If you had to choose one - Ejection, before or after optimal delay?

[overklock]

I'm sure this has been discussed ad-nauseum, but hear me out.

Looking at my OR simulations, my optimal delay is 7.8 seconds, I have a 12 second CTI motor, and a delay drilling tool that goes in increments of -2. It's either a delay of 7 seconds, or 9.

So, what do you folks prefer? Early deployment to account for weather cocking and other variables? Or a slightly late deployment, or as I've heard others call it here "redneck dual deployment".

Is it better to have the rocket in a vertical state while deploying (still ascending)? Or horizontal (past apogee)?

Update, I designed a 3D printable 1 second delay spacer for use with the ProDAT, feel free to use.

https://www.printables.com/model/344900-cti-1-second-delay-spacer-tool

 

[Hobie1dog]

horizontal with a 9 sec delay

 

[overklock]

horizontal with a 9 sec delay

Interesting, even if it's descending at that point? Here's the two sims btw:

 

[dhbarr]

Use a half-click thickness spacer to get ever-so-slightly-closer to 8s? This delay can be plus or minus up to about 1.5s.

 

[Hobie1dog]

I take all simulation programs as being just a guideline, not gospel. I'd rather have the rocket pointing down so that the nose cone is pointing down as if it will be easy to naturally fall off.

 

[MALBAR 70]

I'll usually go with the slightly longer delay as well. I'd rather a small zipper than a shredded 'chute.

 

[neil_w]

Why would a deployment 1 second early shred a chute?

 

[overklock]

Use a half-click thickness spacer to hit every-so-slightly-closer to 8s? This delay can be plus or minus up to about 1.5s.

I believe this is possible with the Aerotech delay adjustment tool, but not the CTI ProDat

 

[Hobie1dog]

remember the old saying, " Over-analysis leads to paralysis" Trying to hit a 1/2 second delay time is rather dreaming, as there's too much variance in manufacturing of these motors. There is a post on here describing how the delay time was 4 seconds off, and it happened twice to the guy.

 

[overklock]

remember the old saying, " Over-analysis leads to paralysis" Trying to hit a 1/2 second delay time is rather dreaming, as there's too much variance in manufacturing of these motors. There is a post on here describing how the delay time was 4 seconds off, and it happened twice to the guy.

Four seconds is a hellova difference to be off.

Suppose you can crunch the numbers all you want, but you're still at the mercy of variances in motor manufacturing.

 

[David Schwantz]

I guess I 've missed something along the line. You say you delay is 12 seconds. And the tool will remove material in -2 seconds amount. To me that comes out to either 10, 8, or 6 seconds of delay. I vote for using 8 seconds. .2 seconds of delay difference from your sim will not even be noticed.

 

[Handeman]

Motor ejection is not an exact science. You can drive yourself crazy trying to get it exact, and then it still won't work right.

If you really want it close, electronic ejection will get you close to apogee every time.

 

[boatgeek]

I usually default to the shorter delay (especially if the OR sim hasn't been tuned to actual altitudes) because virtually every way the sim can be wrong (rougher surface, weathercocking, etc.) shortens the optimum delay. If it's dead on between two notches, I'll either borrow the TARC team's auxiliary spacer to take off one second or do it redneck and drill the delay to the longer delay and then switch to the shorter delay setting and take a turn or two to shave off just a hair more.

 

[overklock]

I guess I 've missed something along the line. You say you delay is 12 seconds. And the tool will remove material in -2 seconds amount. To me that comes out to either 10, 8, or 6 seconds of delay. I vote for using 8 seconds. .2 seconds of delay difference from your sim will not even be noticed.

It starts at 3, and goes in 2 second increments, so -3, -5 etc.

 

[overklock]

Motor ejection is not an exact science. You can drive yourself crazy trying to get it exact, and then it still won't work right.

If you really want it close, electronic ejection will get you close to apogee every time.

That will be my next step, for now, just want to get my level 1.

 

[overklock]

For anyone who's as obsessive as I am, I just designed a 3d printable 1 second delay spacer for the CTI ProDAT.

It measure 1/32" per the usual 1 second rule.

I've attached this at the top of the page.

 

[Handeman]

That will be my next step, for now, just want to get my level 1.

Understood, but there is no reason you can't play with altimeters and electronic ejection with MPR too.

Good luck on the cert.

 

[Banzai88]

I've always opted for the 'slightly early' since you can reasonably predict the orientation of the rocket (pointing up or not quite pointing down yet) and slowing down when the nose pops. That way the laundry is sent into a path that is clear of rocket parts and will aid in slowing the rocket down if it hasn't already.

With the 'slightly late' option, the rocket is often pointed down enough that you risk the body of the rocket falling through the deploying laundry and while the whole assembly is post-apogee and gaining speed toward the ground. Too risky for me, and I've seen more than a few go through just this very thing and end up with tangled recovery gear.

 

[ThirstyBarbarian]

I usually default to the shorter delay (especially if the OR sim hasn't been tuned to actual altitudes) because virtually every way the sim can be wrong (rougher surface, weathercocking, etc.) shortens the optimum delay. If it's dead on between two notches, I'll either borrow the TARC team's auxiliary spacer to take off one second or do it redneck and drill the delay to the longer delay and then switch to the shorter delay setting and take a turn or two to shave off just a hair more.

