Page b4 Accessories
Wing Theories and Accessories
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Contents:
Wing; ...Controls and What They Do; ...Horizontal Tail Surfaces; ...Rudder; ...Flying with rudder; ...Frise Aileron; ...Latches; ...Rig; ...Spiral Stability; ...Aircraft Category; ...Lifting Surfaces; ...Wing Loading; ...Power Loading; ...Parasitic Drag; ...Induced Drag; ...Boundary Layer; ...Control Failure; ...Cables; ...Corrosion and Skin Condition; ...Hoses and Lines; ...Plastic Windows; ...Hobbs Meter; ...Stall Warner; ...Spinner; ...Pitot Heat; ...Cabin heat; ...Oxygen; ...Maintenance failures;
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 downwash whatsoever. The downwash 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
Chord line
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 empenage. A hand-adjustable trim tab or a trim adjustment wheel can be used to relieve rudder pressure.
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.
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.
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° 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° 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° 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.
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.
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.
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.
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.
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.
Pilots Operating Handbook
Return to whittsflying Home Page
Contents:
.Beyond book flying; ...Performance
at density altitudes, ...Emergency;
...Shoulder harness
My fortune cookie 7/24/98
"To teach is to learn twice."
Saying
Do not rely upon everything in print about aviation. Some writers are doers and some are talkers. Watch out for the talkers.
What does it take to make a good pilot? Is there a perfect pilot? Does it mean going by the book? Those who write the 'book' don't fly. They are Legal beagles trying to protect asses. They know numbers and write them without feeling.
The 'book' is in the heart. Flying is not in the book; not in the checklist. The true flying 'book' is written each day on each flight. The true flying book is judgment-knowing what to do and when. More importantly, what NOT to do.
A pilot never thinks of flying as taking a chance, taking risks. The pilot is aware of his total environment. When he's not aware, he asks for help. Knowing when and where to get help is the pilot's judgment support system. A good pilot studies accidents. He learns what can go wrong. You learn from the accident experience of others two basic things.
-- There are accidents beyond the control of pilots.
--The vast majority are pilot error whis is a controllable factor.
What is pilot error? It has very little to do with reflexes. Pilot error is 95% a defect in pilot judgment. The FARs and POH restrrictions on performance are always there setting the margins of safety. Every so often a pilot must fly to the shoulder of those margins. This means flying to the edges of altitude and airspeed.
Just as in flying tgere is more to weather than numbers; a pilot must have a sense of pattern, knowing when enough is enough. Flying, turning back, getting help are all a part of this sense of pattern.
Performance at density altitudes
The POH is not reliable as a source of density altitude aircraft performance. Pilots must consider all the variables with up to 50% safety margin above those of the POH. The POH was accurate only at the moment it was in pre-draft form.
All POH glide distances should be figured with an additional 1000' cushion to allow for pattern turns. A FAA obstacle will increase required landing distance by 120%. In an emergency you must do in one try what it took a skilled pilot several tries to accomplish.
Wings use true airspeed not indicated airspeed to get actual climb rate. Indicated airspeed decreases with altitude while true airspeed increases with altitude. The cruise performance charts is based upon pressure altitude, leaning and gross weight. The greatest variance in POH performance figures will be in fuel consumption. Pilots are well advised to leave a 10% margin of safety from the book figures.
Aircraft are designed to channel impact into structure that will collapse while keeping the cockpit in one piece. The human body can withstand up to 16-Gs if the duration is of the worst impact less than 1/10 of a second. Most aircraft accidents are below these limits. Most serious injuries and fatalities are caused by secondary impact of the victim on the interior cockpit. It is not a bad idea to carry a large pillow. Shoulder harness exists in less than 60% of airplanes and the use of these is less than 75%. Every 5% improvement in use rate will save 20 lives a year. Having the belt and harness made as one would solve the problem.
