On my Salto it was the vario pointer that waved
around when the flow breakaway from the wing
roots impinged on the TE probe aft of the canopy.
The ASI was useless when spinning or sideslipping
also in that glider. As the brakes were weak
sideslipping was sometimes necessary as an
approach control aid but when slipping with
brakes open the brake wake would impinge on the V tail when you got too slow.
Yes there are various methods of determining
airspeed by pitot - static probes that are less
sensitive to yaw and sideslip although at extreme
angles this is quite difficult and they are fairly bulky with high drag.
I'm reading the official NASA history of the
X-15. They had a "ball nose", a round ball in the
nose with 5 holes, one facing the airflow and 4
others at 90 degrees around the ball. They drove
the ball with servos so the up - down pressures
and the left - right pressures were equal and the
middle hole then faced the airstream head on.
From the servo positions they got the AoA and
sideslip angle. You could just measure the
pressures and calibrate the AoA and AoS on a 5 hole probe.
Also interesting was that during one re-do of the
instrument panels in the 3 aircraft, they did a
mid grey panel which the pilots liked better than
the black panel as the instruments had more
contrast against the panel. Also helps in some
aircraft to avoid having to dark adapt and vice
versa when wanting to scan the instruments during
your normal scan pattern. Amusing description of
a "low and slow" familiarisation flight for one
pilot, 70,000 feet and over Mach 4.
On the ASK21 Schleichers likely figured it didn't
matter as the single largest customer (the German
gliding movement) didn't intend to do spin
training in the aircraft, sideslipping is
unnecessary for glidepath control as the brakes
are good, so the airspeed indicator would work
well from the supplied pitot-static sources.
I saw a photo from 30 years ago of your upper
wing surface near the trailing edge pitot probe,
Anthony. Pressure should be equal to pitot until
the thickening separated boundary layer
encompasses the wing probe when the pressure
difference should increase rapidly. Might be
useful on some gliders which are very well
behaved at low speeds and thermal nicely but
don't climb well unless flown a fair bit faster.
ASW24 I'm told, amongst others. It is possible to
buy mechanical pressure switches that close at
very low pressures and make an electrical circuit.
Must not have been found to be a huge advantage
as I haven't seen the idea since.
Once again, it is the stick fore and aft position
that determines the angle of attack (this has
nothing to do with the TRIM which is about force,
not position). Gusts will change this momentarily
but the glider will return to the AoA you hold.
The time constant for this is up to 0.5 seconds
at low speeds, getting less the faster you go.
I had to derive this once as I couldn't find any
references. Recently found one where this was
derived the same way I did it. Blokes name was
John C. Houbolt, famous for another thing. Look him up.
Mike
At 04:19 PM 27/12/2014, you wrote:
You probably could do something very easily for
modern non-flapped gliders. AoA indicators have
been around for a long time. You could have
three critical angles annotated on the device
display: stall, climb and cruise. Flapped
gliders would need to have a method of knowing
what the flap deflection is which would change
these angles a bit depending on the
deflection. The problem would be whether pilots
would want an extra device protruding into the
laminar flow on the forward fuselage or not. I
may have mentioned the following previously: As
an aside, the static system on the P-3 Orion is
excellent for detecting stall - just not in the
expected way. The original static system was on
the forward fuselage. However , it was found to
have disturbed airflow when the bomb bay doors
were open. An alternate static location was
found on the aft fuselage. Arguably it was a
better site as the error correction for the
static system was significantly smaller and it
was not affected by the bomb bay doors being
open. However, the new static ports were in the
wake from the upper surface of the wing. As
soon as the wing root airflow on the wing upper
surface starts to separate, the static system
becomes subject to large pressure disturbances
and the ASI and the altimeter become
unresponsive and both of the needles start to
bounce around. So if you experience buffet in a
P-3 and the ASI and altimeter needles are
bouncing around, it is a stall. During
discussions a few years ago about P-3 stall
warning, I suggested that it may be feasible to
directly tap into the static system and detect
the pressure fluctuations from the flow
separation and hence provide a stall
warning. The proposal was rejected as it needed
a lot of R & D thrown at it to develop the idea.
Something like this may be the 'better mouse
trap' for gliders. A pressure transducer system
connected to the upper surface trailing edge of
the wing at a suitable point on each side that
trips a warning if separated flow is
detected. This would be a direct measurement of
impending stall rather than implied through AoA
or computing speed, g and wing loading etc.
Anthony -----Original Message----- From:
aus-soaring-boun...@lists.internode.on.net
[mailto:aus-soaring-boun...@lists.internode.on.net]
On Behalf Of Michael Derry Sent: Saturday, 27
December 2014 10:29 AM To: Discussion of issues
relating to Soaring in Australia. Subject: Re:
[Aus-soaring] Spin training The report reminds
us how useless the ASI is during spins. You are
better off judging speed using the noise levels
assessed by your ears. Why hasn't some
instrument maker built a better mousetrap than
the one we have ? On Sat, 27 Dec 2014 08:56:09
+1030 "Ulrich Stauss" <usta...@internode.on.net>
wrote: > This is a multipart message in MIME
format. > >
----------------------------------------------------------------
>
http://faculty.chicagobooth.edu/john.cochrane/research/Data_and_Progra
>
ms/CFI/AFFTC-TR-89-27%20Spin%20Test.pdf > > > >
Ulrich > > > > From:
aus-soaring-boun...@lists.internode.on.net >
[mailto:aus-soaring-boun...@lists.internode.on.net]
On Behalf Of Ron > Sanders > Sent: Saturday, 27
December 2014 08:44 > To: Discussion of issues
relating to Soaring in Australia. > Subject: Re:
[Aus-soaring] Spin training > > > >
Bernard, good morning, i would lke o read that
report too please? > > > > Ron > > > > On 27
December 2014 at 08:18, Bernhard
<ec...@internode.on.net> wrote: > > Hello Paul,
good morning all > > > > You might be
interested to know that the US Air Force has
already been > using the ASK21 for spin training
over several > > decades. > > > > Therefore you
might want to refer to a report by the US Air
Force on > the spin characteristics of the ASK
21. It was done > > by experts in the field
and true professionals. When you read the >
report you will find that it was perhaps the
most > > comprehensive study into the subject
ever done. > > > > To save you digging around I
have attached a copy for you! > > > > Kind
regards to all > > > > Bernard > > > > > > > >
On 26 Dec 2014, at 10:05 pm, Paul Bart
<pb2...@gmail.com <mailto:pb2...@gmail.com> >
wrote: > > > > > > On 26 December 2014 at
19:33, Daryl Mackay <darylmac...@gmail.com
<mailto:darylmac...@gmail.com> >
wrote: > > > > > > Suffice to say no
instructor willingly uses the ASK21 for spin
awareness training at Beverley. > > > >
ââ¹Hi Daryl > > >> > Would you mind
explaining why? This is a genuine inquiry as my
club is > about to take a delivery of
one.ââ¬â¹ > > > > > > ââ¹Cheers > > > >
Paulâ¢â¹ > > > > > > > > > Cheers > >
Paul > >
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