Aerotech RMS Delay Drilling

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BrianURocket

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Well yesterday I launched my first Aerotech RMS (29/40-120 casing). It was a G65-10W reload kit. I used the new Aerotech DDT (Delay Drilling Tool) to remove 6 seconds (used the -8 sec end, with washer +2 sec= -6 sec), to leave me with a 4 second delay. Everything went fine, except it appeared that shortly (like 1/2 second max) after it quit burning and went to trailing smoke, the ejection charge went off. It did not reach apogee and was moving full speed, but luckily, no damage to the rocket, but I'm trying to figure out if I did anything wrong. I again reviewed all instructions and haven't found I did anything incorrect. Anyone have ideas or have the same experience?
 
Were any of the delay parts (e.g. insulator, delay itself, spacer, washer, etc.) damaged or dented? If so, that could have made the 4 second delay into a no second delay. That happened to me this weekend, where I had a damaged delay, and it blew 1/2 sec into flight.
 
Well yesterday I launched my first Aerotech RMS (29/40-120 casing). It was a G65-10W reload kit. I used the new Aerotech DDT (Delay Drilling Tool) to remove 6 seconds (used the -8 sec end, with washer +2 sec= -6 sec), to leave me with a 4 second delay. Everything went fine, except it appeared that shortly (like 1/2 second max) after it quit burning and went to trailing smoke, the ejection charge went off. It did not reach apogee and was moving full speed, but luckily, no damage to the rocket, but I'm trying to figure out if I did anything wrong. I again reviewed all instructions and haven't found I did anything incorrect. Anyone have ideas or have the same experience?


I had the nearly identical experience on the F52-11T reload. In that case, the instructions for delay drilling appear to be simply incorrect. If you look at the delay grain lengths for that load, you will see the following:

F52-8T = .500 inch delay grain length
F52-11T = .531 inch delay grain length

While the delays differ by 3 seconds, the length of the delay grain differs by only 1/32 of an inch! So, if you used the tool to take an 11 second delay and make it a 8 second delay by removing 3/32 of an inch, you would be quite a bit shorter that the standard 8 second delay grain.

In my example, I took an "11" and made it a "6" but it was really more like a "1". It blew out while the motor was still burning.

Any possibility that happened to you? I can't find the delay grain lengths for the G52 loads on the AT site....
 
I had the nearly identical experience on the F52-11T reload. In that case, the instructions for delay drilling appear to be simply incorrect. If you look at the delay grain lengths for that load, you will see the following:

F52-8T = .500 inch delay grain length
F52-11T = .531 inch delay grain length

While the delays differ by 3 seconds, the length of the delay grain differs by only 1/32 of an inch! So, if you used the tool to take an 11 second delay and make it a 8 second delay by removing 3/32 of an inch, you would be quite a bit shorter that the standard 8 second delay grain.

In my example, I took an "11" and made it a "6" but it was really more like a "1". It blew out while the motor was still burning.

Any possibility that happened to you? I can't find the delay grain lengths for the G52 loads on the AT site....

I think you hit the nail on the head. Since it was my first reload, I never considered measuring the length of the delay, I was concentrating on following the instructions-which don't say anything about measuring the lenght. I do recall reading about it when investigating the reloads, then discovering they were going to all max delays and to drill them down, so I bought the max 10 sec delays for flexibility and since they were going that way in the future anyway. I bought (2) G64-10Ws at the same time. Today I rechecked the package of the one left, it says G64W-10, and the delay measures only 0.460" length. I found the delay length sheet on the Aerotech site (at least I think the current one), they say 10 sec should be 0.750" long ! They also say a 4 second delay should be 0.562", so I guess I started with slightly less than a 3 sec and reduced that? Sort of makes sense what happened, the ejection charge probably went while still burning. I then measured two G53-10FJ re-loads that are to be 10 sec also-they both measure about 0.500". I couldn't find that on the delay sheet so not sure, but must be similar. So those are possibley a 3-4 sec delay too? Is Aerotech having issues in the packaging department or what is going on? I guess measuring length of the delay is the first step!
 
Were any of the delay parts (e.g. insulator, delay itself, spacer, washer, etc.) damaged or dented? If so, that could have made the 4 second delay into a no second delay. That happened to me this weekend, where I had a damaged delay, and it blew 1/2 sec into flight.

