CFI Workshop - Module 6 Aircraft Limitations
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CFI Workshop - Module 6 Aircraft Limitations
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CFI Workshop - Module 6 Aircraft Limitations
- 1. Presented to: CFI Workshops By: The FAASTeam Date: January 1, 2012 Federal Aviation AdministrationCFI Workshop 6 Core Topic 12 Airworthiness Limitations Where do they Really come from?
- 2. 2Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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. 3Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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. 4Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 You can’t beat the laws of Physics http://dms.ntsb.gov/aviation/AccidentReports/v233vt4542baswfpmqymx q451/R07052011120000.pdf
- 5. 5Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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. 6Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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. 7Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Airspeed Limits
- 8. Federal Aviation Administration 8 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits -
- 9. Federal Aviation Administration 9 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Down Stall Speed (at gross weight) -
- 10. Federal Aviation Administration 10 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Up Stall Speed (at gross weight) Flaps Down Stall Speed (at gross weight) -
- 11. Federal Aviation Administration 11 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Up Stall Speed (at gross weight) Flaps Down Stall Speed (at gross weight) - Vne, Never Exceed
- 12. 13Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Flutter testing Tail Flutter Test.mov
- 13. 14Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 What’s the consequence of operating above VNE? A. Catastrophic airframe failure B. Unknown & untested C. Irreversable airframe stress VNE
- 14. Federal Aviation Administration 15 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Up Stall Speed (at gross weight) Flaps Down Stall Speed (at gross weight) - Vne, Never Exceed
- 15. Federal Aviation Administration 16 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Up Stall Speed (at gross weight) Flaps Down Stall Speed (at gross weight) Vf, Max Flap Extension Speed - Vne, Never Exceed
- 16. Federal Aviation Administration 17 FAASTeam CFI Workshop 6 January 2012 Examples of Airspeed Limits Flaps Up Stall Speed (at gross weight) Flaps Down Stall Speed (at gross weight) Vf, Max Flap Extension Speed - Vc, cruise speed Vne, Never Exceed
- 17. 23Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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)
- 18. 24Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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
- 19. 25Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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? Airspeed Limits - True or False
- 20. 26Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 As gross weight decreases Va will: A. Decrease B. Remain the same C. Increase Extra Credit
- 21. 27Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Weight & Balance Limitations
- 22. 28Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 The forward C.G. limit is critical for: A. Nose wheel strength B. Ability to flare C. Stall recovery C. Tail strength Center of Gravity
- 23. 29Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012
- 24. 30Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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 landingHorizontal Tail Strength, Ability to flare, Nose Gear (Center of Gravity) (weight)
- 25. 31Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 26. 32Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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. Weight Limits – True or False
- 27. 33Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 28. 34Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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
- 29. 35Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 30. 36Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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
- 31. 37Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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…..) outmooseoflbgettofeetfactorsafetyAOPAx feetxfeet 2503905.1260 2603.1200 3.1 1750 2000 2 = = = Weight Ground Run 50’ Obstacle 1750 200 500 2000 260 650 Not including AOPA 1.5 safety factor
- 32. 38Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Weight Ground Run 50’ Obstacle 1.5 Safety Factor 1750 200 500 300/750 2000 260 650 390/975 Can I get out of that strip with the moose???
- 33. 39Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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)
- 34. 40Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 35. 41Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Crosswind The maximum demonstrated cross wind component is?
- 36. 42Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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)
- 37. 43Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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?
- 38. 44Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Alaskan Off-airport Operations Guide
- 39. 45Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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 ___________
- 40. 46Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Engine Limitations
- 41. 47Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 42. 48Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 43. 49Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 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.
- 44. 52Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 • Questions?
