The Tailless Aircraft

This report on tailless aircraft presents the pros and cons of using such an aircraft design for commercial purposes. The report comprises 4 sections discussing the aerodynamics, structural innovations, engines and overall advantages and disadvantages of tailless aircraft. The aerodynamic study of a tailless aircraft highlights the importance of the wave drag and span loading distribution and different designs that can improve the aerodynamic performance effectively. In structural innovations, several existing tailless aircraft are examined to identify how the structures have been designed to create a successful aircraft. In particular, structures used in the control and stability of the aircraft are examined. As regards to engines, the positioning of the engine and the idea of using a Vertical Takeoff has been discussed. The advantages and disadvantages of a tailless aircraft have been detailed.

Introduction

Of the aircraft in use today, the vast majority use a tailplane to house rudder and elevators. Aircraft without such a system remain quite rare. However, the concept of tailless aircraft has long been considered by engineers and aviators as an aerodynamically ideal. In the history of the aircraft design several attempts were made to build an aircraft with reduced tail size which has sometimes resulted in smaller drag and weight but has added to controllability problems. Because of this, tailless designs have mostly been used in military applications. In this report we assess whether it is now possible to seriously use this concept in commercial aircraft.

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Methodology

The information contained in this report was primarily gathered from textbooks and internet research. Four different aspects of the subject were identified and each aspect was researched and written up by one member of the group. Additionally, the group were able to examine a harrier jump jet which visited Perth on 7th May 2010.

Results of findings

The following table summarises what the research has revealed:

Negative points

Lower profile and interference drag

Lift to drag ratio increases by 20-25%

Engines can be positioned in the centre rear instead of a tail, providing the additional advantage of directional stability

Roll control is more efficient due to large wingspan

The tip of the wing aerofoil is not near the stall angle due to backward sweep along with twisted wing tip

Vertical takeoff is not practical since a large commercial aircraft weighs too much for the thrust available from current engine technology to overcome

Directional control is more difficult to achieve without adding a rudder assembly

The triangular spanwise aerodynamic loading distribution does not give the best aerodynamic performance even though the wave drag is the reduced.

Section 1: Aerodynamics

This section of the report discusses the aerodynamics of a tailless aircraft and various factors affecting the same. A tailless a is a revolutionary conceptual change from the classical design that has been prevailing for the past 50 years i.e. a wing attached to a cylindrical fuselage with a tail to ensure the stability and manoeuvrability of the aircraft.

Lower wetted area (area which is in contact with the external airflow) to volume ratio and lower interference drag is the main aerodynamic advantage of a tailless aircraft in comparison with the conventional aircraft.

On the aerodynamic performance side, the maximum lift-to-drag ratio depends on the ratio of the aircraft span to the square root of the product of the induced drag factor and the zero-lift drag area, which is proportional to the wetted area of the aircraft.

() max =

Where Cf is the average friction co-efficient (mainly dependent on the Reynolds number) over the wetted area Swet and is the friction co-efficient.

Since the tailless aircraft have a lower aspect ratio but also a lower friction co-efficient due to its larger chord, we always get smaller relative wetted area. This provides a substantial improvement in aerodynamic performance by increasing the lift-to-drag ratio of tailless aircraft in cruise to about 20-25% as compared to the conventional aircrafts.

The BWB-450 and BWB-800 were designed to compare with the existing fleet of conventional aircrafts as Boeing 747 and Airbus 380. BWB-450 was presented with the span and the aspect ratio being reduced to 80 m and 7.55 respectively, thereby concluding a decrease in 30%fuel burn per seat for the BWB models as compared to other conventional aircrafts and thus requiring 3 instead of 4 engines.

Moreover another such design project was successfully completed, which is based on a similar payload and performance as Airbus 380 with over 650 passengers. The configuration of the project is well suited for the application of laminar flow technology (which results in skin friction drag) to the engine Nacelle and potentially to the lifting surfaces. Also an increase in cruise Mach number increases the drag making the design of aircraft unfeasible.