Does this exist-- program to generate speed-to-fly table?

[platypt...@gmail.com]

Here's what I want to do:

Input a minimum-sink-rate data point plus one or two other data points to establish a polar curve for a particular glider.

Have a computer program spit out a table showing the best airspeed to fly for variometer readings (not netto) of 200 fpm down, 300 fpm down, 400 fpm down, etc up to 1500 fpm down, for 0 mph headwind, 10 mph headwind, 20 mph headwind, and 30 mph headwind.

I only want to consider the best glide over the ground, not the best cross-country speed. I.e. a MacCready ring setting of zero.

This is to make a handy paper MacCready ring thing (but not moveable, and only a half a circle not a full circle) to tape around the vario of rented, borrowed, or club gliders. The arc will have three sets of numbers around it, corresponding to the 0 mph headwind, 10 mph headwind, 20 mph headwind, and 30 mph headwind cases.

Does such a program exist?

One speed-to-fly-explanation website says that "A really desperate pilot should set the ring to zero to maximize the area to be searched for a thermal. ", so I guess I am a really desperate pilot, to be requesting such a thing...

S

[SoaringXCellence]

I don't know of such a program, but you might want to rethink your approach. It doesn't take into account areas of sink or the effects of a headwind.

I suggest you read Reichmann (or maybe it was Cochrane) for his discussion on why 0 MacReady is never the right value unless the air is void of all motion.

[Tim Taylor]

I have an excel spreadsheet that does what you want. Mine gives a table of speed to fly at three different wing loadings. I can send you the excel file but it was not designed for others to use. Alternately you can send me info about your glider and I can set it up for you and send it back.

Tim

[Dan Marotta]

If you use XCSoar, it provides a Speed to Fly info box.

On 6/9/2015 11:04 PM, Tim Taylor wrote:

I have an excel spreadsheet that does what you want.  Mine gives a table of speed to fly at three different wing loadings. I can send you the excel file but it was not designed for others to use. Alternately you can send me info about your glider and I can set it up for you and send it back.  

Tim

--
Dan Marotta

[SF]

The Speed to fly functionality of the ClearNav vario works pretty well for giving you a speed to fly number based on the current conditions. I don't constantly chase the number it displays, but it is a good number to work off of.

SF

[marc....@gmail.com]

On Wednesday, June 10, 2015 at 9:07:21 AM UTC-7, SF wrote:
> The Speed to fly functionality of the ClearNav vario works pretty well for giving you a speed to fly number based on the current conditions. I don't constantly chase the number it displays, but it is a good number to work off of.
>

Somehow, suggesting a ClearNav (or even XCSoar) to someone who is talking about making paper speed rings for club gliders doesn't seem reasonable, but I guess I'm behind the times.

For the original poster, Paul Remde has an good assortment of soaring related spreadsheets here:

https://www.cumulus-soaring.com/soarmn/soaring_files.htm

In particular, polar6th.xls does pretty much what you want. There is also this web app:

https://www.stolaf.edu/people/hansonr/soaring/spd2fly/

Marc

[Charlie M. (UH & 002 owner/pilot)]

Agreed, I believe the OP stated this was for club ships and/or "just hopping in for a flight". Thus, may not have access to much more than basic instruments in these cases.

[platypt...@gmail.com]

On Tuesday, June 9, 2015 at 11:06:13 PM UTC-5, SoaringXCellence wrote:
> I don't know of such a program, but you might want to rethink your approach. It doesn't take into account areas of sink or the effects of a headwind.
>
> I suggest you read Reichmann (or maybe it was Cochrane) for his discussion on why 0 MacReady is never the right value unless the air is void of all motion.

Sink or headwind is exactly what I want to take into account, that's the whole point! Was I unclear on the original post?

If you are trying to race along at an optimal cross-county speed then there's room for all kinds of nuanced discussions around how the basic MacCready theory falls short but if you are just trying to make the flattest possible glide toward the next thermal, given the existing sink and headwind, I don't think there is much rocket science to it is there? Draw the tangent line tothe polar curve, starting at the appropriate point to take into account sink and headwind.

But sure I'd be interested to read anything for more illumination, can you give titles as well as authors?

Anyway, I wrote a program to do exactly this years ago (and it also spit out the corresponding values for non-zero MacCready settings) but I don't have access to it now... someday I will resurrect it but it might be many months before I can tackle that.

