ATPL Moving Mass problem
Thread Starter
Join Date: Mar 2011
Location: Norway
Age: 37
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
ATPL Moving Mass problem
"An aircraft has a loaded mass of 5500 lb. The CG is 22 in. aft of the datum. A passanger, mass 150lb, moves aft from row 1 to row 3 a distance of 70 in. What will be the new position of the CG.(All dim. aft of the datum)"
Heres how i failed, i took 5500lb*X / 70in =150 lb, X= 2.1
So i expected to get new CG at 2.1in+22in = 24.1
Book says it should be 23.9.
What have i done wrong? Any ideas?
Heres how i failed, i took 5500lb*X / 70in =150 lb, X= 2.1
So i expected to get new CG at 2.1in+22in = 24.1
Book says it should be 23.9.
What have i done wrong? Any ideas?
Join Date: Jan 2008
Location: UK
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Heres how i failed, i took 5500lb*X / 70in =150 lb, X= 2.1
I get x = 1.90 from the above:
(5500*x) / 70 = 150
=> 5500*x = 150 * 70
=> x = (150 * 70) / 5500 = 1.90
(and 1.90 + 22 = 23.9)
I get x = 1.90 from the above:
(5500*x) / 70 = 150
=> 5500*x = 150 * 70
=> x = (150 * 70) / 5500 = 1.90
(and 1.90 + 22 = 23.9)
For load shifts (but not load additions or removals) use the following.
MS = ms
Where
M is the total mass (big M = big mass)
m is the mass moved (little m = little mass)
S is the distance that the CG shifted (Big S = big mass shift)
s is the distance that the mass is moved (little s = little mass shift)
In this case we have
M = 5500 lbs
m = 150 lbs
s = +70
MS = ms
Rearranging this gives
CG Shift = S = (ms) / M = (150 x 70) / 5500 = +1.909
Adding this to the original CG gives + 22 + 1.909 = 23.909
MS = ms
Where
M is the total mass (big M = big mass)
m is the mass moved (little m = little mass)
S is the distance that the CG shifted (Big S = big mass shift)
s is the distance that the mass is moved (little s = little mass shift)
In this case we have
M = 5500 lbs
m = 150 lbs
s = +70
MS = ms
Rearranging this gives
CG Shift = S = (ms) / M = (150 x 70) / 5500 = +1.909
Adding this to the original CG gives + 22 + 1.909 = 23.909