Charts and more
Return to whittsflying Home Page
Contents:
VFR Charts; ...Runway
lights; ...All Available Information;
...Aviation Charts; ...Reading
the Sectional;
...VOR box; ...World
Aeronautical Charts (WAC); ...Class Bravo
Airspace; ...Phonetic Alphabet and Time
Zones;
...Its about Miles and How they came to
be; ...It's about time; ...Way
to Go;
NOAA Aeronautical Chart User's Guide is a source of chart terms and symbols with charting symbols organized by chart type. Available from the Government printing office Golden Gate Ave in downtown S. F. at 1-800/638-8972. State charts are obtained from the Aviation Dept. from each state. Years ago I wrote to all the states on a route across the country and back. I received 37 pounds of charts, guides, and information. Do it.
VFR area charts (TAC) are scaled 1:250,000 or 3.5 nm per inch. Sectional charts are 1:500,000 or 7 nm per inch. WAC charts are 1:1,000,000 or 14 nm per inch. Sectionals are replaced every 6 -months as are area charts. Where TACs occur in sectionals they are outlined in white. WACs do not carry airport communications information or Classes D or E airspace. MTRs are not shown either. TACs are used to clarify the separation of Classes B, C, and D airspaces.
To fly without a chart or an out-of-date chart is an FAR violation since you do not have all available information. Even IFR pilots should have VFR charts available. Every color, number and mark on a sectional is significant. I do not believe it is possible to know all the ramifications that exist on a sectional. Even keeping up with the changes is daunting. The more complex the area the more likely it is that there will be errors. Your flying proficiency is directly related to knowing your charts.
AIM 2-3-3 presents threshold stripes for IFR runways such that 4 stripes = 50', 6 = 75', 8 = 100', 12 = 150'16 = 200'. Touchdown zone marks are 500' from beginning of threshold lights. I50' long aiming point marks are 1000' from beginning of threshold lights. Edge lights are usually white but on IFR runway yellow exists on last 2000'. IFR centerline lights are red and white for the last 2000' and red for the last 1000'. Taxiway turnoff lights are now called taxiway leadoff lights and are alternating green and yellow from the runway centerline to the runway hold bar. The new obstruction lighting system is in the AIM 2-2-3
Land and hold short lights have pulsating white lights at the LAHSO point. The runway end lights are red toward the runway and green from the approach side. During low visibility stop-bar lights extend across the taxiway to warn of the hold short position they are called runway guard lights. Yellow clearance bar lights are at the holding position of some taxiways. An airport beacon with a green and two quick white flashes indicates a military airport. A beacon operating at a controlled airport during the daytime indicates that the airport is below VFR minimums either of visibility (3 miles) or a ceiling less than 1000'.
FAR 91.103 says, "Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This includes weather, fuel, alternates, plane performance, runway/airport information, and possible delays. Radio frequencies, ATC services, terrain, airspace, and local services are not in the FARs but belong in your "All Available Information" kit. Materials such as the AIM require that you have a subscription to remain current. The FBO AIM will not satisfy the AAI requirement. Materials are available for on site use at all ATC facilities.
First get your charts, a World Aeronautical Chart is good for planning long trips, a sectional set is required but not mentioned specifically in the FARs, a VFR Area chart is required by FAR if you plan to fly in, under, or over Class B airspace. The first planning step is to draw a course line on the WAC and then transfer it over to your Sectionals and Area Charts.
Using these course lines you are ready to locate any Special Use airspace along the route to note minimum altitudes, hours of operation, and areas where extra precautions may be advisable. Use the Airport/Facility Directory and any available airport guide to get enroute airport information to elaborate on the rather limited chart data. You could use 'Post-it's' but I prefer a black marker to give pattern altitudes and frequencies. This is a good time to get any special frequencies that are not normally available such as Center. You may need access to IFR charts for these as well as IFR approach/departure courses and altitudes. In low visibility conditions you must plan to avoid IFR routes.
All information from charts and publications may be out of date anywhere from thirteen days to six months. The accuracy of your information must be verified by getting all local and distant NOTAMs along the route. Local NOTAMS-L may not be available until you approach an area while airborne. NOTAMs are the latest valid information and may extend, cancel or replace any prior information that is printed.
While enroute listen to Flight Watch on 122.0 or even on the following frequencies that are intended for high altitude aircraft but are available as an option to a pilot who is flying in isolated areas such as behind the Sierras; 135.7 Oakland, 135.92 Seattle, 133.02 Salt Lake, and 135.9 Los Angeles. Many VORs have weather broadcasts where the VOR information box has a small black square in the corner. TWEBs and HIWAS may be broadcast over navaids.
