Aircraft CG and trim - pilots' perspective?

[Stick-N-Rudder]

As a load controller, I would like to know more about the pilots' perspective concerning a/c trim and CG. We were taught that within reasonable limits we should always aim for an aft CG which is more fuel efficient. What I would like to know is if this is the only factor involved, or are there any others, e.g., is it easier to handle an a/c with an aft CG or are there any instances in which you prefer the a/c more nose-heavy?

Also - and concerning the A320/321 in particular - I am curious to know if there are any zones within the operational margins (depending on the ZFW, of course) you don't feel comfortable with, and if so, what MAC ranges would that be, approximately?

Cheers

[Mad (Flt) Scientist]

Not a pilot, but given that you seem to be concerned specifically with the A320 series, this post and the reference it refers to may be of interest. Basically, Airbus state that there's no fuel burn gain for aft cg on those a/c, so you may be going to a bit of trouble to get an aft cg you aren't getting any benefit from.

[Intruder]

I have flown the 747 in virtually the entire allowable CG range. Handling is not noticeably different throughout the range. The only exception seems to be the Classic during autoland, where a forward CG tends to cause the airplane to overtrim nose-up.

Also, I tend to be wary of Takeoff trim settings that are outside the "usual" range. It's nice when the loadmaster alerts me ahead of time that he's loading near the fwd or aft limit...

[BOAC]

Tut tut RB! Company 737 manual says "For fuel efficiency, the bags should normally be loaded in the rear.".

For 'S-n-R' - I have never been skilled enough to notice discernable handling changes on the 737 with CG movement. Pax distribution is pretty crucial, and model specific, and you should fairly quickly be able to pick up a pattern of how/where to load pax and bags for each a/c. My basic guideline (7372/3/4/5/7) with equal A/B/C pax is 100 in 3/4 and rest in 2 (very small trim change in 2). I don't fly 8/9 but I believe the pax need to be biased forwards.

I have NEVER had to have any re-distribution in 20 years. Only problems have been when pax have been badly seated. I don't know how the 'free-seaters' cope!

[Stick-N-Rudder]

For 'S-n-R' - I have never been skilled enough to notice discernable handling changes on the 737 with CG movement. Pax distribution is pretty crucial, and model specific, and you should fairly quickly be able to pick up a pattern of how/where to load pax and bags for each a/c. My basic guideline (7372/3/4/5/7) with equal A/B/C pax is 100 in 3/4 and rest in 2 (very small trim change in 2). I don't fly 8/9 but I believe the pax need to be biased forwards.

The loading guidelines we have from various airlines for 737-300/400/700 (never worked with -200 and -500) are very similar to what you describe, normally fill up at the rear with 100-120 bags, then overspill into 2, with some minor variations.

The 737-800 is a different case and a curious one from my point of view. There are two major tendencies followed by the airlines we operate with: some say 2/3 in hold 3, 1/3 in 2 - using actual baggage weights - and some always require first 140 in bags hold 3, rest in 2 - using standard weights of 13 kg per bag. From my own experience at check-in, I know that the actual bag weight can average 17 or 18 kg most of the time on said flights. Now let's suppose you have a 737-800 with 140 pax seated evenly across cabins, and that those pax have checked in 140 bags. As per standard loading, those bags are loaded into hold 3, and the aircraft is well within CG limits. The loadsheet will show those bags as 1820 kg due to the standard weights used, but in reality they will most likely weigh around 2400-2500 kg. My question is, and particularly considering the low ground clearance of the -800, can this scenario pose a risk or is it not significant enough?

Cheers

[SNS3Guppy]

In the 747, I never do autoland, and have never paid particular attention to whether the airplane behaves one way or the other with respect to CG position. It's a fairly benign airplane. We normally try to load as close to 26% or so. So long as it's with in limits, that's good enough.

[GlueBall]

Rearward CG produces less drag in that the stabilizer's "nose-up trim" [negative angle of attack] is reduced.

[411A]

Aft CG loading is certainly preferred for fuel saving in cruise with many aircraft, my present type included.
Interesting to note, that during certification testing of a new design, a stab trim normal zone (for takeoff) is determined, for all CG locations.
Pretty standard stuff.
However, there is one civil jet transport airplane that, while having a normal CG range for takeoff, it was found that, during certification testing, pole forces were reasonable with just about any CG location, for rotation.
This was primarily due to the stab design....the pilots column moves the entire horizontal stab assembly, not just the elevators.
A quite unique design, and found on only one civil jet type....TriStar.

Lockheed....nothing finer

[CR2]

http://www.pprune.org/archive/index.php/t-280751.html

This old thread is worth re-visiting.