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Flying
Surfaces and Controls
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Contents:
…Wing; …wing terminology; ...Controls and What They Do; ...Horizontal Tail Surfaces; ...Rudder; …More Rudder ...Flying with rudder; ...Frise Aileron; ...Latches; ...Rig; ...Spiral Stability; ...Aircraft Category; ...Lifting Surfaces; …L/D Ratio; ...Wing Loading; ...Power Loading; ...Drag & Performance; ...Parasitic Drag; ...Induced Drag; ...Boundary Layer; ...Control Failure; ...Cables; ...Aircraft Aluminum; ...Corrosion and Skin Condition; ...Hoses and Lines; ...Plastic Windows; ...Hobbs Meter; ...Stall Warner; ...Spinner; ...Pitot Heat; ...Cabin heat; ...Oxygen; ...Maintenance failures; …Paint; …Pilot Induced Oscillation; …The Propeller; …Over-Square Constant-Speed Propeller Operation; …Using Your Non-flight Instruments; …Angles; …Stability; …Flap Chafe Caps; …Static Wicks; …Window Care; …
The force that balances the airplane's weight in flight against
the pull of gravity is caused by the differences in pressures
between the upper and lower surfaces of the wing. A pure airfoil
creates lift without any down wash whatsoever. The down wash from
an airplane's wing is a by-product of lift (through the tip vortices),
not the other way around.
An airfoil in its purest form is a wing with an infinite wingspan.
The flow over the surface will be the same no matter where along
the span we measure it. If the wing has no tips, there can be
no tip vortices. An airfoil having no tip vortices will have no
induced drag since there is nothing to induce downwash.
In the real world of aircraft wings that have wing tips we
know that an angular spanwise flow of air is drawn by the flow
of air off the wingtip. Only a portion of the air low pressure
air flowing over the wing can get to the wingtip before most of
it passes off the trailing edge as relatively low velocity downwash.
Even more air is being drawn from the high-pressure bottom of
the wing to flow from under the wing tip and into the low pressure
above the wingtip. Hence the flow of air above and below the wing
has different flow amount and direction coming off the trailing
edge the wing.
At the wingtip the high pressure air below the wing curls upward
into the lower pressure above the wing to create a vortex. The
airflow from the vortex whirls around, downward and inward above
and behind the wing. Downwash and induced drag are greatest where
the vortex rotates at the highest speed around the tip and over
the top of the wing.
The speed and pressure of airflow across the wing affects the (local) angle of attack. As the airflow moves toward the tip there is a lowering of the angle of attack, a decrease in lift, an increase in downwash, and an increase in induced drag. At the tip there is no lift, no vortex, no drag, and no downwash. Any increase in the angle of attack near the wingtip will increase the concentration of the vortex core hence increasing the lift, increasing the drag, and increasing the power of the downwash.
The velocity in the tip vortex is very high near the core, but decreases the further you move from the core to its outer rings. The core remains near the tip while the outer rings have an effect further inboard. The lift-induced speed of both inner and outer vortices is downwash, the downwash velocity is highest near the tips and lower at the root. Downwash reduces the angle of attack wherever it flows from the wing proportionate to its velocity. The amount of lift available at a given angle of attack will always be less where there is greater downwash.
Approximately 75% percent of lift generated by an airfoil are
the result for differential pressures, and the other 25% are a
result of Newton's third law of motion, "For every action,
there is an equal and opposite
reaction." This is most obvious while in ground effect.
Wing design plans for the stall to begin at the wing root. This provides a gentler break as compared to a tip-break. Some aircraft have stall strips on the leading edges to assure the root stall before the tip stall. Most wings that are slightly tapered have lift distributions that are close to elliptical. An improperly designed wing may have the stall cause loss of aileron control before the break. This is the reason why highly tapered wings have a leveling twist called washout. By reducing the wing incidence toward the tips, you lower the local angles of attack and the lift near the tips. Then the stall moves toward the rood and becomes less abrupt. Draw the wing and use the words as appropriate.
Wing
terminology
Mean Camber line
Upper Surface
Leading
Edge Trailing edge
Lower Surface
Center of Lift
Aerodynamic center of lift is also called center of pressure
is located aft of the center of gravity. This location gives airplanes
a pitch down tendency. This is why the download is required on
the horizontal tail surfaces.
Chord Line
Imaginary line from the leading edge of the wing to the trailing
edge.
The primary controls are the elevators, ailerons and rudder. These provide primary movement around the axes of flight. In combination, they give coordinated movement around the axes of flight. Engine power is an additional primary control of pitch. Again, in combination, it gives coordinated movement. No change in one axis occurs without having some effect on the other axes.
Secondary controls include trim and flaps. Devices that augment engine power and control operations, weight, center of gravity and load factor have secondary effect on control. Complex aircraft may have additional controls. The effect on all controls is dependent on conditions of altitude, speed, temperature and weather.
Neutral pitch is engineered into the placement of engine, wings. horizontal stabilizer and loading limits. The pitch is moderated to a designed degree by elevator, engine power and trim. Any change in elevator or engine power along with the rapidity of change requires coordinated control movement in the other axes. To change only pitch, by whatever means, some additional combination of rudder and aileron is required.
Ailerons "control" bank angle, roll and roll rate but, in combination with the other controls. On application of aileron in a turn, rudder must be "coordinated" to keep the tail behind the nose; elevator is used to counter loss of vertical lift. Ailerons work in opposite directions, usually in differing distance and with an effect called adverse yaw. The down aileron gives lift and drag (induced). The drag resists the turn so that rudder is applied for coordination.
Rudder is used most often in anticipation of known requirements from the other controls. Rudder will induce roll as well as yaw. The rudder can be used to raise a wing in a stall. Anticipatory rudder is applied to counter the effects of power/pitch applications. A rudder-applied yaw is used to make possible crosswind landings. P-factor, torque, precession and slipstream all require use of the rudder. Skillful rudder on the ball and in anticipation is the distinctive mark of a good pilot.
Power is a pitch control. Just adding power (no other control input) will cause the nose to rise and roll to the left. Speed will decrease. In a turn, power will make the left turn possible with little or no rudder but require rudder to "lead" the right turn. There are countless cause/effects in the creation and control of a given airspeed and pitch condition. If you are ever asked about what controls airspeed and pitch, just say, "The pilot".
These two surfaces, stabilizer and elevator or combined stabilator, provide longitudinal stability and control of pitch. Even the simplest of aircraft have a controllable pitch that can be adjusted for hands-off flight using a trim control. Trim adjusts in several different ways but the effect is always the same, stability of flight. All horizontal tail surfaces use the movement of air either relative, prop wash, or wing wash, to produce a down load to counter-balance the engine on the other side of the center of lift. The different washes affect pitch controls differently. A T-tail does not get the same amount of propwash as does a conventional tail. Every tail design has positive and negative facets. Some airplanes don't even need tails.
