39

The most efficient IC engines are large Diesels. At the extreme end are ship engines with better than 50% thermal efficiency resulting in a specific fuel consumption of only 0.260 lbs/hp/hour or 158 g/kW-h. But even supercharged truck diesels achieve above 40% thermal efficiency at high load (this NHTSA study gives 42%). Aerodiesels have achieved 220 g/kW-h ...


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 ...


30

The props are done before starting because you need to make sure the blades and spinners are fully cleaned off while they are stationary. Otherwise, they'd vibrate like hell when starting and shed bits of ice all over. Also, if you just sprayed the props while running the engines would ingest a lot of glycol, which, if it doesn't make the engine flame out, ...


22

No, a turboprop is more like a jet engine with a propeller in the front instead of a fan: Source: Wikimedia In its simplest form a turboprop consists of an intake, compressor, combustor, turbine, and a propelling nozzle. Air is drawn into the intake and compressed by the compressor. Many turbo props have a gear box (as shown in the image above, the ...


22

Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo compressor to pressurize fresh air from the outside: Modern aircraft with supercharged piston engines simply use bleed air from a) the main engine's ...


19

A turboprop plane can be pressurized in the same way a turbofan plane can: via bleed air from the compressor stage of the turbine engine. A turboprop and turbofan are not that different actually. You have a turbine engine core that powers the big fan at the front or the big propeller via a gearbox (although the turbofan still gets some of its thrust from the ...


10

The NK-12 engine uses a differential epicyclic (planetary) gearbox. Unlike the typical planetary gearboxes where one of the gears is fixed, here all three parts are moving: the turbine drives the sun, the planet pinion drives the front propeller, and the ring drives the rear propeller. The gear ratios are the same between the front and rear, but the torque ...


9

How does turbine efficiency compare with internal combustion engines if all the turbine power is converted to mechanical energy? When looking at conversion from chemical energy into mechanical energy: very favourably. The early turbojets had low thrust efficiency, they could not convert their gas generator power into thrust in an efficient way. When ...


8

I was a P-3 Flight Engineer and the Allison T-56 engines had engine driven compressor's mounted on the propeller gearboxes on the inboard engines that allowed for a 30'000 ft. Ceiling.


8

My guess, and it's just a wild guess, is humidity based ice forming somewhere in the inlet and/or the inlet plenum, more or less similar to carburetor icing. The symmetrical torque drop is from the flow restriction and the random vibration is when the ice breaks up. I'll guess that you were flying though what appeared to be clear or clearish air with the ...


6

Jendrassik's own patent from 1939 does not go in-depth into the alloys. However, for the turbine blade legs he mentions "austenitic [stainless] steel" as preferable (see PDF page 3). From that era, a Swiss patent from 1937 on the materials of gas turbine parts also discusses austenitic steel, in particular (translated from German): Alloy of an austenitic ...


5

Ice flying off the propellers can damage something, or someone. Also unbalances the propeller assembly overall, leading to vibrations. Little bit of ice left on the fuselage is not bad, only causes some extra drag until it sublimates off, and of course a little extra weight. Ice Will impact the lift created by the wings, that is very bad, unless the ice is ...


5

Yes it loads up the battery, but the battery is sized to do this. The generator is not necessarily sized to do this, especially on the ground, so this procedure gets you to take the generator out of the system for each start. On an Alternator, like on your car, there is a phenomenon known as 'forward-stripping', which is where there is such a demand for ...


5

Two worlds There are two elements constraining propeller use: The thrust we can get from a free propeller is lower than from a ducted fan at the same airspeed. Propeller efficiency quickly decreases with Mach number. Propeller performance vs speed. Source For these reasons fans are the natural choice for large and fast aircraft, and propellers for slower ...


5

A turbocharged engine is a common gas engine with pistons The limiting factor on a gas engine is how much air can get into the pistons. It is supercharged - that is, an air pump forces more air into the engine than it would draw naturally. The mechanically driven variety is seen on Mad Max. If you use exhaust flow to spin the pump, it is turbosupercharged. ...


