Shorten Delay on AT H250-G
- Thread starter Balsa Bob
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Rocketjunkie
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Aerotech delays burn at 1/32" per second (with the exception of some used in Black Jack loads) not including the part thet burns during the thrust phase of the motor. The amount that burns during the thrust phase depends on the thrust duration and chamber pressure. This is why medium delays for different propellant types are different, even in the same motor size. In your case, you would want to drill 7/64" (3-1/2 x 1/32") to the deepest part of the hole. Place the hole toward the propellant for the most consistant results. Note that delays can vary +-20% or 2 seconds for a medium delay. When shortened to 6-1/2 seconds, it can still vary 2 seconds, or 4-1/2 to 8-1/2 seconds and still be within spec. This is in addition to any inaccuracies in the hole depth.
bobkrech
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Follow the manufacturer's instructions.
https://www.aerotech-rocketry.com/c...tions/RDK_Instructions/rms_delay_mod_inst.pdf
Bob
https://www.aerotech-rocketry.com/c...tions/RDK_Instructions/rms_delay_mod_inst.pdf
Bob
OR, you can do like my buddy did and just go get an RDK kit. If you get on for redlines thats listed as small for those reloads it works. He switched from short to long using a Redline (I want to say RDK 15? 16?) and it worked flawlesly.
Ben
Ben
Isn't the delay for the H250G an odd ball lenght. I noted on the first one I built it was smaller than expected. I believe Gary commented that it was a unique lenght. So I'd be careful drilling it out. Also the H250G's that I've flown seem to be running a higher chamber pressure. The delay insulator was rather difficult to extract.
You may be able to buy a shorter RDK as Ben suggested.
Al
You may be able to buy a shorter RDK as Ben suggested.
Al
In my mind, it should work in any size for the fact that, shorter length, shorter delay. and vise versa for longer. So if the kit comes with a .6, get a .5 or .4 and you should be ok.
Ben
See if this sounds right.
Per the AT assemly drawing, the H250-M delay is .406" long.
That doesn't correspond directly to any of the available RDKs.
The AT modification instructions say drill .024"- .031" per second desired.
Taking .028" as a happy medium, to shorten by 3.5 seconds, you would drill .098" deep.
The original .406" minus .098" gives you .308" as the desired delay element length.
The shortest 'RDK+' kit is the RDK01 at .314" long. That should be slightly more than the 6.5 seconds you want.
Or you can just drill .098"
Per the AT assemly drawing, the H250-M delay is .406" long.
That doesn't correspond directly to any of the available RDKs.
The AT modification instructions say drill .024"- .031" per second desired.
Taking .028" as a happy medium, to shorten by 3.5 seconds, you would drill .098" deep.
The original .406" minus .098" gives you .308" as the desired delay element length.
The shortest 'RDK+' kit is the RDK01 at .314" long. That should be slightly more than the 6.5 seconds you want.
Or you can just drill .098"
Bingo! Get RDK01. I feel more comfortable swapping and using a shorter delay because I have had alot of problems with blow by.
Ben
shockwaveriderz
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I'm going to show my lack of knowledge of composite rocket motor design here and ask, by "blow by" what exactly does that mean?
Does it mean, that sometimes when you drill out a delay, you drill it "too thin" and the chamber pressure is greater than the "burst diaphragm " thickness/strength of the delay?
terry dean
Pretty much. Another thing I have heard it reffered to is with the ignitor being up there igniting the delay if it is to thin it will burn like a bates grain and just burn a clean core, blowing the ejection charge, and then continue to smolder/burn till its gone.
Ben
