Acceptable Streamer Recovery Speed?

So right now I am building a 18mm version of my Mindi P Man-527... it will be on streamer recovery but no matter what motor (other then c6-7) i sim it with it comes out to have a 48-110mph recovery deployment speed...

ive simmed it on

b4-4/53.5mph
b6-4/56.1mph
c6-3/110 mph
c6-5/48.6 mph
c6-7/11.6


I would like to fly it on the c6-5 if that would be an acceptable deployment speed... i don't mind the c6-7 though... but my point is what is an "ok" range for deployment speed when doing streamer recovery? obviously not 110 mph... if i am assuming this right all of the deployment speeds for this rocket still have the rocket ascending if a 7 second delay brings it down to 11mph

If you are using OpenRocket, plot the flight (Vertical Motion vs Time) and see where deployment is taking place. Might have to go with B4-6 or B6-6.... (they still make those, right?)

When you design a rocket for a specific total impulse and thrust, you have to determine what the optimum delay is, and that's the delay you select unless you want to worry about having a zipper or a strip happen on every flight.

You need to run the sim without a deployment, or a long deployment, to determine the time to apogee. The time to apogee minus the motor burn time is the ideal delay time. Once you know this, you choose the delay that is closest to the time predicted in your simulation.

Since the actual time to apogee probably does not exactly match the available delay times, how far off are you, and how far off can you be before there is a problem. Near apogee, gravity determines the rocket velocity. The acceleration of gravity is 32 feet per second per second. If you eject 1 second before apogee or 1 second after, your rocket is traveling at 32 feet per second assuming the launch is vertical. That's about 20 mph. 2 seconds early or late results in a speed of 64 feet per second or about 40 mph. etc. In most cases you can select a delay that gets you within 1 second of apogee for a vertical flight which is 32 fps or about 20 mph.

The allowable delay error in B and C Estes motors is +/- 1.5 seconds. This would put the expected maximum time off apogee at 2.5 seconds, which is 80 feet per seconds or about 50 mph. If you are off by one delay increment, the worst case deployment velocity would be (80 + 64) = 146 fps or about 100 mph. That's possibly above the zipper or strip speed.

Hope that's useful.

Bob

I don't know if there is a rule of thumb for all rockets. Each rocket will have it's own limit.

If you have ever had the window of your car rolled down at different speeds, you are aware of the force of air flow. So we can perhaps make some general observations.

Green: Deployment speed <= 10 mph
Yellow: Deployment speed >10 mph and <=20 mph
Red: Deployment speed > 20 mph

And maybe "Plaid" for deployment speeds above Mach 1.

Keep in mind that these are just broad generalizations. YMMV.

Greg