That's awesome Semmel. I, too, caught the second stage throttle in your previous graph you made but did not comment on it. Your new graph is clearly superior as I did not notice the fairing separation at all. Great work!When I saw the acceleration curves the other day, it made me wonder if we could suss out a more definite mass of the fairing and second stage based on the change of acceleration from staging events.
C_0 = 0.07 # drag constant value at speed far below mach1
The most probable is that our numbers are wrong, but is it possible that the throttle is decrease before MaxQ ?
Quote from: Space Opera on 08/28/2016 01:45 pmThe most probable is that our numbers are wrong, but is it possible that the throttle is decrease before MaxQ ? I think they may actually be throttling down for the supersonic/transonic regime buffeting. John Insprucker sort of hinted at that in a few webcasts, IIRC. If you compare to the velocity plot, it seems to be around Mach 1.
This is awesome work. Are you writing the code in Python? What graphing package are you using?You might try checking your atmosphere against the NASA standard atmosphere of 1976. You can test individual points with this online calculator, or you can just use the model here.
Drag coefficient for an ogive-shaped fairing and long cylinder should be pretty easy to find in some basic aerodynamic texts and/or AIAA papers. This may not allow for easy internet research, but that kind of thing has been methodically studied by NACA/NASA since at least the 1930's.
My own MaxQ calculation show roughly similar results.The most probable is that our numbers are wrong, but is it possible that the throttle decreases before MaxQ ? Because clearly my curves show that the loss of acceleration seconds before MaxQ leads to a significant lower MaxQ than if the throttle was keep constant.
Quite possible. Actually an interesting proposal. I added the region of mach 0.9 to 1.2 to the plot. Not an exact fit but quite close. Interesting interesting interesting.
Quote from: Semmel on 08/28/2016 07:48 pmQuite possible. Actually an interesting proposal. I added the region of mach 0.9 to 1.2 to the plot. Not an exact fit but quite close. Interesting interesting interesting.Does that take into account the lower speed of sound at that altitude (10-ish km)? I think Mach 1 might be around 300 m/s or thereabouts there.
# air pressure depending on hightp = p_0 * np.exp(- g * M * h / (R * T_0))# air density depending on pressure and temperaturerho = p * M / (R * T)
The Saturn 5 is nice and all, but it has rather awkward shape and it had fins at the base, which increase Cd quite a lot.
I took this equation since its a bit simpler:https://en.wikipedia.org/wiki/Atmospheric_pressure#Altitude_variationYou find this equation not only on wikipedia, also many other sites use that form. I dont think the approximation can be responsible for the differences we see. It wouldnt be a well accepted one if that was the case.