99 Miles on Batteries

By Gabriel DeVault, EAA 1308685

I don’t remember when the plan became official. But at some
point, apparently, I committed to flying my E-Gull electric ultralight from
home base (KWVI) to my friend Bob’s home at Pine Mountain Lake (E45), nearly
100 miles away, to present to the local EAA chapter. About two weeks before the
EAA meeting, Bob asked if I was going to make the flight, and I couldn’t figure
out a good reason to say no, so we started planning.

For a month or so before, Bob and I had been tossing around the
idea of a longer cross-country in the E-Gull. Mostly for fun, and just to prove
it could be done, but also to begin establishing the personal and physical
connections required for a real charge network. We began calling and scouting
around the local airports for plug-in spots for our chargers. Everyone was
super helpful and supportive, but few knew specifically what plug type or power
they actually had available. So we’ve now flown or driven to about a dozen
airports to determine in person what is available and are compiling this
information into a database.

As the day drew closer, I started flight planning in earnest. While the E-Gull has a maximum range of about 60 miles, I really like landing with a healthy reserve, so 40 miles or so was established as the maximum leg length. In theory, the E-Gull could make it with just two hops, but we elected for four. Windy.com and SkyVector.com proved to be excellent resources for our ultralight flight planning.


First leg: 16 nautical
miles, Watsonville to Frazier Lake

This is a hop I have done many times. I can fly there and back on
a single charge with plenty of reserve. We needed to get closer to Gustine to
make it as safe as possible, so while a short hop, it was an easy choice to

Second leg: 30 nautical
miles, Frazier Lake to Gustine

Originally, I wanted to fly into Los Banos, but strong winds
around the St. Louis Reservoir convinced me to stay north and fly to Gustine,
which is also closer to the next stop, Turlock. This is a slightly risky route
over remote and rugged terrain with frequent strong and turbulent winds.
Weather assessment is key to a safe hop here.

Third Leg: 19 nautical
miles, Gustine to Turlock

A nearby airport over friendly terrain with mild winds, this was
an easy choice. Though a slightly further leg uphill to Pine Mountain Lake
compared to Oakdale, it was still in my comfort zone.

Fourth Leg: 34 nautical
miles, Turlock to Pine Mountain Lake

This was the toughest leg of the journey, both the longest and the
most uphill with an elevation change of 3,000 feet. Additionally, the E-Gull’s
battery gets warmer with each successive fast-charge, and I knew I would have
to keep an eye on it. Calculations showed I would make it with about 25 percent
state-of-charge (SOC) remaining.

Watching the weather for a few days prior yielded no surprises. So, on Friday evening, September 6, we flew the E-Gull over to Frazier Lake. We tested the generators and various adapters and cables we would need, and loaded up Bob’s Maule that he’d be using as a chase plane. First leg complete!

Saturday morning, a lowish ceiling at Watsonville meant Bob could
not pick me up at KWVI in the Maule as planned, so I drove to Frazier Lake. We
threw the chargers in the Maule and got wheels-up about 9 a.m., a bit later
than planned. I forgot to turn on my hat cam.

Pacheco Pass was my biggest concern due to the frequent winds and
turbulence, and it did not disappoint. Because of the low ceiling, I couldn’t
climb as high over the pass as I would have liked, and I got knocked around a
good bit. It wasn’t unsafe, but it wasn’t very fun. I guess getting a little
out of your comfort zone and skill-building is an important part of developing
as a pilot.

With a sigh of relief, I got over the mountains and into clear, smooth air. Landing at Gustine was uneventful, and Bob already had the generators and charger set up. We had not established any charge power available at Gustine yet. Not five minutes later, like a scruffy angel, one of the local crop dusters flew in and we commenced to chatting about the E-Gull. Everyone loves to talk about the E-Gull. It turned out Mr. Crop Duster had a 220 available in his hangar and was happy to let us use it! We could only charge at 2.6kW with the generators, but now we could charge at 6kW! Bob quickly wired up the necessary adapter, and less than an hour later we were off for Turlock.

On a previous scouting, Bob had ascertained there was a 10-50 plug available at the Turlock airport. By the time I landed, Bob had made the correct adapter cable. However, when we went to plug it in, it didn’t seem to fit, so he wired up the “correct” cable; only this time it really didn’t fit. It turned out the first plug was correct, just had a slightly bent pin, so he got to remake the original adapter all over again. Then we discovered the outlet didn’t seem to be wired correctly either; upon further investigation, one of the hot legs wasn’t hooked up, so we fixed that, too. Just call us the Flying Electricians. Oh, and watch out for the wasps; they were in every opening they could find. Now we were charging at 6kW, so we relaxed in the lovely Turlock Pilot Lounge.

