©M. S. Ramaiah University of Applied Science 1 lty of Engineering & Technology Session Speaker M. Sivapragasam Session 07 Aircraft Lateral Static Stability
ACD505 Session 07
Sep 09, 2015
Thrust is the force which moves any aircraft through the air. Propulsion system is the machine that produces thrust to push the aircraft forward through air. Different propulsion systems develop thrust in different ways, but all thrust is generated through some application of Newton's third law of motion. A gas (working fluid) is accelerated by the engine, and the reaction to this acceleration produces the thrust force. Further, the type of power plant to be used in the aircraft depends on four important factors, namely: the aircraft mission, over all weight, flying range and endurance and altitude of flight.
This assignment work was partitioned into three different parts (A, B and C respectively). In Part-A, a debate was made on the viability of implementation of twin engine propulsion system for long range civil aircrafts. Logical arguments based on literatures collected from various internet and text book sources were made and the conclusion of the usage of twin engine propulsion system for long range civil aircrafts was drawn. In Part-B, for the given mission of the aircraft, suitable power plant was chosen (Turbo fan engine) and corresponding cycle analysis calculations was done. The calculations were repeated for a range of flying altitudes and performance plots drawn were critically examined. Also, for the given Turbo prop engine data, cycle analysis calculations were done. The calculations were repeated for a set of Mach numbers and performance plots drawn were critically examined. The different engine installation techniques for a turboprop engine was also discussed. In Part-C, flow over an axial gas turbine cascade was analysed in Ansys-FLUENT software package. The blade geometry was created in Ansys-BladeGen and then imported to CATIA to create the flow domain. Meshing of the geometry was done in Fluent-ICEMCFD.
The total momentum thrust and propulsion efficiency for the selected turbofan engine for the extreme altitudes of 4km & 18km was estimated as 73541N & 9375N and 47% & 40% respectively. The percentage of cold thrust generated at 4km & 18km was 60% & 45% respectively. Both momentum thrust and propulsion efficiency of the engine was observed to decrease with increase in altitude. The propeller thrust and power for the given turboprop engine for flight Mach corresponding to 0.1 & 0.8 was estimated to be 191669N & 25546N and 6074467W & 6477144W respectively. With increasing Mach number of flight, propeller thrust and power was observed to decrease and increase respectively. For the flow analysis over the axial turbine cascade, maximum static pressure value occurs for +150 (2.67*105 Pa) and minimum for 00 (2.5*105 Pa) flow incidence angles respectively. The maximum Mach number value occurs for +150 (1.89) and minimum for -150 (1.57) flow incidence angles respectively. Further the pressure loss was observed to be minimum for -150 (0.1118) flow incidence angle and maximum for +150 (0.2538) flow incidence angle.
This assignment work was partitioned into three different parts (A, B and C respectively). In Part-A, a debate was made on the viability of implementation of twin engine propulsion system for long range civil aircrafts. Logical arguments based on literatures collected from various internet and text book sources were made and the conclusion of the usage of twin engine propulsion system for long range civil aircrafts was drawn. In Part-B, for the given mission of the aircraft, suitable power plant was chosen (Turbo fan engine) and corresponding cycle analysis calculations was done. The calculations were repeated for a range of flying altitudes and performance plots drawn were critically examined. Also, for the given Turbo prop engine data, cycle analysis calculations were done. The calculations were repeated for a set of Mach numbers and performance plots drawn were critically examined. The different engine installation techniques for a turboprop engine was also discussed. In Part-C, flow over an axial gas turbine cascade was analysed in Ansys-FLUENT software package. The blade geometry was created in Ansys-BladeGen and then imported to CATIA to create the flow domain. Meshing of the geometry was done in Fluent-ICEMCFD.
The total momentum thrust and propulsion efficiency for the selected turbofan engine for the extreme altitudes of 4km & 18km was estimated as 73541N & 9375N and 47% & 40% respectively. The percentage of cold thrust generated at 4km & 18km was 60% & 45% respectively. Both momentum thrust and propulsion efficiency of the engine was observed to decrease with increase in altitude. The propeller thrust and power for the given turboprop engine for flight Mach corresponding to 0.1 & 0.8 was estimated to be 191669N & 25546N and 6074467W & 6477144W respectively. With increasing Mach number of flight, propeller thrust and power was observed to decrease and increase respectively. For the flow analysis over the axial turbine cascade, maximum static pressure value occurs for +150 (2.67*105 Pa) and minimum for 00 (2.5*105 Pa) flow incidence angles respectively. The maximum Mach number value occurs for +150 (1.89) and minimum for -150 (1.57) flow incidence angles respectively. Further the pressure loss was observed to be minimum for -150 (0.1118) flow incidence angle and maximum for +150 (0.2538) flow incidence angle.
