Using new variometer technology to display real time lift coefficient?

[[email protected]]

A question respectfully submitted to the pundits who lurk in these halls:

Please forgive me if this topic has been covered before; I have done a general search on this forum and have found no mention of it anywhere.

Having been away from Soaring for about 35 years, and having just come back last summer, I have been slowly re-immersing myself. Some things have not changed all that much, but wow, have varios ever changed a lot!

My question:

With the new generation of varios out there, specifically those that incorporate inertial sensors, would it not be advantageous for these varios to offer the possibility to the pilot of displaying the sailplane’s real time lift coefficient, CL? It would seem to me that while thermalling, this display would be useful as a ‘lift reserve indicator’, directly related to AOA. No extra sensors would be required, since these new generation varios have all the inputs necessary to calculate CL (i.e. total pressure, static pressure, g force, with the aircraft mass and wing area presumably entered on the ground, before the flight). Granted, the pilot would have to know his max CL for different flap settings, but that’s it!

Would not such a display be desirable?

Has this been implemented already, and I am not aware of this?

[[email protected]]

I have recently implemented this with a sensor box with inertial sensors and airspeed.
I looked at the flight envelope during aerobatics.

It is nice, but it changes constantly.
I fly a flapless glider.

[[email protected]]

On Tuesday, 7 February 2017 02:13:59 UTC-5, wrote:
> I have recently implemented this with a sensor box with inertial sensors and airspeed.
> I looked at the flight envelope during aerobatics.
>
> It is nice, but it changes constantly.
> I fly a flapless glider.

Ok; perhaps a vertical bar depicting CL rather than an actual number.... Thanks for your input.

[Tango Eight]

On Monday, February 6, 2017 at 10:56:51 PM UTC-5, wrote:
> A question respectfully submitted to the pundits who lurk in these halls:
>
> Please forgive me if this topic has been covered before; I have done a general search on this forum and have found no mention of it anywhere.
>
> Having been away from Soaring for about 35 years, and having just come back last summer, I have been slowly re-immersing myself. Some things have not changed all that much, but wow, have varios ever changed a lot!
>
> My question:
>
> With the new generation of varios out there, specifically those that incorporate inertial sensors, would it not be advantageous for these varios to offer the possibility to the pilot of displaying the sailplane’s real time lift coefficient, CL? It would seem to me that while thermalling, this display would be useful as a ‘lift reserve indicator’, directly related to AOA. No extra sensors would be required, since these new generation varios have all the inputs necessary to calculate CL (i.e. total pressure, static pressure, g force, with the aircraft mass and wing area presumably entered on the ground, before the flight). Granted, the pilot would have to know his max CL for different flap settings, but that’s it!
>
> Would not such a display be desirable?
>
> Has this been implemented already, and I am not aware of this?

Use the Force, Luke....

[[email protected]]

On Tuesday, 7 February 2017 15:36:20 UTC, Tango Eight wrote:
> On Monday, February 6, 2017 at 10:56:51 PM UTC-5, wrote:
> > A question respectfully submitted to the pundits who lurk in these halls:
> >
> > Please forgive me if this topic has been covered before; I have done a general search on this forum and have found no mention of it anywhere.
> >
> > Having been away from Soaring for about 35 years, and having just come back last summer, I have been slowly re-immersing myself. Some things have not changed all that much, but wow, have varios ever changed a lot!
> >
> > My question:
> >
> > With the new generation of varios out there, specifically those that incorporate inertial sensors, would it not be advantageous for these varios to offer the possibility to the pilot of displaying the sailplane’s real time lift coefficient, CL? It would seem to me that while thermalling, this display would be useful as a ‘lift reserve indicator’, directly related to AOA. No extra sensors would be required, since these new generation varios have all the inputs necessary to calculate CL (i.e. total pressure, static pressure, g force, with the aircraft mass and wing area presumably entered on the ground, before the flight). Granted, the pilot would have to know his max CL for different flap settings, but that’s it!
> >
> > Would not such a display be desirable?
> >
> > Has this been implemented already, and I am not aware of this?
>
Reichmann pointed out the potential value of a lift coefficient meter in his book. If a meaningfully useable one could be made it would be very helpful for thermalling and as a safety feature.

