Aircraft General Knowledge (AGK)

The airframe (1)

The frame of a plane consists of several parts, which all make flying and steering in the air possible by various actions. I will describe all parts in English and Dutch:

• Wing - Vleugel -> The horizontal part which makes flying an aircraft possible in the first place by generating lift
• Aileron - Rolroer -> These are the parts at the end of the wings, making roll-turns (banking) possible. They are at the end of the wing due to force x moment
• Elevator - Hoogteroer -> This part makes going up and down in an aircraft possible
• Rudder - Richtingsroer -> This part at the end of the tail can move to change direction in flight and is being used to make small corrections
• Flaps - Landingskleppen -> These are parts on the wing which can be used in take-off and landings to fly at lower speeds nearby the ground. They extend to induce more drag, which equals a lower speed and they generate some lift
• Vertical stabilizer - Kielvlak -> This is the standing part of the tail of an airplane, stabilizing the airflow and makes the plane fly into one single direction
• Horizontal stabilizer - Stabilo -> This is the horizontal part of the tail of an airplane, stabilizing the airplane in horizontal flight

Aircraft construction

The aircraft itself can be constructed in several different ways. The most important thing here is the type of aircraft. Bush planes are very light and will be less likely to use heavy stainless steel.

• Monocoque: A construction method where the external skin of the aircraft carries almost all of the loads. There is little or no internal framework. It’s lightweight but can be less tolerant to damage, since the skin itself is the main structure.
  • Outside supports all forces
  • Comparable with a can of coke
• Semi-monocoque: A more common design in modern aircraft. The external skin still carries loads, but it’s reinforced by an internal structure (frames, stringers, bulkheads). This makes the structure stronger, more damage-tolerant, and easier to repair than pure monocoque.
  • Inside supports half of the forces and outside half of the forces
• Truss contruction: This method will support all forces on the inside of the plane. Here the outside could be any material, like leather or vinyl.
  • Inside supports all of the forces

The wings

We could have two types of wings:

• Cessna 172 has the wings above the cockpit: high-wing (hoogdekker)
  • This needs support of the wings which we call: braced wings
• Piper PA-28 tas the wings below the cockpit: low-wing (laagdekker)
  • This doesnt need support of the wings which we call: cantilever wing

Both of this types of planes have their pro’s and cons. A Cessna doesnt need a fuel pump, as gravity does its thing. Als we cannot see traffic above us very good in a Cessna, but not very good under us with a cantilever wing.

There are also planes which have a V shaped tail with a rudder and elevator combined. These types of tails are called a ruddervator.

Tires

We can have 2 types of tyres on arplanes:

• Tube-type: This type has an inside and outside tyre, just like your bicycle
  • More warmth
  • Higher chance of tire blowout
  • Contain slipmark
• Tubeless: This only has an outside tyre

Tyres can slip over the rim during landings, this is the reason maintenance does a little slipmarker on the tyre and rim. This is mostly red.

Hydraulic systems

Hydraulic means litteraly transfer using liquids (hydro). We can transfer different forces using liquids using this formula:

• Force = Pressure x Surface

This means, the less surface and the more pressure, the higher the force.

Liquids are a great way to transfer force, as fluids can not be compressed unlike air.

Brakes

Brakes are systems built on the axes of the airplane to brake it, to lose power. This process converts the kinetic energy of the plane into energy in the brakes, which is warmth. Brakes are mostly powered using hydraulics.

Icing

As we don’t want ice on our plane or in parts of the plane, we have ice-preventing systems as we know two different categories:

• Anti-icing: Systems that prevent ice from happening like windshield anti ice, engine anti-ice or the pitot heat
• De-icing: Systems that remove already built up, like rudder boots on the trailing edge of the wing

Both systems are being used to battle ice during flights.

Fire and smoke in the plane

There are situations that fire and smoke can happen in the cockpit. Let’s dive into the different scenarios.

Engine fire during start

During starting the engine, engine fire can happen. This is mostly because of overpriming the engine, having way too much excess fuel that ignites instantly. Also priming with the throttle which pumps fuel into the carberator, increases the chance of engine fire.

The actual procedure to follow during this situation is specific to your aircraft but the base is something like this:

• Continue cranking for 5–10 seconds to try to suck the flames into the engine

If engine starts:

• Parking brake set
• 1700 RPM
• Prepare seatbelts, doors, fire extinguisher
• Wait max. 2 minutes/120 seconds
• If fire continues:
  • Mixture cut‑off
  • Throttle full open
  • Fuel selector OFF
  • Ignition OFF
  • Master switch OFF

If engine does not start:

• Mixture cut‑off
• Throttle full open
• Continue cranking briefly
• Ignition OFF
• Master switch OFF
• Fuel selector OFF (if possible)
• Extinguish fire using any possible method

Smoke in the cockpit

Smoke can happen in the cockpit due to several causes:

• Short-circuit in the electrical system
  • Disable the complete electrical system and turn off electrical components one by one with the circuit breakers till you found the problem
• Engine fire
  • Mixture lean, disable fuel selector. If fire doesnt extinguish, then make a dive in the hope the fire will be put out because of the high airflow and disable Cabin Heat to prevent transition to cockpit
• Other parts on fire

To correctly battle these situations, we must first know what to do exactly in each situation. These are described in the POH of your aircraft.

Fire types and extinguishers

Maintaining a fire is done by having these three components:

• Fuel (flammable material)
• Oxygen
• High temperature

By taking away only one of these three components, the fire will extinguish. We have four types of fire with possible extinguish methods:

• A = All that can burn, wood, paper, textile, plastic etc
  • All types of extinguishers
• B = “Benzine” or oil
  • All types of extinguishers
• C = Gas
  • CO2 and Halon
• D = Metals, aluminum or magnesium
  • Halon
• F = Fat

Water based extinguishers are not that practical for electrical and type B fires. Water is heavier than fuel. Also, Halon extinguishers are very poisonous so good ventilation is needed when using these. This also counts for CO2 type extinguishers, which are generally not for closed environments.

The piston engine (2)

In planes, the most used engine type is a four-stroke (viertakt) gasoline engine. Four strokes means that the engine uses 4 strokes to complete the fuel burn process. The engine is obviously the most important part of getting the propellor to turn.

