lift-off, but in mid-air, there's only one chance, and the altimeter will only fire once...

Using an e-match or equivalent that in a small packet of loose BP is very reliable.

I used individual flashbulbs to make ejection charges back in the old days. My ejection charges cost me just a few cents each because I got hold of the bulbs before they became really common in the rocketry hobby. I think I still have about 50 of them left over. I soldered leads to the bulb, rolled a post-it note around it and taped it, then insulated the leads at the back of the bulb with a little hot glue. When prepping the rocket, I dropped in the amount of BP that I needed for the particular application and taped it shut. You can do something very similar with e-matches or other reliable ignitor to make ejection charges that will be more reliable than the electronics you use to set them off.

Don't you need a federal license to use black powder in the US?

Yes, you need a LEUP for using Black Powder in anything other than in historic fire arms or hunting. You can purchase and own up to 50 pounds without a LEUP, but its usage is regulated. (This is the law, it doesn't have to make any sense!!!) My regional ATF inspector has already explained this fact of life to me personally...

You can use a BP substitute (which is can be considered chemically similar to BP without the sulfphur), however. The use of BP substitutes (such as Pyrodex) is not (yet) regulated. You can even purchase these substitutes as Wal-Mart.

Go to Pratt Hobbies (http://www.pratthobbies.com/info_pa...ex/pyrotest.htm) and note how smokeless powder must be contained differently that BP to ensure complete ignition.

Go to Quickburst (http://www.quickburst.net) and ake a look at the Hot Coil Kit with PerfectFlite HA45 Altimeter . You won't need a LEUP to use this combination, as you won't be using e-matches and you should be OK with a BP substitute. Ask Dave at Quickburst to be sure.

Then GROUND TEST - GROUND TEST - GROUND TEST.

All the best,

Mike

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Michael Hollman
NAR 84683 L2

www.scamrocketry.com

Most altimiters have a system in place to check continuity to your charges prior to liftoff by means of lights or audible tones. As for the black powder, it's safe when used properly ( as with all things). No one makes a dedicated, premanufactured charge that I'm aware of though many kits are available for the housings and casings. Flashbulbs and Ematches are the most common forms of ignition as mentioned elsware in the thread.

I've been using an appogee components altimiter with total success for a few years. It uses audible tones for continuity checks and max altitude reporting. It has a barametric preasure reader to arm the system after a vertical change of seventy feet ( ?) and sense appogee to fire the first charge. Second charge fires at 750 ft. If your confidence is in doubt, go to a HPR launch and talk to the folks using them. Most are more than happy to help in anyway they can and there are no dumb questions at a launch.

As for the legal issues, this becomes a sticky issue and is the point of contention at the heart of the lawsuit the major rocketry organizations have been fighting against the BATF for the past couple of years. The laws are slopily written and open to interperation by the individual inspection agents as is the method of compliance enforcement. As a rule, no one at a sanctioned launch has ever had a legal issue. For indepth info on the legal issues, check the Tripoli and NAR websites and ALLWAYS check with YOUR local authorities on their interperation of the laws and compliance.