But surely minimum sink rate is only relevant when there is no power
or thrust?

I suppose so. If power were constant with airspeed, then minimum sink
would also be Vy.

Yes, if power available was constant with airspeed, Vy would also be
your min. sink rate speed. The books indicate that power for a
piston-engine propeller combination increases with velocity. The
increase is not linear though. The derivative dP/dV looks to be of
the form y = -mx + b. Kinda like an upside down smiley face with only
the left side showing.

Thrust available looks fairly constant w.r.t. velocity.



It requires finding a minimum value of V*sin(theta) where theta is
the angle of climb (negative when descending).

Sounds good.

As I recall for a gliding aircraft minimum sink comes roughly at the
AoA where (Cl^(3/2)/Cd is a maximum.

I'd have to look it up to be sure, but it looks right.


That's correct. Min sink rate would occur at the AOA where
1/[(Cl^3/2)/cd] is a minimum as it is the point of least power
required. Min. thrust required is proportional to 1/(Cl/Cd).



This is normally at a higher AoA than maximum Cl/Cd and is some
cases is quite close to the stall.

Agreed, except, according to the books, the velocity of minimum power
is ALWAYS less than least drag.


What book are you reading Greg? My references indicate the same for a
Cessna Skylane. If you assume no power available, then, your min.
sink (best endurance) speed is less than your best glide speed.

My Cessna 172SP POH lists a best glide speed of 68 kts. Best
endurance speed isn't exactly mentioned but I've heard it's close to
stall. I just recall someone saying "If you want to stay up for as
long as you can, fly close to stall". Do you know why the POH doesn't
mention that speed? Would that be giving away too much?

Oh, by the way, could you please give a shot at answering my questions
that are contained in my Nov. 27 reply to Gerry Caron? (in this same
overall post)

Thanks,
Alex