On Thursday, June 11, 2015 at 5:55:56 PM UTC-7, wrote:
On Thursday, June 11, 2015 at 7:01:22 AM UTC-7, Andy Blackburn wrote:
On Wednesday, June 10, 2015 at 12:49:41 PM UTC-7, Steve Leonard wrote:
On Wednesday, June 10, 2015 at 1:43:44 PM UTC-5, 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

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--

* 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

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