Does Inverted Flight Invert Lift?

[Duke Leto]

I ought to be able to tell this but I can't.

Been trying to lose altitude during air flight by flipping the craft upside down, since this causes normal planes to undergo reverse lift and drop much faster than normal. The wings don't appear to be installed with an angle of attack relative to the center of thrust, but they also don't really have visible cambers.

This is obviously something Squad might want to abstract for modelling simplicity, so I'd like to know if I am wasting time by inverting.

Edited May 24, 2015 by Duke Leto

[Wanderfound]

I ought to be able to tell this but I can't.

Been trying to lose altitude during air flight by flipping the craft upside down, since this causes normal planes to undergo reverse lift and drop much faster than normal. The wings don't appear to be installed with an angle of attack relative to the center of thrust, but they also don't really have visible cambers.

This is obviously something Squad might want to abstract for modelling simplicity, so I'd like to know if I am wasting time by inverting.

If you want the wings to have static AoA, you need to add it yourself with the rotation tools. They default to zero.

[pandaman]

I don't know for sure, but I always assumed wing were symmetrical in cross section (i.e. no up or down side).

[Murph]

The wings in KSP are all just flat surfaces, so are relying on deflection to generate life, not differential pressure due to greater length over the top of the wing (as in the classic aerofoil). That's a reasonable choice when it's mostly supersonic flight that's being modelled. With that type of wing, it's all about angle of attack, namely the angle of the wing relative to the prograde vector, so it makes no difference which way up you are, only the angle of the wings to the airflow.

Inverted flight would only really be relevant with classic aerofoil shapes, and I'm not sure that KSP's aerodynamics would even simulate that.

The end result should be the same for nose 10° below prograde with the plane normal side up, or 10° below (still down towards the ground) prograde with the plane inverted, assuming that the plane is basically symmetric vertically (simple tails and the cockpit bump shouldn't make a big difference whether they are on top or bottom). If it's significantly asymmetric, there might be some variation.

[sal_vager]

They used to be flat surfaces but are now calculated as if they were a regular "flat" aerofoil, similar to the wings of an Extra 500.

Flying inverted will give the same lift as flying right way up at the same angle of attack, so you need to point your nose down.

[Tank Buddy]

None of the wings in KSP have camber or a non-zero angle of incidence when mounted normally; flight is identical right-side-up and inverted.

[Snarfster]

The only advantage of rolling inverted before "pulling" the nose below the horizon is that you do not pull negative g's. In real life it's sort of uncomfortable to have all your blood try to cram itself into your head.

Plus, some of the older (WWII) fighters could have engine roughness under negative acceleration due to the fuel flow being hampered.

In my opinion, those are the two main factors for rolling inverted to descend at higher speeds.

(Not taking into account wing profile shape, since in KSP there are no "classic" wings.)

[Murph]

The only advantage of rolling inverted before "pulling" the nose below the horizon is that you do not pull negative g's. In real life it's sort of uncomfortable to have all your blood try to cram itself into your head.

Plus, some of the older (WWII) fighters could have engine roughness under negative acceleration due to the fuel flow being hampered.

In my opinion, those are the two main factors for rolling inverted to descend at higher speeds.

(Not taking into account wing profile shape, since in KSP there are no "classic" wings.)

Yeah, I can confirm the engine issues is WWII era planes. I've flown real de Havilland Chipmunk T10s which use the old Gipsy Major engine dating back to the pre-war Tiger Moth. It's basically a poor man's Spitfire, certainly the same tech level as the Spitfire and has been the official pre-Spitfire trainer from just after the war until the present day; it's just smaller and the most it's armed with is a recon/spy camera (used as spy planes over Cold War Berlin). It can't handle negative g to any great extent, the carbs just send the fuel back over the cockpit canopy instead of into the engine, stalling the engine if you let it (but it will windmill start again as soon as it gets fuel). Positive g, no problem at all. In that type of aircraft, the other reason for positive g only (inverted, or otherwise), is being able to see where you are going, with unlimited upward visibility and very little downward visibility.

Sitting in the cockpit, negative g is indeed unpleasant; positive g a whole load of fun. The Chipmunk is rated for +6/-3.

Edited May 24, 2015 by Murph

[Ruedii]

The wings in KSP are symetrical, this means they only create significant lift when they are angled upwards. Most real world planes are designed to fly naturally angled up (angle of attack) between 1 degrees and 10 degrees. However, in KSP the physics aren't quite the same, so the angle is steeper at between 2 degrees to 20 degrees.

If you fly your plane inverted, you will simply angle the nose in the opposite direction.

[Duke Leto]

The only advantage of rolling inverted before "pulling" the nose below the horizon is that you do not pull negative g's. In real life it's sort of uncomfortable to have all your blood try to cram itself into your head.

Right, because Kerbals are totally biologically similar to humans.

OK, thanks for the info, all.

Edited May 24, 2015 by Duke Leto