The engine has the following parts:

• Carberateur: A part of the engine which mixes fuel and air for the correct burn-mix.
• Inlaat: The part where a mix of fuel and air is going into the cilinder
• Inlaatklep: A gate which closes and opens momentarily between the verbrandingsruimte and the Inlaat,
• Uitlaat: The part where the burnt fuel rests are deported out of the engine and is connected to the main exhaust
• Uitlaatklep: A gate which closes and opens momentarily between the verbrandingsruimte and the Uitlaat
• Bougie: The part which makes the mix of air and fuel burn by using electrical sparks
• Nokkenas: This part is connected with gears to the Krukas and decides when the Inlaatklep and Uitlaatklep are being opened and closed. In a four-stroke engine, this happens at half the speed of the Krukas.
• Cilinder: This is a name for the whole burn-part of the cilinder
• Verbrandingsruimte: This is where the actual mix of fuel and air is happening
• Zuigerveren: Attached to the Zuiger and it’s purpose is to isolate the Verbrandingsruimte from the rest of the cilinder
• Zuiger: This is a part which is connected to the Krukas that does the actual motion for the Krukas to be turned.
• Drijfstang: This is the part connected to the Krukas and the Zuiger.
• Krukas: The krukas is a part there all dynamic force of the engine is linked with and at the end of this as, we have the propellor. In a car, here are the wheels connected.
• Carter:
• Krukkast: This is the central part of the engine, and is where the krukas and Nokkenas are located. At the underside of the Krukkast, we have a Carterpan which contains oil and “lagering” for the Krukas

Burning fuel in a 4 stroke engine is completed in 4 phases:

1. Inlaatslag (Intake)
2. Compressieslag (Compression
3. Arbeidsslag (Power)
4. Uitlaatslag (Exhaust)

Engine shapes

There are multiple types of motorshapes. In planes, the most used shapes are:

• Line engines
• Boxer engines (horizontally exposed)

Engine power units

The units which can be used to measure engine power are mostly indicated in Horse Power (HP/pk). This is a worldwide standard, but sometimes the actual measurement method is described. Sometimes BHP % is used in the POHs of the aircraft. The method to measure is a special installation connected to the crankshaft, and measuring the force needed.

We also have an indication of how long you may use full engine power. The indicator for maximum continious power is the maximum power you can use unlimited. Engine power is mostly indicated using Revolutions per Minute (RPM). In the cockpit we cannot read the actual power it delivers, only the RPM of the crank-shaft. The part which the engine powers and is connected to the propellor in front.

At bigger heights, like from 3000ft, we need to pull somewhat on the mixture handle to reduce the amount of fuel going into the engine. At bigger altitude, the process is more inefficient when putting too much fuel into the engine.

• Manifold pressure: Inlet pressure
• Brake horse power: The power the brakes of the plane can withstand.

The power of a piston engine depends on the air density. This is depending on the pressure, temperature and humidity. At a low air density

Turbo-engines are in 2 types:

• Altitude boosted: This type, the turbo always runs till big altitude to help the engine when horse power decreases
• Ground boosted: This is the most existing type of turbo engine and the turbo always runs to increase engine RPM. This works till the critical altitude.

How a turbo system works

A turbo system is basically a turbine and a compressor. The turbine is driven by the exhaust gasses and is connected through an axis with the compressor which is placed in the air inlet system. The compressor will increase the pressure of the air inlet, resulting in an increase in intake speed. This increases the motor-power. Turbine compressors rotate at a very high RPM, around 80.000 RPM to 100.000 RPM in some cases.

The schematic drawing of a turbine-compressor combination.

As a result of the compressed intake and the flow of hot exhaust gasses, the temperatures of a turbo will increase very high. Turbo’s can even be glowing red. Turbo engines therefore often have a intercooler, where inlet air is compressed and colled. This is similar to a radiator. Turbo engines also need some minutes of stationary running before shutting down to completely cool down.

A waste gate is a extra portion at the exhaust part where waste air can flow through in cases of having enough air. Some engines have a automatic waste gate function, in these type planes you can use full power on sea level.

Fuel System (3)

The fuel system and parts of aircraft are categorized into two categories:

• The fuel tanks with the fuel lines to the engine
• The induction system to merge the fuel with air where two types are possible

The fuel system can consist of the following possible parts:

• One or more fuel tanks conistsing tap-points with air vents amd cross-lines
• A fuel selector valve to select a specfiic tank or to open both or close both
• Fuel pumps
• Primer system

Fuel tanks are very often located in the wings, but can also be in the wingtips or fuselage parts.

The goal of the fuelsystem is to drive fuel to the carberator, where the fuel and air mixture is created before being ignited in the cylinders. If fuel tanks are located above the carberator, like on the Cessna 172, the fuel will flow due to gravity feed. We do not need fuel pomps in this case, which saves us some maintenance and another important part which can be broken.

On planes where the fuel tanks are on the same level or lower than the carberator, the fuel needs a pump to do the work. This pump is mostly driven mechanically by the engine. For backup purposes, in most cases we also have a electronic fuel pump which is often called a stand-by pump or auxillary fuel pump.

The fuel output point in the fuel tank is in most cases at the lowest point of the tank. However, we lose some part of the fuel making the difference between all fuel and unusable fuel. On the Cessna 172, we lose around 1,5 USG because of this. The pro of this is that possible dirt and other contamination is sinking to the bottom and not injected into the fuel system.

Fuel venting system

To prevent some underpressure while descending, fuel tanks consists of a venting system. This helps to maintain the atmospheric pressure in the fuel tank and is very critical at high-wing planes to ensure fuel always flows to the engine due to gravity. This does it by maintaining the outside atmospheric pressure so no vacuum can occur. Types of venting are:

• Venting pipes in the tank itself
• Special tank caps

Fuel tanks also have a drain at the bottom side, which can be used if any contamination or water is in the fuel and the color can be checked. Here we also have a strainer where water and contamination can be removed from the tank.

Vapour lock

Vapour lock is a phenomenon where bells of air occur in the fuel lines, making the fuel flow very hard or sometimes even impossible. This is caused by long terms of stationary running while on a very hot, warmed by the sun, platform. To solve vapour lock, turn on the electrical fuel pump and or enhance engine cooling. Using Mogas fuel increases the chance of vapour lock.

Fuel selectors

Fuel selector valves are being used to select where the fuel comes from. By setting this switch, you actually turn a mechanical valve to decide the flow of fuel. In most cases, we set this on both (if applicable) but in some cases to check or to balance the fuel in both tanks we select one of the two tanks only.

Carburation

To let a piston engine work, the mixture of fuel and air must be optimal before being delivered to the cylinders. This mixture can be made using two different systems:

• Carburator system
• Injection system

In the carburator, air and fuel are mixed into a optimal ratio and then will be delivered to the engine cylinders. The carburetor consists of a pipe with a narrowing, the venturi, and a throttle valve which you control with the throttle handle in the cockpit. In the venturi is a sprinkler which is connected to the float-chamber. This system is also called a updraft carburetor

Fuel to air ratio

Chemically, combustion is a reaction of a particle with oxygen. To start a combustion, fuel must be combined with air in a specific ratio. When one of both is too less, no combustion can happen, so the combustion area of an engine is within a certain area.

To ignite 1 grams of fuel, we need 14,7 grams of air. This makes a ratio of fuel 1:14,7 air, or the mixture containing 6,4% fuel.

• Rich mixture: 1:8 or 11,1% fuel
• Lean mixture: 1:20 or 4,8% fuel

In engine descriptions, the version with the ratio is almost always used as where the percentage does make more sense. We need to control the mixture because we can fly in air with a lot of air molecules close to the ground but also in air high up with way less molecules. We need to keep the ratio on about 1:14,7 which we can do by decreasing the amount of fuel. However, in situations where we use full engine power during climbing, we always use a richer mixture, as excess fuel is also used to cool cylinder heads.

