Glider angle of attack indicator by SafeFlight

I've got pitch strings on both sides of the canopy of my ASW-19, Bill,
but I've not seen this behavior. I'll make an effort to look carefully
the next time thermals appear in Pennsylvania! As was said earlier in
the thread, though, strings on the canopy are greatly affected by yaw.
They might help indicate lift, but they won't really be useful AOA
indicators. And if AOA instruments average out rough air fluctuations,
they won't be too useful as incipient lift indicators. Tough problem!

-John

Bill Daniels wrote:
Many pilots who have tried the "pitch strings" report that they give advance
warning when entering an area of lift. When you enter the edge of a
thermal, the strings show a sharp increase in AOA several seconds before the
vario shows lift. This improves the efficiency of "dolphin flying" by
providing an earlier signal of when to start a zoom. One pilot on a
marginal final glide told me, "Without them, I wouldn't have made it home."
An ASI gives the same signal but it's weaker and harder to interpret.

Most AOA sensors have some damping to smooth the signal in rough air.

It probably works better in rough western conditions. As you said, "pitch
strings" are very sub-optimum AOA indicators. I don't use them because
it's such a hassle closing the canopy without trapping the strings between
the canopy frame and fuselage.

I think it's likely that the SafeFlight vane-type AOA indicator works fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.

Bill Daniels


"jcarlyle" wrote in message
...
I've got pitch strings on both sides of the canopy of my ASW-19, Bill,
but I've not seen this behavior. I'll make an effort to look carefully
the next time thermals appear in Pennsylvania! As was said earlier in
the thread, though, strings on the canopy are greatly affected by yaw.
They might help indicate lift, but they won't really be useful AOA
indicators. And if AOA instruments average out rough air fluctuations,
they won't be too useful as incipient lift indicators. Tough problem!

-John

Bill Daniels wrote:
Many pilots who have tried the "pitch strings" report that they give
advance
warning when entering an area of lift. When you enter the edge of a
thermal, the strings show a sharp increase in AOA several seconds before
the
vario shows lift. This improves the efficiency of "dolphin flying" by
providing an earlier signal of when to start a zoom. One pilot on a
marginal final glide told me, "Without them, I wouldn't have made it
home."
An ASI gives the same signal but it's weaker and harder to interpret.

Most AOA sensors have some damping to smooth the signal in rough air.

I was Googling around, and ran across yet another AOA device. Check
out this site:
http://www.adventureairsports.com/aoa.htm
and pay particular attention to the 3rd photograph. Yaw string and AOA
in one, and not very expensive!

-John

On Dec 9, 6:46 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
I think it's likely that the SafeFlight vane-type AOA indicator works fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.

I think that probably works on an ultralight without an aerodynamic nose
cone. Laminar airflow around a nose cone will be nearly parallel to the
skin at any AOA of interest. That's why the AOA sensor has to be on the
sides of the fuselage.

Bill Daniels

"jcarlyle" wrote in message
...
I was Googling around, and ran across yet another AOA device. Check
out this site:
http://www.adventureairsports.com/aoa.htm
and pay particular attention to the 3rd photograph. Yaw string and AOA
in one, and not very expensive!

-John

On Dec 9, 6:46 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
I think it's likely that the SafeFlight vane-type AOA indicator works
fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.

On Dec 9, 10:09 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
I think that probably works on an ultralight without an aerodynamic nose
cone. Laminar airflow around a nose cone will be nearly parallel to the
skin at any AOA of interest. That's why the AOA sensor has to be on the
sides of the fuselage.

Bill Daniels

Good point. They can also be located on a boom extending away from
the fuselage or wing - as usually seen on prototypes, where accurate,
"true" AOA is needed. Often combined with a yaw sensor (just a fancy
yaw string, really) to measure true sideslip.

I wonder if an AOA vane could be mounted on a modified tail TE/combi
probe? The probe would have to be a lot stiffer to work (at least
that's what she said...).

Kirk

Out of curiosity I made a test. I built a cuff with an 21/2 ft arrow
shaft attached, line up with the wing chord. I had several strings
attached on top of each other about half inch apart and different
length. Very interesting to see how the air responds well ahead of the
leading edge but useless for any useable information. With flaps, the
changes I was interested in were to small in any case.
Udo


On Dec 9, 10:04 pm, jcarlyle wrote:
I was Googling around, and ran across yet another AOA device. Check
out this site:http://www.adventureairsports.com/aoa.htm
and pay particular attention to the 3rd photograph. Yaw string and AOA
in one, and not very expensive!

-John

On Dec 9, 6:46 pm, "Bill Daniels" bildan@comcast-dot-net wrote:



I think it's likely that the SafeFlight vane-type AOA indicator works fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.- Hide quoted text -

- Show quoted text -

Good to hear about an actual experiment, thanks.

Why do you say it was interesting but useless? Did it not give you AoA information?
Interesting you say changes with flaps were too small.. to see?

I wonder if a piano wire probe like

http://www.adventureairsports.com/aoa.htm

but on the nose would work. How far out on the wing was your cuff?

Sarah



Udo wrote:
Out of curiosity I made a test. I built a cuff with an 21/2 ft arrow
shaft attached, line up with the wing chord. I had several strings
attached on top of each other about half inch apart and different
length. Very interesting to see how the air responds well ahead of the
leading edge but useless for any useable information. With flaps, the
changes I was interested in were to small in any case.
Udo


On Dec 9, 10:04 pm, jcarlyle wrote:
I was Googling around, and ran across yet another AOA device. Check
out this site:http://www.adventureairsports.com/aoa.htm
and pay particular attention to the 3rd photograph. Yaw string and AOA
in one, and not very expensive!

