Teaching a newbie about dual deployment

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Well-Known Member
Jun 30, 2010
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Does anyone know if Dual-Deployment has ever been used on a BP cluster? I would like to use the motor ejection to eject the drogue & a altimeter to eject the main 'chute at a chosen altitude.
What would I need to do to a rocket to make it dual deployment-able?
Shouldn't be a problem, though I'd probably just used plugged BP motors rather than count on the motors for ejection.

You'll need an altimeter in a compartment that is protected from the ejection charge and you'll need another chute compartment that can be opened when the target main deployment altitude is reached. You'll also need black powder, additional igniters/ematches, charge containers, etc.
Altimeter bays have been discussed here on TRF several times. The typical set up is a compartment in the middle of the rocket where the altimeter sits. It has two connections for charges - one at the bottom for the drogue and the top for the main. Here is a set up for a 4" rocket https://www.rocketreviews.com/reviews/mods/gl_39_avionics_bay.html I hope this help show the general concept, the details may not be applicable.

Note that dual deployment doesn't make sense unless you get an altitude that is quite a bit higher than the setting for the main charge. ie if you get a G-whiz with a fixed 800' main ejection, you won't be buying much if your max altitude is 900'.
Thanks for the feedback. So I couldn't just use a payload bay to house my altimeter & use the 2nd charge to blow the nosecone off along with the main?
That's basically what the altimeter bay I posted does. To do what you said all you have to do is work out how you mount the alt., how to isolate it from the ejection gasses, and how to run the wires to the charges.
Do the ejection canistors just sit ontop of a bulkhead that joins the 2 peices of Bodytube? Is a 3" tube ideal to start off in the world of Dual Deploy?
The charges should sit under the chutes so they tend to push the chute out, not in. On the one I posted, the charges sit in the copper pipes attached to the bay. The bay bolts to the tubes and thus is blowing outward. On other designs, I have run the ematch/charge into the airframe and then packed the chute over it.
I know this doesn't exactly fit what you asked... but this idea always intrigued me... This was done by Yitah (Richard Wu)... you can find his rocketry page here

select [the Fleet] then [FatBoy II]

It's a two engine cluster - one with a short delay for the drogue and the other with a long delay for the main. Don't know if it ever worked, but a nice idea nevertheless.

Dick has given very good advise on how set up a rocket for dual deployment. I want to explain when you should use dual deployment and when you shouldn't.

Dual deployment was developed to increase the probability of in-field recovery and to prevent the loss of high altitude rockets. Whether you need it or not depends on the altitude your rocket will reach and the size of the recovery zone.

Most rockets recovered by parachute descent at a 15 fps rate (~5 m/s). A flight to 1500 ft. (~500 m) means a 100 second descent under chute. This is not a problem on a windless day, but if it's windy you will at a minimum have a long walk. If the wind averages 10 mph (~16 kmh), without dual depoyment the rocket lands 1500 ft (~500 m) from the launch pad. If the wind is twice as strong, you have twice the walk (3000 ft or ~1 km).

Under the same conditions with dual deployment, your walk can be considerably shorter. If the apogee deployment is sized to give a descent rate of 60 fps (~20 m/s), and the main deployment is set for 300 ft (~100 m) at a rate of 15 fps (5 m/s), then in a 10 mph (16 kmh) breeze you only have to walk 600 ft (~200 m) to get you rocket. In this case the recovery distance is reduced by 250%.

For a quick rule of thumb, any rocket of value flying over 2000 ft (~600 m) would benefit from dual deployment if the launch site is windy. Conversely, rockets flying to 1000 ft (~300 M) or less don't need the complexity and expense of dual deployment.

This rule of thumb applies to altimeters that deploy the main at 300 ft (~100 m) and are launched near sea level. If your altimeter deploys the main at a higher altitude, you will see less of an advanage, however if the ground is 3000 ft (~1km) or more above sea level then you may need the extra height to insure that the main fully inflates to insure a soft landing.