Additional carburetor parts

The carburetor contains some additional parts to make it work as expected:

• Idle sprinkler (nullastsproeier): This part ensures enough fuel is sprinkled during idle power, otherwise the engine will stop working
• Acceleration pump : When the throttle value is opened up quickly during acceleration, the sprinkler will start somewhat slower making the engine not run optimal. Some carburetors are equipped with a accelerationpump, pumping extra fuel into the carburetor, solving this problem
• Mixture-handle: The mixture handle itself controls the amount of fuel that is mixed with the air. As you push it forward towards Rich, you get a rich mixture, meaning much fuel per air molecule. By pulling the mixture, this amount will be decreased
• Idle cut-off valve: The plane also has a mixture handle that can be fully pulled to idle cut-off. This means the idle spinkler and carburetor are both disconnected from the fuel, and the engine to lose fuel resulting in a shutdown of the engine. This is the common way to turn off a planes’ engine in general aviation
• Power enrichment system: This system ensures in throttle full-scenario’s, the fuel is somewhat more rich to help the engine cool more efficiently. Excess fuel is used to cool the cylinders

Air inlet system

Air normally reaches the carburetor through the engine air inlet system. This inlet is located at the front of the aircraft, just below the propeller. Before the air reaches the carburetor, it passes through an air filter. This inlet or filter can become blocked by debris, grass, snow, ice, or other contamination, which is why inspecting the air inlet and filter area is part of the preflight inspection.

On carbureted Cessna 172 models, an alternate source of air is provided through the carburetor heat system. When the carb heat control is pulled in the cockpit, a valve in the carburetor air box changes position. Instead of using the normal filtered outside air, the engine draws warmer, unfiltered air from around the exhaust heat muff.

This warm alternate air helps prevent or remove carburetor ice. It can also allow the engine to keep running if the normal air inlet or air filter becomes blocked. However, because the air is warmer and less dense, using carb heat usually causes a drop (~10%) in engine power and RPM. Therefore, carb heat should be used according to the aircraft checklist and operating procedures.

• Carb heat off: Filtered air from outside
• Carb heat on: unfiltered air from the exhaust

Icing in carburetors

The moisture in the air can freeze in the carburetor if the temperature there is below 0 degrees. The temperature in the carburetor is always lower than the outside air temperature, because of the following reasons:

• Vaporizing of fuel: Vaporizing fuel costs energy and this is picked from the air, causing the temperature of the air to drop
• Lower pressure in the venturi: Lower pressure means a decrease in temperature

This is the reason we turn on carburetor heat in every situation in the plane where we don’t use full power or cruise power. In my flight lessons, at every moment (ground excluded) where we need less than 2000RPM:

• In the full circuit
• During landing
• During descending
• During gliding

Carb icing can happen at any outside air temperature, even on hot and sweaty days:

• High humidity: The more moist in the air, the more can be frozen
• Low engine RPM: less heat is more ice

We check for carb ice during the before take-off checklist by setting an RPM of around 1700, and then enabling carb heat. We can check for carb ice in these two ways:

• Set Carb Heat to on: ice melts and RPM increases
• Set Carb Heat to off: RPM increases to above the initial RPM and slowly runs back

During the flight, we can recognize carb icing due to these causes:

• Reduce in Engine RPM
• Reduce in manifold pressure (constant speed propellor planes only)
• Very inconsistent running engine

Other rules about the Carb heating system are:

• Disable it (OFF) mostly on the ground, due to unfiltered air
• Disable it during climbs and go-arounds to get the best engine performance
• Enable or disable Carb Heat, no in between settings
• Carb Heat on means higher fuel usage

Fuel injection

Carburetors have two important downsides:

• Icing in the venturi, possibly causing dangerous situations if not handled properly
• Fuel/air mixture distribution over cylinders is not equal

These problems can be solved by using fuel injection. This system, which is available in modern aircrafts, has an injection in every cylinder controlled by a fuel control unit in between.

Just like the older carburation system we have a throttle valve, controlling how much fuel is pushed to the engine. This fuel now reaches the fuel control unit which equally distributes the available fuel onto the cylinders using the fuel divider. Most gasoline-based engine will inject the fuel continuously, not only when busy in the intake stage.

Fuel injection systems are always equipped with two possible ways of pumping fuel, which can be mechanical, using gravity or electrical. In the fuel manifold the fuel flow is measured, just like described in the disgram above.

Fuel injection systems are more complex and more expensive than carburetor systems, but we don’t need to bother about that carb heat again.

Aircraft fuel types

In aviation we know three types of fuel, each for their own cause.

An important parameter of fuel for planes is the knock resistance (klopvastheid). Fuel with a low knock resistance can burn under high pressure and normal operating temperature, leading to detonation. This is called detonation and results in a rough running engine.

Most planes can, some with some revisions, run on both AVGAS and MOGAS. The primary reason to use one of the two is the price. At this moment, the prices in the Netherlands are around:

• AVGAS: 3,94 per liter
• Mogas: 2,63 per liter

Fluids themselve cannot burn. They first have to vaporize and the vapor needs to have a specific mixture with air to actually burn.

Static electricity and Fuel

Resistance of two substances can produce a separation of electrical load. If the contact is broken, the two substances keep their electrical load. A plane can be loaded statically by precipitation, dust or sand in the air. This can also happen due to the flow of fuel in the tank installation. A passing thunderstorm can also cause a plane to be statically loaded.

Static energy can also cause interference in radio or navigation systems. To unload the plane from static energy, the plane has some static wicks, paths of low resistance with the air to unload itself which are mostly attached to the elevator and ailerons.

When the plane and tank installation have a different static load, a spark can transfer electrical load between the two objects when they are connected. To prevent this from happening and to send the electrical load directly into the ground, we always connect a plane using the ground wire during tanking operations. This is a wire we connect to a conductive part of the plane, like the nose wheel axis.

Fuel contamination

Aircraft fuel must be free of dust, water and other particles. When fuel is in the tanks, fuel can be contaminated. This is the main reson to check the fuel for any contamination with a dip stick and the drain. Water is the most occuring contamination and can leak in due to vapor, leakage and during rain. Water and fuel will not merge, and water is more heavy that fuel, so water will drop down and fuel will float on top of that.

Diesel engines

Diesel engines are very similar to gasoline engines. An important difference is that the diesel engine doesn’t have a ignition system. The compression ratio of a diesel engine is much better and works by pushing diesel in an area of high pressure and high temperature causing the diesel to ignite. Diesel engines need a better and stronger construction because of this.

Diesel engines also don’t have a throttle value, but a constant flow is delivered to the engine, results in a better power to fuel ratio.

Diesel engines have two engine-driven fuel pumps:

• Low pressure pump: Pumps fuel to the high pressure pump
• High pressure pump: Pumps fuel to the injection system with an overflow system, which excess diesel will flow back to the fuel tank

Diesel engines also don’t have mixture handles, but are electronically controlled using FADEC.

The ignition system (4)

After we have discussed the carburetion and injection system of engines, we will now take a closer look at the ignition system of general aviation aircraft. Ignition of the fuel/air mixture is what our propellor causing to turn and giving us thrust.

With gasoline engines, fuel/air mixture is ignited using a spark which is produced by a spark plug using high voltage. This voltage is around 20.000 volts and this voltage is produced by the magneto’s. The goal of the ignition system is to generate high voltage so the spark plugs will spark at the right moment to ignite the fuel/air mixture.

