Talk:Center of gravity of an aircraft

Page Creation

Born2flie: Creating this page for a more formal treatment rather than the one given this important aviation topic in the Center of mass article. --18:05, 29 December 2006 (UTC)

Page move

Page was moved without discussion. Article is a discussion of the "center of gravity" of an aircraft as opposed to center of gravity as discussed in military operations or as discussed in the general physics discussion of the center of a mass. --Born2flie (talk) 19:58, 3 February 2008 (UTC)

The difference is that Center of gravity (military) is a separate concept from physical centers of gravity. This article is about the exact same thing as Center of gravity (or Center of mass), but in a specific context. In this situation one uses a noun phrase rather than parentheses: History of saffron rather than Saffron (history), Education in India rather than Education (India).

In more concrete terms, there is a danger that the title "Center of gravity (aircraft)" will confuse readers. Since other Wikipedia articles reserve parentheses for separate concepts, the reader may conclude that "center of gravity" means something different for aircraft than for other objects. Melchoir (talk) 20:13, 3 February 2008 (UTC)

The article isn't about Center of mass of an aircraft. It is about the aviation term "Center of Gravity", which alone would justify the use of parentheses. The article was devised as an article about the term and the concept within aviation, not a further discussion of the concept of center of mass in physics, only specifically applied to aircraft. And, again, you moved the established page without discussion and without understanding what the article was actually about. --Born2flie (talk) 14:39, 4 February 2008 (UTC)

You are drawing distinctions that I do not understand, and which I doubt that the reader will appreciate. If it's really that big a deal for you, you can move the article back to its previous title. As long as you don't restore the hatnote at the top of Center of mass per WP:RELATED, I won't complain. Melchoir (talk) 23:09, 4 February 2008 (UTC)

Dominated by Helicopter Discussion

This is at the moment more of a discussion of the cg of a helicopter than for aviation in general. Either it needs to be made specific for helicopters alone or needs to discuss the issue of other aircraft. I would suggest that the assertion that cg is more critical for a helicopter is not entirely valid; very many fixed wing aircraft have been lost due to improper loading and a cg out of range as a result. MadScot666 (talk) 01:34, 5 August 2008 (UTC)

As the originator of the article. I used the FAA rotorcraft manual and the FAA weight and balance manual as references. The rotorcraft manual made a great deal about the effects of cg out of range, the general aircraft manual did not and it was weighted more on the side of fixed-wing aircraft. --Born2flie (talk) 01:22, 28 May 2009 (UTC)

Centroid

The article states:

Other terms used interchangeably with arm are station and centroid (used on large transport category aircraft).

I'm not sure I buy the centroid part of this. In my experience, centroid is synonymous with the CG, not the torque arm (see centroid article). I'm going to mark this item for clarifcation in the article. 70.250.198.35 (talk) 05:13, 6 September 2010 (UTC)

I agree that centroid is not an alternative to the moment arm. I have deleted it. I also had a problem with station - stations are numbered 1, 2, 3 etc. They are not distances. I deleted that too. Thanks for spotting those problems

When calculating the center of gravity of an aircraft, and checking the loading of an aircraft, the word moment is used rather than torque. I explain this to myself by saying torque is measured about a center of rotation. Moment is measured about an arbitrary datum. An aircraft doesn't have a center of rotation but it does have a datum assigned to it to aid in specifying limits on the position of the center of gravity. Dolphin (t) 08:02, 6 September 2010 (UTC)

In principle, torque (in the "moment of force" sense) may be measured from any reference point, not just the center of rotation, although in most cases that's certainly the most convenient. The reason why "moment" is used rather than "torque" may be just convention. There's a good discussion of this on the torque wiki page. In some fields (like US physics), "torque" and "moment of force" are considered synonymous, while in others they are used to represent slightly different concepts. I suspect aerodynamics is one field where convention is to use "moment of force", or just "moment", instead of "torque". But to many (most?) readers, the two are synonymous, and the other relevant wiki pages are consistent with that usage. Gdlong (talk) 16:30, 28 October 2014 (UTC)

Wording suggestion for Calc section

I'd like to suggest the following revision in the wording, to provide more clarity:

• Determine the weight and arm of each mass to be carried in the aircraft.
• Multiply that weight by that arm for each mass to be carried, to calculate the moment of each mass.
• Including the aircraft empty weight and moment, add the weights of all mass, and the moments of all mass.
• Divide that total of the aircraft and contents moment by that total (gross) weight to give an overall arm. — Preceding unsigned comment added by Jw4nvc (talk • contribs) 23:08, 21 March 2011 (UTC)

Given example units

We should definitely use SI and not imperial here if we are writing about physics. 91.103.43.50 (talk) 14:26, 26 September 2012 (UTC)

Please, follow this advice here and throughout wikipedia (its an encyclopedia and not a sort of book-of-interesting-facts targeted to a few audiences). 177.204.21.28 (talk) 12:29, 15 June 2013 (UTC)

Actually, this article details specifics to an "aircraft" for which I have only seen in imperial units as far as practical use. Is there an FAR that requires this to be so?108.129.180.14 (talk) 02:55, 15 January 2014 (UTC)

Suggestion

Quite a good article having read through it, slightly short of wikilinks and citations, images would also help. What seems to be missing to me is the process of determining an aircraft's actual centre of gravity, i.e. weighing it. There's enough for a separate article on the subject. Is this something that we would like to cover? Cheers. Nimbus (Cumulus nimbus floats by) 10:15, 14 January 2013 (UTC)

I agree that there is scope for expanding this article to incorporate some information about weighing an aircraft to determines its weight and the position of its CG. I doubt it is sufficiently notable a topic to warrant its own article. I found the lede to be a bit indigestible so I made a few tweaks - diff. Dolphin (t) 10:46, 14 January 2013 (UTC)

You're probably right, at the worst if it got too long it could be split off. Think I have the same FAA handbook that has been used here, perhaps I'll start a section in a sandbox and see what it looks like. Nimbus (Cumulus nimbus floats by) 10:59, 14 January 2013 (UTC)

It's actually the hard copy FAA 'A&C' manual that I have. Just noticed that the article is using templated cites, I struggle mightily with them. Nimbus (Cumulus nimbus floats by) 11:03, 14 January 2013 (UTC)

Center of lift

I was surprised to see no discussion of keeping the CofG forward of the Ctr of Lift so as to ensure stall recovery.

