[Test Results] How much wing does your SSTO spaceplane need? Answer: Maybe none at all.

[Nothalogh]

I did a balance beam test yesterday with one intake open and one closed. The open one definitely has more drag in flight.

Whether it's enough to even be noticeable on a normal craft is unknown.

For now, I'll continue to put the intake close action into my mode switch action group since it only takes a moment for each design.

Happy landings!

Yep, I close intakes as well

[windows_x_seven]

Does the OP's experiment also apply to FAR?

[Claw]

Does the OP's experiment also apply to FAR?

It may or may not, but I wouldn't say that it's directly applicable without just going and actually doing the test in FAR. FAR does aero modeling quite a bit differently.

[Val]

...

2) getting lift out of wings that are really too small for the job.

I disagree with this. It's about removing oversized wings and their weight from SSTOs designs that already have low margins.

Other important benifits are that engines can thrust closer to prograde (without having different angles between engines for vacuum and atmospheric) and keeping nose lower and tail higher during landing and take-off, to avoid tail strikes.

[GoSlash27]

I disagree with this. It's about removing oversized wings and their weight from SSTOs designs that already have low margins.

Other important benifits are that engines can thrust closer to prograde (without having different angles between engines for vacuum and atmospheric) and keeping nose lower and tail higher during landing and take-off, to avoid tail strikes.

Val,

I'd agree with most of this, but the difference in mass between larger wings at low angles and smaller wings at high angles is a pretty tiny percentage of the mass of a spaceplane.

My point is if you already have adequate lift from a design, rotating the wings up as was done here isn't going to have much benefit if any.

Best,

-Slashy

[Val]

... larger wings at low angles and smaller wings at high angles...

Do you have a tool for mounting at other angles than the default minimum of 5 degrees?

The main reason I've only used 5 degrees Incidence angles on my designs, is because that's the only angle I'm able to reproduce consistently.

[GoSlash27]

Do you have a tool for mounting at other angles than the default minimum of 5 degrees?

The main reason I've only used 5 degrees Incidence angles on my designs, is because that's the only angle I'm able to reproduce consistently.

Val,

I believe that each click of fine rotation is around 3/4°. I alter the incidence depending on the ship's mass/ cumulative lift.

Best,

-Slashy

[NathanKell]

Here's a test for all you "no really closing intakes matters" folks.

Ramp intake

Small guidance unit

BACC throttled to 50%.

4x fins for stability.

Launch it five times open and five times closed. Record apoapsis each time.

[Geschosskopf]

I believe that each click of fine rotation is around 3/4°. I alter the incidence depending on the ship's mass/ cumulative lift.

When using the rotate gizmo, you can also switch from angle snap to free (C key) and get analog control over rotation instead of digital. Of course, this way you have no idea what angle you end up with but it's good for hitting very small or unusual angles. I frequently use this for RCS thrusters mounted on curved surfaces.

[Captain H@dock]

When using Shift+WASD, you get 5 degrees steps. (9 of them is 45)

And since you need reliability when designing such things, I don't see how one can do any better except direct editing of the craft file (i've got a tool for that, but it's only for part swapping, I don't dare try moving/rotating parts)

[GoSlash27]

When using the rotate gizmo, you can also switch from angle snap to free (C key) and get analog control over rotation instead of digital. Of course, this way you have no idea what angle you end up with but it's good for hitting very small or unusual angles. I frequently use this for RCS thrusters mounted on curved surfaces.

Geschosskopf,

This is actually what I'm talking about, but it's not truly analog it just has fine steps.

Best,

-Slashy

[Starhawk]

Here's a test for all you "no really closing intakes matters" folks.

Ramp intake

Small guidance unit

BACC throttled to 50%.

4x fins for stability.

Launch it five times open and five times closed. Record apoapsis each time.

I think we've already established that closing intakes has no benefit at all.

Happy landings!

[Geschosskopf]

This is actually what I'm talking about, but it's not truly analog it just has fine steps.

