# Talk:Rockomax Jumbo-64 Fuel Tank

According to the atmosphere page drag force is proportional to area, which is proportional to mass. So shouldn't two X200-16 tanks have the same mass and therefore the same drag as an X200-32? --einsteiner

KSP uses fixed drag values and doesn't calculate them. Because both tanks have a drag of 0.2, two smaller tanks generate twice the drag as one large tank.
Oh, and something about the "area is proportional to mass" thing: When talking about full tanks, that is sort of true. However, if you empty out the tank, it still has the same area, but is lighter. So area is actually not proportional to mass. In this specific case you would be correct though, two smaller tanks should have the same drag as one larger tank. --dgelessus (talk · contribs) 16:02, 27 August 2013 (CDT)
In the real world the drag is proportional to the cross-sectional area and it is irrelevant how massive your object if: The drag on a object with the mass of 1 kg is the same with the mass of 1 g but the same dimensions (and thus the same area). So in real life two X200-16 tanks should behave like one X200-32 and it is also irrelevant if they are filled or empty. But KSP itself doesn't calculate the correct cross-sectional area, but instead uses the vehicle's mass and convert it with the factor of 0.008. It also uses the mass so, a filled tank behaves differently then a empty one. But a X200-32 should behave the same as two X200-16 when they carry the same amount of fuel.
Note to the drag coefficient:
${\displaystyle {\frac {\sum _{i}d_{i}\cdot m_{i}}{\sum _{i}m_{i}}}={\frac {d\cdot \sum _{i}m_{i}}{\sum _{i}m_{i}}}=d\cdot 1}$
The di are the drag coefficients and the mi are the masses. When we use two times the same part, the drag coefficients are equal (the mass too, but this isn't important) resulting in the final drag coefficient being the same. So two X200-16 (or any other number) have always the same drag coefficient (together) as one X200-16 which is the same as the X200-32.
So using the first formula in the atmosphere article, two X200-16 should have the same drag as one X200-32, because d, the dry and full mass (and therefore the “area”) are equal for both configurations. &rho and v aren't specific for the configuration so can be ignored.
Also this why do you post this on the talk page of the Jumbo-64 tank? (For your information: Two X200-32 should behave the same as one Jumbo-64) — xZise [talk] 17:06, 27 August 2013 (CDT)
I just saw the statement that one Jumbo-64 is more drag efficient: This isn't true (see my explanation above). — xZise [talk] 17:14, 27 August 2013 (CDT)