drag management

[king of nowhere]

I reached the point where my spaceplane is almost good enough to go ssto on eve. I realized that my flight profile requires a lot of powered flight before clearing the atmosphere, and i believe i could make the whole thing work if i could minimize drag. i've seen a youtube video of a similar design making it, but it goes faster in the atmosphere with less TWR than my model.

unfortunately, the game gives no indication on how to accomplish that. Having a thing that looks aerodinamic and one that actually is aerodinamic according to this game's physical engine are two entirely different things. sure, i activated the aerodinamic overlay, but a few red arrows aren't all that clear. and most of them are inside the plane, not visible.

today i had a moment of insight, where i decided to look at the game wikia, that reports drag factors.

except, i'm seeing that every single wing has a drag coefficient of 0.2 and a lift generated of 1 (1 what?) every 100 kg of weight, every single fuel tank of 0.3-0.2 (whatever that means) regardless of size or inclination, the MK3 cargo bay has 0.2-0.3 (why the different order over the fuel tanks?), nose cones have 0.1 regardless of shape (i always thought that the more inclined nose cone had better aerodinamic to compensate extra weight...). basically, it's no use at all.

i know about not having open nodes. i reluctantly gave up on having a clamp-o-tron (except a shielded one, but now i'm seeing the wiki reports the same drag values for it than it does for the standard version). I attached the rockets behind radially mounted nose cones, and the thing has nose cones on both ends.

for reference, this is my most successful model

though not by far the only model i tried. for example, this other model does not generate enough lift to take off, despite having a greater lift-to-weight ratio

and this one, that only has the wings rearranged, will tend to deviate on the side mid-flight for no apparent reason

 

 

so, how can i improve my aerodinamic when i'm not getting any useful feedback besides -this flies, this doesn't - ?

[bewing]

Spricigo kinda gave you a big hint: your engine mount is very draggy. An additional hint for Eve is that anything on your craft that is not absolutely required for your return trip to kerbin should be discardable on Eve with decouplers. Which means, things like all but one of your solar panels. It's perhaps smarter to have one big and one tiny solar panel -- that makes it easier to discard the big one.

But as far as determining drag and minimizing it, you do it by building airplane after airplane on Kerbin with different parts, and test flying them, and then judging their top speed and acceleration capabilities. Stock KSP is all about teaching you to do engineering by doing, rather than by feeding you numbers to analyze.

[Spricigo]

6 hours ago, bewing said:

Spricigo kinda gave you a big hint: your engine mount is very draggy.

Not saying the actual don't have its issues, but that was in reference to a previous version (with a Kerbodyne Engine Cluster Adapter Tank filled with mismatched engines,  IOW a part screaming "DRAAAAAGG!!!")

 

The aero overlay is just to get a basic idea. To know how draggy each individual part is you need to check {Display aero data in action menu} under Physics in the debug menu. Then you can open the Part Action Window and see something like this:

 

12 hours ago, king of nowhere said:

(what?) ... ...(whatever that means)... ...(why?)... ... basically, it's no use at all.

Welcome to the world of overwhelming amounts of data available. Digging some info out of it can take a lot of time and effort.

Good luck with your plane. Meanwhile, I been told the cool kids are doing boats those days.

[king of nowhere]

12 hours ago, Spricigo said:

Welcome to the world of overwhelming amounts of data available. Digging some info out of it can take a lot of time and effort.

Good luck with your plane. Meanwhile, I been told the cool kids are doing boats those days.

i tested in case i splash down in the ocean, and my plane can use its propellers to move around in water too. so, i can say i already have a flying boat!

Edited September 17, 2020 by king of nowhere

[zolotiyeruki]

Here are a few tips:

Of all the nose cones in the game, the Shock Cone Intake has by far the least drag.

If you're willing to get a little cheaty, you can stick a Shock Cone on the back of your engines, and then offset them into the engine.  That way, you get the reduction of drag, without the nose cone sitting in the way of the exhaust.

The game has a default calculation for drag, but some parts override that calculation, via values set in that part's .cfg file.  It's also worth noting that there's drag due to the shape, and there's also skin drag.  That's why a plane with a Mk1 LF tank can fly perfectly straight and level and still have non-negligible drag from the fuel tank, even if the tank is fully occluded from the airstream.

Any time you change fuselage diameter, you'll pay a pretty heavy drag penalty.  You may see better results if you stick with Mk3 parts for the entire length of your craft--you'll get more fuel in a shorter craft, and you'll avoid some of the drag penalty from going up and down sizes as much.