The A220, Step Climbs, Rockets and Lift Explained, or not?

The beautiful lines of the A220, it’s maybe my favourite for combined external and cockpit views.

But soon after taking it up for a first beauty ride, I took it back up to check out AoA, thinking about some nagging questions I had.

Roughly at medium weight, cruise speed, and cruise altitude I had around 2 degrees or so AoA. Seems good. So I climb higher, and after levelling out, AoA eventually grows to 3 or 4 degrees or so.

Does this make sense I thought, shouldn’t it stay the same? Aha, no. I kept my mach number the same, but as you go higher a given mach speed becomes less and less IAS. So I needed to turn up the “lift throttle” to continue matching my weight as lower wind pressure was stealing lift away from my wings. The “lift throttle” being AoA. So the numbers seemed to make intuitive sense.

What about the “lift throttle” (AoA) and step climbs? Step climbing is about not exceeding the power limit of your “lift throttle” to match your current weight. AoA tells you how much of your available lifting power you’ve dialled in. As you burn fuel weight your AoA comes down away from your limit, so you can then continue your climb till AoA goes back to the max limit.

Rockets (and helicopters and Harrier Jets) go up in reaction to expelling mass vertically down. But airplane wings too!

What’s your rocket fuel for a wing? Air. It’s the mass of the air that is shifted vertically down that is always equalling lift. Same as the rocket, except air is replaced by the mass of rocket fuel shifted vertically down.

But how does this air shifted down connect to the force of low pressure on the upper wing surface? There is no question “pressure differential lift” = “air pushed down lift” (there is only one lift force you get, but these are the two windows on how that works; they must be the same)

I’m going to propose a radical simple explanation. I say radical because I haven’t found anyone else mentioning it, no matter how much I search (so far). I may be wrong, but none of the experts seem to explain adequately how the equality above works. So frustrating.

Drafting, as in cycling and race car driving is the notion of lower pressure following an object moving in air. For water, think of a boat where the water is always struggling to fill the channel carved in the middle of the wake.

I’m claiming that the low pressure area over the wing originates as a first cause from drafting, and that the increased velocities over the wing are a consequence rather than cause of the lower pressure (paying the Bernoulli principle it’s due).

And that the lower pressure created above is what pulls down on the air from above the wing, to shift it’s mass down in the vertical direction. And that all the contouring of the wing and complex numerical analysis and simulation is about getting the wing to avoid turbulent disruptions to that flow (it’s about nursing the lift, not creating it: you don’t need a contoured air foil to make lift!).

Simply, the wing carves a partial vacuum out of the air from drafting, and that accelerates surrounding air down. Crazy maybe!?

So the AoA as far as the pressure difference explanation, “throttles” the amount of drafting (upper wing obstruction to the oncoming wind), giving control over the pressure difference; for the downward push of air explanation (Newton’s 3rd law), AoA changes how much the passing air gets curved down. But again, the two have to be equivalent.

Thank you A220, you’re a beauty, and you’re more than just looks!

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Not Infinite Flight related. Other than you testing out AOA, that’s about it.