The size and location of the horizontal tail surfaces is usually designed into the aircraft (T-tail exception) so that the air flowing over the wing augments the normal slipstream. An additional source of airflow will be the propeller wash or propwash. Together they give the download required to counter balance the weight of the engine. If this flow over the wings is diverted in some manner by a gust, ice, wind shear, or slip the downloading of the tail surfaces may be reduced. In an incipient stall the first effects you feel and hear are on the tail surfaces. This is buffeting caused by the burbles of air breaking loose from the wing during the incipient stall.
At the stall the wing loses its ability to sustain the weight, gravitational and aerodynamic, of the aircraft. At the wing stall reduced airflow over the horizontal tail surfaces reduces the download capacity of the flight surfaces. The tail goes up and the nose goes down. How much and how abruptly depends on the extent and suddenness of change in the download. A tail surface in the direct of propwash may be overly affected by changes in engine power. On takeoff this effect is to be desired as it enables the nosewheel to be raised sooner. A pilot in flare will need to use additional elevator to counter the decrease in propwash caused by power reduction. The airflow between the airplane and the surface of the earth becomes significant when within half a wingspan. This ground effect redirects the downwash off the wing making it less effective over the horizontal stabilizer and elevator.
Down load on the horizontal tail surfaces is required to hold the nose up and the tail down about the aerodynamic center of lift. When the download on the tail cannot hold the nose up the nose will pitch down. Read Flight Training Handbook on page 277.
In normal flight, including stalls, the horizontal stabilizer doesn't stall. With the elevator down, the effective angle of attack of the tail goes up, just like a wing with flaps down, and since the angle of attack is already high, pushing down forces the tail past the maximum angle of attack. Then it stalls.
Icing of the tail can result in total loss of control. I think that most turbo-props are operated with the c. g. behind the aerodynamic center of the wing, so that loss of control of the stabilizer causes the airplane to pitch up, eventually beyond maximum lift, and without the tail to counter the pitch up, the situation becomes unrecoverable.
The function of a boat rudder, as is commonly perceived, does not apply to airplanes in the air.
Addendum from Roy Smith:
You might be interested to know that it doesn't apply to a boat
either! The worst way to turn a boat is to use the rudder. Rudders
cause drag when moved off the centerline (induced drag) and slow
the boat down. All turns, as much as possible, are done by shifting
crew weight. The rudder is there for fine tuning, and to add additional
turning moment for very fast turns when just shifting weight isn't
enough.
As explained in taxiing, the rudder pedals and brakes are used for ground steering. The purpose of the airplane rudder is to keep the tail behind the nose, it is the first control to become effective on takeoff. The rudder should keep the tail behind the nose in level cruise configuration. This is built in or 'rigged' and trimmed performance often by a small metal 'tab' on the rudder. The 'ball' is centered. Certain changes in pitch, power, or bank require rudder application to keep the ball centered and the tail behind the nose.
The usual application of rudder begins with leg power which gives a relatively course control. Smaller variations of rudder can then be applied or removed by flexing the ankle. The cables and pulleys of the rudder require relatively heavy control forces when compared to that of the ailerons or elevator. The rudder gives the directional stability to an aircraft that makes flying pleasant.
Throughout aviation history the use and effect of the rudder in the air has not changed. The rudder is a participant in every slip, skid or bank. As an aircraft centerline is displaced in level flight by just rudder application you have created 'yaw'. The fact that adverse yaw is the cause of the off center ball never gets mention. The ball merely reflects the effect of adverse yaw. With the aircraft now flying at an angle to the relative wind we have established a yaw or sideslip angle. Left alone the aircraft will not fly with any sideslip angle.
The rudder effectiveness is enhanced by a slight displacement
of the engine, which allows the prop-wash to have greater effect
on the vertical control features than on the horizontal features
of the empennage. A hand-adjustable trim tab or a trim adjustment
wheel can be used to relieve rudder pressure.
More
Rudder
Aaron says that's a misleading statement from Roy.
Rudder
Displacing the rudder to the left, as if to enter in a coordinated
left turn causes a force which acts to push the tail to the right
(left yaw). However, since the rudder is located above the CG
the rudder also creates a moment about the longitudinal axis which
counteracts the ailerons (roll right instead of left) when trying
to maintain the coordinated turn to the left. If the aircraft
rudder was mounted underneath the CG, one could easily turn an
aircraft in a more coordinated manner, and it would turn like
a boat.
The primary difference between a boat rudder and a aircraft rudder is the inefficient placement of the Rudder above the CG in an aircraft which makes the analogy misleading. Because the rudder in a boat is below the CG, the rudder also creates "horizontal lift" acting on an arm which causes the boat to roll into the turn. An aircraft rudder has the opposite effect. Displacing the rudder to the left, as if to enter in a coordinated left turn causes a force which acts to push the tail to the right (left yaw). However, since the rudder is located above the CG the rudder also creates a moment which counteracts the ailerons (roll right) when trying to maintain the coordinated turn to the left. If the aircraft rudder was mounted underneath the CG, one could easily turn an aircraft in a more coordinated manner like a boat.
But that isn't the optimal design. By mounting the rudder so
that there is equal surface areas above and below the a horizontal
line extended from CG, Every maneuver involving use of the rudder
(crosswind landings, stalls, slips, turns, et al.) could be done
in a much safer and efficient manner.
A problem arises in design constraints which prevent a down-rudder:
It would certainly cause a lot of problems in the landing flare
et al. There are certainly other differences between the A/C rudder
and boat rudder. Most of which are related more specifically to
fluid dynamics and the differences between the density/viscosity
of air and water. A rudder in a boat usually has at least 25%
of its surface area ahead of its axis of rotation, which alleviates
the need for much stronger power steering. Rudders do cause a
lot of drag when the turn is initiated, which can result in bent
rudder shafts in the test tank, but the naval architect never
lets that happen twice in his career. After the vessel is established
in the turn, the drag is minimized.
Aaron Prosser
Use of Rudder?
Is there a 'proper' way to place and use one's feet on the
C-172 rudder/brake pedals?
In a way I can't believe I'm asking this. Not that I have a tremendous
amount of time (15 hours), but it seems like it is one
of those basic things that would have been settled by now. I have
looked for the answer in documentation and asked my
instructor about it, but I'm still unclear on the matter.
A little background: The older (1970's) 172's have pedals that
accept the entire foot. So the first few lessons, I put both feet
right on 'em. No problem in the air, but on the ground found it
a little clumsy separating turning action from braking action.
Seemed like no matter how much I tried, I always got brake action
even when I only wanted to turn. I thought it was just
something that would come with time, as I became more proficient.
Then one lesson we were on the takeoff roll and my instructor
noticed my whole foot on the pedal and admonished me to
"stay off the brakes." I asked him later what the proper
technique was, and he said, "To use the brake, lift your
heel." It
seemed like that instruction could apply whether or not the whole
foot was placed on the pedal, but since he seemed to
freak at the sight of my whole foot there, I decided I'd keep
my toes off the top half of the pedal entirely.