- 45. 53Federal Aviation Administration FAASTeam CFI Workshop #2 January 2011 QUIZ
- 46. 54Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. As long as the 10% margin of safety is not exceeded. B. Turbulence is no greater than moderate C. Neither A nor B Question 1 Flying above the red line is permissable:
- 47. 55Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. All control surfaces have been balanced. B. Turbulence is no greater than moderate C. No turbulence is present Question 2 Flying within the yellow arc is permissable as long as:
- 48. 56Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. Compromise stall recovery. B. Lighten pitch control forces C. Place greater stress on the nose wheel. Question 3 A forward center of gravity will:
- 49. 57Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 The aft C.G. limit is critical for: A. Tail wheel strength B. Spin recovery C. Nose wheel strength Question 4
- 50. 58Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Exceeding the max gross weight limit will: A. Improve takeoff and climb performance B. Cause undue stress to the aircraft C. Cause fatigue problems Question 5
- 51. 59Federal Aviation Administration FAASTeam CFI Workshop #2 January 2011 NOW THE ANSWERS
- 52. 60Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. As long as the 10% margin of safety is not exceeded. B. Turbulence is no greater than moderate C. Neither A nor B Question 1 Flying above the red line is OK:
- 53. 61Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. All control surfaces have been balanced. B. Turbulence is no greater than moderate C. No turbulence is present Question 2 Flying within the yellow arc is OK as long as:
- 54. 62Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 A. Compromise stall recovery. B. Lighten pitch control forces C. Place greater stress on the nose wheel. Question 3 A forward center of gravity will:
- 55. 63Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 The aft C.G. limit is critical for: A. Tail wheel strength B. Spin recovery C. Nose wheel strength Question 4
- 56. 64Federal Aviation Administration FAASTeam CFI Workshop 6 January 2012 Exceeding the max gross weight limit will: A. Improve takeoff and climb performance B. Cause undue stress to the aircraft C. Cause fatigue problems Question 5
- 57. 65Federal Aviation Administration FAASTeam CFI Workshop #2 January 2011 END OF CFI WORKSHOP MODULE 6
Notas del editor
- Robert Wesner and John Steuernagle AAL, (907) 457-9241 x241, robert.f.wesner@faa.gov Presenter note: This is a highly interactive presentation. An audience comprised of flight instructors should be able to recall a good deal of the information presented and participate actively in discussion. That said – discussion should always come back to how limitations are taught and how to motivate pilots to consider them seriously, not only in training but throughout their flying careers. Presentation Note: You will find that some slides are hidden in the “Slide Show” view. You may wish to use the presentation as is depending on the time available, the content includes all the required Core Topic information. You may also un-hide the hidden slides with a right mouse click to present the entire show when time and audience permits. 2011/11/10-007 (I) PP
- It’s the first of June 2010 about 5:05pm in Anchorage, Alaska. The 33 year old Commercial Pilot with single-engine land & sea ratings has 1700 hours total time with 81 hours make & model The flight will depart runway 25 at Merrill Field and terminate one half mile later on Ingra street in downtown Anchorage
- The aircraft is a 1976 Cessna 206. The pilot, his wife, their 2 children and a nanny are on board. The maximum allowable takeoff weight is 3600 pounds click The calculated empty weight of the aircraft is 2165 pounds. click Leaving a useful load of 1434 pounds click Although the pilot estimated the weight of fuel, passengers, and cargo at 1400 to 1450 pounds the actual weight was about 650 pounds heavier. click The takeoff cg was calculated to be between 4 & 8 inches aft of the cg limit. click
- click Due to selfless and heroic actions of people on scene the pilot & 3 passengers survived with extensive injuries. The pilot’s 4-year old son, held on his mother’s lap without a seat belt of his own, was pinned In the wreckage and perished in the post-crash fire. Although the pilots decisions & actions leading to this accident were particularly egregious, aircraft limitations are regularly ignored by the pilots – sometimes with tragic results. This is why it’s imperative for flight instructors to stress and operate within aircraft limitations throughout the learning process – not just as a one-time presentation in ground school. You can read the factual report on the ntsb website
- So where do limitations come from? ( Click) First of all from physics. ( Click) i.e. the sum of forces acting on an aircraft determine the maximum rate of climb ( Click) Physical laws are immutable and the penalties for violations are severe. ( Click) Limitations also stem from regulations (Click) that govern aircraft certification. ( Click) Regulatory limitations are also based on physics but usually include a safety factor ( Click) For example CFR 12.65 specifies the minimum max gross weight climb gradient for land and seaplanes.
- In this presentation we’ll discuss: (Click) Weight & balance limitations (Click) Landing and Take off performance (Click) Stall speed (Click) Airspeed limitations (Click) Power plant limitations and – if we have time and you’re interested we can discuss (Click) Float and (Click) Ski limitations
- Let’s begin with airspeed limitations.
- What does the bottom of the white arc refer to? Collect answers from audience then (Click)
- Correct – the flaps down stall speed at gross weight. Do you think we could maintain level flight in this aircraft below 40 knots indicated without stalling? If so - how could we do it? Operate below max gross weight. It looks as if the next arrow is pointing to the top of the green arc. What does that signify? Discuss – then (click)
- Yep – that’s the flaps up gross weight stalling speed. Could we fly this aircraft flaps up below that speed? Right – just fly at a lower weight. (click) Now we’re looking at the red line. What does that signify? (click)
- That’s right – the red line refers to Vne – never exceed.
- Here’s an example of what can happen when you exceed Vne. Click on URL & select video. Largest file size is best picture but slowest download.
