Pitch rates in OR simulations

[Dane Ronnow]

I've got a question about pitch rate in OR simulations. (I searched the forum for info on this, but couldn't find anything that addressed this specifically. Forgive me if I missed it somewhere.)

I'm building a 2.6 inch MPR, designed to fly on three different Aerotech composites—F67, G74 and G80. The rocket is 37.5 inches in length, weighs just over 21 oz. without motors, and has the following calibers of stability with those motors:

F67 - 1.65
G74 - 1.61
G80 - 1.41

The simulation pitch rates are essentially flat in zero wind. With 5 mph of wind, pitch rates are between 12 and 15 degrees/sec (depending on motor used) and twice that with 10 mph wind.

Are those pitch rates excessive? Or are they normal for those wind speeds?

Attached are screen captures of simulation plots for each motor, in 5 mph wind.

Thanks much for any advice I can get.

 

[H. Craig Miller]

Posting the OpenRocket design file may allow others to provide additional information in answer to your questions.

 

[Dane Ronnow]

Sorry, I should have done that to begin with.

 

[SpaceManMat]

That doesn’t look good to me. One thing to be careful of is that stability is dynamic over the flight. Suggest you post the graph stability vs time

 

[Dane Ronnow]

Below are plots for Stability vs. Time in zero, 5 and 10 mph wind, all with the G80 motor. The fourth plot is 5 mph with pitch rate plotted.




For the sake of comparison, I increased the fin area to see if the pitch rate decreased. It didn't. It increased from 12 degrees/sec (at the first deviation) to a little over 15 degrees. This tells me the oscillations in pitch is due to the wind acting against the fins, not any instability of the rocket.

I'm thinking now that what appears to be wildly fluctuating pitch deviations on the graph is simply the angle of attack changing with the wind, followed by the restorative force bringing it back past zero to the opposite side, and so on, dampening the change in AOA as the velocity increases.

 

[gtg738w]

I'm thinking now that what appears to be wildly fluctuating pitch deviations on the graph is simply the angle of attack changing with the wind, followed by the restorative force bringing it back past zero to the opposite side, and so on, dampening the change in AOA as the velocity increases.

Exactly, when it leaves the rod, it is at an angle of attack relative to the wind. The pitch rate is the fins trying to correct that. You can see it in real data too:

 

[Dane Ronnow]

Exactly, when it leaves the rod, it is at an angle of attack relative to the wind. The pitch rate is the fins trying to correct that.

Thanks, Russ. I appreciate your input. Does FlightSketch give you that tilt data?