Squad, what did you do to the drag in 1.8.1???

[Shaun]

I haven't played KSP in a few months because I mainly fly atmospheric avaition. After one of the recent updates I noticed drag was all over the place and my aircraft could no longer reach airliner speeds (Mach 0.72-0.84). I thought my save was corrupted or perhaps it was a mod, so I did a clean install and new sandbox save. Here are the results with the following constants: Stock Gull, modified without floats, Mach 0.65 @ 6,000 metres. An aircraft with such few parts shouldn't be draggy and should fly like a dream.

Version 1.8

Most of the drag is concentrated on the most frontal and rear components in a 'line of nodes'; the advanced nose cone has a fair amount of drag (0.60); the tail connector has half of this (0.30) and the components in-between about half again (0.15), which makes sense because they're only causing skin friction with a tiny amount of form drag due to the angle of attack, negative in this case. Similar results with secondary 'line of nodes'; the engine nacelle: Intake has 0.21 drag, engine has 0.17 and tanks have 0.02.

 

Version 1.8.1

Overall drag is far higher, and middle components must be creating some invisible form drag or something; the advanced nose cone has a slightly higher amount of drag (0.83); but the tail connector has far more (1.15) and the components in-between almost that of the nose cone! (0.74). Results with the engine nacelle: Intake has 0.21 drag, engine now has higher drag (0.23) and tanks have close to the same drag at 0.18!) Also note the far greater thrust required!

Now, the 1.8.1 Bugfixes displays this: "Fix DragCube generation discrepancies in partdatabase - was affecting drag and thermals."

I don't know if this is something to do with this, but something has to be done, and I wonder if there's a way to transfer the drag model from 1.8 to 1.8.1 as a mod to fix this issue.

Edited February 10, 2020 by Shaun

[OHara]

In version 1.8.0 craft tended to re-enter the atmosphere faster than previously, and burn up before slowing down. At the bug-tracker report, we noticed that several of the parts had nonsense entries in the file 'PartDatabase.cfg'.  Version 1.8.1 has restored some but not all of those entries to closer to what they were in 1.2--1.7.

For a while it was useful copy PartDatabase.cfg from an older version, delete the "version = ..." line, and then run KSP.
Maybe you want to use the same method, but copying 1.8.0 (that the players reporting the linked bug considered to be the buggy version) onto 1.8.1.
The point of that file is that KSPs can re-generate it to include its aero analysis of parts from mods, which can frustrate the method of copying-over between versions.

[MechBFP]

These drag values are likely accurate but probably a bit too high across the board now as well.

That plane design is fairly draggy for such a small engine though so if the drag values are off, it’s not by much. 

[Shaun]

27 minutes ago, MechBFP said:

These drag values are likely accurate but probably a bit too high across the board now as well.

That plane design is fairly draggy for such a small engine though so if the drag values are off, it’s not by much. 

Yeah, a few parts like the structural fuselage are way off and too draggy, so a middle-ground would be nice; all the corrections and fixes of 1.8.1, just lower drag. Alternatively, the drag is already multiplied by 8 in KSP, so I may reduce this.