The Pegasus Project is submitted by a Team of ALTRAN Engineers from different disciplines:
One of the aims for the Altran Pegasus team was to create a design different from the well-known quadcopter design extended by a wing. The Pegasus team thought the design should be simple but somehow an eye catcher. The team considered a number of ideas. The design involved in order to address the sometimes conflicting requirements that are required to fulfill flexibility, easy maintenance, easy and simple accessibility of all equipment’s and payload and last but not least the safety of cargo operators and people in the environment of the vehicle.The Pegasus air vehicle is designed around the cargo compartment and the ability to lift off vertically. The front two vertical lift fans and the cargo is balanced with the rear forward propulsive fans/propellers. The overall structure is a robust Kevlar fiber over pink foam that in mass production this structure is also cost effectively produced. The electronics and motors are off the shelf components with only the rotors and propellers 3D printed and optimized for this particular application so as to maximize efficiency and performance.Altran is pleased to submit the Pegasus design for consideration by Airbus and Local Motors as a design solution for the Cargo Transport Design Mission. Pegasus shall meet both the 3kg payload at 100km and the 5kg at 60km requirements.
The Pegasus vehicle is all composite vehicle. It is made of Kevlar fiber overlaid pink foam providing excellent strength with minimal weight. The vertical lift is provided by four electric motors and forward propulsion is provided by two electric motors. Forward flight depends on a high aspect ratio wing to provide lift. The high efficiency wing provides an effective L/D of over 20. All the rotors are ducted to provide maximum safety.
The drag was the calculated using basic formulas.
The Drag coefficient CD = CDf+CDi. It is assumed that the total drag is made up of friction, CDf and induced drag CDi. Other drag components are not considered at this preliminary stage.
CDf was calculated from Reynolds number and multiplied with a form factor. Computations were done for wing and fuselage separately due to different form factors. Total friction drag added up and divided by reference area to get total CDf. The CDi is calculated from textbook formula. The total drag coefficient was 0.0131. This drag then was input into the frame sheet.
The figure of merit is assumed to be on the high side at 0.8. Altran believes with optimization and customized 3D printed rotors at FOM of 0.8 can be obtained. Also for propellers in this class a propeller efficiency of 88% is high but with customized 3D printed propellers and tuned specifically for the airspeed for either the 100km or the 60km mission a propeller efficiency of 88% is possible.
The vertical lift propulsion details were limited to 4 motors due to weight and space restrictions.
The max thrust required is = 1.4 * weight => 350N.
The VTOL propulsion system characteristics are:
· 150 kV (RPM/V) motor
· 20”x14” props
· System weight 5,54 kg (motors, ESC, prop)
· Max drain 242,46A
· Normal drain 133,4A
· Hover time 9,5min
· Required battery capacity 24Ah
For horizontal flight 2 motors were selected with minimum battery discharge in mind. Redundancy was also an important design consideration as well. The thrust of 11.6N was based upon the total drag at design CL. The horizontal propulsion specifications are:
· Props 15x8
· System weight 2.3kg
· Max drain 180A
· Normal drain 32A
Required Ah = 24Ah => battery is shared for both systems
The control surfaces will be standard with the ailerons having a chord of max. 20% wing chord and a span of 25% wing span. No flaps will be required for this configuration, because slow flight is not relevant for mission and in this case take-off and landing are vertical. The horizontal tail plane will be mobile and will act as stabilizer.
The vehicle consists of a fuselage incorporating all avionics equipment, the motors and the cargo bay.
All components are easily accessible and maintenance technicians will find everything in reach.
The motors are distributed in pairs of two in the front two in the back for vertical movement and two in the back for horizontal movement of the vehicle.
This is considered to be the best tradeoff between safety and weight introduced to the vehicle.
As avionics equipment redundancy cannot be achieved due to weight limitation the safety parachute will guide the vehicle safely to ground in case of maneuverability is degraded.
For conventional landing a simple landing gear consisting of two front wheels and two rear wheels is attached to the vehicle.
The Wings are made from Kevlar over pink foam with aluminum profile embedded to strengthen the connection between wings parts and fuselage.
The same material is used to form the nose and the aft fuselage sections. They are each connected to the fuselage by aluminum tubes.
The center fuselage is also made from Kevlar over pink foam and embeds cut outs to attach the spars from wings, nose and aft fuselage sections.
For simplicity, robustness, ease of maintenance and reliability the landing gear is of non-retractable and non-steering type.
The payload is accessible from top or bottom of the vehicle. This gives a maximum flexibility and allows simple cargo loading from top and bottom. With no restriction in case cargo loading is automated. Also the flexibility for sensor payloads facing up or down is given. The paylod shall be fixed by velcro straps.
The Pegasus construction techniques lend itself to a robust design. The structure is based upon proven robust manufacturing techniques. The kelvar over pink foam is similar to the construction of the Desert Hawk hand launched that has been used extensively in Iraq and Afghanistan. The electronics will have a conformal coat to make them robust to moisture and dust.
The vehicle can be easily disassembled without special tools. The modular design is made for simple disassembly.
The wings are unmounted from the fuselage and wings can be separated into wingtips and primary wing.
The vehicle components (fuselage, wings, wingtips, landing gear, nose, center, aft fuselages) can be easily carried by two persons.
A transportation box can easily be manufactured to hold all parts securely in place and load the unmounted vehicle to any means of transport.
Any failure of the aircraft in flight (loss of power or control) should be planned for (example: parachute recovery system) so that the vehicle would not pose a serious threat to people or property on the ground.
For conveniance of reading this text is also put into a Word document attached.