OpenRocket question?

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lucifer911
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OpenRocket question?

Postby lucifer911 » Wed Sep 02, 2015 9:26 pm

Hi guys,

I have been using the Java Openrocket program to conduct simulations to see how high my rocket would have went if I used the correct motor with the 5 second ejection charge.
I made the mistake of using a C6-0 booster rocket for the launch which caused my nosecone to snap. So I wanted to do the sim to determine the altitude difference had I have used the C6-5 motor.

I am using a 56er low powered rocket on ausrocketry.

For some strange reason there is almost no altitude difference when using C6-0 and C6-5 motors.
Does this sound correct? on the C6-0 motor it is designed as a first stage booster rocket which would eject gases to ignite the second stage. Surely this would have a negative impact on a rocket if used as a single stage motor vs a motor with an ejection charge?

here are 2 screen shots..
Attachments
OpenRocket1.JPG
OpenRocket2.JPG

Lister
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Re: OpenRocket question?

Postby Lister » Wed Sep 02, 2015 9:34 pm

here is the data i just got from the same motors.. i changed the ejection time to 5 seconds manually as is required with most motors.

p.s you need to add a parachute to your design to get an accurate ground hit speed... looking for under 25fps
Attachments
Untitled-2 copy.jpg
Untitled-1 copy.jpg
Last edited by Lister on Wed Sep 02, 2015 9:39 pm, edited 1 time in total.

vance2loud
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Re: OpenRocket question?

Postby vance2loud » Wed Sep 02, 2015 9:36 pm

Add a parachute to your simulation. Openrocket need something to happen at ejection. In the parachute section you can set it to eject at motor eject or at other times during your flight, so for your simulation set it for motor eject of this stage.
Then you should see a difference.
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lucifer911
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Re: OpenRocket question?

Postby lucifer911 » Wed Sep 02, 2015 9:50 pm

this looks better..
sorry didn't realise OpenRocket would need the parachute for it to detect the altitude difference when using difference ejection charge times..
Attachments
OpenRocket3.JPG

Lister
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Re: OpenRocket question?

Postby Lister » Wed Sep 02, 2015 9:56 pm

also convert it to imperial measurements for altitude etc as all things in the air around the world are in imperial and thats what most people read things in.

also add the payload bay and altimeter to your sim :)

Lamp
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Re: OpenRocket question?

Postby Lamp » Thu Sep 03, 2015 3:47 pm

lucifer911 wrote:For some strange reason there is almost no altitude difference when using C6-0 and C6-5 motors.
Does this sound correct? on the C6-0 motor it is designed as a first stage booster rocket which would eject gases to ignite the second stage. Surely this would have a negative impact on a rocket if used as a single stage motor vs a motor with an ejection charge?


I suspect the reason for this is the rocket has no chute in either case. Open rocket would not differentiate the difference in drag from having a nosecone in place compared to not having or trailing the nose cone on a shockchord during coasting so the end result is the sim of both launches would have apogee at around the same altitude.

When you put a parachute and shock chord in, it calculates the drag from the chute at the the point of ejection. The C6-0 sim would give you a high speed deployment warning and the drag from the chute would be calculated from motor burnout, meaning a much reduced simulated altitude. If you change the motor designation to C6 (none) with a chute, it will sim a fully ballistic flight because there is no deployment and apogee will again be almost the same as the C6-5 sim with a deployed chute (landing velocity will be vastly different though!).
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lucifer911
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Re: OpenRocket question?

Postby lucifer911 » Thu Sep 03, 2015 4:03 pm

Lamp wrote:
lucifer911 wrote:For some strange reason there is almost no altitude difference when using C6-0 and C6-5 motors.
Does this sound correct? on the C6-0 motor it is designed as a first stage booster rocket which would eject gases to ignite the second stage. Surely this would have a negative impact on a rocket if used as a single stage motor vs a motor with an ejection charge?


I suspect the reason for this is the rocket has no chute in either case. Open rocket would not differentiate the difference in drag from having a nosecone in place compared to not having or trailing the nose cone on a shockchord during coasting so the end result is the sim of both launches would have apogee at around the same altitude.

When you put a parachute and shock chord in, it calculates the drag from the chute at the the point of ejection. The C6-0 sim would give you a high speed deployment warning and the drag from the chute would be calculated from motor burnout, meaning a much reduced simulated altitude. If you change the motor designation to C6 (none) with a chute, it will sim a fully ballistic flight because there is no deployment and apogee will again be almost the same as the C6-5 sim with a deployed chute (landing velocity will be vastly different though!).


yep here is my video with the C6-0 motor.. the parachute ejected but this probably happened while the rocket was travelling at 100m/s which caused the shockcord to rip through the shoulder of the nosecone causing the nosecone to detach from the body. I have watched this video and tried to estimate the apogee of the rocket. Maybe it did fly to about 90m.. I don't think this was a 150m altitude launch when I watch this video over and over again. By the way I made the mistake when using a booster as a single stage.. I will not use this motor again as a single stage. (just a silly noob mistake)

[youtube]/watch?v=zTcKJQn5TeM[/youtube]


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