It is not against the FARs to fly while having out-of-date
charts in the aircraft. You may even used them but if such use
should cause an accident or an FAR violation. An additional action
can be brought against you for
not having current charts.
The first charts were published in 1926 of the principle airways. They were long and narrow and extended only 40 miles to each side of the airway. 1 inch equaled 8 miles. (A sectional has 1 inch to 7.8914 miles). Water was colored blue, cities yellow, railroad black and highways white. Airports were red circles. Sea level land was dark green, at 1000' it became light green, at 2000' light brown, above 3000' darker brown. The charts were useful but so narrow that any diversion for weather could fly you off the map.
Open the San Francisco Sectional and locate the lower left corner that has 36° with 125° below and to the right. Now fold the chart so that only ocean is visible except at the upper right corner which shows Point Reyes. Leave the Legend to the right out flat as you not that the vertical line is not straight but has a slight curve. The bottom line is also curved, as you should note by the width of the white margins. Note the caution box below the 125 ° related to uncharted hazards below 200 feet.
The 36° line is the degrees of Northern Latitude it is parallel to the 37° line about 9 inches above. The top of the sectional goes slightly beyond the 40° line of latitude or 40th parallel. The space between every degree on the sectional is divided into 60 divisions and each division is a nautical mile. This is true only on the vertical lines. There are sixty divisions between the vertical lines but they vary in distance from 48 to 45 nautical miles due to the tapering of the distance toward to pole. You never measure distance on the horizontal lines of latitude.
Vertically between 36° and 37° there are divisions and subdivisions. Half way between every degree either vertically or horizontally there is a full line marking the thirty-minute (30')or halfway point between degrees. It is very easy to confuse a 30' line with a degree line. Degree lines will have their numbers to the lower left at every interior intersection. Horizontally each nautical mile is one-minute. There are sixty minutes in every degree. From the degree line every five degrees has a marking that extends farther to the left; every ten degrees has a marking extending farther both left and right. Use of these subdivision markings makes it easier to count degrees.
Go back to the lower left corner of the sectional. Count up the 125° line of west longitude or meridian five spaces. Mark this line and then repeat the process on the 124° meridian. Use a straight edge to connect the two points with a line. This Line is knows as the 36° 05' N. Go back to the left corner and count over on the 36° parallel for 15 spaces and mark the crosshatch. Go up to the 37° parallel and repeat the count and mark. Draw a vertical line between the two marks. This line is known as the 125° 15' W line of longitude or is it the 124° 45' W meridian. Which?
We have created a problem for ourselves. 36° 05' N worked because we were counting toward 37°. By counting from 125° to the right we may tend to use the 15 count when it is actually the 45' point from 124°. I deliberately tried to expose you to one of the most common errors in locating coordinates. You must always start your count for latitude from the bottom and the count for longitude from the right. The next most common error is in not using a long ruler to draw your lines. It is very easy to draw a line between two points that are not going to give a parallel line.
Where these two lines cross is a point that is unique in the world. 36° 05' N-124° 45' W. Every place on the earth can be so identified and located. Locate Mt. Whitney near Death Valley and see what coordinates you get. Check with the coordinates given on the chart legend. Practice at least ten different locations by giving yourself coordinates that would be located on the San Francisco Sectional. Next mark at least ten airports on both sides of the sectional and determine the coordinates.
To locate a particular airport for which you do not have a designator. You can put the geographical coordinates into your Loran or GPS and the navaids will work just as well. Fifteen years ago I did this while going to Medford, Oregon from the Nut Tree. Crossing the threshold the Loran indicated 1/2 mile to airport center. (I taught LORAN in WWII)
The quadrangles bounded by the ticked lines are but 1/4 of
the area in a degree square. It isn't a square or a rectangle
but it does measure 60' to a side. Every quadrangle is 30 nautical
miles high but the width is quite variable. Call them wreckedangles?
Each figure that has land has a highest known obstruction elevation.
