Our current projects are very publicity-shy. But we can explain the background and some of the aspects of the design of our Volpire GF ™ that we keep getting quizzed about.
We have designed the VertiLectric Volpire GF ™ concept shown here in early 2021 to demonstrate how the requirements of the intriguing GoFly competition can be met. Even with a utility-focused aircraft.
The Boeing-sponsored GoFly competition was launched in 2017 and called for teams to design an aircraft that fulfills a very challenging combination of requirements, including VTOL capability and performance demands, compliance with very low noise limits, and a size of less than 8.5' (2591mm) in any direction while being able to carry a passenger weighing 200 lb (91 kg). The challenge can be flown manned, or remote-controlled with a pilot dummy on board.
Originally, the GoFly competition was supposed to end in early 2020 with a fly-off and the announcement of the winners, but none of the participating teams came close to fulfilling the requirements.
Three years later, the GoFly prize is still unclaimed. But GoFly insists that all people involved in a team have to be at least 18 years old. For us, that means that two years after our first inquiry about the age limit, we're now old enough to fly airplanes solo (minimum age 16) and with passengers (minimum age 17) respectively, but somehow still not all old enough to enter an unmanned prototype in the GoFly competition and finally prove that this cool challenge can actually be met.
Why is the pilot in a prone position?
For a single-person aircraft, it’s the pilot position with the smallest frontal area. That minimizes parasitic drag. A tailsitter concept is also the simplest way to combine vertical take-off and landing with efficient cruise flight. This is crucial to meet the GoFly challenge requirements, so Volpire GF ™ takes off (and lands) with the pilot in a standing position and transitions 90 degrees forward into cruise mode.
A prone flying position is also real fun. Have you ever flown a hang glider? Flying in prone position is the closest we can get to realizing the dream of flying like a bird. It feels natural and provides incomparable downward visibility.
The Volpire GF ™ provides great visibility. The pilot has perfect downward visibility, a feature that no other motorized aircraft offers. Forward and sideways visibility is equally great. Upward visibility is at least as good as in a conventional high-wing airplane. Visibility straight back (and vertically downwards in vertical flight) is provided by a display that works like a car's rear view mirrors and backup camera.
Isn’t the prone position tiring?
No, even if that might be surprising. It’s been tested extensively, and hang glider pilots for example routinely fly for hours in this position, with the added weight of a helmet. True to the GoFly challenge's requirements, Volpire GF's endurance is just more than 30 minutes.
But for pilots that prefer head support, Volpire GF ™ provides an ergonomic chinrest. Its electromechanical actuation is controlled with a switch on the flightstick.
What about autonomous flight?
Volpire GF ™ is completely fly-by-wire and allows partially or completely autonomous flight. The prototype would be flown via FPV.
What about pilot sizes?
The GoFly rules call for a pilot up to 5’9” (175 cm) tall. The Volpire GF ™ is designed for pilots up to 6’1” (185 cm), the maximum height that we can accommodate within GoFly's exterior size limits.
One of the basic differences between the Volpire GF ™ concept and our other designs is that the dimensional restrictions in the GoFly rulebook do not allow the implementation of zero-zero rescue capability in the ultra-compact Volpire GF ™.
Why five propeller blades?
You have noticed that these blades would stall in hover? Congrats! The renders are meant to convey the concept, not as a master copy, so we've taken the liberty to change a few things from our actual layout :)
The GoFly rules limit the dimensions of the aircraft and thereby the disk area, which causes a relatively high disk loading. An increased number of blades helps to cope with that, especially if the blade tip speed should be kept low.
In most flight conditions, the propeller tip speed of the Volpire GF ™ is ~ 40% lower than common, cutting noise emissions by up to 85%. Distributing the load between more blades also reduces the load on each blade. Combined with the lower tip speed (which reduces centrifugal forces on the blades by 64%) this makes it possible to design the blades very light. Which in turn makes it easier to ensure that a blade could never penetrate the fuselage in case of a bird strike or other proprotor damage.
Why are the tips of the propeller blades bent?
The bent blade tips have five advantages: They improve safety around the parked aircraft through increased visibility of the tips and elimination of any sharp corners. The bent tips also provide small improvements in noise mitigation, propeller efficiency, and they further minimize any potential for fuselage penetration.
Are the counter-swept wings a decorative feature?
No, they have aeroacoustic reasons.
Why is the Volpire black?
Most aircraft, especially those made from composites, are painted white to minimize heat absorption. That makes perfect sense. But in the virtual design concept stage, the Volpire GF ™ is immune to solar radiation, so we took full advantage of a freedom that we don't have on actual builds.