S

[Steve Leonard]

On Wednesday, June 10, 2015 at 1:43:44 PM UTC-5, platypt...@gmail.com wrote:

> Sink or headwind is exactly what I want to take into account, that's the whole point! Was I unclear on the original post?
>

As a matter of fact, your initial post was not clear. You said you wanted to know the best speed to fly for a variometer reading of 200 feet per minute down (not netto). Well, what is the air doing then? You could be flying 60 knots or 120 knots to get a variometer showing 200 feet per minute down (not netto), depending on what the air is doing. Or, you may not ever be able to get the variometer to show that little down. If the word "Not" slipped in there unexpectedly, your question becomes more clear. And that is what I assumed you meant.

No real need for a computer program to make this table. And I would make a simple table. It is not a ring you place around a variometer. You have the polar, you know the theory, you drew the lines, why not just type up the table?

Best L/D, no wind, for air going down 100 feet per minute is the line from the zero horizontal speed, 100 foot per minute vertical speed (on the opposite side from your polar), tangent to the polar. You can see the speed you should fly (tangent point), and the L/D you will make good (basically, horizontal speed divided by vertical speed). Headwinds move the origin point of your line towards your polar, tailwinds move the origin point away from your polar. For L/D with headwind or tailwind, you have to subtract or add, respectively, wind speed from or to flight speed to get ground speed to calculate L/D.

Can I ask why you want to make a program to create something you can create in less than 10 minutes, including time to type it up? The program won't likely save you much time in making the chart for a second, third, or fourth plane, as you still have to find the polar, pull data from it, enter it into the program, see that the polar it draws sort of matches what you see from your data source, and then trust the results. And if you make a ring, what happens when you go to a glider with a different number of degrees between each 100 ft/min increment in lift or sink?

My advice would be to make a simple table, not a ring. Put it on card stock and encase it in plastic (waterproof it). Tape it to the panel when you fly.

Just my 2 cents worth. BTW, I could have made a couple of those tables in the time I have spent typing this. :-)

Steve Leonard

[Dan Marotta]

True, but I have a copy of XCSoar on my Android phone and it's always with me...

--
Dan Marotta

[Charlie M. (UH & 002 owner/pilot)]

As I remind my 2 teenagers (which I supply cellphones for....), not everyone has a "smartphone", thus some of the apps & programs people mention have no relevance to me.
Glad they help out others though.

[Martin Gregorie]

On Wed, 10 Jun 2015 13:32:08 -0700, Charlie M. (UH & 002 owner/pilot)
wrote:

> As I remind my 2 teenagers (which I supply cellphones for....), not
> everyone has a "smartphone", thus some of the apps & programs people
> mention have no relevance to me.
> Glad they help out others though.

Alternative answer:

Get a satnav off eBay (Binatone B.350, Medion S.3747 or equivalent will
do nicely), plus a suction mount so you can attach it to the canopy.
Install XCSoar or LK8000 on the satnav and go fly a club glider.

The mechanical vario in the glider should have a McCready ring calibrated
for the aircraft (all our club gliders have these and IMHO so they should
at all other clubs) or you can use Block Speed theory.



--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Bob Pasker]

On Thursday, June 11, 2015 at 4:03:27 AM UTC-4, Martin Gregorie wrote:
> The mechanical vario in the glider should have a McCready ring calibrated
> for the aircraft (all our club gliders have these and IMHO so they should
> at all other clubs) or you can use Block Speed theory.

as a consummate renter, I have never had a McCready ring in any glider. Many don't even have (working) varios, but rather uncompensated VSIs

[Andy Blackburn]

Steve,

I thought I knew where you were going and then you lost me.

To make the card you have to use the polar - or more easily a quadratic curve fit if you want to just do it by simple math instead of reading a graph. But since the stronger the airman sink rate the faster you need to fly and the faster you fly the more rapidly the glider sinks through the air you need to add these effects together to get the speed for a given vary reading. This has always been the somewhat maddening thing about speed rings. You see the vario needle pointing at -2 kts and the speed the ring says 75 kts, so you push over to 75 kts and the needle moves up to -3 kts and a speed of 80 its - then the sink changes and you are chasing the vario needle versus the airspeed needle again. It is possible to print this out on a card, but I don't know how useful it will be since you only have the glider rate of sink, not net as you point out. I can't imagine trying to do this looking at the vario, the airspeed and a printed card, trying to line all three up.

