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Nice packages!

I've got a question on how you determine your listed max-liftoff weight, and what constraints are used.

Is there an average body tube size you use as part of the calculation? Maybe I just keep thinking of edge cases like a fat lightweight rocket where it's at the liftoff weight for a long delay, but by nature will need a shorter delay despite meeting the listed weight on the package. ( I think I'm just having flashbacks to a flyer bringing up what was essentially a paper mache brick with a motor tube and stubby fins saying "But its under the manufacturer's liftoff weight limit!!")
 
"Maximum lift-off weight" is only a suggestion/recommendation based on years of experience, customer feedback and typical rocket construction and flight conditions. It is not meant to cover every possible vehicle and flight scenario, there are too many variables involved as you noted.
Nytrunner said:
Nice packages!

I've got a question on how you determine your listed max-liftoff weight, and what constraints are used.

Is there an average body tube size you use as part of the calculation? Maybe I just keep thinking of edge cases like a fat lightweight rocket where it's at the liftoff weight for a long delay, but by nature will need a shorter delay despite meeting the listed weight on the package. ( I think I'm just having flashbacks to a flyer bringing up what was essentially a paper mache brick with a motor tube and stubby fins saying "But its under the manufacturer's liftoff weight limit!!")
Click to expand...
 
It's interesting that the additional impulse in the Black Max D16 over the C12 comes as higher thrust, where the D20 white lightning has similar thrust to the C18, but a longer burn. These 18mm composite motors really are a nice complement to the BP motors and fill a niche in 18mm motors. Especially for all those slightly too heavy rockets with 18mm motor mounts. I think I, for one, am going to enjoy launching them. Very cool.
 
I recently purchased a couple 3-packs of F-24Ws and flew the first one today. No issues with the flight but I ran in to an anomaly with assembly. The dark blue delay spacer stuck out ~1/32" too far past the delay liner, which prevented the aft closure from reaching the threads. I trimmed the spacer to meet the liner, which is how the assembly directions showed, and it closed up just right.
 
Did you contact Juerg? I know that a shipment was successfully shipped to the UK recently.

We have a shipment heading to Juerg around the end of the month and he still has inventory for immediate delivery.

Reinhard said:
Are there any updates? I inquired with a vendor last week and he was not able to provide any details when the motors will become available.

Reinhard
Click to expand...
 
The delay spacer is supposed to protrude slightly, it compresses the delay O-ring when the closures are tightened.

SandiaMan said:
I recently purchased a couple 3-packs of F-24Ws and flew the first one today. No issues with the flight but I ran in to an anomaly with assembly. The dark blue delay spacer stuck out ~1/32" too far past the delay liner, which prevented the aft closure from reaching the threads. I trimmed the spacer to meet the liner, which is how the assembly directions showed, and it closed up just right.
Click to expand...
 
AeroTech said:
Did you contact Juerg? I know that a shipment was successfully shipped to the UK recently.

We have a shipment heading to Juerg around the end of the month and he still has inventory for immediate delivery.
Click to expand...

Thanks for the update.

No, I haven't been in contact with Jürg. Besides that he seems to be rather busy/hard to reach, I figured I'd better ask here, because there are others too that monitor this thread.

Reinhard
 
It used to be a straight single-use, but we had problems with both fiberglass and aluminum single-use cases. The current incarnation seems to be the most reliable version so far.

Walter Longburn said:
Have you ever considered making the K250 a DMS motor..? (possibly with the carbon fiber case) I wouldn't even care if it didn't have tracking smoke.
Click to expand...
 
AeroTech said:
The delay spacer is supposed to protrude slightly, it compresses the delay O-ring when the closures are tightened.
Click to expand...

The fact the OP referred specifically to the F24 kit caught my attention... so to that end, the fact is that
I too, purchased (recently) a pack of aerotech F24-4 reloads for my rms 24/40 case. What I found was a bit troublesome...

I found that the delay elements were NOT of the HDK-11 type. If they were, as specified by the HDK cross reference sheet, the delay length SHOULD have been 0.531" length with a BLACK delay spacer of .094" length.

What I have are delay elements of about 0.47' length, with a GREEN spacer that apparently is 0.14" length. THIS corresponds to a delay element from ab HDK-04 18mm kit with the spacer corresponding to an HDK-02 spacer.

