DGCA POF 13. High Speed Flight

Results

Q1. Identify which of the following is the correct formula for Mach number:

TAS / M a = constant

M = IAS / a

TAS = M / a

M = TAS x a

Ans: – TAS / a = constant

Q2. What is the result of a shock-induced separation of airflow occurring symmetrically near the wing root of a sweptwing aircraft?

A severe nose-down pitching moment or “tuck under”.

A high-speed stall and sudden pitch up.

Severe porpoising.

Pitch-up.

Ans: – A severe nose-down pitching moment or “tuck under”.

Q3. Mach number is:

the ratio of the aircraft’s TAS to the speed of sound at sea level.

the ratio of the aircraft’s TAS to the speed of sound at the same atmospheric conditions.

the ratio of the aircraft’s IAS to the speed of sound at the same atmospheric conditions.

the speed of sound.

Ans: – the ratio of the aircraft’s TAS to the speed of sound at the same atmospheric conditions.

Q4. For an aircraft climbing at a constant IAS the Mach number will:

increase.

decrease.

remain constant.

initially show an increase, then decrease.

Ans: – increase.

Q5. The term ‘transonic speed’ for an aircraft means:

speeds where the airflow is completely subsonic.

speeds where the airflow is completely supersonic.

speeds where the airflow is partly subsonic and partly supersonic.

speeds between M 0.4 and M 1.0

Ans: – speeds where the airflow is partly subsonic and partly supersonic.

Q6. At M 0.8 a wing has supersonic flow between 20% chord and 60% chord. There will be a shock wave:

at 20% chord only.

at 20% chord and 60% chord.

at 60% chord only.

forward of 20% chord.

Ans: – at 60% chord only.

Q7. As air flows through a shock wave:

static pressure increases, density decreases, temperature increases.

static pressure increases, density increases, temperature increases.

static pressure decreases, density increases, temperature decreases.

static pressure decreases, density decreases, temperature decreases.

Ans: – static pressure increases, density increases, temperature increases.

Q8. For a wing section of given thickness, the critical Mach number:

will decrease if angle of attack is increased.

will increase if angle of attack is increased.

will not change with changes of angle of attack.

is only influenced by changes in temperature.

Ans: – will decrease if angle of attack is increased.

Q9. At speeds above the critical Mach number, the lift coefficient:

will start to increase.

will start to decrease.

will remain constant.

is directly proportional to the Mach number.

Ans: – will start to decrease.

Q10. As air flows through a shock wave:

its speed increases.

its speed decreases.

its speed remains the same.

it changes direction to flow parallel with the Mach cone.

Ans: – its speed decreases.

Q11. If an aeroplane accelerates above the critical Mach number, the first high Mach number characteristic it will usually experience is:

a nose-up pitch or “Shock Stall”.

a violent and sustained oscillation in pitch (porpoising).

Dutch roll and/or spiral instability.

a nose-down pitching moment (Mach, or high speed tuck).

Ans: – a nose-down pitching moment (Mach, or high speed tuck).

Q12. High speed buffet is caused by:

the shock waves striking the tail.

the high speed airflow striking the leading edge of the wing.

wing flutter caused by the interaction of the bottom and top surface shock waves.

the airflow being detached by the shock wave and the turbulent flow striking the tail.

Ans: – the airflow being detached by the shock wave and the turbulent flow striking the tail.

Q13. The “area rule” applied to high speed aircraft requires:

that the cross-sectional area shall be as small as possible.

that the variation of cross-sectional area along the length of the aircraft follows a smooth pattern.

that the maximum cross-sectional area of the fuselage should occur at the wing root.

that the fuselage and the wing are be of a ratio of 3 : 1.

Ans: – that the variation of cross-sectional area along the length of the aircraft follows a smooth pattern.

Q14. An all moving tailplane is used in preference to elevators on high speed aircraft:

because the effect of the elevator is reversed above the critical Mach number.

because shock wave formation on the elevator causes excessive stick forces.

because shock wave formation ahead of the elevator causes separation and loss of elevator effectiveness.

because it would be physically impossible for a pilot to control the aircraft in pitch with a conventional tailplane and elevator configuration.

Ans: – because shock wave formation ahead of the elevator causes separation and loss of elevator effectiveness.