G. Robert Shiplett 19:07, 15 January 2013 (UTC)— Preceding unsigned comment added by Grshiplett (talk • contribs) 19:07, 15 January 2013‎

Keeping the CofG forward of the center of lift? That is an old wives' tale; it has no basis in aeronautics. To ensure safe low-speed handling, including stall recovery and spin recovery, the CofG must be within the CofG limits specified by the aircraft manufacturer. These limits are known simply as the forward CofG limit and the aft CofG limit - they have no other name.

The lift on an airfoil can be considered to act at a point known as the center of pressure, not the center of lift. The center of pressure is not a fixed point because it moves about, dependent on the angle of attack on the airfoil. The only aerodynamic point on an airfoil that is fixed is the aerodynamic center - it is typically around 25% of the chord of the airfoil (where 0% is the leading edge and 100% is the trailing edge). However, the aft CofG limit is always behind the aerodynamic center. Consequently the aircraft CofG is often behind the aerodynamic center. Dolphin (t) 23:45, 15 January 2013 (UTC)

Overweight operations

Can anyone cite a reference for the assertion that "Overweight operations are not permitted with passengers aboard."?

Given the number of recent incidents of passenger aircraft burning fuel prior to a premature unscheduled landing, I suspect this is not a true statement. e.g "After using up fuel, the plane landed at Schiphol Airport in Amsterdam." Mesdale (talk) 13:19, 23 August 2013 (UTC)

Large airplanes have a maximum landing weight. Except in a serious emergency such as fire on board, they aren't supposed to land heavier than the maximum landing weight. In the case you cited, the airplane was intended to go from Paris to Detroit so it was carrying a large amount of fuel. Shortly after take-off the crew discovered they were unable to retract the wing flaps from their take-off setting. It isn't feasible to fly across the Atlantic at the low speed necessary with flaps in the take-off position so the crew decided to land and have the problem rectified. The aircraft was too heavy for landing because of all the fuel on board. Consequently the crew flew around for a while to burn off fuel to get the weight down to maximum landing weight or lower. Eventually, when enough fuel had been burned the crew landed the airplane in Amsterdam. Some very large airplanes have the ability to dump fuel into the atmosphere but most don't, so they must fly around long enough to burn the fuel. Dolphin (t) 02:02, 24 August 2013 (UTC)

A reference for the statement that passengers can't be aboard an airplane when it is operating overweight is Federal Aviation Administration Advisory Circular AC 21-4B "Special Flight Permits for Operation of Overweight Aircraft" - see Advisory Circulars and select 21-4B. In Appendix 1, page 3, of this Advisory Circular you can read that carriage of passengers or property for compensation or hire is not permitted in operations on a Special Flight Permit. Dolphin (t) 02:24, 24 August 2013 (UTC)

The 'maximum landing weight' is an arbitrary limit calculated by the Type's Test pilots during the testing phase that takes into account the skill of an 'average pilot', the possible wind speeds (gusts) likely to be encountered, as well as the stress limits of the aircraft's undercarriage and the loads likely to be applied to it. These control how gently an aircraft must land in order to prevent structural damage, however a skilled pilot in good conditions will be able to land the aircraft at more or less the same weight it took off at, the point being that the weight of the aircraft must be transferred via the undercarriage to the ground as gently as possible. In addition, more runway will be needed to allow for the slower speed reduction when braking due to the greater weight and higher landing speed.

In the case of an uncontrolled fire on board the only important thing is to get the aeroplane on to the ground (or even ditching it in the sea if neccasary) as soon as possible, as there is no telling how long the pilot will have control of the aircraft, hence in this circumstance delaying landing for dumping fuel is likely to be A Very Bad Idea as landing an over-weight aircraft while you still have control of it is less likely to cause injury or death to those onboard than wasting valuable time dumping fuel until the fire possibly makes the aircraft un-flyable.

Commercial aircraft are insured and landing an over-weight aircraft even if it causes some damage to the aircraft is likely to be a more desirable result, both for the passengers and crew, as well as for the airline and insurers, than waiting for the aircraft to crash killing all on board. Neither airlines nor insurers like the latter. If they think the cost of repairing damage due to an over-weight landing that the passengers and crew walked away from is expensive, wait until they have to pay out after an accident like Swissair Flight 111 or UPS Airlines Flight 6.— Preceding unsigned comment added by 95.144.50.207 (talk) 10:48, 23 February 2019 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Center of gravity of an aircraft/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Born2flie: Needs to discuss how CG is computed for aircraft loads as well as different classes of aircraft and how they are affected by CG changes. --18:06, 29 December 2006 (UTC) Born2flie: Added in a bunch of information from the FAA's Airplane Flying, Rotorcraft Flying, and Weight and Balance Handbooks. Could probably use some diagrams showing reference datums and explaining arm and moment and balance calculations. Look at cutting some images from the handbooks. --20:20, 5 January 2007 (UTC)

Substituted at 21:37, 26 June 2016 (UTC)