Climb performance

Spare thrust

Walk up a hill with a heavy bag. What decides how steep you can go? The strength you have to spare. Same for an aeroplane.

In a climb, part of the weight pulls backwards along the path. Thrust must beat drag and that part too.

T = D + W sin γ

So the thrust left over after drag sets the gradient.

Gradient % = T − D / W × 100

Lose one engine of two. You lose half the thrust, but drag stays. So you lose far more than half of the climb.

Half the thrust: three quarters of the climb gone.

Gradient against the air. Rate against the clock. Same climb, two measures.

Rate of climb = TAS × 101.33 × gradient / 100

Steepest or fastest

Two ways to climb. Stairs or escalator. Stairs are steeper. The escalator gets you up sooner.

Same aeroplane, two speeds. Both start from the same runway.

Run the clock.

Check each after the same number of seconds. VY is always higher: it has the best rate.

Now put a hill in front. VX clears it. VY does not.

Height per mile is what clears a hill, and VX has the best angle.

VX gives height in the shortest distance. VY gives it in the shortest time. VX is the slower one.

Which speed is which? Look at drag again next. For now:

And wind? Rate of climb does not care. You climb inside the moving air. Only the path over the ground changes.

So a headwind helps you clear a hill, but does not change the climb limit mass.

The four segments

This lesson is part of the Navigation plan. See plans

Net and gross

This lesson is part of the Navigation plan. See plans

The drag valley

This lesson is part of the Navigation plan. See plans

Ceilings and drift-down

This lesson is part of the Navigation plan. See plans