Parts of the ignition system are:

• Magneto’s
• Voltage distribution system to distribute the voltage over the spark plugs
• Spark plug cables : to conduct the voltage from the distributor to the spark plugs
• Spark plugs which generates a spark and ultimately ignites the fuel/air mixture in the ignition phase of the cylinder

Magneto ignition

In aircraft the engines use magnet-based systems to generate high voltage. This magnets are typically the dynamo’s where aircraft engines have two of, the left and right magneto. These magnets will spin around very fast. As long as the engine runs, the magneto’s will turn, making them completely separate from the electrical system which you control with the Master switches and alternator. Also we have some redundancy in if there is a problem in the L magneto circuit, we can run on R and still land the aircraft safe and sound. However, using one of two magnetos will result in a ~10% performance loss.

The magnetos are connected with gears to the crank shaft, the main shaft of the engine that rotates and is connected to the propellor, and they rotate within a coil. A rotating or moving magnet inside a coil produces electrical current, which is delivered to the spark plugs.

The produced voltage is dependent of the turning speed of the magnet. How faster the engine runs, the more voltage is produced. When starting, this system needs a impulse, mostly installed on the left magneto, which delivers more voltage in a short while and igniting just later to start the engine smoothly.

Start vibration

An alternative solution to the impulse link is an electrical start vibration system. The starting vibration will give the left magneto a pulsing voltage. This will result in a serie of sparks, but can only be used if having enough battery power.

Ignition moment

The ignition must happen on the right moment to be effective. If the fuel/air mixture is not ignited at the right moment, this will work against you instead of helping you further.

• Pre ignition: This is when the mixture is ignited too early
• Detonation: This happens when the pressure builds up in the cylinders and igniting at the wrong moment, leading to engine damage.

Some causes of detonation are:

• High engine temperature and too less cooling
• Too lean mixture
• Hot spots in the engine, like a hot spark plug
• Fuel with too low knock resistance or too low octane number
• Pre ignition

Spark plug contamination

A spark plug that has the right working temperature, will clean itself and will be free of carbon or lead. With running stationary for a long time, the optimal temperature will not be reached and can result in the engine running too rough. This is the reason we set the engine for around 1000 rpm during taxi and stationary, which is higher than the complete idle RPM, which is around 600-650RPM.

Diesel engines and ignition

Diesel engines doesn’t have spark plugs. Diesel engines will suck air and compress this. At the end of the compression stage the diesel will be injected into the cylinder, causing it to ignite due to the high pressure and temperature. Mostly similar to gasoline-driven engines but doesn’t have spark plugs.

Ignition switch

General aviation planes have a ignition switch where we control the ignition system with. This mostly have 5 different modes:

• OFF : Here the magnets are connected to the ground of the plane and disconnected from any source of power. No sparks will be produced in this setting, during normal situations
• R : Only the right magneto works in this setting
• L : Only the left magneto works in this setting
• Both : Both magnetos are working in this setting
• Start : The starting engine is powered in this setting and only the left magneto as impulse

During the before take-off checklist, we test the magneto’s on working and stability. If one of the two is not working properly, we will confronted with this at this moment. If the engine is running on one of the two magnetos, we should get a ~10% RPM drop. If one of the two is defective or inoperative, the RPM will not drop during the switch to R or L, and then can result in the engine turning off as we set a defective and non-voltage generating magneto.

A magneto can also be defective due to a grounding problem. During the run up, we will not see an RPM drop on one of the two separate settings. This can make the plane dangerous, and we may not park this plane without a good indication mark, as the magneto’s will be still powered. Rotating the prop results in a engine start. This will be minimized by disabling the engine using the mixture to idle, where no fuel is left in the cylinders and nothing to burn.

Engine cooling (5)

When burning fuel, a huge amount of heat is produced. As this will increase at higher RPMs and higher throttle settings, the engine needs to be cooled. Proper engine cooling extends the lifetime of an engine. At the best working temperature, the engine runs optimally which we want. We then get the most out of the engine. Other cons of high engine temperatures are thin or burnt oil, defective pistons, spark plugs and such.

In general aviation aircraft, these types of engine cooling is being used:

• Air cooling
• Liquid cooling

Most aircraft use air cooling or a combination of both. Liquid cooling is often used for cylinder heads and with diesel engines.

Apart from the cooling system, excess warmth is also dispatched through oil and oil coolers. Fuel also helps cooling the engine. Using a more rich mixture will cool the engine as this evaporates. This evaporation will help to cool the cylinder heads.

Air cooling

The cooling with air is very easy on airplanes. As air will flow through the openings at the front when flying this already has a major impact. The propellor also blows some air into the inlets at the front. Inside, most parts are equipped with big metal parts which pickup most of this air to cool and conduct the heat out. Most parts have cooling fins, making the contact-surface bigger and better cooling. Inside the engine compartment, some baffles (leiplaten) are added to redirect the airflow for optimal cooling.

Optimal cooling of the engine is reached during the cruise phase, as this redirects the most air at the highest speed into the air intakes. During climbs or running stationary the cooling will be worse.

Cowl flaps

Cowl flaps are used to redirect the airflow in a sucking motion, enhancing engine cooling and performance. These are often used in turbo-compressor engines. These are mostly open during taxi, take-off and climb and closed on cruise. Then re-opened at landing. If a plane has any problems with cooling in cruise, they can be re-opened.

Liquid cooling

An engine can also be cooled with liquid. Liquid can reach places with tubing where air cannot flow through. However, this is another extra reservoir, radiator and pump which can be defective. Liquid cooling is also more stable, and the radiator will only be opened when the cooling liquid reaches around 80-85 degrees celcius. Also the liquid will expand when being warm and contract when its cold, so an expansion reservoir is also installed.

Engine lubrication (6)

An engine needs to be lubricated using oil. The oil has these primary functions:

• Decreasing friction between parts
• Decreasing temperature and wear
• Cooling by conducting due to friction and burning which is called internal cooling
• Transporting small parts of wear and burnt carbon particles
• Securing metal surfaces from corrosion and from burnt fuel
• Closing the gap between cylinder wall and piston

We can use oil in two separate ways to get oil at the right places where engines can use both simultaneously:

• Pressure lubrication: Primary way, uses pressure built up by a pump to flow the oil around the circuit, reaching the crank shaft, bearings and camshaft.
• Splash lubrication: Uses splashing to cool and lubricate the bottom of the pistons and cylinders and bottom of the crank shaft

Oil circulation systems

In airplane engines, we can use two different oil circulation systems:

• Wet sump : In a wet sump system, oil is stored in the oil cump (carterpan), installed at the bottom side of the engine. The oil pump will pump this oil from the sump to the oil filter and then through the systems. From the engine, every droplet of oil that leaks is redirected back to this sump. This system is cheap and light and therefore used in much smaller airplanes
• Dry sump : In a dry sump system, oil is stored in a separate tank. The engine has a small carter to catch oil which drops back from the engine after doing its job. A separate scavenge pump will pump the oil which reached the carter to the oil reservoir. A dry sump system needs therefore two pumps, one for the system and one to pump oil back to the reservoir. This system is mostly used in aerobatic planes, where the engine is inverted so you can fly at inverted positions without an engine that turns off.

Oil cooling

To cool the oil and regulate the temperature of the oil we have a oil cooling system, equipped after the oil pump, before the oil is pumped into the engine. This cooler is a thermostatic temperature regulator which is cooled by the cooling air which flows in the engine compartment. This also works with a bypass system, redirecting directly or via the cooling compartment. If the oil pressure is high, this will also open to always have oil in the engine.

