Quote:
Originally Posted by Crumpp
This is the expression for the average acceleration:
a = F/m
m = 9000lbs/32.2 = 279.5 lb-s^2/ft
a= 5864lb/279.5lb-s^2/ft
a = 20.98 ft/s^2
It is all in the formula, blackberry.
Think about it. Do you know what the acceleration would be if just gravity is acting alone on the airplane?
32.2ft/s^2.....
Do you think our acceleration is going to greater or smaller than the acceleration of gravity at the beginning of the dive when we have the most excess thrust?
GREATER THAN
Why is our average acceleration lower than that of gravity???
20.98 ft/s^2 < 32.2ft/s^2......
Because there is an aerodynamic braking force acting on the aircraft that lowers the average acceleration.
Yes the formulation requires constant acceleration but that does not mean it does not accurately describe the motion of the aircraft.
|
g=32.2ft/s^2=9.8m/s^2
At the beginning of 45 degree dive, dive acceleration is greater than g due to bigger engine thrust and smaller air braking force, and at the end of dive, acceleration is smaller than g due to smaller engine thrust and bigger air braking force.
But we need to calculate acceleration very accurate. In a 15 seconds long 45 degree dive, if my average acceleration is slightly than yours, for example, is 3ft/s^2 or 0.9m/s^2 more than yours. I'll be 50km/h faster than you in the end. That's a hugh advantage.
Do you remember the 60 degree dive between P47D and fe190G in 1943 summer? At the end of dive, P47D had a much greater speed than fw190G, sth. like 50km/h difference is huge enough.
I have a question for you:
At 1st second, you begin to 45 degree dive,
At 2nd second, your speed increase a little, acceleration is greater than g.
at 3rd second, your speed increase a little more, and acceleration is still greater than g.
.....
at 20th second, you reach the equilibrium point, and acceleration is ZERO. Your speed remains same.
at 21st second, your speed is same as 20th second.
at 22nd second, hour speed is same as 20th second.
......
How about the 19th second? what's your acceleration? It should be smaller than g, but I need more accurate data.
Is the acceleration at 19th second nearly zero or around 0.5*g?