Simple angle of attack sensor

http://cumulus.atmos.und.edu/winds_introduction.php

Note first picture.

I think it's easy to see how a pair of AOA sensing ports could be added to a glider nose.

Bill D wrote, On 7/29/2013 8:16 AM:

http://cumulus.atmos.und.edu/winds_introduction.php

Note first picture.

I think it's easy to see how a pair of AOA sensing ports could be
added to a glider nose.

There are a number of AOA systems using that technique already on the
market, but no glider pilots have reported on them that I can remember.
It's time to stop talking about them and instead, install one and try it.

I am considering installing an AOA probe when I get my new motorglider
(Phoenix U15) next year, using one of these unheated probes:

http://dynonavionics.com/docs/SkyView_AoA.html

They are cheap at $200, and there are no additional costs for the panel
indicator, as it displays on the Dynon SkyView panel display the glider
will have. At that cost, I'm willing to experiment without knowing that
it will be useful.

Has anyone used one of the Dynon AOA probes? How well did it work? Did
it seem suitable for gliders?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

According to my SZD-55 manual (issue IV, March 1993), such an AOA sensing device is mandatory in Canada (page 12a of the Flight Manual/POH). The SP3 system works on the pitot and pressure from another port just below the nose pot (about 1.5" down). It works reliably giving audio warning 3-5 kts above the stall. Once properly adjusted (one-time deal) it is reliable, and has a very low draw (higher when it is alerting - which usually only happens in the flare - or if you're about to stall).

"Electronic STALL WARNING SYSTEM designed to meet the requirements of JAR 22.207 and FAR 23.207 as well. Awarded the O.S.T.I.V. prize, being installed on gliders since 1991 and certified in Poland. Easy to install. No aerodynamic burden. Only one additional pressure sensing hole in the nose of the glider, or in the lower surface of the wing of the aeroplane. Ideal for sailplanes, motogliders and ultralight aeroplanes. The device signals close to stall condition in the range between 5 and 10 percent over the stall speed in straight and circling flight over the whole loading and ballast range. You set the alarm threshold only once, individually for your glider. How does it work ? The difference between pressures Pt and Pc is the function of the two variables : speed and angle of attack. The device measures, calculates and detects the moment when the combination of these two parameters informs you about an approaching stall."
see - http://www.olk.com.pl/indexen.php?bo...roducts&lpx=26

There is a discussion on this topic on the DG website at:http://www.dg-flugzeugbau.de/ueberziehwarnung-e.html.

Tested and available since 1991 - why re-invent the wheel?

2D

On Monday, July 29, 2013 11:16:55 AM UTC-4, Bill D wrote:
http://cumulus.atmos.und.edu/winds_introduction.php



Note first picture.



I think it's easy to see how a pair of AOA sensing ports could be added to a glider nose.

Simple? lol! ;-)

The Butterfly Vario will include an AOA sensor soon.

On Monday, July 29, 2013 10:16:55 AM UTC-5, Bill D wrote:
http://cumulus.atmos.und.edu/winds_introduction.php



Note first picture.



I think it's easy to see how a pair of AOA sensing ports could be added to a glider nose.

and others:

The photo shows in essence a 5-hole hemispherical probe using the nose of the glider as the probe. 5-hole probes are fairly common instruments in wind tunnels and sometimes even flight.

The center port measures total pressure. Total pressure is accurately measured for angles up to about 15 degrees off axis, and even for angles up to 20 degrees, the error is a small percentage.

The other four ports will likely trigger transition locally on the nose. They will each create about a 7-degree wedge of turbulent flow, which could/would significantly reduce the amount of laminar flow on the fuselage.

I would suggest using a conical 5-hole probe (google it). These can be quite small in size and are easy to calibrate. One can determine total pressure, static pressure, yaw angle, and angle of attack. I have calibrated probes of this type to angles up to 45 degrees. A decent set of calibration curves can be made from CFD calculations which model the probe and the nearby portions of the glider.

As mentioned above, the probe can be quite small, a 3/16" probe could work well. It can be mounted to the fuselage, or possibly better, the leading edge of the vertical fin.

