Open Rocket Errors ( recovery device deployment at high speed)

Hello Everyone. I build rocket in open rocket but I have some problems when run similations. I updated my .org fiel. Can anyone help me?
Problems are :
1) Recovery device deployment at high speed
2)openrocket discontinuity in rocket body diameter
These are teacher's conditions :

• Within the content of AST 312 Rocket Propulsion project, each of the student groups will design a multi-stage amateur rocket which can carry 5 kg payload to 8000 m altitude.
• After reaching the target altitude nose cone of the rocket should be detached from the fuselage and payload should be released together with its own parachute. Both of the payload and rest of the rocket assembly (Nose + Fuselage of the rocket) should also be safely landed using suitable independent parachute systems.
• The payload’s vertical descent velocity should be less than 2 m/s and the rocket assembly’s vertical descent speed should be less than 7 m/s.

• Stability of the rocket should be between 1.5 – 2.2.

 

1. That warning could be inconsequential, but it probably means that your deployment is not set to "apogee." I don't have OpenRocket with me to check, so take a lookk at that.
2. Body diameter discontinuity means you have two adjoining tubes that are not the same diameter. Check your inside and outside diameters. Even small discrepancies, like one is 4.01 and one is 4.0, will produce this error.

 

I disregard the "discontinuity in rocket body diameter" if it's obvious where the location is. My Lifting Rocket has a F1 style thrust chamber, which open rocket deems a discontinuity.

High Speed Recovery Device Deployment is usually due to selecting the wrong motor delay. Deployment is either way before apogee, or way after. Look at the flight plot and select a delay that initiates deployment as close to apogee as possible. The summary will tell you the optimal delay.

 

Recovery device deployed at high speed often occurs when you have deployment while the rocket motor is still burning or if descent rate is over it's preset of something like 50fps or something. Try a larger drogue to see if that goes away, that usually cures that 'warning'.

 

Make sure your drogue (if you have one) or your main chute is set to deploy at apogee. That will eliminate the high speed deployment warning. Then use the information shown by lakeRoadster to find the best delay if you are using motor ejection.


Tony

 

I took a quick look and don't see the where the discontinuity error is occurring. Sometimes that error is hard to find, but also it usually doesn't matter if the discontinuity is small.

I would be more concerned about those fins surviving a supersonic flight and/or landing.

Note that your materials are not set properly, so the calculated rocket weight is not accurate (this will affect your simulations). For instance, the front fins are listed as cardboard, at the default thickness of .118". I'm guessing that neither of those is correct.

 

Dear Onur

By now, you have probably flown the rocket. From the file you provided, which I have looked at now, I could not detect the discontinuity. As noted above, if you set the deployment to apogee, most of the issues regarding high speed deployment will disappear.

Also, to optimise the rocket, you may wish to change the fin shape and dimensions to maximise the likelihood of a successful flight. Usually one calibre fin span - the diameter of the rocket body is about right, and for good measure a little longer than you have them will minimise the stresses on the fins.

Good luck with your flight.