POWERPLANTS ATA 70 – 80 Part 2

If you are reading this new article we assume that the explanations in part 1 have caught your attention, so continue through the air intakes.

Description:

Two nacelles are hooked under the lower surface of the wing. This implementation has 2 advantages:

1 - At high incidence, the flow admitted into the air intake has a low rate of distortion, and therefore, presents a healthy vein. Go-arounds on approach are thus carried out without problems.

2 - The flow is slowed down at the level of the wing; the Mach number at the air intakes isonly around 1.9 for a Mach 2 cruise flight. The slowdown is associated with pre-compression thus increasing the efficiency of the whole propulsion.

Grégoire studies the air intake ramp in subsonic position.

The purpose of the air intakes is to reduce the air speed from supersonic outside the engine to subsonic speed inside by applying the principle of Bernouilli's theorem (divergent/convergent).

Engine air intakes provide optimal airflow to the engines over the entire operating range. A rectangular section structure with a flat side going from the front of the nacelle to the intake of the engine which gradually transforms into a circular section at the level of the engine face.

Depending on the speed of the plane and the engine speed, the temperature, the ramps are more or less closed, allowing speed regulation by air intake computers (AICU), two per engine, located partly avionics.

The upper part of the air intake is not directly against the wing lower surface,

A space is provided between the wing and the nacelles, so as to evacuate the boundary layer of the wing outside the air intake, and thus not reduce its efficiency, and consequently, the thrust of the propulsion assembly. , it is separated by a space of a few centimeters, this space avoids injection into the air inlet of the external boundary layer at low energy level.

This boundary layer trap is a single partition extending from the front of the nacelle, on axis, and extending outward and rearward, at the front and top of the air intake, the structure has the shape of a fixed dihedral.

In the air intakes there are two hinged sections, mechanically connected:

The ramps.

Between the front and rear ramps is an internal trap. It is through this air intake trap that the so-called secondary air is taken and sent over the rear ramp into the secondary flow duct. A cross-section of the front half of the air intake looks like a single-walled rectangle. A cross-section of the rear half is double walled, with the outer wall being flat and the inner wall circular. The circular part is called subsonic diffuser.

These surfaces include a moving ramp and discharge gate that adjust intake air flow to meet engine requirements.

Above the subsonic diffuser are intake conduits placed in the wall of the secondary flow line.

This duct directs a portion of the secondary air flow into a cascade duct that channels air, between the inner and outer walls, to the lower secondary air doors.

When the doors are open, air passes through and around the engine in a ventilation flow.

This secondary flow is taken from the internal trap which also has the role of eliminating the boundary layer, at low energy level, attached to the front ramp. Among other things, it plays the role of an automatic by-pass which allows, to a certain extent, to compensate for fluctuations in engine demand.

Each nacelle is made up of 2 air intakes separated by an emerging central partition (or bow) dividing the air intake which extends forward beyond the external partitions, the aim of which is to make the flows of the adjacent motors, in particular, in the event of malfunction of one of them.