Piston Engines
Piston Engines
Piston Engines
Using the altimeter in the cockpit how can we measure "pressure altitude"?
A rich mixture in terms of piston engine fuel system supply to the induction manifold is a mixture of air to fuel.
For maximum endurance the mixture control should be set to:
What is the best method for limiting the effects of vapour locking?
The purpose of the accelerator pump is?
In an aircraft equipped with a float type carburettor and a constant speed propeller, carburettor icing would probably first be detected by
How is a stable idle achieved in the carburettor?
The octane rating of a fuel characterises the :
For piston engines, mixture ratio is the ratio between the :
Which power settings are most likely to promote detonation in petrol engines?
Which statement is correct regarding fuel energy density?
What effect does the mixture fuel-air have on the flame front velocity
On a climb the decrease in pressure causes ....
When the carburettor air intake is in "Hot Air" the power output of the engine is reduced because:
What is the normal indication that a petrol engine is suffering from "Detonation"?
When would a pilot most likely expect carburettor icing?
Tetra ethyl lead is added to some aviation gasoline fuels to:
The colour of Aviation gasoline 100 LL is:
What is the purpose of the priming pump?
What is the purpose of power enrichment in a carburettor?
2 Groups of engines
1. Piston engines 2. gas turbine engines systems
Piston engines 2 arten
a) Unboosted/ Normal aspirated engine b)boosted
Unboosted/ Normal aspirated piston engine
the ambient air is drawn into the cylinder by the piston
boosted piston engines
a charger delivers compressed ambient air (more air mass) into the cylinder
Turboprop
gas turbine driving a propeller to create the thrust force
Turbofan
gas turbine driving a fan that creates thrust force as the reaction force to the acceleration of the air in the nozzle
Grundprinzip Piston engine
The high pressure inside the cylinder during combustion creates a force on typ of the piston, which is transmitted to the crankshaft, creating torque.
Was kann bei inverted cylinders passierenN z.B. beim Sternenmotor
Es entsteht ein Hydraulicing (oil flood) => Oil flows down into the cylinder head and blocks the movement of the piston. This oil must be drained (Säubern) from the cylinder by removing the spark plug before engine start
Welche Piston engines kommen am häufigsten in Airplanes vor?
Horizontal opposed air-colled engines ==> Boxer => 4-6 cylinder
Sternenmotor
Kurbelwellen in der Mitte => Ungerade Anzahl Zylinder ( bei 2-Reihiger Motor = gerade Zylinderanzahl) => Daraus ergibt sich die Zündreihenfolge
Verschiedene Arten Otto-Motoren
a) Reihenmotor b) V-Motor (Nockenwelle entscheidet, ob schneller oder langsamer Motor) c) Boxermotor (jeder Zylinder hat 2 Kerzen
vgl Bild
1) Zylinder 2) Kurbelwelle (Crankshaft) 3. Kurbelgehäuse (Crankcase) 4. Heat exchange
vgl. Bild
1. Vc (Clearance Volume) 2. TDC Top dead centre 3. bottom dead centre 23. Distance: length of stroke 4. Piston 5. Connecting Rod 6. connecting rod force 7. Crankshaft
Torque
F Rod * Arm F Rod= Connecting rod force
V Total im Zylinder
Vc + Vs = Vt Vc = Clearance Volume = Between TDC and the top of cylinder Vs = displacement between TOD and BDC
Compression ratio
\(Compression ratio = {Vs + Vc \over Vc}\)
Stroke
Distanve between TDC and BDC
Long Stroke engine where teh sroke is greater than the piston Bore (Zylinderbohrung) führt zu ?
Kraft mal Arm ist hier grösser => Grösser Tork
Short Stroke Engine where the stroke is less than the piston bore ist der Fall, wo?
Bei Rennmaschinen
3 factor for the power output of a single cylinder engine
1. Weight of air mixture taken in (Wie viel Gemisch) 2. Amount of compression 3. Number of working/power strokes per Minute = Drehzah
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Lernkarten
Why you use a acceleration pump?
for extra fuel => Mit dem Throttle wird die beschleunigungspumpe bedient --> Throttle öffnet die drosselklappe und dass sofort Fuel kommt, benötigt man eine Beschleunigungspumpe ==> Noch mehr Fuel reinbringen
during sudden acceleration, the amount of air grows so rapidly that the slight time lag before the FF is sufficiently increased would prevent the engine from accelerating smoothly
When you havent a automatic mixture cntrol (AMC), what happens during a climb?
the air density decreases => mixture gets richer as an airplane gains altitude ==> Mixture zurücknehmen
If the mixture level is retarded into the cut off position, what happens
this shuts off the fuel supply => stop an airplane piston engine ==> No combustible mixture left inside the cylinder = prevents serious injuries to anyone who tries to turn the propeller while the ignition is on
2 Arten von icing?
1. Carburettor icing
2. Induction filter icing
Wann kann es im Carburettor Ice geben? wieso?
widest range of possible Carburettor icing is OAT -10 - + 30, but highest possibility 0-15 ==> temp. drop inside the venturi due to static pressure decreases and the presence of humid air => small spread
Wie macht sich Eis (Carburettor + Icing by the filter) bemerkbar?
a) decresing engine power
b) decreasing RPM
c) decreasing MAP
d) rough running
==> some aircraft are equipped with a Carburettor air temperature
Wie bemerkt man, wann das Ice wegschmilzt?
