An oblique shock at Mach 2.5 with a 15 degree ramp gives a total pressure ratio of 0.96, and a second identical shock follows. The combined ratio is
Answer: C
Total pressure ratios multiply, giving \( 0.96 \times 0.96 = 0.9216 \). Chaining several weak shocks in this way keeps the product high, whereas a single strong normal shock at the same Mach number would lose far more.
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An intake bleeds 4 per cent of its captured mass flow overboard. If the capture is \( 120 \ \mathrm{kg/s} \), the flow reaching the engine is
Answer: D
The bleed removes \( 0.04 \times 120 = 4.8 \), leaving 115.2 kilograms per second. Bleed costs both this mass flow and the drag of dumping it, which is why the quantity is kept to the minimum the shock interaction requires.
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Static temperature is 220 K and the flight Mach number is 2.0. Using \( T_0 = T(1 + 0.2M^2) \), the total temperature is
Answer: A
Substituting gives \( 220 \times 1.8 = 396 \) kelvin. That stagnation temperature is what the intake structure and the compressor face actually experience, and it sets a materials limit quite separate from the turbine's.
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An intake has a recovery of 0.97 at Mach 0.85 and 0.85 at Mach 2.2. The fractional loss in recovery between the two conditions is
Answer: B
Correct answer: 12.4 per cent
\[ \frac{0.97 - 0.85}{0.97} = \frac{0.12}{0.97} = 12.4\ \mathrm{per\ cent}. \] The loss reflects the shock system that a supersonic intake must contain: at Mach 0.85 there are no shocks at all, while at Mach 2.2 the flow must be brought through several before it reaches the compressor.
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Statement I: Supersonic flow cannot be decelerated to subsonic speed without a shock wave.
Statement II: Supersonic flow accelerates in a diverging passage rather than slowing in one.
In the light of the above statements, choose the correct answer.
Answer: C
Both statements are true and the second is the reason. Because the area velocity relation reverses above Mach one, smooth deceleration is impossible and the shock supplies the discontinuous transition at the cost of a total pressure loss.
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Statement I: Multi-shock intakes are preferred above about Mach 1.6.
Statement II: Total pressure loss across a normal shock rises steeply with upstream Mach number.
In the light of the above statements, choose the correct answer.
Answer: D
Both hold and the second is the reason. Splitting the deceleration across several weak oblique shocks keeps the product of their pressure ratios high, where a single strong shock would waste an unacceptable fraction of the available pressure.
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Statement I: A rounded intake lip matters most at static conditions.
Statement II: On the ground the streamtube contracts sharply into the intake from a wide region ahead.
In the light of the above statements, choose the correct answer.
Answer: A
Both are true and the second is the reason. The flow must turn hard around the lip at take-off, and a sharp edge would separate immediately, which is why supersonic aircraft with sharp lips often carry auxiliary blow-in doors.
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Statement I: Spillage drag is worst when the engine is throttled back at high speed.
Statement II: The capture area is fixed while the engine's demand for air has fallen.
In the light of the above statements, choose the correct answer.
Answer: B
Correct answer: Both Statement I and Statement II are correct
Both are correct and the second explains the first. The capture area is fixed by the geometry, so at high speed a large streamtube approaches; when the engine is throttled it cannot swallow all of it, and the excess must be turned aside around the cowl. Turning that air costs momentum, which appears as drag.
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Statement I: Flow distortion is assessed separately from total pressure recovery.
Statement II: A compressor can surge on distortion even when the average recovery is entirely acceptable.
In the light of the above statements, choose the correct answer.
Answer: C
Both hold and the second is the reason for treating them separately. A blade passing through a low pressure sector sees a momentarily higher incidence, so uniformity matters to stability in a way the average value cannot capture.
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Statement I: A boundary layer diverter improves engine stability.
Statement II: Fuselage boundary layer air is low in total pressure and highly distorted.
In the light of the above statements, choose the correct answer.
Answer: D
Correct answer: Both Statement I and Statement II are correct
Both are correct and the second explains the first. The boundary layer along the fuselage is thick, slow and low in total pressure, and feeding it into the intake would both reduce recovery and present the compressor with a badly distorted flow. A diverter holds the intake off the surface so that air passes underneath rather than into it.
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