sorry if its a bit vague but got to start somewhere.


I can't really help you with your question, but just a hint at why
you're getting few answers: QNH is a European term for what in this
mostly American forum is known as "altimeter setting".

If I understand your question correctly, however, your interest is in
the effect of pressure and density altitude on take-off power settings.

--
Thomas Borchert (EDDH)