What do you do when you have a whole warehouse sized facility and an industrial sized CNC foam cutter? Clearly, the only choice is to build giant RC aircraft, and that’s exactly what the folks at [FliteTest] teamed up with the illustrious [Peter Sripol] to accomplish. Did it work? Yes. Did it work well? We’ll let you be the judge after taking a gander at the video below the break.
[Peter Sripol], known for building manned ultralight electric aircraft from foam, was roped in as the designer of the aircraft. A very light EPS foam is used to cut out the flying surfaces, while a denser green foam board is sourced from the local home building store to construct the fuselage.
The build is anything but ordinary, and kids are involved in the construction, although the video doesn’t elaborate on it very much. You can see evidence of their excitement in the graffiti on the wings and fuselage- surely a huge success on that front! As for flying? Four large motors provide locomotion, and it’s barely enough to keep the beast flying. A mishap with the Center of Gravity demands a last minute design change which renders the rudder almost useless. But, it does fly, and it is a great step toward the next iteration. Just like every good hack!
Yaw wag usually occurs on flying wings that use a pair of small winglets instead of a large vertical stabilizer on the centerline. Split rudders, also known as differential spoilers, can be used for active yaw control by increasing drag on either wing independently. However, this requires very rapid corrections that are very difficult to do manually, so this is where ArduPilot comes in. [Think Flight] used its yaw dampening feature in combination with differential spoilers to completely eliminate vertical stabilizers and yaw wag. This is the same technique used on the B-2 stealth bomber to avoid radar reflecting vertical stabilizers. [Think Flight] also used these clamshells spoilers as elevons.
Using XFLR5 airfoil analysis software, [Think Flight] designed built a pair of flying wings to use these features. The first was successful in eliminating yaw wag, but exhibited some instability on the roll axis. After taking a closer look at the design with XFLR5, he found air it predicted that airflow would separate from the bottom surface of the wing at low angles of attack. After fixing this issue, he built a V2 to closely match the looks of the B2 bomber. Both aircraft were cut from EPP foam with an interesting-looking CNC hot wire cutter and laminated with Kevlar for strength. Continue reading “Eliminate Vertical Stabiliser With ArduPlane”→
Electric RC aircraft are not known for long flight times, with multirotors usually doing 20-45 minutes, while most fixed wings will struggle to get past two hours. [Matthew Heiskell] blew these numbers out of the water with a 10 hour 45 minute flight with an RC plane on battery power. Condensed video after the break.
The secret? An efficient aircraft, a well tuned autopilot and a massive battery. [Matthew] built a custom 4S 50 Ah li-ion battery pack from LG 21700 cells, with a weight of 2.85 kg (6.3 lbs). The airframe is a Phoenix 2400 motor glider, with a 2.4 m wingspan, powered by a 600 Kv brushless motor turning a 12 x 12 propeller. The 30 A ESC’s low voltage cutoff was disabled to ensure every bit of juice from the battery was available.
To improve efficiency and eliminate the need to maintain manual control for the marathon flight, a GPS and Matek 405 Wing flight controller running ArduPilot was added. ArduPilot is far from plug and play, so [Matthew] would have had to spend a lot of timing tuning and testing parameters for maximum flight efficiency. We are really curious to see if it’s possible to push the flight time even further by improving aerodynamics around the protruding battery, adding a pitot tube sensor to hold the perfect airspeed speed on the lift-drag curve, and possibly making use of thermals with ArduPilot’s new soaring feature.
A few of you are probably thinking, “Solar panels!”, and so did Matthew. He has another set of wings covered in them that he used to do a seven-hour flight. While it should theoretically increase flight time, he found that there were a number of significant disadvantages. Besides the added weight, electrical complexity and weather dependence, the solar cells are difficult to integrate into the wings without reducing aerodynamic efficiency. Taking into account what we’ve already seen of [rcflightest]’s various experiments/struggles with solar planes, we are starting to wonder if it’s really worth the trouble. Continue reading “Electric RC Plane Flies For Almost 11 Hours”→
Airplanes and spacecraft have a big problem. The more engine or fuel you have, the more engine and fuel you need. That’s why aircraft use techniques to have lightweight structural members and do everything they can to minimize weight. A lighter craft can go further and carry more payload or supercargo. Electric motors are very attractive for aircraft, but they suffer from having less efficiency per kilogram than competing technologies. H3X thinks they can change that with their HPDM-250 integrated motor and inverter.
Although the 15 kg motor is still in testing, the claimed specifications are impressive: a peak power of 250 kW for 30 seconds and continuous torque of 95 Nm and 200 kW sustained. The company claims 96.7% efficiency. The claims are for the motor running at 20,000 RPM, so you’d need to add the weight of a gearbox for practical applications, but the company says this adds a mere 3 kg to the overall weight.
Spectrum recently published a post on a new lithium sulfur battery technology specifically targeting electric aviation applications. Although lots of electric vehicles could benefit from the new technology, airplanes are especially sensitive to heavy batteries and lithium-sulfur batteries can weigh much less than modern batteries of equivalent capacity. The Spectrum post is from Oxis Energy who is about to fly tests with the new batteries which they claim have twice the energy density of conventional lithium-ion batteries. The company also claims the batteries are safer, which is another important consideration when flying through the sky.
The batteries have a cathode comprised of aluminum foil coated with carbon and sulfur — which avoids the use of cobalt, a cost driver in traditional lithium cell chemistries. The anode is pure lithium foil. Between the two electrodes is a separator soaked in an electrolyte. The company says the batteries go through multiple stages as they discharge, forming different chemical compounds that continue to produce electricity through chemical action.
The safety factor is due to the fact that, unlike lithium-ion cells, the new batteries don’t form dendrites that short out the cell. The cells do degrade over time, but not in a way that is likely to cause a short circuit. However, ceramic coatings may provide protection against this degradation in the future which would be another benefit compared to traditional lithium batteries.