3.1 DESIGN TARGETS FOR A UHCA PROPOSAL
The proposal configuration and layout parameters have been selected in such a way as to eliminate risky explorations and to allow realistic comparisons of the flight and economical figures with existing aircraft; it should also coincide with most of the results from the UHCA market survey.
For the cross-section the ovoid was chosen. The ovoid is a conventional design for aircraft (747) and was also preferred by most of the airlines.
The size has been limited to 80 m x 80 m in consideration of possible airport developments. The number of seats in a 3 class lay-out is assumed to be around 600, so it will be competitive in the market. In a high density class layout it should also be possible to seat over 800 passengers over a shorter distance in that cross-section. With a wider cross-section it could be redesigned to an 3 class 800 seater.
Another possibility in terms of flexibility would be a wider cross-section with an shorter fuselage that could be stretched to an 800 seater. This second possibility was not chosen, because of the initially mentioned targets.
3.1.1 Weight estimation
The evaluation of the mass is a rough approximation, because there were only some geometrical values to start with. Influence of the huge dimensions, which might offer new and exclude present construction methods could not be taken into account.
Here, the single masses of the A340-300 were extrapolated. The extrapolation factor was giver for the main aircraft parts for UHCA by B. Thramer of Deutsche Airbus. At the end, the maximum take off weight {MTOW) will be estimated by addition of the single masses.
The MTOW is decisive for the required cruise height thrust, the take-off lift, the wing load and the thrust-weight-ratio at a specific wing area and engine size.
The MTOW for 600 seats will be 531 000 kg.
3.1.2 Flight range,
There should be a range of R = 7000 nm with full paxload, so it is possible to use it as a very-long-range aircraft and satisfy all airline demands. The wing size offers a sufficient fuel capacity for that range.
3.1.3 payload at design range
The primary purpose of an aircraft is to safely transport a specific load from one point to another. This aircraft is going to be designed as an passenger carrier. The transportation volume is given by the amount of people and their luggage. A standard passenger has a weight of 75 kg and his luggage 20.25 kg, making a total of 95.25 kg (210 Ibs) per passenger.
| MPL | = Npass x Mpass [kg] |
| NPass | = 598 |
| MPass | = 95.25 [kg] |
This is about 11% of the MTOW (it is 10% for the 747-400 at 7140nm and 11% for the A340 at 6900 nm).
3.1.4 The Wing
The limit for the wing span is considered to be under 80 metres. A moderate aspect ratio has been chosen to stay in that limit. That also avoid aeroelastic swinging in the stress calculations.
It is, due to the landing gear bays, a 3-section trapeze wing with:
| Aspect ratio | 8.2 |
| Taper ratio | 0.2 |
| Sweepback C/4 | 32° |
| Profile root thick. | 14% |
| Profile tip thick. | 10% |
As a design target the tank capacity is of no concern for the wing, because it is big enough to hold sufficient fuel for the design ranges.
The wing load is, because of the thrust/weight ratio, the cruise speed of Ma = 0.85 and the take off requirements, of concern. It is with M/S = 700 kg/m2 standard for today’s large aircraft.
A modern transonic profile (A340) has been used.
3.1.5 The engines
The GE90 from General Electric, which is currently under development for the B777, has been chosen.
It has a bypass ratio of 8.45 and a static thrust at sea level of T0 = 378 kN / 85 000 Ib per engine. As its competitors, PW 4000 and RR Trent 800, it is based on a tuned gas generator combined with a larger fan.
Even a static thrust of T0 = 342 kN (like it will be used for the B777) would be sufficient for the start requirement of the aircraft (see appendix III.6.3 with the thrust/weight ratio of 0.26) .