Q15. Mach Trim is a device which:

moves the centre of gravity to maintain stable lateral stick forces in the transonic region.

automatically compensates for pitch changes while flying in the transonic speed region.

prevents aircraft from exceeding its critical Mach number.

switches out the trim control to prevent damage in the transonic region.

Ans: – automatically compensates for pitch changes while flying in the transonic speed region.

Q16. What is the movement of the centre of pressure when the wing tips of a sweptwing aeroplane are shock-stalled first?

Outward and forward.

Inward and aft.

Outward and aft.

Inward and forward.

Ans: – Inward and forward.

Q17. The airflow behind a normal shock wave will:

always be subsonic and in the same direction as the original airflow.

always be supersonic and in the same direction as the original airflow.

may be subsonic or supersonic.

always be subsonic and will be deflected from the direction of the original airflow.

Ans: – always be subsonic and in the same direction as the original airflow.

Q18. As airflow passes through a normal shock wave, which of the following changes in static pressure (i), density (ii), and Mach number (iii) will occur?

(i) decrease (ii) increase (iii) < 1.0

(i) increase (ii) decrease (iii) < 1.0

(i) increase (ii) decrease (iii) > 1.0 or < 1.0

(i) increase (ii) increase (iii) < 1.0

Ans: – (i) increase (ii) increase (iii) < 1.0

Q19. An aerofoil travelling at supersonic speed will:

have its centre of pressure at 50 % chord.

have its centre of pressure at 25% chord.

give a larger proportion of lift from the lower surface than from the upper surface, and have its centre of pressure at 50 % chord.

give approximately equal lift from the upper and lower surfaces, and have its aerodynamic centre at 50% chord.

Ans: – have its centre of pressure at 50 % chord.

Q20. A bow wave is:

a shock wave which forms on the nose of the aircraft at Mcrit†.

the shape formed when the shock waves on the upper and lower wing surface meet at the trailing edge.

a shock wave that forms immediately ahead of an aircraft which is travelling faster than the speed of sound.

the shape of a shock wave when viewed vertically.

Ans: – a shock wave that forms immediately ahead of an aircraft which is travelling faster than the speed of sound.

Q21. When an aircraft is flying at supersonic speed, where will the area of influence of any pressure disturbance due to the presence of the aircraft be located?

Within the Mach Cone.

In front of the Mach Cone.

In front of the bow wave.

In front of the Mach Cone only when the speed exceeds M 1.0

Ans: – Within the Mach Cone.

Q22. The temperature of the airflow as it passes through an expansion wave:

increases.

decreases.

is inversely proportional to the square root of the Mach number.

remains the same.

Ans: – decreases.

Q23. The influence of weight (wing loading) on the formation of shock waves is:

a higher wing loading will increase Mcrit†.

low wing loading will give a higher Mcrit†.

wing loading does not influence Mcrit†.

wing loading and Mcrit† are directly proportional.

Ans: – low wing loading will give a higher Mcrit†.

Q24. What influence does an oblique shock wave have on the streamline pattern (i), variation of pressure (ii), temperature(iii), density (iv) and velocity (v)?

(i) parallel to surface (ii) increase (iii) increase (iv) increase (v) decrease

(i) normal to wave (ii) decrease (iii) decrease (iv) decrease (v) increase

(i) parallel to wave (ii) decrease (iii) decrease (iv) decrease (v) increase

(i) parallel to chord (ii) increase (iii) decrease (iv) increase (v) decrease

Ans: – (i) parallel to surface (ii) increase (iii) increase (iv) increase (v) decrease

Q25. Wave drag is caused by:

shock waves interfering with the smooth airflow into the engine intakes.

flying faster than Mcrit†.

the conversion of mechanical energy into thermal energy by the shock wave.

flying faster than VMO†.

Ans: – the conversion of mechanical energy into thermal energy by the shock wave.

Q26. What is the effect of a shock wave on control surface efficiency?

Increase in efficiency, due to increased velocity.

Increase in efficiency, due to the extra leverage caused by the shock wave.

Decrease in efficiency, due to the bow wave.

Loss of efficiency, due to control deflection no longer modifying the total flow over the wing.

Ans: – Loss of efficiency, due to control deflection no longer modifying the total flow over the wing.

Q27. At what speed does an oblique shock wave move over the earth surface?

Aircraft ground speed.

The TAS of the aircraft plus the wind speed.

The TAS of the aircraft less the wind speed.

The TAS relative to the speed of sound at sea level.

Ans: – Aircraft ground speed.

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