From that lesson on, the normal position of my feet is heels on
the floor, toes on the bottom portion of the pedals. So when
I do want to use the brake, I not only have to lift my heel, I
have to reposition my foot (to get my toes to the top of the pedal).
Is this correct?
Where I need clarification is, do you place your entire foot
on the pedal and extend your knee to steer, keeping you ankle
joint/toes retracted unless you also want to brake, or do you
stay completely away from the top half of the pedal until you
want to hit the brake?
And is it true the newer 172's have only a half-size pedal? Which
half and how do you use that system?
Ken Wiebe, Student Pilot
Flying with
Rudder
When you first try to fly with rudder, you will find that
the rudder affects the roll axis. Normal coordinated use of the
rudder and ailerons gives the expected yaw effect of the rudder.
Due to cross-axis coupling use of the rudder alone gives roll
because of the rudder's position above the center of gravity.
Left rudder alone gives a left yaw and a right roll. For a given
rudder application more yaw than roll will occur because of the
relative moment arms.
The wing on the outside of a turn becomes a drag factor causing adverse yaw. It is the difference of the drag between the raised and lowered ailerons that produces the yaw away from the intended direction of flight. This induced drag is mostly due to a greater angle of attack rather than the higher airspeed. It is the downward deflection of the ailerons that effectively increases the angle of attack. More rudder is required entering a turn than when the desired bank is achieved, because the ailerons are deflected more when rolling in and out. The geometry of the aileron pulleys allows relative up or down movement of the two ailerons to be different. Some modification of yaw is possible by doing this. At a 30-degree bank the ailerons are neutral. Rudder must be applied to counter this adverse yaw. A reason very little rudder is required in the left turn is because the yaw effect of the ailerons is countered by the P-factor of the propeller. More rudder is required in right turns since the P-factor is added to the yaw of the ailerons.
The rudder's steering function in the air is only related to a small degree to that on the ground. It is used to correct or offset the undesired steering effects of propeller, propeller slipstream, wing, and aileron. Pressures in level cruise flight are reduced if the small trim tab on the rudder has been correctly adjusted. As speed is reduced in level flight the nose must be raised. More and more right rudder will be required. In descents light left rudder might be required. The proof of poor rudder use by a student can be demonstrated by having the student climb in a given direction without reference to the panel. Over several minutes the plane will begin its gradual left turn. A request to get back to the assigned heading results is a great deal of bank and little turn. As I instruct, I often find myself, unconsciously, holding right rudder for my student. Aircraft except for the training aircraft have a rudder trim to ease the amount of rudder pressure required as when climbing to high altitudes.
The need for right rudder in the climb is due to several factors the most obvious of which is the P-factor. That is the increased thrust of the downward moving propeller blade brought about by the raised pitch attitude. The most significant factor in these changes is P-factor. P-factor is caused by the differential in thrust between the rising and falling propeller blade. Any addition of power or raising of the nose increases the differential and causes the nose to pull to the left. Additional right rudder must be applied to keep the ball centered. This rudder application must be and not as an afterthought in reaction. Some flight situations, such as slips, crosswind landings, Dutch rolls, and IFR approaches require the rudder to be misused (abused) from its design intent.
Rudder applications are mostly required in making coordinated rolling maneuvers where the rudder counter reacts to adverse yaw. Rudder application is best used in anticipation of the roll to come. Only the rudder can effectively stop the wing drop that occurs in an uncoordinated stall. Opposite rudder lifts the wing where aileron only makes things worse. In the making of crosswind landings the authority of the rudder determines the pilot's ability to keep the aircraft centerline parallel to the runway centerline. Once a rudder is fully depressed more authority can be obtained by increasing speed or propeller wash.
Use of the rudder to yaw the aircraft or even to counter any yaw will cause a pitch change that must be anticipated by the pilot. I usually teach Dutch rolls in a climb and the propeller disk is tilted and left yaw is more evident. For this reason and the slow speed involved when doing the Dutch rolls far more right rudder is requires over longer periods. Some aircraft require no right rudder at all. This propeller plane effect, P-factor, is also evident when doing forward slips.
Frise Aileron
Leading edge is in front of hinge line so that airflow reduces
control pressure required to hold deflection. This aileron is
the
primary reason adverse yaw has been reduced in modern aircraft.
There is more down movement than up movement along
with the descending leading edge. The net result is that there
is not so much rudder requirement to correct for adverse yaw.
This has effectively inhibited flight instruction. Pilots can
no longer feel the as much yaw in a bank and thus do not use rudder
correctly. Some aircraft (Pipers) can be flown with feet on the
floor if the aileron movement is not abrupt. In any established
maneuver, such as an approach to landing, elevator will control
the airspeed and the angle of attack.
Aileron movement changes the pressure distribution over the ailerons
and thus changes the pressure over the wing chord
ahead of the aileron. This effect is true only before the stall
burble. Once the air breaks from the wing surface any movement
of the aileron will be ineffective on the wing pressure. It is
because of this airflow separation that the use of the ailerons
is
ineffective until the angle of attack is reduced and the airflow
reattaches to the wing surface.
It is a shame, considering the cost of an aircraft, that the latching mechanisms of doors and other such should be so inferior in design and construction. If door locks do not work properly, report it to maintenance. Do not tolerate a situation that has caused so many needless accidents. It is not wise to live with a known discrepancy. It is a violation of the FARs to fly with a known discrepancy.
No two planes are exactly the same because of the infinite variations of rigging. Rigging is the total alignment of the parts of the aircraft, wings, flaps, controls, and fuselage. You may have see a car go down the road without the back wheels tracking behind the front. An out of rig airplane can fly much the same way. There is no way to see this, but 'identical' airplanes usually fly differently. The rigging of an airplane will not perform as well as it should. It will not have the stability that allows hands-off flight nor will it react in the stall and spin as it should.
Some minor defects of rigging can be corrected with the fixed tabs on rudder or ailerons. Some controls can be adjusted by bungee cords or springs. Poor stall characteristics can be manipulated by the use of leading edge stall strips or by slots in wings or horizontal tail.
Every time you bank an airplane you are changing the bank angle and affecting the airplane's spiral stability. Most G.A. planes will hold a 30-degree bank with less than a half-turn of the trim wheel in cruise. In this situation the ailerons are neutral and the yoke should be level with the instrument panel. At less than 30-degrees the bank will tend to decrease and aileron must (should) be held against the bank to offset any roll generated by the yaw rate. At more than 30-degrees bank the bank will tend to increase and aileron must be held against the increase in bank to offset any roll generated by the yaw rate. All of these flight conditions assume that coordinating rudder is applied. A blending of pitch and roll attains a constant bank. The vertical fin provides roll vertical stability.
In a bank we are dealing with four separate flight elements, roll, yaw, lift, and stability. We want an IFR plane that will not enter, on its own, into a divergent descending spiral, or into convergent spiral especially if the entry is rather quick. You should determine just how your plane flies in VFR by checking how well a bank is maintained and held into a standard rate turn and what it does in level flight hands-off. You need to find out how the plane behaves and what you should do to make it behave.
