The laminar-turbulent transition of the flow under a full-scale generic hypersonic vehicle forebody is investigated by mean of the Linear Stability Analysis coupled with the "e~N" method. Flight Mach numbers 4, 8 and 8, different angles of attack and wall thermal conditions are considered. Several instability mechanisms are identified : Mack's oblique 1~(st) mode, Mack's acoustic 2~(nd) mode, crossflow instability and an additional unstable mode due to the entropy layer. Crossflow instability is dominant at Math 8 and 8, whereas the oblique 1~(st) mode prevails at Math 4. This mode is stabilized by a radiating wall, compared to an adiabatic one. In any case, none of the instability modes that have been found is strong enough to provoke by itself a natural transition in flight : computed N factors do not exceed 10. Attempts to correlate the results with the Re_θ/M~e = Gate criterion are presented and discussed.
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