[[email protected]]

On Monday, February 6, 2017 at 10:56:51 PM UTC-5, wrote:
> A question respectfully submitted to the pundits who lurk in these halls:
>
> Please forgive me if this topic has been covered before; I have done a general search on this forum and have found no mention of it anywhere.
>
> Having been away from Soaring for about 35 years, and having just come back last summer, I have been slowly re-immersing myself. Some things have not changed all that much, but wow, have varios ever changed a lot!
>
> My question:
>
> With the new generation of varios out there, specifically those that incorporate inertial sensors, would it not be advantageous for these varios to offer the possibility to the pilot of displaying the sailplane’s real time lift coefficient, CL? It would seem to me that while thermalling, this display would be useful as a ‘lift reserve indicator’, directly related to AOA. No extra sensors would be required, since these new generation varios have all the inputs necessary to calculate CL (i.e. total pressure, static pressure, g force, with the aircraft mass and wing area presumably entered on the ground, before the flight). Granted, the pilot would have to know his max CL for different flap settings, but that’s it!
>
> Would not such a display be desirable?
>
> Has this been implemented already, and I am not aware of this?

Sounds like you are trying to find a use for stuff in the instruments.
My question would be what are you trying to accomplish?
UH

[Dave Walsh]

At 16:24 07 February 2017,
wrote:
>On Monday, February 6, 2017 at 10:56:51 PM UTC-5,

>wrote=
>:
>> A question respectfully submitted to the pundits who lurk
in these halls:
>>=20
>> Please forgive me if this topic has been covered before;
I have done a
>=
>general search on this forum and have found no mention of
it anywhere.
>>=20
>> Having been away from Soaring for about 35 years, and
having just come
>ba=
>ck last summer, I have been slowly re-immersing myself.
Some things have
>n=
>ot changed all that much, but wow, have varios ever
changed a lot!
>>=20
>> My question:
>>=20
>> With the new generation of varios out there, specifically
those that
>inco=
>rporate inertial sensors, would it not be advantageous for
these varios
>to=
> offer the possibility to the pilot of displaying the
sailplane=E2=80=99s
>r=
>eal time lift coefficient, CL? It would seem to me that while
>thermalling,=
> this display would be useful as a =E2=80=98lift reserve
>indicator=E2=80=99=
>, directly related to AOA. No extra sensors would be
required, since
>these=
> new generation varios have all the inputs necessary to
calculate CL (i.e.
>=
>total pressure, static pressure, g force, with the aircraft
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>rea presumably entered on the ground, before the flight).
Granted, the
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>ot would have to know his max CL for different flap
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>=80=99s it!
>>=20
>> Would not such a display be desirable?
>>=20
>> Has this been implemented already, and I am not aware
of this?
>
>Sounds like you are trying to find a use for stuff in the
instruments.
>My question would be what are you trying to accomplish?
>UH
>
Doesn't an extra "yaw string", mounted on the vertical side
of the canopy, tell you the angle of attack (roughly)? I think
it's all explained on the DG website. No electronics involved.

[[email protected]]

Also did that. Works great, and shows nice things during spins!

I think audio aoa makes most sense, but you also have the audio vario.
Somehow intuitively providing feedback on attitude/velocity during thermalling might improve the tendency to thermal with a too shallow bank angle,or flying the incorrect velocity for the bank angle.

[Dan Marotta]

Too much audio - too many distractions. How about a vibrating seat
cushion? It could be programmed to increase the frequency and amplitude
of the vibrations as AoA increased and give you an electric shock just
before the critical angle is reached. Of course, if you have a sore
back, you'd be flying around at too high an AoA just for the good
vibrations... =-O

On 2/7/2017 11:15 AM, wrote:
> Also did that. Works great, and shows nice things during spins!
>
> I think audio aoa makes most sense, but you also have the audio vario.
> Somehow intuitively providing feedback on attitude/velocity during thermalling might improve the tendency to thermal with a too shallow bank angle,or flying the incorrect velocity for the bank angle.