The three axes of the aircraft are not equally stable. The pitch axis has a trim control that lets the pilot adjust the pitch stability for a desired flight condition. The vertical axis has a trim control that allows the pilot to relax on the rudder. However, it is the roll axis that is usually without such a control with some exceptions.
The roll axis or lateral axis is not stable because the pilot
needs this instability to maneuver the aircraft. We can let go
of the yoke in pitch and yaw for a length of time. Try the same
thing with the bank and subtle differences arise. The ailerons
resist the initial change, then accept it and then maintain their
new position. The new position is maintained until the overbanking
tendency takes over. The tendency to roll on over is caused by
the outside wing moving faster in the turn and the propeller's
slipstream hits the rising wing the most. Flaps increase this
effect.
Countering these over-banking effects we have dihedral. Dihedral
is the up slope of the wing from the wing-root to the tip. The
shape of the wind and its sweep also make a difference. Low-wing
aircraft have more dihedral than high wing aircraft. The effect
of dihedral and wing shape will vary with the power and pitch
attitude of the aircraft.
The conflict between the instability and stability of the aircraft explains why the aircraft can maneuver and will hold one position only for a few moments. One of the roll stability demonstrations I use with students is to put the aircraft into a 30-degree bank and put in anywhere from 1/3 to 1/2 turn of trim and let go. The aircraft will perform a turn that can be held with just light touches of rudder. The usual design of light aircraft is to make the 30-degree bank more stable than any other bank. Less than 30-degrees bank and the aircraft will strive to level off. More than 30-degrees and the aircraft will eventually roll over.
Aircraft Category
Manufacturers have the FAA test a new plane model for production.
Engineering design and tests are given as evidence
to justify certification in one of three categories -- normal,
utility, or acrobatic
Requirements appear in FAR 23. Differences in the categories
are based on strength and spin recovery. Wing loadings
are 3.8 G's for normal, 4.5 G's for utility, and 6 G's for acrobatic.
Negative G loadings are assigned as well. The structure
must be designed and tested to exceed the certified limits by
150%.
Certification can be held in more than one category depending
on the tests passed. The C-150 and C-152 are utility all the time,
a C-172 is either normal or utility depending on load carried.
The POH sets the requirements for each category. Spins are not
allowed in all utility aircraft.
General aviation categories are for aircraft less that 12,500
pounds gross weight. Normal, utility, and acrobatic correspond
to certification categories. The FARs describe general maneuvers
the aircraft is allowed to perform. Normal category aircraft can
do normal flying, stalls, lazy-eights, chandelles, steep turns
to 60 degrees. Utility aircraft can do all of the normal maneuvers
plus (approved) spins and 90-degree banks. Acrobatic aircraft
are unrestricted except for placarded maneuvers in operating limitations
An aircraft may be certificated in more than one category.
Exceeding allowable gross can cause the structural load on the
aircraft to exceed its capability as in turbulence. Normal category
aircraft can withstand 3.8 positive G's. Over gross aircraft can
be permanently damaged in turbulence even if operated at maneuvering
speed Va. Categories have limit loads that are maximum anticipated.
These loads an aircraft can safely support in flight. The manufacturer
normally designs a 150% safety factor into the structure. At a
predicted ultimate load structural failure will occur. If flight
occurs with simultaneous pitch and roll, as in a bank, the limit
loads drop by over 30%. For this reason turns are not a good idea
in turbulence.
Normal, utility or acrobatic category airplane are required to
be controllable for landing by power and trim in the event of
total loss of elevator control. These categories must be able
to make a 2-degree climb in a go-around in their most "dirty"
configuration. Properly restrained passengers should survive at
26-G .05 second deceleration without restraint failure. a 9-G
forward, 3-G upward (Acrobatic 4.5) and 1.5 G side-load. Part
23 aircraft designed in the 80s and later are not multi-category.
Single engine in all three categories in landing configuration
must be able to land at 61 knots CAS.
Correct control inputs in a stall must be able to prevent a spin entry. The one-turn spin test required is really a test of recovery from an abused stall. Normal category only aircraft are not approved for spins.
Aircraft can be classified by weight and as of August 1996
the classification table is for purposes of wake turbulence separation:
Small...less than 41,000 pounds s(changed from 12,500 pounds_
Large...greater than 41,000 but less than 255,000 pounds
Heavy... greater than 255,000
The rudder and vertical stabilizer form a variable airfoil
the elevator and horizontal stabilizer form a variable airfoil,
The wing by itself is an airfoil. The wing plus the aileron and
flaps is a variable airfoil. The span of any of these airfoils
is its length. The width is called to chord.
Dividing the chord into the span gives the aspect ratio. Aircraft
with long wings have a high aspect ratio while jets will have
a low aspect ratio. Its aspect ratio and its airfoil determine
the aircraft's sensitivity to control input in various situations.
The airfoil develops lift by having different air pressure on
either side. The movement of the rudder will create a differential
in lifting forces on either side to move the tail left or right.
The elevator does the same to move the tail up and down. The wing's
differential pressures between the upper and lower surface at
different wing angles of attack cause to aircraft to go up, down
or fly level.
This pressure differential can be demonstrated very simply by using pieces of paper. Hold a piece of binder paper upward by the edges between both arms with the thumbs and forefingers of each hand. Allow the paper to droop away from you. Allow it to form a curved airfoil. Blow directly across the top of the curve and you will be creating a pressure differential great enough to cause the paper to rise. It will rise farther than it would were you to blow directly across the bottom because the curve creates a higher air speed and therefore a lower pressure. The curve is a more efficient creator of low pressure.
This low pressure can be more dramatically demonstrated by holding two pieces of binder paper from the top edge between thumb and forefinger so that they hang parallel about three inches apart facing each other. Hold them parallel to your line of sight so you can see between the sheets. Now blow. The sheets come together because relatively fast air between the sheets form a low-pressure region. Nature does not like vacuums so, as with lifting surfaces, the pull of the low pressure combined with the push of the adjacent high pressure moves the intervening surface which in this case is a piece of paper.
When an aircraft is in level unaccelerated flight the amount of lift created by the wing will equal the weight of the aircraft, the downward 'lift' of the tail surfaces used to counter the weight of the engine and any drag however created. When an aircraft is capable of such flight at one times the force of gravity (G-1)we can determine its wing loading by averaging the number of aircraft pounds supported for each square foot of wing surface. The higher the pounds per square foot the more like a rock becomes the airplane.
Typical aircraft has an L/D of 10 to 1. For every ten pounds of weight there is one pound of drag. There are two kinds of drag; induced is produced by surfaces producing lift and parasitic which is produced by friction.
Drag varies with airspeed. Induced drag decreases with airspeed. Parasitic drag increases with increased airspeed. Minimum drag exists when the two forms of drag are equal. In most aircraft this is very close to Vy in level flight. At Max L/D a 10% reduction in weight will give the same 10% increase in mileage.
