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CFI Workshop 6 Core Topic 12 Airworthiness Limitations

CFI Workshop 6 Core Topic 12 Airworthiness Limitations. Where do they Really come from?. You can’t beat the laws of Physics. 1 June 2010, 1705 hrs, Anchorage, AK Pilot age 33 Commercial, single-engine land & sea 1718 hours TT, 81 hours make & model Phase of flight Takeoff / climb out.

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CFI Workshop 6 Core Topic 12 Airworthiness Limitations

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  1. CFI Workshop 6 Core Topic 12Airworthiness Limitations Where do they Really come from?

  2. You can’t beat the laws of Physics 1 June 2010, 1705 hrs, Anchorage, AK Pilot age 33 Commercial, single-engine land & sea 1718 hours TT, 81 hours make & model Phase of flight Takeoff / climb out

  3. You can’t beat the laws of Physics Aircraft Cessna 1976 U206F Souls on board – 5 Maximum allowable take off weight - 3,600 Lbs. Empty weight – 2165.5 Useful load – 1434.5 Fuel, occupants, & cargo weight – 2092.7 Pilot’s estimate – 1,400 – 1,450 Lbs Takeoff weight – 4258.2 658 over max & 3.95 – 8.22 In. aft of cg limit

  4. You can’t beat the laws of Physics http://dms.ntsb.gov/aviation/AccidentReports/v233vt4542baswfpmqymxq451/R07052011120000.pdf

  5. Where do limitations Come From? Physics Example: The maximum rate of climb that an airplane is capable of is governed by the forces on it. Wing area, power, and thrust all influence the rate of climb. Violating limitations imposed by physics typically results in bent metal. Regulation Establishes legal limitations based on the rules that the airplane was certified under. Regulatory limitations are based on physics, but usually have a safety factor added. Example: 23.65 says “Each normal, utility … must have a minimum climb gradient of at least 8.3 % for land planes or 6.7 % for seaplanes…… “ (at maximum gross weight)

  6. We’ll discuss: Weight and c.g. limitations Landing and Take off performance Stall Speed Airspeed limitations Power Plant limitations How Floats affect limits How Skis affect limits

  7. Airspeed Limits

  8. Examples of Airspeed Limits -

  9. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) -

  10. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) Flaps Up Stall Speed (at gross weight) -

  11. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) Flaps Up Stall Speed (at gross weight) Vne, Never Exceed -

  12. A. Catastrophic airframe failure B. Unknown & untested C. Irreversable airframe stress VNE What’s the consequence of operating above VNE?

  13. Flutter testing Tail Flutter Test.mov

  14. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) Flaps Up Stall Speed (at gross weight) Vne, Never Exceed -

  15. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) Flaps Up Stall Speed (at gross weight) Vne, Never Exceed Vf, Max Flap Extension Speed -

  16. Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) Flaps Up Stall Speed (at gross weight) Vne, Never Exceed Vf, Max Flap Extension Speed - Vc, cruise speed

  17. The Operating Envelope (V-n Diagram) Stall Line 10% safety margin Va, Maneuvering Speed 3.8 g (Normal category 25 fps gust n, g 50 fps gust 1 Speed, V o Gust Lines Vd (Dive Speed) Vc (bottom of Yellow arc) Vne (red line) Vne (red line)

  18. The Operating Envelope (V-n Diagram) 10% safety margin 3.8 g (Normal category) n, g 1 Speed, V o Vd (Dive Speed) Vne (red line)

  19. The Operating Envelope (V-n Diagram) 10% safety margin 3.8 g (Normal category n, g 50 fps gust 1 Speed, V o Gust Lines Vd (Dive Speed) Vne (red line)

  20. The Operating Envelope (V-n Diagram) Stall Line 10% safety margin 25 fps gust 3.8 g (Normal category n, g 50 fps gust 1 Speed, V o Gust Lines Vd (Dive Speed) Vc (bottom of Yellow arc) Vne (red line)