The given figure is rounded upward to the next hundred and then
an additional hundred is added. Maximum elevation figures on a
sectional have a fudge factor to account for possible errors.
After rounding any elevation to the next highest hundred, another
hundred is added. In mountains an additional 300' is added. These
margins may only partially correct for altimeter setting errors.
You are required by FAR to have an altimeter setting from within
100 miles. The closer the setting location the better.
The sectional aeronautical chart is essential to all forms of
visual navigation. Your eyes use a comparison of land features
to chart features to determine how relationships compare. When
comparisons match, you know where you are.
A sectional is aligned to true north. The Lambert Conical Projection of the chart makes all straight lines very nearly the direction you fly before figuring in isogonic variation and deviation. This works very well when you know that the winds given by the FSS and Weather Bureau are also measured by direction from true north.
The lines of longitude and latitude on the sectional divide it into a series of wrecked-angles (sic) with 30 ticks marked on each side. Only the north-south ticks can be used for distance measuring since the lines of latitude are parallel. Each wrecked-angle has a Maximum Elevation Figure, which, within 100', tells the MSL altitude required to overfly all obstacles.
Within many wrecked-angles the topography is shown in eight colors which shade from green to dark brown to indicate altitude. Most chart symbols resemble earth features. Small roads are shown only when deemed useful for navigation. Fly with the chart open and pointed in the direction you are going. In each quarter of a degree depicted there is a maximum elevation figure. In most areas this figure is rounded to the next higher 100' but in mountainous areas it is rounded to the next higher 100' plus an additional 300'.
Airports are either magenta (uncontrolled) or blue (controlled). It is important that the pilot become totally familiar with the chart legend as it applies to information available at the airports and through the use of radios. Airspace depiction is shown by types of line/color combinations to cover Classes B, C, D, E, and G. It is illegal to fly without a current chart for the area.
The Hazardous In-flight Weather Advisory Service is broadcast over VORs that have a Small solid square in the lower right corner of the VOR information box.
Arcata, California VOR gives TWEBs or Transcribed Weather Broadcasts about route information, NOTAMs and special information. A solid circle around a white T in the upper left corner of the VOR box shows this ability.
The altitude of your transponder mated encoder is always based on 29.92 and computer adjusted for the ATC read-out. Nothing you do to your altimeter will make a difference in what ATC sees. Every new radar controller is required to confirm your cockpit altimeter setting to compare with his read-out.
World Aeronautical Charts (WAC)
WACs have half the scale of Sectional Charts so the price is cheaper for the area depicted. Class B and C airspace is only outlined without altitudes. Class D and Class E surface (CZ of non-tower) is not shown at all. Space limits have eliminated many obstacles, towns, and frequencies. Maximum elevation figures (MEF) cover 60 nautical mile wrecked angles (sic). WACs are best for fast airplanes or for long flight planning. (Required Practical Test Knowledge-frequent oral test question) WAC charts show MOAs but do not show MTRs. The width of a MTR can vary up to ten miles to each side. See AIM 3-41 +.
Expect to pay a landing fee if landing at a Class B airport. Wake turbulence and extensive taxiing to expensive parking is to be expected. If you do not have the rating and equipment for flying into Class B you can expect to hear from the FAA. FAR 91.129 gives the operational requirements. Most of the large Class B airports do not allow student operations. A student endorsement is required in those Class Bs that allow student operations. You cannot enter Class b unless your are given a clearance.
FAR 91.131 requires you to have an encoding transponder. Your transponder will warn TCAS equipped aircraft of your location and proximity. VFR aircraft are not required to have a VOR but you will be expected to abide by any headings and altitudes assigned regardless of your altitude and location. You are usually free to select your own route and altitude below Class B but you should advise ATC of any changes you Class C or D field that will give the same amenities at far less cost. At any unfamiliar airport you should request progressive taxi instructions. Prior to departures in underlying Class B airspace you will be given specific instructions as to direction and altitude restrictions. Readback all sucmake as they occur. FAR 91.117 limits speeds below Class B to 200 knots or slower. Speed in Class B has an upper limit of 250 knots.
I have yet to find a reason to fly into a Class B airport. There is always an underlyingh information and make sure that you understand what is expected.