Fuel consumption is gauged by pounds of fuel per horsepower per hour. This value is normally .5 lbs/hp/hr. Extra lean mixture will give .4 while rich will give .7. TAS increases with altitude but to obtain the same CAS more power is required with a higher fuel flow rate. It is best to fly maximum efficiency by indicated airspeed rather than by power settings.
Modifications on aircraft affect efficiency more than speed. It is most important to keep the front half of the wing chord clean and smooth as well as the front half of the propeller clean and smooth. For a given weight CAS determines aircraft efficiency regardless of altitude or temperature. The TAS to CAS ratio increases by 1.7% per thousand feet of altitude increase. (TAS is 17% higher than CAS at 10,000' --100 CAS =117 TAS). Aircraft efficiency is best determined at a constant weight using calibrated airspeed.
Lower air density affects lift and drag the same as it affects the indicated airspeed. This is why the same ias is used for all landings at all airports. Improving efficiency in the propeller, fuel consumption, and aircraft efficiency by 5% each would amount to a 15% improvement in performance. The optimum speed of most aircraft for efficiency of fuel consumption, propeller, endurance and time is about 10% faster than the Vy airspeed. This is the Vz speed and should be flown in climb, cruise, and descent.
Wing loading is a measure of how much weight the wing must lift at gross weight expressed as pounds per square foot of wing surface area. Wing loading affects stall speed, maneuvering speed, and twitchyness in turbulence. The weight carrying ability of the aircraft is a function of wing area. greater wing area lowers the stall speed. The lower the weight per pound the better the short field capability.
Power loading is the prime measure of climb performance. The more power per pound of aircraft weight the better the climb. Power must be increased dramatically by four times to double the speed. The increase of power will reduce cabin load and increase fuel consumption so as to reduce range and carrying ability below practical considerations. I one flew a 180 h.p. Yankee that carried 14 gallons of fuel before being at refueling minimums. Aircraft went 146 knots but you had to land every hour and a half for fuel.
Drag
& Performance
Parasitic drag is caused by the aircraft skin and protrusions.
It increases with speed.
Induced drag is caused by lift, increases at slower speeds and
higher angles of attack.
A fixed pitch propeller is most efficient at only one power setting.
Maximum range occurs in flight that has the highest ratio of speed
to fuel flow or at maximum lift over drag.
Maximum range is achieved at the minimum power setting that gives
level flight.
Parasitic Drag
The structure of the aircraft that creates wind resistance or any friction produces parasitic drag. It exists as with all parasites as a constant fixed burden to its host. It affects performance and efficiency.
Induced drag exists in ever increasing amounts as the amount of lift increases. The greater the lift requirement per unit of wing area and thus the higher the induced drag. Long wings have low induced drag, short wings have high-induced drag. The proportion of the wing reduced by fuselage location and wing tip vortices reduces wing efficiency. The slower you fly, the higher the angle of attack, the greater the weight, the greater the induced drag. The induced drag increases exponentially far beyond the factor of decreased speed, increase in wing loading. This is one more reason a pilot must, at altitude, determine his skill limits at flying slow while maneuvering.
As the backside of the power curve is approached and the maximum endurance airspeed is reached, airspeed can be controlled most easily by pitch and altitude by power. Once on the backside, where no more power is available, the only available option is to lower the nose and sacrifice altitude. You must lower the nose or stall. In this situation at low altitude you have run out of options.
As air flows over an air foil the thin layer of air right next to the surface does not move relative to the surface because of viscosity. A dusty wing stays dusty. This thin layer of air is called the boundary layer. The subsequent layers of air increase in speed until finally one layer acquires velocity sufficient to create a pressure differential.
The rarest emergency is caused by control failure. Uncommon and unmanageable unless you pre-plan possible scenarios. You must take immediate action to keep the aircraft from getting into an extreme attitude. Rudder can be used to control roll in banks less than 15 degrees. It is a good idea to practice flight with only the rudder. Rudder can be used to counter the effects of a jammed aileron. An aircraft with a jammed aileron can be landed in a slip preferably against a crosswind. Touch down slowly and use the "crunch" of aircraft parts to take the shock.
A jammed rudder could yaw you into a spin. Avoid climbing turns. Use power and ailerons in small amounts. Get into a higher than normal speed slip if the rudder is stuck deflected. Land crosswind in a slip.
Jammed elevators can only be countered by power, C.G. changes and trim tab position. A free-floating elevator is best controlled by trim. A right rudder and left aileron slip may help lower the nose. A left rudder, right aileron will raise the nose. Use power all the way to the ground. Use a shallow approach to a long runway. Remember, power raises the nose.
Asymmetric flap position is the only critical flap failure. Get into a slip that will counter the yaw/roll effects of the split condition. The wing with the least flap will stall first. This condition seldom occurs but when it does it catches you by surprise. Undo whatever you did first. Bring flaps up or down as the case may be. Being low and slow is the worst possible situation. The strength of the forces attempting to roll the aircraft can only be partially countered by aileron and rudder. Any bank that you allow will be too much.
These simulated control conditions can be practiced at altitude by having the instructor lock a control while you regain control with what is left. Get close to the ground before you attempt any major changes. Don't touch down until you are as slow as your controls allow.
Cables of 1/16" to 1/4" with 7 strands of 7 wires (7 x 7) where strength is required and 7 x 19 where flexibility is required (controls). The yoke rod has attached linkage to the two sets of cables via pulleys under the cabin floor. These pull on a bell crank attached to the 'axle' of the elevator. Turning the yoke moves cables via pulleys to bellcranks in the wings, which have short pushrods to the ailerons. By making the bellcrank asymmetric the ailerons can be made to move more in one direction than in the other. This is used to limit adverse yaw in turns. Service manuals tell how much a given control should be able to move in a given direction. Mooney uses push rods instead of cables for its control operation. An unexpected control failure can be mitigated if the aircraft is properly trimmed. This, alone, is a good reason to always fly a trimmed aircraft.
Any binding or uneven movement should be checked. Listen for cable sounds. Changes in the time flaps or gear take to move should be checked. Only one rudder pedal should be able to be moved at a time. The best time to check controls is when it is very quiet and you can hear things that don't sound right. All control cables require lubrication as do all hinges and pushrod connections. Failure to lubricate opens parts to wear and corrosion. Any part not lubricated can 'freeze' in position and cause the cable to wear a flat spot to wear and eventually fray the cable. Cable tension should be maintained and any sign of loose cables should be reported as a maintenance item. Cable tension changes with temperature conditions. Too loose or too tight is equally dangerous. Unbalanced controls and loose cables cause control flutter at high speeds.
Control damage can be caused over a period of time by such
things as corrosion, wind pressures, improper rigging, interior
route exposures, and pilot abuse. Use every preflight as an opportunity
to find potential damage. Elevator failure is most
likely to occur. 50% more likely as rudder failure; 200% more
likely than aileron failure. In the event of any control failure
practice at as much altitude as you can whether control exists
at landing speeds. Plan what to do according to what you
determine.