- Here’s an example of what can happen when you exceed Vne. Click on URL & select video. Largest file size is best picture but slowest download.
- So what’s the big deal about operating above VNE? Is the airplane going to come apart because we got a little too fast? Answer: Unlikely but could happen Irreversable airframe stress sounds pretty scary – is that REALLY going to happen if I get preoccupied in a descent? Answer: (Click) Yes – it’s really going to happen. Whenever we exceed any limitation we’re getting that much closer to a component failure. If you bend any metal long enough it will fail. Fatigue is cumulative. The airframe remembers each stress cycle and at some point it will fail. It’s not as if the flying machine gets sick and gets better – it’s always going to suffer from the abuse inflicted on it and that brings us to our third choice Unknown and untested. (Click) It’s true that airframes are flown above Vne in certification testing – that’s part of how the Vne is developed but the manufacturer doesn’t calculate the airframe lifespan with the assumption it will be flown outside of limitations so there’s no way to predict how early a fatigue failure will occur.
- How about the top of the white arc – what does that signify? (Click)
- Correct – the Maximum Flap Extension Speed. You know what’s coming next – what happens if we operate with flaps extended above this value? Discussion: Now we come to the top of the green arc – what’s that signify? Discussion: White arc flap operating range, green arc normal operating range top of green design cruise speed. then (Click)
- Right – the top of the green is Vc – design cruise speed. Now what are your thoughts about the yellow arc? Discussion: Flying in turbulence anywhere in the yellow arc results in stressing the aircraft beyond the manufacturer’s design limitations period.
- Here’s a very busy chart of the operating envelope with respect to speed. Let’s break it down to discover what’s really important for pilots. (Click)
- The Orange lines represent the operating envelope for an airplane certified in the normal – 3.8 g - category. (Click) The yellow line represents aircraft speed. (Click) This line represents Vd or dive speed – at this speed you’re getting very close to flutter. (Click) And here is Vne. (Click) There is a 10 % safety margin between Vne & Vd but, for reasons we’ll discuss you really don’t want to be operating there. (Click)
- Now we add gust lines. Within this speed range the airframe can withstand a 50 foot per second gust. At higher speeds though….. Click a 25 foot per second gust is the limit. By the way – 25 fps gusts are very common in light to moderate turbulence.
- a 25 foot per second gust is the limit. By the way – 25 fps gusts are very common in light to moderate turbulence. (Click) The speed at which we transition from 50 fps to 25 fps becomes the bottom of the yellow arc (Click) Now we add the stall lines. At these speeds the aircraft will stall before it’s stressed beyond design limits. (Click) Finally and for extra credit how shall we label this speed? Wait for answers then (Click)
- Now we add gust lines. Within this speed range the airframe can withstand a 50 foot per second gust. At higher speeds though….. (Click) a 25 foot per second gust is the limit. By the way – 25 fps gusts are very common in light to moderate turbulence. The speed at which we transition from 50 fps to 25 fps becomes the bottom of the yellow arc (Click) Now we add the stall lines. At these speeds the aircraft will stall before it’s stressed beyond design limits. Finally and for extra credit how shall we label this speed? Wait for answers then (Click) Correct! That’s Va – Maneuvering speed
- In theory, an airplane should be able to sustain a sudden deflection of any single flight control as long as the airplane is below V a
- 1 – True and gusts in excess of 25 fps are common. (Click) 2. – Also true. Operating in the yellow arc with any turbulence is very stressful to the aircraft. (Click) 3. – That’s true damage associated with severe turbulence is common. (Click) 4. – False – Larger engines make it easier to fly too fast for conditions (Click) 5. – That’s true. Vne is determined with respect to structural considerations as well as flutter. (Click) 6. – 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. (Click) 7.- 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? (Click)
- Now for extra credit what do you think about this question: Discussion then click Correctamundo and that means we have to be especially carefull in turbulence with light loads.
- Now let’s take a look at weight & balance limitations.
- We’re going to explore weight limitations next and where the weight is concentrated determines the center of gravity so how would you complete the statement above? (Click) Yep – the further forward the cg is the stronger the nose wheel has to be (Click) B is also affected by forward cg. A forward cg makes it more difficult to flare. Stall recovery, on the other hand, is easier with forward c.g. (Click) The further forward the c.g. the stronger the tail must be – who can tell us why? The center of lift on most of the airplanes we fly is developed aft of the center of gravity. So we have to trim the tail down to hold the nose up. Thus forward c.g.s require stronger tail structure. (Click)
- Here’s an illustration that shows the principal. With the CG forward of the CL the tendency is for the aircraft to pitch down. (Click) So we rig the tail with enough down force to keep the nose up.
