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Need some help understanding terms

JB3DG

JB3DG

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southafrica
Hi guys

I'm working on a simulation of the Hydra 70mm rocket and need some cues on what's going on here.

bFSQfIb.png


As labeled, these are the aerodynamic roll moment coefficients. I'm guessing Clp is the roll damping moment provided by the fins and I am guessing 1/rad means that I multiply by the roll rate in radians/sec.
I'm a little confused about the Cldelta in that middle column, and the Cl Total values.

To expand a little on what happens, there is a clockwise roll torque from the fluted rocket nozzle motor that spins up to around 600-2400 RPM in the first 1.1 seconds of flight. However there is a sharp reversal from the fins as soon as the motor firing ends, as illustrated by this chart.

IwyAGg8.png


Can someone expound a little how I would sum up all the aerodynamic roll coefficients and what are they affected by beyond the standard 1/2*Rho*V^2*Sref*D?

Thanks
JB
 
It depends on what simulator you are working on. All those coefficients are in the MSFS legacy flight model as they are in FSX and P3D, but they are all not used in the Modern model or to be exact they are generated internally. But the internal generation is heavily based on a simple subsonic airplane.
Their main use in a missile is to create inertial stability so it has a predictable flight path. You can adjust pitch, roll and yaw stability in MSFS through the flight tuning section of the flight_model.cfg.
Roy
 
In my case, I'm using P3D's PDK to create an external flight model (the sim doesn't fight back that way) so I'm having to code everything myself. So this is more to understand the math behind things rather than how to do it in a particular sim.
 
Cl total is the total rolling moment coefficient. It is negative therefore it tends to reduce roll and it varies with Mach number
Cldelta is the roll moment component generated by the motor which is positive therefore increases roll. Varies with Mach Number
Clp is, as you said, roll moment component generated by the fins which is negative and varies with Mach number.
I believe the fin roll would be subject to the "standard" effect, but that generates a force and you are dealing with moments/stability here.
You could study the MSFS flight model physics given in the SDK, but I find it tough going. Something like "Introduction to Aircraft Flight Mechanics" by Thomas Yechout is a better read.
Roy
 
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