Aircraft
aluminum
All aluminum alloys have the same density, one size sheet
will weigh the same, regardless of the alloy.
Plain aluminum has about one forth the strength of 2024 alclad
aluminum but is the MOST resistant to corrosion
6061 has about 85 percent of the strength of 2024 alclad aluminum.
2024 is clad (alclad ) with a thin coating
( about .001 inch thick ) of pure aluminum for corrosion resistance.
The 2024 is alloyed with copper. The copper increases the strength but makes it subject to corrosion that causes the sheet of metal to thicken up and get spongy. 6061 is alloyed with zinc. It is resistant like pure aluminum but as strong as 2024. The strength differential of 2024 vs 6061 is that for the same strength given by the use of 2024 alclad, 18% more aluminum sheeting would be required using 6061. Using the stronger material for the same mass is the best choice. Cessnas and Pipers are built from 2024.
Corrosion is ever with airplanes and us. It is a part of aging. Preventive methods have improved but given the opportunity corrosion always wins. If the aircraft environment contains moisture, oxygen, carbon dioxide, hydrogen sulfide, salts, fungus, slime, chlorine, and high temperatures corrosion is going to be a problem. Corrosion will etch a surface and make it dull. Localized corrosion will pit a metal surface. Where two different metals are alloyed we can get intergranular corrosion stress areas. Filiform corrosion occurs beneath paint and will produce a blister where the surface has been poorly prepared in its worse form it is called exfoliation. under exfoliation the metal literally comes apart in layers. Galvanic corrosion occurs where dissimilar metals meet, as may occur around a rivet. The bending of a piece of metal may cause an area of stress corrosion. One type of metal corrosion also occurs.
Skin cracks, corrosion, and loose rivets need to be sought below the aircraft. Working rivets show gray streaks of aluminum dust. Corrosion is an electrochemical process that destroys metal. Corrosion usually requires contact between differing metals but can occur between similar metals if moisture is allowed to accumulate. Keeping moisture out prevents corrosion. Prevention, detection, and elimination are required. Rivets are color-coded to limit use where galvanic corrosion is likely to occur. Galvanic corrosion is an exchange of electrons between dissimilar metals but it can occur between differing alloys.
Fretting is a combination of fatigue and corrosion failure. It occurs when two surfaces are vibrating together when aircraft is in use. These movements are usually quite small with localized damage and often lead to cracks and failure. Fretting appears as gray dust or streaks in the vicinity of rivets or Dutz fasteners. Improper cleaning or repair can accelerate fretting damage. Shot peening is often used to slow damage that occurs in heat treatable aluminum alloys. Leaving grease layers on components can serve as protection against fretting.
Corrosion is aircraft cancer. It is often concealed by a seam, joint or paint. Chemical corrosion comes from the atmosphere or applied cleaners containing metallic salts. Once begun, its growth rate increases. Corrosion begins to form when the oxides, sulfates, or hydroxides formed from moisture take the place of metal. Corrosion is a chemical change. In time corrosion spreads and reduces the metal strength to zero and will cause blistering of any paint covering. Corrosion forms in crevices, welds (engine mounts). Smooth surfaces resist corrosion.
Uniform corrosion covers a wide area and occurs slowly. Filiform corrosion is uniform corrosion that causes bubbles beneath pain. concentrated corrosion is usually concealed in lap joints that such that allow moisture to intrude. Pitting is a type that grows from when paint or preventive means have been misapplied. When this occurs between two surfaces it is called fretting.
Sealing the surface or sealing an adjoining surface can halt corrosion. Cadium is often used as such a sealant. Surface oxidation makes a seal over an aluminum surface. Paint is most common sealant. Frequent flying is perhaps the overall best preventative.
Inspection for corrosion is simple. Visually inspect for grayish-white powder on aluminum and red deposits on steel. Landing gear wells are vulnerable due to moisture on wet runways. The best protection is shelter. The worst location is coastal regions or big cities. Corrosion can occur at any time, place, or climate. A product knows as Boeshield is used to protect along with ACF-50 or Corrosion-X. Coastal aircraft should be treated annually. See FAA AC 43-4A.
Where pressure exists a rigid line is better except when flexing is likely to occur. Lines are designed to carry fluids or gases of low, medium, and high pressure. Damage to lines occurs normally through aging or exposure to corrosives or oxidation. Misdirected lines, poor maintenance practices, and chafing accelerate the process.
Most of the lines are routed so that ordinary pre-flight is unable to catch anything but the obvious. 100 hour and annual inspections are supposed to detect chafing, leaks, cracks, broken braiding, twists, and kinks before they cause accidents. Stiffness and damage to the cloth cover indicate prefailure of hoses.
It is good aviation practice to change all lines at a minimum of every five years regardless on condition. Changing all hoses every few years is cheap safety insurance. More often may be required where abuse has occurred. Hoses should be changed at engine overhaul. Fuel lines should have fire resistant covers installed.
Aircraft windows rank third in aircraft maintenance costs. Must of this is due to improper cleaning or protection from the elements. Repair may require use of a pressure chamber. Most damage comes from inside the cockpit due to metallic contact. Another major source of windshield and window damage is the reflected heat from interior heat shields that protect the interior and cook the plastic windows.
Damage consists of crazing, scratches, yellowing, delamination, milkiness, and cracking. It is better to polish, stop drill, cover, and repair a plastic window early than late. Repair can be made at less than 50% of replacement cost.
Works from engine oil pressure through an electrical pressure switch and keeps time based on hourly operation time in 6 minute intervals. Hobbs is the manufacturer's name for the hourmeter. The Hobbs meter is an electric clock keeps time about 10 to 20% faster (more) than does the tachometer. This is because the tach counts the number of times the propeller turns. The tachometer hour is based on 2400 rpm for one hour. The time during start, taxi and flight training operations usually are at much lower rpm. You are expected to write both the tachometer and Hobbs time in the time sheet so that an instrument failure can be quickly detected. When the engine runs the Hobbs meter runs.
The Stall warner is placed on the leading edge of the left wing for a purpose. The left wing is most likely to stall due to insufficient right rudder application. There are several different types of stall warners. They are activated by the low-pressure (suction) airflow that occurs on the leading edge of the wing at high angles of attack. The electric vane types can only be checked with the master on. First covering the hole with a cloth and using the mouth to gently suck can check the suction type. Under no circumstances should you blow. The horn has several sounds from a whimper to a raucous squawk. The volume increases and the pitch lowers as the stall gets closer. There is usually a 10-knot speed difference between the initial stall sound and the actual occurrence of the stall.
Va varies with the weight of the aircraft. Control coordination assures that the stall warner will go off before the stall. Normal category stall horns must activate 10 knots prior to stall; aerobatic 5 knots.
