A couple of Boeing G limit question
 

I'm a new member in this forum. I have a couple of questions about Boeing G limit.
1. I ever read somewhere in the net that Boeing aircrafts have less G limit when they're ujan dirty configuration than in clean. Can someone please confirm this?
2. What is the limit in clean vs in dirty configuration?
3. What is the reason for the different value?
Thank you very much for your information guys

1. Almost all aircraft have different values for load limits with flaps/slats extended than in clean configuration.

2. Depends on type. For B737 is 2.5/-1.0g in clean configuration and 2.0/0.0g when "dirty".

3. Flaps when extended can't sustain as much load as when retracted. It's basic physics really.

Same values are true for the 747.

Note that these are the 'normal' loads where it's certified that nothing adverse will happen. Exceeding those limits will require an inspection and may result in damage or permanent deformation (e.g. you can bend the airplane). However the "limit" loads beyond which the airframe may structurally fail are quite a bit higher (by regulation, at least 50% higher).

2.5/-1 clean and 2/-0 flaps down are standard across most transport aircraft, as it is the certification criteria.

Whenever you change stall speeds you change the stall limited maneuver speed (Vp). Since the maximum weight to be carried by the wing is the weight the wing carries at the stall. The relationship is Vp=Vs(n)^0.5, where n is the design limit load:)

So the different limit between configuration is just a matter of design made by airplane manufacturers?

The limit load is reduced for flaps down to the values listed above. There is also a stall speed change which further reduces Vp.

"So the different limit between configuration is just a matter of design made by airplane manufacturers?"

No, the difference is written into the certification regulations.

The actual "g" limits may be greater than the regulatory level but can never be less.

Boeing Commercial Airplanes do not limit G
 

The control systems on Boeing Commercial Airplanes do not provide G limits. As mentioned above, by regulation the systems and structure must support the range of -1 to 2.5 g flaps up and 0 to 2.0 g flaps down. Large control column forces required to command large maneuvers serve as deterrent against over commanding. One of the reasons for explicit G limits in the Airbus control systems is the use of relatively low force side-stick controllers.

Dealing with hard landings on the 74C, there was one special aspect. The fowler flaps could shift doing damage upon retraction. Understanding a pilot wants to hope for the best I have seen several crunch...Another hard landing indicator on the DC-10/MD-11 are the PPROV. Hard landing inspections are generally a pain in the A$$.

Thank you guys for your awesome reply! I really appreciate your awesome explanations.