• VX vs VY: Best Angle of Climb vs Speed for Best Rate of Climb

During the initial take off phase, the intention of every pilot must be to increase height in the most efficient manner, as the saying goes, ‘speed and height, keep dentures upright’.

If an aeroplane flies high and encounters a problem, there would be sufficient time to prepare. In the case of it flying fast, it could make the most of that excess speed by gaining height and so increase available time.

In order to make aeroplanes ascend in the most efficient way possible, engineers calculate two different speeds for each model of aeroplane, the speed for best angle of climb, VX, and the speed for best rate of climb, VY.

Although they have similar names, there are really major differences between them. Following, we tell you about them.

VX Speed for best angle of climb

The speed for best angle of climb, also known as Vx, is that in which the aeroplane gains more height whilst achieving the shortest possible horizontal distance.

This distance is what pilots should aim to achieve following rotation, as it’s the one which gives the highest safety margin of all.

Vx must be maintained until a safe altitude is reached, usually 500 feet from the ground, since from this height, if an engine were to fail, it would be possible to return to the runway by performing a 180º turn.

To give you an example, our Diamond DA20 has a Vx, or best angle of climb, of 65 knots.

VY Speed for best rate of climb

The speed for best rate of climb, also known as Vy, is the speed at which our aeroplane has the best performance in ascent, that is, the aeroplane will achieve more height quicker but whilst flying the shortest possible horizontal distance.

In addition, you should know that the angle of attack of an aircraft flying at Vy is less than when flying at Vx.

Our Diamond DA20’s, to give an example, have a Vy of 75 knots.

How to calculate the speed for best angle of climb VX

Now you know what each of the speeds mean, you may be asking yourself where you might be able to look them up. It’s quite easy:

In the POH (Pilot Operating Handbook) of an aeroplane there are power charts. These diagrams relate to the power of the aircraft, speed and thrust force. Based on them, it is possible to find out Vx, Vy or the maximum gliding speed.

POH is a pilot’s definite reference guide as all information relating to systems, capacities, limitations and other characteristics can be found in them.

The speed for best angle of climb, Vx, is obtained at the point in which the difference between the available thrust and aircraft drag are maximum, or to put it in other words, it’s the point in which there is a greater excess of thrust.

The speed for best rate of climb, Vy, is obtained at the point in which the difference between the available power and the required one is maximum, or when there is increased excess power.

Be rigorous when keeping to adequate speed

Every training pilot will hear their instructor telling them repeatedly to keep their speed when they first start flying because it’s essential to maintain adequate speed, especially when flying low.

Flying at flight level 290, a metre won’t make a difference, however, with headwind, a metre might be the extra altitude needed to reach the runway, following an engine loss.

On many occasions , this may pass inadvertently but with aircraft as aerodynamic as the Diamond DA20, just a metre will allow it to move forward for up to 11 horizontal metres.

This distance is calculated based on the gliding ratio but we will explain about this in a further post. Stay tuned and you won’t miss it!

And if you’d like to continue learning about the speed of aeroplanes, don’t miss the linked post – you’re gonna love it!

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