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Theory demonstrates that one ought to increase speed in an headwind, and decrease speed in a tailwind to achieve maximum range. A lengthy discussion on the theoretical solution was answered, though not clearly, here. It is unlikely that a pilot will have the Thrust Required chart on which to draw a tangent line through the x-axis intercept at the given wind speed.

What simple techniques should the pilot employ to determine the best speed to fly given specific environmental conditions (fixed headwind or tailwind)?

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  • $\begingroup$ Max range is basically how long you can stay in the air at the fastest airspeed. Your optimum range, regardless of headwind, will be to set your airspeed for your economy cruise setting at that altitude. Speeding up in a headwind will just increase your fuel burn and probably reduce your range. $\endgroup$ – Ron Beyer Jan 20 '18 at 0:30
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    $\begingroup$ Not true. There is a tradeoff between speeding up to spend less time in the headwind and the increase in fuel burn. There is a theoretical speed that should be flown in a headwind. It is the point of the curve tangent to a line that intersects the x-axis at the negative of the headwind. $\endgroup$ – Mark Jones Jr. Jan 20 '18 at 0:31
  • $\begingroup$ This is tough. Have you researched the Carson speed? $\endgroup$ – acpilot Jan 20 '18 at 4:06
  • $\begingroup$ The discussion given as reference by the OP is quite comprehensive. Using the polar of your own plane, you can tabulate at home the best range speeds for different wind conditions, and have them handy in the cockpit... $\endgroup$ – xxavier Jan 20 '18 at 8:35
  • $\begingroup$ @acpilot I had not researched Carson speed, but I found this paper: "Fuel Efficiency of Small Aircraft." cafe.foundation/v2/pdf_tech/MPG.engines/… $\endgroup$ – Mark Jones Jr. Jan 20 '18 at 9:36
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An old technique is "Half the Headwind, all the Tailwind".

So if you're flying into a headwind of 20kts, increase your cruise speed by 10kts. If it's a 20kt tailwind, decrease your Cruise Speed by 20kts (but only as far as BestEnduranceSpeed).

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  • $\begingroup$ I like the stickiness of that technique. Where did you hear/learn it? $\endgroup$ – Mark Jones Jr. Jan 22 '18 at 18:18
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    $\begingroup$ It's an old Ferry Flight / Coastal Command technique, ie it goes back YEARS <g>. Ina headwind you need to punch into the wind, but if you increase speed too much you'll burn much more fuel as the drag curve rises. So a ballpark Half-The-Headwind is a simple compromise. If you want anything more accurate than that, then you'll need tables of Weight v FuelFlow v Airspeed, and a few hours of calculating Groundspeeds and MilesPerGallon with differing winds. $\endgroup$ – RAC Jan 24 '18 at 10:25
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Since speed is increased in headwind, and decreased in tailwind, that's a good starting point. Let's assume it's a headwind.

Increase the speed in increments, and calculate the range using the fuel flow figures and ground speed. Some engine trend monitors are capable of doing that.

Keep increasing until the range starts going down, and go back one step.

Full disclosure: I'm not a test pilot.

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  • $\begingroup$ I believe this is the closest technique. However, deciding the "speed increment" and minimizing the number of times this method is attempted are two open elements of the question that would make the method useful. $\endgroup$ – Mark Jones Jr. Jan 20 '18 at 14:28
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In a good day, with no wind, you can make trial glides and note down the values of the variometer and of the anemometer. Four or five points are enough to draw a best-fit parabola. Once you have it, you find the best range speed for any wind condition by tracing a tangent to the parabola that starts at the value of the wind. You note down the airspeed given by the tangent, and that's the best range speed for that wind condition. You may make a list of winds and the corresponding best range speeds and have that list handy at the cockpit.

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  • $\begingroup$ Do you have an example of this? I'll try it out. $\endgroup$ – acpilot Jan 20 '18 at 13:39
  • $\begingroup$ @acpilot Here's an example curve with tangents, taken from the reference given by the OP: [img]i.imgur.com/wXgl4hZ.jpg[/img] $\endgroup$ – xxavier Jan 20 '18 at 13:51
  • $\begingroup$ How do you determine thes placement tof the tangent? $\endgroup$ – acpilot Jan 20 '18 at 13:53
  • $\begingroup$ While the technique may work, it describes an exhaustive method that is impractical. First, on a good day, there is NEVER "no wind." Second, the range of altitudes and airspeeds for a high performance aircraft makes this simple method an enormous undertaking. Variometers are useful on gliders, but they are not as accurate on most other aircraft. $\endgroup$ – Mark Jones Jr. Jan 20 '18 at 14:26
  • $\begingroup$ @Mark Jones Jr. Well, a good day, 'with no wind', is desirable because of the lack of turbulence, that makes measurements easier. In itself, the wind has no influence on them, as the plane flies always within the mass of air, moving or not. That doesn't matter for polar-drawing... It's true that airplane instruments aren't exceedingly accurate, but they are enough for practical purposes, as is the case here... And the method isn't 'an enormous undertaking'. I have drawn those curves many times... $\endgroup$ – xxavier Jan 20 '18 at 14:33
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Best Endurance

Vg plus headwind component OR minus tailwind component

Or Carson Number (Cost = 16% increase in fuel consumption) Carson = Vg x 0.32 Headwind = Carson + (Headwind/3) Tailwind = Carson - (Headwind/3)

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  • $\begingroup$ Most of what I've read suggest Carson's Number is only good for small aircraft and not high performance aircraft. Have you heard differently? $\endgroup$ – Mark Jones Jr. Jan 20 '18 at 21:36

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