737NG cruise CG
Thread Starter
Joined: Apr 2002
Posts: 387
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From: shoe box
737NG cruise CG
I'm hoping someone here can help with more info about the cruise cg on the perf init page in the 737-800.
I believe there are a couple of default values used - 26.2% by the FAA and 5% by the CAA.
Why do they use different figures, and does this translate to much of a difference in the max alt?
Also, what do people generally use? Our company uses 26.2% and we never touch it, but are there any companies out there that have their own settings and why?
I believe there are a couple of default values used - 26.2% by the FAA and 5% by the CAA.
Why do they use different figures, and does this translate to much of a difference in the max alt?
Also, what do people generally use? Our company uses 26.2% and we never touch it, but are there any companies out there that have their own settings and why?
Joined: Feb 2006
Posts: 112
Likes: 0
From: UK
Well FR drivers are not allowed to touch the default of 5%...
And yes it does make a difference of approx 2000' (if I remember correctly)
Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins
And yes it does make a difference of approx 2000' (if I remember correctly)
Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins
Joined: Aug 1998
Aviation Qualifications: ATPL
Posts: 6,623
Likes: 847
From: Ex-pat Aussie in the UK
I normally enter a value about halfway between the take-off CG and the ZFW CG values on the load sheet. 26% is typical. 5% is the forward limit = highest stalling speed, so the worst case for the buffet limit display.
(Stall speed increases with forward CG, as the tail carries less of the load/provides more down force, which then has to be taken up by the wings, i,e a higher angle of attack for any given weight.)
(Stall speed increases with forward CG, as the tail carries less of the load/provides more down force, which then has to be taken up by the wings, i,e a higher angle of attack for any given weight.)
Joined: Jan 2003
Posts: 18
Likes: 0
From: UK
"Well FR drivers are not allowed to touch the default of 5%...
And yes it does make a difference of approx 2000' (if I remember correctly)
Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins"
Plain-plane you don't remember correctly. It's a few hundred feet you lose at the most, especially since FR load their aircraft with a forward CG anyways.
The gain in manuever margin far outweights the minor loss in altitude capability by leaving the CG at 5%.
And yes it does make a difference of approx 2000' (if I remember correctly)
Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins"
Plain-plane you don't remember correctly. It's a few hundred feet you lose at the most, especially since FR load their aircraft with a forward CG anyways.
The gain in manuever margin far outweights the minor loss in altitude capability by leaving the CG at 5%.
Joined: Sep 2005
Posts: 56
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From: here and everywhere
We use 18% CG on the PERF-INIT page for the whole flight which I find the number to be quite realistic.
It makes a huge difference especially when you do a 5-6 hour sector with respect to fuel!
It makes a huge difference especially when you do a 5-6 hour sector with respect to fuel!
