Roelant van der Bos wrote:

I simplified it a bit too much, perhaps. It would come out of the
"non-lifting parts" limit (basically the fuselage and everything in it).
Generally, the effect would be to reduce the cockpit allowed load, but
not always, depending on the exact weight of fuselage and installed
equipment. The amount of water ballast allowed would not likely change,
since it is carried by the wing (a lifting part), not the fuselage.

A glider designed to carry a motor will have a higher "non-lifting
parts" limit (perhaps from more structure, stronger lift pins, etc) than
a similar non-motorized one, in order to preserve the cockpit load.

Not really. For allmost every turbo equipped glider the max.
total weight is the same as the one for the pure glider, and in some
cases the turbo has one even lower. The discus 1 for example has a
MTOW of 525 kg without the engine, but with the turbo it reduced to
450 kg.

An increased "non-lifting parts" limit would not necessarily increase
the total allowed weight, which depends on several factors (landing gear
strength and tow hook mounting come to mind as possibilities).

I don't know why the Discus 1 turbo has such a lower MTOW, but I'd guess
the major effect is you would fly it with a lot less water ballast -
about 100 liters less! I don't think this reduction has anything to do
with the "non-lifting parts" limit, but might be related to required
climb rates or other regulation.

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Eric Greenwell
Washington State
USA