Bob Krech

Thank you for all that! You have told me the the advantages & disadvantages of dual deployment and if I really need it . I was wondering if my Level1 Rocket would benefit from it, it's maiden flight puts her up to around 3000ft/4000ft , and even higher once I can start using those bigger motors. I do have a 4x 24mm cluster with 3x 18mm outboards, and she hits 2000ft just on E's, so I was going to use that as my test rocket and maybe I can learn from my mistakes & problems that may go wrong with it .

Thank you
Yes, that was a good backgrounder bob. BTW, I have done things that weren't necessary in this sport, just to do them. You don't want to do anything stupid or dangerous, but unnecessary isn't always bad ;)
I have done things that weren't necessary in this sport, just to do them. You don't want to do anything stupid or dangerous, but unnecessary isn't always bad

Absolutely true. It can be a good learning experience.

Bob Krech
Originally posted by Karl
I was wondering if my Level1 Rocket would benefit from it, it's maiden flight puts her up to around 3000ft/4000ft , and even higher once I can start using those bigger motors.

I would recommend not introducing the complexity of flying with electronics for one's Level 1 certification flight unless you feel 100% certain that you won't screw it up. That is: complete confidence in yourself that you know what you're doing.

I am an experienced flyer and can prep and launch a motor ejection rocket in ~15 minutes including recovery attachment and packing and motor building. It takes me way more than an hour to prep and launch a dual deployment rocket, which in addition to the above, includes making and installing 2 ejection charges and packing the extra 'chute. There are many more failure points added with dual deployment that you learn to overcome over time with successful cracks at it. Personally, I am still experimenting with drogue and main placement and recovery harness length to minimize tangling.

Since I've given you the "why nots", now consider this . . . It sounds like you have a bird that can stand the extra added weight of electronics and additional recovery system components. You can always use it to learn how to do dual deployment with smaller impulse motors before attempting your Level 1 flight. Just because you don't need dual deployment, there is no reason you can't still fly a rocket to 1000' or 1500' and test out your dual deployment skills. In fact, flying low with dual deployment lets you see some of your screw-ups. For example, I see a lot of main 'chutes coming out at apogee for new dual deployment rookies (sorta eliminates the benefit of all the extra prep time invested, eh?). The primary reason is usually not electronics malfunction or miswiring, rather it is usually that the forces of the popping and yanking required to get one section open causes the other to get yanked open, too. If this can be easily seen from the ground, the more experienced flyers can advise you on how to solve that little problem. BTW, a longer recovery harness, tighter couplers/nosecone, and/or plastic rivets are all potential solutions to this problem, depending upon your circumstances.

Good luck with your flight. I have relied on the experience and expertise of other flyers more than anything else I have done in rocketry to learn how to do dual deployment correctly. It is a godsend once you master the skills, and YES it does require skill.

HTH, --Lance.
I agree with everything that Lance said. I did dual deployment on my L1 bird. It did add a bit of stress to the flight. I just have a couple comments from personal experience. First, I don't use a drogue chute. I just split my rocket in the middle with 5x the rocket length of cord and let it flat spin in. It has always worked for me and makes prep time a little easier. Second, shear pins are your friends. Keeping that nosecone on in a typical dual deploy situation is tough. I know with my rockets the flat spin tends to try and deploy the laundry. Not so with a couple nylon screws (2-56 or 4-40) as shear pins. However, shear pins will not work that great with a paper (non-glassed tube). They tend to stretch the holes a bit and may not shear. Most of my airframes are glassed, but a couple friends of mine drill a small pilot hole, then soak it with epoxy. Then they drill their shear pin hole. Either way - once you have DD down, you usually won't go back. :)

Basics to dual deploy:

I have tried drogue chutes, don't like them...they add complexity and don't really do much. I just split at the top, with a ridiculously long shock cord. (I use 40' on my Magnum)

Definately go with shear pins. I would recommend 1 2-56 pin for your 3" rocket. Even with paper tubes, I would just soak the hole in the tube with CA and you should be fine. I even use shear pins on both the drogue separation point, as well as the main separation point.