No damage noted. It appears the delay provided is the wrong length.
 
I do recall reading about it when investigating the reloads, then discovering they were going to all max delays and to drill them down, so I bought the max 10 sec delays for flexibility and since they were going that way in the future anyway.

This was exactly my thought process as well.

One thing to note - the delay grains in my case ARE the correct length per the Aerotech website. This was not a packaging issue but rather an oddity in the delay grain lenghts that I am unable to explain. (Why does 1/32 " = 3 second delay difference for this load?) This would seem to indicate that the delay drilling needs to be carefully considered by looking at the spec delay lengths for the different delays and seeing if they are consistent with the 1sec=1/32" rule.

Or.... just go to electronics for the ejection. This is my next step as it seems to me that getting a reliable motor ejection is more a matter of luck than science. The accuracy of the delays is just too variable for my taste.

Besides - that means I get to buy more stuff...:D
 
This business of drilling delays seems a bit imprecise. If the 10 sec. delay is .750" long then that would seem to indicate closer to 1/16" per second instead of 1/32" per second. Of course when the engine is under boost, the delay grain is burning right along with that, and we don't know how fast it burns under these conditions. It might burn close to 1/2" under boost, then what is left would burn much slower after the main propellant has burned out.
 
This business of drilling delays seems a bit imprecise. If the 10 sec. delay is .750" long then that would seem to indicate closer to 1/16" per second instead of 1/32" per second. Of course when the engine is under boost, the delay grain is burning right along with that, and we don't know how fast it burns under these conditions. It might burn close to 1/2" under boost, then what is left would burn much slower after the main propellant has burned out.

I read this thread earlier today and today while driving, well not actually
driving as I was on the I-55 parking lot :eyeroll:, was thinking the same thing
if the delay is burning while under boost it could burn faster due to the heat
and pressure and then slower after burnout.

Or they might have different compositions of delay grains?

Got me...
 
bjphoenix said:
This business of drilling delays seems a bit imprecise. If the 10 sec. delay is .750" long then that would seem to indicate closer to 1/16" per second instead of 1/32" per second. Of course when the engine is under boost, the delay grain is burning right along with that, and we don't know how fast it burns under these conditions. It might burn close to 1/2" under boost, then what is left would burn much slower after the main propellant has burned out.

During the motor burn, the delay is burning much faster than it does after the motor burns out, so you can't just take the delay length and divide it by the burn time to get the burn rate.
 
I have had this happen on an 18mm D24 reload. Originally a 7 second delay, following the instructions, I thought it would take it to a four. More like a 2. Shreaded the chute, no harm for the rocket.

I think you really need to be precise on the drill length.

I am trying not to drill anymore.

Andrew
 
one thing to think about.. there are Two different delay grain formulas.

Standard delay grains are used for MOST AT reloads. but there are a few that use "Slow Delay" grains (different formula)

you can usually tell a slow delay grain by a blue stripe on the side of the paper. (but that is not 100%)
 
Just an update for all. I contacted Aerotech and they have asked for the lot numbers. FYI-I did have one measurement stated incorrectly, the G53-10FJ measures 0.620", not 0.500" I originally typed.

At first glance it appears I got incorrect delay lenghts (at least on the G64-10W) and the current delay length on the Aerotech website may not be correct for these two motors. I'll update once Aerotech helps me resolve it.
 
OK, finally received some delays from Aerotech to help me verify since the current chart on their website isn't right either. In the end, the G64-10W (lot 03231101) has been packaged with the wrong delay. It is about 0.210 short, which ends up being more like a 3 sec delay as it is shorter than a G64-4W. Be aware if you have a G64-10W with this lot #, I just received another in the mail I ordered from a vendro, and wouldn't you know it-same lot #-same problem. I have asked Aerotech to make a new delay chart, even since they are going to change to all long delays so everyone can verify if they are starting in the right place, as I'm only comfortable with the G53-10FJ and G64-10W that they verified for me. They seemed somewhat hesitant, not sure of the reason-this seems pretty critical to me. ell see.
 
It is a little concerning that the delays are either being packaged incorrectly, or that the delay information on the Aerotech website is incorrect. Please do keep us informed.