Well, due to the Planck Length, there's no such thing as analog at all, even in real life . But when using "free" instead of "snap" with the rotation gizmo, the margin of error in the movement of your mouse greatly exceeds the tiny discrete angular steps between one part position and the next, so it closely approximates analog.

[GoSlash27]

Well, due to the Planck Length, there's no such thing as analog at all, even in real life . But when using "free" instead of "snap" with the rotation gizmo, the margin of error in the movement of your mouse greatly exceeds the tiny discrete angular steps between one part position and the next, so it closely approximates analog.

Geschosskopf,

Maybe your mouse, but not mine. I have no problem rotating parts in discrete "clicks" in free mode. This is how I'm setting inclination angles lower than 5°.

Best,

-Slashy

[Captain H@dock]

Maybe your mouse, but not mine.

I'm wondering, could this be screen resolution dependent too? I have no idea how KSP transforms mouse input to angle steps....

[GoSlash27]

I'm wondering, could this be screen resolution dependent too? I have no idea how KSP transforms mouse input to angle steps....

Captain H@dock,

I dunno. I'm sure it'd be more difficult to see the change if you have poor resolution, but it's still the same fixed amount per "click" (mouse movement of 1 pixel). I'm not playing at a high resolution (1280x720 window) and I can see the movement okay.

Best,

-Slashy

[Stoney3K]

Here's a test for all you "no really closing intakes matters" folks.

Ramp intake

Small guidance unit

BACC throttled to 50%.

4x fins for stability.

Launch it five times open and five times closed. Record apoapsis each time.

Just enable "Display Aerodynamic Data in Action Menus" on the ALT+F12 screen and right-click the intake. The drag number (in kN) is displayed there.

Opening or closing that intake makes zero difference on the part drag. *If* there is drag from the intake flow, it's an induced drag force that is calculated in a different subsystem and not added to the "total" part drag.

[Stoney3K]

OK, different but related question: Which wings does everyone use for their SSTOs? I found the big airliner wings to be too draggy, even though they have massive lift.

Shuttle wings are better, but you need quite a lot of them if you want to get a 100+ ton plane off the ground and up to some decent speed.

[GoSlash27]

Stoney3k,

It depends on how big the spaceplane is.

It turns out that all wings are equally draggy, so the important thing is to use enough wing area for the job.

I do use wings to carry fuel whenever possible just to cut down on the spaceplane's length.

Best,

-Slashy

[eddiew]

Flight of the Brawndo:

http://s52.photobucket.com/user/GoSlash27/KSP/Brawndo/story

It's efficient designs like this that make me want to spend an evening getting my spaceplane on... but I'm determined to stay off KSP until 1.1 hits so's be be ultra-keen. Stop tempting me, devil!

Nonetheless this is a great lesson is how low drag wins out over TWR. Everyone who struggles with breaking the sound barrier despite having 10 engines needs to check out some builds like this one

And I've never tried the slanted wing-thing myself... always assumed it would just make the nose point downward during neutral/level flight. Maybe I was expecting too much from the aero model ^^;

- - - Updated - - -

It turns out that all wings are equally draggy

Is that drag per lift, per area, or per weight...? (Or does the game balance everything out so that one square metre of wing adds the same amount of lift and drag no matter which part you're using?)

[Val]

...

Is that drag per lift, per area, or per weight...? (Or does the game balance everything out so that one square metre of wing adds the same amount of lift and drag no matter which part you're using?)

It's drag per wing area. So 2 different wings with the same area have the same drag.

...

And I've never tried the slanted wing-thing myself... always assumed it would just make the nose point downward during neutral/level flight. Maybe I was expecting too much from the aero model ^^;

Yes, like most of us, you were probably taught that lift works like this.

Pictures showing lift without Angle of Attack. It's not wrong, but it's not the full picture. At least 2 things are missing in relation to KSP.

