Started this thread (Avoiding Vne) some weeks ago with a kind invitation to
respond to the idea of pulling the airbrakes while still in the rotating
mode of a spin. The idea behind it is when rotation has been stopped with
the glider at a pitch angle of say 60° or more this will be at a lower speed
then when the airbrakes stay closed all the time. Possibly a build up of
speed to over Vne can then be avoided after that. Of course airbrakes should
be closed again in the following pull up manouvre.
Any comments?


"Denis" schreef in bericht
...
Bruce Greeff wrote:

As I understand it the modern thin section wings are flexible enough
that the load limit is imposed by control freedom limitation, and the
wing must withstand 1.725 times this load in test. Flutter is the
subject of speed limitation which give speeds and margins that the
designer/manufacturer must demonstrate flying to. The regulations imply
that the glider must be demonstrated safe at a minimum of 23% margin
above the placarded Vne. So your margins for flutter, versus ultimate
strength are 1.23 vs 1.725 in JAR22 (unless I got the math wrong)

It's perhaps mathematically true but your argument is wrong (if your
conclusion is to say that there is more risk of flutter than
overloading). You cannot compare pourcentages of load and speed !

It takes less tenth of second at any moment to take the 2 or 3 g's that
will exceed your (supposed) 72.5% load margin, whereas it will take
several seconds to take the 60 or 65 km/h of margin in speed (supposing
23% margin), or depending of the dive angle you might never get over the
speed margin...

And although it may be true that some parts of the wing (e.w. center
section) has more stress margin due to deflection limit, it does *not*
guarantee you that all the parts of the wing has the same extra margin:
in the Nimbus 4 accident the central wing did not break, but the outer
wing did, with fatal consequences :-(


--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?