The oil filter is a paper filter in a metal case, around the size of a can of soda and is replaced every 50 flight hours.

Engine oil types

Oil consists of hydrocarbons and needs additives to lubricate the engine in a broad working temperature range. A cold engine needs to have the same lubrication as a warm engine. Oil has the following properties:

• Viscocity : The viscocity of the oil states how syrupy the oil is. The higher the number, the thicker, and the more resistance of flowing, also dependent of the temperature of the oil

In plane engines, we use both single grade and multigrade oil types. Single grade has big difference in temperature ranges and multigrade is “graded” for multiple temperature ranges. In the summer, we need to use thinner oil.

The indication is:

• Single grade oil : oil 80 or 100
• Multi grade oil : 15W50

Multigrade has the gradation in the name. During cold operations, the first number states the viscocity and at high temperatures the second number. Due to different additives the oil becomes more thick with a higher viscocity. In this number, the W stands for “Winter”, so Viscocity 15 during Winter (cold start) and 50 during engine operating temperature.

Oil pressure

In the oil system, the oil pressure is regulated by the oil pump which is directly driven by the engine. The oil pump delivers pressure at a very low temperature. To prevent the pressure exceeds the limits during high RPM situations, the engine contains a pressure relief valve. Via the pressure relief valve the oil will be pumped back to the carter. This flap will open at a certain pressure and stabilizes the oil pressure.

The most important indicator of the oil system is the oil pressure meter. A minimum pressure is needed to take care of having enough oil in the engine and enough cooling and lubrication.

• Low oil pressures: Lead to bigger wear, high temperatures and in worst case engine failure
• High oil pressures: Lead to leakage, damaged oil filter or damaged oil cooler

The normal and allowed ranges and limits are described in the POH. On the indicator, we get a good view of what is normal, too high or too low.

Too low and too high oil pressure can have similar causes, so let’s sum them up in a table:

A high oil pressure can happen if the engine is just started and cold. The oil is too thick and will be pumped hardly into the engine. When the engine has warmed up the viscocity will lower and the oil pressure will be within normal operating ranges. An engine takes around 10-20 minutes to fully warm up every component.

Oil temperature

Next to the oil pressure, the second most important indicator of the engine health is the temperature. The temperature will decide the viscocity and the lubricating properties of the oil. High engine temperatures can be caused by:

• Too much heat production in the engine, high environmental temperature
• Flying at high RPM too long
• Lean mixture
• Too less cooling in the engine, possibly during climb
• Too low engine oil-value
• Defective or dirty oil cooler
• Defective indicator

The oil temperature is dependent of the operating temperature in the engine. If this temperature is too high, then we can take some steps to try and resolve this high temperature by picking less RPM, flying faster for more and better airflow, riching the mixture or to open the cowl flaps.

High oil temperatures often happen with low pressure. By the high pressure, the pressure drops as the oil gets thinner. If the engine cooling is enhanced, the temperature and pressure will be normalized.

Oil usage

Every engine will use oil but the amount of oil is dependent on several factors. The oil usage will be dependent on:

• Type of oil
• Condition of cylinders
• Condition of pistons
• Condition of piston springs

A new engine which doesnt have already lubricated piston springs uses more oil. The same counts for older engines with much wear to the piston springs.

Constant Speed Propellors (7)

Constant Speed Propellors or variable pitch propellors are propellors where the angle of the propellor blades can be adjusted based on the phase of flight. Planes with this feature often have more blades than 2 on each propellor and are equipped with a blue Prop RPM handle in the cockpit, next to the black throttle and red mixture. Pro’s of planes with this feature is that they are much more efficient, generating more thrust with less engine RPM. With the black handle, we control fuel inlet pressure which is called Manifold pressure and with the blue handle we control the speed of the propellor, the RPM and indirectly the blade angle.

Planes equipped with constant speed propellors are also equipped with a governor. This is a part in the plane that actually sets the correct propellor blade based on the handle setting.

• When taking off and climbing: blades are set to full fine ( High RPM )
• When cruising : blades are set to coarse blade angle ( Low RPM )

As the propellor will always rotate at the same RPM, the angle of attack and drag can reduce when in horizontal flight as we go at a faster airspeed. This makes the plane setting a more coarse blade angle to increase this, making the engine run on lower RPMs than with fixed pitch propellors and having more control + efficient use of engine power.

Most blade-change systems are hydraulic, but some are also powered electrically. Hydraulic systems make use of the oil pressure to control the mechanism, so this also uses engine oil.

How this system works:

1. When setting the handle to Low RPM which is fully backward, the spring on the governor (the vertical pipe and part of the constant speed unit) will push on the fly weights which are those two balloons, making them fly outwards. They rotate at the crank shaft speed as a gear connects the governor to this crank shaft
2. The fly weights are engine RPM sensitive, making them fly outwards due to high RPM and fly inwards at low RPM due to centrifugal force
3. The fly weights are connected to the pilot valve, which is a valve that can complete the oil circuit to the propellor, in Low RPM settings this valve will open, at High RPM the valve will close
4. The propellor hub is hydraulically powered by the high pressure oil pump pushing the blade to a bigger angle.

Overloading the engine

When a high manifold pressure is combined with a low engine RPM the engine can fill up the cylinders too much, causing extreme pressure and temperature in the ignition space and can overload the pistons and crank shaft. This also increases the chance of detonation. Refer to the POH of the plane for recommended setting combinations.

Pre-flight check

During the pre-flight check, we will check the governor operation. This can be done when the engine is running and when it is in normal operation temperature. We will set the handle over the full range for a few times and check if the RPM changes value. Doing this multiple times will ensure the warm engine oil reaches the system and guarantee fully operation.

Single acting variable pitch propellor

Smaller planes are often equipped with single acting variable pitch propellors, where the blade angle is controlled one-way with oil pressure. The oil pressure ensures a coarse blade angle where centrifugal forces will ensure a fine pitch angle.

Loss of oil pressure

As we already discussed, when powered hydraulically, the system uses the engine oil to function. The pitch of the blades is mechanically limited to help us in failures. When oil pressure is lost, the propellor blades will set by spring force to the fine pitch setting (high RPM) making it a fixed pitch propellor and us able to land safely. This also needs a limited airspeed and limited engine RPM setting as the engine RPM can now be exceeded by the low propellor drag.

Engine Instruments (8)

The engine is of course one of the most important systems in our aircraft. Without the engine we were not able to produce enough thrust to produce lift, and being able to fly. As we have several instruments in the cockpit that tells something about the current state of the engine at any time, we will dive into the properties of each indicator and system.

Let’s take a look at the types of engine instruments we have in our cockpit:

• Pressure-indicators
• Temperature indicators
• Revolutions per minute (RPM) indicator
• Fuel indicators

We will dive deeper into the various indication systems and what we can expect from our plane.

