Presented to: CFI Workshops By: The FAASTeam Date: January 1, 2012 Federal Aviation Administration...

Presented to: CFI Workshops

By: The FAASTeam

Date: January 1, 2012

Federal AviationAdministration

Downloaded from www.avhf.com

CFI Workshop 6 Core Topic 12

Airworthiness Limitations

Where do they Really come from?

2Federal AviationAdministration

FAASTeam CFI Workshop 6January 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




• 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




http://dms.ntsb.gov/aviation/AccidentReports/v233vt4542baswfpmqymxq451/R07052011120000.pdf



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)



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



Airspeed Limits


8FAASTeam CFI Workshop 6January 2012

Examples of Airspeed Limits

-




Flaps Down Stall Speed (at gross weight)

-




Flaps Up Stall Speed

(at gross weight)


-





(at gross weight)


-

Vne, Never Exceed



Flutter testing

Tail Flutter Test.mov



What’s the consequence of operating above VNE?

A. Catastrophic airframe failure

B. Unknown & untested

C. Irreversable airframe stress

VNE





(at gross weight)


-

Vne, Never Exceed





(at gross weight)


Vf, Max Flap Extension Speed

-

Vne, Never Exceed





(at gross weight)


Vf, Max Flap Extension Speed

-

Vc, cruise speed

Vne, Never Exceed



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)



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



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



As gross weight decreases Va will:

A. Decrease

B. Remain the same

C. Increase

Extra Credit



Weight & Balance Limitations



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



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)



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.



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



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.



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



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.



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



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

3.11750

20002

Weight Ground Run 50’ Obstacle

1750 200 500

2000 260 650

Not including AOPA 1.5 safety factor



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???



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)



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.



Crosswind

The maximum demonstrated cross wind component is?



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)



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?



Alaskan Off-airport Operations Guide



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 ___________



Engine Limitations



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.



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.



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.



• Questions?


FAASTeam CFI Workshop #2

January 2011

QUIZ



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:



A. All control surfaces have been balanced.


C. No turbulence is present

Question 2

Flying within the yellow arc is permissable as long as:



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:



The aft C.G. limit is critical for:

A. Tail wheel strength

B. Spin recovery

C. Nose wheel strength

Question 4



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



January 2011

NOW THE ANSWERS



A. As long as the 10% margin of safety is not exceeded.


C. Neither A nor B

Question 1

Flying above the red line is OK:



A. All control surfaces have been balanced.


C. No turbulence is present

Question 2

Flying within the yellow arc is OK as long as:



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:



The aft C.G. limit is critical for:

A. Tail wheel strength

B. Spin recovery

C. Nose wheel strength

Question 4



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



January 2011

END OF CFI WORKSHOP MODULE 6

Presented to: CFI Workshops By: The FAASTeam Date: January 1, 2012 Federal Aviation Administration...

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Transcript of Presented to: CFI Workshops By: The FAASTeam Date: January 1, 2012 Federal Aviation Administration...