If five pressure transducers are used, one for each point, aoa, yaw, airspeed, and altitude could be calculated from a single probe. Since both airspeed and altitude are calculated from the connected flight data computer, it is possible to electronically calculate the climb rate corrected for total energy. One could also alert the pilot either visually or audibly for excessive aoa or yaw.

As with any probe of this type, it could be contaminated by rain, which is why most aircraft pitot-static probes are heated. The Kulite Flow Angle Probe FAP-250 (google it) is only 0.25" in diameter and may be more resistant, since the sensors are quite small and are nearly surface mounted. This probe is calibrated to up to 35 degrees off axis.

That's my 2 cents.

But, if your plane has flaps that deflect much, the "approaching stall angle" for flow relative to that fixed probe changes. A bunch. I would hazard a guess that if your plane has flaps that go 30 degrees or more, and you set the "warning" point for adequate warning with thermaling flap, it will never go off with flaps 30 or more. The calibration shifts whith flaps.

Not saying it can't provide some warning some of the time, but if your ship has flaps, expecially larger deflection flaps, this 5 hole probe is NOT going to do what you want it to without some flap position input to the system for sounding the alarm.

That's my nickel's worth (Inflation, Neal.) :-)

On Wednesday, August 21, 2013 7:34:46 AM UTC-5, Steve Leonard wrote:
But, if your plane has flaps that deflect much, the "approaching stall angle" for flow relative to that fixed probe changes. A bunch. I would hazard a guess that if your plane has flaps that go 30 degrees or more, and you set the "warning" point for adequate warning with thermaling flap, it will never go off with flaps 30 or more. The calibration shifts whith flaps.



Not saying it can't provide some warning some of the time, but if your ship has flaps, expecially larger deflection flaps, this 5 hole probe is NOT going to do what you want it to without some flap position input to the system for sounding the alarm.



That's my nickel's worth (Inflation, Neal.) :-)

Of course, but that really isn't a big deal, really - you establish the calibration curve for a few selected flap positions and display accordingly. No hardware change in the probe or display, a flap position switch, and some software in the computer/display.

Way better than what we have now!

Kirk
66

At 12:49 21 August 2013, kirk.stant wrote:
On Wednesday, August 21, 2013 7:34:46 AM UTC-5, Steve Leonard wrote:
But, if your plane has flaps that deflect much, the "approaching stall
an=
gle" for flow relative to that fixed probe changes. A bunch. I would
haza=
rd a guess that if your plane has flaps that go 30 degrees or more, and
you=
set the "warning" point for adequate warning with thermaling flap, it
will=
never go off with flaps 30 or more. The calibration shifts whith flaps.
=20
=20
=20
Not saying it can't provide some warning some of the time, but if your
sh=
ip has flaps, expecially larger deflection flaps, this 5 hole probe is
NOT
=
going to do what you want it to without some flap position input to the
sys=
tem for sounding the alarm.
=20
=20
=20
That's my nickel's worth (Inflation, Neal.) :-)

Of course, but that really isn't a big deal, really - you establish the
cal=
ibration curve for a few selected flap positions and display accordingly.

=
No hardware change in the probe or display, a flap position switch, and
som=
e software in the computer/display.

Way better than what we have now!

Kirk
66

I have the best stall warning device ever - the glider. Nose high attitude,
low airspeed, rearward stick position, shuddering, reduced effectiveness of
controls. Zero cost and complexity.

On Wednesday, August 21, 2013 7:49:04 AM UTC-5, kirk.stant wrote:

Of course, but that really isn't a big deal, really - you establish the calibration curve for a few selected flap positions and display accordingly. No hardware change in the probe or display, a flap position switch, and some software in the computer/display. Way better than what we have now! Kirk 66

For planes like your LS-6, Kirk, you might even get adequate warning with a single set point. A bit earlier warning with no flap, and a little less warning with thermal or landing flap. Planes like my Zuni, where you don't set and forget the flaps, the system becomes more complicated.

Not well done, but my comment was intended to say "It may seem simple for some cases, but it is not a simple solution that will work just that easily for all sailplanes."

I tend to add the audio airspeed (open the side scoop) when I enter the pattern. Helps with ventilation, and adds an extra airspeed sensor that doesn't require a look inside. Not AOA, but another reference.

Steve