[Andy Blackburn]

On Thursday, June 11, 2015 at 7:01:22 AM UTC-7, Andy Blackburn wrote:

I need to figure out how to turn off autocorrect when on RAS - corrections in CAPS below:


> To make the card you have to use the polar - or more easily a quadratic curve fit if you want to just do it by simple math instead of reading a graph. But since the stronger the airmaSS sink rate the faster you need to fly and the faster you fly the more rapidly the glider sinks through the air you need to add these effects together to get the speed for a given varIO reading. This has always been the somewhat maddening thing about speed rings. You see the vario needle pointing at -2 kts and the speed the ring says 75 kts, so you push over to 75 kts and the needle moves up to -3 kts and a speed of 80 Kts - then the sink changes and you are chasing the vario needle versus the airspeed needle again. It is possible to print this out on a card, but I don't know how useful it will be since you only have the glider rate of sink, not netTO as you point out. I can't imagine trying to do this looking at the vario, the airspeed and a printed card, trying to line all three up.

9B

[Steve Leonard]

Actually when you do the simple, graphic solution, you find that the speed you should fly if your ring is set to 2, and you are flying in air that is going down 1, is the speed you should fly if the ring was on 3 and the air was still. And believe it or not, the speed ring shows just exactly this. It does combine the higher glider sink rate due to higher speed with the air mass sink rate to point towards the correct speed to fly.

If you put together the chart, you will come up with a speed to fly for each wind speed and no air mass vertical motion. That is the easy part. If you know what the glider sink rate should be at that speed, and you see that the sink rate is higher, you can then adjust roughly based on a chart. This is not to be something that you are trying to extract every possible inch of distance the computer says you can get. This is a ballpark. The air will change as you fly through it. It may go down slower in just a couple of seconds. If you are going to try and chase it that much, I will leave you to your own devices. My vision is a 5 by 5 table at most. 0, 10, 20, and 30 knot wind columns, rows for 0, -100, -300, -500 air mass sink rates. And you can probably narrow it down more from there if you see the speeds don't vary too much.

Steve Leonard

[Bob Pasker]

what is just as interesting is what happens when the answer is off by some amount.

for example, how badly would the flight be affected by -10, -5, +5, and +10 knots/mph/kph off the optimal speed to fly?

--bob

[Steve Leonard]

I am sure Andy or someone can make you a spreadsheet to show that.

:-)

I would get out my handy dandy calculator. Or maybe get lost looking at a cloud or something....

Steve Leonard

[Andy Blackburn]

Roger - got it. The speed ring only knows what the glider is doing, not the airmass so it's a bit of an iterative solution. It's easy to figure out best glide speed for any given sink rate (OP question I believe), the trick is doing some simple math in your head to: 1) read the vario, 2) read the airspeed, 3) estimate the sink rate of the glider based on #2, 4) use the difference to pick a speed to fly. Easier if you have a Netto or speed to fly.

Honestly, if the needle points down I speed up. If it points way down, I speed up a lot. I've done the math on flying off-optimal STF. Precision only matters if you are in a long line of sink and the effects compound.

Might be best to just have a linear rule of thumb on three dimensions: 1) for every X increase in sink, fly Y knots faster, 2) for every Q knots in headwind, fly R knots faster and 3) for every A knots faster you fly subtract B knots from the vario reading to get netto so you know what the air is doing. If you center it around best L/D plus 10 knots, 2 knots of sink and 10 knots of headwind, the liner rule of thumb should work reasonably well.

9B

[platypt...@gmail.com]

Andy--

* The "card" is in the form of a half-ring. It looks exactly like half a MacCready ring. It is taped around the lower half of the vario (sink portion only). To tell the best speed-to-fly through sink. It doesn't deal with what to do in lift. Think of it as MacCready ring set to zero, but with three added bands of numbers to deal with 10 mph 20mph and 30 mph headwinds, not just zero-wind conditions.

* I've also done this using a printed card that was separate from the vario but the ring mounted around the vario is much much easier to use.

* Yes absolutely there is some "chasing" involved. I mean, not chasing the airspeed up and down, but when you hit sink, you'll go through a gradual acceleration before the vario needle is finally pointing right at the airspeed number you are actually flying, and that's when you stop accelerating. You can't instantly know what speed you'll need to accelerate to, like you would if you were using netto. But this is nothing new, there's a long long history of pilots using MacCready speed-to-fly rings on non-netto variometers.

* If I were using a netto variometer it would be very easy to create the ring using a graphical printout of the polar curve, and a ruler. It would only take 10 minutes or 30 minutes at most to get data for a wide spread of sink rate points and 3 different wind conditions. It's using a non-netto vario, that makes the numbers more of a pain to come up with, especially if you to produce the appopriate airspeed to fly for nice ROUND numbers on the vario (100 fpm, 200 fpm, etc). If you are happy with a scattershot collection of numbers for the vario values on the ring, rather than round numbers, it's a little easier to make the ring, but a little less nice to use.