I LOVE overchuting the rocket at main deployment. There is nothing cooler then seeing the rocket barrelling for the ground, and then at main deployment, it just stops and sits there. With this, you run the risk of drifting forever if you deploy at apogee, though.

I don't think some of the readers realize you're in the UK and are certifying under UKRA rules that are somewhat different that the NAR and Tripoli L1 rules.

In the US, both NAR and Tripoli require that you fly an actual H or I impulse motor for your L1 certification flight, and clusters and multi-stage rockets are not allowed for certification flights. If I read the UKRA certification rules correctly, UKRA only considers the total impulse, so clusters of lower impulse motors and multi-stage rockets are permitted for L1 certification flights.

Although clusters and or staging is permitted for certification flights, why would you want to do this simply because there are just so many things that can go wrong.

I believe that your L1 cert flight should be as simple as possible and should be done using one motor whenever possible. I went to UKRA's website to familarize myself with your rules and rocketry regulations. It appears that you have to have a license to purchase any engine larger than a D in the UK.

If this is a problem for you, then I would think it would be much easier simply to find another club member that is HP certified and ask him if you could borrow a casing and have him purchase a L1 reload for you, and then fly it in a simple, dumb 2 kg, 10 cm rocket that flys to ~500 m.

Once you're certified, do your staged, cluster flights with dual deployment if that's you desire. Just don't make the certification flight any more difficult than it has to be.

Bob Krech
IIRC , I asked a RSO about certing without the Explosives certificates that we need for APCP motors and he said he wouldn't let someone cert without the required papers. We can buy upto a Estes E9 but I think they too are going to need a licence. :(

I don't see that there is an age requirement for L1 cert in the UK, but since you are only 15 is there a problem with getting the proper licenses for composite motors? It seems pretty straight forward.

Again, in the UK it appears that there are no restrictions on BP motors, at least up to the Estes E class.

The problem is that APCP is completely regulated in the UK, and you need at minimum, an Explosives Certificate. (We in the US are very lucky that we do not have these requirement for smaller motors.)

The Explosives Certificate needs to state that it is for Aerotech Rocket Motors, UN.0349 and UN.0351, (or other brands) and also Black Powder, UN.0027 and UN.0028 for small ejection charges.

There are two versions of this certificate. The acquire only version would allow you to legally acquire APCP at the field and legally fly it. You could not keep any motors at the end of the launch, nor can you transport them off the field. This should meet the UKRA requirement if you can have someone else purchase and store the APCP motors for you.

If you want to keep and transport motors, you will need the Acquire and Keep version of the Explosives Certificate that requires you to have a Registered Premises Storage Certificate, Mode B and also a Recipient Competent Authority Transfer Document (RCA), but this should not be a requirement for the L1 certification.

Your UKRA Members Handbook has most of this information (pg 32) and Pete's Rockets has some further information on this topic.


Hope this is useful.

Bob Krech
Yep, the only cert I have as of yet is my ' Registered Storage Cert ' Which I think means I can buy and store motors at the address that I registered. Nope there isn't any age in UKRA that you have to be before you can cert, I suppose that's one of the good things ! I just need to get my COER1 form in the post , get copy's of both certs and then I can get my RCA. I don't think there is any age on getting these forms, I listed my real age and they had no problem with it understanding that I would be sensible and trusted with the motors.
Im trying to get my forms out of the way before Xmas then I can get some APCP motors for Christmas, and spend most of next year concentrating on bigger stuff.
It looks like the Reg'd store cert is going to be a thing of the past, over here, by about Feb, for under 5kg of propellant (accoring to Pete Davey). As for E9s, you don't need a liscence for them, but technically you need a RCA to transport them, 'cos of the amount of BP in them. But its a catch 22 'cos you need your liscence before you can get a RCA. At least you can buy them 'above' the counter, now, and can launch them at UKRA gigs without having to call them a long-burn-D ;)