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Slide 1
Session Speaker M. SivapragasamSession 07Aircraft Lateral Static StabilityM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySession ObjectivesAt the end of this session, student will be able to: Differentiate two types of lateral motion of an aircraftDerive the conditions for yaw stability of an aircraftEstimate the hinge moment coefficient of rudderExplain the requirements of rudder sizingDerive the conditions for roll stability of an aircraftDescribe the effects of yaw-roll couplingExplain directional stability of an aircraft
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral StabilityIn our last class we considered the airplane stability with respect to a disturbance in angle of attackThis disturbance was assumed to be in a vertical plane.We assumed that the airplane response in pitch was sufficiently slow so that the pitch rate could be ignored.In this class we study stability of airplane to a disturbance in sideslip.We will assume that the response of the airplane is sufficiently slow so that yaw rate and roll rate can be ignored. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral Stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyStatic Directional StabilityStatic directional stability is a measure of the aircraft's ability to realign itself along the direction of the resultant windThis ensures that the disturbance in sideslip is effectively eliminated.A disturbance in sideslip could be caused by horizontal gust, wind turbulence, or momentary (small) rudder deflection.,
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyYaw Stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRestoring Moment : Fin
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyYaw Stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of Side wash
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDirectional Stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyYaw Control
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyHinge Moment : Rudder
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyTakeoff and Landing During cruise, aircraft tend to turn towards the wind in order to minimize their drag.Therefore, the objective is to achieve 0o yaw.At take-off and landing this is not possible.The aircraft must remain aligned with the runway, even in the presence of a very strong sidewind.Therefore, the rudder must be able to provide a moment that can keep the aircraft aligned with the runway.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyTakeoff and Landing
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyAll moving FinRecently, the concept of an all-moving fin has become popular.The advantage is that all of the fins surface can be used to overcome a sidewind during takeoff and landing.
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRudder Sizing RequirementsAn airplane having an adequate level of static directional stability and symmetric power generally tends to maintain zero sideslip Rudder deflection may not be warranted. However, under some critical conditions, it is possible that the static directional stability alone may not be sufficient to maintain zero sideslipOperation of the rudder becomes absolutely essential.The rudder should be designed to provide sufficient control authority under several conditionsSome of the are discussed in the following slidesM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRudder Sizing : Cross-windIf the aircraft encounters a crosswind during the ground run, it produces a sideslip.An aircraft with positive directional stability will tend to realign itself with the direction of the resultant wind so that the sideslip is eliminated.During takeoff aircraft has to aligned to the runwayTo prevent this, the rudder should be capable of generating a yawing moment to counter that due to directional stabilityAircraft sideslips but is properly oriented to the runway Takeoff performance will be below par because of higher drag due to sideslip. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRudder Sizing : Engine FailureOn multi-engined aircraft, either partial or total failure of one or more engines gives rise to an asymmetric powerthat generates a significant yawing moment.If this yawing moment is not countered by the rudder, the aircraft will develop a sideslip in some cases, may go out of control because of aerodynamic roll-yaw coupling.The rudder must be designed to have sufficient control authority to handle such conditions. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral : Roll StabilityLateral stability is the inherent capability of the airplane to counter a disturbance in bank. In level flight, both wings are in a horizontal plane and the bank angle is zero.However, because of some disturbance, if the airplane banks but very slowly so that the roll rate is negligibly small, then there is no aerodynamic mechanism to generate a restoring rolling moment unless sideslip develops.Therefore, the airplane is neutrally stable with respect to a disturbance in bank without sideslip. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral : Roll StabilityHowever, once banked, the airplane develops a sideslip in the direction of the bank because of a spanwise component of the weight. As a result of this sideslip, if a restoring rolling moment is induced then the airplane is said to be laterally stable.Once the wings are back in level condition, the disturbances in bank angle and sideslip are eliminated, airplane returns to its original, steady level flight condition. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll Stability Mechanism
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySideslip Due to roll
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRestoring moment
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll Stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll Control : Aileron
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyAileron Example
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySolution
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDihedral and Yaw
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyAircraft With Anhedral
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll & Yaw CouplingIt has already been stated that rolling can create yaw due to aileron effectsHowever, even neglecting the aileron effects, rolling produces a sideslip velocityThis sideslip velocity is effective yaw. This yaw is used by dihedral to provide roll stabilityHowever, even without dihedral, the yaw will cause a certain amount of restoring momentM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyCoupling Due to SweepbackSweptback wings are often used for aircraft flying at high subsonic airspeeds in order to diminish the effects of compressibilityThe airspeed seen by the sweptback wing is the flow perpendicular to its reference line, not the free stream velocity.This decreases the local free stream airspeed but also has an effect on a yawing aircraftM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDifferential Lift due to YawThe leading wing normal velocity, V nl, is greater than that of the trailing wing, V nt. Therefore, the lift on the leading wing is higher, causing a restoring rolling moment.
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyYaw-roll Coupling : Fin EffectWhen the aircraft is side slipping, the fin sees a velocity component normal to its surface.This causes a certain amount of lift and a rolling moment around the geometric datum line of the fuselage.
