Question
An aircraft has a mass of 60,000 kg and a limiting positive load factor of 2.5. VA is calculated as the EAS at which full positive elevator deflection will give the limiting load factor at the stall, and is 237 kts. If the aircraft mass is reduced to 40,000 kg by fuel burn, what will be the new VA?
Answer
The formula is VA = VS1g x sq root of limit load factor
New VA = Stall speed at new lower weight of 40,000 x sq root of 2.5
First we need to know the stall speed at 60,000, which we can get from the above formula:
237 = VS x sq root of 2.5
VS = 150
Stall speed at 40,000 will be less than 150
Reduction factor = 40000/60000 = 0.666
sq root of 0.666 = 0.81
150 x 0.81 = 122
So the stall speed at 40,000 will be 122
New VA = 122 x sq root of 2.5
= 193