--
Dan, 5J

[[email protected]]

> Sounds like you are trying to find a use for stuff in the instruments.
> My question would be what are you trying to accomplish?
> UH


Goal: To increase the pilot's awareness of how close to the stall the aircraft actually is. This could be of some use during thermalling flight, especially at low level or when encountering gusty conditions. A poor man’s AOA meter, if you will. If properly implemented, it should help avoid stall/spin accidents... I believe that aircraft landing on carriers carry such technology (AOA indicator), as well as certain business jets. Before the days of microprocessors, this would have been difficult to implement. See Soaring magazine, March 1975 to give you an idea of pre-microprocessor attempts to do this.

Since many modern varios already have sensors receiving and interpreting the required inputs to calculate CL, it should be simply a software modification to actually calculate this value. Perhaps the most difficult part of the whole implementation would be to present the pilot with this information so that it would be useful to him (Visual? Audio?).

[Bruce Hoult]

On Tuesday, February 7, 2017 at 9:42:02 PM UTC+3, wrote:
> > Sounds like you are trying to find a use for stuff in the instruments.
> > My question would be what are you trying to accomplish?
> > UH
>
>
> Goal: To increase the pilot's awareness of how close to the stall the aircraft actually is. This could be of some use during thermalling flight, especially at low level or when encountering gusty conditions. A poor man’s AOA meter, if you will. If properly implemented, it should help avoid stall/spin accidents... I believe that aircraft landing on carriers carry such technology (AOA indicator), as well as certain business jets. Before the days of microprocessors, this would have been difficult to implement. See Soaring magazine, March 1975 to give you an idea of pre-microprocessor attempts to do this.
>
> Since many modern varios already have sensors receiving and interpreting the required inputs to calculate CL, it should be simply a software modification to actually calculate this value. Perhaps the most difficult part of the whole implementation would be to present the pilot with this information so that it would be useful to him (Visual? Audio?).

Having to input weight and wing area (which admittedly doesn't change on most gliders) before flight seems like not only a pain and error-prone but also not entirely useful as different wing profiles have different useful max CL as well, and that is not published information even for "as new" gliders.

Maybe better to do an in-flight calibration where the pilot flies the glider briefly at their personal comfort limit near the stall and presses a button to calibrate the instrument. This could be done in straight and level flight, with the pilot judging it by buffet, sink rate, sound from airflow breaking away from the wings or whatever. Or it could be done in the first in-anger thermal.

Maybe also have "+1 knot" and "-1 knot" buttons to fine tune it later.

[ND]

On Tuesday, February 7, 2017 at 1:42:02 PM UTC-5, wrote:
> > Sounds like you are trying to find a use for stuff in the instruments.
> > My question would be what are you trying to accomplish?
> > UH
>
>
> Goal: To increase the pilot's awareness of how close to the stall the aircraft actually is. This could be of some use during thermalling flight, especially at low level or when encountering gusty conditions. A poor man’s AOA meter, if you will. If properly implemented, it should help avoid stall/spin accidents... I believe that aircraft landing on carriers carry such technology (AOA indicator), as well as certain business jets. Before the days of microprocessors, this would have been difficult to implement. See Soaring magazine, March 1975 to give you an idea of pre-microprocessor attempts to do this.
>
> Since many modern varios already have sensors receiving and interpreting the required inputs to calculate CL, it should be simply a software modification to actually calculate this value. Perhaps the most difficult part of the whole implementation would be to present the pilot with this information so that it would be useful to him (Visual? Audio?).

i think good training is better than making an instrument "think for you" in this case. good fundamental training allows you to recognize an oncoming stall. outsroucing it to an instrument is needless, and in my opinion more dangerous than doing this one the old fashioned way. you have to learn to feel the glider. your ass is a more sensitive instrument for this purpose. like evan said, use the force. having said that, i've read some stuff about people putting yaw strings on the side of their canopy and making the critical angle of attack. THAT is a poor man's AOA.

[[email protected]]

Training is frequently the answer, and yet things that should be overcome by training keep happening.

Maybe we need training on how to do training so we can train the trainers.

9B

On Tuesday, February 7, 2017 at 1:44:38 PM UTC-8, ND wrote:

> i think good training is better than making an instrument "think for you" in this case. good fundamental training allows you to recognize an oncoming stall. outsroucing it to an instrument is needless, and in my opinion more dangerous than doing this one the old fashioned way. you have to learn to feel the glider. your ass is a more sensitive instrument for this purpose. like evan said, use the force. having said that, i've read some stuff about people putting yaw strings on the side of their canopy and making the critical angle of attack. THAT is a poor man's AOA.

