Distributed propulsion



Distributed propulsion is a type of flight propulsion system in which thrust is delivered by several propulsors arranged on the aircraft. Its goal is to increase performance in fuel efficiency, emissions, noise, landing distance and manoeuvrability. DP is typically accomplished by spanwise distribution of partially or fully embedded multiple small engines or fans along the wing. Alternatively, it may involve ducting exhaust gases along the wing's entire trailing edge.

Definition

A simple definition of DP can be described as a propulsion system where the vehicle thrust is produced from an array of propulsors located across the air vehicle. While a formal definition of a DP system has not yet been established,in general the distributed thrust capabilities of a DP system should serve an enabling role in improving the system-level efficiency, capabilities, or performance of the air vehicle. Otherwise, any aircraft with more than one propulsor could be classified as such.

Technologies

The Distributed Propulsion concept has been applied in aviation around 4 main technologies :

Jet-Flap / Distributed Jet

In this configuration, a high velocity jet flow is injected at the trailing edge of the wing to increase lift at low speed or increase cruising performance. This airflow is commonly extracted from the main jet engine of the aircraft and redirected to several exits along the wing.

Independent Propulsors Distribution

This distribution uses independent thrusters units, i.e. each propulsors can be controlled independently of the others, and its engine is directly supplied with fuel without intermediaries: no generator, no turbine, etc.

Non-Independent Propulsors Distribution

This distribution uses mutually dependent thrusters units, i.e. each propulsors is connected to a central engine that receives the throttle control, provides the mechanical energy needed by the propulsors and serves at least 2 of them.
For instance, the Wright brothers were using chains to distribute the power from their combustion engine to the 2 propellers on their Wright Flyer. The aircraft is a more recent project including non-independent propulsors, the 3 separates fans are powered by one motor unit.

Distributed Electric Propulsion (DEP)

The propulsors do not share a common mechanical driveshaft or mechanical power source with the power-producing components of the system. Instead, the power sources can be any combination of electrical power-producing devices and energy storage devices, while the propulsors can be any combination of thrust producing devices such as electrically-driven propellers or fans.

Additional features

Recent analytic and experimental distributed propulsion studies suggest several improvements in aircraft performance :

Global Improvements

Fixed-wing Aircraft">Fixed-wing aircraft">Fixed-wing Aircraft

These implementations are often proposed in conjunction with blended wing body or hybrid wing body aircraft. While some of these concepts were tested on full scale aircraft in the 1960–70s, such as the Hunting H.126, they were not fielded in production aircraft. More recently, several full-size and smaller unmanned aerial vehicle projects have proposed DP approaches to meet noise abatement, fuel efficiency and landing field length goals. Advancements in materials engineering, cryogenic cooling systems, novel fuels and high fidelity computational fluid dynamics modeling and analysis have been credited for the renewed interest.
File:Neva-ESP-Wohler-b-Mark-V-2018.jpg|thumb|Wohler-b-Mark-V, octocopter designed by . Based on 8 electric ducted fans Athena.|alt=

Multi-copter

Since flight controllers were invented, distributed propulsion has had new applications, including multirotor propulsion. Multirotors are vehicles capable of flying by means of several thrusters that generate vertical thrust. Rotors are controlled by the flight controller which integrated the formula of DEP. The common architectures of these aircraft are tricopter, quadcopter, hexacopter and octocopter.

Classification

have tried to propose a classification of such a propulsion system. Note : it's a non official classification.

DP Configuration

Intensity classes group designs according to the number of propulsion units they employ.
Distributed propulsion intensity classesABCDE
Number of propulsion units34-67-1011-2020<

Thrust-to-weight ratios

For distributed propulsion, this ratio can be defined as the total aircraft thrust produced divided by the Maximum Take-Off Weight rather than dividing only by the propulsion unit weight, given the strategy's potential to reduce the weight of the rest of the aircraft.
Thrust-to-weight ratio intensity classesIIIIII
Thrust-to-weight ratio based on MTOW<0.100.10 to <0.150.15<

Example

Thus, the following convention describes specific systems:
DP Configuration -Intensity class -Thrust-to-weight -
For example, the 1945s Blohm and Voss 238 V1 aircraft would be denoted as DPL-B-I,since the aircraft employs six piston engines and has a thrust-to-weight ratio less than 0.10.