What is the best L/D ratio you can get?

[Gaarst]

Title. I got to 12 with a high aspect ratio design (plane was very similar to a glider, only with engines) and that is pretty terrible compared to real world planes. Am I just that bad at building planes or are all planes less efficient in KSP?

(You can view L/D ratio by enabling the Aero GUI in the Cheats menu)

Edited February 12, 2017 by Gaarst

[AeroGav]

The shape of your wing has no effect on L/D ratio.    For the wing itself, L/D is only affected by mach number and angle of attack.

However the rest of the craft also generates drag, and this pulls your average down massively.

A craft with very large wings will get a good L/D because it will be able to get enough lift at a very low mach number (under 0.3) whilst keeping AoA low.

Or, it will be able to fly very high at more reasonable speeds, and still keep a low AoA.    The thin air and low aoa lessen fuselage drag and stop it pulling the numbers down.

If you rearrange the wing segments on your glider to make it look like a supersonic fighter, provided this doesn't mess with CoL/CoM and create a load of trim drag, it will perform exactly the same.

I've seen >10 to 1 under 100ms .   This decays as you get nearer the transonic region.   

From mach 0.9 to 1.1, I've never gotten better than 2:1.      After that it gets better again,  from about mach 1.5 up to orbital velocity at high altitude, l/d is pretty constant.  The best I ever saw in this spaceplane regeime is about 4.3 to 4.5

L/D varies a lot less in KSP than it does in real life.    You can't hope to reach 20:1 like airliners do at 0.82,  but in real life you can't get  4:1 from mach 1.3 to orbit.       Otherwise everyone would be using spaceplanes instead of rockets.

[Gaarst]

20 minutes ago, AeroGav said:

The shape of your wing has no effect on L/D ratio.    For the wing itself, L/D is only affected by mach number and angle of attack.

However the rest of the craft also generates drag, and this pulls your average down massively.

A craft with very large wings will get a good L/D because it will be able to get enough lift at a very low mach number (under 0.3) whilst keeping AoA low.

Or, it will be able to fly very high at more reasonable speeds, and still keep a low AoA.    The thin air and low aoa lessen fuselage drag and stop it pulling the numbers down.

If you rearrange the wing segments on your glider to make it look like a supersonic fighter, provided this doesn't mess with CoL/CoM and create a load of trim drag, it will perform exactly the same.

I've seen >10 to 1 under 100ms .   This decays as you get nearer the transonic region.   

From mach 0.9 to 1.1, I've never gotten better than 2:1.      After that it gets better again,  from about mach 1.5 up to orbital velocity at high altitude, l/d is pretty constant.  The best I ever saw in this spaceplane regeime is about 4.3 to 4.5

L/D varies a lot less in KSP than it does in real life.    You can't hope to reach 20:1 like airliners do at 0.82,  but in real life you can't get  4:1 from mach 1.3 to orbit.       Otherwise everyone would be using spaceplanes instead of rockets.

Thank you for your explanation.

I don't usually build spaceplanes (or anything build to sustain supersonic speeds for that matter) but that is always good to know.

My plane achieves 12.8 at sea level and flying at ~75m/s, so yeah it definitely is easier to get a good L/D ratio at lower speeds. The fact you can't reach real life L/D ratios at subsonic speeds is a bit sad, I actually like flying slowly and just watch the scene, guess I'll have to stick to my 8h autonomy "powered glider" 

[AeroGav]

Best supersonic ratio i've got that i actually can find a screenshot for.  Mk1 fuselage, wings are angled with 5 degree incidence and the body is only at 0.181 degrees AoA

This mk1 does not have any built in incidence.  But the wing area is much larger relative to body.  Gets 3.7 to 1  when i pitch up to 4 degree aoa after activating nukes..    not bad for a seaplane.

 

Edited February 12, 2017 by AeroGav

[Gaarst]

Reached 13.2 (at 100m, 77m/s) using this plane.

Edited February 13, 2017 by Gaarst

[fourfa]

That's a beauty!

[Gaarst]

18 minutes ago, fourfa said:

That's a beauty!

Really? It's fairly simple to reduce drag to a minimum, and the design is based on your average glider with high aspect ratio. Thanks still!

[bewing]

A canard design can do a little better.