Staging Questions

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drew
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Staging Questions

Postby drew » Tue May 22, 2012 5:30 pm

So with WWW2012 almost here I thought it would be best if I’d fire off a few questions to the experts regarding staging. I’m hoping to attempt a minimum diameter two stage flight at Williams. Specifically I’ll be using a 38mm booster (glassed blue tube) to a 29mm sustainer (Blackhawk 29). Electronics will be as follows:

Booster – Raven2 (standard or 250G) for deployment duties (single deploy) and sustainer ignition with either a Wooshtronics EasyAs RDF or Big Red Bee BeeLine TX (16mw).

Sustainer – Raven2 (standard or 250G) in a 29mm Raven AV Bay for dual deploy duties and either a Telemini (10mw) or Big Red Bee BeeLine TX (16mw) in the nose for tracking.

Given this I’ve got a few questions I’d like to pose to the masses. Most of these questions revolve around the staging itself.

1) Ideally I’d like to ignite the sustainer motor as soon as practical. The booster motor I’ll be using has ~1.5 seconds of burn time. Given the relative low burn time and the fact that I’m going for raw speed I’m wondering if I should program the Raven to ignite the sustainer shortly after launch. I was thinking maybe 0.5 seconds after launch detect to light the sustainer motor. I’m thinking a second to give the motor time to ignite and come up to pressure should be suitable. Comments?

2) What options should I configure in the Featherweight Interface Program to ensure both high performance and safe operation in reference to the sustainer motor ignition.

3) Shear pins. I’ll be honest; I doubt I’ll be using them. I’m pretty certain I read a comment from Adrian Adamson where he’s given up using them on airframes 38mm and below. Given I probably won’t be utilising shear pins are there any recommendations you guys can provide? I was thinking of maybe just using a bit of tape on each “joint” in the rocket.

Not long now folks. I have to admit, I’m really looking forward to seeing all of you next week!
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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cryoscum
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Re: Staging Questions

Postby cryoscum » Tue May 22, 2012 5:43 pm

Hi Drew

Some questions I've been asking myself in the past. As far as shear pins go, I almost never use them, certainly not on something small, but I generally don't even consider them below 6". This is a matter of opinion, but I haven't needed them.

As for speed: I would set the raven to ignite the sustainer exactly at launch detection. You'd likely be using a standard igniter (not one of PK's bloody fast thingos) and, by the time the sustainer motor is up to pressure, you're already at 1 or 1.5 seconds, i.e. at the point of booster burn-out (or just prior). Made the mistake last year and hence lost to SUmo... This way it's pretty much as simple as you can get...

Cheers
N
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

drew
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Re: Staging Questions

Postby drew » Tue May 22, 2012 6:05 pm

Couple more questions (I knew I'd forget!). The interstage coupler will use the sustainer motor as the coupling point of the two rockets. How much of the motor should I have exposed to provide a safe coupling length? I was thinking of doubling the motor diameter and using that length (58mm). Comments?

Also, there's approximately 1" from the sustainer fins to the base of the 29mm airframe. I have the opportunity to provide as little or as much 29mm coupling length from the interstage coupler to re-establish a clean laminar flow before air encounters the transition itself. How long should the 29mm section of the transition protrude before encountering the transition to 38mm? I've really got no idea on this one folks so any advice would be appreciated!
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

drew
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Re: Staging Questions

Postby drew » Tue May 22, 2012 6:10 pm

Thanks for the quick response Nic, I expected nothing less! It also reminds me that I need to head to the bottle shop and grab you a handle of Bundy.

In reference to the igniter, I'll be using a e-match. The sustainer motor is a Cesaroni and apparently they come with e-matches as their default igniter. I was also considering raiding a pack of the 18mm Aerotech motors that I've never used and trimming one of the grains to seat the e-match in but I'm unsure as to whether I'll do it.
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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cryoscum
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Re: Staging Questions

Postby cryoscum » Tue May 22, 2012 6:22 pm

Yeah, also heard the CTI's are relatively easy to ignite. Still suggest you should just make the sustainer ignite at launch detection, i.e. in truth a second or two after launch was detected. Remember: there are delays in everything, including when the raven detects launch. I was late with my sustainer ignition by 1 second last year. It cost me 0.6 Mach on the end-total, forcing the sustainer to actually go through the trans-sonic region again and lost me the trophee to the Pink Ones ( :!: ). Go a bit early rather than a bit late...
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Staging Questions

Postby ROCKet STAR » Tue May 22, 2012 7:14 pm

I recall reading (can't remember where) that CTI motors have a pyrodex pellet in the top grain to aid ignition, and as such come up to pressure much quicker than Aerotech motors. I am wondering whether CTI would know the average ignition times for their motors, given that they offer a seemingly much more reliable ignition? If it is available, find out the delay in the Raven's launch detect, and subtract the two from your 1.5s booster burn time.

I guess that in reality there is going to be a certain amount of luck involved! :D
Chris Barnes

AMRS# 29 - L3

UKRA - L3


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