Now here’s where the battery heat comes into play. Normally, I
just fly once or twice in a day, and battery heat is just not a concern. But
today we are rapid-charging and flying the fastest duty-cycle we can. This does
not give the battery much time to shed its heat and recover between flights.
Yes, it needs better airflow. Yes, there are a million things I could and should
do to make it better. And maybe someday I will, when I get around to it …

Putting my 100 or so hours of E-Gull flight experience to work, I had previously judged the battery would be cool enough for the next leg when the temperature is less than 110 degrees Fahrenheit. This was not a snap decision, and we had discussed it extensively before the journey.

I took off for Pine Mountain Lake just after 1 p.m. with the battery at 108 degrees Fahrenheit. I climbed at max cruise power (25kW) which gives about a 600-fpm climb. Keeping a close eye on temps and altitude, I finally hit the battery thermal limit at about 3,000 feet, and I needed about 4,000 feet to make it safely to Pine Mountain Lake. I should note the actual battery thermal limit is a bit higher than the personal limit of 120 degrees I set for myself. So throttling back to 15kW, I continued toward the Sierra foothills. 15kW still provides for 200-300 fpm climb, and my battery temperature held steady as I snuck up on 4,000 feet and the mountains ahead.

For all the riskier sections of the journey, Bob and I had
discussed specific go/no-go criteria. For this leg, the criterion was 4,000
feet, battery temperatures below the thermal limit, and more than 50 percent
SOC remaining as we crossed San Pedro Lake. I had all of these with a margin,
and a nice little tailwind to boot, so I could start to relax and enjoy the
scenery around me.

As I came back to cruise power (~10kW), the noise and vibrations receded, and for the first time on this journey, I was really enjoying myself. I knew I had my destination made, and it was no longer work, but actually quite fun! The experience of flying an electric airplane is hard to convey. It’s almost like soaring, but a little louder, less intimidating, and certainly less “sporting,” but sometimes it’s okay to cheat a little. It’s also a lot like driving an electric car; that silent but steady push is almost magical. Dare I say it is perhaps most akin to riding a Zero Motorcycle, but even better!

Wheels-down at PML felt great! One of my best landings ever, just greased it in. Karen, Bob’s partner, even got it on video from the ground. Looking down, I saw 31 percent SOC remaining, which was even better than I had hoped!

We showed off the airplane at the local EAA monthly meeting, and
then taxied it over to the monthly Pine Mountain Lake Aviation Association
meeting. The food and discussion were just great — did I mention people love
talking about the E-Gull? Pine Mountain Lake might have been the nicest
aviation community I have encountered to date. Taxiing the E-Gull back through
the neighborhood on a moonlit night, guided by Bob on his golf cart, was a
memorable experience by itself.

After sleeping like a log, I awoke to the alarm clock going off
way too early, and it was time to do it all over again. After a leisurely and
delicious cup of coffee and watching the wild turkeys cruise around the
neighborhood, I got back to checking the weather and packing up. Declaring
myself ready, I went down to the hangar to check on the E-Gull — aaannnddd it
wasn’t fully charged. I was goofing with the charger settings and forgot to
reset them correctly. Well poop, I get it charging properly, but I know the
battery will gain ~10 degrees temp, which I wish I had in reserve for later.

About half an hour later, around 9 a.m. and behind schedule, we were
off. Right from takeoff, I knew I was in for a treat — smooth and clear skies,
low winds, and the beautiful Pine Mountain Lake greeted me as I rose into the
blue. After an easy climb to 4,000 feet, I’m again struck at the magnificence
of the experience. Not just the views, or the electric power, but the E-Gull
itself. It is just a fantastic machine. Instantaneous power, excellent
handling, incredible views — it’s just a confidence-inspiring platform. I’m convinced
electric is the future.

Clearing the final ridge to the valley ahead, I brought the power
back to a modest 6kW and just soared in easy mode all the way down to Turlock.
Electric power is so freaking cool!

Now that we have an established charge spot at Turlock, it’s easy. Bob’s got the charger plugged in and waiting for me. I taxi right up and plug in. What service! Bob, you’re hired!

We met another amazing denizen of the local airport, and proceeded
to talk all things aviation. He provided us with nice cold beverages and
surprisingly nice facilities. I am again somewhat taken aback by the kindness
and generosity of the aviation community. What a wonderful return to the roots
of flying this turned out to be! I have an electric car, and many folks, as
well as I, have noted how on longer trips, the longer charge stops really force
you into a different and generally more relaxed state of mind. You can’t charge
any faster, so you might as well just enjoy it.

