Rr322101-aircraft-stability-and-control

Set No. 1

Code No: RR322101

III B.Tech Supplimentary Examinations, Aug/Sep 2008 AIRCRAFT STABILITY AND CONTROL (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. The axis system associated with an airplane may be explained with a sketch. Now explain the equilibrium of forces and moments acting on the airplane, illustrated with sketches and plots. How are these forces and moments controlled? [16] 2.  Consider  a complete airplane with fwd-horizontal tail. Develop an expression for dCm with a jet engine. Suggest a combination of wing-engine combination dCL f ixed

for best static longitudinal stability from your analysis.

[16]

3. Describe the occurrence of hinge moments on the horizontal tail from the pressure distribution due to angle of attack α and the deflections δe and δt from elevator and tab. Hence define the terms ’floating tendency and restoring tendency’. Describe ways and means to alleviate or control these hinge moments. [16] 4. The geometrical and aerodynamic characteristics of a glider are given as follows; Wing AR=8(NACA 23012, a0 = 0.104,α0L = -1.2 ),Hor.Tail AR = 4 (NACA 0009. dε a0 = 0.110 per degree), Tail volume ratio V =0.6,rate ofchange  of down wash dα = 0.5,tail efficiency ηt = 0.9 ,Aerodynamic centre at 0.24c,

dCm dCL

F us

= 0.087,Elevator

area ratio Se /St =0.35, floating tendency Chα = −0.003 , restoring tendencyChδ = −0.0055, Residual hinge moments Ch0 = 0 . Calculate the Stick free neutral point, ′ [16] N0 . 5. Explain the term Dihedral Effect. How does it affect the lateral stability of airplane? Consider an airplane with wigs having positive dihedral. Hence illustrate that such a wing experiences rolling moments due to side slipping. [16] 6. Consider swept-back wing and examine and analyze its directional stability. Obtain an expression describing (Cnβ )wing and hence prove that sweep-back produces positive directional stability and sweep- fwd produces negative directional stability. [16] 7. The equations of longitudinal motion of airplane with elevator locked conditions are given below: (CD + d)u + 12 (CDα − CL )α + C2L θ = 0 CL u + (1/2CLα + d)α − dθ = 0 (Cmα + Cmdα d)α + (Cmdθ d − hd2 )θ = 0 . Describe the coefficients of the variables . Assume that there is no damping, no variation in angle of attack, no inertia and no airplane drag. Hence obtain the simplified equations of motion and suggest a method to extract frequency and time period and time to half the amplitude of the oscillations. [16] 1 of 2

Set No. 1

Code No: RR322101

8. The oscillatory mode from the lateral-directional stability quartic is given by λ2 + Bλ + C = 0, where B = 2.97 and C = 38.36.Obtain the characteristics of the oscillation and its simple analysis in terms of stability derivatives. [16] ⋆⋆⋆⋆⋆

2 of 2

Set No. 2

Code No: RR322101

III B.Tech Supplimentary Examinations, Aug/Sep 2008 AIRCRAFT STABILITY AND CONTROL (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. Describe the concept of stability associated with an airplane? Explain different modes making the airplane depart from stability and then its return to the cruise condition. Make use of sketches and plots. [16] 2. Establish from the basic equation of moments Cmc.g developed for an airplane with wing-aft-tail combination that elevator is the longitudinal control for such configuration. Now define the terms elevator effectiveness and elevator power. Hence show dδe CL that a plot of elevator angle δe v/s CL leads to the expression δe = δe0 + dC L [16] 3. Define the terms ’floating tendency and restoring tendency’. What is floating of a control surface? Describe ways and means to alleviate or control these hinge moments by an arrangement known as Trim tab. [16] 4. The geometrical and aerodynamic characteristics of a glider are given as follows; Wing AR=8(NACA 23012, a0 = 0.104,α0L = -1.2 ),Hor.Tail AR = 4 (NACA 0009. dε change a0 = 0.110 per degree), Tail volume ratio V =0.64,rate of   of down wash dα = 0.5,tail efficiency ηt = 0.9 ,Aerodynamic centre at 0.24c,

dCm dCL

F us

= 0.08,Elevator

area ratio Se /St =0.35, floating tendency Chα = −0.003 , restoring tendency Chδ = −0.0055, Residual hinge moments Ch0 = 0 . Calculate the Stick free neutral point, ′ [16] N0 . 5. Prove that an airplane with swept back wing produces left rolling moments when it meets right side-slip i.e. it produces positive dihedral effect i.e −Cl′ β . Make use of sketches and plots in this respect. [16] 6. Explain the Weather Cock stability of an airplane with illustrations. What is the contribution of wing, fuselage, power unit and empennage to this phenomenon? Make use of sketches and plots. Hence describe the stability criterion. [16] 7. The characteristic equation of dynamic longitudinal stability of an airplane was obtained as below; Aλ4 + Bλ3 + Cλ2 + Dλ + E = 0 , where A = 1 ,B = 4 ,C = 10 ,D = 1.0 , E = 3.8 . Work out the period, N1/2 and t1/2 of the phugoid oscillations.Provide the basis of your recognizing the oscillation to be as such. [16] 8. Describe the phenomenon of spinning of an airplane. What are its characteristics? Make use of figures to explain the balance of forces. [16] ⋆⋆⋆⋆⋆