  21. The Operating Envelope (V-n Diagram) Stall Line 10% safety margin Va, Maneuvering Speed 25 fps gust 3.8 g (Normal category n, g 50 fps gust 1 Speed, V o Gust Lines Vd (Dive Speed) Vc (bottom of Yellow arc) Vne (red line)

  22. Airspeed Limits Va is the design maneuvering airspeed at which the airplane will be able to do a limit maneuver without stalling. (3.8 g for normal category airplanes)

  23. Airspeed Limits - True or False 1. The bottom of the Yellow arc is the airspeed above which the airplane is at risk of damage from a 50 fps gust. True and gusts in excess of 25 fps are common. 2. If the Air is turbulent, Slow down to below the yellow arc. Also true. Operating in the yellow arc with any turbulence is very stressful to the aircraft. 3. If an airplane has been flown in severe turbulence above VC, additional inspection should be conducted. That’s true damage associated with severe turbulence is common. 4. The installation of larger engines makes it less likely that a pilot will be able to fly well into the yellow arc. False – Larger engines make it easier to fly too fast for conditions

  24. Airspeed Limits - True or False 5. Vne is set by structural considerations as well as flutter. That’s true. Vne is determined with respect to structural considerations as well as flutter. 6. Flutter is very sensitive to slop in control systems and to the balance of the control surfaces. The airplane is certified to Vd which is 10% over Vne. This is also true. A light coating of frost was enough to cause aileron flutter on a CE – 210 in Virginia. The aileron was torn from the airframe but luckily the pilot was able to land successfully. If it had been tail flutter the outcome would have been much worse. 7. The ASI on most GA aircraft is accurate enough to operate right up to Vne. Maybe true maybe false. It depends on the health of your pitot/static system & ASI. The question is though – are you willing to bet your life on it?

  25. A. Decrease Remain the same Increase Extra Credit As gross weight decreases Va will:

  26. Weight & Balance Limitations

  27. A. Nose wheel strength Ability to flare Stall recovery Tail strength Center of Gravity The forward C.G. limit is critical for:

  28. Examples of Weight and Balance Limits • Typically based on climb, strength • Nose Gear limits, ability to flare, trim • Tail gear structural limit, stick forces going to zero, spin resistance, longitudinal stability, can’t push fwd on balked landing (weight) Horizontal Tail Strength, Ability to flare, Nose Gear (Center of Gravity)

  29. Weight Limits – True or False 1. Maximum gross weight is selected early in the design of most airplanes and the rest of the airplane is designed around that number. Yes – that’s true. 2. Exceeding maximum gross weight routinely can result in fatigue problems. You bet – exceeding max gross weight – even by a little bit will result in fatigue problems. As the fleet ages we’re seeing more of this. 3. Exceeding maximum gross weight results in lower climb rates and can result in structural failure. Well duh – of course we’re going to climb slower but the insidious thing is the possibility of structural failure. 4. When exceeding Max Gross Wt. Stall speed goes up, controllability can be reduced, ability to maneuver without entering an accelerated stall can be reduced. Yes this is all true when you exceed weight limits.

  30. Weight Limits – True or False 5. Structural limits have a 1.5 margin of safety built into them for unexpected conditions, and to minimize the chances of having fatigue problems, not because you really wanted to carry that much stuff. See the second statement above (Exceeding maximum gross weight routinely can result in fatigue problems).The safety margin is there for a reason and the reason is not so you can overload by 50%. 6. Contrary to rumors, airplanes are not generally capable of taking a lot more than the required loads. (In many if not most cases, the existing gross weight limit is set because of a failure in the static test program. This is sobering. In many cases the max gross weight limit was set because the airframe came apart in static testing.

  31. Forward c.g. limit The forward center of gravity limit (and the angled limit if present) are typically critical for: Ability to flare during landing. Ability of the horizontal tail to take the structural loads. Nose gear loads. The installation of heavier engines often makes airplanes nose heavy and subject to violating the forward limit.

