At a lower weight, Va/Vra actually decreases. So, are you saying more G is possible at a decreased Vra due to a lower weight?
No. The applicable FAR is:
(c) Design maneuvering speed VA. For VA, the following apply:
(1) VA may not be less than VS1 √n where—
(i) n is the limit positive maneuvering load factor at VC; and
(ii) VS1 is the stalling speed with flaps retracted.
(2) VA and VS must be evaluated at the design weight and altitude under consideration.
(3) VA need not be more than VC or the speed at which the positive CN max curve intersects the positive maneuver load factor line, whichever is less.
So unless the manufacturer chooses (3) Va is, by definition, the minimum speed at which you can pull 2.5g without stalling. If you define Va using (c) (1) and (2) then you cannot pull more G at a lower weight.
At the dive speed, excessive aircraft vibrations develop which put the aircraft structural integrity at stake. Source -
VD/MD | The Flying Engineer
I'm afraid the Flying Engineer is writing for dramatic effect! All FAR25 aircraft have to demonstrate freedom from dangerous vibrations (flutter) in flight at VDf/Mdf and, as I wrote earlier, by calculation to well beyond that speed.
Additionally, the margins required by regulations - whether for loads or for anything else - are not there to be used by someone who feels a bit "adventurous" today. They are there to cater for many circumstances, which include inadvertent excursions in 'g' or speed, but also include errors or uncertainties (especially the latter) in the underlying engineering. They also allow for simplification of the design cases, to a few cases with decent factors of safety, rather than many thousands of cases considering all kinds of combinations of manoeuvres and inputs. It would be a foolhardy man who took the margins in the regs and decided they were all available for use "on demand".
Absolutely 100% agree !!!
I would not neither, but 6g alone does not mean anything for the load on the airframe, you need to know the weight of the airplane at that point in time. The certified g load is defined for maximum takeoff weight, at lower weight more g is possible, however 6g is quite a number.
A quick check on the numbers says that the aircraft at the time of the incident referred to was at 130400 lb. MTOW for a B727 31 was, I think, 190,500 lb so the structure, even if it just met the FARs, would be good for 5.5g
In short, I am having a discussion with someone who feels the Loads defined in FAR 25.301, the factor of Safety in FAR 25.303, and the Strength and Deformation definitions in FAR 25.305 will provide a margin of safety for an aircraft which hypothetically would be accelerating through Vd+50 and pulling upward of 2-3.8g.
I contend no such margin exists nor is defined by Part 25.301, 303 and 305.
There are NO requirements relating to strength and deformation above Vd/Md so formally arguing about margins is meaningless. In practice, we agreed earlier that excluding compressibility effects the loads at a given weight/g are independent of airspeed in which case the margins above VD/Md would be the same as at Vd. But, if compressibility kicks in then the centre of pressure moves aft and at any given g one needs more download on the tail, and to get a given total aircraft g the loads on the wing will be increased, reducing the structural margins. OTOH, the increased tail loads from trim changes and from airspeed increases will increase the control hinge moments significantly, so depending on the size of the hydraulic jacks you may not have enough control power to pull 2.5g anyway.