Aero Engineering 315

1. Aero Engineering 315 Lesson 30 Turn Performance

2. “Turning” the tables…

3. Turn Performance Overview • Define bank angle and load factor • Calculate load factor needed to sustain a level turn at a given bank angle • Calculate initial turn rate and radius for level turns, pull-ups and pull downs

4. L W Turn Performance Definitions • Load factor – Lift/Weight (measured in g’s) n = L/W • Bank angle (f) – angle created by rotating the aircraft about the aircraft reference line • Turn rate (w) – radians/second or degrees/second • Turn radius (r) – feet f

5. L sin f L cos f Level Turns • Level flight means constant altitude (no vertical acceleration) • In level flight, bank angle creates a specific load Example: level turn at f= 60° n = 1/cos 60° = 2

6. 6 4 Level Turn Load Factor 2 0 10 20 30 40 50 60 70 80 Bank Angle Level Turn Load Factor In a level turn: If bank angle is known, you can find load factor and vice versa for a level turn

7. L sin f L cos f = W 2 L = nW = CLMAXr VSTALL S/2 2nW CLMAXr S VSTALL = L sin f r Level Turns • Constant velocity turn • Stall speed in a turn: • Stall speed increases as n½ • Extra pilot care when performing high bank angle turns near the ground f L = nW

8. Level Turn Performance Concepts For good turn performance we want: • Small turn radius • High turn rate To achieve this we should turn with • Low velocity • High load factor Note: Turn radius and rate are functions only of velocity and load factor. A B-52 and an F-16 at the same airspeed and “g” have identical turn radii and rates.

9. Level Turn Design Considerations To get small turn radius (r) and large turn rate () • Maximize “g” loading • Structural considerations (max g for the structure) • Physiological considerations (human g limits) • Aerodynamic considerations (stall limitations) • Minimize wing loading, W/S (n = CL q S / W) • Maximize lift coefficient • High lift devices • Pitch vectored thrust • Maximize thrust-to-weight ratio (T/W) • High “g” creates very high induced drag

10. Human/aircraft structural limits Stall limits Aeroelastic limits F-16 Turn Performance Limits* *F-16 COMBAT AIRCRAFT FUNDAMENTALS, page 46

11. Homework #36 An SR-71 is in a 20° banked level turn at Mach 3.0 and an altitude of 80,000 ft. Assume the ambient temperature is 390°R. • What is the aircraft’s turn radius in NM? • What is the aircraft’s turn rate in deg/s? • If the pilot increases the bank angle to 45° while maintaining a level turn at Mach 3.0, what would the new turn radius be in NM? What would happen to the aircraft load factor?

12. 20o bank r = 118 nm 45o bank r = 43 nm 10o bank r = 244 nm SR-71 Mach 3 80,000 ft

13. S FR = = L -W S FR = = L S FR = = L +W WV2 g r WV2 g r WV2 g r g(n-1) V g n V g(n+1) V w = V/r = w = V/r = w = V/r = Vertical turns (loops) Pull-down Vertical Portion Pull-up

14. V2 g(n+1) r = 5.0 GR 4.7 GR 4.7 GR V2 gn V2 gn r = 4.0 GR r = 4.0 GR GR = denominator term in g’s 3.3 GR V2 g(n-1) r = 3.0 GR 3.0 GR

15. Next Lesson (31)… • Prior to class • Read text 5.12 • Complete homework #36-37 • All sections of Fighter Design Project • In class • Discuss V-n diagrams