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral StabilityAn aircraft that tends to return to level flight after it has been disturbed is considered to be laterally stable.Factors that effect lateral stability are:Dihedral AngleThis is the upward and outward slope of the wing. If the wing tip is higher than the wing root relative to the horizontal plane, the aircraft has positive dihedral. Negative dihedral is termed anhedral.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of Dihedral
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyStability Interaction
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyPendulum Action
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyLateral StabilityWhen an aircraft rolls, the lower wing presents a larger span as seen from the direction of the approaching aircraft. The effect is to roll the aircraft back towards the horizontal. This will always be a restoring moment.If the restoring moment is insufficient to restore level flight the aircraft will begin to sideslip.With dihedral, upper wing has a reduced angle of attack.The greater lift on the lowered wing will restore level flight.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of Sweepback
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of SweepbackSweepback Angle is the angle at which the wing points backwards from the root to the tip.Sweepback is used mainly on high-speed aircraft and its primary purpose is to delay the formation of sonic shock waves These are produced at high speeds and cause a large increase in drag.The secondary effect of sweepback is to improve lateral stability. M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of Sweepback on Directional stability
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of sweepbackWhen a side-slip occurs, the lower wing presents a larger span as seen from the direction of the approaching airSimilar to dihedral, the effect is to roll the aircraft back towards the horizontal.In general, as the sweepback angle is increased the dihedral angle will be reducedM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDirectional StabilityDirectional Stability is displayed around the vertical axis and depends to a great extent on the quality of lateral stability.If the longitudinal axis of an aircraft tends to be parallel the flight pattern of the aircraft through the air, in straight or curved flight, that aircraft is considered to be directionally stable.Directional stability is accomplished by placing a vertical stabilizer or fin to the rear of the centre of gravity on the upper portion of the tail section.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDirectional StabilityThe surface of this fin acts similar to a weather vane and causes the aircraft to weathercock into the relative wind.If the aircraft is yawed out of its flight path, either by pilot action or turbulence, during straight flight or turn, the relative wind would exert a force on one side of the vertical stabilizerBasically return the aircraft to its original direction of flight.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyEffect of SweepbackWing sweepback aids in directional stability.If the aircraft is rotated about the vertical axis, the aircraft will be forced sideways into the relative wind.Because of sweepback this causes the leading wing to present more frontal area to the relative wind than the trailing wing.This increased frontal area creates more drag, which tends to force the aircraft to return to its original direction of flight.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDirectional Stability StaticStatic directional stability is a measure of the aircraft's resistance to slipping. The greater the static directional stability the quicker the aircraft will turn into a relative wind which is not aligned with the longitudinal axis.In an equilibrium condition an airplane flies so that the yaw angle is zero.To have static directional stability, the appropriate positive or negative yawing moment should be generated to compensate for a negative or positive sideslip angleM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDirectional Stability Static
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDSS Weathercock StabilityThe main contributor to the static directional stability is the fin.Both the size and arm of the fin determine the directional stability of the aircraft.The further the vertical fin is behind the center of gravity the more static directional stability the aircraft will have. As mentioned previously all rotational motions of the aircraft occur around the center of gravity.Directional stability refers to motions around the normal axis.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyStability Criteria
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyExample
This figure shows the variation of yawing-moment coefficient with sideslip angle.This positively sloping line indicates a directionally stable caseM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySome observationsThe moment associated with yawing and rolling are cross-coupled, angular velocity in yaw produces rolling moments and vice versa. If a pilot steps on a rudder pedal causing the aircraft to yaw one wing will advance and the other will retreat.The faster moving wing produce more lift than the other which will cause a roll in the same direction as the yaw. This will be exaggerated by wing dihedral.M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySome observationsAt a normal flight, i.e., steady rectilinear symmetric motion, all the lateral motion and force variables are zeroes.There is no fundamental trimming problem: control surfaces (ailerons and rudder) would be normally un-deflected.Lateral control provides secondary trimming functions in the case of asymmetry.Effects of CG movement are negligible on lateral and directional stabilityDue to cross-coupling effect, (e.g., the rolling motion will cause sideslipM. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyWing Contribution to DSS
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyFuselage and Nacelle contribution
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll and Yaw coupling
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyAileron Adverse Yaw
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyRoll Control : Spoilers
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyFrise AileronsThe idea is to counteract the higher lift induced drag of the down wing with higher profile drag on the up wing.Frise ailerons are especially designed to create very high profile drag when deflected upwards.When deflected downwards the profile drag is kept low. Thus, they alleviate or, even, eliminate adverse yaw
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyDifferential Deflection of AileronsThe roll rate of the aircraft depends on the mean aileron deflection angle.The individual deflections 1 and 2 do not have to be equal.Differential deflection means that the up aileron is deflected more While the down aileron is deflected by less The idea is to counteract the higher lift induced drag of the down wing with higher profile drag on the up wing.
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologyWing placement effect
M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & TechnologySummaryIn this session following topics were discussed:Two types of lateral motion of an aircraftConditions for yaw stability of an aircraftEstimation of the hinge moment coefficient of rudderRequirements of rudder sizingConditions for roll stability of an aircraftEffects of yaw-roll couplingDirectional stability of an aircraft M. S. Ramaiah University of Applied Sciences#Faculty of Engineering & Technology
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