Color markings

All of the indicators in an aircraft are marked with colors to tells us easily if units are within limits or not. Here we can take these into account:

• Green area: Normal operating range, everything healthy
• Yellow area : Operating area with possible precaution but indicators can reach this in situations like take-off
• Red line : Minimal and maximum value for safe use
• Red area : Non-normal area and will indicate possible failures if not reacting to them

Pressure indicators

The engine indicators measuring and showing pressure are:

• Oil pressure : this shows the pressure in PSI and the rate of circulation
• Fuel pressure
• Manifold Pressure: This shows the fuel pressure after the throttle valve and is the amount of fuel injected into the cylinders. This is expressed in inches of mercury (inHg)
• Static and Dynamic pressure
• Hydraulic pressure

We can indicate pressure primairily with the Pascal unit. One pascal is equal to one Newton per square meter (1 N/m²). In most cases, some older or American units are used in aircrafts:

Pressure is mostly measured by flexible metal boxes or pipes. We have two types which are mostly used:

• Aneroid: This is a method where a diaphragm is used. This diaphragm is placed in a box with the pressure connected to the static pressure system with a determined amount of pressure inside the diaphragm. This diaphragm expands and contrapts based on the static pressure in the box, giving an indication by a grear connected indicator needle.
• Bourdon-pipe: A bourdon pipe is a mechanical solution of measuring high amounts of pressure. This is a flexible pipe which will stretch when the pressure inside increases. This stretching movement is then transferred using a gear to the indicator needle, showing the actual state of the pipe behind.

Temperature indicators

Temperature in aviation is often measured in these three units:

• Celcius (C) : This is the primary method around the world to measure temperature, which has a logical scale:

  • 0 degrees: freezing
  • 100 degrees: cooking

• Kelvin (K) : This is the temperature of absolute zero molecule movement, which is 273,15 degrees celcius

  • Kelvin = Celcius - 273,15

• Fahrenheit (F) : This is an American scale, where 0 degrees celcius is 32 degrees Fahrenheit

  • Fahrenheit = Celcius × 1,8 + 32

We get some indications about temperatures in our aircraft, telling us different things:

• Cylinder Head Temperature (CHT): Measuring the temperature of the cylinder head metal. This is important because the cylinder head is one of the hottest and most stressed parts of an air-cooled piston engine and too hit CHT can lead to a rough running engine. High temperatures can be resolved by
  • More rich mixture
  • Decrease of engine RPM
  • Enhancing cooling, open cowl flaps or fly at a higher speed
• Exhaust Gas Temperature (EGT): EGT shows the temperature of the exhaust gases leaving the cylinder. This tells the pilot how combustion is behaving and especially important when leaning the mixture
• Oil Temperature: The temperature of the engine oil and so the mean engine temperature, giving us indications of possible overheating
• Coolant Temperature: The temperature of the coolant fluid, giving us indications of possible overheating
• Outside air temperature: This indicator measures the temperature outside of the aircraft, enables us to make TAS calculations or assess risk of ice deposits

Revolutions per minute (RPM) indicator

We only have one RPM indicator per engine. As we may only fly with planes with one engine with the PPL license, we need to monitor only one indicator.

RPM indicators show the amount of rotations the propellor makes in a minute. In planes where the propellor is mounted directly on the crank shaft, we also get the RPM of the crank shaft with this indication. With fixed-pitch propellor planes, this means engine RPM equals propellor RPM. More RPM is more power (thrust).

Some engines like Rotax have a gearbox between the crank shaft and the propellor which allows the propellor to rotate at a lower RPM than the engine. This RPM indicator will show the RPM of the propellor in such cases.

Propellor RPMs are often limited to around 2700 RPM. Above this rotation speed, the tips will reach the speed of sound (Mach 1) and this heavily decreases the performance of the propellor.

RPM indicators are very often mechanically powered. A flexible cable is connected to the engine on one end. The other end is connected to the RPM indicator in the cockpit. This other end has a magnet connected to it which rotates in a copper tube. This will produce eddy currents, resulting in the copper tube rotating in the same direction. The rotation of this tube is then somewhat limited by a spiral spring.

Some planes are equipped with a torque indicator as indicator for the amount of engine power. A torque meter is often used when the crank shaft and propellor are separated by a gearbox and is determined by performing oil pressure measurements in the gearbox.

• Torque (Nm) = force (N) × arm (M)
• Power (Watt) = torque (Nm) × revolutions per second

_Nm = Newtonmeter, unit of rotation power where we multiply the amount of newton against the amount of meters (_10 N × 0,5 m = 5 Nm)

Some planes also show a percentage of the maximum power or the engine power rating (EPR), but this is mostly used on Jet airliners.

Fuel indicators

The engine indicators measuring and showing properties about the fuel are:

• Fuel pressure: This shows the pressure of the fuel in the tubes to the carburetor. This is required when the plane has a fuel pump as primary circulation force, where a low fuel pressure can indicate a low tank or a defective fuel pump
• Fuel quantity indicators: This logically shows how much fuel there is in a certain tank using a floating object, connected to a metal arm which is electronically powered. This is by far the most inaccurate instrument in a plane, so always do a physical inspection with a dipstick. Its also unaware of the attitude of the plane.
• Fuel temperature: This indicates the temperature of our fuel and is mostly equipped in diesel aircraft. Diesel can partly freeze (waxcrystals) when under -20 degrees celcuis
• Fuel flow: This measures how much fuel travels through the fuel injection system every hour. This can be used to determine our fuel calculations, and is often measured at the injector or a specfic measurement-wheel in the tubes

To calculate different units:

• 1 pound (lb) = 0,4536 kg
• 1 US gallon (USG) = 3,785 liter
• 1 Imperial Gallon = 4,546 liter
• 1 Quart (qt) = 0,95 liter or 0,25 USG

The electrical system (9)

The electrical system in planes is being used to power the electronic devices and instruments. The only connections the electrical system and the engine have are:

• Starting engine
• Electrical air/fuel mixture pump FADEC (if equipped)

All the primary components of the electrical system are (and fail in case of electrical failures):

• The alternator (dynamo): The propellor to power delivery device and is the primary source of power if the engine runs
• The battery : provides power when the engine is not running
• Busses : One or more electrical busses where power from the alternator or battery is distributed over multiple electrical devices
• Circuit breakers : Each part of the electrical system have a circuit breaker, a poppable weak link of the circuit to prevent overloading and as result damage to devices
• Wires : to connect each part to each other and to deliver power
• Ammeter : This indicator will show the actual power-usage/delivery
• Master switch : To provide the complete electrical system power from the battery and/or alternator. This is mostly a double switch, where we can also select only the battery or only the alternator in case of failures
• Avionics master switch : To provide all navigation and communication devices power from the battery/alternator

All devices which we often use are powered by this electrical circuit:

• Radio’s
• Navigation systems
• Transponder
• Turn coordinator (only electrical primary flight indicator for fallback scenarios)
• Flight displays
• Fuel quantity indicators
• Lights
• Pitot heat
• Clock
• Hobbsmeter (hour-counter on the RPM indicator, just like KM’s in a older carr)
• Electrical trim
• Starting engine
• FADEC
• Flaps

Voltage and current

Some definitions we must know when talking about the electrical system:

• Current : Current is the power of the electrical load indicated in Ampere (A). This unit measures the amount of electrones transported per second
• Voltage : Voltage is the electrical potential difference indicated in Volts (V). This unit measures the pressure (speed) of the electrodes transported per second

Types of power

We can have two different types of power, namely:

• Direct current (DC) : Here the electrons will always flow in the same direction, from negative (-) to positive (+).
• Alternating current (AC) : Here the electrons will switch direction periodically, which is indicated in Hertz. 400Hz means 400 switches of direction per second. In airliners, the alternating current flow hertz is 400Hz, but at your power outlet at home, 50Hz or 60Hz is being used, depending on your country.

