Delay Time Confusion (Aerotech F39-6T reloads)

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jb62

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Hello everyone, I have a new mid power kit, I got it put together and was going to Launch it this weekend but it was a bit too windy. However, I was a little confused by the delay times on the package for the reloads I bought for its first flight.

I bought some Aerotech F39-6T reloads and on the package it says:

F39-6T(3)* and it says "* = NAR certified delay times"

In Open Rocket simulations is says, with that motor, that optimal delay time is 5.47 seconds.

Open rocket only list these options for the motor:
3T
6T
9T

Aerotech packaging list:
6T(3)*
9T(6)*
12T(9)*

Does this mean I should use the F39-6T(3)* That I bought ? Or should I get the F39-9T(6)* ?
This is really confusing, because this is the only reload that I have seen this on and Usually I go the number right before the propellant type designation. I assume that I should have gone with he F39-9T(6)* but it is kind of confusing the way it has been done.

Anyway, thanks for the clarification.

*Edit: Changed/fixed title to better represent thread topic*
 
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F39-6(3) worked ok in my big daddy, so I assume that I got some that were actually close to 6 second delays.
Rex
 
Aerotech lists their delay times from ignition. The three in parentheses, is the approximate delay after burnout. At least that is what I was always told.
 
Dang, I have to say I never noticed that before. I'm thinking the post above is probably right. However, I wonder why it's not labeled as such on say the 29/40-120 reloads? Well, actually the G64-7W is labeled as a "G64-7W(8) although all remaining delays for the G64 as well as all delays of the E16W and F40W don't have the additional data point :confused2:. I'll inquire.
 
This may be older.... (or sadly, newer)

The Aerotech catalog lists it as "number of seconds of delay from burn out" a G64-4W would have a 4 second delay.

Same Catalog lists the F39 as having either a 6 or 9 second delay.



Quite confusing..... but I'd follow the number after the dash and measure it from burnout.
 
Those motors were certified 21 years ago under the delay times of 3-6-9 seconds. Since then the delays have been changed to 6-9 and (12 at one time), and I guess did not have to be /were not certified. Aerotech is showing the delays (3-6-9) at the time the motors were first certified, why is beyond me. The new 2 grain G-64's do not have the *= at all, but the old single grain ones have it, because they were certified that way. The current combined motor cert lists, are not up to date on all motors. Some have the old original cert info although grain numbers, total impulse and propellant weight has changed. Ignore the (#) https://www.aerotech-rocketry.com/c...ts/NAR/reloadable/rms-24_40/f39t_nar_cert.pdf
 
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My info is definitely old. I was told this back at the turn of the century (THAT makes me feel old, lol). It also only applied to reloads. They may well have changed in the years since. I haven't flown since 2006, and, I'm just starting to get my feet wet again.
 
Delay time has always been after propellant burnout.

The parentheses issue was simply: Aerotech submitted a time delay and NAR test data differed a lot. Rather than fail the test, they were certified as long as the label indicated the actual tested delay time.
 
Delay time has always been after propellant burnout.

The parentheses issue was simply: Aerotech submitted a time delay and NAR test data differed a lot. Rather than fail the test, they were certified as long as the label indicated the actual tested delay time.

Hmm, which has lead to a lot of unnecessary confusion.

My explanation was from misinformation, however, it did lead me to use the delays listed in parentheses over the years.
 
That delay starts burning at ignition so I always thought that if it said was a 10 second delay, 10 seconds after ignition (I didn't say lift off for a reason) your deployment event takes place. And I have never seen delay times after burnout listed in parentheses.
 
Shreadvector gets it right for both issues.

If you look at the S&T report, you can see the -6, -9 and -12 delays were not supported by the data, hence, the "NAR certified" times. If the AT stated times had been within the tolerance band for each motor, they could have gone with their original designation only.

After failing a certification test for delay time, another option is for the vendor to resubmit motors for testing and certification with delay grains that will give their expected results.

Bill2654 is correct that in composite motors, the delay grain is lit when the motor is lit. But to pass the certification testing, the delay grain should have enough material in it to give the designated delay after burnout of the thrust producing material.
 
Shreadvector gets it right for both issues.

If you look at the S&T report, you can see the -6, -9 and -12 delays were not supported by the data, hence, the "NAR certified" times. If the AT stated times had been within the tolerance band for each motor, they could have gone with their original designation only.

After failing a certification test for delay time, another option is for the vendor to resubmit motors for testing and certification with delay grains that will give their expected results.

Bill2654 is correct that in composite motors, the delay grain is lit when the motor is lit. But to pass the certification testing, the delay grain should have enough material in it to give the designated delay after burnout of the thrust producing material.



That's sorta kinda what I was trying to relay, the motors were certified at those delays. I did not know that the intended delays were 6-9-12 and only came out to 3-6-9. The S&T data published does not indicate that. It indicates that 3-6-9 second delays were tested and look to be good by the averages. It does not indicate that a 6 second delay was tested and averaged at 3 seconds and so on. Confusing it is, still don't know why it is indicated on the packs of motors. If you buy F39-6 motors you are getting a 6 second delay.
 
That's sorta kinda what I was trying to relay, the motors were certified at those delays. I did not know that the intended delays were 6-9-12 and only came out to 3-6-9. The S&T data published does not indicate that. It indicates that 3-6-9 second delays were tested and look to be good by the averages. It does not indicate that a 6 second delay was tested and averaged at 3 seconds and so on. Confusing it is, still don't know why it is indicated on the packs of motors. If you buy F39-6 motors you are getting a 6 second delay.
AT intended to sell F39 motors with 6, 9 and 12 second delays, and the motors were labeled as such. At a later date the motors that AT supplied to NAR S&T for recertification tested as 3, 6 and 9 second delays. For whatever reason, AT did not change the motor labels to denote the change bur reprinted the instructions with the NAR S&T measured delays. This was not prohibited at the time, but after that we changed the S&T labeling requirements so this can not be done today.