- You’ve all seen weight and balance limits graphed like this red box. (Click) At lower weights you can stay within nose gear stress limits, and you can flare & trim with a forward center of gravity. As weight increases though the CG must move aft to avoid exceeding design and control limits. (Click) This upper weight limit is typically based on climb performance criteria and airframe strength. (Click) The aft limit is predicated on tail wheel strength, pitch control forces approching zero, spin resistance, longitudinal stability – see control forces approaching zero – and the ability to control pitch with full power application as in a go around from a balked landing. (Click) Finally – the forward limit is determined by the empenage strength, the ability to flare, and nose gear design limits.
- It’s time for some more True or False questions. These all have to do with the maximum gross weight limit. What do you think about this statement? (Click) Yes – that’s true. (Click) 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. (Click) Well duh – of course we’re going to climb slower but the insidious thing is the possibility of structural failure. (Click) Yes this is all true when you exceed weight limits. (Click) See the second statement above. The safety margin is there for a reason and the reason is not so you can overload by 50%. (Click) This is sobering. In many cases the max gross weight limit was set because the airframe came apart in static testing. (Click)
- Here are some forward c.g. limit considerations. As airplanes are modified they often acquire additional weight and, in the case of engine mods, the weight is usually on the nose. That may make the airplane go faster and increase gross fuel sales figures at your FBO but it requires additional down force on the tail or more weight added aft of the c.g. to compensate.
- Here are some attributes associated with loading close to or aft of the aft c.g. limit: Why would aft c.g. be critical for spin recovery? Discuss Tendency to hold nose up, flat spin potential, difficulty in breaking stall. (Click) Stick forces become very light as the aft c.g. is approached. How about a balked landing? Discuss What happens to pitch when we add power to go around? That’s right & we’re already aft c.g. so it’s harder to prevent a stall (Click) Longitudinal stability is compromised with aft c.g. & a stall can result in a major change in direction (Click) What about nose down trim? That’s right. You may run out of nose down trim and that could be a big problem on a go around. (Click) We’ve already mentioned that an aft c.g. will impose more load on the tail wheel.
- Now just a little discussion of takeoff performance Book numbers are often optimistic. That’s why it’s important to document your performance with mission loading. Documenting performance with a pilot & half tanks will give you impressive numbers but you’ll be unable to duplicate those figures at gross weight. Better to look at a worst case scenario and then operate with a lighter load. (Click) There is no safety margin in takeoff numbers. (Click) That’s why AOPA Air Safety Institute recommends that pilots add 50% to published takeoff distances.
- This program was developed in Alaska so the following is predicated on getting a moose out of a bush strip. That said, overloading opportunities are not just found in Alaska – they’re everywhere and pilots have to know how to deal with them. (Click) First of all don’t fly above Gross Weight! So how do you know how much moose you have to transport? You could follow Dirty Harry’s advice “you got to ask yourself – do I feel lucky?”. Remember – we’re betting our life – and maybe our family’s lives here so the only way to be sure (Click) is to weigh it.
- When you’re operating out of a tight space you have to do a little more calculating. We’re using a Super Cub in this example and the standard max. gross weight is 1750 lbs. You can get an STC to increase That max. to 2000 lbs but the POH is predicated on 1750. Here’s how to do the math. (Click) Let’s say that the pilot, fuel, oil, rifle, survival and 200 pounds of moose added to the empty weight total 2000 pounds. Right away we know we’ll need several trips to get the whole moose out but we’re not overloaded. We just need to know if we can clear the trees at the end of the strip. Divide 2000 by 1750 for a factor of 1.3. Multiply the ground run (200 feet or 500 feet over an obstacle) by 1.3 (Click) and we get 260 & 650 feet respectively. There’s no built in safety factor for these numbers. To be conservative we should add our own safety factor. The AOPA Air Safety Institute recommends a safety factor of 1.5 (Click)
- So – here we’ve added the safety factor with and without obstacle. Irrelevant if you’re operating out of a 3,000 foot runway vitally important if you’ve only got a few hundred feet to work with. Try it with an example from your world and we recommend you teach your students to add a safety factor too.
- You might think we’re done but runway composition, slope, contamination, density altitude, and wind all affect performance. Here’s some wind facts to consider. (Click) Discuss each comment.