Phonetic alphabet and Time Zones
In 1914 the U.S. Army adopted a phonetic alphabet but Spanish pronunciations created problem In 1927 a worldwide agreement of words and spelling was reached but some words were uncommon. In 1952 an International Civil Aviation Organization (ICAO) alphabet was made using Able, Baker, Charlie, Dog but it too had problems. The current alphabet was adopted in 1956.
Related to this 1996 version are the names of the time zones around the globe. Alpha time zone begins 7.5 degrees west of Greenwich, England and extends to 22.5 longitude westward. Each successive 15° of longitude is given a alphabetic name. Eastern time is named Echo and Pacific time s Hotel. Even during daylight savings time the names remain the same. All aviation time is referenced to Zulu.
Zulu time is relative to the sun, the exact same moment all over the world is recorded by clock time in Greenwich. Why Greenwich? In 1735 John Harrison, a carpenter designed an accurate chronometer. By knowing just when noon occurred in Greenwich with the chronometer, a navigator could use an astronomical table to determine his longitude.
Different Miles and How they Came to Be
Under the Roman Empire, Rome became the center of the western world. All roads led to Rome and all distances were measured from Rome. The distances were based upon one thousand Roman paces of the Roman soldier. A Roman pace is equal to two of our steps and very near 64 inches. The Latin for a thousand paces is 'mille passus'from which we derived the word mile.
Many different miles of differing length.haveexisted from the old London mile of eight furlongs. This was measured by German 'feet' but at the time of Queen Elizabeth a shorter foot was used giving a distance of 5280 feet. which is now the statute mile.
The first paths for ships were called Porotan Charts. These were lines drawn across the Mediterranean between the coastal ports. Where many of these lines crossed the mapmakers would draw wind roses. The wind rose initially varied but settled on the eight points. The predecessor to the compass rose and our eight-wind direction terms.
Thales of Miletus (640-546BC) made a gnomonic projection (use of shadows) of the region where he lived. Hipparchus in the 2nd century BC had used sterographic (showing heights) and orthographic projections (perspective). Eratosthenes in 3rd century BC calculated the size of the earth circumference to be 24,000 miles. He developed a 16 point wind rose and use of 'degree". He also wrote a description of known world.
Ptolemy, a 2nd century Greek, made a world map and made a world size error when he calculated size of world's circumference to be only 18,000 miles. Jean Picard did not correct this until 1669, 200 years after Columbus. Eratosthenes' calculations had been lost to the western world. Ptolemy used the first conic projection plane map with the top as north. This made possible drawing of rhumb (one direction) lines from point to point on the globe. He devised the 60 minute and 60 second divisions of the 360 degrees in a circle. A mile at sea, on this world of Ptolemy, was essentially equal to a mile on the land. The length of a statute mile was 1000 (mille, from the Latin) Roman paces. A Roman pace is two of our steps. Each Roman road had occasional small obelisk statues placed to indicate the distance from Rome much as Mexico today does from Mexico City. Hence, statute miles.
A 1466 Chart of Nicolaus Germanus divided the degree into 60 equal spaces called miles. This was based upon an earth of 18,000 mile circumference and gave us a nautical mile the same length as a Roman statute mile. Other cartographers including Hipparchus and Mercator gave us a world with an overlying grid with numerical markings of longitude and latitude. Gerardus Mercator (Gerhard Kremer), Flemish, in 1569 drew world globe map with 180 degrees E/W longitude 0 to 90 N/S latitude. He made errors which were corrected by Edward Wright who published the computations required as "Meridional Parts" and made this knowledge universal. In combination, we now had a world, which could be mapped in degrees of longitude and latitude. Each degree of longitude had divisions of 60 miles equal to a statute mile and each mile was again divided into 60 units called minutes and each minute was again divided into 60 units called seconds.
This was the kind of map and scale used by Columbus. The navigators
of his time had not the timing device to make possible the exact
determination of longitude. The best 15th Century data available
to Columbus came from Ptolemy. The error by Ptolemy directly resulted
in Columbus' declaring that he had reached and was exploring India.
Columbus thought he had sailed through enough degrees of longitude
to reach India. He may well have, had the world been 18,000 statute
miles in circumference.