I just went the the NAR website to look at the certification data, hoping that the delay length was listed as part of the cert. No such luck...
 
I have only been doing reloads for a little over 18 months, but everyone knows that Aerotech delays have been their real short coming.

I have seen some that are suposed to be 7 seconds are really 3 seconds and some that are supposed to be 4 seconds be 10.

Andrew
 
I have only been doing reloads for a little over 18 months, but everyone knows that Aerotech delays have been their real short coming.

I have seen some that are suposed to be 7 seconds are really 3 seconds and some that are supposed to be 4 seconds be 10.

Andrew

I've been drilling AT delays since I started using reloads last year. I've only had one problem, and that was with a 38mm G reload. And I'm still not sure if it was the delay or something I did wrong.
 
BUT! You have to watch the depth really close. You seem to know how to use a caliper correctly. Most don't and then cry when they have a zipper longer than the body tube. Kinda like getting a wedgy.

I recommend that if you don't know what your doing don't do it.

Andrew
 
That is fine, but if AT is not always packaging the correct delays in the first place, I guess we should be measuring the delay length as part of the motor assembly process. That means that we need to have a reliable chart that shows the length that the delay should be in the first place - otherwise the drilling can have real bad consequences.
 
That is fine, but if AT is not always packaging the correct delays in the first place, I guess we should be measuring the delay length as part of the motor assembly process. That means that we need to have a reliable chart that shows the length that the delay should be in the first place - otherwise the drilling can have real bad consequences.

Doug-exactlty. This should be our concern. I hope I've made progress with AT. If we don't start in the right spot, it'll never work. Hope they get it straight-and soon.
 
I've been drilling AT delays since I started using reloads last year. I've only had one problem, and that was with a 38mm G reload. And I'm still not sure if it was the delay or something I did wrong.

I have drilled a lot of delays and have only had problems on a couple of loads. The 38mm G67 Redline has been short the couple of times I have used it. This makes me not want to use this reload anymore.
 
I have drilled a lot of delays and have only had problems on a couple of loads. The 38mm G67 Redline has been short the couple of times I have used it. This makes me not want to use this reload anymore.

I've flown G67R's 2 or 3 times, and only had a problem with the last one I flew. I wonder if it was a short delay, and I made it worse by drilling it.
 
I'm resurrecting this thread just to ask a quick question. I have to drill a couple of delays today for tomorrow's launch (10 seconds to 4 seconds). No problem there. But which way does the drilled end face when it's installed? I'm assuming the drilled end faces the grain, but I want to be sure. But if this is the case, the igniter will have to go a little deeper into the core to be able to reach the delay. Correct?
 
I'm resurrecting this thread just to ask a quick question. I have to drill a couple of delays today for tomorrow's launch (10 seconds to 4 seconds). No problem there. But which way does the drilled end face when it's installed? I'm assuming the drilled end faces the grain, but I want to be sure. But if this is the case, the igniter will have to go a little deeper into the core to be able to reach the delay. Correct?

I don't think it matters if the ignitor touches the delay grain or not, as long as it's at the top of the propellant grain. Once the propellant ignites, it's definitely going to also ignite the delay grain. In fact, on the single grain reloads for the 29/40-120 case, you're supposed to put a piece of masking tape at the top of the propellant grain so the ignitor can't push past it. The key is lighting the top of the propellant, because AP motors burn from the top down (unlike BP motors which burn from the bottom up). Even though there's a space between the top of the propellant grain (and the ignitor head) and the delay grain, the delay grain always gets lit.

https://aerotech-rocketry.com/uploads/777bd3df-bc26-4153-8fab-e01a4ee8a8f3_rms_29_e23-f22_20030.pdf
 
Got it. Thanks! It makes sense about the tape on the short grains for the 29/40-120. There's quite a gap between the top of the grain and the delay, so it must get pretty hot in the space between the two.
 
Are there any more current experiences with the Aerotech RMS Delay Drilling Tool to relate here, good or bad?
 
I've used the AT drilling tool many times. Haven't had any problems at all.
 
But is the delay grain length on the AT site now correct? I have a lot of various "10 second" delays to drill and want to make sure I am starting with an actual 10.
 
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