Spinners may have no authorized repair procedures. Spinners must be balanced or centrifugal forces can cause it to shatter or at best cause excessive vibration. Some aircraft are certified with the spinner as a requirement to meet cooling specifications. the most common cause of spinner damage is having someone move the aircraft by pushing on the spinner. I once met a pilot pushing on the spinner of 56K. I asked him why and his reply was that his checkout instructor told him never to touch the propeller. Spinners should always be checked for cracks, loose bolts or 'working' rivets. A defective spinner makes an aircraft unairworthy.
If there is an expectation of possible precipitation the pitot heat should be checked for operation during the preflight. It should be used on prior to entering any precipitation so that it can get warm before it is needed. Pitot heat is an ice preventive not anti-ice. A heater coil around the pitot air-intake will warm air the airspeed indicator and prevent the formation of ice. If not applied a pitot blockage can cause airspeed to drop to zero. A properly operating airspeed indicator measures ram air pressure against static air pressure. In conditions than lead to a blocked pitot it is important to know your aircraft performance and appropriate power settings without an airspeed indicator. A blocked pitot can also show an increase in airspeed as altitude is gained because it acts as an altimeter. The pitot should be checked for IFR or rainy operations as part of the preflight. On some aircraft (older C-182) the pitot heat also heats the stall warner. Named after a French physicist/dentist
On a recent local ferry flight I found I had no indicated airspeed at a point too late to abort the takeoff. At a few hundred feet the airspeed began to function. I believe that during a three day stop that ice had accumulated in the pitot tube. Next time that it appears such ice is possible I will turn on pitot heat during taxi and even activate alternate air to meet the possibility of the static hole being frozen.
The cabin heater is obtained from the same shroud around the exhaust system that provides carburetor heat. Like the carburetor heat the heat control is a diverter that allows selected amounts of air passing over the heater muff to enter the cockpit. The outside temperature, the engine temperature and the efficiency of the ducting also affect the amount of heat. Cabin heat can be maintained during descents by running the engine at reduced power.
If the exhaust system should leak carbon monoxide (CO) into the heater muff it could enter the cabin even without cabin heat on. With cabin heat on the problem and effect would be compounded. CO can enter the cabin through openings in the firewall or other openings. If you should smell the engine odor in the cabin, immediately let fresh outside air in and have the system checked for CO as the first opportunity. Carbon monoxide detectors have a 3-month life and should be replaced frequently.
During preflight check all air intakes and ducts that can be made visible. When the shroud heat is not used in the cabin it is available as carburetor heat and serves to cool engine parts by removing engine heat. Heater and exhaust parts are going to have a longer life if you avoid shock cooling of the engine and its parts.
Cryogenic oxygen is make by compressing air during which process all carbon dioxide and water are removed. The air is then cooled and liquefied to -200 C and gases other than oxygen are distilled out. What remains is oxygen that is 99% purse with less than 4 parts per million of other elements. Any contamination is unlikely to occur in manufacture. Problems tend to arise at the user level.
At altitude, you are under physiological stress over and above all the other stresses of flying. Hypoxia gives you that 'good' feeling that may be accompanies by dizziness, headache, sweat, vision problems, and fatigue. The situation is even worse at night. You lose 24% of your vision capability at 8000' and 50 % at 12,000. Only oxygen can give you normal vision.
Aviation grade oxygen is not supposed to have as much moisture as medical oxygen but I have read that they are very much the same and come from the same production system. Only in freezing conditions should this difference be considered a problem.
One oxygen system, the continuous flow is good to 25,000'. The system has a cylinder, a regulator, and individual re-breather masks. The pure oxygen is mixed with the last breath exhaled. The mask used determines the oxygen mix.
The diluter-demand system is very much the same but the mask has its own regulator. The pilot can adjust the percent of oxygen being used. The mask is more efficient and fits tighter.
--Rigging of ailerons backwards can result in reverse control
unless safety checked by the 'thumbs-up' control check.
--Loose objects in cockpit are common cause of jammed controls.
--Full flaps stuck down can be caused by electrical failure. Aircraft
can be flown under such conditions but only very
slowly and carefully.
--Wiggle elevators to feel looseness of hinge brackets.
--Control yoke failures of Cessnas make 100-hour inspections necessary.
--A loud pop in the control system is usually indicative of a
cable failure.
Paint
Paint provides airplanes with appearance and protection. FAR
Part 43 considers paint as maintenance. As a minor repair
paint must be signed off by the person doing the painting in the
aircraft logbook. Rebalance of flight controls may be a
consideration after painting is completed. If the original paint
is removed and the plane repainted no weight and balance
entries are required.
The quality of the paint job depends on the preparation. Chemical
stripping is traditional but is having environmental
problems. Media blasting using plastic beads both clean and remove
surface corrosion while they roughen the surface for
better paint adhesion. Traditional aircraft paint jobs were primed
after stripping with zinc chromate before being sprayed
with synthetic enamel, which cures, by oxidation. Aircraft come
from the factory with acrylic lacquer because it is quick
and easy when applied over a two-part wash primer. Polyurethane
is a two-part application that cures over a two-epoxy
primer. Polyurethane dries with a 'wet' look. It is the most durable
of all paint finishes.
Wing-walks, steps and some other special places require specialty
paints are available where needed. Low pressure
spraying is beginning to replace high pressures used in the past.
All paint is helped when kept clean. Aircraft quality
waxing is good for all aircraft surfaces and it makes for good
pilot exercise.
Pilot
Induced Oscillations
This is aircraft movement that are either initiated or increased
because of pilot response lag due to sensory perception
and response delays. With experience a pilot can inhibit his behavior
to reduce the oscillations. The classic situation is
when a pilot lands nose-wheel first and has his reactions accentuated
by the nose-strut and yoke movements.
Propeller
The propeller has the same capacity to kill as does the famous
'unloaded' gun. The most dangerous situation is the
malfunctioning magneto switch. This is where the key can be removed
from any position. In some cases the magneto
switch fails to ground the P-lead or the P-lead is broken. Some
'dieseling' can occur if the spark plugs are badly fouled.
A propeller that happens to be at a critical firing point can
be fired by just the wind. It has happened.
Items:
1. Always walk around propellers.
2. Move the propeller backwards, if at all.
3. Never curl your fingers around the blade when moving.
4. Don't push/pull by the propeller.
5. Don't hand prop.
6. No pets or children allowed by propellers.
7. The magnetos are always ON.
As a metal, aluminum is very intolerant of abuse. Any nick that
you can catch with your fingernail is a potential stress riser
and breaking point of aluminum. All nicks should be removed by
a qualified mechanic. Every annual inspection and
100-hour must include approval of the propeller for return to
service.
Even minor repairs must be made by a mechanic. Major problems
require removal and repair by a certified propeller
repair facility. Internal damage to propellers can only detected
by removal and electronic analysis. While there is no
FAA requirement, manufacturers recommend a 2000-hour re-conditioning.
Any change is pitch or length is capable
of changing the vibratory characteristics and cause unanticipated
failures.
