How to calculate or estimate drag?

[Tazin]

Hey guys, is there any way in stock or via mods to see in VAB or SPH what is the drag of my vessel? when designing planes i often wonder i adding wings (more lift but more drag) will be worse or better, or if different intakes have different drag values, etc., and a 5 minute test flight adds up significant time when trying out different options . . .

Related question, is drag a fixed number, or is it dynamic through flight depending on wich areas are exposed to the prograde, and the speed?

[Gaarst]

I don't know about calculating it, but it does depend on the orientation of the craft (that is the reason why some crafts will flip during ascent or reentry, to set drag forces with the aerodynamics).

I don't know any mods to calculate drag, but with KER, you can look at the terminal velocity of the craft to get a quick approximation of its drag.

[Mastikator]

https://en.wikipedia.org/wiki/Drag_equation

https://en.wikipedia.org/wiki/Drag_coefficient

Wings add drag, so it will take more thrust to make it go faster, and as you can tell by the drag equation area and velocity are factors. Lift is also a factor of velocity, so the faster you go the less wings you need and the less wings you have the faster you can go. But less wings also means higher slowest speed and less glide.

And the shock cones have the least drag per air intake as of 1.0.4 AFAIK

[Violent Jeb]

pfft.

time to let MJ shine over KER.

My friends, MechJeb has an "atmospheric drag" value, which you can have visible through your entire flight!

No need to get the terminal velocity and do the maths.

It provides your atmospheric drag value in m/s much like the nav speedo.

FWIW, typical flights will experience anywhere between 1-15 m/s drag. This represents constant losses while the air counters your momentum.

With a fairly aerodynamic shape and no fairings, I can consistently keep my maximum drag values below 5, as long as you don't cap ~250m/s below 10,000m

Note that atmospheric is thickest (and thus the most drag is present) around 8000-12000 m, after ~20-25k, drag decreases substantially until it is largely moot above 35000m (unless you try and hang out there for too long)

All of this information has been acquired using mechjeb to get my atmospheric information. This makes it an essential mod for me

[Tazin]

Nice catch for MJ! i don't use mechjeb but i think i will install it and get the information tools without the stuff that sort of feels like cheating (not hating on people who play different than me). But still, i feel like there should be a simpler mod to do some basic and simple calculations in the buiilding process of stock aero planes: add total lift and divide by weight, add total drag of exposed parts . . . or at least something that shows the inherent drag of each part, so one can choose part properly.

[Red Iron Crown]

M/s doesn't make sense to me as a unit of drag. Surely it should be N or kN.

[Tazin]

The value Violent Jeb is talking about is "total m/s lost due to drag". To me it makes sense, but that value would include piloting, trajectory, and a lot of stuff that i don't care about in plane design. What i mean is, if i put wings in an orange tank, it is more draggy than a MK2 plane, so how do you put a number on that difference, right on the SPH?

[Red Iron Crown]

The value Violent Jeb is talking about is "total m/s lost due to drag".

IIRC that refers to drag losses during flight, a number that should accumulate over time while flying in atmo. Similar to the counters for steering losses and gravity losses.

[NathanKell]

If you want a drag dispaly, and other stuff, get AeroGUI.