[Bruce Hoult]

On Wednesday, February 8, 2017 at 12:44:38 AM UTC+3, ND wrote:
> On Tuesday, February 7, 2017 at 1:42:02 PM UTC-5, wrote:
> > > Sounds like you are trying to find a use for stuff in the instruments..
> > > My question would be what are you trying to accomplish?
> > > UH
> >
> >
> > Goal: To increase the pilot's awareness of how close to the stall the aircraft actually is. This could be of some use during thermalling flight, especially at low level or when encountering gusty conditions. A poor man’s AOA meter, if you will. If properly implemented, it should help avoid stall/spin accidents... I believe that aircraft landing on carriers carry such technology (AOA indicator), as well as certain business jets. Before the days of microprocessors, this would have been difficult to implement. See Soaring magazine, March 1975 to give you an idea of pre-microprocessor attempts to do this.
> >
> > Since many modern varios already have sensors receiving and interpreting the required inputs to calculate CL, it should be simply a software modification to actually calculate this value. Perhaps the most difficult part of the whole implementation would be to present the pilot with this information so that it would be useful to him (Visual? Audio?).
>
> i think good training is better than making an instrument "think for you" in this case. good fundamental training allows you to recognize an oncoming stall. outsroucing it to an instrument is needless, and in my opinion more dangerous than doing this one the old fashioned way. you have to learn to feel the glider. your ass is a more sensitive instrument for this purpose. like evan said, use the force. having said that, i've read some stuff about people putting yaw strings on the side of their canopy and making the critical angle of attack. THAT is a poor man's AOA.

I don't feel any need for this instrument myself. I'm perfectly happy doing minimum controllable airspeed exercises and recognising the onset of the stall with my own senses. Often when I'm sitting back and letting someone else fly I'll be hearing the airflow sound change as gusts partially stall the wing. Suggest to them that they fly a couple of knots faster and suddenly we're climbing much better.

[[email protected]]

One can use stall speed to calculate the CL max.

[[email protected]]

Thanks to all for the useful input. I was mostly interested in throwing this topic up in the air, and seeing where it landed.

For myself, I agree with a previous post that training is important. Indeed, I would argue that training gives the best reward for the time spent.

However, you can supplement training with other goodies (most everyone is flying with some sort of TE compensation for their varios, some have varios that depict the real time wind vector, and many have moving map displays with little tiny ‘amoebas’ crawling all over them for example…)

Someone alluded to seat-of-the-pants flying to ‘feel’ how close you are flying to the stall. This works, and is used by all of us most of the time. I submit that when a pilot is distracted (low level circling in a rough thermal, on a windy day, with the associated drift illusions, and then throw in a FLARM target….) perhaps his feel may be momentarily masked or overridden….Then, wouldn’t it be nice to have a little audio ‘blip’ to warn us that we are suddenly 5% above the stall?

In addition, if we follow this seat of the pants flying to a logical extreme, perhaps we should get rid of the ASI (fly attitude), and also drop the altimeter (we can, after all, look at how big the houses and trees are getting).

Thanks again for all the thoughts.

rp

[Tango Eight]

On Wednesday, February 8, 2017 at 9:44:26 AM UTC-5, wrote:

> if we follow this seat of the pants flying to a logical extreme, perhaps we should get rid of the ASI (fly attitude), and also drop the altimeter (we can, after all, look at how big the houses and trees are getting).

