How do you caculate lift in this game

[Sathurn]

I beginning to think being an actual pilot is a serve handicap in KSP. I for the life of cannot make a jet plane much less a space plane.

I realize the aerodynamics is a place holder, so ....

How does 1.6 lift of the swept wing equate to needed flying speed?

Does the game use "stall speeds" and how do you calculate them?

How do you make a plane take is both light enough to fly, yet heavy enough not to flip over at it's early conveniences. (I think pilot error is a large part of my problem)

[rryy]

To answer the last question, the amount of mass on a plane doesn't really matter as much as its position. The center of mass on a plane must be in front of the center of lift, or else it will uncontrollably flip over. You can see the center of mass and lift in the SPH by clicking on the buttons on the bottom left. The blue marker is the center of lift and the yellow one is the center of mass.

I'm not sure how lift in the game works, but I think that planes in the game do not stall.

[Sathurn]

yeh, real planes have a cog forward of col, so that when you "stall" the nose falls restore flying speed over the wings.

So far anything with a forward center of gravity just stays on the ground for me.

[Nicholas4132]

The lift number on wings means essentially nothing. The amount of lift wings give is based primarily on the angle of attack, so at an AoA equally zero will give you roughly zero lift. I think the lift number is just multiplied by the AoA to get lift, but there isn't a real reason to try and calculate this yourself. to figure out how much lift a plane needs, just look at your plane and ask: do my wings look big enough? After a while it is just intuition.

There are no wing stalls in the game, though with an angle of attack higher than 45 degrees, wings start to lose lift and gain drag. There are engine stalls: if a jet isn't getting enough air, it may flame out, losing all thrust. In multi-engine aircraft this may cause a flat spin. To see of much air your engines are getting, look at the "Intake Air" resource in the upper right menu. The amount of Intake Air is determined by altitude, speed, and the types and amount of intakes on your craft. (The ram air intakes are the best)

Keep the center of lift behind the center of mass. Also, don't place control surfaces near the tips of wings. The game makes no distinction between elevators, flaps, or ailerons. Also, keep landing gear perpendicular to the ground. Any kind of camber or toe-in on lander gear may cause craft to veer off the runway.

[Sathurn]

I tried building in AOA by making the front landing gear taller than the back. But my plane just run off the end of the runway, or jump in the air spinning. I have not tried rotating the wings so they have a built in aoa though.

I don't have a joystick on my laptop, so my controls are all or nothing. Unless there is a trick I need to know.

[Nicholas4132]

If you hit CAPS LOCK then your controls will enter "precision mode."

[numerobis]

Lift is f(AoA) * rating * speed * air density.

The function f we haven't worked out exactly, but it is zero at zero angle of attack, reaches a maximum around 35 degrees, then goes back down (for wings; for control surfaces the function is different). It's smooth, so no stalls.

[K^2]

Real f(AoA) is also smooth for most surfaces, because separation doesn't happen throughout the entire wing all at once. The stall is just the place where lift starts to decrease rapidly. But yes, it's more abrupt for real wings than in KSP.

What about drag, by the way? Does it depend on AoA at all?

[falofonos]

Far as I've seen the drag just operates by giving the area of the projectile with most drag more retrograde (?) force. So a cone with lots of stuff on the pointy end will have a much higher drag at the pointy end.

Put as much as you can at the back of your plane, at the moment the flight model doesn't calculate airflow or shielding of parts. The aerodynamic model will be changed, so we can all enjoy a new learning curve at some point.

[kahlzun]

In the stock game it is weird, and doesn't make much sense.

There is a mod called "FAR" (Ferram Aerospace) which claims to add realistic drag/lift, including stalls.

I haven't used it myself, but from what I've seen, it looks to be legit.

[numerobis]

What about drag, by the way? Does it depend on AoA at all?

Drag for wings depends on the angle of attack, but I haven't analyzed it. Drag for other parts does not.

Good point about the smoothness of the function; I meant something non-technical, that lift never decreases rapidly (at least, no more rapidly than it increases elsewhere in the curve).

[bsalis]

yeh, real planes have a cog forward of col, so that when you "stall" the nose falls restore flying speed over the wings.

So far anything with a forward center of gravity just stays on the ground for me.

Same applies to KSP.

A plane will lift off the runway when the CoL is in front of the CoM. The control surfaces move the CoL. So you need to increase the proportion of control surfaces to lifting surfaces, and/or move the control surfaces further from the CoM.

[K^2]

Drag for wings depends on the angle of attack...

Good to know. Thanks. If you ever figure out relationship with lift, let us know.

[numerobis]

There's two types of drag to consider here:

Every part has a drag coefficient, which enters the normal KSP drag equation, which is quadratic in speed. For most parts that coefficient is fixed (usually 0.2, but 0.3 for SRBs and so on) whereas for wings the coefficient depends on the angle of attack. This has no relationship to lift.

But there's also parasitic drag. Lift is a vector that goes "up" compared to the wing -- but up compared to the wing is not necessarily up compared to gravity. Calculate the lift (which requires knowing that unknown function f), then sin(AoA) of the lift is slowing you down, whereas cos(AoA) of it fights gravity. That is all linear in speed.

[PS: might want to check my sin/cos claims for sanity, it seems fishy now that I type it.]

[Sathurn]

Since we don't seem to have a reliable way to calculate lift, (that we know of), how far forward of the COL do you typically put the COG?

[Nicholas4132]

The closer the CoG is to the CoL, the more agile the plane is, but less stable. The further they are from each other, the plane is more stable. Depending on the size of the plane, it is desirable to have the CoG and CoL to have about the distance of the length of a FL-T200 tank to a FL-T400 tank from each other. What you have to watch out for is that the CoG moves in-flight as fuel drains.