When the world was computed to be 24,000 statute miles in circumference
all the degrees and their divisions were longer and did not conform.
More accurate computation of the world's circumference kept changing
and finally came to 24,902 statute miles. The circumference of
the earth has always been measured as 21,600 nautical miles (360
degrees X 60 nautical miles per degree). However, the individual
nautical mile has ballooned by nearly a third through this recalculation
of the earth's size. The Nautical or Sea Mile is the length of
a minute of latitude. The U.S. Nautical Mile at one time was 6,080.27
feet. This figure was revised to 6,076.i feet/ This came to be
know as the International Nautical Mile. The British use the Admiralty
Mile of 6,080 feet. Some countries still use the 1929 International
Hydrographic Burea mile of 6,076.097 feet. The Geographical Mile
uses the Equator as a great circle and a minute mile is 6l,087.1
feet long. For many of the same reasons the U. S. has failed to
convert to metric, later cartographers decided to use statute
miles for land and the expanded nautical mile at sea.
Now we can see the background for the difference between nautical
and statute miles and Columbus' reasoning. We have Columbus sailing
around an earth at least 1/3 larger than he was led to believe.
Based on available knowledge Columbus was quite justified to assume
that he had actually reached and explored India.
For the navigator, it is very important that distance only be measured along the lines of longitude, which has evenly spaced tick marks throughout. The elongated orange peel appearance of the region between lines of longitude means that various latitude lines will have tick marks at differing intervals although always 60 ticks per degree. Only at the Equator do the tick marks correspond to the size of those along the lines of longitude.
Johann Henrich Lambert from Alsace devised the Lambert conformal conic projection in which the line you draw is the way you go. This is the charting used on aircraft. As with any flat map of a round surface it has areas of inaccuracy. Sectionals are most inaccurate (stretched) in the six inches at the top and bottom. The center ten inches of the sectional for 5 inches up to five inches down from center is somewhat contracted in size.
A sailing ship's speed over a nautical a mile was, historically, measured by means of a knotted (knots) rope tied to a log. A sand filled timing glass would be used to measure the time from leaving the log dead (much as a dead man might appear) in the water (dead reckoning) and the number of evenly spaced knots passed along the rope. All of this would be recorded in the logbook. Since the chronometer was yet to be invented, sailors had no way to determine longitude except by this dead reckoning. Within crude limits, speed and compass indications could be used to determine estimated distance and estimated longitude. Magellan in 1519 had access to charts, globe, theodolites, quadrants, compasses, magnetic needles, hourglasses, and timepieces. He was unable to determine exact longitude.
An 18th Century a chronometer (weighed over 36 pounds) was
first used to get longitude. A chronometer differs from a clock
or watch because it has a temperature adjustment for greater accuracy.
Captain Cook in 1768 had three different clocks for his voyage.
In 1779 he sailed with 4 chronometers and a nautical almanac which
enabled him to determine longitude. The very first effort to make
a calculator was financed by the British to make the making of
the nautical almanac easier. The effort was stopped when the mechanical
calculator was only a year from being completed. The original
design was completed in 1991 and found to work accurately.
Interesting to speculate where the world would be had it been
completed in the 1700s. 30 years ago I knew a pharmacist who spent
his evenings at an all-night pharmacy working out prime numbers
on rolls of butcher paper with a pencil. Did we miss a 300-year
head start on computers by so little?
_______________________________________________________________________
Revolutions per minute - rpm
First counted by paddle wheel ship captains._____________________
The ancients recognized the pole star as being a constant reference for determining direction. The Norsemen in the 11th century used a needle of magnetic iron inserted in a straw and floated on water to point to the pole star. Petrus Peregrinus de Maricourt invented the pivoted floating compass with lubberline and sight for bearing. The modern compass is little more than one hundred years old.
The compass card, due to wind rose origins is older than the magnetic needle. Names of the cardinal compass points are from the ancient terms for wind direction.
Variation was understood by 1800 as a problem. Edmond Halley at end of 17th century mapped lines of variation and drew isogonic lines (lines of variation) on his maps. George Graham showed that variation was subject to diurnal (seasonal) changes with variation being less in winter.