That's my favorite lesson! 20 minutes spent thermalling with no ASI improves just about anyone's flying. No altimeter patterns are excellent practice as well. I cannot recommend too highly. Excellent BFR and Spring check ride material too.

best,
Evan Ludeman / T8

[Bruce Hoult]

On Wednesday, February 8, 2017 at 5:44:26 PM UTC+3, wrote:
> Thanks to all for the useful input. I was mostly interested in throwing this topic up in the air, and seeing where it landed.
>
> For myself, I agree with a previous post that training is important. Indeed, I would argue that training gives the best reward for the time spent.
>
> However, you can supplement training with other goodies (most everyone is flying with some sort of TE compensation for their varios, some have varios that depict the real time wind vector, and many have moving map displays with little tiny ‘amoebas’ crawling all over them for example…)
>
> Someone alluded to seat-of-the-pants flying to ‘feel’ how close you are flying to the stall. This works, and is used by all of us most of the time. I submit that when a pilot is distracted (low level circling in a rough thermal, on a windy day, with the associated drift illusions, and then throw in a FLARM target….) perhaps his feel may be momentarily masked or overridden….Then, wouldn’t it be nice to have a little audio ‘blip’ to warn us that we are suddenly 5% above the stall?
>
> In addition, if we follow this seat of the pants flying to a logical extreme, perhaps we should get rid of the ASI (fly attitude), and also drop the altimeter (we can, after all, look at how big the houses and trees are getting).

Legally-required minimum equipment.

We had (and won) a fight against the local tower guys several years ago. When we called "joining" they told us (along with the traffic, which is useful) the QNH and expected us to read it back. We told them it's a waste of everyone's time and that by the time we've decided to join circuit we're not looking at the altimeter any more. We also convinced them to only tell us about the traffic actually in or very near the circuit, not the ones still five minutes away.

We have students who are near solo do a flight or two with instruments covered. Not a big deal even in a heavy and slippery glider such as the DG1000. I wouldn't want to try to do an outlanding into a 100m field without ASI, but if you've got 400 or 500 meters of space then it's just not an issue.

[[email protected]]

Speaking of technology I just watched a seminar by Infineon - they make sensors. In the pressure transducer they make for exercise trackers can have high definition to tell that someone is climbing or descending stairs or help determine what kind of activity they are doing.
They can sense a air pressure difference of 50mm/2 inches!!!

These were energy efficient for use with battery powered systems of course.

Chris

[Richard[_9_]]

On Thursday, February 9, 2017 at 9:21:16 AM UTC-8, wrote:
> Speaking of technology I just watched a seminar by Infineon - they make sensors. In the pressure transducer they make for exercise trackers can have high definition to tell that someone is climbing or descending stairs or help determine what kind of activity they are doing.
> They can sense a air pressure difference of 50mm/2 inches!!!
>
> These were energy efficient for use with battery powered systems of course.
>
> Chris

I remember being told that the sensors used in the LXNAV equipment measure 1cm or altitude 100 time per second.

Richard
www.craggyaero.com

[JS]

On Thursday, February 9, 2017 at 9:44:49 AM UTC-8, Richard wrote:
> On Thursday, February 9, 2017 at 9:21:16 AM UTC-8, wrote:
> > Speaking of technology I just watched a seminar by Infineon - they make sensors. In the pressure transducer they make for exercise trackers can have high definition to tell that someone is climbing or descending stairs or help determine what kind of activity they are doing.
> > They can sense a air pressure difference of 50mm/2 inches!!!
> >
> > These were energy efficient for use with battery powered systems of course.
> >
> > Chris
>
> I remember being told that the sensors used in the LXNAV equipment measure 1cm or altitude 100 time per second.
>
> Richard
> www.craggyaero.com


When I was testing an Air-Glide S on the bench, discovered it takes very little disturbance of the ISU to get readings.
Jim

[Bruce Hoult]

On Thursday, February 9, 2017 at 8:21:16 PM UTC+3, wrote:
> Speaking of technology I just watched a seminar by Infineon - they make sensors. In the pressure transducer they make for exercise trackers can have high definition to tell that someone is climbing or descending stairs or help determine what kind of activity they are doing.
> They can sense a air pressure difference of 50mm/2 inches!!!

Sure. I've used a couple of these in little projects. Dead easy to hook up to any Arduino, Raspberry Pi etc.

https://www.sparkfun.com/products/11824

Relative accuracy of 0.02 hPa means about 15 cm at sea level I think.

There are better ones available but this chip sells for 3.73 Euro for one, or 2.25 Euro if you buy 1000 of them http://eu.mouser.com/ProductDetail/Bosch-Sensortec/BMP180/

The Sparkfun board is more because ... it not just the chip, it's the chip on a board, easy to use for amateurs or for prototyping.