Carbon fan blades
I agree with most, so I guess I'm just picking at knats. But being a technical forum that's where we learn.
Polar fan mass should mostly affrect acceleration and fan mass flow should mostly affect the turbine energy to keep the RPM constant. Some features act like flywheels and are good but both Boeing and Airbus care about the mass that they have to balance on the wing, therefore less weight sells.
Polar fan mass should mostly affrect acceleration and fan mass flow should mostly affect the turbine energy to keep the RPM constant. Some features act like flywheels and are good but both Boeing and Airbus care about the mass that they have to balance on the wing, therefore less weight sells.
I suppose a lighter fan would absorb less energy spooling up. Then less power would be required to reach a given RPM in a given time period, and perhaps the engine could be sufficiently responsive with fewer turbine stages. Of course, that assumes spool-up time and not maximum RPM is the limiting factor.
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I suppose a lighter fan would absorb less energy spooling up. Then less power would be required to reach a given RPM in a given time period, and perhaps the engine could be sufficiently responsive with fewer turbine stages.
But during acceleration (such as GA) or deceleration, the lighter rotor will respond faster.
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barit1
"But during acceleration (such as GA) or deceleration, the lighter rotor will respond faster"
Except the designers have re-invested that improved rate into larger blades, with more surface area, and longer chord, such that the net effect is to move more air than the smaller Titanium blades they replace? So the improved acceleration is a 'wash', essentially? The modified resin/matrix allows for significant improvement in aero over the Ti, so lighter, more effficient, less machinery by weight.
The design also won a design award for composites. They're beautiful.
Three thousand pounds of mass per second.
"But during acceleration (such as GA) or deceleration, the lighter rotor will respond faster"
Except the designers have re-invested that improved rate into larger blades, with more surface area, and longer chord, such that the net effect is to move more air than the smaller Titanium blades they replace? So the improved acceleration is a 'wash', essentially? The modified resin/matrix allows for significant improvement in aero over the Ti, so lighter, more effficient, less machinery by weight.
The design also won a design award for composites. They're beautiful.
Three thousand pounds of mass per second.
Last edited by Lyman; 10th Nov 2012 at 03:28.
It seems to me that greater aerodynamic efficiency would (of course) reduce the power needed to spin the fan, but lower operating RPM, by itself, would not. All else being equal, a slower fan making the same thrust will need more torque to spin it, and the total power required will be the same.
But all else is seldom equal. It seems reasonable that slowing the fan would reduce losses to internal drag and friction. And, as mentioned, a slower fan absorbs less energy on spool up, which should add to its responsiveness.
But all else is seldom equal. It seems reasonable that slowing the fan would reduce losses to internal drag and friction. And, as mentioned, a slower fan absorbs less energy on spool up, which should add to its responsiveness.
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I don't think so, lomapaseo. Moving mass at a steady state with less energy is the definition of higher efficiency, no? (from barit1).... The aero efficiency increases, due to increased latitude with design/material, so more work is done with less expenditure of energy. RPM is erm......rate, not NET? The gaspath thrust past LPT is not neglected, the number of stages and their respective capture rate leave a remainder. This does not moot their number; it is a ratio that gets selected based on core power, as TurbineD says. In this engine, the exhaust is ten percent of the power available. Actually, with a bypass ratio of 9/1 more like 11.13 per cent?
I think some credit for the success of this engine and its airfoils should be shared. The use of welded compressor disc/blade rotors, Titanium alloys in high temp areas, and coatings are not inconsequential.
Rgds
I think some credit for the success of this engine and its airfoils should be shared. The use of welded compressor disc/blade rotors, Titanium alloys in high temp areas, and coatings are not inconsequential.
Rgds
Last edited by Lyman; 10th Nov 2012 at 14:42.