  32. Aft C.G. Limit The aft center of gravity is usually critical for: Spin recovery Stick forces Balked landing Longitudinal and directional stability Nose down trim Tail Wheel Loads

  33. Takeoff Performance Takeoff performance numbers are generated by an experienced flight test pilot with a lot of time in the airplane simulating an average pilot with a new engine. They are often optimistic with respect to what can be expected in the field. There is no Margin of Safety incorporated into the published takeoff numbers! AOPA recommends that pilots add 50% to published takeoff distances.

  34. Can I get out of that strip with the moose??? Piano or other heavy object ………. Don’t Fly above Gross Weight!! Don’t guess – weigh it! Al Hikes Photo

  35. Can I get out of that strip with the moose??? Example: PA-18-150 with stock prop Flight manual says that the take off run is 200 ft (500 over 50’ obstacle) at 1750 lb. What is the take off distance at 2000 lb? (I assume you have the one ton STC…..) Not including AOPA 1.5 safety factor

  36. Can I get out of that strip with the moose???

  37. Take off wind issues Head winds decrease takeoff distances. For a head wind of 10 % of the take off speed, the take off distance will be reduced 19%. (Roughly) A tail wind of 10 % of the take off speed will increase your take off distance by 21%. A cross wind will increase your take off distance. (More drag from control surfaces and even a direct cross wind has a headwind component in the crab)

  38. Tail Wind Example C-172 sea level 20 deg C short field, hard surface ground roll 980 ft. 51 knot lift off speed. Consider a 5 kt tail wind (10% of lift off speed) 980 x 1.21 = 1186 ft. Cessna handbook calculation is 10% for every 2 knots for the 172. That results in a distance of 1225 ft. A little more conservative than the Axioms of flight estimate.

  39. Crosswind The maximum demonstrated cross wind component is?

  40. Crosswind The maximum demonstrated cross wind component is: The highest cross wind component demonstrated during flight testing. The ability to handle a cross wind is highly dependent on pilot and runway conditions. (Especially in gusty conditions) There is a point at which the airplane runs out of available aileron and/or rudder deflection. When the controls are at their stops, pilot ability no longer matters. 14 CFR part 23.233 requires that all airplanes be able to land in a cross wind up to .2 times flaps up stall speed. For a C-172 the minimum required is 44 kts x .2 = 8.8 knots (The 172 exceeds the minimum required)

  41. Discussion: What minimums do you set for your students? How do you teach them to evaluate their performance and adjust personal minimums to reflect their ability?

  42. Alaskan Off-airport Operations Guide

  43. My Short Field Performance Aircraft ___________ Gross Weight ___________ Test Weight_________ Airfield ___________ Elevation ___________ Density Altitude ________ Wind Direction _______ Wind Speed _______ X Wind Component ______ Indicated Approach Speed ___________ Flap Setting ____________ Landing Distance _____________ Takeoff Flap Setting __________ Rotation Speed __________ Rotation Speed x .70 __________ Vx __________ Vy __________ Distance to Rotation __________ Distance to 50 feet AGL ___________

  44. Engine Limitations

  45. Engine Limitations RPM Engine RPM limits are established to ensure that the engine will probably make TBO without catastrophic failure (Wear out before fracture) Some flat pitch propellers are capable of exceeding the engine red line rpm during takeoff or climb. Allowing this to occur routinely can dramatically reduce the life of the engine or lead to premature catastrophic engine failure. Yellow arc on Tachometer and “avoid continuous operation” ranges are usually present because of a vibration problem in the propeller engine combination. Poor TAC calibration can result in inadvertent operation in these ranges resulting in propeller failure or crankshaft failure.

  46. Engine Limitations Temperature Temperature limits are established to avoid break down of oil, excessive heat damage of internal parts (like pistons) or cracking due to thermal stresses. There are often telltales on the engine that will indicate that an engine has been over temped. While low temperature limits are not usually established, operating at low oil temperatures can result in poor oil flow through oil coolers, water contamination in the oil and resulting internal corrosion.

  47. Some notes on Professionalism Walk the talk. Don’t let your students see you do anything you don’t want them to do in a week or so. Have your students brief on limitations before flight – don’t just hop in and go. If it’s not important to you it’s not important to your students.

  48. Questions?

  49. QUIZ

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