Cruise

[andy]

My MX7-180 has 31" ABI tundra tires and unfaired ABI standard HD main gear legs. It's pretty draggy. I cruise at 90 - 100 mph and lean for a fuel burn of about 10 gph. The airplane will operate leaner but the engine will run cooler at 10 gph. That's especially important in hot weather and during extended climb. Drag increases as the square of airspeed. The advantage of increasing MP and RPM for a few more MPH of airspeed is vastly outweighed by the cost of increased fuel burn. Three hours of flying at 75% power might get me to my destination 10 minutes earlier at the expense of 6 more gallons of fuel than flying at 65% power.

Range is great with 40 gallon main tanks and 30 gallon auxiliary tanks - about 6:30. I can't fill the mains to the top because fuel will siphon out the vent tubes. Maule recommends that the mains be filled to 2" from the top. I use the bottom of the filler neck, which is about 1.5" from the top. Even then, there is some siphoning out the vent tubes when the wings aren't level. Maule offers a kit to prevent the siphoning at about $300 per wing but I've read that it still happens under some conditions.

At 10 gph with 68 gallons of fuel and 90 kts ground speed, range is about 612 nm.