24/40 E28 and F39 "certified" delay times?

[SolarYellow]

Either I'm massively confused or this thread is collectively wrapped around the axle like this mattress around this driveshaft.



Multiple people are saying to ignore the values in the parentheses, but as in the image two posts above this one, those numbers are 3, 6, and 9, which is how the motors are marketed, and which are closest to the test results on the certification sheet at https://www.nar.org/SandT/pdf/Aerotech/F39.pdf

So it seems like the baseline would be to expect the motors to perform fairly closely to the tests, which is approximately matching their advertised delay. It's the numbers outside the parentheses that should be ignored, unless one is at high elevation, like 6000 ft.

On the other hand, launching with a small, MD rocket from a Mojave dry lake at 3000 ft, you'll probably get to 6000 ft or higher, so maybe the delay burn will slow down during your flight. Worth having a logging altimeter and looking at the data.

 

[Steve Shannon]

Either I'm massively confused or this thread is collectively wrapped around the axle like this mattress around this driveshaft.

View attachment 544649

Multiple people are saying to ignore the values in the parentheses, but as in the image two posts above this one, those numbers are 3, 6, and 9, which is how the motors are marketed, and which are closest to the test results on the certification sheet at https://www.nar.org/SandT/pdf/Aerotech/F39.pdf

So it seems like the baseline would be to expect the motors to perform fairly closely to the tests, which is approximately matching their advertised delay. It's the numbers outside the parentheses that should be ignored, unless one is at high elevation, like 6000 ft.

On the other hand, launching with a small, MD rocket from a Mojave dry lake at 3000 ft, you'll probably get to 6000 ft or higher, so maybe the delay burn will slow down during your flight. Worth having a logging altimeter and looking at the data.

I understand why you’re confused but maybe you don’t know that Johnly is the chair of the NAR S&T Committee. I feel like I know him well enough to say that you should believe what he says.

 

[Johnly]

Please realize that these motors were certified nearly 30 years ago, well before I became a member of the NAR S&T committee.

Here's the account of the situation provided by Bob Krech, the NAR S&T Chief Technology Officer that was posted to another another TRF discussion in 1995. I've highlighted an important piece of data in his response.

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 but 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've made a request to Aerotech for a copy of the current instructions for the F39 and E28 reload kits.
I thought that the instructions had been revised to eliminate the delay times in parenthesis some time ago, but it could have been caused by something as simple as someone selecting the old file to print, rather than the updated version.

John Lyngdal
NAR S&T Co-Chairman

 

[SolarYellow]

Can you post a picture of the motor instruction so I can read the manufacturing date code?
Yes, ignore the value in the parenthesis as it is no longer correct.

So per your post, above, the values in parentheses (3, 6 and 9) are actually the correct values. The values not in parentheses, 6, 9 and 12, are the ones to be ignored.

 

[DeltaVee]

Please realize that these motors were certified nearly 30 years ago, well before I became a member of the NAR S&T committee.

Here's the account of the situation provided by Bob Krech, the NAR S&T Chief Technology Officer that was posted to another another TRF discussion in 1995. I've highlighted an important piece of data in his response.

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 but 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've made a request to Aerotech for a copy of the current instructions for the F39 and E28 reload kits.
I thought that the instructions had been revised to eliminate the delay times in parenthesis some time ago, but it could have been caused by something as simple as someone selecting the old file to print, rather than the updated version.

John Lyngdal
NAR S&T Co-Chairman

I've purchased at least half a dozen packages (combined) of F39's and E28's over the last two years. They have all had the parenthetical values as described. I don't believe the instruction sheet has EVER changed. If it has I certainly have not gotten an instance of it.

So per your post, above, the values in parentheses (3, 6 and 9) are actually the correct values. The values not in parentheses, 6, 9 and 12, are the ones to be ignored.

I'm quite confident that the 6, 9, and 12 are the "correct" (or at least as correct as could be) values... lets just say that when I use an F39-6 on a rocket that sims out to need about a 6 second delay (yes it's all fungible), the flight looks pretty nominal from the ground. Just don't bother looking for F39-12s... I've never seen them for sale since I got back into this hobby in 2016/2017. The ONE thing I know is that I have not had anywhere near the experience of others when it comes to drilling delays for the 24/40 motors. I can shave what should be 4 seconds off of a delay and if it takes off 2 seconds it's a win to me. At this point I just don't do it for the 24/40 reloads. The only delays I've drilled in AT motors that even come close to providing the calculated delay are the ones provided in the RMS+ reloads(the 14 sec delays) or the DMS motors (eg. G80-14 DMS). That's just been my experience... YMMV.

*

 

[Johnly]

It seems that I'm guilty of typing one thing and thinking something different. My apologies.
The F39-6(3)T should have 6 second delays and the F39-9(6)T motors should have 9 second delays.
We recently retested the E28-7T motors and the average delay for the set was 6.24 seconds.