4

I can’t say for sure about the jet engine mentioned. If I think of it like a piston engine, the fuel pump pressurizes the fuel lines. That in no way means that the fuel is entering the combustion part of the engine (cylinders in my case). It just means that the fuel lines leading to the fuel distribution point (carburetor or EFI) are being fed fuel at a ...


3

They are completely different things, a turboprop is similar to a jet engine as it has compressors, the main difference is that there's a shaft that spins a propeller instead of turning a fan. A turbocharger is device for piston engines, it uses pressure coming from the exhaust manifold of a piston engine to compress air going into the intake manifold. It'...


3

Very well as the Carnot efficiency is what drives the theoretical limit, and that is driven by the temperature of the combustion. 1 - T_h/T_c (in Kelvin) Turbines have very hot combustion chambers (diesels too, gasoline less so (due to knocking)). So a turbine operating in cold air will have great performance. In electricity generation Natural Gas ...


3

Very poorly actually. What saves turboprops and turboshafts is power to weight, smoothness and reliability. If you want just maximum MPG and don't have to go trans sonic, recip wins hands down. Piston engine Specific Fuel Consumption is roughly .45 lbs/hp/hr for a normally aspirated carbureted engine (that figure comes from my own Lycoming engine's power ...


3

To generate a given thrust, a turbofan accelerates less air but faster than a turboprop. This means that turbofans can fly faster. However thermodynamically it is more efficient to accelerate a greater mass of air slower, so turboprops are more efficient and that translates into lower fuel burn.


3

The pump just creates the pressure. The fuel doesn’t have anywhere to go until you move the condition lever to idle. Think of it like your faucet: There is water pressure there, but it doesn’t flow anywhere until you open the valve.


3

On most (probably all) PT6 installations, the fuel pumps send much more fuel than the engine needs. That extra fuel is then returned to the fuel tanks. This is true both during operation and before engine start.


3

Piston powered aircraft can also be pressurized, the models that are have turbo-superchargers, an exhaust driven turbine that pressurises the air going into the cylinders. Some of the air from the turbos goes to the passenger cabin. The level of pressure is controlled by outflow valves just like jet powered aircraft.


3

For more background, this question is about the usage of Breguet Range Equation (I find this explanation better suited for this question) There are many problems with your calculation: Time unit of speed should be the same as the time unit of SFC. For your first calculation, since you used mph for speed and lb/(hp*h) for SFC, your SFC term shouldn't have 1/...


2

I think there are some confusion here, in particular, as @user3528438 said, with units used in formulas. I'll also try to highlight problem with another point of view. 1. Formulas comparison First of all, be really careful when using the first formula. At first, I thought it was not consistent regarding range R units. The way you make calculation ...


2

It’s all dependent upon what operating speeds your aircraft will be in. Propellers can move a great volume of air at slow speeds but accelerate the gas to a lower exit speed than does a turbojet or a turbofan. This is the principal reason that a helicopter is the most efficient means of VTOL flight out there for a heavier than air aircraft. But as speeds ...


2

Assuming that both props are rotating clockwise as seem from the rear, the orientation of the exhaust pipes makes sense if the goal is to ensure that the exhaust gasses are kept clear of the wing. The rotating propwash will tend to carry the exhaust from the right-side pipe (in rear view) of each engine well below the wing. If the left-side exhaust pipes ...


2

Large airliners don't fly at slower speeds. It's simple economics. If you have to connect two destinations 10,000 miles apart, you'll do maybe 2 round trips a week. Your passengers have no other choice, except a flight that takes even longer. You also have the luxury of flying between two very large cities. If you have to connect two destinations 100 ...


2

No, one is https://en.wikipedia.org/wiki/Otto_cycle one is https://en.wikipedia.org/wiki/Brayton_cycle, thermodynamicly extremely different


1

Well, propellers deliver thrust and turbofan engines deliver power to the fan axis, it is just a matter of choice. Finding the thrust that a propeller generates at a specific airspeed and altitude, can be derived from the drag of the whole airframe in those conditions. Statistically, this sort of data can be found in reference books on pre-design of ...


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