F135 blade failure could hold up STOVL JSF

LMAggie · by **LMAggie** » 07 Feb 2008, 01:20

P&W says they had another fan blade incident that could impact BF:1 first flight.

F135 Blade Failure Could Hold Up STOVL JSF
By Guy Norris

(STOVL) Lockheed Martin F-35 Joint Strike Fighter, BF-1, could be delayed following a repeat of the Pratt & Whitney F135 engine turbine blade failure that led to a hold up in flight tests last year of the conventional take-off and landing (CTOL) JSF.

The failure of the low pressure (LP) turbine blade is thought to have occurred in engine six which was undergoing flight clearance "proof test" ground runs prior to installation in the first STOVL F-35, BF-1. The tests were aimed at proving, on an engine-by-engine basis, that the specific unit was safe to use in BF-1, and that it did not exhibit the same combination of assembly characteristics, tolerances and other factors that led to a similar failure on a test stand engine on August 30.

The August failure, which contributed to a prolonged delay for both ground and flight tests of AA-1, the first conventional flight test F-35A, was traced to an unsteady flow regime in the wake of the stator upstream of the LP turbine third stage. P&W is developing a fix involving redesigning the stators and is planning to test the improved configuration by the middle of this year. In the meantime it cleared specific engines to allow flight test to resume of AA-1 in December 2007, and hoped tests of engine six would similarly clear the way for BF-1 to start tethered hover pit tests originally set for April.

To this end, P&W confirms it is "currently conducting proof testing of F135 CTOL and STOVL propulsion systems in order to validate low-pressure turbines for ground and flight testing. The proof testing was developed to specifically address a 3rd stage turbine durability concern previously identified during development testing."

According to information revealed at the December roll-out of the BF-1 in Fort Worth, Tex., the aircraft was expected to make its first flight from a conventional take-off roll in late May or early June. This was to be followed with a gradual "build-down" to STOVL tests by around the end of 2008. It's unknown right now if and by how much the recent failure, which occurred on Monday, will affect the F-35B test schedule.

Lockheed Martin won't comment on specific dates for the start of flight tests, although sources suggest the internal target date for first flight has, until recently, been May 19. Test results of the resdesigned stator are meanwhile not expected to be known until around the third quarter.

P&W says in a statement that "on February 4, during proof testing of a F135 STOVL engine variant on a Pratt & Whitney test stand in West Palm Beach, Florida, an incident occurred involving a single 3rd stage blade. The engine is being inspected and Pratt & Whitney is working in concert with the Joint Program Office and Lockheed Martin to determine next steps."

Ironically the test problem with the F135 occurred on the same day that the Pentagon once again proposed to cut the alternative General Electric Rolls-Royce F136 engine from the FY 2009 defense budget. The competing engine has twice previously been rescued by Congress from the brink of cancellation, the last time in 2007 on the heels of two F135 test incidents. The first was when damage was sustained during STOVL flight release testing in May 2007 when a deliberate hard stall of the shaft-driven lift fan caused the shaft to break, while the second on August 30 concerned the original LP turbine blade failure.

Source: http://www.aviationweek.com/aw/generic/ ... TOVL%20JSF

That_Engine_Guy · by **That_Engine_Guy** » 07 Feb 2008, 01:25

"...an incident..."

Not cool if you're hovering!?

seruriermarshal · by **seruriermarshal** » 07 Feb 2008, 02:04

Seems like on August 30 last year . They must have fixed the problem .

ATFS_Crash · by **ATFS_Crash** » 07 Feb 2008, 02:26

Makes you wonder if General Electric wouldn't have been a better choice.

checksixx · by **checksixx** » 07 Feb 2008, 03:04

Who is making the blades and are they DS Single Crystal or something else??

That_Engine_Guy · by **That_Engine_Guy** » 07 Feb 2008, 04:14

Aviation Week wrote: ... could be delayed following a repeat of the Pratt & Whitney F135 engine turbine blade failure that led to a hold up in flight tests last year of the conventional take-off and landing (CTOL) JSF.

The failure of the low pressure (LP) turbine blade is thought to have occurred in engine six which was undergoing flight clearance "proof test" ground runs prior to installation in the first STOVL F-35, BF-1.