We use both of these type of power, mostly depending on the king of application. A battery for example always delivers DC power and an alternator can deliver both. However, alternators that deliver AC power are much cheaper so we can convert that power to DC. General Aviation aircraft mostly have a DC power system of 14 or 28 volts.

Electrical circuits

An electrical circuit conststs of a source of power, like a battery or alternator and one or more users of power, connected by copper wires. Power can only flow if the circuit is closed.

In planes and cars, the negative pole of the battery is often connected to the frame, functioning as common earth. This saves a lot of wire as only the positive pole needs to be connected from the battery to the device and the negative can be picked elsewhere.

The alternator

The alternator is the primary source of power in an aircraft while the engine is running. The alternator is powered by the engine using the V-string. The battery is used to charge and to power the devices when the engine is not running and to provide power to the starting engine to start the engine and make the alternator work.

• Generator: DC dynamo
• Alternator: AC dynamo

A dynamo works by a rotating magnet between static magnets. This causes the rotating magnet to spin at a very high speed, providing power using magnetic induction in a coil.

DC generator

A DC generator is a dynamo that generates DC power. This works with a stator and rotor, where the stator is a permanent magnet with a rotating coil with a lot of wires. One of the wires is shown in the diagram below:

The rotor is connected via the V-string with the engine causing it to rotate as the engine runs. This produces an induction-power which then is picked up at A.

The downsides of this construction are:

• Brushes are maintenance-intensive
• Low RPM is low power generation
• Expensive

Most planes are because of these reasons equipped with an alternator (a AC dynamo).

AC alternator

An AC alternator works similar to the DC generator, by using magnetic induction. But the construction is somewhat different, so AC power is being produced instead of DC power. The construction is completely reversed, the magnet rotates instead of the coil. The magnet is then very often a electromagnet. The power is then picked from the stator which doesn’t rotate, making this solution more robust and less prone for failures.

Because the alternator uses an electromagnet, a small amount of power is needed to power the device. Without power no magnet can rotate. This power is called excitation current.

After the AC alternator, a rectifier unit is placed to convert these alternating current into direct current, usabe by the rest of the plane and charging the battery.

Alternator control unit

The power the alternator is producing is dependent on the RPM of the engine. To prevent damage or outages due to peaks and lows, the electrical system has a alternator control unit which is basically a voltage regulator. A device which keeps the power steady at around 12 to 14 volts.

The battery

The battery has the following primary functions:

• Delivering power when the engine is off
• Delivering excitation current to the alternator
• Delivering power to the starter engine
• Delivering power if alternator fails (back-up power)

Power in a battery is produced by a chemical reaction. There are different types of batteries which are indicated:

• Nickle-cadnium (NiCd): Lighter with the same capacity and better resistant to low temperatures
• Lithium

Sometimes we have multiple batteries to have back-up batteries or a separate excitation battery.

In most planes a lead-sulfur battery is used, just like in cars. This contains of plates of lead submerged in sulfur. This reaction between those two materials produces power, which is reversable. This means we can charge and discharge the battery, or pick power from the battery or charge it back. The battery is placed in a battery box which contains a drain for air ventilation.

Voltage and battery capacity

Batteries always deliver 12 volts or 24 volts. Because the battery must be charged by the dynamo, the voltage of the battery is always lower than the device that charges it.

The capacity of a battery is indicated as ampere-hours (Ah). A battery with a capacity of 50Ah can provide 50 Amps over 1 hour. When you halve the amps, the duration doubles (25 amps for 2 hours, 12,5 amps for 4 hours etc.)

The battery has a specific rating for this Ampere-hour, but this is the theoretical amount. The actual amount is often lower where these conditions lower the capacity:

• Age
• Temperature (cold = less Ah)

Ampere meter

The Ampere meter is a indication in the cockpit which shows the condition of the electrical system. This measures the amount of amps flowing through the wires. We know two different variants of this indicator:

• Zero-centered : This type is often in Cessna and Cirrus planes. This measures the power from and to the battery. In the center we have the 0, and on the left -30 amps and on the left +30 amps. This must be slightly to the right to be in a healthy condition, the battery is slightly charged and the whole electrical system is powered.
  • Location: Between battery and bus
• Load meter: This type is the total amount of power in the electrical system. The lowest amount is 0 and the highest amount is 60. When less devices are turned on, the meter shows a low value and with much devices the meter goes up.
  • Location: Between alternator and bus

Busses

A bus is a distribution strip, which basically is a static collection of power outlets where all devices get their power from. From the bus the power goes to the circuit breakers and then to the actual devices.

Mostly we have these busses:

• Main bus
• Avionics bus
• Essential bus
• Non essential bus

Circuit breakers and fuses

Fuses are weak links in the circuit which have the goal to break the circuit if a high power is detected. We have two types of these fuses:

• Smelting fuses (right): Smelting fuses have a thin wire which can only withstand the rated power. If more power is connected, the wire will smelt breaking the link. The fuse then needs to be replaced before working again.
• Cirbuit breakers (left): Circuit breakers do the same as smelt fuces but pop if a high power is detected. We can easily re-pop them back into position to make the connection again. These are often called automatic fuses

Circuit breakers have a contact with a multi-metal strip. If the power (amps) will exceed the rated limit, the metal will warm up, bending the metal and causing the circuit to break. Circuit breakers that pop must first be cooled down to connect them again. If a circuit breaker pops during flight, EASA recommends to let it disabled when its not needed for a safe resumation of the flight. For example, we can land without flaps or lights or even radio. Altough it would be nice to have them.

Relay

A relay is a electromagnetic switch. An example is a starting relay. To power the starting engine, a huge amount of power/current is needed. Turning the key to START causes a small power to the starting relay, powering an electromagnet which results in a closing of the ignition and causing the starting engine to rotate.

Electrical system disruptions

In the electrical system, two types of disruptions or failures can occur:

• Disruptions where the alternator does not provide power
• Short circuit where something in the system causes a short circuit with possible fire, smoke or electrical smell. This can also lead to a circuit breaker/fuse failure

The general guidelines and sympthoms for both types of disruptions are:

• Low ammeter indication -> alternator error
• Low voltage annuciator -> alternator error
• Electrical smoke -> short circuit
• Ozone-smell -> short circuit

In a case of a alternator error its recommended to land the plane at the nearest airfield as an alternator error will cause the plane to pick power from the battery. This will provide power for around 10-15 with a max of 20 minutes. Power down unnessesary devices where possible.

The alternator can sometimes be reset by switching the master switch to off and back on.

Pitot-static instruments (10)

The pitot-static system is a system with three indicators from the cockpit connected:

• Speed indicator
• Altitude indicator
• Vertical Speed indicator

Pitot-static instruments

The Pitot and the static port are 2 openings on a plane which measures a different type of pressure:

• Pitot: Measures dynamic pressure -> Speed
• Static port: Measures static pressure -> Altitude

These two components are connected to 3 of the basic 6 instruments we must have in a cockpit:

1. Airspeed (Ports/Analogue)
2. Artificial horizon (Gyro)
3. Altitude (Ports/Analogue)
4. Turn coordinator (Gyro/Electrical)
5. Heading/Compass (Gyro)
6. Vertical speed (Ports/Analogue)

Static port

The static port is an opening (mostly on the left side) that measures the static air pressure while in the air. The pressure it measures is displayed on your altitude indicator.