This is exactly what I do too. I opt for the shorter delay because there are a lot of ways for the rocket not to reach the projected altitude. And if I really want to get the delay closer, I will do what you do — set the drill for the longer delay and drill that out, then set the drill to the shorter delay, and just drill a tiny bit more without hitting the stop.

Aesthetically speaking, I prefer the rocket to reach apogee and arc over. But if the optimal delay is right in the middle, and I’m concerned about damage, I opt for shorter.

And as others have said, the delays are never exact. They can vary a lot sometimes.

 

[overklock]

This is exactly what I do too. I opt for the shorter delay because there are a lot of ways for the rocket not to reach the projected altitude. And if I really want to get the delay closer, I will do what you do — set the drill for the longer delay and drill that out, then set the drill to the shorter delay, and just drill a tiny bit more without hitting the stop.

Aesthetically speaking, I prefer the rocket to reach apogee and arc over. But if the optimal delay is right in the middle, and I’m concerned about damage, I opt for shorter.

And as others have said, the delays are never exact. They can vary a lot sometimes.

Setting it for the longer delay, then setting it to shorter is actually really smart. I wound up designing a 3d printable file that should work in one second increments, but if for whatever reason it doesn't, I'll do this method.

 

[sriegel]

Update, I designed a 3D printable 1 second delay spacer for use with the ProDAT, feel free to use.

https://www.printables.com/model/344900-cti-1-second-delay-spacer-tool

I don't have a printer but would love one for both the 38 and 54mm drills if you would be willing to print and ship them!

 

[overklock]

I don't have a printer but would love one for both the 38 and 54mm drills if you would be willing to print and ship them!

The prodat 29 is the same as the prodat 38, so that shouldn't be an issue, PM me and I can get one shipped to you.

Unfortunately I do not have a 54mm prodat tool to do the precise measurements needed to create this. I can look into ordering one and hit you up afterwards if you'd like.

Just a reminder that obviously I haven't tested this in the field but I did just print it and it fits perfectly into the prodat 29/38.

 

[Banzai88]

I don't have a printer but would love one for both the 38 and 54mm drills if you would be willing to print and ship them!

The 54mm tool is a totally different design and has individual second increments on it.

https://www.apogeerockets.com/Rocket_Motors/Cesaroni_Accessories/Pro-54_Delay_Adjustment_Tool

 

[dhbarr]

The prodat 29 is the same as the prodat 38, so that shouldn't be an issue, PM me and I can get one shipped to you.

Unfortunately I do not have a 54mm prodat tool to do the precise measurements needed to create this. I can look into ordering one and hit you up afterwards if you'd like.

Just a reminder that obviously I haven't tested this in the field but I did just print it and it fits perfectly into the prodat 29/38.

I don't have mine handy, but wouldn't a random washer from the hardware store get pretty close?

 

[overklock]

I don't have mine handy, but wouldn't a random washer from the hardware store get pretty close?

As Banzai88 pointed out, the delay tool for the 54mm has single seconds on it.

For the ProDAT 29/38, it's not like the Aerotech tool. A washer has nowhere to go.

https://www.apogeerockets.com/Rocket_Motors/Cesaroni_Accessories/Pro-38_Delay_Adjustment_Tool

 

[Steve Shannon]

It’s really a bogus question because the delay just isn’t that accurate and if you build the rocket well it just doesn’t matter, but, theoretically (like all bar debates) and assuming the same interval before or after apogee: Before.
Why? Your rocket is decelerating and it takes time for your chute to be ejected and to open.
Let’s say you have to choose one second before or one second after.

If I were able to time ejection to one second before and it takes half a second to get the chute out and unfurled, now I’m only a half second before apogee and my rocket is going very slow.
If I choose one second afterwards, now my rocket is traveling at the velocity resulting from falling for one and a half seconds. That’s faster.
But really, as long as you build well and use a high quality chute, either way should be fine.

 

[overklock]

It’s really a bogus question because the delay just isn’t that accurate and if you build the rocket well it just doesn’t matter, but, theoretically (like all bar debates) and assuming the same interval before or after apogee: Before.
Why? Your rocket is decelerating and it takes time for your chute to be ejected and to open.
Let’s say you have to choose one second before or one second after.

If I were able to time ejection to one second before and it takes half a second to get the chute out and unfurled, now I’m only a half second before apogee and my rocket is going very slow.
If I choose one second afterwards, now my rocket is traveling at the velocity resulting from falling for one and a half seconds. That’s faster.
But really, as long as you build well and use a high quality chute, either way should be fine.

That’s fair enough point on the actual delay of the parachute deployment.

 

[dhbarr]

As Banzai88 pointed out, the delay tool for the 54mm has single seconds on it.

For the ProDAT 29/38, it's not like the Aerotech tool. A washer has nowhere to go.

https://www.apogeerockets.com/Rocket_Motors/Cesaroni_Accessories/Pro-38_Delay_Adjustment_Tool

If a drill bit sticks out of it somewhere, that's where the washer would go.

 

[overklock]

If a drill bit sticks out of it somewhere, that's where the washer would go.

That’s actually a great point. Didn’t really consider placing it underneath.

Well, either way, there’s another option available now as well

 

[wsume99]

For anyone who's as obsessive as I am, I just designed a 3d printable 1 second delay spacer for the CTI ProDAT.

It measure 1/32" per the usual 1 second rule.

I've attached this at the top of the page.

This is what I did for the aerotech delay drilling tool. Shortest print time I've ever had.