The rookie pilot had offers from a few of the most experienced test pilots and Long EZ pilots in the world, including SpaceShipOne pilot (and Long EZ builder/owner) Mike Melvill. But Yates was more concerned about the experimental power system than the airplane.
“Despite being an inexperienced pilot I still thought I was the best guy to fly this plane on this day,” Yates says. “I know the powertrain very well, I know where the limits are and how far I could push it. I didn’t want to be the guy that built the airplane that killed Mike Melvill.”
Standing next to his modified airplane in the sweltering Midwest heat, many of the visitors at Airventure aren’t immediately aware of the significance of the airplane. There are many Long EZs here in Oshkosh and the airplane has been a staple of the Experimental Aviation Association’s fly-in since Burt Rutan introduced the design here back in 1979. But Yates’ Long EZ is different than the rest.
When the electric vehicle pioneer bought the used airplane it had a 118 horsepower, four-cylinder gasoline-powered engine that is fairly standard for a Long EZ. Over the course of several months Yates and his team pulled the four-cylinder engine out of the Long EZ. They then pulled the 193 kW (258 hp), liquid cooled electric motor out of his record setting battery powered motorcycle and mounted it to the back of the Long EZ.
With the very well used (Yates calls it “abused”) lithium polymer battery back from the motorcycle in the back seat, the Long EZ was being prepared as a test bed for some of the technologies Yates needs to develop for his transatlantic flight. But after setting speed records for an electric motorcycle, first up for the Long EZ was a speed run.
The team spent many months preparing the airplane, and when not working in the hangar, Yates spent the time getting his pilot’s license. He started flight lessons in May and by the end of June he had his private pilot’s license in hand.
“Aviation doesn’t reward the reckless” – Chip Yates Initially. Yates hoped to get more cockpit time in a Long EZ before trying his electric powered version. He’s spent around 100 hours flying in the back seat of one, so he was familiar with the feel. And he had spent plenty of time talking to other Long EZ pilots about what to expect. But before last week’s speed run, he had only flown a Long EZ for about 15 minutes, and that was the day before in his electric Long EZ – his first flight time out.
“The first flight went fine, it behaved great and I landed exactly where I intended to,” Yates says. “It’s not me, it’s the plane, it’s a great airplane.”
Yates exudes energy and confidence. But he says despite what some may think, he doesn’t see himself as a daredevil. “Aviation doesn’t reward the reckless,” he says. The Long EZ is designed to fly in excess of 200 miles per hour, so Yates knew there would be no problem as far as the airplane is concerned. He knew the main issue was going to be with the batteries.
After examining the airplane and checking the weather after the first flight, everything looked good for a second flight at Inyo Kern airport in California, north of Mojave. On July 19 everything was set for the rookie pilot to put himself in the record books. A chase plane arrived at 8:00 a.m. and the fire department was on hand just in case. Yates had also coordinated with the nearby Naval Air Weapons Station China Lake to have them track his flight on both radar and video.
With more than double the horsepower of a conventional Long EZ, and about 100 pounds lighter, Yates had no problem getting off the ground. “I looked down [after takeoff] and I was climbing at 120 knots (138 mph),” Yates says. He didn’t need to climb out that fast, so he dialed back the power to about 30 percent which he says allowed him to climb at 80 knots (92 mph) and 500 feet per minute. “I didn’t want to wear out the battery pack climbing.”
Within a few minutes he was at his chosen altitude of 2,000 feet above the ground. And already the battery pack was showing it’s age.
“The internal impedance is the problem,” Yates tells us. “When you put a load on it, it causes a giant voltage drop.”
The 233 pound lithium polymer pack consists of 102 cells for a total of 428 volts. Capacity is 11.7 kWh at 600 amps. Yates said after setting the speed record at Bonneville, the pack was nearly worn out and he was only able to get 450 amps during the flight.
But the big problem was the voltage drop he would see anytime he touched the rotary power dial.
“I got up to 180 mph very easily, but my voltage was getting pretty low,” Yates says. “I was down at around 320 and 270 is the magic number, I can’t go below that.”
There are warning lights on the panel of the Long EZ that light up when he hits 270 volts. They came on as he passed 190 mph.
“Creeping up on 200, my red lights came on, which means back off, you’re going to destroy the batteries,” Yates says with some excitement still in his voice. “So at that moment I had to decide, do I back off and save the battery pack, which is essentially destroyed anyway, or do I punch through and get 200.”
There are warning lights on the panel of the Long EZ that light up when he hits 270 volts. They came on as he passed 190 mph. We already know his decision. After climbing away from the airport, Yates was now heading back towards the airport, pointed at I-395. In level flight, with little to no wind, Yates turned the dial and the custom propeller spun at around 2,000 rpm as he saw 200 miles per hour on his GPS. The speed was confirmed at 204.4 miles per hour by the radar at China Lake.
“I was able to hold 200 for about 15 seconds, and that’s with the battery at 270 volts the entire time,” Yates says. But as predicted it was the end of the battery pack, “I could smell at least one cell had opened and vented in the cockpit.”
Unlike some lithium based batteries, the cells in Yates’ custom pack are sealed aluminized pouches that are designed to vent when the fail. He says there was no chance of them catching on fire.
Yates ended up losing power over the runway where he was planning on landing. With more than 1,000 feet of altitude, he swung wide in a modified circle-to-land approach to avoid making the tight turn back to the runway. He had multiple runways to choose from, but in the end managed to make a dead stick landing where he intended to touchdown on with no power left in his electric airplane.
“I landed the instant I was aligned with the runway,” he says.
Since last week’s flight Yates hasn’t had much time to evaluate the equipment. After getting home from Oshkosh he plans to install a new battery and make some other modifications to the Long EZ. Next up is working on air-to-air “refueling” using batteries carried by another airplane and a cable that will connect to the nose of his Long EZ. This will be the first step in developing the technology needed for his non-stop transatlantic flight.
All photos by Jason Paur/Wired
