Large Turbo Fan Containment Tests.

[Sheep Guts]

I'm probably jumping into the realm of engineers here. Are containment tests today in developemnt of Hi bypass engines still relevant? Or are the regulators and the manufacturers missing something.
N1 Fan blade seperation tests seem to be the standard examples used in testing of engine containment. Probably, and most definetly for the old Turbo Jet for sure. But are these huge by-pass designs now making this test out dated. When they fail a blade in these tests, surely the majority of the blade exits the engine, posing a lessor chance of no containment.

With the likes of QF32 incident, and quite a few CF6-80 uncontained failures and probably others I havent listed in the last few years. I just watched again the video ABC on QF32 and brings to mind one cant test the disintegration of a 200kg turbine wheel at 1000s of rpms..:ugh:

[Machaca]

Are containment tests today in developemnt of Hi bypass engines still relevant?

Absolutely.


Or are the regulators and the manufacturers missing something.

What "something" are they missing?


N1 Fan blade seperation tests seem to be the standard examples used in testing of engine containment.

Yes, for testing fan blade separation. Only.


But are these huge by-pass designs now making this test out dated.

No. The larger blades make containment more challenging.


When they fail a blade in these tests, surely the majority of the blade exits the engine, posing a lessor chance of no containment.

Surely not!


With the likes of QF32 incident, and quite a few CF6-80 uncontained failures and probably others I havent listed in the last few years.

Those were not fan blade separation incidents.


...one cant test the disintegration of a 200kg turbine wheel at 1000s of rpms

Not practical to contain a ruptured or released disk.

Due to the tremendous efforts of countless persons involved with the development and manufacturing of turbine engines, disk separation is exceedingly rare.

[Sheep Guts]

Thanks Mach! Niclly disected... Haha!
To narrow what I meant regarding
"When they fail a blade in these tests, surely the majority of the blade exits the engine, posing a lessor chance of no containment"

Was that fact in being a High bypass turbo fan engine compared to and older engine or turbo jet. A similiar test would have most of the shatered N1 blade exiting through the bypass other than the engine core so to speak.

Am I right in thinking this is factor? Surley Yes, due to centripedal force on its own.

[keesje]

Most serious engines incidents seem indeed HPT failures.

I wonder if a new regulatory approach towards this type of failures should be pushed to stimulate innovation..

http://i45.photobucket.com/albums/f65/seth_k/aa2.jpg

The AA 767 CF6 HPT part that made it to the other engine, via the keel beam..

[Turbine D]

Fan blade containment testing is important on all jet engines, regardless of size. It is one of several tests that are required to assure the basic design is acceptable. Containment testing serves two purposes:
1. It demonstrates the engine's capability to keep a broken off or ruptured fan blade inside the fan casing, not permitting it to penetrate the aircraft fuselage, or wing.
2. It also demonstrates the engine's capability to continue to generate power, albeit reduced power, for a period of time permitting the flight crew to make corrections in flight settings and to shut the engine down once control is established with an engine out situation.

Other testing is also done to simulate bird strikes, ice ingestion, hail ingestion and high volume of water (rain) ingestion.

Containment is mainly achieved by a kevlar wrapper around the outside of the fan casing, think bullet proof.

Turbine blade out testing is also done to demonstrate containment. It is desirable to have a broken turbine blade or blades exit out the turbine exhaust and not the turbine casing.

Fan, compressor and turbine discs are a much different situation. Given rotational speeds and mass, containment in a general sense is not possible. This is where engineering design and life management comes into play. Discs are designed with substantial safety margins based on their material (alloy) capability/properties. They are subjected to overspeed testing to assure they do not burst short of the design point plus an additional margin. They are critical components and are treated as such in service with a restricted cyclic life limitation and planned NDT inspections. The worst possible situation is to have a disc break loose and overspeed beyond capability (QF32). To prevent that from happening, a break away disc should slide back so that its blades contact the nozzle vanes behind it to slow or stop rotational speed short of burst overspeed rotation. For whatever reason, that didn't happen on QF32.

As a matter of interest, the AA 767 incident at LAX should never have happened. The pilot on a previous flight reported unusual engine vibration at speed but not idle in their write up after landing. The vibration is a key indicator something is not right in an engine. The engine should have been taken off wing and disassembled for inspection. Had they of done that they would have discovered a crack had developed off of one of the disc posts where the HP turbine blades are inserted. Instead, the plane was taken to a remote location and the engine run up in speed causing the crack to quickly run to the center bore and the disk exited. The result, loss of both engines and the aircraft was written off as a complete loss. It didn't have to happen.

