Center of Gravity and takeoff weight

[michal 44]

Is there anything in the aviation that allows for slightly higher takeoff weight if center of gravity is slightly aft (still within the limits). Some folks on some other forums claims this is the case.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[Guest jrewing]

My answer would be that the aircraft has to be operating within the weight and balance limits specified by the manufacturer in the approved flight manual. I did a quick scan of 14 CFR 23 and 25, but didn't see any allowance for an increased takeoff weight.John

[AlaskanFlyboy 7]

They may be thinking the Normal and Utility Categories that are on the weight and balance charts. But, that's not exactly a good description of it.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

[Donstim 109]

What class of airplanes are you asking about? For part 25 airplanes, certain performance parameters (like stall speeds) are based on the forward cg limit. In some cases, multiple cg envelopes are established to allow operation at higher takeoff weights.Don S.

[michal 44]

Don,Any category. In short is there any category of airplanes for which MTOW depends on position of CG. I am not familiar with part 25, what about part 121 or 135, those that air taxis or airlines operate under. What is part 25?Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[Guest jrewing]

Michael,14 CFR 25 describes Airworthiness Standards for Transport Category Airplanes. You can browse these regs at http://ecfr.gpoaccess.gov/, look under Title 14.There is a theoretical concept that an aircraft in unaccelerated flight with an aft CG will experience a lower overall structural load. The idea is that with an aft CG, the tail plane doesn't need to generate as much down force and the wing will be at a lower angle of attack. Perhaps this is what the original claim is based upon?In any event, there are theories and there are regulations. Following the regs and the Approved Flight Manual is safer for both the aircraft and for the pilot who wants to hang onto his certificate.John

[Guest Shalomar]

I am by no means an expert. But I will try to clarify without misinforming. Civil aircraft are certified to 3 Gs. When overloaded, you take a *big* chance your flight will be smooth. Your stall speed is higher. Climb rate lower. More fuel burn for same speed. Hope the takeoff runway is smooth. There was a story of a DC-3 loaded to max with aluminum beams. Sluggish, very "sluggish". Turned out the beams were steel.Best Regards, Donny:-waveFLYing? It's cool. Trillions of birds and insects can't be wrong.

[RFields5421 1]

Aft CG - http://www.ntsb.gov/events/2003/AM5481/default.htm"The National Transportation Safety Board determines that the probable cause of this accident was the airplane

[Guest Shalomar]

If the CG is within limits, but toward aft, the aircraft can cruise more efficiently cuz of less trim being needed. "Q" comes into play.Best Regards, Donny:-waveFLYing? It's cool. Trillions of birds and insects can't be wrong.

[Guest Adverse Yawn]

In theory yes. I doubt this is actually practiced though.The basic idea is that for a controlable and stable in pitch a/c, the CofG needs to be ahead of the Centre of Lift (CofL). Therefore the tailplane must produce downforce to prevent the nose pitching down in straight and level flight. The aircraft pitches around the CofL not the CofG you see.If the tailplane produces a downforce, then the main wings have to produce more upforce...the wing loading is higher. If the wing loading is higher then the stall speed is higher too. That means, for the same weight, if you move that weight forwards, then in flight, the wings have to produce more lift (higher angle of attack) to counter the extra downforce generated by the tailplane which counters the increases nose down pitching momement of the nose because the CofG is more forward than usual.Therefore, the reverse is true. If you move the weight back, then you reduce the wing loading and therefore you also reduce the stall speed. Not only that, but because the wing loading is lower, the angle of attack in striaght and level flight is lower so you burn less fuel!Rather than use this phenomenon to increase T/O weight, the aircraft will be opportunly loaded with the chart max T/O weight for the runway, temp, winds, etc - but instead the load will be placed to put the CofG near the rear limit.The downside of a rear CofG is that the aircraft is more difficult to fly, the pitch forces will be lighter meaning the possibility of over flaring or over rotating and the pitch stability will be lower making it harder work to hand fly.

[Donstim 109]

Michael,Part 25 contains the airworthiness certification requirements for transport category airplanes, generally turbojet airplanes with a maximum takeoff weight greater than 12,500 lbs and a passenger capacity of more than 9 people, or propeller-driven airplanes with a maximum takeoff weight greater than 19,000 lbs and a passenger capacity of more than 19 people.In contrast to part 25, parts 121 and 135 are operating rules. Airlines operate under part 121, while air taxis operate under part 135. Generally, the airplanes used in part 121 operations are part 25 airplanes, while the airplanes used in part 135 operations may be either part 23 or part 25 airplanes.I can't speak for part 23, but for part 25, as I said in my earlier message, airplane manufacturers may provide multiple cg envelopes that my allow a higher takeoff weight in certain situations.The cg envelope determines the fore and aft boundaries of cg that the airplane may be loaded to. Airplane performance parameters that are affected by cg, like stall speed, must be determined at the critical cg position. For example, the stall speeds for the airplane are determined at the most forward cg position allowed by the defined cg envelope. For operators who are able to give up some loading flexibility, an airplane manufacturer may specify an alternate cg envelope containing a more aft forward cg limit. Stall speeds could then be reduced, potentially allowing a higher takeoff weight.Does this address your question? If not, maybe you could be more specific?Don

[AlaskanFlyboy 7]

I'm still wondering if he's beeing confused by the Normal and Utility Categories, which on most charts the Utility Category's CG limits are more aft than in normal category on most light planes I've seen. I doubt a jetliner would have such categories though.----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

[Donstim 109]

Yeah, hard to tell. I doubt if the answer I gave is really what he was looking for. Hopefully, he can clarify his question a bit.Don

[michal 44]

>Does this address your question? Yes it does.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[michal 44]

>In theory yes. I doubt this is actually practiced though.Yeah, I guess that was my main question - if in theory it is so, does any operator out there (say operating large jet aircraft) actually puts it to use. I simply repeated what was said on another (foreign language) forum and since I never heard of such a practice I was very curious. Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg