81

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 ...


70

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 ...


61

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


40

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

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 ...


31

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 ...


31

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 "...


29

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 ...


29

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

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. ...


26

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. ...


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

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 ...


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.


24

Simple Answer: Running the engine lean or rich at different altitudes. Longer Answer: There are a couple of reasons you want to adjust the mixture of a aircraft engine. Since air density changes with altitude, it's a good idea to be able to change the fuel/air mixture at different altitudes. If you did not adjust the mixture at high altitudes you may ...


24

The life of an aircraft engine is measured in hours of operation since some major service was done to it. When looking at ads for planes there are three regulatory terms that you'll see in engine descriptions: New (TSN) This one is pretty self explanatory - A brand new engine, produced with all brand new parts that comes to you right from the factory (or an ...


24

Bold Method has a great post today about why aircraft engines have more than one spark plug per cylinder. There are a few basic reasons. Reliability Having two sparks plugs is more reliable. If one spark plug becomes inoperative for some reason, there's a second to provide the spark for the power stroke. It should also be noted that the spark plugs are ...


23

The big advantage of radials at the beginning was their large frontal area, which meant they could be air cooled. An inline air cooled engine can run pretty hot on the rear cylinder. The bigger the engine, the more of an issue cooling becomes. There are some huge air cooled radials, in sizes that would be unthinkable for an air cooled inline engine. As ...


23

The answer is probably indeed A. Pegoud with a Bleriot monoplane in the fall of 1913, as answered by RedGrittyBrick. After that, a real craze started in Europe with stunt pilots flying briefly inverted at air shows. The first purpose-designed airplane for inverted flight was probably a Grade monoplane which flew first in the spring of 1914. I have found ...


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