AeroTech Delay Cheatsheet

OKTurbo · Aug 31, 2005

Here is something I thought I'd share. It's a one page "cheat sheet" for the AeroTech 24/40 and 29/40-120 hobby motor delays.

The delays are drawn full scale, so all you have to do is hold the delay grain up to the drawing. You can do a quick check to make sure you have the right length delay, or pick a shorter/longer delay for the motor you're wanting to assemble.

For example: You have a G64-4W in your stash, but you need a 10 second delay for the rocket you want to fly. If you have a G33-5J reload that you're willing to break up to fly the rocket....use it's delay in the G64 and you're set with a 10 second delay.

Note that the 24/40 and 29/40-120 delays are the same diameter, but different lengths. The 24mm delays will work in the 29mm, but you'll need to have the right delay spacer.

shockwaveriderz · Aug 31, 2005

I don't know but thats why I am asking: are we allowed to use delays from one motor in another motor? Are delays on Hobby motors allowed to be drilled like on HPR motors? I guess the RMS hobby motors don't use those RDK delays?

OKTurbo · Aug 31, 2005

Originally posted by shockwaveriderz
I don't know but thats why I am asking: are we allowed to use delays from one motor in another motor? Are delays on Hobby motors allowed to be drilled like on HPR motors? I guess the RMS hobby motors don't use those RDK delays?

I don't know the official answer....This is just my own cheatsheet.

As far as I know, the hobby delays are the same formula except for the "slow" delays. No, they are not the same as the RDK delays. The formulas may or may not be the same, but dimensionally they are different.

The official AeroTech press release on drilling of delays does say RDK, but the info that they give on delay lengths include the hobbyline motors, so I'm not sure if drilling of these delays is approved or recommended by AeroTech. Maybe Gary R. will see this and comment.

MarkM · Aug 31, 2005

Originally posted by OKTurbo
For example: You have a G64-4W in your stash, but you need a 10 second delay for the rocket you want to fly. If you have a G33-5J reload that you're willing to break up to fly the rocket....use it's delay in the G64 and you're set with a 10 second delay.

I don't think this is entirely correct. I'm pretty certain you can use delays from other motors, but I always thought they had to be of the same propellent type since the delays burn differently depending on propellent. If this is right, your example would result in an incorrect delay timing since the G64 is white lightening while the G33 is Black Jack...two very different propellents with very different burn rates. But, perhaps I'm wrong on this.

cjl · Aug 31, 2005

Yes - the burn rates are different. A G33-5 will have the same delay element as a G64-10, though. Here's the delay chart that I use (includes HPR): https://www.aerotech-rocketry.com/c...Flyers_Data_Sheets/aeroTech_delay_lengths.pdf

shockwaveriderz · Aug 31, 2005

can any of the rdk delay units be used with RMS hobby motors?

I don't understand how a -5J delay will become a 10 sec delay if you put it in the G motor/

whats a delay spacer?

OKTurbo · Aug 31, 2005

Originally posted by cjl
Yes - the burn rates are different. A G33-5 will have the same delay element as a G64-10, though. Here's the delay chart that I use (includes HPR): https://www.aerotech-rocketry.com/c...Flyers_Data_Sheets/aeroTech_delay_lengths.pdf

cjl,

That's the chart I used to make up the drawing.

shockie...the G33-5J is a BlackJack motor and burns much slower than the G64-10W White Lightning motor. Don't forget that the delay element starts burning at motor ignition also. The delay burns much faster due to the pressure in the motor as the propellant grains burn, then the delay burn rate slows down during coast.

The delay spacer is the small cardboard tube/spacer that you put in with the delay grain...unless the delay grain is full length like the G33-5J. The delay part of the motor consists of an o-ring, the delay liner/insulator, the delay grain, and the delay spacer (if needed).

Hope that makes sense. There are some good drawings of the assembled AeroTech motors on their website.
https://www.aerotech-rocketry.com/customersite/resource_library/AT_rms_assy_dwgs.html

No...the RDK delay grains are a different diameter and cannot be used in the hobby line motors

bobkrech · Aug 31, 2005

Originally posted by shockwaveriderz

can any of the rdk delay units be used with RMS hobby motors?

The answer is no. The reason is that the diameters are different.

I don't understand how a -5J delay will become a 10 sec delay if you put it in the G motor

The simple answer is because that's what was measured.

