We have designed the VertiLectric Volpire GF concept shown here to test and demonstrate how the GoFly competition requirements can be met. This competition was launched in 2017 and called for teams to design an aircraft that fulfills a set of specific, challenging requirements. 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.
We are not participating in the GoFly competition. GoFly demands that all people involved are at least 18 years old. For us, that means that we are old enough to fly ourselves and in some months also passengers in self-designed airplanes, but somehow not old enough for the GoFly competition.
The Volpire GF is loosely related to our Volpire. For now, the original Volpire is pretty publicity-shy, but we can explain some of the aspects of Volpire GF’s design that we keep getting quizzed about:
Why is the pilot in a prone position?
Because it’s wonderful. 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.
It’s also the position with the smallest frontal area in cruise flight and the natural choice for tailsitter layouts.
Forward and sideways visibility in prone position is similar to a conventional pilot position. Upwards visibility is somewhat restricted, but less so than downwards visibility in a conventional airplane. Visibility backwards (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 its scope, Volpire GF's endurance is less than one hour.
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 designed to allow partially or completely autonomous flight.
What about pilot sizes?
The GoFly rules call for a pilot up to 5’9” (175cm) tall. Volpire GF is designed for pilots up to 6’1” (185cm). That’s the height of our tallest team member and also the maximum height that we can accommodate within Volpire GF's exterior dimension limits. Minimum pilot height is 5’3” (160cm).
One of the basic differences between Volpire GF and Volpire are different safety concepts and Volpire's zero-zero rescue capability (i.e. zero minimum altitude and zero minimum airspeed). It allows a safe recovery of aircraft and pilot even in the unlikely event that there is an issue that would prevent a safe landing using its multi-redundant distributed propulsion system. CG issues due to the dimensional restrictions in the GoFly rulebook do not allow the implementation of zero-zero rescue capability in the Volpire GF concept.
Why five proprotor blades?
The prop pitch in the renders is too high for hovering. But we get to keep a few secrets for now, right? It’s not the only one :)
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 coping with that, especially if the blade tip speed should be kept low.
In most flight conditions, Volpire GF’s proprotor tip speed 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 proprotor 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 and proprotor efficiency, and they further minimize any potential for fuselage penetration.
Are the counter-swept wings a decorative feature?
No, they have aeroacoustic reasons.