Bob
 
AT intended to sell F39 motors with 6, 9 and 12 second delays, and the motors were labeled as such. At a later date the motors that AT supplied to NAR S&T for recertification tested as 3, 6 and 9 second delays. For whatever reason, AT did not change the motor labels to denote the change bur reprinted the instructions with the NAR S&T measured delays. This was not prohibited at the time, but after that we changed the S&T labeling requirements so this can not be done today.

Bob

I know this is an old thread, but....

I just purchased an F39 reload kit and I'm pretty sure it's of fairly recent manufacture. It still has 6(3)* 9(6)* and 12(9)* on the packaging... In fact the E28 reload kit has the same nonsense! However while those are Blue Thunder, the two kits I have that are White Lightning, have no such ambiguous designation. So My question is: What is the verdict on this thread? Is an F39-9(6)* a 9 or is it a 6??? (and is a 6 a 3 and so on and so on...)
 
In general, if Bob Krech tells you something you can trust it. That said, if you do not believe him email Aerotech.
 
I know this is an old thread, but.... So My question is: What is the verdict on this thread? Is an F39-9(6)* a 9 or is it a 6??? (and is a 6 a 3 and so on and so on...)



The number in the parentheses is the correct delay. An F39-9(6)* is a 6 second delay
 
awesome! Thank you! At least now my stuff won't post-hole.... I'm surprised that there are kits with this sort of labeling still out there... I guess that means that the E18 and F39 kits I just bought must pre-date the rule change.
 
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No.

It simply means the motors did not have to be recertified after the rule change.


The label will only change if and when the motors are recertified.

awesome! Thank you! At least now my stuff won't post-hole.... I'm surprised that there are kits with this sort of labeling still out there... I guess that means that the E18 and F39 kits I just bought must pre-date the rule change.
 
Got it... so I guess the question remains... if I bought the F39-9 is it a "9" now or is it still a "6"? THANKS

From what I'm gathering from the thread, if it only says "-9" and not "-9(6)," then it is a nine.
 
I'm in agreement with Shreadvector. The time in parenthesis was the original certified delay time. When a shorter delay (or longer) was introduced, rather than recert, they just put the "real" number followed by the delay time that they certed at. This can be seen when you compare the actual NAR certification delay tests with the thrustcurve listings. This is also backed up by my own experience. :) My E28-4T(2) is listed as a 2 second delay under the NAR cert. https://nar.org/SandT/pdf/Aerotech/E28.pdf
But a 4 second delay in Thrustcurve. https://www.thrustcurve.org/motorsearch.jsp?id=51
I can tell you it isn't a 2 second delay, definitely a 4.
 
I'm in agreement with Shreadvector. The time in parenthesis was the original certified delay time. When a shorter delay (or longer) was introduced, rather than recert, they just put the "real" number followed by the delay time that they certed at. This can be seen when you compare the actual NAR certification delay tests with the thrustcurve listings. This is also backed up by my own experience. :) My E28-4T(2) is listed as a 2 second delay under the NAR cert. https://nar.org/SandT/pdf/Aerotech/E28.pdf
But a 4 second delay in Thrustcurve. https://www.thrustcurve.org/motorsearch.jsp?id=51
I can tell you it isn't a 2 second delay, definitely a 4.

So are you saying that the number in front of the parenthesis can be relied upon now? I do have hope that AT will reply to my enquiry in the not too distant future regarding this topic.
 
So are you saying that the number in front of the parenthesis can be relied upon now? I do have hope that AT will reply to my enquiry in the not too distant future regarding this topic.
Yes, the number NOT in parenthesis. Definitely not a 2-second delay on the E28-4T (2). I tried to find a video of my last launch so you could count the seconds, but apparently I missed that flight with my camera phone. Here's one for reference (not me for sure!) but easy to count the delay. At 1:55. https://youtu.be/9LHiUX30KQk?t=112
 
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Yes, the number NOT in parenthesis. Definitely not a 2-second delay on the E28-4T (2). I tried to find a video of my last launch so you could count the seconds, but apparently I missed that flight with my camera phone. Here's one for reference (not me for sure!) but easy to count the delay. At 1:55. https://youtu.be/9LHiUX30KQk?t=112


Thank you!
 
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This is the answer I got from Aerotech regarding the parenthetical stuff:

The numbers in parenthesis are from NAR data observed at sea level,
Our numbers are taken at 6,000 feet. As a rule of thumb, delay material
burns faster at lower elevation due to increase pressure, so that is why
the variation is noted for contest purposes. Also delays can vary up to 20%
either way according to NFPA standards and actual physical practice.

Now charts that I've seen give pressure at sea level as 29.92 inches Hg while at 6000 feet it gives 23.99 inches Hg.
That means that pressure at 6000 feet is 80% that of sea level. I imagine that the delay consumption rate during thrust
would be relatively unaffected since the chamber pressure ought to dwarf the value of the atmospheric pressure... that
*could* account then for the 3 second shortage across the board for all delay times I suppose since the chamber presssure
would drop close to atmospheric once the main propellant charge was expended. Still the size of the difference does make
me skeptical somewhat about this explanation... but I guess I would not fully dismiss it. It just seems unlikely since if this
is in fact the cause it would be more commonly known I would think.
 
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