The long answer is that:

1. The burn rate of a delay column composition increases with pressure.

2. The burn rate of a delay column composition is constant at a constant pressure.

In the example previously mentioned, a 0.750" delay column is used in both the G33-5J and the G64-10W. We know that the linear burn rate of the delay column of each motor is the same after each motor has burned out, so if you look at the pressure/time history of a G33J and the time/pressure history of a G64W, you will see that the G33J has a significantly longer 3.3 second burn time than the 2.1 seconds for the G64W, and therefore the delay column in the J motor burned significantly more during thrusting than in the W motor.

How much? Check out https://www.aerotechrocketry.com/cu...tions/RDK_Instructions/rms_delay_mod_inst.pdf

A standard delay composition burns about ~1/32" per second at atmospheric pressure. The G33-5W delay burns ~5/32" after burnout while the G64-10W delay column burn ~5/16" after motor burnout, so during thrusting the delay column in the G33 must have burned about 3/4"-5/32"=19/32" while during thrusting in the G64 the column only burned only 3/4"-5/16"=7/16". The ratio of (19/32)/(7/16) ~ 1.36, and the ratio of the burn times for the motors is ~1.55, so while the trend is clearly shown it's not an exact match because of the pressure variations in the two burns.

whats a delay spacer?

A delay spacer is a cardboard tube. The delay cavity in a motor family has the same length so the sum of the delay column length and the spacer length has to be constant.

Bob

Rocket Guy 1317 · Aug 31, 2005

Originally posted by OKTurbo
I don't know the official answer....This is just my own cheatsheet.

As far as I know, the hobby delays are the same formula except for the "slow" delays. No, they are not the same as the RDK delays. The formulas may or may not be the same, but dimensionally they are different.

The official AeroTech press release on drilling of delays does say RDK, but the info that they give on delay lengths include the hobbyline motors, so I'm not sure if drilling of these delays is approved or recommended by AeroTech. Maybe Gary R. will see this and comment.

I have switched Delay before. I had a F40-7 and a G64-4 so swapped delays and made it a G64-7 and an F40-4.

shockwaveriderz · Aug 31, 2005

thanks for the responses guys....I apprecaite it!

OKTurbo · Aug 31, 2005

So now that you understand what I was going for, is the cheat sheet useful?

Maybe it would sound better if I called it the "AeroTech 24/29 Hobby Line Delay Grain Matrix".

shockwaveriderz · Nov 12, 2005

This thread has been dormant for a while but after doing some thinking I now have some additional questions:

for example lets look at a F12J has a delay length of .625" (20/32) with delays of 3 (std) and 5 slow.

Questions:

1. Can any delay/delay spacer conbination used as long as the length og the dealy/delay spacer equals .625" in length?

2. WHat is I wanted a F12J with a longer delay than 3 or 5? What kind of delay would I get if I used a 10 sec delay from another motor? a F40-10T or D15-10W or a F52-11T ?

I obviously an trying to figure out to mix and match different delays to get custom delays times....

For example if I used any of the above delays , what kind of actual delays would I end up with?

I am also looking for math formulas so that if I decide to use a delay from one motor I can calculate its delay in the new motor.

tia

OKTurbo · Nov 12, 2005

Originally posted by shockwaveriderz
...snip...

for example lets look at a F12J has a delay length of .625" (20/32) with delays of 3 (std) and 5 slow.

Questions:

1. Can any delay/delay spacer conbination used as long as the length og the dealy/delay spacer equals .625" in length?

***for the 24/40 case, Yes. The delay plus spacer is .625" long.***

2. WHat is I wanted a F12J with a longer delay than 3 or 5? What kind of delay would I get if I used a 10 sec delay from another motor? a F40-10T or D15-10W or a F52-11T ?

***On the F12J the longest delay possible is the 5 second. The "slow" delay elements are made of a different material that burns slower. Notice that both the F12-3J and the F12-5J have the same length delay elements with no spacer. The 5 sec delay is longer due to the "slow" delay material. You can't fit a longer element in there.....there isn't any more room.***

I obviously an trying to figure out to mix and match different delays to get custom delays times....

For example if I used any of the above delays , what kind of actual delays would I end up with?

I am also looking for math formulas so that if I decide to use a delay from one motor I can calculate its delay in the new motor.