RPM increases => more engine power
Wann bildet sich ICE beim air filter ?
under the same condition as surface icing on aircraft
How is the function of the anti ice by the Carburettor ?
uses unfiltered engine intake air from inside the engine cowling => the intake air is heated by the exhaust muffler
What happens by the prevent Carburettor icing and how you realize, when the ice is gone?
a loss of power due to the heated intake air's lower density => the mixture becomes richer => the ice is gone when the RPM increases
What you make to conteract filter iceing in an engine equipped with an injection system ? effect on engine power? Advantage compared with a Carburettor system?
Alternate Air dores => haven't an effect on engine power ==> Advantage: no Carburettor icing can occur when you haven't a Carburettor system (you have an injection system)
Ignition: Instead of teh battery ignition, which system is used ?
a magneto ignition system => independent from the aircraft's electrical system => Electricity for ignition is provided as long as the engine turns even for in flight engine start with wind milling propeller
How is the function of the Magneti ignition system?
The magneto rotating a permanent magnet inside a framework of soft iron around which TWO COILS are wound. Primary coil: few turns secondary coil: thousands of turns
Double or Dual ignition system ?
two completely independent magneto type ignition systems are used to improve the safety ==> Bessere Verbrennung
Wie startet man eine Piston?
direct cranking electric motor driven starters, powered by the airplane battery or external power => Drehen das magnet Feld bis 20'000 V hat für die Zündung ==> electric starter motors are usually limited in cranking time !
What is a open circuit or hot magneto
the ignition is on => the slightest movement of the propeller may start the engine if any of fuel-air mixture is present inside the cylinder
By the starting, the electric motor driven starters does not rotate fast enough to ensure ignition (20'000V) during the cranking period. How you can solve this problem?
With a magneto with impulse coupling (snapper magneto) => give one of the magnetos a brief acceleration by spring force => The fast rotation produces a hot spark for ignition => you hear a clicking
In older aircraft you have not a magneto with impulse coupling (snapper magneto). What do you make?
starting vibrators are used => low DC voltage of the battery in AC and delivers it to the primary coil of the magneto to generate high voltage in the secondary coil
In case of extrem cold weather, what happens by the ignition of the engine?
battery does not have sufficient power to crank the engine or/and the oil viscosity is too high
For what is the magneto check and how is teh function?
if both ignition systems are working and if both ignition system fire at the same time => Position left and right only used for checking
What happens by the magneto check?
RPM drop => not more drop than 150 RPM ===> no RPM drop => An open mass circuit in the previous ignition or an inoperative magneto
What is the dead cut check?
the magnetos are properly grounded, the ignition switch has to be turned off while the engine runs idle => As soon as it is certain that the engine will die, the switch can be turned to BOTH
What is a spark plug fouling ?
a rough running engine => spark fouling happen when an incorrect fuel grade is used or the mixture is too high ==> Too rich mixture can lead to carbon deposits at the spark plug tip
Retarded Ignition ?
Spätzündung heisst => -> unbrauchbar
preigntition
Frühzündung => Vorzündündung ca 25 Grad vor dem OT ==> Jedoch beim Enginestart Zündung nicht mehr 25 Grad vor der dem OT sondern beim OT beim Engine Start
When you must open the cooling flaps
Clim, T/O, Approach (für G/O), cruise with excessive cylinder heat temperature or oil temperature
The most important property of the lubricant is the viscosity. how is it expressed =
expressed by the commercial aviation oil number and changes with temperature ==> The greater the number the higher the viscosity => Oktanzahl: Index für klopffestigkeit bzw detonationsresistenz
mineral oil used in new or overhauled engines
How you can difference between Compounded and mineral oils
Compounded oils carry letters in front of the commercial aviation oil number =>> UNION OIL MD 80 (compound oil) Mineral Oil: Union Oil 80
In a wet sump lubrication system => how is teh pressure pump builds up a pressure high enough to lead the oil to the system. How is the oil lead to the system?
In a wet sump lubrication system => how is teh pressure pump builds up a pressure high enough to lead the oil via channels ==> Pressure must built up by the engine start after 30 seconds
one method to set BBP for max. engine power during fligh is ?
the mixture at full until max. EGT is indicated then enrich the mixture until a certain EGT (Temp.) drop is indicated
Aircraft pistons use normaly which injection system?
continupus flows Indirect injection
Difference Direct and indirect fuel injection
Indirect: Aircraft Direct = Car ==> vgl. Bild
Contigental Fuel injection system?
a low pressure indirect fuel injection => injects fuel into the valve port in each cylinder head => FCU = Fuel control unit
Acceleratetion Pump
Zusätzlicher Fuel in einer Kammer => When full throttel = ganzer Fuel geht in die Machine
Bei der Accelration Pump, was regelt die Feder ?
langsame Bewegung des Throttels = Feder bremst die Einspritzung => Schnelle Bewegung = Ganzer Fuel wird eingespritzt
Brennt fuel ?
Nein, nur das Gasgemisch
Primen ?
Bei der Acceleration Pump => schnelle Bewegung des Throttels und langsam nach hinten = Kammer kann sich wieder ganz füllen
Carborator ?
Vergasser
Was machen bei Engine fire ?
Schlüssel weiter drehen => Anlassen will man muss das Benzin, welches sich angesammelt hat, in den Brennraum ziehen
Indirect Fuel Injection => Vergleich mit carborator ?
(Carborator = Vergasser) Vorteil Indirect: jeder Zylinder bekommt das selbe Gemisch, da hier alle Einspritzungen am Selben Ort stattfinden a) bessere Beschleunigung b) längere Lebensdauer c) Kein Vergaser Vereisungen ======> Nur Vorteile
