View Single Post
  #7  
Old September 1st 03, 06:25 PM
Rich Stowell
external usenet poster
 
Posts: n/a
Default

"Chris Hoffmann" wrote in message ...
The first thing that jumped out at me from your report is this:

Another myth cited in the AOPA study is "watch your airspeed, or
you're going to stall this airplane!"


Pardon me, but if your airspeed gets below stall speed, you ARE going to
stall. Further, if your airspeed is below the usual 1.3 Vso safety cushion,
you are getting to the point where all it takes is a turn too steep, or a
bit of tailwind, or a yank back on the yoke, and you are LIKELY to stall.
This is not "myth".



Ah, but therein lies the rub! Within the ability of the structure to
withstand G-load without deforming/breaking, the airplane can be
stalled at ANY airspeed. In that context, every airspeed is a
potential "stall speed" provided the G's applied are sufficient to
exceed critical angle of attack. "Getting below stall speed" is only
meaningful if the instantaneous G-load is specified.

For example, if I pull 3.8 G's while at Maneuvering speed, Va, the
airlane will stall (Va = 1.95Vso). If I am in wings-level flight (1
G), then the stall speed is Vso. An infinite number of G and speed
combinations exists in between Va and Vso that will result in a stall,
even 1.3Vso is a stall speed at the appropriate G-load (G can also be
interpreted as bank angle).

Airspeed alone means nothing with regard to when or whether the
airplane will stall. We need to think in terms of airspeed AND G-load
-- these are the two parameters that will give us a clue as to our
margin to the stall, or whether or not we are moving closer to, or
farther from, critical angle of attack.

To reduce the likelihood of stalling: If airspeed is decreasing,
G-load MUST also decrease; if airspeed is increasing, then the
airplane can tolerate an increase in G's. We need to develop a sense
of changes in both speed and G to have any reasonable chance of
sensing our proximity to stall.

Also, even the AOPA study correctly identifies the "watch your
airspeed" statement as a myth. I was just expanding on it...



On the other hand, this:

"Just don't let airspeed get below a safe value and
stalls are not a problem."


is not an axiom to fly by. Students *should* know/be taught that a stall can
occur at any speed, any attitude, of course. But I see nothing wrong with
training students to keep their airspeed where it's supposed to be in the
pattern and on approach, which, I believe, is the context from which those
two quoted remarks were taken.


Sensing airspeed AND G-load trends are critical, not airspeed alone.
The V-G diagram is the best illustration of the interaction of speed,
G, stall, and structural damage.

Be Safe,

Rich
http://www.richstowell.com
Ads