Basics, Limitations

Chapter 10.1

Airspeed Limitations

In the AFM there are the maximum and minimum airspeeds, fixed or variable, for the aircraft used, each of which is related to certain flight conditions.

Note: some airspeeds may vary depending on the aircraft’s mass.

Airspeed Limitations

Variable Maximum Speed

VA MANOEUVERING SPEED

• In the AFM, and on a placard in the aircraft, no indication on the ASI
  

• Maximum indicated speed at which the controls can be fully deflected in one direction, without overloading the aircraft structure

• Va decreases at lighter mass (see AFM)

Airspeed Limitations

Fixed Maximum Speeds

V NE NEVER EXCEED SPEED

• Red line at the upper end of the yellow arc (CAUTION RANGE) on the ASI
  

• Speed limit that should not be exceeded at any time

Airspeed Limitations

Fixed Maximum Speeds

V NO NORMAL OPERATING SPEED

• Upper end of the green arc on the ASI
  

• Speed that should not be exceeded except in smooth air and then only with caution

Airspeed Limitations

Fixed Maximum Speeds

V FE FLAPS EXTENDED SPEED

• Upper end of the white arc on the ASI
  

• Highest speed permissible with wing flaps in a prescribed extended position.

Airspeed Limitations

Fixed Maximum Speeds

V LO LANDING GEAR EXTENSION SPEED

• No indication on the ASI/ PLACARD
  

• Maximum permissible speed for the extention or retraction of the landing gear

Airspeed Limitations

Fixed Maximum Speeds

V LE LANDING GEAR EXTENDED SPEED

• No indication on the ASI / PLACARD
  

• Maximum permissible speed with the landing gear extended

Airspeed Limitations

Variable Minimum Speed

Vs STALLING SPEED, in general

• No indication on the ASI
  

• If the Vs are undershot, the aircraft will make uncommanded movement. This movement is usually a pitching forward around the transversal axis. Depending on the aircraft, tipping (rolling) around the longitudinal axis may also be possible. Furthermore, these movements can also be overlaid with a yaw around the vertical axis.
  

• Vs varies as a function of mass, load factor and airplane configuration.

• Vs decreases with decreasing mass (Normally no information in the AFM).
  

Airspeed Limitations

Variable Minimum Speed

Vso STALLING SPEED, Landing Configuration

• stall speed or the minimum steady speed at which the aircraft is still controllable in landing configuration (flaps and landing gear extended and power lever at idle position).

• The lower end of the white arc on the ASI indicates Vso for the maximum take-off mass.

• Vso decreases with decrease of weight.

Airspeed Limitations

Variable Minimum Speed

Vs1 STALLING SPEED, Clean Configuration

• Stall speed or the lowest steady speed at which the aircraft is still controllable with flaps retracted, landing gear (where possible) retracted, power lever at idle.
  

• The lower end of the green arc on the ASI indicates Vs1 for the maximum take-off mass.

• Vs1 decreases with decrease of weight.

Maximum Limitations for Aircraft, Airworthiness Category

Before performing exercises where the structure may be subjected to heavy stresses, it should be checked in the AFM whether the aircraft is approved for such situations, corresponding to a particular category of operation of the aircraft.

The airworthiness requirements according FAR 23 / CS-23 define three categories:

Maximum Limitations for Aircraft, Airworthiness Category

NORMAL CATEGORY aircraft are those which are not intended for aerobatics

Non-aerobatic flights include:

• All flight maneuvers required to perform a normal flight
  

• Stalls, except «abrupt» stalls

• Lazy Eights, Chandelles and Steep turns with less than 60° bank angle

Maximum Limitations for Aircraft, Airworthiness Category

UTILITY CATEGORY aircraft are those which are intended for moderate aeroatic operations. Aircraft included in the utility category may be used in all prescribed situations for normal and moderate aerobatics.

Moderate aerobatics includes:

• Spins, if the airplane is approved for this manoeuvre
  

• Lazy Eights, Chandelles and Steep turns with more than 60° bank angle

Maximum Limitations for Aircraft, Airworthiness Category

ACROBATIC CATEGORY aircraft is reserved for those which have no limits other than those that are indispensable.

These limits are generally determined during test flights and are included in the AFM.

Certification in more than one Airworthiness Category

In the AFM, aircraft which are certified in several categories, the critical values are specified separately according to its CATEGORY for:

• the maximum value of the positive or negative load factor.
  

• the maximum mass.

• restrictions on the distribution of fuel and load.

Certification in more than one Airworthiness Category

The operating limitations are displayed on a placard in the cockpit.

Certification in more than one Airworthiness Category

The limitations concerning the loading of the airplane is given in the Center of Gravity Moment Envelope.

The Load Factor n

The load factor is the ratio between the acceleration of the aircraft and the ground acceleration (Local factor). It is expressed by a non-dimensional figure

The abbreviation for the load factor is n.

Each change of the flight vector has an acceleration (n) as a consequence.

Acceleration in the direction of the longitudinal axis / X and in the direction of the vertical axis / Z is designated as a load factor.

The permissible value of the load factor depends on the flight speed, flight altitude and angles of attack.

The Load Factor in Flight

In a turn, in addition to the mass, the effect of the centrifugal force (Fz) must be compensated. The resulting force (Fr) is greater than the mass vector in level flight.

The Load Factor in Flight

The load factor as a function of bank (in coordinated turns)

The Influence of the Load Factor on the Airplane

V STALL and Load Factor

In a correctly flown turn the load factor increases. This results in an increase in the minimum speed when the bank increases:

V STALL in turn is higher than in straight and level flight. The increase depends on the bank

Change the bank and enter another Vso, and observ how the Stall Speed increases with increasing bank!

The Influence of the Load Factor on the Airplane

The Flight Envelope