The August failure, which contributed to a prolonged delay for both ground and flight tests of AA-1, the first conventional flight test F-35A, was traced to an unsteady flow regime in the wake of the stator upstream of the LP turbine third stage

So the issue is with third stage turbine blades, not a "fan" blades. BIG difference.

Also note the "unsteady flow in the wake of the stator upstream of the LP turbine third stage" Something ahead of the blades is causing fatigue on them. If the flow is not evenly applied across the face of the turbine it will cause high stress.

Imagine a garden hose spraying on a child's pin-wheel, each time a blade comes around to the stream it "smacks" into it. If you have an unsteady flow into a turbine, each blade will "smack" into the described "unsteady flow wake" say 10-15 THOUSAND times a minute (RPM)? At that rate, fatigue will set in rather quickly. :shock:

It has happened on current generation engines as well. Say when a single "old" part number turbine vane is installed with an entire set of "new" vanes. Just a minute flow difference between the singe "odd-ball" and the others can cause rapid fatigue in the rotating hardware downstream.

Another cause would be a compressor stator that isn't properly engaged into the synchronizing ring that controls the pitch of the variable stators. Instant flow change on the compressor blades as they slam into that flow at 12,000 (or so) RPM.

From published info...

The (F135) engine consists of a 3-stage fan, a 6-stage compressor, an annular combustor, a single stage high-pressure turbine, and a 2 stage low-pressure turbine....A two-stage low-pressure turbine on the engine provides the horsepower necessary to power the Rolls-Royce designed Lift Fan.

This would indicate the third stage turbine blades are the last stage in the LPT and would be driving the 3-stage fan (N1) compressor, not the Lift Fan which has an additional 2 turbine stages. (Shall we venture to call that the LFDT - Lift Fan Drive Turbine?)

This is why ALL F135s would be affected as the "incident" was not specifically centered in the LFDT of the -600.

Lets not all forget these are the first engines of their type. Most "new" engines will have a few teething pains. By the time the F135 enters full-production it will have substantially more flight/test time behind it.

Keep 'em flyin' :thumb:

EDIT - Formatting

asiatrails · by **asiatrails** » 07 Feb 2008, 04:57

Repeat failure which occurred on 05 February.

Remember this is a contra rotating engine, the same as the Pegasus, RB199, RB211 / Trent families. In the Rolls-Royce engines the matching of the spools and aerodynamic flows to prevent issues like this took a lot of detailed hard design work. The engine has to contra rotate to prevent precession in the hover.

LMAggie · by **LMAggie** » 07 Feb 2008, 06:56

AA:1 flew today, and the incident occured on a STOVL configured engine, so one can deduce that this has to do with the effects that the STOVL system is having on the main engine. Thats as far as I can go. :-)

Hopefully the smart guys at P&W can figure it out.

VPRGUY · by **VPRGUY** » 07 Feb 2008, 08:04

The (F135) engine consists of a 3-stage fan, a 6-stage compressor, an annular combustor, a single stage high-pressure turbine, and a 2 stage low-pressure turbine....A two-stage low-pressure turbine on the engine provides the horsepower necessary to power the Rolls-Royce designed Lift Fan.

TEG, not to question you're knowledge, but to me this reads somewhat like this: "Nine stage compressor, and three stage turbine". I know the fan and compressor are technically two seperate entities, but they're both in front serving to get the air moving so I lumped them together. The way I understand this statement is that the high-pressure turbine drives the 6-stage compressor, and the two-stage low pressure turbine drives both the three stage bypass fan as well as the lift fan. Your description would have the F135 having five turbine stages, with two sets of two-stage low-pressure turbines (one each for both the bypass fan and lift fan). I"m basing this off my knowledge of the F-16 engines, which of course have a high-pressure turbine for the high-pressure compressor section, and a low-pressure turbine for the low-pressure compressor section. Or maybe I've just been away from the F-16 too long now...

dwightlooi · by **dwightlooi** » 07 Feb 2008, 09:59

seruriermarshal wrote:Seems like on August 30 last year . They must have fixed the problem .

The answer is yes, they have fixed the problem. But, the tested engine that failed, the current flight test engines and all the current engine stock do not have the fix.

The LP turbine was redesigned to solve the problem. However, the redesigned LPT and engines with it won't be available until latter this year. Instead of waiting for the engine redesign and holding flight tests up, P&W decided to simply "proof test" a half dozen or so engines already built to the old spec at operating conditions far exceeding what will be experienced during flight testing. The engines that pass are delivered as flight ready so testing of the airframes can proceed with them at least until the "new" engine batches arrive.

