The purpose of the venturi in a carburettor is to ? Students > orientation
Create suction necessary to cause fuel to flow through carburettor main jets.
The mixture controller of a carburettor ?
The mixture controller of a carburettor Varies fuel supply to main discharge nozzle.
A turbocharger system in a reciprocating engine is normally driven by ?
A turbocharger system in a reciprocating engine normally driven Varies fuel supply to main discharge nozzle.
this short illustration explains clearly principle. An aircraft magneto switched off 1 grounding primary circuit 2 opening primary circuit 3 opening secondary circuit 4 grounding secondary circuit the combination that regroups all of correct statements Varies fuel supply to main discharge nozzle.
a magneto essentially a self contained generator which gear driven the engine
the ignition switch in cockpit when selected off ground magnetos to earth through primary circuit
it works also the secondary circuit but usually this the primary circuit which grounded. Spark timing related to engine speed in way that Faster engine functions more spark advanced. The ignition timing of a piston engine needs to be advanced at 'high rpm' because flame rate time complete combustion remain constant. An impulse magneto coupling Gives a retarded spark at starting. The impulse coupling a spring loaded mechanical coupling which delays rotation of magneto during an engine start after a short period of rotation device allows magneto to catch up in effect spinning mag shaft faster than engine turning it
the faster it turns hotter spark the bigger voltage impulse making easier starting after engine running rotational forces move spring loaded arms which make impulse coupling work at low speeds out of way the impulse coupling only works at very low engine speeds. If an engine fails to stop with magneto switch in off position cause may be Excessive carbon formation in cylinder head. The magneto switch controls primary magneto circuit grounding it this done to isolate individual magnetos during rpm drop check
if this wire broken therefore cannot be earthed then magneto will continue to supply current to engine it will continue to run
the correct answer as stated excessive carbon formation this forms hot spots which remain heated continue to ignite mixture even though plugs are not sparking!. 8 An impulse coupling installed on a magneto of a piston engine to Provide a stronger spark on top dead centre engine starting. The impulse coupling a spring loaded mechanical coupling which delays rotation of magneto during an engine start after a short period of rotation device allows magneto to catch up in effect spinning mag shaft faster than engine turning it
the faster it turns hotter spark the bigger voltage impulse making easier starting after engine running rotational forces move spring loaded arms which make impulse coupling work at low speeds out of way the impulse coupling only works at very low engine speeds. 9 The part of a piston engine that transforms reciprocating movement into rotary motion termed Provide a stronger spark on top dead centre engine starting. The impulse coupling a spring loaded mechanical coupling which delays rotation of magneto during an engine start after a short period of rotation device allows magneto to catch up in effect spinning mag shaft faster than engine turning it
the faster it turns hotter spark the bigger voltage impulse making easier starting after engine running rotational forces move spring loaded arms which make impulse coupling work at low speeds out of way the impulse coupling only works at very low engine speeds. 10 In a piston engine if ratio of air to fuel approximately 9 1 mixture Provide a stronger spark on top dead centre engine starting. Rich 9 1
correct 15 1
weak 20 1. 11 Spark plug fouling more likely to happen if The aircraft descends continuously at idle power.
plug fouling can occur due to rich mixtures with low cylinder temperatures this the condition engine will be in during descent at idle power
this the reason during your flight training you are told not to let engine run at idle rpm too long normally you would increase rpm to around 1000 1200 rpm. 12 To maintain a constant mixture at low and high power settings in a piston engine a carburettor fitted with A diffuser (compensating jet). As engine speed airflow through venturi increase proportion of fuel to air rises as a result of different flow characteristics of two fluids this causes mixture to become richer
to overcome this effect some carburettors are fitted with a diffuser (compensating jet)
as engine speed progressively increased above idling fuel level in diffuser well drops progressively uncovers more air holes these holes allow more air into discharge tube by reducing pressure differential prevent enrichment of air/fuel mixture
the process of drawing both air fuel through discharge tube also has effect of vaporising fuel more readily particularly at low engine speeds. 13 A piston engine may use a fuel of a different grade than recommended Provided that grade higher. As engine speed airflow through venturi increase proportion of fuel to air rises as a result of different flow characteristics of two fluids this causes mixture to become richer
to overcome this effect some carburettors are fitted with a diffuser (compensating jet)
as engine speed progressively increased above idling fuel level in diffuser well drops progressively uncovers more air holes these holes allow more air into discharge tube by reducing pressure differential prevent enrichment of air/fuel mixture
the process of drawing both air fuel through discharge tube also has effect of vaporising fuel more readily particularly at low engine speeds. 14 In very cold weather pilot notices during startup a slightly higher than normal engine oil pressure this higher pressure Is normal if it decreases after startup. As engine speed airflow through venturi increase proportion of fuel to air rises as a result of different flow characteristics of two fluids this causes mixture to become richer
to overcome this effect some carburettors are fitted with a diffuser (compensating jet)
as engine speed progressively increased above idling fuel level in diffuser well drops progressively uncovers more air holes these holes allow more air into discharge tube by reducing pressure differential prevent enrichment of air/fuel mixture
