Stuck with a Mass and Balance question can you help please!

[flipper]

Can anyone possibly bail me out with this feedback question. I have been struggling with it !

What is the CG as a percentage of the MAC at the DOM for the aeroplane crewed as shown?
Moment Table seat A or B Moment
70kg -35
80kg -40
40kg -45
100kg -50
110kg -55
120kg -60
Seat C
70kg +35
80kg +40
90kg +45
100kg +50
110kg +55
120kg +60
Special equipment
1000kg +15000

There is a diagram which shows a cockpit with the Cpt position as A ,1st Officer as B and Engineer as C ,behind the 1st Officer.

BEM 18000kg
Pilot 100kg
1st Officer 90kg
Flt Engineer 80kg
Special equipment 1000kg
MAC 3m
CG at BEM 6.6m
CG at BEM 20% MAC

The answer is I think supposed to be 9.3% -but being a dope I can't work it out! Can anyone help. Thanks flipper

:confused:

[Mad (Flt) Scientist]

Assuming everything is metric and allowing for typos:

18,000kg aircraft, c.g. at 6.6m : moment 18000*6.6=118800kg-m
1000kg equip (assumed at 15m) : 15000kg-m moment
100kg pilot (assumed at -0.5m) : -50kg-m
90kg FO (at -0.5m) : -45 kg-m
80 kg FE (at +0.5m) : 40 kg-m

Total moment: 118800+15000-50-45+40=133745kg-m
Total mass: 18000+1000+100+90+80=19270kg

Therefore c.g. at 133745/19270=6.94m

20% mac is 6.6m so c.g. is 0.34 m aft of that

0.34m/3m (mac) is 11.3%

So c.g. is at 20% + 11.3% = 31.3%

I can't get 9.3% out of those numbers.

[flipper]

Mad (Flt) Scientist,
Thanks for your efforts with that. I shall print it off and have a bash.
Regards flipper

[schuler_tuned]

Hi flip,
won't even start to try and give an answer (managed to scrape my pass with 77%, PHEW!!). I thought it was the hardest exam of them all, so work hard, &
1, practice what happens to the CG when you move mass,
i.e. w = d
W D
2, remember that in the back of CAP 696 you have the trim sheet with all the boxes to work out the limiting load from MZFM, TOM and LM. Use the example, and be able to do it second nature
3, And if you get a % of MAC question I think the answer is 22%!!!!!!
Best of luck,
Schuler.

[flipper]

Schuler-tuned,
Thanks for the info and advice.
Regards
flipper