flight computer ergonomics and function

On Sunday, June 16, 2019 at 2:05:01 PM UTC-5, danlj wrote:
I'm curious.

After two successive near-midairs about 5 years ago, I installed PowerFlarm and a transponder that wouldn't deplete my battery during flight.

This required, due lack of panel space, that I give up my beloved ILEC S-10 flight computer (and its remote control). An Oudie IGC and and S-80 were recommended to replace it. The change has led to some conclusions about what flight computers should do in the cockpit.

1: Speed to fly
Flight computers all seem to calculate wind, and to be able to use the glider's polar. Not all use wind to revise STF.
It seems to me that we could use two rather different STF indications:
A: expected arrival altitude at next waypoint given polar, altitude, wind, and and optionally achieved mean L/D
B: best immediate speed for optimal L/D given polar, wind, and lift/sink over the last X seconds (user selectable)

(does any current flight computer offer these sorts of enhancements?)

2: Waypoint modification
Requiring the pilot to make an alphabetic search during flight to make a waypoint change is beyond stupid (it's a dangerous distraction).
- There are too many options for naming waypoints - recalling which name it was given is sometimes impossible.
- seldom are ICAO designations used, which aren't in any case easier to recall.
It seems to me that the best UI would have the ability to quickly limit the waypoint choices and swiftly move through the limited choices by spinning a knob or touch-pressing a knob-equivalent.
One is faced with either
- the need to modify one or more waypoints of a task
- the need to create a new task, the simplest of which is direct-to
Logical ways to create a limited set of waypoint choices include:
- distance (I think everybody offers this)
- direction (bearing, heading, or azimuth)
- distance & direction
- waypoints near current leg
- waypoints near current task

Do any current flight computers offer waypoint selection direction as well as distance?

Danl J

Comments below force a response.
1: the most efficient calibrated airspeed for progress over the ground DOES vary with the wind. A published rule of thumb is with a headwind, add 1/3 the headwind component to best glide; with a tailwind, fly at minimum sink.
Jean Marie Clement has created a beautiful graph showing that the most efficient CAS against headwind is a curve -- it looks like it's an hyperbola. It's reproduced on page 51 of Brigliadoris' Competing in Gliders.

2: The Oudie IGC manual is quite clear that ONLY polar and pre-set MacCready are used in calculating speed to fly and arrival altitude. Wind is specifically not used in their calculation, and you can of course set your MacCready to the mean climb in the last thermal if you like.

The S8x manual does not indicate whether current lift/sink is used to modify the instant STF arrows indication, nor whether wind is taken into account.. The STF *is* based on the next waypoint, polar, and (I think) MacCready. I haven't used this, and will reconfigure my S80 now that I've updated the firmware and watch its behavior.

3: Does anyone on this forum actually ever do the research before replying? Just curious. The B/S ratio applies to more than thermals...

While Oudie does not take account of wind in determining STF it most definitely does in determining arrival height.

Wind affects STF to reach a fixed point on the ground as high as possible after your last climb. However it does not change STF for best progress on task - fly Mcready and accept what the wind does to your ground speed.

"The S8x manual does not indicate whether current lift/sink is used to modify the instant STF arrows indication, nor whether wind is taken into account. The STF *is* based on the next waypoint, polar, and (I think) MacCready."

Lift/sink does drive the speed up slow down arrows. Wind does not, nor does the next waypoint. As well as polar and Mcready it also considers wing loading. When changing Mcready ballast or bug settings LX devices tell you the zero lift figures for Mcrwady STF and glide ratio.

By the way, if you want to look for a waypoint in a particular direction on your Oudie drag your finger in that direction on the screen - sort on any column heading by touching it, touch the wp you want and goto. But you surely know all this.

On Monday, June 17, 2019 at 5:53:34 PM UTC-6, waremark wrote:
"The S8x manual does not indicate whether current lift/sink is used to modify the instant STF arrows indication, nor whether wind is taken into account. The STF *is* based on the next waypoint, polar, and (I think) MacCready."

Lift/sink does drive the speed up slow down arrows. Wind does not, nor does the next waypoint. As well as polar and Mcready it also considers wing loading. When changing Mcready ballast or bug settings LX devices tell you the zero lift figures for Mcrwady STF and glide ratio.

By the way, if you want to look for a waypoint in a particular direction on your Oudie drag your finger in that direction on the screen - sort on any column heading by touching it, touch the wp you want and goto. But you surely know all this.

Agreed the Push/pull arrows on the S80 do account for lift and sink. I am disappointed that the Speed tape display does not account for lift and sink, it simply displays the calm air speed to fly speed, which is of little value on an active display. The S80 tells me that when I set the MacCready Value.

