On Mar 21, 2:05*am, Bruce Hoult wrote:
On Mar 21, 3:15*am, bildan wrote:

The idea that the gross weight limit isn't a hard rule is just wrong.
Aircraft manufacturers gain nothing by understating load capacity.
The certificated max weight is as high as can be safely allowed.

That is clearly not true. A lot of aircraft design is trading off one
desirable feature against another.

We're talking gliders not airplanes. I claim it's precisely true.
Trade-offs you mention were made by the engineers who signed the
airworthiness documents. Estimates made on the flight line don't even
remotely rise to that level of expertise.


In the case of powered aircraft the MTOW is the weight used to
establish the published takeoff run, the distance to clear a 50'
obstacle, the rate of climb, the service ceiling, and probably others.
If you're operating out of short strips then you want to know how much
load you can carry. If you're operating a cessna off a 4 km runway at
sea level with no obstructions then it will be perfectly safe to
operate somewhat over MTOW, especially if the extra weight is carried
in the wings.

Although an overweight glider could make an aero tow takeoffs
hazardous under some conditions for the same reasons.


In the case of, for example, our club's DG1000 basic trainers, the
aircraft is permitted to do unlimited aerobatics with a +7/-5 G rating
at MTOW. If that's not a requirement on a particular flight and you're
happy with the +5/-3 G like most other gliders then you could operate
at some higher weight.

Yes, you can fly an aerobatic glider at a heavier weight if flown
within standard class G limits. But, we were not talking about
aerobatic gliders.


There is really no excuse for operating outside the CG envelope. *The
JAR 110 Kg seat limit is a little restrictive for us chubby Americans
but, hey, it's an incentive to cut back on the bacon burgers and
fries.

Seat weight is one thing, CofG is quite another. With the tail ballast
box full, those same DG1000's are within the published CofG limit even
with two pilots well over 110 kg each.

We're not talking about 'CofG' we're talking about gross weight. The
seat is primary structure just like a wing spar and is only designed
to support 110 Kg. In many, if not most, gliders, if the seat
structure fails, the flight controls would be jammed - just as
catastrophic as a wing failure.

Bottom line, if you fly outside the airworthiness certification
limits, you're a fool claiming to be smarter than the engineers who
designed the glider. Yes, I know the BGA allows over gross flights.