[taildraggernut]

Originally Posted by Crumpp

Taildraggernut, if the elevator is so effective in a stall, why do power on stalls sometimes result in a nose up attitude descent??

Take a wild guess!

Well one of the most OBVIOUS reasons is because you have POWER ON you are creating PROPWASH which acts on the ELEVATOR making it even more EFFECTIVE, now can you tell me why even in a POWER OFF stall some aircraft can 'mush' down in a NOSE UP DESCENT?

I'll save you the bother as I don't think you actually could answer it without consulting google.

when you have made a smooth and progressive decceleration down to the aircrafts 'minimum' stall speed in level flight you will find you are using 'maximum' deflection of 'up elevator' to maintain attitude, because your airspeed is so low and you have used up all elevator travel you run out of pitch authority but the aircraft has found equlibrium with the EFFECTIVE elevator at max deflection holding the aircraft at it's maximum angle while the minimum airspeed is still sufficient to maintain the elevators EFFECTIVENESS to hold the attitude, the nett result is you hold the aircraft in a stall with a constant pitch moment about the lateral axis thanks only to an elevator which is still EFFECTIVE, now here is the really salient part, it's thanks to things like washout, slats, slots etc etc that ensure the outboard sections of the wing stalls last that prevent the aircraft from making a complete departure and entering a spin, even a Spitfire should be able to carry out that excercise due to it's washout maintaing that lateral stability.

Heres our dear old friends the NACA to explain it all to you.

Spitfire MkV handling trials........I wonder if these have been shown before?

https://docs.google.com/viewer?a=v&q...hUeuiqgiZzKi2g

please forgive typos in my quote as I am cutting and pasting text from a PDF image.

Stalling characteristics in the gliding condition of
flight In the gliding condition with the gun ports covered,
the airplane showed no tendency to roll off. Figure
8 shows a stall in which the controls were held approximately
in the positions required at the first sign of the
stc.ll. At speeds of about l0 miles per hour above the
minimum speed, the tufts at the trailing edge of the left
wing root wore observed to reverse and buffeting was :felt
in the elevator and rudder controls, This buffeting
caused a fairly violent and unmistakable shaking of the
airplane. In figure 8 and the following time histories,
the buffeting is indicated on the figure by an oscillation
of the normal acceleration record. Actually all the instrument
records showed vibrations, but it was thought
unnecessary to indicate thls fact on the time histories.
The approximate amplitude of the variation In normal acceleration
is shown by the plotted curve, but no attempt
has been ms.de to reproduce the frequency of the oscillation
that was recorded.
At approximately 6 miles per hour above the minimum.
speed, the tufts fluctuated above the entire left side of
the center section and some right aileron motion was needed
to maintain trim. A mild pitching and yawing oscillation
developed, but no tendency to roll was observed. In
no case did the flow ahead of the ailerons separate from
the wing surface..
The shaking of the airplane caused some movement of
the controls, in spite of the efforts of the pilot to hold
them fixed. The uncontrolled stalls may be distinguished:
from the controlled stalls by the fact that a large amount of up elevator was applied during the controlled stalls
Figure 9 shows a gliding stall with :the gun ports
covered in which the stick was moved far back after minimum
speed was reached. Use of the ailerons finally resulted in the development of a rolling oscillation and the
violent buffeting continued throughout the stall. As in
the previous stall s the only portions of the wing from
which the flow separated were the left side of the center
section and the extreme tips. Lateral and longitudinal
control sufficient to prevent any violent motions were
still available beyond the stall,

Again..

the only portions of the wing from
which the flow separated were the left side of the center
section and the extreme tips. Lateral and longitudinal
control sufficient to prevent any violent motions were
still available beyond the stall

I should really come back to some qualities of the 109 here from this quote from the RAE report..

When the slots were fully open the aircraft could be turned quite steadily until very near the stall. If the stick was then pulled back a little more the aircraft suddenly shuddered, and either tended to come out of the turn or dropped its wing further, oscillating meanwhile in pitch and roll and rapidly losing height ; the aircraft immediately unstalled if the stick was eased forward. Even in a very tight turn the stall was quite gentle, with no tendency for the aircraft to suddenly flick over on to its back and spin.

The part in bold is describing a stall with the incipient stages of a spin, so in this case the evidence shows that slats have absolutely failed in prevention of the condition, the BIG factor here is that the slats DO make facility for an almost instantaneous recovery almost of an automatic nature.