From a d/V standpoint, how useful is lift?

[Right]

I'm not 100% sure what the game means by lift, but I typically see a colloquial usage and a fluid dynamics usage. Colloquial usage seems to often mistake lift with 'change in vector due to angle of attack'. In principle, a flat wing cannot generate lift. An airfoil can.

I think my question can be most easily answered in this form: is there an advantage in game to using a fixed wing, over say a structural panel if it had equal mass and surface area?

Along similar lines, if the game employs the fluid mechanical behavior of lift, a light craft traveling parallel to the horizon at sufficient speeds should ascend slowly. (0° Angle of attack for the craft & wings)

I could be wildly overestimating my understanding of the concept though.

Edited October 5, 2015 by Right

[FancyMouse]

I thought a brisk can still fly if it's fast enough?

Really, even paper planes (which is flat at all) can generate plenty of lift. What's wrong with a flat wing?

[Alshain]

The game calculates lift and drag from a coefficient set in each parts config file. The angle of attack/deflection does affect both.

Peeking at the part files you can sort of see how they accomplish this. This means the part shape itself is irrelevant, and therefore airfoils are not truly recognized. Since 1.0, there are various checks for occlusion so parts that aren't in the "airflow" do not perform, but anything can be a lifting surface if you mod.

    MODULE
    {
        name = ModuleLiftingSurface
        useInternalDragModel = True
        deflectionLiftCoeff = 7.8        // 27,41m^2
        dragAtMaxAoA = 0.6
        dragAtMinAoA = 0.0
    }

Edited October 4, 2015 by Alshain

[NathanKell]

Things with ModuleLiftingSurface (Or ModuleControlSurface which derives from it) perform like airfoils. You get rather more lift from them than the flatplate lift you get from non-airfoils.

That doesn't really have anything to do with delta v, however.

[Red Iron Crown]

I'm not 100% sure what the game means by lift, but I typically see a colloquial usage and a fluid dynamics usage. Colloquial usage seems to often mistake lift with 'change in vector due to angle of attack'. In principle, a flat wing cannot generate lift. An airfoil can.

Flat wings create lift in principle, that's how paper airplanes fly IRL.

I think my question can be most easily answered in this form: is there an advantage in game to using a fixed wing, over say a structural panel if it had equal mass and surface area?

The fixed wings produce more lift per unit of drag, I believe. Likely more lift per unit mass, too.

Along similar lines, if the game employs the fluid mechanical behavior of lift, a light craft traveling parallel to the horizon at sufficient speeds should ascend slowly. (0° Angle of attack for the craft & wings)

There are no parts in KSP that generate lift at 0° angle of attack. All wings are treated as symmetrically profiled.

Edit to add:

Wings can be advantageous from a delta V standpoint by allowing less engine mass (<1 TWR takeoff is possible) and by reducing gravity losses during ascent, sometimes reducing the delta-V required to get to orbit.

Edited October 5, 2015 by Red Iron Crown

[GoSlash27]

Right,

It's related, but much more loosely.

The main source of DV loss in spaceplane design is drag, so there is an advantage in designing a spaceplane to be aerodynamically cleaner.

So how does lift help? Well...

There are 2 kinds of drag in KSP; induced drag and parasitic drag.

Induced drag is a by-product of creating lift. Parasitic drag is the result of pushing a mass through the air.

It so happens in KSP that wings only produce induced drag while everything else produces parasitic drag. It also happens that induced drag is *much* lower than parasitic drag in KSP.

Using wings to create your lift instead of structural panels, body lift, or raw thrust means that you will create dramatically reduced drag during the launch. This means less DV wasted to drag and cosine losses, which means less DV required to achieve orbit.

Best,

-Slashy

[Van Disaster]

Flat wings create lift in principle, that's how paper airplanes fly IRL.

He means "flat surfaces at 0 AoA produce no lift", I suspect. And they don't, only you'll never realistically manage that Anyway lift created by a surface at an angle is still lift, why else do you pitch an aircraft up when it slows down... it's not all due to aerofoil shape. Supersonic wing cross-sections are generally practically flat but you can still fly them subsonically.

Anyway - under old-FAR I saved about 300 dv by sticking wings on a medium sized rocket, so it might be worth the try. Rockets tend to get out of the area of atmosphere most useful for wings quite quickly though, so they might just end up being mostly sources of extra mass & drag.

[KerikBalm]

There's a lot of misunderstanding of bernoil's principle and how AoA is measured.

Suffice to say, in any aeronautical engineering textbook, you will find the formulas used mean that the wing generates zero lift at 0 AoA.

Yes, the same formulas that are used to design the spaceshuttle, airlines, etc... they are well tested.

[Right]

Love all the answers, I'm very impressed and flattered.

So I found this short video that sort of clears up up some questions as it explains the two competing explanations of lift. The first explanation covered was my understanding, but now I realize its more nuanced.

NathanKell and especially GoSlash, nailed the crux of my concern. Thanks everyone for the replies!