Propeller care:
1. Minimum rpm over unimproved surfaces. Keep it moving if possible.
2. Start up over pavement or surface free of lose objects.
3. Make frequent visual inspections.
Oversquare
Constant Speed Propeller Operation
One analogy used in this type of operation is related to gearshift
operation in an automobile. With an over square setting of the
manifold pressure in inches at 25 and an rpm of 2200 you are
effectively trying to climb a hill in overdrive. You can't hear
pinging in an airplane.
Using
Your Non-flight Instruments
The health of your engine is reflected in the oil pressure,
oil temperature, fuel pressure and cylinder head temperature instruments.
Green is in the normal operating range; anything else should get
your attention. Any wavering or near the edge indications need
A&P attention.
At any loss of oil pressure, reduce power. Continental engines
take oil pressure measurements from the below the pump point used
by Lycoming. It is because of these different pressure points
that Lycomings tend to have higher pressure reading than Continentals.
If your aircraft has a thermocouple oil temperature gauge, temperature
fluctuation is probably gauge error.
Likewise, a low pressure without a high temperature is usually
an instrument problem.
High temperatures can be the result to too much oil as well as too little. Low octane fuel can cause higher operational temperatures. Inadequate airflow over the cooling vanes of the cylinders will immediately cause high cylinder temperatures to be followed by hot oil readings.
The engine tachometer may be mechanical or electric to count the propeller revolutions per hour. The numbers on the tach are used to determine required maintenance but not hours of actual operation. Tachometers can have errors in readings that require adjustment. Running up in a crosswind can cause the tach reading to vary.
Spark plugs are designed to be self-cleaning. Lead fouling occurs when engine internal temperatures are too low to completely vaporize the lead additives in the fuel. At some point small balls of lead can short out the spark plug. This shorting results in rough engine operation. The lead can be removed in most cases by increasing engine speed while leaning the mixture to raise the internal engine temperature sufficiently to vaporize the lead. Unleaded fuel can leave additive deposits on the lower plugs as well but these may be from difficult to impossible to remove by leaning. Oil fouling will leave the plugs wet. This fouling is caused by oil leaking past the rings.
Fuel pumps come in several types. Only a few models of high-wing
aircraft have fuel pumps since gravity can do the job unless the
aircraft is capable of an extremely high climb angle.
A fuel line break on carbonated aircraft may be indicated by lost
pressure restored by use of the fuel pump. This could mean that
you are spraying fuel throughout the engine compartment. Shut
off the fuel supply immediately. Absence of fuel is quickly shown
by the fluctuations of the fuel pressure gauge. I fuel line leak
exists if there is a loss of power and drop in fuel-pressure.
Fuel-injected pressure gauges are really fuel flow indicators.
A carburetor float may stick and flood the engine with sufficient fuel to make it stop. I had this happen once at low altitude. I pulled the mixture and the engine restarted. Years later I learned that this is the appropriate procedure. Worked for me.
The manifold gauge is an aneroid barometer that measures airflow into the engine. At full power the pressure will approach the ambient air pressure. A broken gauge or line will cause serious erratic engine performance.
The Exhaust Gas Temperature gauge is a thermocouple attached to one or more cylinders that will give a reading of temperatures in the exhaust system. These temperatures can be used as a measure of engine fuel efficiency. If a cylinder has a fouled plug of stuck exhaust valve the EGT readout will tell you.
Angles
Incidence is the angle from the horizontal fuselage that the
wing is mounted either directly or by strut.
Decalage is the angle of placement of the horizontal stabilizer measured as the angular difference from that of the placement of the wing. There is usually a download on the horizontal stabilizer that counters the weight of the engine forward of the center of gravity. Stall the horizontal stabilizer and the nose drops. The engine or rudder of airplanes may be set at an angle to offset the left turning tendency of the aircraft due to the engine power or propeller thrust.
Stability
Of the three axes, it is the longitudinal or roll axis that
is the least stable. Your ability to turn the aircraft easily
depends on this lateral instability. The aircraft resists the
initial input of the ailerons and then will continue with little
or no resistance. This lack of resistance is because the outside
wing is moving faster and if the turn is to the left the power
facilitates the turn even more. Unplanned turns tend to be more
to the left than to the right. If the wings have dihedral the
turn is somewhat self-correcting and the aircraft will tend to
level itself. The Navion comes to mind as a very stable platform
for instrument flying.
The three axies of the aircraft are not equally stable. The pitch axis has a trim control that lets the pilot adjust the pitch stability for a desired flight condition. The vertical axis has a trim control that allows the pilot to relax on the rudder. However, it is the roll axis that is usually without such a control with some exceptions.
The roll axis or lateral axis is not stable because the pilot
needs this instablity to maneuver the aircraft. We can let go
of the yoke in pitch and yaw for a length of time. Try the same
thing with the bank and subtle differences arise. The ailerons
resist the initial change, then accept it and then maintain their
new position. That is the new position is maintained until the
overbanking tendency takes over. The tendency to roll on over
is caused by the outside wing moving faster in the turn and the
propeller's slip-stream hits the rising wing the most. Flaps increase
this effect.
Countering these over-banking effects we have dihedral. Dihedral
is the up slope of the wing from the wing-root to the tip. The
shape of the wind and its sweep also make a difference. Low-wing
aircraft have more dihedral than high wing aircraft. The effect
of dihedral and wing shape will vary with the power and pitch
attitude of the aircraft.
The conflict between the instability and stability of the aircraft explains why the aircraft can maneuver and will hold one position only for a few moments. One of the roll stability demonstrations I use with students is to put the aircraft into a 30-degree bank and put in anywhere from 1/3 to 1/2 turn of trim and let go. The aircraft will perform a turn that can be held with just light touches of rudder. The usual design of light aircraft is to make the 30-degree bank more stable than any other bank. Less than 30-degrees bank and the aircraft will strive to level off. More than 30-degrees and the aircraft will eventually roll over.
Flap
chafe caps.
A row of small (about 3/8 inch) holes running from the inboard
edge to the outboard edge, and located just aft of the
inspection covers located by the leading >edge of the flap.
There are 12 on the right wing and 14 on the left >wing. Each
hole has a small plug (or cap) installed. They are to prevent
metal to metal chaffing which wears through the metal. The
plastic comes in between the flap and the flap well in the wing
and prevents metal to metal contact and wear.
Static
Wicks
Static wicks are the five inch plastic covered wires the extend
from the trailing edges of selected aircraft flying surfaces.
The function of a static wick is to allow removal of static electricity
from the plane. Static electricity accumulates on the
aircraft as it flies below a charged cloud, precipitation or dust.
A build up of this static electricity will affect your radio
reception or transmission as well as the ADF and other avionics.
The problem can appear as 'white noise' or hissing static. The placement of the wicks and number of wicks is essential to correct function. A broken wick should be replaced since it could cause the a receiver to become desensitized. Aircraft flown in IFR conditions should have wicks.
Window
Care
…Depth of ;cracks can be measured.
…Pledge works but must be applied often.
…Never use paper to wipe windows.
…Pilots are allowed to cut and fit side windows.
…Thicker windows cut sound.
…There are kits for refinishing.
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