On Tue, 28 Dec 2004 at 16:55:05 in message
, Peter Duniho
wrote:
It does this as long as the lift is slightly less and the speed drops to
produce _less_ drag and lift, leaving more engine power and thrust to
climb.

At an airspeed just above stall, a reduction in speed results in MORE drag.
There is a reduction in parasitic drag, but there is a greater increase in
induced drag, with a net increase in total drag (and that's ignoring drag
caused by the rudder and any other control surfaces that require a change in
position).

HI Peter. How easy it is to get slightly confused on Usenet! What I was
trying to say is that if you maintain the same AoA then the lift drag
ratio remains the same, but because the lift required when climbing is
less than when flying level you can climb at a reduced speed but with
less drag. So under some conditions if you just raise the nose a little
you can find a new steady state where speed is slightly reduced but with
the same thrust you can climb at the same AoA..

There is a maximum lift drag ration at a modest angle of attack. Above
_and_ below that angle of attack that ratio worsens.

When climbing extra work must be done against gravity. That extra work can
come from increasing power or from reducing speed and therefore drag.

The extra work comes ONLY from a net surplus of power.

I agree with that. However that net surplus can come from either more
engine power or reduced drag. Because even in a modest climb the engine
thrust vector plus the lift vector combine to match the weight. Put
another way if you are flying below the maximum lift drag ratio and you
increase the AoA to the optimum whilst keeping the same power the
aircraft should climb. This is self evident if you are flying level at
high speed and at a climbing power setting. Bring the nose up increasing
the AoA and your aircraft will definitely climb. Agreed?

A reduction in speed
is only guaranteed to produce a net increase in power available if the new
airspeed is higher than Vbg. It can sometimes also produce a net increase,
if the old airspeed was sufficiently higher than Vbg, and the new airspeed
is close enough to Vbg, even if less than, but you need to know more about
the old and new airspeeds in that case to say for sure what happens. More
importantly, a reduction in speed is guaranteed to produce a net decrease of
power available if the OLD airspeed is lower than Vbg (as it is when just
above stall speed).

I think that is another way of saying what I have just said? I cannot
remember if we started off with an assumption that the aircraft was only
just above stall speed? If so then you are correct of course.

Even in a steady glide the required lift is less than that needed in
level flight! That is easier to see because the drag vector helps the
lift match the gravity vector.

--
David CL Francis