Drag Calculation

[Alpha Carinae]

Hello guys,

I've been trying to calculate my Delta-v and I was able to find formulas on how its done. 

I tried myself but didn't really work!! I tried launching a basic rocket ( I don't change my heading) and as per the formula I should be able to get to 480 m/s but I don't, I always get 360 m/s.I believe that this due to drag of the atmosphere, I doubt wind is taken in consideration. 

Can someone tell me if there is a certain angle I should follow or maybe another formula to know how much drag is affecting me and if so, where to find drag coefficient and the related detail in the menu.  

Please note that I use Xbox to play KSP.

 

Thanks a lot

Bader

[OhioBob]

Drag is a complex calculation in KSP.  Each face of each part has its own drag coefficient, which is modified according to Mach number and orientation to the air flow.  The drag produced by each part is computed separately and then those values are summed to get the total drag.  The vehicle as a complete unit has no drag coefficient that you can look up.  All you can really do it take measurements during flight tests and deduce the drag coefficient from the measurements, which might allow you to derive an empirical formula.

If you go to the cheat/debug menu, you can open the Aero GUI window.  This will display aerodynamic data in real time.  A couple properties displayed are dynamic pressure and ballistic coefficient.  If you take the mass of the vehicle and divide it by the ballistic coefficient, that gives you the product C_dA.  Multiply C_dA by the dynamic pressure and that's the drag.  You really don't need to know the drag coefficient by itself, C_dA will suffice for any calculations you need to perform.  But if you really insist on knowing C_d alone, then just divide C_dA by the reference area.  The reference area is whatever you define it to be, like cross-sectional area of the rocket.

[Alpha Carinae]

Thanks a lot.

When you want to construct a rocket to get to a certain altitude you need to put fuel tanks and whatnot. How do you do you know what speed you will reach, and how far you will get?

Aren't their anything in the game (Xbox) to tell you these information?

I use the Dv formula = isp*g*ln(Mfull/ Mempty) but the figure I get is always less than the actual one. I do it from 0 altitude on Kerbin and not in vacuum.