- Here’s an example of tail wind effect on takeoff
- Now just a few words about crosswinds. The maximum demonstrated cross wind component is what? Discuss with audience then (Click)
- The maximum demonstrated cross wind component is the highest cross wind component successfully compensated for during flight testing. Will the airplane handle more? Maybe yes maybe no – but if you exceed the max demonstrated component you’re now the test pilot. Good luck. (Click) So true – and recency of experience is very important. We need to take every opportunity to help our students to understand that practice is vital. You gotta use it or lose it. (Click) Obviously this is true and when that happens …… (Click) No amount of pilot skill will salvage the situation. If we’re landing a go around should have been initiated before this – if on takeoff hopefully we realized how strong the cross wind was and aborted before becoming wind blown and airborne. (Click) Certification standards only require a cross wind capability equal to .2 times Vso. (Click) As you can see the C172 easily beats the minimum.
- Discussion: (Click) How do you set and adjust minimums for your students? (Click) How and when do you make your students’ responsible for their personal minimums? Discussion
- Here’s one way to get students involved with personal minimums. It’s a publication that prepares Alaskan pilots for Off-airport/unimproved airport operations.. You can download a copy at faasafety.gov. Click on Online Resources, then Resources by Type of Operation, and then Alaskan Resources. (Click)
- You’ll find this chart on Page 1. We encourage pilots and flight instructors to measure performance periodically and to document the results. That way the student can see progressive improvement throughout training but, more importantly, they will know what they are capable of before attempting operations at short and or obstructed landing sites. By the way – the guide works well On-Airport 500.
- Finally let’s take a look at engine limitations.
- (Click) We’ve all heard stories of engines that packed it in before their time but exceeding RPM limits makes it much less likely we’ll reach TBO without incident. (Click) Not to mention increased strain on the prop itself (Click) Excess vibration is not our friend. It accelerates the onset of fatigue problems and may lead to structural failure (Click) Over temping can be just as hard on an engine as over reving. Rapid heating and cooling are not good either. Plan descents to keep the engine warm and make the go around (Click) decision early so you can add power gradually. (Click) This is true of turbines and recips alike (Click) All true. Many Alaskan operators cease recip operations at 20 to 30 below zero. Turboprops operations cease about 10 degrees cooler. Even in milder winter temperatures preheating the engine is a very good practice. (Click)
- (Click) We’ve all heard stories of engines that packed it in before their time but exceeding RPM limits makes it much less likely we’ll reach TBO without incident. (Click) Not to mention increased strain on the prop itself (Click) Excess vibration is not our friend. It accelerates the onset of fatigue problems and may lead to structural failure (Click) Over temping can be just as hard on an engine as over reving. Rapid heating and cooling are not good either. Plan descents to keep the engine warm and make the go around (Click) decision early so you can add power gradually. (Click) This is true of turbines and recips alike (Click) All true. Many Alaskan operators cease recip operations at 20 to 30 below zero. Turboprops operations cease about 10 degrees cooler. Even in milder winter temperatures preheating the engine is a very good practice. (Click)
- Finally a few notes on Professionalism: (Click) As instructors we’ve gotta walk the talk. It’s no good to tell your student it’s important to calculate weight & balance if we don’t even discuss it before flight. and speaking of walking the talk…………… (Click) Of course you can do things with an airplane that your students aren’t ready for or may never be ready for. That’s fine – just don’t let them see you do it because if they do - they’ll be trying to emulate your performance before you know it. (Click) We know that 6,500 foot runway is at least a mile more than we need so how about having your student brief you on takeoff distance required and abort criteria before takeoff. If you make it a part of their routine now it will stick with them after the checkride. (Click) Finally treat all limitations as vital safety of flight items. If they’re not important to you there’s no way they’ll be important to your students. Presenter: The next two slides discuss float and ski flying. Include or bypass at your option.
- Optional: Point 4 is a good argument for egress training. Float plane mishaps often end with the airplane upside down. Very disorienting unless you’ve had some training and practice.
- Optional: Make point that all these points have to do with performance. They don’t address surviving in cold & possibly wet conditions when you land somewhere on skis but can’t use the airplane again to get home. Especially in winter we may exit the airplane with only what we’re wearing and what’s in our pockets. Good argument for cold weather survival training. You can’t treat a ski-equipped airplane like the wheeled counterpart. Be especially conservative with respect to speed. There are numerous instances of crashes due to ski dump on descent. When the forward ski cable fails the ski can rotate 90 degrees introducing considerable drag in the process. In extreme cases skis have damaged the lift strut with consequent wing failure. For best results – fly slow and inspect the ski system before takeoff and after landing.
- 15 minute Q&A, then on to a Quiz.
- Read & discuss questions. Answers are provided the second time through the questions.
- 15 minute Q&A, then on to a Quiz.