Here is how to maximize range for the current wind conditions. For crosswinds, see below.
First, a few comments about the problem. In still air, best glide speed approximates max range speed since it will be VERY close to best miles per gallon (or kilometers per liter).
We address this in the book but here is more detail. As the book says, use best glide speed in no wind, fly faster in a headwind, and slower in a tailwind (but never slower than min-sink speed). These approximations don’t address ENGINE efficiency at each power setting, nor do they tell how much to speed up or slow down. But there’s a way to solve that if you’re willing to do some work.
Get Your Fuel Burns
You need to find out how much fuel flow your motor burns at different speeds. That can be done with an inline fuel-flow measuring device (like the Tiggy), or by measuring fuel decrease over time, which would require extremely accurate fuel quantity indications, time and patience. Competition pilots do that for navigation tasks.
These tests involve using speedbar. HAVE A RESERVE and be somewhere you don’t mind landing under it.
On a super smooth day, go up to 500′ or so, do a circle to determine wind direction and speed (use the PPGpS app), then fly INTO the wind. You will later add the wind speed to your values to get your True Air Speed. All the next measurements are done at one altitude and into the wind while being able to look at altitude, ground speed, and fuel flow. Yes, it’s a bit of a pain. You must be able to record the values, too. Thus the need for smooth air since your hands will be doing other than fondling brake toggles.
Fly as slow as you’re comfortable. That will be trimmed slow with lots of brakes. Hold altitude and do this long enough to get a good reading on fuel flow and ground speed. Record the values.
Go to hands up, still trimmed slow, let it stabilize and record the values. You’ll be hands-up for the remaining tests.
Go trimmers half-fast. Record the values. Repeat for trimmers full fast, then trimmers full fast with half speedbar, and finally timmers fast with full speedbar.
SPEEDBAR USE CAN BE DEADLY!!! It has contributed to fatalities. Know EXACTLY what your wing manual says about its use, especially if it has a speedbar/trimmer interconnect (like PK system) or tip steering. Techniques that work, or are even recommended on one wing can be deadly on another. I’m just going from observations. SOME wings (like the Dobermans I fly) should NOT be flown anywhere near full bar, in my opinion. Love the wing. But speedbar is a dark side that I don’t provoke.
Have your hands in the brakes, ready to react. You won’t use them unless sh*t hits the fan, then immediately let up the bar and deal with the remains of your wing.
You should end with a list of speeds and fuel flows. Add in the headwinds to get a list of what would best be called True Airspeed and fuel flows. These numbers will vary by altitude, but the differences at our typical altitude ranges are small.
What if it’s Crosswind?
You’ll be flying a heading that track towards the destination. It keeps you on course. Even if the wind is perpendicular to the course, you’ll lose groundspeed just like you had a smaller exact headwind. That’s the “Effective Headwind” and what is used in the spreadsheet’s speed-to-fly calculation.
Enter the wind offset from your course. So if your destination is due east and the wind is from the SE, that’s a 45 degree offset. Enter airspeed, wind speed and wind offset in degrees. You’ll get a heading to fly and groundspeed. The “effective
One Last Complexity
So we know how much a crosswind slows us down, and that there will be an effective headwind even if the wind is straight across our course because we must turn into it.
Picture yourself flying northward up the beach. An east wind is blowing 19 and you’re flying 20. You’re pointed almost directly into the wind, angling only slightly north and making only a few miles northward (track made good). Uggh. This will take forever. How much good will speeding up do?
Right now nearly all your effort is being spent just avoiding getting blown back, you’re pointing nearly directly into the wind. The “Effective Headwind” is huge. But if you speed up by 5 mph, you’d get to turn more towards the destination. That makes the “Effective Headwind” decrease! So speeding up has more benefit near than what is indicated on the chart, but it becomes insignificant once the wind speed gets less than about 75% of cruise speed.
Copy it and save on your own Google Sheets space since it’s not editable. Then enter your own values to see what the best speed to fly is. Enter your actual recorded airspeeds and fuel flows along the left side. Use whatever units you want for Gallons Per Hour (GPH) and those units will then apply to the Miles per Gallon (MPG). So if you enter liters in the fuel flow field, you’ll get Liters per Gallon out of the MPG field.