 

[SolarYellow]

View attachment 544620

I'm quite confident that the 6, 9, and 12 are the "correct" (or at least as correct as could be) values... lets just say that when I use an F39-6 on a rocket that sims out to need about a 6 second delay (yes it's all fungible), the flight looks pretty nominal from the ground. Just don't bother looking for F39-12s... I've never seen them for sale since I got back into this hobby in 2016/2017.

Which 6 and which 9 are we talking about? Where are 12 and 3?

Is that "F39-6" you describe one that you bought as an F39-6? If so, as I understand this thread, it would have been marked like the one in the image above: F39-9T(6)*.

If it was an F39-6T(3)*, then you would have bought it as an F39-3. You can find 3, 6, and 9 for sale. You cannot find 12 for sale, which indicates that the 3, 6, and 9 in parentheses are the numbers that most correctly indicate the actual performance, not the 6, 9 and 12.

It seems that I'm guilty of typing one thing and thinking something different. My apologies.
The F39-6(3)T should have 6 second delays and the F39-9(6)T motors should have 9 second delays.
We recently retested the E28-7T motors and the average delay for the set was 6.24 seconds.

The motors are marketed as having delays of 3, 6 and 9 seconds. Those are the numbers in parentheses on the package insert. Those are the test result numbers on the NAR certification document. https://www.nar.org/SandT/pdf/Aerotech/F39.pdf

The numbers not in parentheses are 6, 9 and 12. If an F39-9(6)* motor should have a 9 second delay, then an F39-12(9)* motor should have a 12 second delay. But nobody is saying such a thing exists, except maybe AT in their original development testing at 6000 ft. elevation.

This is frustrating because all the documents and reports say we should be ignoring 6, 9 and 12 not-in-parentheses numbers, and going with the corresponding 3, 6, and 9 in-parentheses numbers, and then it keeps being said that the opposite is true.

Hence the mattress meme...

 

[rharshberger]

Which 6 and which 9 are we talking about? Where are 12 and 3?

Is that "F39-6" you describe one that you bought as an F39-6? If so, as I understand this thread, it would have been marked like the one in the image above: F39-9T(6)*.

If it was an F39-6T(3)*, then you would have bought it as an F39-3. You can find 3, 6, and 9 for sale. You cannot find 12 for sale, which indicates that the 3, 6, and 9 in parentheses are the numbers that most correctly indicate the actual performance, not the 6, 9 and 12.



The motors are marketed as having delays of 3, 6 and 9 seconds. Those are the numbers in parentheses on the package insert. Those are the test result numbers on the NAR certification document. https://www.nar.org/SandT/pdf/Aerotech/F39.pdf

The numbers not in parentheses are 6, 9 and 12. If an F39-9(6)* motor should have a 9 second delay, then an F39-12(9)* motor should have a 12 second delay. But nobody is saying such a thing exists, except maybe AT in their original development testing at 6000 ft. elevation.

This is frustrating because all the documents and reports say we should be ignoring 6, 9 and 12 not-in-parentheses numbers, and going with the corresponding 3, 6, and 9 in-parentheses numbers, and then it keeps being said that the opposite is true.

Hence the mattress meme...

You are the one making it difficult, several well known and knowledgeable, and credible people (NAR S&T, and a former TRA President) have expressly said ignore the number in parentheses.

 

[SolarYellow]

@Johnly's post #36 implies
1. That there is no F39 that has an actual three-second delay.
2. That a motor with packaging marked F39-12T(9)* will have an actual 12-second delay.

But he also in other posts references the NAR certification tests as indicating the actual situation. In the NAR document, there is a motor that tests to a 3-second delay. There is not a motor that tests to a 12-second delay.

I think it's time for me to pop my own chute on this one. I am pretty sure I get it, and I don't think saying the same thing more times will help anyone who doesn't see the problem I'm seeing to see it.

 

[DeltaVee]

I've got some F39-6(3)'s (sorry) lying around and we'll be having a launch a week from tomorrow if the weather holds out. I will fly one of these baddies in my Estes Sahara, equipped with an altimeter 3... IF the weather holds out (LRF is looking pretty grim right now) and IF all goes well, and IFI remember, I'll post the results here! ;-)

 

[Johnly]

I was able to review the Aerotech instructions and only the E18W group have been corrected by removing the parenthesis time.
The F39 group instructions and F12 group instructions were the outdated style as was the instructions for the F22J for the 29/40-120 hardware.
I request to update the instructions was made to Aerotech.

John

 

[4regt4]

I was able to review the Aerotech instructions and only the E18W group have been corrected by removing the parenthesis time.
The F39 group instructions and F12 group instructions were the outdated style as was the instructions for the F22J for the 29/40-120 hardware.
I request to update the instructions was made to Aerotech.

John

Thanks. That's appreciated, it was confusing...