Hope this helps your understanding.

[barit1]

Turbine D has it right, but to summarize:

Blade failures--fan, compressor, and turbine--are expected now and then (bird strikes, ice, secondary damage, etc.) and so containment of high-energy shrapnel is a major concern. If the broken fragments are initially contained, they may get blown out the back end in a lower-energy state, and that is expected and manageable.

Disc failures are uncontainable, and so great engineering effort is expended to make them extremely rare. For example, while the CF6 turbine disc failures got a lot of attention, remember that this is a very widely-used (10.000+ produced) machine, some of them 40 years old, and millions of operating hours every year. So failures are indeed extremely rare, and it takes a good amount of effort to keep it that way.

[lomapaseo]

All true except that there is no run-on power requirement after a full blade out release.

The FAA and Nasa have funded numerous studies in the last 50 years examining the practicality of containing disks (Kevlar etc.) The conclusion was that it isn't practical for something that has to be flight weght.

[Turbine D]

lomapaseo

You are correct about fan blade out and continued run-on power requirement. That is a requirement for the bird ingestion test.

[lomapaseo]

You are correct about fan blade out and continued run-on power requirement. That is a requirement for the bird ingestion test.



The run-on power requirement comes from the frequency of multiple engine events. Anything to do with the environment you fly in presumes multiple engine involvement Rain/hail inlet ice, flocking birds and maybe someday volcanic ash.

The bird requirement gets a little complicated since it presumes an air-turn-back with a missed approach (contaminated runway etc.) and the need to do a go-arround. I don't recall anybody doing one of these on the newer engines certified to this standard. A couple of events with older engines which were definitely high pucker factors

[Turbine D]

Lomapaseo,

The bird testing and continued run on requirement comes from this section of certification testing:

PART 33--AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES
Sec. 33.76 Bird ingestion.
(4) Ingestion of a large flocking bird under the conditions prescribed in this paragraph must not cause any of the following:
(i) A sustained reduction of power or thrust to less than 50 percent of maximum rated takeoff power or thrust during the run-on segment specified under paragraph (d)(5)(i) of this section.
(ii) Engine shutdown during the required run-on demonstration specified in paragraph (d)(5) of this section.
(iii) The conditions specified in paragraph (b)(3) of this section.
(5) The following test schedule must be used:
(i) Ingestion followed by 1 minute without power lever movement.
(ii) Followed by 13 minutes at not less than 50 percent of maximum rated takeoff power or thrust.
(iii) Followed by 2 minutes between 30 and 35 percent of maximum rated takeoff power or thrust.
(iv) Followed by 1 minute with power or thrust increased from that set in paragraph (d)(5)(iii) of this section, by between 5 and 10 percent of maximum rated takeoff power or thrust.
(v) Followed by 2 minutes with power or thrust reduced from that set in paragraph (d)(5)(iv) of this section, by between 5 and 10 percent of maximum rated takeoff power or thrust.
(vi) Followed by a minimum of 1 minute at ground idle then engine shutdown. The durations specified are times at the defined conditions. Power lever movement between each condition will be 10 seconds or less, except that power lever movements allowed within paragraph (d)(5)(ii) of this section are not limited, and for setting power under paragraph (d)(5)(iii) of this section will be 30 seconds or less.

I know the GE90 engine was tested to this requirement (composite fan blades with Ti leading edge wrap arounds) and the test engine continued to run at full power for the duration of the requirements. The fan blades were virtually undamaged upon inspection after testing. The weight of the bird is determined by the area of the fan inlet. I think for the GE90, the weight was ~ 8 pounds.

[grounded27]

Seems to be a large issue that no one has addressed here. Most of these modern failures have been on engines designed decades ago and modified by adding stages, increasing fan diameter etc then upping the thrust rating. In short, engine manufacturers are not designing as many new engines as they are attempting to squeeze more thrust out of the same old design. The bearings (positioning) and shaft's (spans) take a harmonic beating that emanates into disks, blades and blade contact with the case. Attention to engine cool down periods has been a short response from the manufacturers, shaft warping on hot engines is becoming a large problem.

A 6 foot tall fan blade is one hell of a projectile thus the attention of fan blade containment.

[lomapaseo]

shaft warping on hot engines is becoming a large problem

Fortunately engineers are up to the challenge.