***Every 1/32nd of an inch is a change of 1 second in the delay time (Except for the "slow" delays). Compare the length of a known delay and add or subtract 1/32" for each second. The extra length in the delay is the "burn time".***

tia

troj · Nov 12, 2005

Originally posted by OKTurbo
Here is something I thought I'd share. It's a one page "cheat sheet" for the AeroTech 24/40 and 29/40-120 hobby motor delays.

The delays are drawn full scale, so all you have to do is hold the delay grain up to the drawing. You can do a quick check to make sure you have the right length delay, or pick a shorter/longer delay for the motor you're wanting to assemble.

One thing to be aware of is the scaling that happens when you print.

Depending on how close two delays are in length and the scaling your driver does, you may end up thinking you have one delay when you truly have another.

Before relying on such a printout, spot-check your copy for accuracy using know delays or you may cause yourself problems.

-Kevin

shockwaveriderz · Nov 12, 2005

ok: ok lets see if I got this right. The largest delay train/delay spacer combo for the F12 would be.625".

Lets say I wanted to use the slow -10 delay from the D13 that is .500 in length then I would need a .125" length delay spacer?

also since the thrust duration of the d13 is 1.5 sec, the math would be:

thrust duration + delay Time = 1.5 sec + 10 sec = 11.5 sec total delay time .

to determine the burn rate of the .500 length delay .500/11.5 = .0435" per sec delay burn rate

The thrust duration of the F12 is 3.6 sec ... so if i multiply 3.6 x .0435 = 0.1566 " of the delay train will be used during the thrust duration.

If i then subtract 0.1566 from .500 = 0.3434 " delay length left

If I divide that by .3434/ .0435 = 7.89 sec delay time.

so I almost get a F12-8 ????? rounding off...

by the way does anybody have an idea what the At delay train composition is? If its not cool to post that kind of info here please email me direct. tia

Somebody want to check my math?

OKTurbo · Nov 12, 2005

Is there a 10 second delay available for the D15 RMS24/40? It's not shown in the current AeroTech catalog.

edit***nevermind. I see that you were talking about the D13 for the 18/20 motor.

Careful....there is one major error in your calculations. You can't just add the burn time and the delay time. The delay grain burns faster when the motor is under pressure....and to complicate it more, the pressure changes during the burn.

You will have to calculate how quickly the delay grain burns for each propellant type AND each motor since even the same propellant types may have different thrust/pressure/nozzles.

With the two delay types (Standard and Slow) the longest delay you can get with the F12 is 5 seconds after propellant burn out since it uses the full length of the delay cavity with the slow delay material.

The chart is simply to show what other motors in the lineup have the same delay sizes. If the pdf file is printed out without any scaling (Page scaling = NONE) the delay lengths will be actual size.

shockwaveriderz · Nov 12, 2005

ok: well double poop!...

SO now i have to take into account pressure too huh> now how the heck would I be able to do that comparsion between motors?

also I noticed the AT dadatsheet shows the thrust duratuion of the f12 as 3.6 sec while the www.thrustcurve.org actual test date shows it at 2.93......

so even if i can figure out a way to introduce pressure I still have to use real versus manufacturer numbers..... and of course the number can be somehwhere in between too....

John Taylor · Oct 18, 2019

OKTurbo said:
Here is something I thought I'd share. It's a one page "cheat sheet" for the AeroTech 24/40 and 29/40-120 hobby motor delays.

The delays are drawn full scale, so all you have to do is hold the delay grain up to the drawing. You can do a quick check to make sure you have the right length delay, or pick a shorter/longer delay for the motor you're wanting to assemble.

For example: You have a G64-4W in your stash, but you need a 10 second delay for the rocket you want to fly. If you have a G33-5J reload that you're willing to break up to fly the rocket....use it's delay in the G64 and you're set with a 10 second delay.

Note that the 24/40 and 29/40-120 delays are the same diameter, but different lengths. The 24mm delays will work in the 29mm, but you'll need to have the right delay spacer.

John Taylor · Oct 18, 2019

Sorry to double post. Anybody know the measured delay element length for a G76-7 It states it is a HDK-25.
I need to know the length please, I have a launch tomorrow. I have a G76-4 now and a supply of different elements and spacers.
I realize of course realize I will have to use the correct spacer to make it flush.

Rocketjunkie · Oct 18, 2019

Here's all the Aerotech HDK and RDK sizes. HDK/RDK number, length, and the motors it's used in. Slow is a different formulation. Do not assume a 1/32" per sec burn rate.