John Smith wrote about deviation in 1627 by John Smith. He saw it as a problem encountered through use of metal nails in his compass box. Captain. Mathew Flinders in 1801-2 found way to correct by use of "Flinder's Bars as did Lord Kelvin through use of Kelvin spheres. Placement of soft iron spheres at sides of compass could be used to correct deviation.
The development of the gyro compass began in 1851 when Leon Foucault used suspended cannon shot on a long wire pendulum to show the rotation of the earth as well as the inertia of the free swinging ball. By 1852 he had created the gyroscope but had trouble applying continuous power. By 1900 the electric gyroscope was invented by both Elmer A. Sperry and Anschutz-Kampfe of Germany. By 1911 gyro compasses were in use soon to be followed by gyro repeaters (selysn(sp) units) and gyro pilots.
Controlled airports
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Controlled Airports....Class D Airport Patterns and Procedures; ...
I like to think that avoiding airports where you lack competence is a sign of good judgment. I have never flown into SFO. I've never had a reason and haven't looked for one. I have been into Boston's Logan but I did not feel welcome. Meigs field in Chicago was an unhappy experience because of the management. They had me park in a jet tiedown at $60 per night in a C-150 after they delayed giving me fuel until after closing time. All, very deliberate.
The basic rule is that you should not fly into a situation for which you are neither knowledgeable nor trained. Training would teach you to study the airport diagrams, checkpoints for call-up, arrival routes, and post-landing procedures. Frequencies including those of clearance delivery, the most likely unfamiliar procedure, are organized in anticipated order. You may want to rehearse or even write down what you expect to say. Expect to copy some sort of arrival and departure clearance procedure with a read-back for an accuracy check. Your ability to listen is going to be just as important as your talking. Small aircraft are an endangered species around large aircraft.
A week ago, 10-10-98, I flew into Santa Ana's John Wayne Airport
in the L.A. Basin. Cloud altitudes and poor visibility and unfamiliarity
made the use of ATC assistance very necessary. We found that one
one runway
At Santa Ana was in use. The G. A. runway was under repair. IFR
would have meant extensive delays and routing.
By opting for a VFR arrival we had more pilot control of our options. Our First choice was to remain on top of the clouds at 4,500 as long as we could. The limiting factor of this decision was the need for an area large enough for a VFR descent below the clouds. We found and used such a hole some 15 miles from the airport. In addition to vectors we used GPS to retain our situational awareness.
As we neared the airport we were told to circle some four miles to the north while awaiting instructions. After two or three turns we were Given a heading and told to fly directly over the airport and tower to make a left downwind to the runway. We were filtered in between two airliners for our landing.
Two days later our departure was arranged quite contrary to
our VFR requests. We were told to climb to 8500 and proceed VFR
through the Class B airspace on a 310° heading. We had
requested VFR through the
corridor at 4500. The higher altitude made us fly into stronger
headwinds but avoided much heavy traffic both in weight and numbers.
As we departed Class B we descended and turned to get more
favorable winds. Several years previously we had been forced to
fly completely around the Class B airspace on an IFR flight to
the same destination.
Interesting how choices can make such a large difference.
Don't expect a welcome mat if you're flying a C-150. An arrival at a major airport of a C-150 could back up traffic for miles. Coming into Class B airspace requires a clearance, an encoding altimeter and communications equipment. Be sure you know the procedure for making transponder code changes as well as the proper terminology. You are probably VFR so you must remain clear of clouds and have three mile flight visibility. Your greatest aircraft hazard is from behind.
Follow all instructions as precisely as you can. If in doubt,
get clarification. When you need help ask for it. Don't loiter.
Such instructions as 'hold short' must be read back. As a stranger,
it might be wiser to read back everything every time. Expect to
hear changes in your instructions. Keep ATC advised of your flight
conditions. Allow plenty of room so ATC will have time to make
adjustments. Course changes are usually
easier for ATC to make than altitude changes.
Class D Airport
Patterns and Procedures
Except for traffic conditions where ATC (Air Traffic Control)
has override powers, airport pattern directions, and altitudes
are decided by local jurisdictions.