Brian

On Monday, June 17, 2019 at 4:20:46 PM UTC-7, danlj wrote:
Comments below force a response.
1: the most efficient calibrated airspeed for progress over the ground DOES vary with the wind. A published rule of thumb is with a headwind, add 1/3 the headwind component to best glide; with a tailwind, fly at minimum sink.

Not to maximise speed in continuous cross-country soaring from one thermal to another, no. That depends only on the expected lift in the next thermal and the polar.

For a final glide to a fixed point on the ground -- airport, turnpoint (where you are going to significantly change direction), mountain peak or ridge -- then yes you should change your speed roughly as you indicate.

3: Does anyone on this forum actually ever do the research before replying? Just curious. The B/S ratio applies to more than thermals...

Some of us do, yes.

MacCready theory optimises cross-country speed over a closed course with the assumption that wind speed and direction are constant throughout the course and independent of altitude. These assumptions are approximately true most of the time, so departing from MacCready speed has little benefit. However, if there is a leg where this is not true, the optimum airspeed may be different. A downwind dash would be a special case of this.

I did some numerical simulations some years ago for the case where one is flying to a turn point against a strong wind and found a faster speed into wind followed by a slower speed after the turn was marginally better. Clearly, if your computer tells you to fly at 60 knots against a 60 knot headwind, you are not going anywhere! Another issue is that you have to maintain sufficient altitude to connect with the next thermal. This may require trading off speed for altitude and experienced cross-country pilots have their own rules for dealing with these circumstances. Flight computers and associated software are imperfect at dealing with these more complex issues which are up to the pilot to solve.

Mike

For thermal XC if your computer is telling you to fly at 60kts then you're
probably flying dry and have MacCready set pretty low. So no you won't get
anywhere.
You need to climb faster and set MacCready higher

The wind only affects the rate of climb you need to make progress, speed to
fly between climbs is determined by "normal" MacCready

Flying Ridges or Wave, or final gliding to a fixed point, is a different
ball game

KN



At 07:44 18 June 2019, Mike the Strike wrote:
Clear=
ly, if your computer tells you to fly at 60 knots against a 60 knot
headwin=
d, you are not going anywhere!
=

Simple table that tells you how much to increase MC at certain headwind component would be enough to solve this issue.

On Tuesday, June 18, 2019 at 7:43:16 AM UTC-7, krasw wrote:
Simple table that tells you how much to increase MC at certain headwind component would be enough to solve this issue.

Unfortunately not.

The problem of optimum MacCready speed in wind relates to both wind shear and the relative horizontal velocity of the thermals. With a uniform atmosphere in which the wind speed is constant with height and in which thermals move at the same speed as the wind, standard MacCready theory applies. In these ideal conditions, there is no advantage in changing speed upwind or downwind.

In the case where thermals move more slowly than the wind (the more general case) or where they don't move at all (wave), the optimal speed will generally be faster upwind and slower downwind. This is what many experienced cross-country pilots have intuitively figured out in the real world.

Mathematical analyses of these have been done by several folks, including John Cochrane and Branko Stojkovic. Long enough ago to be forgotten.

The solution of speed to fly with wind is not easy, since the effects of wind shear and thermal speed are variable and may not be known well enough for a satisfactory general mathematical solution.

Mike

On Tuesday, June 18, 2019 at 5:34:40 PM UTC-4, Mike the Strike wrote:
On Tuesday, June 18, 2019 at 7:43:16 AM UTC-7, krasw wrote:
Simple table that tells you how much to increase MC at certain headwind component would be enough to solve this issue.

Unfortunately not.

The problem of optimum MacCready speed in wind relates to both wind shear and the relative horizontal velocity of the thermals. With a uniform atmosphere in which the wind speed is constant with height and in which thermals move at the same speed as the wind, standard MacCready theory applies. In these ideal conditions, there is no advantage in changing speed upwind or downwind.

In the case where thermals move more slowly than the wind (the more general case) or where they don't move at all (wave), the optimal speed will generally be faster upwind and slower downwind. This is what many experienced cross-country pilots have intuitively figured out in the real world.

Mathematical analyses of these have been done by several folks, including John Cochrane and Branko Stojkovic. Long enough ago to be forgotten.

The solution of speed to fly with wind is not easy, since the effects of wind shear and thermal speed are variable and may not be known well enough for a satisfactory general mathematical solution.

Mike

Thank you Mike. But a saving grace is that the achieved XC speed for some range around the optimum STF does not vary very much, exactly because it is an optimum: it is the top of a roundish hump in the curve. In that sense a "simple table", or even a rough guess, of the correction, if any, for the wind, is "enough". Lacking precise data on the local shear etc, fancier methods wouldn't do any better.

And, to paraphrase UH, the left-and-right controls are far more important (for task speed) than the up-and-down. Deviate to where the air is half a knot sweeter and you'll get there faster, even if your STF is 10 knots off.