the process of drawing both air fuel through discharge tube also has effect of vaporising fuel more readily particularly at low engine speeds. 15 Excessive pressure in cylinders of an engine equipped with a constant speed propeller can be caused the combination of High manifold pressure low rpm. With constant speed control pitch of variable pitch propeller changed automatically a governor after pilot sets desired engine/propeller speed with propeller speed control governor acts to keep propeller speed at same value if governor detects propeller speed increasing it increases pitch a little to bring speed back within limits if governor detects propeller speed decreasing it decreases pitch a little to bring speed again back within limits this operation may be compared to an automatic gearbox in an automobile where gears are changed automatically to keep engine operating at a reasonable speed
during a power change on an engine equipped with a constant speed propeller a wrong combination of manifold pressure rpm values results in excessive pressures in cylinders this the case when one simultaneously selects a high manifold pressure low rpm. 16 When in flight a piston engine stopped and propeller blade angle near 90° propeller said to be High manifold pressure low rpm. With constant speed control pitch of variable pitch propeller changed automatically a governor after pilot sets desired engine/propeller speed with propeller speed control governor acts to keep propeller speed at same value if governor detects propeller speed increasing it increases pitch a little to bring speed back within limits if governor detects propeller speed decreasing it decreases pitch a little to bring speed again back within limits this operation may be compared to an automatic gearbox in an automobile where gears are changed automatically to keep engine operating at a reasonable speed
during a power change on an engine equipped with a constant speed propeller a wrong combination of manifold pressure rpm values results in excessive pressures in cylinders this the case when one simultaneously selects a high manifold pressure low rpm. 17 The richness of a fuel/air mixture ratio the Real mixture ratio relative to theoretical ratio. As name implies mixture refers to ratio of fuel/air that goes into cylinders of an engine combustion for an internal combustion engine to operate it requires three things fuel air ignition fuel air are mixed in a ratio of approximately 15 1 (15 parts of air to every 1 part of fuel) to create combustion in a carbureted engine (non fuel injected) fuel air are mixed in carburetor before being introduced into cylinders
carburetors are calibrated to operate with mixture control set to 'full rich' when operating at sea level as aircraft gains altitude it becomes necessary to reduce amount of fuel entering carburetor because amount of air automatically decreasing with altitude due to lower atmospheric pressure if pilot fails to decrease amount of fuel as altitude gained result will be an overly 'rich' mixture creating problems such as fouled spark plugs excessive fuel consumption
overheating problems tend to occur when operating with an excessively lean mixture (too little fuel) a lean mixture creates better performance (to a point) as well as higher operating temperatures reduces fuel consumption the problem arises when pilots fail to enrichen mixture (add fuel) as altitude lost during a descent this results in an excessively lean mixture which can cause engine roughness fuel starvation even permanent engine damage the point to remember that fuel mixture must be decreased (leaned) as aircraft climbs increased (enrichened) as aircraft descends it also suggested to lean mixture during ground operations at higher altitude airports (generally above 3000 ft amsl)
the term 'richnes refers to 'real mixture ratio' relative to 'theoretical mixture ratio'. 18 Dual ignition provides a factor of reliability and Improves combustion efficiency. As name implies mixture refers to ratio of fuel/air that goes into cylinders of an engine combustion for an internal combustion engine to operate it requires three things fuel air ignition fuel air are mixed in a ratio of approximately 15 1 (15 parts of air to every 1 part of fuel) to create combustion in a carbureted engine (non fuel injected) fuel air are mixed in carburetor before being introduced into cylinders
carburetors are calibrated to operate with mixture control set to 'full rich' when operating at sea level as aircraft gains altitude it becomes necessary to reduce amount of fuel entering carburetor because amount of air automatically decreasing with altitude due to lower atmospheric pressure if pilot fails to decrease amount of fuel as altitude gained result will be an overly 'rich' mixture creating problems such as fouled spark plugs excessive fuel consumption
overheating problems tend to occur when operating with an excessively lean mixture (too little fuel) a lean mixture creates better performance (to a point) as well as higher operating temperatures reduces fuel consumption the problem arises when pilots fail to enrichen mixture (add fuel) as altitude lost during a descent this results in an excessively lean mixture which can cause engine roughness fuel starvation even permanent engine damage the point to remember that fuel mixture must be decreased (leaned) as aircraft climbs increased (enrichened) as aircraft descends it also suggested to lean mixture during ground operations at higher altitude airports (generally above 3000 ft amsl)
the term 'richnes refers to 'real mixture ratio' relative to 'theoretical mixture ratio'. 19 With a piston engine when detonation recognised you Reduce manifold pressure enrich mixture. The sudden release of heat energy from fuel in an aircraft engine caused the fuel air mixture reaching its critical pressure temperature
detonation occurs as a violent explosion rather than a smooth burning process
when detonation recognized you should reduce manifold pressure enrich mixture
detonation can be caused by
too lean mixture
too high manifold pressure
using low grade fuel
an overheated engine. 20 'vapour lock' the phenomenon which Heat produces vapour bubbles in fuel line. The vapour lock a stoppage in a fuel feeding line caused a fuel vapour bubble. Exclusive rights: Content under private and protected license, reproduction prohibited and prosecuted.
