Carbon fan blades

[Yankee Whisky]

Are there any carbon fibre fan blades in use in modern engines ? If so,

how are they protected from disintegration when hit by an object ?

I seem to have read somewhere that a new P&W design incorporates them,

if that is true.

[TURIN]

Yup.

General Electric GE90

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/GE90_dsc04644.jpg/300px-GE90_dsc04644.jpg

Carbon fibre blades with Titanium leading and trailing edges.

[DaveReidUK]

I seem to have read somewhere that a new P&W design incorporates them.

You probably read it here:

http://www.pprune.org/tech-log/499251-did-pratt-just-switch-carbon-fans-their-new-engine.html

if that is true.

It isn't.

[Yankee Whisky]

Thanks everyone for your info. I was with RR when the proverbial sh't hit the fan and I lost my job as a result (RB211/Lockheed L-1011 lawsuit). Therefore, I am very interested in what solutions are being discovered to reduce (I don't think I can use the word eliminate) the disintegration of a blade when hit by a big bird ! Is the titanium structural and able to contain the failure ?

Anyone has the stats on the failure rate of the GE carbon fan with titanium L/E ? What are the resultant secondary damages ?

[Yeelep]

Not an engineer, but I think the primary purpose for the titanium may be to prevent erosion.

[FlightPathOBN]

bird o matic

[EEngr]

how are they protected from disintegration when hit by an object ?
I'm not a structural or propulsion engineer, but I did some work on carbon fiber energy storage flywheels some years ago. My understanding of the failure modes of carbon fiber is that it 'delaminates' and produces something akin to cotton candy. The resulting material is much easier to contain (within the flywheel housing or in the case of an engine, the cowling).

I suspect that the design approach is to let the blade disintegrate after a certain sized impact and then to contain the parts of the blade.

[Lyman]

EEngr

Isn't the purpose of a flywheel to "store" energy? The purpose of a fan to "shed" it?

A lightweight rotor is not the goal in energy storage? I am curious as to why a light wheel is desirable for retaining energy?

A light fan is more responsive to changes in rpm, as well, is that not also a reason for CF?

[Yankee Whisky]

Quote

I'm not a structural or propulsion engineer, but I did some work on carbon fiber energy storage flywheels some years ago. My understanding of the failure modes of carbon fiber is that it 'delaminates' and produces something akin to cotton candy. The resulting material is much easier to contain (within the flywheel housing or in the case of an engine, the cowling).

I suspect that the design approach is to let the blade disintegrate after a certain sized impact and then to contain the parts of the blade.


That makes sense and containment was indeed one purpose of the CF blades plus the reduced gyroscopic affect from the weight saving, but probably not in aerodynamic profile thickness.
I can see that a carbon flywheel could have been useful in an artificial horizon instrument before the arrival of solid state sensors and GPS. What other applications were there ?

[Turbine D]

To answer some of the questions posed here with some background information:
1. When the GE90 engine was in the conceptual stage of design, composite fan blades were part of the design. The basis for this came from the GE36 engine experience, an engine which had composite propulsors.
2. Composite fan blades are very strong given the methodology of construction and the materials used. Two key reasons on the GE90 for going this way was weight savings (300 lbs. per engine) and freedom of aerodynamic design. The "swept wing" aerodynamic design permits more air to be drawn into the engine producing added thrust. At the time, there wasn't a capable titanium process to yield the shape that was desired. The fan blades are about 4 feet long.
3. The thin titanium shield around the fan blade leading edge is to prevent erosion, particularly from sand. There is no titanium shield required on the trailing edge.
4. As I stated above, the fan blades are very strong and resist damage due to impact better than titanium fan blades. The experience in service has been remarkably good in this respect. For a substantial operating time, no fan blades required removal for bird strikes until several aircraft experienced large bird strikes, i.e., 9 to 10 lb. birds where the fan blades required removal and repair. As the engines have aged, the main cause of removal for servicing involves tip erosion probably from shedding ice prior to TO. There is a required procedure to accomplish this and of course there can be fan unbalance and tip rubbing while the procedure is carried out.
5. The fan casing on the GE90 is perfectly capable of containment should a whole fan blade completely break off as demonstrated as part of the engine certification program.
6. On the GEnx and Leap engines, the fan casing metallic material has been replaced by a composite fan casing. Again, it saves engine weight while being extremely strong, resisting penetration by foreign objects and the tendency to want to turn oval under full power.
7. A lighter fan has several advantages, one of which is less required LPT blade stages which drives the fan and another being reduced pressure on shaft bearings and seals.

