83
An odd number of cylinders is required by the combination of the single-crank radial design, the four-stroke (Otto) work cycle, and the desire to keep the power strokes evenly spaced in time.
To keep the design simple and lightweight, a single-bank radial airplane engine has one crank, which means that the pistons must reach the top of their travel in ...
76
Broadly speaking, there are three families of motor fuel that you're probably interested in: Diesels, Kerosenes, and Gasolines.
The difference between the families mainly has to do with the molecular weight (and thus boiling point / vapor pressure) of the fuel components - in order above from heaviest to lightest. The differences within each family are ...
74
The engine in a typical light airplane (say a Cessna 172 or a Piper Cherokee) has a lot in common with the engine in a classic 1960s VW Beetle (Type 1): Both engines are horizontally opposed four-stroke four-cylinder spark ignition gasoline engines. Their parts even have similar metallurgy, and broadly similar failure rates.
In fact if you remove the gearbox ...
71
Weight.
Piston APUs for trucks are designed for frugal and quiet operation. This one produces 5.2 kW electrical power and weighs 375 lbs.
The APU for the A320 and B737 is a noisy screaming unit that produces 90 kW electrical power, 445 shaft kW. It weighs 375 lbs as well.
The main difference is in the weight of the engine itself. The turbine engine of the ...
66
Several issues:
As you mentioned, high specific fuel consumption. About to that of turboprops, but without the reliability. If you're going to live with that SFC, you might as well as go with turbines.
Poor reliability. They are very sensitive to tuning and timing. A 4 stroke piston aircraft engine will run with all kinds of things wrong with it. Cam ...
54
Because of the quantity of water in the fuel, as opposed to a careful introduction of water into the combustion process. Typical water contamination is bad in fuel tanks as water is denser than aviation fuels and settles at the bottom of the tanks. Aviation fuels are also hydrophobic (non-polar) and so do not readily mix with water. Therefore water will ...
45
Firstly, to understand the answer, we need to understand that the Cessna 152's and 172's run a 4 Cylinder, Horizontally-opposed Engine. Each Cylinder has 2 spark plugs, one on the top side of the cylinder head, and one on the bottom side. The spark plug ignites the fuel/air mixture that has been sucked into the engine, and causes a controlled burn to push ...
45
Constraints
Different applications have different constraints:
Aviation: very light weight, highly reliable
Marine: very high endurance
Automotive: moderately light weight, responsive
Motorcycle: very light weight, very compact, very responsive
Different technology ages yield different solutions due to additional constraints, always limited by the then ...
44
Automobile engines are not similar. They are liquid-cooled and therefore can be built to much tighter tolerances with regard to thermal expansion and contraction.
Air-cooled aircraft engines must deal with a large range of operating temperatures and oil is consumed due to the relatively looser fit of the piston rings.
43
It is a fitting for a Hucks Starter.
Photos from Vintage Wings Canada
41
Jet engines are only efficient at high altitudes and high speed (25,000+ feet or so and 300+ knots or so true airspeed). The cost of making and operating an airplane capable of flying there is very high, and most general aviation flights have no need of such performance (or expense) hence, propeller airplanes.
Reciprocating engine propeller airplanes are ...
38
They are both internal combustion engines that have a turbine in their exhaust that is used to power a compressor to pressurize the air before it is used for combustion.
In the turboprop, the turbine also powers the prop. In between the compressor and turbine, the fuel/air mixture is burnt without significant moving parts. Without the turbine and ...
34
Reading the answers here tells me to put a few facts into the discussion:
Piston engines are the most fuel efficient aviation engines. Their drawback is a constant power output over speed, so that thrust is inverse to speed. This helps for acceleration at take-off, but limits maximum speed. A modern piston engine uses 240 g of fuel for providing 1 kW of ...
34
Well, first let's clear up a few terms:
When you say "rotary" engine I'm assuming you're referring to radial engines, a type of piston engine that used to be pretty common on aircraft. (These days opposed piston engines are what you typically find on piston-powered aircraft, rotary engines are yet another design, but their usage died out around the end of ...
33
You should always pull the carb heat when throttling back no matter the conditions for 3 reasons:
Ice forms from moisture (duh!), and there's much more moisture in hot tropical air than cold arctic air, so being in a tropical location does not lower the icing potential. The temperature drop is caused by the Venturi Effect which aerates the fuel in the ...
32
All your plane's systems are happier when you're flying, including the pilot.
