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Study of a turbojet and ramjet propulsion system

(WP3 – Main Propulsion)

Thomas ELIA - Henri FERIEN - Mathias GHESTEM - Antoine MOSNAY

Ecole Nationale Supérieure des Arts et Métiers - Châlons-en-Champagne


Works on the primary propulsion system of

a MSV launched from a carrier aircraft are

generally based on the study of rocket

engines. Due to security reasons linked to

the storage of propellants, take offs from

public airports are not authorized. Motivated

by the innovative spirit of the challenge, we

decided to work on a new propulsion mode

that would make the MSV autonomous,

allowing it to consume kerosene from civil

aircrafts, to take off from regular airports

and without needing to be launched from

another aircraft. Thus, we have decided to

combine a turbojet with a ramjet, and will

approve the viability of this solution.

Overall Approach

Pre-sizing an aerobic propulsion system

requires knowledge of all the parameters

that have an effect on the flight, as well as

the loops that need to be considered:

These loops allow us to highlight the strong

coupling between the parameters.

First, we study the ballistic phase, to

determine the engine performances that

need to be reached: Mach 4.1 at a 32000

meters altitude and with an 80° incline.

Then, choosing a NACA wing profile, we

design the MSV, inspired by the Lockheed

SR-71 and the Concorde.

We estimate the aerodynamic coefficients

up to Mach 2.5, with an empirical approach

used for fighter aircrafts. For bigger Mach

numbers, we rely on numerical simulations

with Star CCM+.

Then, we implement a pre-sizing algorithm

using the aerodynamic results, the

calculation of the atmospheric parameters

and the detailed study of the engine

equations. We proceed by iteration to

converge towards the required air inlet






performances. The step by step integration

of Newton’s second law gives us the flight

profile. Our initial approach consists in

working with a rectilinear trajectory with a

constant slope during the propulsion phase.

After the pre-sizing, we propose a global

optimization method of our MSV. This

method causes the MSV’s geometry to vary

and uses a corrected specific impulse taking

into account the drag, thus affecting the

flight plan and the fuel consumption.