New answers tagged engine
1
Stroke in this context means the duration of one of the four processes (intake, compression, power, exhaust) in a four stroke engine. An illustration shows the mechanics:
Duration of each process is measured in crankshaft degrees and is shown with a timing diagram:
Events are points in time which can be used to identify the beginning or end of a process.
...
8
The duration of the stroke is simply the time the piston takes to run from the bottom to the top of the cylinder or vice versa, half a rotation. So if the engine is running 2000 rpm, or 33.33 revolutions per second, or 16.66 strokes per second, the stroke duration is .06 seconds, half of one full revolution.
That's the physical mechanical stroke. However ...
1
If the fuel control is hydromechanical (old engines) or electronically trimmed hydromechanical (not so old engines designed in the 70s and 80s), you set each thrust lever to achieve a target value on the fan RPM (N1) indicators or Engine Pressure Ratio indicator (EPR) indicators (for a pure jet). Each engine will be set to its takeoff thrust setting, which ...
1
Why does the spool speed increase with altitude for a turbofan engine (single spool & double spool)?
As you note - as altitude increases, air density decreases.
The work done by the compressor stages therefore also decreases at any given rotational speed. If we assume constant power applied to the compressor stages (not entirely correctly) then the speed will increase until the work done matches the power input.
The overall work done by the engine will ...
15
@kevin has given the general answer, so I will only give the answer to the very specific question you asked:
What is the significance of 104%
None.
As was explained by Kevin, 100% is the design reference point. Engineers are generally very good at predicting performance, so they will typically only be off by a tiny amount. They are also typically ...
44
This happens when the maximum output was changed after design.
100% is simply a reference to a certain value. In the space shuttle's case, the engine output was increased after the initial design. Instead of updating the engine value everywhere, they decided to simply keep the initial value constant.
The same goes for N1 in turbo engines. 100% N1 is simply ...
4
The difference between a ducted propeller and a turbofan is mainly determined by the difference between a propeller and a fan.
A propeller has relatively few blades, which are relatively long and slender.
A fan has many blades, with a relatively large chord. Like a household fan.
A parameter to catch blade count and chord relative to blade length, is the ...
-1
NO. Start with the prop. What amount of power will turn that prop at 2700 rpm. 1 hp? Nope.
Let us go back to James Watt once again and see what the horse is doing: lifting weight!
Horsepower and torque have been melded together in modern definitions from applications to internal combustion limits. In order to brag about horsepower, we want rpm high ...
1
When you put a prop at the end of the shaft of an engine, and wish to turn that prop at a given rpms, the existence of the atmosphere induces a resisting torque that must be compensated by an equal and opposite acting torque supplied by the engine. At any stable rpms, the relation is:
power supplied = angular speed x torque.
Obviously, and for a give ...
-1
It all depends on the propeller one can use:
The prop should rotate at as much RPM as possible because force is proportional to speed squared and one want a small PropPhiW as possible (the AOA required by the prop-speed / airspeed geometry). Lower PropPhiW means increased efficiency.
The prop's tips should rotate below the speed of sound, or else massive ...
-2
There are no mechanically significant shock loads on an airplane engine in normal operation.
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