Aerotech delay kits, Hobby line style
HDK KITS for 18mm Motors
HDK-01 .281 D24-4T
HDK-02 .375 D24-7T
HDK-03 .407 D13-4W
HDK-04 .469 D24-10T
HDK-05 .500 D13-7W
HDK-06 .500 slow D13-10W

HDK KITS for 24mm Motors
HDK-07 .344 D15-4T E28-4T
HDK-08 .407 D9-4W F39-6T
HDK-09 .438 D15-7T E28-7T
HDK-10 .500 D9-7W F39-9T
HDK-11 .531 E18-4W F24-4W
HDK-12 .625 E11-3J E18-7W F12-3J F24-7W
HDK-13 .625 slow F12-5J

HDK KITS for 29mm Motors
HDK-14 G71-4R
HDK-15 .375 E23-5T G76-4G
HDK-16 .406 F52-5T G71-7R
HDK-17 .500 E23-8T F52-8T F40-4W G71-10R G33-7J
HDK-18 .531 F52-11T G64-4W
HDK-19 .562 E16-4W G76-10G
HDK-20 .657 G64-7W G33-10J
HDK-21 .657 E16-7W F40-7W G64-10W
HDK-22 .750 F22-5J F40-10W
HDK-23 .750 slow F22-7J
HDK-24 .750 G33-5J
HDK-25 G76-7G

Aerotech delay kits, High power style
RDK01 .314 G77-4R/LMS, G77R-S, H238T-S, H220T-S
RDK02 .375 G79-4W/LMS, F62T-S, F62T-S, G104T-S, H165R-S, H210R-S, H268R-S
RDK03 .438 G79-7/LMS, F37W-S, G54W-S, G79W-S, H128W-S, H180T-S, I200W,S
RDK04 .469 F20-4W/LMS, F62T-M, G77R-M, G104T-M, H238T-M, H220T-M
RDK05 .563 F20-7W/LMS, F37W-M, G54W-M, G75J-S, G79-M, H128W-M, H97J-S, H180W-M, I200W-M
RDK06 .594 F62T-L, G104T-L, H238T-L, H220T-L, H165R-L, H210R-L, H268R-L
RDK07 .656 F37W-L, G54W-L, G79W-L, H128W-L, H180W-L, I200W-L
RDK08 .719 G75J-M, H97J-M
RDK09 .406 G67R-S, H242T-S, I357T-S, I300T-S, I435T-S, H148R-S, I218R-S, I285R-S, I366R-S, J420R-S
RDK10 .469 H242T-M, I357T-M, I300T-M, I435T-M, I600R-M
RDK11 .500 G61W-S, G67R-M, H123W-S, I161W-S, I211W-S, I284W-S, J350W-S, J570W-S
RDK12 .594 G61W-M, H123W-M, H242T-L, I161W-M, I211W-M, I357T-L, I300T-L, I284W-M, I435T-L, J350W-M, J570W-M
RDK13 .625 I195J-S
RDK14 .656 H73J-S, H112J-S, I154J-S, H148R-L, I218R-L, I285R-L, I366R-L, J420R-L
RDK15 .719 G61W-L, H123W-L, I161W-L, I211W-L, I284W-L, J350W-L, J570W-L
RDK16 .781 H73J-M, H112J-M, I154J-M, I195J-M
RDK17 .531 H148R-M, I218R-M, I285R-M, I366R-M, J420R-M
RDK18 .500 G77-10R/LMS, G77R-L, H165R-M, H210R-M, H268R-M
RDK19 G77-7R/LMS
RDK20 G79-10W/LMS
RDK21 .432 J460S,J800S,K1100S
RDK22
RDK23 .547 J460M, J800M, K1100M
RDK24 .593 J180S
RDK25 .616 J275S, J415S, K550S, J540M, K695M
RDK26 .639 J460L, J800L, K1100L
RDK27 .685 J180M
RDK28 .708 J275M, J415M, K550M
RDK29 .761 J315L, J460X, J540L, J800X, K695L, K1100X
RDK30 .778 J180L
RDK31 .803 J275L, J415L, K550L
RDK32
RDK33
RDK34 1.014 J90S, J135S, K185S
RDK35 1.106 J90M, J135M, K185M
RDK36 1.175 J90L, J135L, K185L
RDK37 .524 J540S

AeroTech Delay Cheatsheet

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