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Principles Of Flight > Ch 31 - Limitations > Flashcards

Ch 31 - Limitations Flashcards

1
Q

Limit Load

A

The maximum load expected in surface

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2
Q

Ultimate Load

A

The failing (breaking) load of the surface

Based on a factor of safety

Safety factor is usually 1.5 which is the expected maximum load it can take before failing

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3
Q

Factor of Safety

A

The ratio of the ultimate load to the limit load

Usually 1.5 for AC

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4
Q

AC Load Factors - Limit Load Factors and Ultimate Load

A

Limit Load. 1.5 Ultimate Load
+VE. -VE. +VE. -VE

Normal. 2.5. -1.0. 3.25. -1.5

Utility. 4.4. -1.76. 6.6. -2.64

Aerobatic 6.0. -3.0. 9.0. -4.5

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5
Q

The Manoeuvre Envelope

A

The performance boundaries necessary for safe flight

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6
Q

Vs1g

A

Stall speed at 1g

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7
Q

Va

A

The design manoeuvre speed - where you will stall before you bend the AC

Won’t bend the AC no matter how hard you pull, you will just stall

Va = Vs1g x the square root of the limiting load factor

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8
Q

Effect of Weight on Va

A

A 10% heavier AC will have a ~5% increase in Va

Va - the design manoeuvre speed

Use the 3 step process

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9
Q

Compressibility on the Manoeuvre Envelope

A

Altitude simply rounds off the edges of the V-n graph

High altitudes, the reduction in density causes compressibility effects which increase the stall speed and therefore Va.

Altitude poses a problem for the envelope

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10
Q

The Effect of Flaps on the Manoeuvre Envelope

A

Greatly restricted when the flaps are extended. The flaps are only designed for slow speed flight therefore the maximum load limit is 2g for transport AC.

Stall speed increases though

CP moves back towards the flaps (camber changing)

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11
Q

Vb - Maximum Gust Intensity

A

The design speed for maximum gust intensity

The speed at which the AC can withstand the greatest expected vertical gusts ±66fps at FL200

Normally found between Va and Vc

Can withstand 50ft/s gusts

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12
Q

Vra

A

The speed for normal turbulence conditions

Found between Vb and Vmo/Vc

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13
Q

Vc

A

The design cruise speed

After this speed you will start to over stress you AC which we wont fly near

Vertical gust of 50ft/s

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14
Q

Vmo

A

The normal operating speed which we will never exceed (even in an emergency descent)

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15
Q

Vd

A

Design Die Speed

The speed at which the AC will fall apart

FL200 with gust Requirements of 22fps

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16
Q

Vmo

A

The maximum operating speed which must not be intentionally exceeded

17
Q

Mmo

A

The maximum operating speed at altitude. Must remember to change to Vmo on the descent as your Mach speed will remain constant whilst you IAS will increase (you may go over your Vmo)

18
Q

Vne

A

The never exceed speed for Light AC

19
Q

Vno

A

The normal operating speed for light AC (cruise speed) the slow end of the yellow or the fast end of the green band

20
Q

Vle

A

The maximum speed at which you can operate with the landing gear extended (down and locked)

21
Q

Vlo

A

The maximum landing gear operation speed which is usually lower than Vle

22
Q

Vfe

A

The maximum speed that the AC can fly with flaps extended in each prescribed conditions

23
Q

Gust Loads

A

Gust loads are the sudden extra loads felt when an aeroplane flies through a vertical or horizontal velocity gradient (I.e turbulence)

24
Q

Gust Load Factor

A

Load Factor = Lift / Weight

Lift is proportional to the coefficient of lift so a change in AoA has a large effect on the Load factor

25
Q

Factors that affect the gust load factor:

A

Density ratio and altitude

Cl relationship to AoA

Wing Loading

Airspeed

26
Q

Density Ratio and Altitude on Gust Load Factors

A

When climbing at a given IAS the TAS increases as the altitude increases. This is because the density ratio decreases with alt.

As the altitude increases, the gust load factor decreases. This means that the AC is subjected to smaller loads at higher altitudes.

27
Q

Cl relationship to AoA on Gust Loads

A

Depends on aspect ratio and sweep back

Straight wings experience greater gust loads than swept wings

Higher aspect ratio Wings experience greater gust loads

A low aspect ratio, swept wing will experience a significantly smoother right than a straight wing high aspect ratio aeroplane

28
Q

Wing Loading

A

The weight per unit of wing area.

An AC with a higher wing loading has a greater Cl for that uni of Aerofoil.

Gust load factor is greater in light aeroplanes with relatively lower wing loading.

29
Q

Airspeed on Gust load Factors

A

Gust load factor increases as airspeed increases.

30
Q

Gust Load Factor Summary

A

AC with higher gust load factors are more sensitive to turbulence. Factors that increase the gust load factors are;

Flying at low altitude

Flying at high speed

Straight wing

High aspect ratio wing

Low wing loading (large wing area with lighter weight)

31
Q

Aerolasticity

A

If aerodynamic forces acting on a structure become large enough, they can cause the structure to twist about its torsional axis. The happens because all structures are elastic to a greater or lesser degree.

As airspeed, and thus aerodynamic force increases, so too will the opposing elastic forces. Integration known as aero-elastic coupling

Can cause the structure to fail if pushed too far - torsional divergence speed

Must be faster than Vd/Md

32
Q

Flutter and Resonance

A

Natural frequency is the frequency a structure will oscillate at if disturbed (can have several)

Subjecting a structure to a particular frequency of vibration is known as the forcing frequency - if this is substantially different form the natural frequency, it will only cause a small vibration.

As it approaches the natural frequency, the vibration will increase. When equal, the vibration will be very large - known as resonsant frequency.

When the wing/tailplane resonate, the behaviour is known as flutter.

Could lead to failure

33
Q

Flutter Prevention

A

Greater stiffness

Or moving the mass distribution - the flexural axis forward - underslung engines positioned forward which damps the potential oscillations

34
Q

Control Surface Flutter

A

Occurs at high speed, the only remedy is to reduce the speed immediately

Caused by the inertia of the control surface interacting with the torsional twisting of its associated main surface,

35
Q

Factors Influencing Flutter

A

Elasticity

Backlash

Aero-elastic Coupling

Mass distribution

Mass distribution

Structural Properties

IAS

36
Q

Aileron Reversal

A

Low speed aileron reversal - when you are travelling close to the stall speed, downgoing aileron may stall the wing which causes opposite roll

High speed aileron reversal - torsional twisting when you deflect the aileron downwards, it actually causes the upgoing lift to go down

Principles Of Flight (32 decks)

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