Composite fan blades

[acbus1]

Composite fan blades led to the downfall of Rolls-Royce in 1971 as I understand it.

What was the problem with the blades then?

How have they solved the problem now,or are the black fan blades I see on some high bypass engines not composite after all?

[Soddit]

I wonder if this belongs in Aviation History and Nostalgia?It's probably a bit simplistic to say that composites led to the downfall of RR in 1971. The decline ( and I do not want this to lead to acrimony) perhaps started with the premature death of Adrian Lombard without a natural successor. The actual composite fan blades you are thinking of ('Hyfil') were a product of 1960s RAE research. RR placed most of their faith in the Hyfil blade fitted to the RB211 : it was the birdstrike test which showed then to be fatally flawed and subsequent replacement with a titanium fan. The consequential problems of delay, cost overrun and failure at that time to reach contractual specification ( the subject aircraft was, of course, the L1011 Tristar) resulted in the dismissal of most ( with the exception of 3) of the Board of Directors, the insolvency of RR and the Government take over. As for later developments...you will doubtless read more up to date wisdom than I possess on this subject.

[casual observer]

The GE90 has been in service for more than seven years with composite fan blades, and the GE90 fan has been performing quite well in the field.

[CCA]

Didn't GE get some sort of dispensation with the GE90 fan blades, for the bird injestion test. I remember something but did a quick search with no luck.

[casual observer]

No. For the bird ingestion test, the GE90 had to pass the exact same tests as the PW4000 and the Trent 800. They did use slightly different rules for the blade out tests. Based on my limited understanding, for traditional metal blades, the blade in the blade out test would be released at the dovetail (beneath the platform), while for the composite blades, it would be released at the root of the flowpath (above the platform). The justification has to do with the composite material properties, but I don't know enough to clearly explain it here. So, I won't pretend to be an expert. :D

[lomapaseo]

>The justification has to do with the composite material properties, but I don't know enough to clearly explain it here. So, I won't pretend to be an expert.
<

Close!, but it was more like design loads and inspectability rather than just the material properties.

In return for only running a slightly less severe amount of released blade they heaped a whole lot of hurt on the follow on maintenance requirements for these blades.

Of course any engine (GE, RR, P&W) will be in a tight pinch if a single retention lug between blades happens to let go some day.

[acbus1]

Tanks for the input guys......really fascinating info. Am getting closer to answering the question I raised at the beginning.

But..........

Was todays blade material allowed in service because it is better at absorbing bird strikes than the RR "hyfil" was? Or is it solely the test requirements,as described above,that have changed since the 70's?

Was'nt rain (or whatever prcipitation) erosion also a problem with the 70's composite fan?

I notice a metallic looking leading edge to the current fan blades. Is this metal and if so how on earth do they ensure good integrity with the composite part of the blade?

[casual observer]

The bird ingestion tests are a lot more stringent now than 30 years ago. However, composite material technology is a lot more advanced. That's why it's working with the GE90 but it didn't with the RB.211. My understanding is Rolls composite blades in the late '60s would delaminate too easily. It couldn't stand up to any FOD (and hence birdstrikes).

Yes, the GE90 has a metal leading edge. It serves at least two purposes that I know of. One is aerodynamic. The other is protection from FOD damage (and hence delamination).

[acbus1]

Many thanks Casual Observer....good info.


Just one more thing,as I raised previously......how do they manage to "glue" (or whatever) a metal leading edge onto a composite fan blade in such a way that the whole thing stays in one piece...the stresses,vibration and deformations are pretty horrendous,and failure is not an acceptable option to say the least!

[lomapaseo]

>ust one more thing,as I raised previously......how do they manage to "glue" (or whatever) a metal leading edge onto a composite fan blade in such a way that the whole thing stays in one piece...the stresses,vibration and deformations are pretty horrendous,and failure is not an acceptable option to say the least!

<

Answers to that kind of detail would be considered proprietary by all three manufacturers.

[acbus1]

OOOPS !! Think I'll stop there then!

Thanks for the info everyone! :)

[Genghis]

Interesting thread - but I have heard in the last few days that the composite fanned GE90-115B has failed its 5.5lbf bird test. Doesn't this raise questions on the integrity of composite blades at higher rpm's/fan diameter.....

[lomapaseo]

>Interesting thread - but I have heard in the last few days that the composite fanned GE90-115B has failed its 5.5lbf bird test. Doesn't this raise questions on the integrity of composite blades at higher rpm's/fan diameter.....
<

Don't you mean *lower* RPM

[gas path]

The GE90-115b has flown on the 747 test bed at it's rated power, so I believe that the required tests (bird strike and blade off tests would have already been proved.
For the current engine (-76b and on!) the bird strike tests were no major problem. For the blade out test it was released (from memory) a third way up.
The blade is manufactured from composite layers, layered at 0^ 45^ and 90^ with metal pins inserted to add to the strength. The leading edge and trailing edge are titanium. with the blade (aft of the L/E strip) coated with polyurethane to prevent erosion.

The fan is extremely good with no major problems, unfortunately it's let down by the rest of the engine at the moment:(

[Genghis]

Just because the engine is operating on the flying test bed doesn't mean it is certified . The FTB is part of the certification process so that doesn't necessarily imply it has passed its bird-strike tests. However, the 5.5lb test is a new one and is possibly not yet required for certification?