August 5, 2022, ©. Leeham News: This week, we look at two eVTOLs that don’t fit the terminology we use; Multicopters, Vectored thrust, or Lift and Cruise. The Vertical VX4 and Archer Maker are Lift and Cruise designs, but they use vectored thrusters for the cruise thrust, Figure 1.
Vertical Aerospace, a Bristol UK-based upstart, has iterated its way to the VX4 architecture. Its pilot plus four passenger VX4 VTOL is designed to takeoff and land vertically but to fly in a classical aircraft wing mode with a V-tail controlling pitch and yaw and ailerons on the wings controlling roll.
The Vertical wing is large. It shares the 15m wingspan with Beta Technologie’s Alia-250, but the wingarea is 35% larger.
While the Beta design is a pure Lift and Cruise design, the VX4 is a hybrid with four vectored thrust propellers/rotors ahead of the wing and four lift rotors aft of the wing.
The vectored thrust units have variable pitch rotors, whereas the lift ones are fixed pitch units that stow. A unique feature of the VX4 is a four-blade lift rotor concept that stows as two blades on top of each other (Figure 1). It forces some kind of mechanism for the stow. The four blades increase the rotor solidity so that it can work with a higher power to match the five-blade forward units.
The Vertical project has gathered a seasoned team of aerospace people, and this might be the background to the impression of a large and generously sized VTOL when I saw the full-sized mockup at the Vertical stand at Farnborough.
Vertical focuses on battery and rotor technology as its core IP, with partnerships with GKN for structures, Rolls Royce for electric motors/inverters, and Honeywell for the Fly-By-Wire.
Using vectored thrust for 50% of the propulsive units saves a dedicated forward flight motor and propeller. The vectored thrust units must still go from 80% thrust and power while hovering (the remaining 20% is for aircraft control with RPM changes and redundancy should one vertical lift unit fail) to around 15% thrust/power in forward flight.
The optimization problem we discussed in Part 28, Vectored thrust VTOLs, remains; it’s just less severe.
If Vertical’s VX4 is generously sized, the Archer Maker is the opposite. It’s a two-seater functional prototype to test the concept and flight dynamics of a 12-rotor “six by six” concept, Figure 2.
If the functional prototype validates the concept, the production model will be a larger variant of the 80% scale Maker. One can presume a four-passenger production model based on this information.
The Lift plus Cruise concept is the same as for the Vertical VTOL; it’s just divided over 12 smaller rotors than eight larger ones.
Here is a summary of the advantages and disadvantages of the concepts:
The disadvantages are;
It remains to see which choice will prevail, the Wisk, Beta, EVE pure Lift and Cruise principle that avoids the propwash problems (by using pusher forward flight thrusters) or the mixed vectored thrust Lift and Cruise designs of Vertical and Archer.