MESOS Flight to 293K ft - RASAero II Prediction 290K ft

[Chuck Rogers]

They are both work arounds to try to get better results from existing software. You can adjust the surface roughness to change shear friction drag to better match measured performance, but shear friction drag could be modeled perfectly and the "error" could all be in the supersonic wave drag model used by the program.

Alan:

Actually, that is not the case. This is one of the reasons I use multiple sources of data to check out the aerodynamic models in the RASAero II software.

Comparing the RASAero II Flight Simulation apogee altitude with flight data is the ultimate comparison. But I also compare RASAero II with wind tunnel data and free-flight model data from NACA and NASA references and other sources.

On the RASAero web site ( www.rasaero.com ) on the Home Page on the left-hand side you can select "Comparisons with Wind Tunnel Data" and see RASAero II comparisons with NACA and NASA wind tunnel data and free-flight model data. Here you can check whether I'm getting the wave drag and the friction drag correct for smooth wind tunnel models. The free-flight models are a great way to also check the base drag, as there are no sting effects from the installation of the sting at the base of the model, the model is literally in free-flight. Some examples are below.













With the carefully controlled wind tunnel tests, and the free-flight model tests, I can check out the wave drag models. This helps assure that the wave drag models are correct before I start the comparisons with flight data.

Note that for comparison with wind tunnel data, you have to have the same Reynolds numbers as the wind tunnel tests. The default for the RASAero II Aero Plots is to plot the aero data at sea level, in the RASero II Flight Simulation Reynolds number is automatically varied during the flight. For comparisons with wind tunnel data you use the Mach-Alt feature in RASAero II, see Pages 84-86 in the RASAero II Users Manual.


Charles E. (Chuck) Rogers
Rogers Aeroscience

 

[jsdemar]

John, can you elaborate a little more on how to calculate the resonate roll rate? Or point me to a reference. I would like to learn how to do it. I always assumed it is a fairly complex calculation.

We could start a new topic in the research area of the forum to discuss dynamic stability of high-performance flights.

In general, to find the resonant roll rate, calculate the transverse moment of inertia (pitch axis, I_t, about the CG) and the axial moment of inertia (roll axis, I_r).

p_r ~= sqrt( µ / (I_t - I_r) ) in radians/sec.

µ is a dynamic viscosity factor, like a damping coefficient. As the rocket gets smaller in diameter, or air is thinner, resonant roll rate goes up. (I don't remember the actual equation and all the factors).

The transverse MoI will be larger than the axial MoI for most things that look like a rocket. So, the resonance will get lower as the difference gets larger (long rocket or a light rocket with heavy masses on the ends, or other mind exercises).

I'll try to find a reference to get all the factors and units correct. Somewhere I have a cheat sheet on this.

 

[Chuck Rogers]

To All:

Updated Charts for the RASAero II Comparison with MESOS 293K Flight Data (Rev B) have been added to the RASAero web site on the Home Page ( www.rasaero.com ) and on the Comparisons with Flight Data Page. All of the charts were included in different posts in this Thread, they are just rearranged in terms of the order of the charts to better reflect the progression of the analysis.


Charles E. (Chuck) Rogers
Rogers Aeroscience