1. Camber in wings only provide part of the lift, in most flight regimes.
   
2. KSP does not model cambered wing profiles.
   

So we all have a natural tendency to mount wings with zero Incidence. When really we shouldn't.

Wings in KSP always need Angle of Attack to provide lift. So if you mount wings with no Angle of Incidence, then the whole craft needs to be pointed up for the wings to lift it.

When wings are mounted with Incidence, the nose can be lowered closer to the direction of movement, reducing drag from the fuselage. Drag from the wings will of course remain the same, but that is usually much less than drag from fuselage.

And in real life even cambered wings are mounted with incidence, for the same reason.

"Wings are typically mounted at a small positive angle of incidence, to allow the fuselage to have a low angle with the airflow in cruising flight. Angles of incidence of about 6° are common on most general aviation designs."

Source

The amount of incidence you need depends on mass and wing area. I usually go for 5 degrees Incidence and a wing area 1/8th to 1/6th of the mass in t. (not counting wing area from Mk2 fuselage)

Edited September 11, 2015 by Val
Expanded and clarified. And grammar.

[GoSlash27]

^ What Val said, except it's drag per cumulative lift rating.

One wing panel with a lift rating of 8 units will behave just like 2 panels of 4 units each and so on AFA lift and drag are concerned. KSP doesn't care if they're wet wings or simple panels. The only difference is the weight, and that is negligible at the scale of the total spaceplane mass they're lifting.

I try to keep the total number of panels down in order to avoid structural weakness. Having floppy wings means you'll need to strut them, which adds drag.

I try to keep the total lift rating within a range suitable for the mass of the spaceplane.

Best,

-Slashy

[Stoney3K]

Has anyone tried to use control surfaces as flaps to improve your lift rating at takeoff and landing? Because that's where you would most need it: Slow ascent, descent and on the runway.

In the upper atmosphere (10km+) and on supersonic/hypersonic flight regimes the speeds are much higher so each wing will be pulling more weight, meaning you would need less lift anyway.

I tried adding a few flap-like surfaces and use the 'deployed' state as a control, but I could never get them to work as flaps.

[Captain H@dock]

Has anyone tried to use control surfaces as flaps to improve your lift rating at takeoff and landing? Because that's where you would most need it: Slow ascent, descent and on the runway.

In the upper atmosphere (10km+) and on supersonic/hypersonic flight regimes the speeds are much higher so each wing will be pulling more weight, meaning you would need less lift anyway.

I tried adding a few flap-like surfaces and use the 'deployed' state as a control, but I could never get them to work as flaps.

I have. For instance I'm about to send a such a spaceplane to Laythe. This SSTO will be capable of touching down at around 30 m/s with tank full (on Kerbin testing).

Refer to this post for details on flaps configuration for KSP: http://forum.kerbalspaceprogram.com/threads/131184-The-Art-of-landing?p=2134481&viewfull=1#post2134481

Val mentionned that KSP wings provide zero lift with an AoA of zero degrees. If they also provide zero drag under such conditions, this would mean adding flaps to spaceplanes could have almost no side effects.

Still, I don't equip my regular spaceplanes with them since I don't need Short Take off and Landing Capabilities on Kerbin. Also, these flaps don't work very well with gliding landings.

Edited September 22, 2015 by Captain H@dock

[Val]

...

Val mentionned that KSP wings provide zero lift with an AoA of zero degrees. If they also provide zero drag under such conditions, this would mean adding flaps to spaceplanes could have almost no side effects.

...

Also, these flaps don't work very well with gliding landings.

Agreed. Adding flaps doesn't really hamper performance, but deploying them does.

From my personal experience with low TWR take-off, where flaps are needed the most, they seem to create more drag than lift. So I never use flaps for take-off.

But I do find flaps quite useful for bleeding off speed at a steep approach to the runway. And if I have fuel left I may do a powered landing with flaps deployed. It lowers touch down speeds a bit and is especially useful, if landing in terrain.