Given that the HDK-12 kit has 0.625" long delays that will give the F24 a seven second delay, what *I* have in this package comes out to a TWO second delay because the delay I have is about 5/32" shorter than the HDK-12 delay.

The best part is that the delay+spacer that I have in this kit comes out to be about .01 -.015" shorter than the HDK-12 delay elements I have and that is *barely* noticeable.

IF the F24 4 second delay should be 0.531" then it's quite clear that the delay I have is much shorter and definitely WRONG.

I hope this sort of thing does NOT happen often...
 
DeltaVee said:
<snip>I too, purchased (recently) a pack of aerotech F24-4 reloads for my rms 24/40 case. What I found was a bit troublesome...

I found that the delay elements were NOT of the HDK-11 type. If they were, as specified by the HDK cross reference sheet, the delay length SHOULD have been 0.531" length with a BLACK delay spacer of .094" length.

What I have are delay elements of about 0.47' length, with a GREEN spacer that apparently is 0.14" length. THIS corresponds to a delay element from ab HDK-04 18mm kit with the spacer corresponding to an HDK-02 spacer.<snip>
Click to expand...
Huh, just looked at my sealed F24-4 pack (date code 05151705), and they have a green spacer as well. Same as a sealed E18-4 pack (01231803). The delay length for the F24-4 is about 0.47", and for the E18-4 is about 0.50". My previous 3-pack of E18-4 (just one left) also has a green spacer and 0.50" delay lengths - I don't recall that the delays were too short in flight. I've had this happen once before in 15+ years. I've contacted Aerotech Warranty.
 
Last edited:
I don’t know what happened in this specific case but part of our manufacturing process is to adjust the delay and spacer length in production based on lot testing. Propellant and delay burn rates vary from batch to batch and with different lots and suppliers of materials. Otherwise the delay times would be out of spec.

dpower said:
Huh, just looked at my sealed F24-4 pack (date code 05151705), and they have a green spacer as well. Same as a sealed E18-4 pack (01231803). The delay length for the F24-4 is about 0.47", and for the E18-4 is about 0.50". My previous 3-pack of E18-4 (just one left) also has a green spacer and 0.50" delay lengths - I don't recall that the delays were too short in flight. I've had this happen once before in 15+ years. I've contacted Aerotech Warranty.
Click to expand...
 
AeroTech said:
I don’t know what happened in this specific case but part of our manufacturing process is to adjust the delay and spacer length in production based on lot testing. Propellant and delay burn rates vary from batch to batch and with different lots and suppliers of materials. Otherwise the delay times would be out of spec.
Click to expand...
Thanks. How does that work when using a HDK? They have a fixed grain length, not associated with a propellant lot.
 
dpower said:
Thanks. How does that work when using a HDK? They have a fixed grain length, not associated with a propellant lot.
Click to expand...

I was just about to ask that VERY question... the explanation of variations in burn rate is completely reasonable and totally believable from what I know about mixing stuff together from concrete to cocktails with propellant somewhere in there... (not that *I'VE* ever engaged in the latter....)

But it does put the expectation of a 4 second delay for a given HDK 11 element used in an F24W motor somewhat dicey ground doesn't it?
 
DeltaVee said:
I was just about to ask that VERY question... the explanation of variations in burn rate is completely reasonable and totally believable from what I know about mixing stuff together from concrete to cocktails with propellant somewhere in there... (not that *I'VE* ever engaged in the latter....)

But it does put the expectation of a 4 second delay for a given HDK 11 element used in an F24W motor somewhat dicey ground doesn't it?
Click to expand...
Karl got back to me quickly, stating the same as post https://www.rocketryforum.com/threads/aerotech-open-thread.125657/post-2055931. The delays supplied with the motor will be +/- 1s. I appreciate the answer!

Regarding HDKs, he stated they're in compliance with a large percentage of the motors, so are not altered. So it seems YMMV more with HDKs than those supplied with the motor. I used these back before I was comfortable drilling delays, now I just get the longer delay packs and drill them with the 18-38 RMS DDT, or a drill bit with stop adjusted using a 1/32" graduated ruler.
 

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