Ideally, you'd fly often in order to keep your engine happy (distributing clean oil throughout the system to protect against corrosion and heating it enough to drive off water from the crankcase).
As a rule of thumb Blackstone Labs (the oil analysis folks) consider piston engines "...
31
Detonation, as the name suggests, is an explosion of the fuel-air mixture inside the cylinder. Under normal operation, the spark plugs each ignite a point in the fuel/air charge, which then propagate through the cylinder and provides a consistent, regulated burn in a process called deflagration. This extends the time that the burning fuel pushes on the ...
31
A magneto is a gear driven electric generation device connected to the crankshaft of the engine. It supplies the ignition system (spark plugs) with power.
Each engine has two magnetos. Each cylinder has two plugs. Each magneto supplies one plug in each of the cylinders. This makes the ignition system redundant. If a magneto fails, the other magneto can ...
30
Two more reasons the gas turbine supplanted the piston engine for aircraft use:
Power output. Aircraft piston engines have a practical limit on how much power they can put out, before becoming inefficient. This worked out to be around 3000hp. Two of the largest and most powerful piston aircraft engines that were also reliable enough for aircraft use are the ...
28
Aviation engines run at near max RPM through out the flight. A car on the other hand doesn't use the full RPM spectrum except in bursts.1
If a car engine was utilized the same way an aviation engine is, it won't last long.
So an aviation engine is sturdier, heavier, and weaker (hp) for the same displacement, but also provides higher torque (big cylinders)....
28
Water-injection in jet engines and piston engines is mixed with fuel
before it enters the combustion
This is actually somewhat wrong (or at least imprecise) and I think it is adding to the misunderstanding. The water and fuel are never "mixed" in the traditional sense as liquids. An aerosol of fuel is injected... Also, an aerosol of water is injected. The ...
27
Deliberate momentarily inverted flight
The first reported deliberately inverted flight was probably in a Blériot model XI.
Inverted flight was also being considered. Several pilots had inadvertently found themselves upside down as a result of wind gusts, but no one had yet attempted it intentionally. Adolphe Pegoud decided he would be the one to try.
Pegoud ...
27
Your reasoning is correct if engine mass is not important. Ships use huge engines, because increasing the number of cylinders beyond 8 will have diminishing returns in terms of smoothing out the torque ripples, and bigger cylinders help to increase efficiency. But aircraft need to keep the mass of the engine down.
Wartsila-Sulzer RTA96-C turbocharged two-...
27
straight out of the Airplane Flying Handbook, pp 9-4
Operating the engine at idle speed for any prolonged period
during the glide may result in excessive engine cooling, spark
plug fouling, or carburetor ice. To assist in avoiding these
issues, the throttle should be periodically advanced to normal
cruise power and sustained for a few seconds.
...
27
There are several benefits:
piston engines are best for driving propellers. At the same shaft horse power $P$, propeller thrust $T$ varies with the inverse of air speed $v$: ($T_{Prop} = \frac{P}{v}$). This means that the power requirement to keep a piston-powered aircraft flying will increase with the third power of airspeed at high speed. In order to fly ...
27
When you shut down a radial the unscavenged oil in the case (oil coating the surfaces that didn't get pumped back to the reservoir tank) runs down and seeps past the rings of the cylinders directly below and to each side at the bottom. In theory, it can create an hydraulic lock if there is enough oil collected in a cylinder, that happens to be on its ...
26
As others have noted, airplane engines and car engines have very different duty cycles. An airplane engine will typically run at full power for a few minutes during takeoff & climb, then at a large fraction of max during level flight, which may last for hours, and be throttled back only during descent and landing.
An auto engine, by contrast, only ...
26
This is a hot-mag check to verify that when you shut the engine down, you are really putting it in a safe(r) state. Think about how the mag-switch works, when you switch to R or L, it grounds the P-Lead on the other side (so switching to R grounds the P-Lead on the Left side). If you don't see the RPM drop, you may have a hot mag on that side.
An un-...
25
Feathering is only possible with variable pitch propellers and means that the blades are turned such that their mid-to-outer section is aligned with airflow and they create minimal air resistance. This is done when the engine is shut down and the propeller should create minimal drag. This means also that all accessories on this engine will not be powered ...
25
Cessna 150s have a mechanical tachometer driven by a mechanical tach drive cable geared to the engine.
The tach needle is moved by sensing spinning magnets driven by the tach cable.
They do wear out over time and yours has reached the end of its life.
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