-John

On Dec 9, 6:46 pm, "Bill Daniels" bildan@comcast-dot-net wrote:



I think it's likely that the SafeFlight vane-type AOA indicator works fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.- Hide quoted text -
- Show quoted text -

The probe was about 3 ft from the cockpit wall.
You would need something a lot more precise to be of use for flying
efficiently day to day
I could see a resolution of a 1/2 degree or better. with adjustable
dampening. I was trying to see if the theoretical match the real
thing.
To optimize performance you should have something to compare it with
and record it. That is why the annual Idaflieg is such a big deal in
Germany it takes a lot of effort and equipment.
I found that the theoretical for me was close enough and all I needed
was time to fine tune my settings and speed vis a vis other gliders.
When the big day came I gave R.Johnson the speed and flap setting I
thought best and it work out not bad.

Udo



On Dec 10, 10:10 am, Sarah Anderson wrote:
Good to hear about an actual experiment, thanks.

Why do you say it was interesting but useless? Did it not give you AoA information?
Interesting you say changes with flaps were too small.. to see?

I wonder if a piano wire probe like

http://www.adventureairsports.com/aoa.htm

but on the nose would work. How far out on the wing was your cuff?

Sarah



Udo wrote:
Out of curiosity I made a test. I built a cuff with an 21/2 ft arrow
shaft attached, line up with the wing chord. I had several strings
attached on top of each other about half inch apart and different
length. Very interesting to see how the air responds well ahead of the
leading edge but useless for any useable information. With flaps, the
changes I was interested in were to small in any case.
Udo

On Dec 9, 10:04 pm, jcarlyle wrote:
I was Googling around, and ran across yet another AOA device. Check
out this site:http://www.adventureairsports.com/aoa.htm
and pay particular attention to the 3rd photograph. Yaw string and AOA
in one, and not very expensive!

-John

On Dec 9, 6:46 pm, "Bill Daniels" bildan@comcast-dot-net wrote:

I think it's likely that the SafeFlight vane-type AOA indicator works fine
as long as you are fairly good at keeping the yaw string centered.
SafeFlight has been around selling these things to airplane owners for a
long time. It's nice to see them offering a product for gliders.- Hide quoted text -
- Show quoted text -- Hide quoted text -

- Show quoted text -

On Dec 9, 2:40 pm, Eric Greenwell flyguy

And yet, I never see any gliders with "pitch strings" on them, not even
on contest winners' gliders, presumably the pilots most interested in
getting the most from their efforts. If it's effective, why hasn't
something so cheap and easy spread throughout the fleet?

Eric,

I installed "pitch strings on my ASW 24 last year at Uvalde when my
ASI failed on takeoff. I landed quickly, swapped an old ASI into the
panel (which didn't work either) and taped two long (2 ft.) strings
low on the canopy. I could barely see the strings flapping wildly
around but discovered 40+ years of flying allowed me to do OK at
thermaling anyway, even with full water. But when I got back that
night, I removed the "whiskers"--the strings were so long that they
trailed on the ground and gave the airplane a very odd look--and
substituted short (~4") ones higher on the canopy following the advice
of ex F-14 driver Bif Huss, who has them on his Discus 2. I took a
grease pencil with me and marked the positions for min. sink and best
glide on the inside of the canopy.

They work fine. They're not revolutionary: they given different
indications when I'm skidding or (more of a problem) intentionally
slipping slightly, the range of movement is relatively small, and of
course they're sensitive to being knocked off during canopy cleaning.
It's just one more input. Interestingly, I'm confident I could fly the
glider at slow speeds very efficiently if my ASI fails again, which is
reason enough to keep them. And a quick glance at them from time to
time does reassure me I'm not cutting it too close trying to slow the
glider down. I refer to them a little more when I'm low, just to be
safe. I haven't noticed them responding early as I enter an updraft
but will pay attention the next time I fly, most likely not until next
spring.

I do get a lot of questions about them but, as you note, they haven't
spread throughout the fleet. Maybe if I started winning, that might
change!

Chip Bearden

Eric Greenwell wrote:

Does anyone know of documentation that supports the idea showing the
pilot the AOA will actually improve a glider pilot's thermalling? Or
even that the range of AOA needed to be "efficient" is too small for a
pilot to obtain it easily by using airspeed, or by just looking out the
canopy, once he's flown the glider enough to be familiar with it?

This document addresses the "best" thermalling speed, as part of an
effort to include climbing ability in handicapping gliders:

http://www.tux.org/~milgram/papers/thermaling2005.pdf

It's written by Judah Milgram, the translator for "Fundamentals of
Sailplane Design". I'm still digesting it, but it seems to say the
theoretical speed is slower than you would deduce from the straight
flight minimum speed; in fact, for bank angles less than 30 degrees, the
best speed is actually lower than the straight flight minimum sink speed.

There are some caveats: without polar measurements in a turn, you have
to make some assumptions that may not be true, and ignore real world
handling issues from flying slowly.

Practically speaking, I suggest that circling "efficiently" (regardless
of the value of an AOA meter in achieving it) only has value in weak,
smooth thermals; otherwise, where you are in the thermal is more
important than minimizing your glider's sink rate, so you have to fly
fast enough to maneuver well and accept losses from the excess speed and
bank angle changes.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org