Adjustable 18 mm delays?
 

Hello All,

I have an old model rocketry book (originally published in 1971 and re-printed in 1972) called "Model Rocketry: Hobby of Tomorrow." It was written by Peter Lowry and Field Griffith, who were both 17 years old at the time.

In the chapter on model rocket motors, they not only described the old Rocket Development Corporation/Enerjet variable delay system for "D," "E," and "F" motors (a separate ejection charge module that was ignited by a fuse of variable length that was lit at launch), but they also described a different variable delay system that they said was under development for "1/4A" through "C" 18 mm motors. As they wrote on Page 28 of the book:

"Another delay-ejection charge package that is being worked on now is a unit the same diameter as an engine but just including the delay and ejection charge. These units would fit almost any small 1/4A through C type engine and would be made with various delays. The procedure for their use would be to select the one needed and glue on a booster engine."

"The advantages of variable delay are numerous. You have complete control over the coasting flight of your rocket. You never run out of booster engines. You don't have to buy a great number of engines with various delays. Instead, a set of booster engines and a couple of delay-ejection charge units will be sufficient."

Were these variable delay-ejection charge units for 18 mm (0.69") diameter model rocket motors ever put into production, even briefly? While the 2.75" long Series I and Series II booster motors would have had motor mount compatibility problems due to their greater length with these delay-ejection charge units installed, the delay-ejection charge units would have been perfect for use with the 1.75" long Series III "Shorty" booster motors. (However, if a delay-ejection charge unit that would be glued *inside* the front ends of Series I and Series II booster motors could be developed, these motors would still fit in existing models.)

I believe that was SEMROC they were talking about. Maybe carl could fill you in on the details.

S.

AVI made motors that were modular in this manner, but, as far as I know, the delays were always glued in at the factory - the user did not perform this task. (I thought I could find a pic of one, but I struck out.)

Carl McLawhorn and I have discussed these in the context of Semroc, but I can't recall many details. I thought there was an old catalog online that showed some modular Semroc motors, but I couldn't find it. But here's an old Semroc catalog: http://www.ninfinger.org/rockets/ca...70semroc54.html

Hopefully Carl will jump in here and shed some light on this and on AVI.

Doug

[Edit]Here's a pic of a modular AVI D6.1-6.75:


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I remember that book, and vaguely recall the delay module bit.

This could have been, well, vaporware. Like FSI Pulsators or almost everything that AVI announced.

I have not memorized the NFPA codes, but I would bet that a "Model Rocket Motor" cannot have an externally burning fuse - even for a delay and even if it is inside a conduit of some sort.

It might have been possible with the codes (or lack thereof) of the 1960's, but I doubt it now.

Here we go again with NUISANCE regs from the NFPA or some other regulatory body that would not have applied back in 1971. Having NFPA or any other regulatory body other than the FAA involved in model rocketry is about as much fun as taking a bowlin' ball into the woods deer hunting.

The NFPA is the main reason for no more BP SU F100s or high thrust SU BP G-size Rokitflite motors also...geez thanx I feel safer all over....PUKE ! :mad:

Given the choice of OVER-regulation of ANYTHING or NO regulation, I will choose NO regulation EVERY time other than items related to the FDA.

NFPA deals with many fire codes. The "P" stands for "Protection". Please tell us all your personal feelings about NFPA regulations on fire sprinkler systems in schools or office buildings, and your feelings about regulations requiring fire extinguishers and regular inspections of those extinguishers.

And, if you feel like expounding, please tell us about fire exits and signs for schools and movie theaters. Those cost money to install and they are forced to do so by regulations.

And you are careful to specify "OVER" regulation. Please tell us exactly how to measure that. Not some vague personal opinion, but rather explain a measureable quantifiable method of determining exactly what is tolerable levels of regulation to prevent fires, injuries or deaths.

Uhhh....
Okay....
I was only speaking toward the NFPA in their ill-concieved attempt regarding regulation of rocket motors; not sprinklers, fire exit signs, etc.
They are over-reaching into an area they DO NOT NEED THIER STINKIN SNOOTS IN !


I do not think tha the NFPA should be involved in HOBBY ROCKETRY AT ALL. For them to be involved AT ALL with OUR hobby is what I define as OVER regulation.
Seeing as rocket motors are NOT intended to be used indoors ANYWAY, it should not matter AT ALL whether or not they are above 80n of average thrust unless they can prove with QUANTIFIABLE EVIDENCE that the said rocket motor is more likely to burn the structure down. Even then it STILL should not matter as their intended use is NOT within an enclosed structure.
I would logically offer that a G104 or F101 that burns about 1/3 the time of an F20 or G33 is much LESS likely to ignite other materials just from the sheer reduction in burn time alone. I think their average thrust rule is a load of crapola that they pulled out of some donkey's backside with zero actual testing to prove/disprove their threshold has any real meaning in protection.
Their 80n avg thrust threshold rule makes about as much sense as BATFE attempting to regulate AP as an explosive. Total bunk from an entity that have no impact on the activity.

As a whole I actually am against laws/acts/agencies that have provisions that aim to protect the stupid from themselves. Last time I checked there was NO Constitutional Amendment guaranteeing the right to be STUPID. If one decides to "touch off" a G104 or G339 or a G33 within a dwelling the end result is most likely to be the same one. At best a very large mess/bad outcome and it would not matter if the motor was a G33 or an H250.

NFPA does not only write fire code for structures.

http://www.nfpa.org/aboutthecodes/l...d_standards.asp

Please identify which of the codes are infringing your personal freedoms and propose how to eliminate them or revise to a more freedom-friendly version.

I imagine the change in the safety code regarding the user not modifying motors (which also made tandem motors verboten) might have been the reason for the modules being factory-installed.Interesting...were those Semroc D6 motors 0.69" in diameter and just longer? (Cox made 0.69" X 2.75" D8 motors, but their delays were short due to the limited space inside their cases. Being D8s rather than D6s, they may have had at least semi-core burning propellant grains.) I like the checkerboard pattern printed on the Semroc D6 motors--you could glue on fins, add a short slip-on length of body tube with a nose cone, and the motor could be the rocket's decor scheme! :-)

Thank you also, Doug, for posting the pictures of your motors--a nice trip down memory lane for me! That AVI D6 looks like a C6-0 with its glued-in delay-ejection charge unit, which would have permitted a longer propellant grain to be loaded in the existing 0.69" X 2.75" case. If the sub-caliber delay-ejection charge unit would clear thrust rings and motor clips (like the narrower front ends of reloadable 18 mm AeroTech motors), Estes and/or Quest could also make D6 motors using their existing A through C size motor cases.