Hans

 

[DeltaVee]

So here it took a bit more time since we had to postpone for a week. As I mentioned I have a pack of F39-6(3)'s (as marked on the package). These were purchased within the last 12 months. Our launch site is around 100 feet above sea level so make of it what you can. I ended up flying my Estes Ventris with this motor and on board it carried a jolly logic altimeter three, and the jolly logic chute release set for 300 feet. Now to be sure I was having some bluetooth glitches but the data seems fine. You'll note that the flight graph gets "wiggly" right after apogee, which was recorded at 6.5 seconds. The recorded burn time is 1.2 seconds, thus if ejection occurred there (which I suspect is the case judging from the squirrely nature of the plot after that point) then that indicates a post thrust delay of 5.3 seconds. Where the graph indicates ejection occurs (IF it really is the ejection point at 7.75 seconds) indicates then a post thrust delay of 6.55 seconds. The rocket certainly wasn't tumbling prior to ejection! The amusing part is that both values are within the allowed "20%" tolerance... I think the JL Altimeter three simply got the ejection point wrong... you can see where the chute was released by the change in slope between 250-300 feet. Based on all this, I think the "6" is "right" (or at least as right as it could be for such things!!!)

 

[rharshberger]

So here it took a bit more time since we had to postpone for a week. As I mentioned I have a pack of F39-6(3)'s (as marked on the package). These were purchased within the last 12 months. Our launch site is around 100 feet above sea level so make of it what you can. I ended up flying my Estes Ventris with this motor and on board it carried a jolly logic altimeter three, and the jolly logic chute release set for 300 feet. Now to be sure I was having some bluetooth glitches but the data seems fine. You'll note that the flight graph gets "wiggly" right after apogee (which was recorded at 6.5 seconds. The recorded burn time is 1.2 seconds, thus if ejection occurred there (which I suspect is the case judging from the squirrely nature of the plot after that point) then that indicates a post thrust delay of 5.3 seconds. Where the graph indicates ejection occurs (IF it really is the ejection point at 7.75 seconds) indicates then a post thrust delay of 6.55 seconds. The rocket certainly wasn't tumbling prior to ejection! The amusing part is that both values are within the allowed "20%" tolerance... I think the JL Altimeter three simply got the ejection point wrong... you can see where the chute was released by the change in slope between 250-300 feet. Based on all this, I think the "6" is "right" (or at least as right as it could be for such things!!!)

View attachment 546918

Gotta love how good certain altimeters are for proving that a motor is performing properly.

 

[4regt4]

Yes, thanks. From this, the delay was most certainly not the (3) value.

Hans.

 

[DeltaVee]

Gotta love how good certain altimeters are for proving that a motor is performing properly.

For sure... but they do glitch from time to time! That same altimeter I used in my Estes Sahara... thanks to a bluetooth glitch the altitude it hit with an E18 was suggested to be over 200,000 feet! I kid you not! It also is useful to verify stuff when you drill the hobby line delays. For example, that E18 I was using came with a 7 second delay... I drilled out what should have been 2 seconds worth and then used another drill bit to dig it out just a wee bit more. Alas the altimeter betrayed me on that flight (as stated!) HOWEVER looking at the flight video I took, the delay sure seemed to be the *full 7 seconds*. The only "working theory" I've got is that with the e-motor, at least, and the long distance between the top of the grain (where the igniter is situated against the taped c-slot), the delay element possibly starts burning around the edges without lighting up the center of the drilled out element... this is all idle speculation... but it's the only thing that would make sense. That "theory" would also suggest that an F reload would "work better", and almost makes the case (in my mind) that the drilled end for say an E18 or E28 should be facing the ejection charge.... if that were really the reason... Interestingly I've never had anything like this happening with RMS delay (eg F37-14 or G54-14 etc etc) or the DMS delay drilling...

 

[GalantVR41062]

I was able to make my way to a flying field and launch my Recon 1 1/2 rocket on a Aerotech E28-7T in the 24/40 case.

I assembled the motor per the instruction sheet with the "7sec" delay.


I have a OR simulation for this rocket and I have changed parameters in the sim to match live flight characteristics the best I can and I am happy with the results.


I fly in Minnesota, about 900' ASL. Weather conditions were mild and low wind. The dampled light and higher clouds did not provide the best situation for full video. The launch video and apogee event audio are good.



I loaded up my noise maker and Flight sketch mini in the nose cone to record the flight data and assist in recovery as I was concerned on the potential LZ with this flight profile. The rocket did land just off field in the woods, about 40 feet up in a tree and after some shaking and climbing I was able to retrieve the rocket.

The flight was good, nice and straight boost and I heard and saw the apogee event and visually tracked the rocket down, to the trees.







I have flown this rocket on this load a few times and visually has looked similar in flight profile. I am seeing a 1.15sec burn and 6.45sec delay. The Flight sketch data, video and visual line up. With the 20% variation this could result in a 5.16 - 7.74sec delay.