Single-engine Class B Aircraft - Take-off — Page 302, Lesson 380

Let me walk you through this take-off performance work for a single-engine Class B aeroplane. We're going to correct a take-off distance for runway surface and slope, then look at the certification rules that govern take-off speeds. First, the correction work. We calculated a take-off distance of 2300 ft, and that figure assumed a paved, dry runway. Now we change the conditions. Let's put the aeroplane on wet grass. Both of those variables — the grass surface and the wetness — increase take-off distance. Wet grass increases the distance by 30%, which is a factor of 1.3. So we take our 2300 ft and multiply by 1.3, giving 2990 ft. Now add an upslope of 1%. An upslope increases take-off distance by 5%, a factor of 1.05. So 2990 ft times 1.05 gives us 3140 ft. That's the total gross take-off distance. Now, to comply with field length requirements and obtain a net take-off distance, we must compare that take-off distance against the available distances at the airfield, to ensure it does not exceed the limits laid down by the authorities. Those regulations are in CAP 698, page 1, section 2 — that's the document you'd turn to for the field length rules. Now the certification requirements. These come from EASA's document CS-23, and only two main specifications apply to the take-off phase, both concerning take-off speeds. The first concerns VR. VR is the speed at which the pilot makes a control input with the intention of getting the aeroplane out of contact with the runway. The certification specification states that for the single-engine aeroplane, VR must not be less than VS1. VS1 is the stall speed, or the minimum steady flight speed, obtained in a specified configuration — and the configuration concerned here is the take-off configuration. The second specification concerns the speed at screen height. The speed at 15 m, or 50 ft, above the take-off surface must be more than the higher of two values: a speed that is safe under all reasonably expected conditions, and 1.2 times VS1. That speed attained at screen height is commonly called the take-off safety speed. One important note: these certification regulations about VR and the take-off safety speed are not found in CAP 698, so you must commit them to memory.