Learning hub · Performance · Lesson 2

Climb, cruise and landing performance

Take-off is only the start. This lesson follows the rest of the flight: how the aeroplane climbs, how far and how long it can cruise, how far it can glide, and what decides the landing distance.

About 13 minutes, plus the quiz. Part of Performance. It builds on Density altitude and take-off performance.

1. Two best climb speeds

An aeroplane has two useful climb speeds, and they answer different questions.

• Vx, the best angle of climb speed, gives the most height for a given distance over the ground. You use it to clear an obstacle after take-off.
• Vy, the best rate of climb speed, gives the most height in a given time. You use it to reach your cruising altitude quickly.

Vx is lower than Vy. Both numbers are in the flight manual. As you climb, Vx tends to rise and Vy tends to fall, until they meet at the aeroplane’s absolute ceiling, where it can no longer climb.

The idea behind them: the angle of climb depends on spare thrust (thrust minus drag), and the rate of climb depends on spare power (power available minus power needed). Remember which speed does which job. The manual figures are only true for the stated mass, flap setting and conditions.

2. What changes the climb

Anything that reduces spare power or spare thrust reduces the climb. The usual causes are the same ones as in the take-off lesson.

• Density altitude. Thin air gives the engine less power and the propeller less thrust. The climb is weaker the hotter and higher you are.
• Mass. A heavier aeroplane has less spare power and climbs more slowly.
• Flaps, drag and speed. Flaps down, a wrong speed or a dragging item all reduce the climb. Climbing at the wrong speed costs both angle and rate.
• Wind. The wind does not change the rate of climb through the air. It does change the angle over the ground. A headwind makes the climb path steeper over the ground, which helps with obstacles. A tailwind makes it shallower.

A climb gradient is height gained as a percentage of distance flown. It is groundspeed that matters, not airspeed:

gradient (%) = rate of climb (ft/min) ÷ groundspeed (ft/min) × 100

One knot is about 101 ft/min (6,076 ft in 60 minutes), so you can multiply knots by 101 to get ft/min.

3. Cruise: power, range and endurance

In the cruise you choose a power setting from the table in the flight manual. Each combination of power, altitude and mixture gives a true airspeed and a fuel flow. Two terms matter.

• Endurance is how long you can stay airborne. It is best at the lowest fuel flow that still holds level flight, which means flying slowly.
• Range is how far you can go. In still air the best range comes from flying at about the speed of best lift-to-drag ratio, which is faster than the speed for endurance.

Wind changes the range. Into a headwind, flying a little faster gives more distance per litre. With a tailwind, a little slower is better. The simple sum is:

endurance (h) = usable fuel (L) ÷ fuel flow (L/h) and range = endurance × groundspeed

Those sums give a figure before reserves. Fuel planning, including the reserve, is in the flight planning lesson.

4. The glide

With the engine at idle or stopped, the aeroplane still flies, along a descending path. The best glide speed (in the manual) gives the greatest distance, and it is close to the speed of best lift-to-drag ratio. The glide ratio is the distance flown divided by the height lost. A ratio of 9 to 1 means 9 units forward for each unit of height.

Rules for the glide: a headwind shortens it, a tailwind lengthens it, and a heavier aeroplane glides at a higher speed but, in still air, no farther. Flaps, a windmilling propeller and gliding faster or slower than the best speed all reduce the distance. You will use this in the engine failure lesson.

5. What decides the landing distance

The landing distance is how far it takes to stop. Manuals give the ground roll and often the distance from 50 ft above the runway, which includes the flare. Figures from an American handbook (Pilot’s Handbook of Aeronautical Knowledge) show the size of the effects:

Factor	Effect on the landing distance (approximate)
Landing mass 10 per cent higher	about 10 per cent longer
Approach speed 10 per cent too fast	at least 21 per cent longer
Each 1,000 ft of altitude	about 3.5 per cent longer (the true airspeed is higher in thin air, so the groundspeed at touchdown is higher)
Tailwind	longer, and by more than a headwind of the same size shortens it
Wet, soft or snowy surface	longer, sometimes much longer (next lesson)

The speed effect is the one pilots can control. Holding the speed in the manual, with a stable approach, saves runway. Landing long and fast on a wet runway is a common route to a runway excursion.

A worked example, with invented numbers. The manual gives 380 m from 50 ft for the mass used in the table. Today you land 10 per cent heavier, so add 10 per cent: 418 m. Then compare the airfield’s landing distance available (LDA, in the AIP) with the figure, with a margin on top.

Training only. Real flights use the performance data in the approved flight manual. The percentages above are guidance to understand the factors, not to plan with.

6. Try it yourself

Work each one out on paper first, then open the answer to compare. The numbers are invented.

1. Your invented aeroplane climbs at 600 ft/min at 80 kt true airspeed. (a) In still air, what is the climb gradient? (b) With a 15 kt headwind, what is the gradient? Use 1 kt = 101 ft/min.
   Show the answer

   1. (a) Groundspeed 80 kt, so 80 × 101 = 8,080 ft/min. Gradient = 600 ÷ 8,080 = 0.074, so about 7.4 per cent.
   2. (b) Groundspeed 65 kt, so 65 × 101 = 6,565 ft/min. Gradient = 600 ÷ 6,565 = 0.091, so about 9.1 per cent.
   3. The rate of climb did not change. The headwind made the path steeper over the ground.
2. An invented aeroplane has a glide ratio of 10 to 1 at its best glide speed of 65 kt. The engine fails 2,500 ft above the ground. (a) How far can it glide in still air, in nautical miles (1 NM = 6,076 ft)? (b) A field is 3 NM away, straight ahead, and there is a 10 kt headwind. Can you reach it?
   Show the answer

   1. (a) Distance = 2,500 × 10 = 25,000 ft. 25,000 ÷ 6,076 = about 4.1 NM.
   2. (b) The headwind cuts the groundspeed from 65 to 55 kt. The distance shrinks in the same ratio: 4.1 × 55 ÷ 65 = about 3.5 NM.
   3. That is only 0.5 NM more than the field, with no allowance for a turn, for the time to decide, or for a flare. It is marginal, and a closer field would be a better choice.
3. The manual of an invented aeroplane gives a landing distance of 380 m from 50 ft. You land 10 per cent heavier than the table mass, and you cross the threshold 10 per cent faster than the speed in the manual. Estimate the distance with the table above. The runway has an LDA of 520 m. What do you do?
   Show the answer

   1. Heavier by 10 per cent: 380 × 1.10 = 418 m.
   2. Speed 10 per cent too fast: at least +21 per cent, so 418 × 1.21 = about 506 m.
   3. The LDA is 520 m, so only 14 m remain, with no margin at all, and a wet surface would exceed it. This is not acceptable. Fly the right speed, reduce the mass, or use a longer runway.

7. Watch

A video on the best rate and best angle of climb speeds and how they relate to the power curve. Check the wording against your own course material.

Open on YouTube if the player does not load. Not made by VectorEFB; check what you learn against your flying school’s material and your instructor.

More to watch

A second view of the same two speeds from an instructor. This video is American, so wording and some rules differ from European (ICAO/EASA) practice.

Open on YouTube if the player does not load. Not made by VectorEFB.

8. Check yourself

Five original practice questions. Answer them, press Check answers and read each explanation.

Next: Runway surface, slope and crosswind limits. Back to the learning hub.