Questions about motor case and such...

[8thPaladin]

I am building a couple of rockets and have not decided on which to use for my L2 cert. I have a couple of Madcow rockets on the bench slowly getting there. My question is about motors. I have a V2 5.5" with the 75mm motor mount, and a DX3 also with the 75mm motor mount. The V2 has room for shock cord attachment on the centering ring, the DX3 does not as there is about a half inch between motor tube and rocket. The directions say use a motor with the attachment on top of the motor. If using this, do I have to use an altimeter for deployment? or does the motor have the delay built in like the 38mm I used for my L1 cert? with just a way to vent the gases around the attachment?

Can a 75mm motor have the delay on top for single deployment? or do I have to use altimeter and separate charge for deployment? As I am still very new and have lots to learn, I am just trying to figure this all out.

I would like to stay with single deployment as I have yet to research altimeters, dual deployment, and such. Lots to learn!

Thanks,

Michael

 

[jd2cylman]

No motor deploy for 75mm and up. You'll need to use an altimeter. Or use a 75-54mm adapter and use a 54mm motor that does have an ejection charge.

 

[Nytrunner]

Unless I'm mistake, 75mm motors Don't have motor delays.. The pressures are too great to be contained by a delay grain. They do have a smoke grain at the top, and a threaded closure for recovery hardware.

I believe Some 54mm motors have motor delays, but perhaps not all. If the motor says -P and doesn't have a delay number, it's Plugged and requires electronic deployment.

Since you admit your new to electronics, I'd suggest spending more time flying L1 motors and try out incorporating a deployment altimeter into your rockets.

You're in UT, so you've got a lot.of.room, but if you continue to go motor deploy, you'll find yourself walking a long long way to recover stuff. May want to invest in a Chute Release if you want to do Motor deploy L2.

Tracking equipment is another good idea to investigate.

 

[ttabbal]

Since you are in UT, try to come out to a UROC launch. There are a number of us that can get you up to speed on deployment electronics. You can even see a few setups in person.


https://www.uroc.org/index.php/events-calendar/event/14-october-launch

 

[OverTheTop]

Go electronic instead of motor ejection and you will love it!

Good advise in the posts above.

 

[blackjack2564]

If you have not built yet, attach/glue, a Y-recovery harness [kevlar] to motor mount. This is just a loop of kevlar, with each end glued to opposite side of motor mount, after notching top centering ring for kevlar to pass under.

This loops just long enough to stick out top edge of fincan tube. Your recovery shock cord then attaches here.
Now you can use motor eject as eyebolt in motor closure no longer needed. Both your projects can easily be lifted on larger 54mm motor with "kick" heck a K-1100 has 375lbs of thrust in a medium size case..more than enough to fly the V-2 or DX. Just use an adapter to use 54mm motor, problem solved.
This attachment technique, comes in handy when there is no room on CR for an eyebolt.

See here [a sticky on top of high power page]:
https://www.rocketryforum.com/showt...-quot-Stock-quot-3IN-DARKSTAR-CJ-Step-By-Step

click on #11, #12 & #23 for pictures and explanation of how to do this.

 

[Reinhard]

Unless I'm mistake, 75mm motors Don't have motor delays.. The pressures are too great to be contained by a delay grain. They do have a smoke grain at the top, and a threaded closure for recovery hardware.

I believe Some 54mm motors have motor delays, but perhaps not all. If the motor says -P and doesn't have a delay number, it's Plugged and requires electronic deployment.

It's a regulation thing. Motors exceeding 2560Ns (K impulse) aren't allowed to have motor ejection anymore. Back in the days, you could get 75mm and 98mm motors with motor ejection. On occasion, casings with those forward closures pop up in the yard sale section, but current reloads can't be flown in them unless the closure gets plugged because the lack of a delay o-ring and related design features.

Reinhard

 

[Steve Shannon]

It's a regulation thing. Motors exceeding 2560Ns (K impulse) aren't allowed to have motor ejection anymore. Back in the days, you could get 75mm and 98mm motors with motor ejection. On occasion, casings with those forward closures pop up in the yard sale section, but current reloads can't be flown in them unless the closure gets plugged because the lack of a delay o-ring and related design features.

Reinhard

Please forgive the clarification. Rocket motors exceeding 2560 Ns are not prohibited from having motor ejection. The actual regulation is this:

4.10.2 A high power rocket launched with an installed total impulse greater than 2560 N-sec (576 lb-sec) shall use an electronically actuated recovery system as either a primary or backup deployment method.

So technically a large motor could provide motor ejection, but the rocket it flies in must have electronic recovery also.



Steve Shannon

 

[Reinhard]

Thanks for the clarification. So I guess making delays unavailable on the big motors was a voluntary thing on the part of the manufacturers?

Reinhard

 

[Steve Shannon]

Thanks for the clarification. So I guess making delays unavailable on the big motors was a voluntary thing on the part of the manufacturers?

Reinhard

Yes; delays are sometimes unreliable (thus the reason for the requirement) and even more so for larger motors where the flyer has more at stake, so why create an unrealistic expectation. As far as I know (fair warning: I will always be still learning) there's nothing preventing a motor manufacturer from certifying a delay for a larger motor, but samples for every delay time would have to be submitted. Certifying a -p version of a motor saves a lot of money. Large motors sell in the lowest quantities, so there's really no economic justification for certification with multiple delay times.

 

[ttabbal]

While I wouldn't mind having it as a backup deployment, I see why manufacturers might not want to pay to certify them that way. And I have read a number of accounts of issues with delays in larger motors. Having them blow through or extinguish when the pressure drops at burnout.

With electronics available so inexpensively, running redundant electronic deployment is not expensive considering the cost of the motors at 75mm+. So I don't think much is lost by not having motor deployment. And it gives me the option of using an eyebolt in the forward closure for recovery attachment or forward mounted retainers. If you are doing apogee only deployment, a single Eggtimer Quantum can even be somewhat redundant with its emergency main deployment option. That doesn't help with failure of the battery or single altimeter, but it's something.

Even if the rocket doesn't come with a av-bay, you can always build one into the nose cone for single deploy or chute release dual deploy.

 

[8thPaladin]

I will be there, hoping for L2 cert flight if everything goes as planned... if not will launch my other ones ��

 

[8thPaladin]

Thanks for all the information and clarification. Will start looking at altimeters. Always learning something new!

 

[ttabbal]

I will be there, hoping for L2 cert flight if everything goes as planned... if not will launch my other ones ��

Sounds good. I'm planning to be there, so feel free to come by and ask questions etc.. I can bring my L3 av-bay if you want to see one guy's way of doing things in a spacious 6" coupler. so. much. room..

If I manage to get off my duff long enough to finish it up, I might even bring some Hybrid gear.