Class A Aircraft - Take-off — Page 406, Lesson 494

Right, so we’ve finished with V1, VR, and V2. Now there are two more speeds we have to check before we can call the take-off speeds done. The first is VMCG. VMCG is the minimum control speed on the ground. Remember the theory we covered earlier: V1 must never be less than VMCG. In our example, it isn’t, so we’re fine. To find VMCG, we use the table in Figure 14.19. Using our example airfield conditions of 25°C and 2000 ft pressure altitude, VMCG comes out to 112 knots. Now, the last speed to calculate is VMBE — that’s the maximum brake energy speed. The graph for this is on page 15 of section 4 of CAP 698, and we’ve already described how to use it. Using Figure 14.14, with our airfield conditions of 2000 ft pressure altitude, 25°C, and our regulated take-off mass of 57 900 kg, the graph isn’t actually applicable — we’re in the shaded area. But as an example, VMBE is 175 knots. However, there are corrections to make. We had a 2% upslope, and that means we need to increase VMBE by 4 knots. There’s also a wind correction: we assumed a 20 knot headwind, and that means VMBE must increase by 6 knots. So the total correction increases VMBE to 185 knots. Now, all the relevant take-off V speeds have been calculated based on our regulated take-off mass of 57 900 kg. Next, we have the correction for stopway and clearway. The speeds in the tables we’ve just used are based on a balanced field length — that means TORA equals TODA equals ASDA. Those speeds are not valid if the take-off mass has been derived using stopway or clearway. Where that’s the case, V1 may be adjusted for the effects of stopway or clearway using the table in Figure 14.20. Then we have the thrust setting, expressed as % N1. The thrust setting values are shown in CAP 698 on pages 20, 21, 22, and 23 of section 4. Use the tables on those pages to select the appropriate thrust setting for take-off and for the climb, using the conditions at the airfield. Finally, the stabilizer trim setting. The stabilizer trim setting appropriate to the CG position and take-off mass can be read from the table in Figure 14.21, and these are shown in CAP 698 at the bottom of pages 18 and 19 of section 4. So to recap the whole picture: we’ve got V1, VR, V2, then VMCG and VMBE as the two additional checks, then the stopway/clearway correction to V1, then the thrust setting in % N1, and finally the stabilizer trim setting. That completes the take-off speed and setting calculation for our Class A aircraft.