Can Aerotech single use motor delays be modified?

[Bill S]

I've got an rocket that I launched yesterday (Estes Longship) on an Aerotech E20-4. Ejection was a tad early, but the only other option is a 7-second delay. I'd like to find say a 5 second delay. Is it possible to modify the delay charge? I'd read here that some Aerotech engines can have their delays modified. I wanted to continue to use the E20 engines due to the slower takeoff vs say an E30. I don't want to get into reloadable cases, etc.

 

[jimzcatz]

yes, there's a tool available from your dealer that does this, or you just pop the black powder out, use a 1/8 inch drill bit in the hole. Find the top of the delay grain and drill 1/32nd inch per second you want to trim from the delay. Make sure you replace the BP and cover.

 

[neil_w]

I've got an rocket that I launched yesterday (Estes Longship) on an Aerotech E20-4. Ejection was a tad early, but the only other option is a 7-second delay. I'd like to find say a 5 second delay. Is it possible to modify the delay charge? I'd read here that some Aerotech engines can have their delays modified. I wanted to continue to use the E20 engines due to the slower takeoff vs say an E30. I don't want to get into reloadable cases, etc.

I feel like almost all my rockets fall between the available 4- and 7-second delays for both the E20 and the E30. Wish they offered a -5 or -6 (like, 4/6/8 instead of 4/7).

 

[Bill S]

yes, there's a tool available from your dealer that does this, or you just pop the black powder out, use a 1/8 inch drill bit in the hole. Find the top of the delay grain and drill 1/32nd inch per second you want to trim from the delay. Make sure you replace the BP and cover.

Just to make sure I understood you correctly:

I popped the rubber cap off of one of the E20-7s, and I see what you mean about black powder. So if I removed the powder, I'd see another surface (the delay grain I assume), and drilled say 1/16" depth hole with a 1/8" drill bit it would now have an approx 5 second delay? Then put the powder back and replace the cap.

 

[jimzcatz]

1/32nd inch per second. Use that with what you started with

 

[mhanna]

I thought modifying a single use motor makes it a "research motor" (except LMS single use motors).
Not so anymore?

 

[jimzcatz]

Incorrect, it never was. Manufacturers have always supported delay adjustment. I have been doing it over 30 years.

 

[prfesser]

Incorrect, it never was. Manufacturers have always supported delay adjustment. I have been doing it over 30 years.

It's my understanding that when TMT tested a motor in years gone by, each delay was timed to determine accuracy. Permitting adjustment of delays (other than adjustments specifically recommended by the manufacturer) came about when it was agreed that all delays would be the same length, and the user could adjust to suit. I don't know exactly when that came about.

 

[Rocketjunkie]

If the manufacturer gives the OK to shorten the delay, it is within the safety code. Aerotech has always permitted this and only when pressured they formally stated it was OK to drill delays in SU motors. I've been doing it since before there were reloadables.

 

[mhanna]

Good to know, learn something every day.

 

[UhClem]

If the manufacturer gives the OK to shorten the delay, it is within the safety code.

Not quite true. NFPA 1127 was modified a while back specifically to allow for delay alteration in high power reloads. (4.5.3) No such change was made for high power single use (4.5.2) or any low power motor.

 

[jimzcatz]

There ever was a restriction in single use. We always had manufacturer's blessing. I personally got the word straight from Gary, Scott, and Wayne

 

[Steve Shannon]

Not quite true. NFPA 1127 was modified a while back specifically to allow for delay alteration in high power reloads. (4.5.3) No such change was made for high power single use (4.5.2) or any low power motor.

Thanks for including the reference. I’ll take a look at that, but NFPA 1125 does allow for model rocket motors with user adjustable delays to be certified. Didn’t you or someone suggested a fix for this conflict during this last review period?

8.1.8.1 Any user-adjustable delay reductions shall be accomplished using the manufacturer’s instructions and delay adjustment tool, if provided.

 

[tfish]

There ever was a restriction in single use. We always had manufacturer's blessing. I personally got the word straight from Gary, Scott, and Wayne

We must have missed that memo!

Tony

 

[CoyoteNumber2]

I've had people literally tell me, "You can't shorten a delay without the tool."
Thank you @jimzcatz for spreading the good word.

 

[BMcD]

I've had people literally tell me, "You can't shorten a delay without the tool."
Thank you @jimzcatz for spreading the good word.

"...if provided."

 

[CoyoteNumber2]

"...if provided."

???

 

[n27sb]

I don't think that I have ever seen an Aerotech tool for the small SU motors. Where can I get one, I could sure use one.

 

[Steve Shannon]

We must have missed that memo!

Tony

Yeah, that memo never came out. No low power SU motors other than DMS have been certified with adjustable delays. I know people do it but it’s not allowed according to the safety codes. If the manufacturers want to issue letters and help make appropriate NFPA changes it’s something that maybe could be discussed.

 

[UhClem]

Didn’t you or someone suggested a fix for this conflict during this last review period?

The most recent revision cycle was delayed so that it could be synched with 1125. That just finished which means that it will be five years before the next edition.

I seem to recall sending something to the NAR representative to the NFPA committee to fix 1127 with a hint about doing the same to 1122.

 

[Steve Shannon]

The most recent revision cycle was delayed so that it could be synched with 1125. That just finished which means that it will be five years before the next edition.

I seem to recall sending something to the NAR representative to the NFPA committee to fix 1127 with a hint about doing the same to 1122.

That’s what I thought I remembered, that Steve Lubliner was trying to incorporate it.