Class-D airport departures
From a single runway there are nine standard departures that may
be requested if there are no special considerations. If departures
can be made from both ends then we have a total of eighteen. If
left traffic is standard there are two of these eighteen that
need not be requested. They are the two left standard (45 degree)
departures, one from each end.
1. If no request is made you are expected to make a left standard departure. The tower may ask for confirmation of as standard departure just to make sure.
From any runway you can request a...
· straight out
· left crosswind
· left downwind
· left 270
· right standard
· right crosswind
· right downwind
· right 270
...on course (destination) may be appended to any of these. You can optionally just say request left/right turn on course (destination) The advantage of naming a destination is that other aircraft are given a more specific idea of the flight line you will be flying. A low visibility or weather related departure would be to request a climb in the pattern.
Typical call would be..."Podunk tower Cessna 1234X ready 32 request right 270 on course Lost Hills" No punctuation should be used in talking or writing airplane.
Class-D airport arrivals
To a single runway there are seven standard arrivals. There are
two non-standard arrivals that are relatively hazardous. If no
special considerations interfere any of the seven may be requested.
If the pattern direction is known a 45 degree entry into the pattern
need not be requested. However, the tower must be advised that
you will report right or left downwind. As a standard procedure,
except for the downwind entries, all other arrivals require a
two-mile report unless otherwise advised. The purpose of the report
is to allow the tower time to locate you and plan a safe sequence
for
your arrival.
--straight in
--right base
--right downwind
--right standard (45)
--left base
--left downwind
--left standard (45)
--direct entry to left downwind (not recommended)
--direct entry to right downwind (not recommended)
All of these can be modified by pilot request or ATC suggestion. A modified entry may be at other than a precise number of degrees relative to the runway. I recently heard an aircraft over the airport request and be approved for an overhead arrival. Ask and you may receive.
A typical call might be..."Podunk tower Cessna 1234X the dump at 2100 with Alpha request right base 32 will report two-mile base" Again, no punctuation should be used when writing or talking airplane.
The standard 45 entry has some dimensions that can be used to standardize a landing approach. The ideal towered runway is about 5000', close to a mile. Entering on a 45 and aiming at the runway threshold and turning downwind at mid field would place the aircraft a half-mile from the runway and a half-mile from abeam the numbers. Flying from the numbers to the 'key position would be another half-mile. Base would be a half-mile as would the final. This gives the aircraft a two-mile landing procedure with the first half-mile for pre-landing procedures, the downwind extension for slowing, trimming and configuring the aircraft, the base leg for descent and setting the length of the final approach.
The two-mile reports for the straight in and base arrivals can be segmented much as the standard arrival and used to organize your landing procedures.
Two-mile reports
The two mile report should be 'measured' from the runway threshold.
the 'measuring can be done for the straight-in by using a known
site directly in line with the runway or by using a call that
says abeam (beside) a known site. The last recourse is to visualize
the runway flipped toward you two times. If you use GPS, you should
know the point on the airport used as its position and adjust
your GPS reading accordingly.
The two-mile base reports can be done much the same as the straight in except for the use of the runway flips. Your entry line should be aimed at a point anywhere from a quarter to a half-mile before the threshold.
There is an instance where the 45 entry and two-mile reports can and do present pilots with illusions that can affect their airport arrivals and landings. A pilot using the 45 entry at a runway of 3000' or less should plan to turn downwind abeam the departure end. Flying to midfield before turning will reduce all the flight segments to 1/4 mile. The best way to see this effect is to compare the pattern of a 5" drawing and a 3 inch drawing of a 45 entry. The best advice I have for flying a pattern at a small or unfamiliar small airport is to keep the downwind twice as far as you think you should and you will be about right.
Where parallel runways exist, any requested departure may be restricted by ATC until they authorize a turn for reasons of conflicting traffic. At any airport, a particular departure may by limited because of terrain, noise abatements, or local considerations where turns are only allowed after reaching a particular point or altitude. Every airport will usually have a place where the preferred or prohibited flight procedures are explained and/or illustrated.
Intersecting runways make possible restricted clearances to land. The restriction most often requires the pilot to land and hold short of the intersecting runway. A pilot should not accept such a clearance unless able to comply.