Mk3 Part Drag is huge

[Voqk]

Hi all, self explanatory but I cannot get the Mk3 parts not to generate a ton of drag. You can see examples below - but no matter how I terminate the stack (engine mount, Mk3 to 2.5m adapter, etc) the body parts all seem to *each* generate drag. Is this intentional?

[Lt_Duckweed]

Yes it is intentional.  Notice that your heading marker is above your prograde marker, this means that some portion of the airflow is impacting the underside of your fuselage, which in ksp generates a lot of drag.

The best way to do this is to make sure the body of the craft points prograde.  But, you need angle of attack for the wings to make lift.  The way to solve this is to "build in" angle of attack on the wings by angling them a few degrees relative to the fuselage.  One tick of the rotation tool while holding shift and in snap mode should do the trick, this will give 5 degrees, which is very efficient at supersonic speeds.  This is called angle of incidence.

Edited January 23, 2022 by Lt_Duckweed

[18Watt]

In addition to what @Lt_Duckweed said, I would add,

• The screenshots you provided were right at the start of trans-sonic flight, which is where drag will be the highest.
• To me, it looks like there is not quite enough wing area for that aircraft to be efficient.  Adding wing area will probably reduce the profile drag you are getting from the Mk3 parts.

It does look like you have built in some positive incidence in your wings.  However,  at 300+ m/s at sea level I would expect the fuselage to be pointing more pro-grade, even without positive wing incidence.  That’s another clue that some more wing area could help.

Yes, more wing will also add more drag.  However, it will lift more than drag, and you will likely see a benefit.

And yes, the big Mk3 parts are indeed draggy.  For a space plane that size, I would normally use 4-7 RAPIERS to overcome the drag.

 

[Voqk]

Thanks for the responses both. I had originally observed this drag when flying directly to prograde, so I pitched up to see if I could ping the drag to a specific part (I have some mods installed and wondered if the drag box was incorrectly configured.

However, eyeball comparing the locked-to-prograde drag to the pitch, I think I was incorrect and that there is a single (albeit large) drag on prograde, and the multiple drag sources at a higher AoA is not related.

I've got plenty of thrust to make orbit actually (KSPIE Closed Cycle Nuclear Turbojets and Krusader rocket nozzle) so didn't really bother with more lift from wings. But will play around with with more wing surface to see it's affect on drag - I wasn't aware of 'profile drag'.

Thanks!

[king of nowhere]

You should also check the drag relative to the size of the plane. I mean, sure, those red arrows look impressive, but the blue lift arrows are also huge; that plane is big, looks like several hundred tons. So you should compare the drag to the weight. If the drag is a lot lower than the weight, then it's normal; big wings need to make big drag to generate big lift.

if the drag is high also compared to weight, then it's a problem.