CTI delay times?

[Spurkey]

With an end-lit motor (CTI or AT) when does one start counting the delay time - from when the propellant burns out (similar to Estes BP motors) or from when the propellant is first lit? I've always calculated my CTI delay times thinking that the delay starts burning once the propellant burns out, which is also how RockSim appears to do it. At my last launch however the RI doing my inspection told me that this was incorrect, that because the propellant is lit from the forward end nearest the delay element the delay element gets lit immediately. With a BP motor that's lit at the aft end, you must burn through all the BP in order to get to the delay element.

Are RockSim and I wrong?

 

[CarVac]

The delay grain DOES start burning the instant the motor is lit (or rather, should), but the time given for the delay is from burnout. That is why Aerotech motors come with different thickness delay grains for the same delay time on different motors.

 

[JordanT]

The delay grain DOES start burning the instant the motor is lit (or rather, should), but the time given for the delay is from burnout. That is why Aerotech motors come with different thickness delay grains for the same delay time on different motors.

Is this true for CTI as well? I ask because we had this discussion at my last launch too, but we didn't have a definitive answer at the time (I know, we should ask Jeroen!).

I'll be honest - I rarely care. If I'm off by the burn time duration of the small motors I fly, it won't make a real difference in my deploy success or failure. But it would be nice to know anyway!

 

[Wingarcher]

Is this true for CTI as well?

It's true for all core burning motors of any type.

N

 

[Jeroen_at_CTI]

Delay is defined from motor burnout to ejection charge firing. Not from ignition.

 

[sodmeister]

Delay is defined from motor burnout to ejection charge firing. Not from ignition.

Could you imagine the other way around :y: That would be a lot of ZIPPERS and shredded chutes !


Paul t

 

[CarVac]

I used to think it was the other way around, until I flew a G54 (the longest burning motor I had flown up until then), and my ejection was 3 seconds late.

 

[Spurkey]

Delay is defined from motor burnout to ejection charge firing. Not from ignition.

Answers don't get more definitive than that. Thanks for the replies everyone.

Jeroen: perhaps this information could be added to your FAQ? I don't think it'd need a whole entry, the first sentence from your above post could just be inserted somewhere into https://pro38.com/faqs.php#delayadjust

 

[sodmeister]

I used to think it was the other way around, until I flew a G54 (the longest burning motor I had flown up until then), and my ejection was 3 seconds late.

Last time I flew my G-Force on an AT S/U G40-4W.......well the last time ,it smashed into the ground and 2 seconds later .....POOF :eyeroll:

So I guess it was more like 7-9 seconds.Now that I think of it ,that`s how I lost my ARCAS ,except there was no POOF at all

Paul T

 

[Sparkytfl]

That nose cone looks like an ice cream cone.

 

[tibadoe]

I had the same question about ejection timing since I haven't flown a high power motor. Glad you brought it up. I finally did open up my L1 motor and got to read through the directions. Now I know.