At 08:57 AM 9/08/02 +1000, you wrote:
>The DG web site expresses serious reservations. They state that the TAS will
>have to be 450Kts ! Flutter ?
>Also that the characteristics of carbon fibre are completely untried at
>those temperatures
>
>Bob Ward
Once you get above the tropopause the temperature is more or less constant.
In the South Island of NZ this time of the year the trop will be at no more
than about 30000 feet. So really DG ought to tell all their customers not
to go to 30000 feet in wave anywhere if they are worried about the
temperature.
As for the properties of carbon fibre being completely untried at those
temperatures, remember this when you next fly on a Boeing or Airbus both of
which have large amounts of carbon in the structure(try the fin of just
about all Airbus models nowadays). The entire wing of the AV8B is made of
carbon and while it spends most of its time trucking bombs at low level it
probably flys at 30000 or so on ferry flights.
I was referring to the weight and balance but I'm sure the team have taken
flutter into account. Using the TAS as the flutter limit is generally
recognised as being very conservative with the real limit being somewhere
between the IAS and TAS.
I get a TAS/IAS ratio of about 3.42 at 62000 feet and -60 degrees. This
gives 135 KTAS for 40 knots IAS. I'd bet some aeroelastic analysis has been
done on the DG 505 by some moonlighting NASA people setting a reasonable
TAS limit they can live with.
Not everything on the DG website(or from the German glider industry in
general) is reliable. After all I heard the other day that one German
manufacturer is still maintaining that there is no gel coat cracking problem.
Einar Enevoldson is a retired NASA research pilot. Note that he lived long
enough to retire! Seems to me that says something about his approach to
these things.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
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