Below is a photo of a GE90 Fan blade. One of these is on display in the museum of modern art in NYC as an example of modern freeform design. I know of at least two fan blades being donated to charities for fund raising auction events.

http://i1166.photobucket.com/albums/q609/DaveK72/40562b08-8c63-4f51-95bb-819751a3e743Large.jpg

GE 90 Certification Test - YouTube

TD

[DaveReidUK]

resisting penetration by foreign objects and the tendency to want to ovulate under full power

Ah, so you've met my wife ...

[Turbine D]

DaveReidUK,
Ah, so you've met my wife ...
Good catch!:ok:

I change the wording...
Regards,
TD

[Turbine D]

msbbarratt,
Is the point that GE weren't interested in greater thrust, just improved efficiency?
Actually GE was interested in both. Since most of the thrust is developed by pushing air through the fan by-pass, the geometric shape of the composite fan blade increased by-pass flow, thus higher thrust. At the same time, less stages of LPT blades were required to drive the lighter fan, thus improving efficiency. In going from 76,000 lbs of thrust (early certified model) to 115,000 lbs of thrust, some architecture changes were made to engine components to increase fan speed, fan diameter, engine core speeds and turbine temperatures, but the number of LPT blade stages remained constant at 6 stages even with the larger fan blades on the GE90-115B.

TD

[EEngr]

I can see that a carbon flywheel could have been useful in an artificial horizon instrument before the arrival of solid state sensors and GPS. What other applications were there ?Energy storage: Chrysler Patriot - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Chrysler_Patriot)

The app I was working on was the use of flywheels in UPS/Static inverter systems.

[lomapaseo]

Actually GE was interested in both. Since most of the thrust is developed by pushing air through the fan by-pass, the geometric shape of the composite fan blade increased by-pass flow, thus higher thrust. At the same time, less stages of LPT blades were required to drive the lighter fan,

I can't get my head around the number of turbine stages being less becauses the fan weighs less for the same flow rate. I would have thought that the number of turbine stages would have been related to constant flowrate (all else being equal)

[Lyman]

The rotor mass is less, takes less energy to maintain its RPM, and the energy is more quickly translated into flow. I think the stress on the rotating machinery is less as N1 fluctuates, also.

Is the serpentine design to allow more blade length without adding diameter to the rotating disc? Less tip speed for given swept area?

[Yankee Whisky]

Quote; Energy storage: Chrysler Patriot - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Chrysler_Patriot)

Interesting. Also the reply about rotating mass etc.:) The inner fan portion compresses air into the LP compressor which makes this section more effective delivering air to the HP compressor. Am I right in this ?

[Kerosene Kraut]

The 747-8 needs a RAT (first 747 ever with it) as it's (GEnx) lightweight blades couldn't deliver enough energy when windmilling.

[bvcu]

One problem with these blades , and the sheer size of the engine case has been tip rub . This meant a minor cropping to prevent this and reduced efficiency. The mention of the LPT is apt at the moment as that is this engines [115] achillies heel . Being replaced very regularly due to major failures and lots and lots of boroscope inspections ! The GE boys are keeping very very busy , but to be fair not many inflight failures due to the quality of the inspections and monitoring.

[Turbine D]

lomapaseo,
I can't get my head around the number of turbine stages being less becauses the fan weighs less for the same flow rate.
The way I look at it is this (could be wrong): The function of the LPT is to extract energy from the core flowpath gas to provide torque to drive the fan and booster. Once the core engine is designed and tested by itself, the available energy becomes known. Then the LPT can be designed to extract only the energy necessary to drive the fan and booster to maximum speed plus a margin. A lighter fan and booster requires less torque than a heavier fan and booster. From then on it is up to the turbine aero and design folks to come up with the proper number of LPT stages required, less being better. The object is one of low weight, low cost and long life. To achieve these goals, the trend is towards higher stage loading with fewer stages. Sometimes it becomes a problem as bvcu points out in his posting, where design margins get too slim and the life goals are not met as predicted.

Lyman,
The rotor mass is less, takes less energy to maintain its RPM, and the energy is more quickly translated into flow.
I believe this to be correct.
Is the serpentine design to allow more blade length without adding diameter to the rotating disc? Less tip speed for given swept area?
I don't know the answer to these.

TD

[lomapaseo]

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.

[Chu Chu]

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.

[barit1]

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.

Quite right. Steady-state, the driving torque to the fan should be independent of the rotor weight (or more properly, its moment of inertial).

But during acceleration (such as GA) or deceleration, the lighter rotor will respond faster. :8

[Lyman]

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.

[Chu Chu]

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.

[lomapaseo]

A slower fan equates to a slower turbine (except for geared fans) and loss of turbine efficiency requiring more turbine stages. So are we chasing our tail here?

[Lyman]

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