1 of 1

Set No. 3

Code No: RR322101

III B.Tech Supplimentary Examinations, Aug/Sep 2008 AIRCRAFT STABILITY AND CONTROL (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. The axis system associated with an airplane may be explained with a sketch. Now explain the equilibrium of forces and moments acting on the airplane, illustrated with sketches and plots. How are these forces and moments controlled? [16] 2. Explain the term ’Stick Fixed Static Longitudinal Stability’ of an airplane for a conventional airplane by appropriate sketches and plots. Does the horizontal tail contribute to this type of stability? Illustrate by considering a wing-tail combination. Develop the criterion for stick fixed static longitudinal stability. [16] 3. Explain the occurrence of hinge moments on the horizontal tail from the pressure distribution due to angle of attack α and the deflections δe and δt from elevator and tab. Hence define the terms ’floating tendency and restoring tendency’. Describe ways and means to alleviate or control these hinge moments. [16] 4. Define stick free static longitudinal stability of an airplane and the stick free Neutral point. Hence show that Stick Free Neutral point is worked out  for props off  
 ′ Chα at dε dCm + aw V ηt 1 − dα 1 − Chδ τ with usual nocondition as N0 = xac − dCL tations.

f us,nac

[16] 5. An airplane with positive dihedral develops left rolling moments when it meets 2Γ dCL y SΓ right side slip. Prove that Cl′ β = − 57.3 ,with standard notations. [16] dβ b S ηv Chδr F = − GqSrCcrnδr (Cnψ )F ree . Hence 6. Consider the pedal force gradient given by dP dψ describe the phenomenon of RudderLock. Explain the effect of addition of a dorsal fin. Make use of sketches and plots. [16]

7. Obtain expressions for Cmδ , Cmdδ, Cmdα andCmdθ .Explain the significance and role of these stability derivatives in the longitudinal dynamics of airplane. [16] 8. The oscillatory mode from the lateral-directional stability quartic is given by λ2 + Bλ + C = 0, where B = 2.97 and C = 38.36.Obtain the characteristics of the oscillation and its simple analysis in terms of stability derivatives. [16] ⋆⋆⋆⋆⋆

1 of 1

Set No. 4

Code No: RR322101

III B.Tech Supplimentary Examinations, Aug/Sep 2008 AIRCRAFT STABILITY AND CONTROL (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. The axis system associated with an airplane may be described with a sketch. Now explain the equilibrium of forces and moments acting on the airplane, illustrated with sketches and plots. How are these forces and moments controlled? [16] 2.  Consider  a complete airplane with aft-horizontal tail. Develop an expression for dCm with a jet engine placed on its wings. What is the best possible location dCL f ixed

of engine on the best placement of the wing from your analysis?

[16]

3. Make use of sketches /plots to explain the occurrence of hinge moments on the horizontal tail from the pressure distribution due to angle of attack α and the deflections δe and δt from elevator and tab. Hence define the terms ’floating tendency and restoring tendency’. Describe ways and means to alleviate or control these hinge moments. [16] 4. Define stick free static longitudinal stability of an airplane and the stick free Neutral point. Hence show that Stick Free Neutral point is worked out    for props off
 ′ Chα dε dCm at + aw V ηt 1 − dα 1 − Chδ τ with usual nocondition as N0 = xac − dCL tations.

f us,nac

[16] 5. Prove that an airplane with swept back wing produces left rolling moments when it meets right side-slip i.e. it produces positive dihedral effect i.e −Cl′ β . Make use of sketches and plots in this respect. [16] 6. Develop an expression for the yawing moments developed by a wing-fuselage combination. What makes such a combination produce +ve static directional stability? Illustrate with sketches / plots. [16] 7. The characteristic equation of dynamic longitudinal stability of an airplane was obtained as below; Aλ4 + Bλ3 + Cλ2 + Dλ + E = 0 , where A = 1 ,B = 5.102 ,C = 14.35 ,D =0.363 , E = 0.637 . Work out the period, N1/2 and t1/2 of the phugoid oscillations.Provide the basis of your recognizing the oscillation to be as such. [16] 8. The characteristic equation of lateral dynamic stability is ; Aλ4 +Bλ3 +Cλ2 +Dλ+ E E = 0, which gives an approximate solution of λ = − D for spiral stability. Since all the coefficients of the characteristic equation are functions of lateral stability derivatives, then show that for spiral stability, the dihedral effect lv must not be too small ,nor the weathercock stability nv too large. [16] ⋆⋆⋆⋆⋆ 1 of 1