About an hour later, we were fully charged and pressed on to
Gustine. It was a short and easy flight. Our previous host even generously
agreed to meet us back there and opened his hangar for our charging needs.
Again we talked airplanes. It’s so nice to have a common interest; I don’t find
many to talk airplanes with in my everyday situations.

I am working on my private, as it will be necessary for my next
project, an electric Sonex Xenos. I will also need a tailwheel endorsement. Bob
generously offered to let me practice taxiing the Maule while we waited for the
E-Gull to charge. I wish I had video, as I’m sure I looked like a loon, weaving
and figure 8-ing around the grass infield. Taxiing taildraggers is pretty dang
fun all by itself.

After 15 minutes of that hoonery, the E-Gull was charged and
ready to go. The battery temp was 108, and I needed to climb over 3,000 feet
into stiff headwinds over Pacheco Pass to make it home. Again, Bob and I
discussed go/no-go parameters. As long as I got to 3,000 feet and my ground
speed was more than 50 mph, I’d have plenty of reserve.

Just as predicted on windy.com, I had mild winds over the valley
and made my climb to 3,000 feet within battery thermal limits. As I pushed over
the Pacheco Pass mountains, my ground speed started to drop. It got gusty and
turbulent, and at times my ground speed went as low as 48 mph. But my average
speed was still higher, and my instrumentation cheerfully assured me that I was
well within my margins. I actually felt pretty cool and confident — maybe that
skill-building from the previous day was paying off.

Cresting the final ridge to the Salinas Valley, Frazier Park awaited in all its green, grassy glory. Because of the stiff headwinds, I wanted to be very sure I had the field made before reducing power. I switched to a full motor-off glide and planned for a straight-in approach. This airplane really thinks it’s a glider sometimes, and I could tell that I was going to overshoot by a mile. I flicked on the regen switch, which allows the motor to spin and pushes about a 1/2kW of regen power back into the battery and makes a pretty decent airbrake, and I was still too high. So I made for a base leg entry instead. I’ve learned to not aim for the numbers at Frazier Lake, because I then have to taxi 1,000 feet down a bumpy grass strip to the taxiway. I added a bit of power and floated it way down to a nice landing, well timed to exit midfield. Even though I had one more leg, it felt like I was home. I had 31 percent SOC remaining, which was perfect.

Bob and I had been discussing air-to-air charging, regenerative
towing, and all sorts of ludicrous ideas enabled by electric power, and we
decided to test one of them. Bob pulled ahead on the taxiway and held still
while I came up behind him and then applied the brakes. Under my guidance, he
then applied more and more power until the E-Gull was trembling and bucking in
his prop wash; I looked down and saw that I was regenerating power at a mere
200W. So there you have it — we may have created the least efficient form of
recharging ever invented. We turned 200 hp into about 200W. It would take 50
hours to fully recharge at that rate.

I had a friendly hangar at Frazier Lake, with a 14-50 plug available for my use. A short charge later and we were off again, and for the final time. This short and familiar hop refused to go down without a fight, and I was bucking 20-plus-mph headwinds most of the way to Watsonville. When your cruise is only 60 mph, those headwinds hurt. Still, it’s a flight I have done many times and I enjoyed it. The E-Gull flies better than anything else I have experienced so far, in my admittedly limited repertoire. A full regen descent and hefty slip to make the numbers, and I was truly home.

In the end, the E-Gull and its electric drive performed
flawlessly and exactly as expected. We made all of our destinations with energy
reserves equal to or better than planned. What we are coming to understand is,
electric aircraft are totally viable for recreational and day trips right now,
but the charging infrastructure is not. There are airports with fuel every
20-30 miles, and you only need a credit card to fill up. Every airport we had been
to had sufficient electric infrastructure for charging, just no actual outlet
to access it.

I believe electric aircraft can be safer, quieter, cheaper to own
and operate, and even bring a new and uniquely enjoyable form of flying to the
masses. My next electric aircraft will be a two-seater capable of two hours
duration. I believe this will bring it solidly into the “practical air
transport” category, and essentially comparable with existing electric car use
scenarios of about two to three hours of travel and 30-60 minutes of charging.
I can live with that. The lack of charging infrastructure is quickly going to
become the primary factor in what holds back electric aviation and all of its
myriad benefits from further development and adoption.

While autonomous flying cars may eventually supplement or replace
some portions of air travel, they can never replace the joy of flying our own
aircraft, and I think electric aviation increases the accessibility and
acceptability of personal aircraft and flying to a much broader audience. In
fact, I think electric aviation may just be the salvation of recreational GA
flying. By my math, electric aircraft will be less than half the cost to own
and operate compared to traditional aircraft. I think electric light-sport
aircraft are going to be extremely popular, just as soon as the FAA will allow
them. But we’re gonna need a place to charge.

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