How much fuel do you need to carry to go 245 nm?


On Tuesday, October 18, 2016 at 3:59:30 PM UTC-7, airshowbob wrote:
The Arcus-J is flying. Here is a video taken during its first few test flights in Moriarty:

https://youtu.be/HQVWCASrZyw

As most of you have probably seen, its first three OLC flights were pretty impressive, with a combined distance of ~4,300 km. It is certainly a testament to the exceptional skill of the pilot, and the outstanding performance of the Arcus platform. But it’s possible that these flights could have been done in a conventional motorglider, or even a non-powered glider. I won't dwell too much on the flights themselves. You can read the flight reports on the OLC site. So, what makes the jet version special?

What is not obvious from the flight statistics is the optimization planning prior to the flights. Dennis has an excellent team, including some of the best weather-guessers on the planet. On Thursday, the weather forecast for the Minden area did not look promising. However, the weather looked very good for the southern Sierras, making basing out of Inyokern for the weekend the optimum choice. So, Thursday morning, Dennis and I hopped in the Arcus-J, climbed to 16,000' (at 80 – 85 knots), and motored south at 145 knots. Our performance numbers indicated that the 245 nautical mile flight would be very close to the Arcus-J's fuel range with two people on board, so we did look for some lift hoping to get a few miles of assistance to extend our range a bit. We wasted a fair amount of time looking for wave, but there was none to be found. Being its first long powered cross-country flight, we were also being very conservative. We made a fuel stop at Bishop, and Dennis continued on with Bill Hill in the back seat. At Inyokern, they had plenty of fuel to practice some touch-and-goes. We have a plan to add a bit more fuel, so the transition from Minden to Inyokern will be an easy 2 hour flight.

On Friday's long wave flight, it was clear that the Arcus-J's ability to climb well at higher airspeed (about 80 knots) provides a comfortable margin above stall in the often severe turbulence of the Sierra wave rotor. The climb rate remains good, even at higher speeds, reduced power and higher altitudes. There is no specific airspeed limit with the engine extended, so moving quickly out of sinking areas is easy, even if pushing upwind.
Once we contacted lift, we simply shut down the engine (one switch) and commanded a pylon retract (one momentary switch). The pylon controller automatically waits two minutes for engine cooldown before opening the engine bay doors and retracting the engine. The glide ratio with the engine extended is still 38:1, so there is no hurry to get it retracted (glide ratio of the extended piston engine is 13:1).

On the last leg of our OLC flight, we extended south to beyond Rosamond, before turning for home at about 12,000'. We were slightly below glideslope home, so we extended the engine (one momentary switch) and started it (one switch). Even after cold-soaking for 8 hours at high altitude, the engine started smoothly. We then climbed to 13,500’ and motored home at 193 MPH. (We had enough fuel remaining to have motored at this speed for close to an hour.) Our home-bound leg only took a few minutes, but after 8 hours in the air, it was nice to make the run at high speed, and above the rotor.
The next two days were uneventful. We added fuel, maybe a few teaspoons of oil (the engine only holds a pint of oil) and flew a lot. We had one small issue with a fuel pressure light (probably a faulty sender), but otherwise, the Arcus-J performed flawlessly. We also spent the early part of the week getting several other pilots checked out in the aircraft. Keep in mind that Friday’s 1200 km flight happened only 16 days after the Arcus-J's first test flight on September 28 in Moriarty.

So, is a jet self-launch sailplane for everyone? Of course not. We recognize that every aircraft is a collection of flying compromises. If you’re concerned about the price of the engine or fuel, if you think it’s too noisy for your airport, if you don’t care to go fast with power, then it’s not for you.
However, it’s hard to argue with the safety aspects of a simple, low drag, vibration-free, self-launching capability that allows you to climb well, run fast, and get reliable restarts, even after cold-soaking at altitude.

Yes, I am aware that this isn’t the first jet motorglider (the Hutter 13 had a BMW turbine in 1949). It’s also not the only one currently flying (I personally own two others), but there is really no comparison between the Arcus-J and anything else. In short, it will out-run and out-climb any other motorglider (except my jet Salto). It is easy to operate, and easy to maintain (the engine can be removed in about 10 minutes). Its modern, digitally-controlled engine starts reliably, and is extremely simple to operate.
The Arcus-J is simply an elegant aircraft with excellent soaring performance and the capability to allow the pilot to maximize the day while maintain wide safety margins. I’m very proud to have been part of its creation.

BC