S

[Steve Leonard]

On Thursday, June 11, 2015 at 7:55:56 PM UTC-5, platypt...@gmail.com wrote:

> * The "card" is in the form of a half-ring. It looks exactly like half a MacCready ring. It is taped around the lower half of the vario (sink portion only). To tell the best speed-to-fly through sink. It doesn't deal with what to do in lift. Think of it as MacCready ring set to zero, but with three added bands of numbers to deal with 10 mph 20mph and 30 mph headwinds, not just zero-wind conditions.
>
> * I've also done this using a printed card that was separate from the vario but the ring mounted around the vario is much much easier to use.
>
> * Yes absolutely there is some "chasing" involved. I mean, not chasing the airspeed up and down, but when you hit sink, you'll go through a gradual acceleration before the vario needle is finally pointing right at the airspeed number you are actually flying, and that's when you stop accelerating. You can't instantly know what speed you'll need to accelerate to, like you would if you were using netto. But this is nothing new, there's a long long history of pilots using MacCready speed-to-fly rings on non-netto variometers.
>
> * If I were using a netto variometer it would be very easy to create the ring using a graphical printout of the polar curve, and a ruler. It would only take 10 minutes or 30 minutes at most to get data for a wide spread of sink rate points and 3 different wind conditions. It's using a non-netto vario, that makes the numbers more of a pain to come up with, especially if you to produce the appopriate airspeed to fly for nice ROUND numbers on the vario (100 fpm, 200 fpm, etc). If you are happy with a scattershot collection of numbers for the vario values on the ring, rather than round numbers, it's a little easier to make the ring, but a little less nice to use.
>
> S

So, I guess the choice is yours. Quick, and "scattershot" numbers and be able to use it this weekend, or wait until you can resurrect the program and make it the way you like. If I were making one of these, I would color code, and put zero wind closest in, then 10 and 20 MPH headwinds and to heck with trying to put the speeds on a nice, round sink rate.

Steve Leonard

[Andy Blackburn]

Yes, the trick is getting the speed for even-knot sink indications on an uncompensated vario. I have a spreadsheet that I can probably modify to make a brut force table for any glider for which you have three velocity vs sink rate pairs (to make a quadratic polar curve fit) that you can then use to build a ring for 1 knot increments. Send me a PM with an email address.

9B

[platypt...@gmail.com]

When I had the old computer program running, I did have a function that showed how much faster or slower you could fly and have your performance only reduced by X percent. As you might imagine, it was a lot more critical to hit the right numbers if you were going for best cross-country speed, than simply going for flattest glide through sink and /or headwind for non-racing recreational flying. In the latter case you could be at least 5 mph slow without losing much. I really need to get that program running again one of these days. S

[Andy Blackburn]

On Friday, June 12, 2015 at 6:49:47 AM UTC-7, platypt...@gmail.com wrote:

Okay, I got out my dog-eared copy of "Cross Country Soaring" and pulled the right formula out of the math section. Here is a spreadsheet that takes three points off of a polar of your choosing, adjusts it for actual takeoff weight versus the weight the polar was measured at and creates a quadratic formula for the polar. It then calculates the locations on a speed ring for any given speed to fly. If you assume Mc=0 it will give you speed for best L/D, but it also works if you want to make a ring that rotates for different Mc values.

It does the calculation for zero wind and for a wind velocity you can input. Everything is in knots and pounds. Headwinds are negative numbers. Inputs are in red and a graph of the polar is produced for the weight used to create the polar, for the actual takeoff weight as well as for the designated wind condition at actual takeoff weight. It's in 1-knot STF increments, so you can either place even speed increments around the ring at irregular intervals or put irregular increments of STF at even increments around the ring, whatever is easier for you to use in the cockpit.

Here's a link to download the Excel file:

https://drive.google.com/folderview?id=0Bw1ChKkWEYLNfmRXY3JzWEdJcjBCOEdxNlh4dHBtakZwUGdxUjltU0tDYkN0UmxXOFNPTms&usp=sharing

Building this was an interesting review of some basic cross-country soaring principles. It reminded me that I should never, ever fly best L/D if I can avoid it when racing. The speed penalty huge and the benefit is marginal.

9B

[Andy Blackburn]

Also - the polar pre-loaded in the spreadsheet is for an ASW-27. You need to provide the polar for the glider you are flying - preferably a polar where you know the takeoff weight and the takeoff weight for the glider you are flying as it makes a bit of a difference.

9B