OpenRocket Engine Delay Question

[Joe Mac]

Happy New Year, Rocket Sages!

I have been using OpenRocket for the last few days for the FIRST time to create a sim of a modified Estes Saturn V (2157) with a 5 engine cluster and the program is SO awesome that I am already almost finished (just double checking all measurements for accuracy and "touching up" left to do. I have tried using the trial version of RockSim a couple of times (once recently), but the GUI is not nearly as intuitive for me as OR is. Suffice it to say that I am absolutely thrilled with OR and my only hope it is accurate with launch simulations with differing engines combinations to about 10% or so. If this proves to be the case, then I just got the best Christmas present for myself than I have in many, many years (for free)!

So, the "problem" that I am experiencing is this:

When I sim any of the 5 engines as one with a "0" delay, it appears that OR considers the zero delay as an EJECTION event, causing the program to report a highly unsafe parachute deployment speed (as the others with a true ejection delay are still under power or coasting).

My understanding is that Estes "0" delay engines (mainly designed for staging) do not have an ejection charge at all, but rather just "burn through" to ignite the next stage engine.

I definitely want redundancy for ejection purposes in case one or more of the engines in the cluster do not ignite, so I would not use say a 4 "0" + only one with an ejection charge cluster configuration. But I do have quite a few more "0" engines on hand than any other type, so would like to use up one or two with each five-clustered launch.

There is little doubt that even one ejection charge with deploy the chutes, but I am concerned that if FIVE charges go off at once that it my cause a catastrophic tube failure so it would be great to start with a few launches of only 3 (or 4 max) with ejection charges.

Am I missing something, or is this an OR abnormality? It would be great to successfully sim different configurations using zero-delayed engines.

If any of you sages can help, I'd appreciate it!

BTW, this is why I have recently tried to use RockSim again... to check to see if it allows "0" delay engines to be used in a cluster without "thinking" that there was an ejection charge too, but it was way too cumbersome to recreate the Saturn V compared to OR!

I have successfully sim'd many, many engine combinations (about 10) in OR with ejection occurring at less than 5 m/s velocity, so I would think substituting a "0" delay engine or two would result in an early failure due to premature ejection (not pun intended).

Thanks for you help ahead of time!

Joe Mac

 

[kruland]

Joe,

OpenRocket does interpret 0 delay as ejection charge. In my experience a booster motor burn through can generate enough pressure to eject a parachute. I've only experienced this in small diameter rockets though. On a rocket as complex as the Saturn V, I would not risk it by trying to use up some booster motors.

Kevin

 

[Joe Mac]

Kevin,

Darn, I was afraid that you were going to say that. :sad: Thanks for the super-quick reply though!

I have a super-large baffle built into the design (6" long and, of course, almost 4" wide). Combined with the rest of the voluminous space in there, I would think it unlikely the only one "0" would pop the top, but guess it could.

Is there anyway to override that setting in OR just to see the altitude stats? I can choose "none" on Estes "E" engines and it works fine, but not for "D's" or any other.

Thanks again!

Joe Mac

 

[kruland]

Joe,

If you specify a delay of 'P' (for plugged) then OR will not interpret burn out as an ejection event.

Kevin

 

[Joe Mac]

Kevin,

One more thing that I just thought of that I think would mitigate an ejection event if I were to use an "0" delay engine is that I have modded the rocket to that an Altimeter Two will work in it without issue... that is, I have drilled several 1/8" diameter holes near base of the "cone" that will allow the outside air pressure to equalize inside the rocket. This should definitely help to vent any pressure caused by a zero delay engine.

Joe Mac

 

[kruland]

Joe,

I'm sorry to hedge so, but I don't know.

Kevin

Kevin,

One more thing that I just thought of that I think would mitigate an ejection event if I were to use an "0" delay engine is that I have modded the rocket to that an Altimeter Two will work in it without issue... that is, I have drilled several 1/8" diameter holes near base of the "cone" that will allow the outside air pressure to equalize inside the rocket. This should definitely help to vent any pressure caused by a zero delay engine.

Joe Mac

 

[Joe Mac]

Kevin,

Sure enough! I think that is why I get great sim results when using a cluster with some plugged E9's, but OR doesn't give you that option for most (if not all) engine size choices, such as "D". That's exactly what made my realize that it was figuring "0" delays as an ejection charge, because it doesn't with E's "plugged" and sims those just great.

Joe Mac

 

[kruland]

Joe,

Just type P in the delay box. It will take it for any motor. You can even make an Estes A8-14 if you want.

Kevin,

Sure enough! I think that is why I get great sim results when using a cluster with some plugged E9's, but OR doesn't give you that option for most (if not all) engine size choices, such as "D". That's exactly what made my realize that it was figuring "0" delays as an ejection charge, because it doesn't with E's "plugged" and sims those just great.

Joe Mac

 

[Joe Mac]

Kevin-

U R awesome, thanks!

Joe Mac

 

[Joe Mac]

Kevin-

I just tried that a few times... it takes the P, but reverts to 0 when simulated. Perhaps because OR "knows" there are no plugged versions of that type...?

U R still awesome though brother, thanks for your time on this.

Joe Mac

 

[T-Rex]

Instead of 'P' try typing 'None' Just tried it and it allowed it on a 1/4A3-T motor

 

[kitbasher99]

Why not make a few of the engines have a longer delay than what you are planning on using. That way OR won't think there was an early ejection charge and give you a full flight.The longer delay engines would fire after primary deployment has occurred and act like a redundant ejection charge.

 

[scsager]

For what it's worth... In the real rocket - your idea to use some -0 motors is fine. In the simulation, the rocket won't be over pressurized if all motors have the same ejection.

The answer you are looking for is "None". Type "None" in the delay drop down for a motor that has no ejection.

 

[Joe Mac]

Thanks to all of you, I really appreciate the help! I ran the sims using "none" and OR entered them as a P for plugged and it all worked. I do wonder why the Estes E engine delay pull-down has None in the list, but the others don't though...
Scott- Your right on target with the extra long delays... I had already done a few of them like that and they worked fine, which was another reason that I thought using zero delays should work OK.

Thanks again y'all!

Joe Mac

 

[kruland]

Man, you'd think I'd know how that software works! Thanks for the correction.

Instead of 'P' try typing 'None' Just tried it and it allowed it on a 1/4A3-T motor