This opening is placed at the opposite direction of incoming air, to truly measure static pressure. In some planes, this is integrated in the pitot-probe.

When having problems with altitude or vertical speed (like in the winter), we have a second option of static air, the alternate static port/alternate air. This takes the air from the cabin, which is mostly at a higher altitude than it is really. (Around 100 feet higer than true altitude).

A third option can be to smash the vertical speed indicator, then this air will flow through the static system. Our vertical speed indicator obviously would not work anymore, but is the least needed instrument against airspeed and altitude.

Position error

The static port cannot always be at the right spot on an airplane. It must measure the static pressure so it must be on the side, but speed, AoA and flaps can influence the airflow around the static port and also the static pressure. This im-perfect placement causes an error in the measurement, called the position error. This has a small influence on the measured altitude, speed and vertical speed. Also some errors caused by manoeuvres can happen. Some planes have multiple static ports to minimize these errors.

This same also applies on the pitot probe, although this only measures dynamic pressure.

Alternate static air/port

Some planes have an extra alternate static port in case the normal port is broken or something. This can be opened in the cockpit, so the air pressure of the cockpit can be used to measure the altitude, speed and vertical speed. The pressure in the cockpit is often somewhat lower than the outside air pressure, so the altitude meter can indicate too much. In the POH you can find a altitude correction table.

Pitot probe

The pitot probe measures the dynamic pressure (incoming amount of air) that will be applied to the aircraft during flight. This is mostly the airspeed, the Indicated Airspeed (IAS).

When shutting down the plane, we will place a red cap onto this probe. This is to prevent insects or ice to build up and have a non-working speed indicator in flight.

The airspeed will be measured by both the static port and pitot port. It measures the difference between the dynamic pressure and static pressure which results in a airspeed.

Airspeeds

Airspeed in aviation can be measured in 4 different terms which sound ridiculous but this has their specific reasons.

Other important notes from the course

• At shutdown, we pull the mixture to clean the engine cilinders. This to reduce the chance of “hot-prop”, turning the propellor can start the engine due to the magneto still powered if key still in the hole
• Flaps is “Vleugelklep” in Dutch
• Braced Wing(with strut) is Cessna 172 type planes
• Cantilever wing is Piper type planes
• Monocoque construction is a can of coke
• Semi monocoque is reinforced in the inside
• Max zero fuel mass: important to calculate balance if fuel is almost up (weight of the plane including passengers and baggage)
• Vertical stabilizer is “Kielvlak” in Dutch
• Horizontal stabilizer is “Stabilo” in Dutch
• Multi-engine airplanes have ruddertrim to compensate for single engine failures
• Lift is the force that pushes you in the air (draagkracht)
• Slats are leading edge flaps -> increases lift
• Flutter is aerodynamic imbalance
• Torsieschaar is torque link and a shimmy damper
• Shimmy is a bike without hands that vibrates
• Shockdamper works with gas and oil
  • Gas for damping
  • Oil for suspension (vering)
• Hydraulic means “hydro” and means transferring pressure by hydro, for example brakes
  • Unhealthy then touched
  • Thin and low viscocity
• Crabbing is needed to line up with the wind, at around 15 feet before landing, you turn the right direction to minimize deviating from the track to the runway
• Touchdown load is horizontal and vertical load
• Slipmarker is a red piece of painting that marks the tire and rim to align and makes a slip visible
• Tubeless means a tire without a “tube” (binnenband)
• Tube type: tire with a tube
• De-icing is melting existing ice (revive)
• Anti-ice is preventing ice (prevent)
  • Pitot heat/wind shield/carb heat
• Engine fire at starting: cranking to crank the fire into the engine
• Krukas connected to propellor and piston as
• Nokkenas connected to krukas turning 50% of the krukas
• Stijgstroom carberateur -> lucht stijgt ,gemonteerd onder de motor
• Turbo charging is compressed air into the engine (turbo)
• Compressed gas into a tighter squeeze produces heat and needs cooling
• Waste gate is a pressure relief gate
• FADEC means automatically controlled mixture
• Vapour lock happens with warm weather and makes the engine go running stutterly
• More throttle means more air, not more fuel -> thats what the mixture is for
• CVV gas uses heat and can produce ice -> Thats why we need to enable it under 2000 RPM. This can happen even when its 28 degrees celsius outside
• Warm air is thinner -> RPM drop
• Nullast sproeier prevents the engine from turning off when idle
• Lean to a RPM drop and then add about 1/2 cm
• Exhaust Gas temperature
• For prop-rpm planes which are called “constant speed propellor planes”
  • This means the plane changes the blade pitch to maintain a certain RPM
• Throttle will control the air inlet pressure
• RPM will control the actual RPM of the propellor
• Engines will use fuel as colling, sometimes a little more fuel is needed to cool the engine
• Gasoline
  • AVGAS 100 LL is blue
  • MOGAS is yellow
  • Jet A1 is colorless or black
• Magnetos are the powering system for the spark plugs, they are connected to the krukas and will deliver power as long as the propellor turns. These work indepenmdently from the electrical system of the master switch for redundancy
• If setting the ignition to off, you actually connect the primary coil of the magneto’s to the ground (-)
• A propellor pushes air behind it to get a forward movement (Air is thin water)
  • “Luchtschroef”
• If a multi engine plane has one engine failure, they set the propellor to “feather” (vaanstand) to reduce drag of the propellor
• Maximum Angle of attack of the blades and of most planes is around 15 degrees
• PSI is pounds per square inch
• In a cessna 172, these components are connected to the Master switch, and will fail when having power failure:
  • Flaps
  • Avionics/Navs/Radios
  • Transponder
  • Lights outside
  • Lights inside
  • ELT
  • Autopilot
  • Turn coordinator
• Other flight instruments are based on pressures and gyros. Gyro’s are powered by the vaccuum system
• Magnetic compass is a stupid device and must only be used in straight and level flight
  • Turning from north will result in a wrong but then corrected turn
  • Turning from south will result in a inverted turn
  • When accelerating, this will give an other heading because of the CG of the device
• Alternator is a electrical device that picks the energy of the krukas and stores it in the battery (Alternating current)
• The battery works about 15 minutes without charging (in a failure, spare your juice)
• Ammeter and load meter are the same, but ammeter shows if its actually charging. Load meter only shows the current load on a scale from 0 to 60
• Circuit breakers only prevent overheating
• Airspeed indicator uses static port to compensate static pressure from the dynamic pressure, which assures that the dynamic pressure (and so speed) is correct at every altitude
• Air speed indicator is in real life a pressure meter
  • Air molecules meter
• Altitude meter is a barometer which converts a set pressure to altitude (pressure decreases as altitude increases)
  • This has a small correction of -20 ft when its cold and +20 ft when its warm weather
• This doesnt work with sensors at the bottom of the airplane, as we ould have a different altitude every nanosecond and as other traffic in the vicinity which we want to avoid
• Vertical speed indicator sucks pressure and has 2 second delay
  • It has a button on the back side which sets the meter to “0”
• A gyroscope is rigidity (standvastigheid) and preccession in turns
• The vaccum is the part after the engine which sucks air and provides force to the gyroscopes
• Skidding and slipping turns

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