Drag from non-laminar trailing surfaces?

[chd]

Does KSP penalize you for rear-facing flat surfaces, which in the real world would be a significant source of drag?

In this example, are my two side-pods draggy in KSP as shown, or no? I can certainly put reversed nose cones on them if need be, but why spend the money if the game doesn't model it... :-)

Thanks!

[bewing]

Yes, all parts have "drag cubes", which list the drag coefficient in all 6 directions. So the rearward-face will definitely always produce drag.

[Lt_Duckweed]

Yes, it is modeled.  In fact, at subsonic speeds, backface drag is nearly as bad as frontal drag.

[Spricigo]

8 hours ago, chd said:

I can certainly put reversed nose cones on them if need be, but why spend the money if the game doesn't model it... :-)

More generally: why spend money and add mass if the drag is not as significant in comparison?

Something to consider is ascent profile.  A craft that ascend in typical gravity turn may go with an open node just fine, while a spaceplane need to fly at sea level to cross transonic  and expend a lot of time climbing will be in a lot of trouble.

 

[Wobbly Av8r]

All the previous responses are certainly in agreement with my experiences in KSP, but I would suggest you take it a bit further and explore where the drag on your design comes from - you'd be surprised.

Using the 'Debug Menu' (same access as 'Cheat Menu') there is an Aero tab - activate the option "Show aero data in Parts Window" or something similar to that - you'll see a new ">Debug" tab attached to the PAW's which include drag information. Regarding what you're looking for here, there are a few rows of data that begin with "YP" and "YN" (Y-axis Positive / Negative) - these values are the exposed portion of the drag cube described by @bewing and  @Lt_Duckweed above. You'll be surprised at where your vessel's drag might be coming from - parts that "look" like they are streamlined may literally look like a large, draggy, flat plate to the game's physics engine; if care is not taken in construction (and sometimes certain parts properly installed are still VERY drag-intensive) it can result in problems that are mystifying and frustrating. The blunt mating surface of a large fuel tank can cause aerodynamic mayhem - even though it "appears" to have some form of aerodynamic streamlining attached to it.

One word of caution when activating this function - deactivate it before returning to the VAB / SPH as keeping the option available during construction can cause performance stutters  that make it almost impossible to build / modify anything in the VAB.

Edited October 3, 2020 by Wobbly Av8r

[Lt_Duckweed]

3 hours ago, Wobbly Av8r said:

One word of caution when activating this function - deactivate it before returning to the VAB / SPH as keeping the option available during construction can cause performance stutters  that make it almost impossible to build / modify anything in the VAB.

More specifically, nuclear engines are one of the parts that cause it to stutter, don't know if there are others but thats the biggest offender for me.

3 hours ago, Wobbly Av8r said:

Regarding what you're looking for here, there are a few rows of data that begin with "YP" and "YN" (Y-axis Positive / Negative) - these values are the exposed portion of the drag cube

To add to this, there will be 3 numbers in each row.  First number is currently exposed area of that face of the drag cube (taking node occlusion into account), second number is how streamlined this face of the drag cube is (0 is infinitely pointy, 1.00 is a flat plate, anything bellow .45 is good, bellow .3 is really good), the third number is the total area of that face of the drag cube. So you can compare the 1st and 3rd values to see how much of that face is currently covered.