Download Maneuver Loads

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Typical time history of unchecked pitch manuuver
Steady roll maneuvers
• FAR 25.349
• Constant roll velocity with no roll acceleration
• Standard specified that roll maneuvers be performed at 0 (-g ) 2/3 of +g limit load factor
• Roll maneuvers are calculated at VA, VC, VD.
• At VA: ailerons are deflected to stops to obtain maximum roll rate
• At VC: ailerons are deflected to match the maximum roll rate obtained at VA
• At VD: ailerons are deflected to match the 2/3 roll rate obtained at VA.
At the end of the maneuvers a time history analysis is made to extract critical loads at critical
Accelerated roll maneuvers
• Almost same as the steady roll maneuvers except that loads are calculated at maximum roll
acceleration point rather than zero roll acceleration point.
• Performed at the same load factors and speeds as the steady case.
• Manuevers are performed by sudden application of aileron to result in maximum angular
•Loads are calculated at maximum roll acceleration point (or at zero roll velocity point) by a
time history analysis as shown above.
Rudder maneuvers may result in critical vertical tail loads
Two main types of rudder maneuvers are applied.
1- Rapid movement of rudder with a given pedal force
2- Oscillating rudder motion
Abrupt rudder
• Conditions are specified in FAR 25.351(a)
• Maneuvers are executed at speeds from VMC (minimum control speed) to VD (dive speed)
• Maneuver:
- Deflect rudder to maximum
- A/C yaws to sideslip angle
- As A/C returns to steady sideslip angle, rudder is neutralized
• Maximum rudder deflection is limited by:
- maximum deflection is limited by stops
- maximum 300 lb pedal force
Step 1: When the rudder is deflected, the effect on vertical tail is due to rudder deflection.
Acceleration is towards right and inertia load is towards left. High hinge and rudder loads are
generated. This situation is depicted in Fig. 1
Figure 1
Step 2: As the A/C yaws, angle of attack on vertical tail changes and airload on the vertical
tail finally overcomes rudder deflection and forces yaw angle to a steady value. Remember
that A/C CG is ahead of rudder therefore vertical tail force and rudder force create opposing
yawing moment. At this step A/C has an oscillating side slip angle and A/C swings. Figure 4
shows a typical abrupt rudder time history analysis plot. As it can be seen the red curve which
indicated the sideslip angle oscillates due to the yawing moment generated due to the effect
rudder and vertical tail loads.
At this step high torsional loads occur on the vertical tail.
Figure 2
Step 3: Finally as the rudder is neutralized, the force effect of rudder is removed and only yaw
effect is seen. The loads incurred at this stage is shown in Fig. 3. At this step high bending
moment occurs on the vertical tail.
Figure 3
A typical abrupt rudder time history plot is given in Fig.4. As it can be seen from Fig. 4 peak
tail load (max. fin torsion and possible max. fin shear load) may occur at maximum overswing
sideslip angle which is shown by the red curve. The black curve shows the history of rudder
load. This peak load occurs due to the couple on the tail provided by the sideslip angle on tail
and the opposite effect of the rudder deflection.
Finally, as the sideslip angle reaches a steady value, the oscillation on the rudder force
diminishes and rudder force reaches a steady value.
Oscillatory rudder input
• is another consideration for fin design loads
• oscillation may be due to:
- pilot induced
- control system malfunction
• Note that if the oscillatory rudder input occurs near the Dutch-Roll frequency of the aircraft,
then the load on the veritcal tail can build quickly.
Roz Savage Rowing for Change - TeaTime-Mag
Roz Savage Rowing for Change - TeaTime-Mag