Comparative Flight Performance Evaluation of the Flying-V and a Reference Aircraft

Abstract

The Flying-V is a novel aircraft configuration that has shown a promising fuel saving potential compared to a conventional aircraft. The V-shaped configuration of the Flying-V integrates the passenger cabin and cargo volume into the lifting surface and has fins to provide lateral and directional stability. Several studies have been conducted into various aspects of the Flying-V, including the aerodynamics, structure and handling qualities. The objective of this research is to evaluate the flight performance characteristics of a Flying-V aircraft and compare results to a reference aircraft, by simulating takeoff, landing, climb and cruise using a flight mechanics model. More specifically, the performance characteristics of the Flying-V-1000 (FVK) and Airbus A350-1000 (A35K) are evaluated and compared. The subject of flight performance answers practical questions about what an aircraft is capable of. Using an in-house developed flight mechanics toolbox, various sub-models are integrated to create a flight mechanics model. The aerodynamic model is based on data from a vortex-lattice method developed by Airbus, enhanced with empirical zero-lift drag and wave drag models. Other sub-models that have been integrated include an inertia model, a propulsion model, a pilot model and a landing gear model.
On average, the FVK features a 25% shorter takeoff distance than the A35K. This difference is mainly due to the significantly smaller minimum unstick speed of the FVK, which is a consequence of the FVK’s larger tailstrike attitude. For both aircraft, geometric tailstrike constraints determine the minimum unstick speed, rather than the elevator effectiveness. The shorter takeoff distance of the FVK also leads to an averaged 30% shorter Balanced Field Length (BFL). The relative difference between the BFL of both aircraft is larger than for the takeoff distance, because the FVK is able to brake more effectively than the A35K.
The landing distances and approach speeds of both aircraft are similar, although the total landing distance is distributed differently over the phases of the landing manoeuvre. Due to a combination of a higher touchdown attitude and smaller ground attitude, the derotation distance of the FVK is significantly larger than for the A35K, assuming equal derotation rates for both aircraft. The FVK is able to compensate its longer derotation distance with a shorter braking distance to achieve a similar total landing distance as the A35K. An analysis of the pilot’s vision during the landing flare manoeuvre has shown that the FVK’s obscured segment can be twice as large as for the A35K. For landings performed with poor visibility, this could be problematic for the FVK.
Due to its larger maximum L/D, the FVK has better climb performance characteristics than the A35K. With One Engine Inoperative, the FVK is able to meet the climb gradient requirements of CS25.125 for altitudes up to 8000 ft at Maximum Takeoff Mass. The absolute service ceilings of the FVK and A35K were found to be 13.4 km and 12.0 km, respectively.
Evaluation of the Specific Air Range (SAR) parameter shows that the FVK outperforms the A35K in terms of cruise efficiency. The maximum trimmed aerodynamic efficiency, transonic efficiency and Range Parameter (RP) were found to be respectively 17%, 21% and 21% higher for the FVK. The Mach numbers and lift coefficients where the RP maxima are located suggest an optimal cruise altitude of 12.0 km for the FVK and 11.3 km for the A35K.