VPRGUY wrote:TEG, not to question you're knowledge, but to me this reads somewhat like this: "Nine stage compressor, and three stage turbine". I know the fan and compressor are technically two seperate entities, but they're both in front serving to get the air moving so I lumped them together. The way I understand this statement is that the high-pressure turbine drives the 6-stage compressor, and the two-stage low pressure turbine drives both the three stage bypass fan as well as the lift fan. Your description would have the F135 having five turbine stages, with two sets of two-stage low-pressure turbines (one each for both the bypass fan and lift fan). I"m basing this off my knowledge of the F-16 engines, which of course have a high-pressure turbine for the high-pressure compressor section, and a low-pressure turbine for the low-pressure compressor section. Or maybe I've just been away from the F-16 too long now...

The F135 has ONE high pressure turbine stage which is coupled to the outer shaft and drives the 6-stage compressor. The TWO low pressure turbines are coupled the inner spool and drives the 3-stage fan. In the STOVL version, the inner spool can also be connected to the lift fan via a clutch and gearbox.

The F136 is of a somewhat different design, having ONE high pressure turbine stage driving a 5-stage compressor (one stage less than the F135), but THREE low pressure turbine stages (one more than the F135) driving the 3-stage fan. GE benefits from their experience with the GE90 and GEnx commercial engines and are the purveyors of the highest pressure ratio axial compressors in the industry. It looks like they are able to do with 5-stages what P&W need 6-stages to accomplish. Adding an additional stage to the LPT allows the engine to better harness the combustion energy to drive the fans and probably makes it slightly more efficient in dry thrust.

checksixx · by **checksixx** » 07 Feb 2008, 17:27

checksixx wrote:Who is making the blades and are they DS Single Crystal or something else??

Guess nobody knows...I'll see if my Uncle knows who's making the parts and how they're being made...I'll update if I hear anything...

That_Engine_Guy · by **That_Engine_Guy** » 08 Feb 2008, 03:42

VPRGUY wrote:TEG, not to question you're knowledge, but to me this reads somewhat like this: "Nine stage compressor, and three stage turbine". I know the fan and compressor are technically two seperate entities, but they're both in front serving to get the air moving so I lumped them together. The way I understand this statement is that the high-pressure turbine drives the 6-stage compressor, and the two-stage low pressure turbine drives both the three stage bypass fan as well as the lift fan. Your description would have the F135 having five turbine stages, with two sets of two-stage low-pressure turbines (one each for both the bypass fan and lift fan). I"m basing this off my knowledge of the F-16 engines, which of course have a high-pressure turbine for the high-pressure compressor section, and a low-pressure turbine for the low-pressure compressor section. Or maybe I've just been away from the F-16 too long now...

The compressors are considered separate. True there are 9 stages of TOTAL compressor, and 3 turbine stages TOTAL but the arrangement is a "dual-spool" thus an N1 and N2 (Low/High Speed) "rotors". It happens to be on this model engine the N1 (Low Speed) would be considered the "Fan".

You're right on there NOT being 5 turbines (More on that below); I was basing my turbine count off the the JSF/F-35 web site.
So much for trusting a DOD web site to give clear/accurate data!? :doh:

It said...

The (F135) engine consists of a 3-stage fan, a 6-stage compressor, an annular combustor, a single stage high-pressure turbine, and a 2 stage low-pressure turbine....A two-stage low-pressure turbine on the engine provides the horsepower necessary to power the Rolls-Royce designed Lift Fan.

I took the Lift Fan's turbine to be a separate unit behind that of the N1 (fan) 2 stage low-turbine. This would have given a "triple-spool" arrangement like the RR RB199. After doing some further reading, I realize they DO use the same low-pressure turbine for the engine's Fan (N1 Compressor) and the LiftFan.

dwightlooi wrote:In the STOVL version, the inner spool can also be connected to the lift fan via a clutch and gearbox.

Adding an additional stage to the LPT allows the engine to better harness the combustion energy to drive the fans and probably makes it slightly more efficient in dry thrust.

But the more horsepower you pull from the exhaust gasses, the more you'll slow those gasses down, reducing "core" thrust. It is important here to remember Newton's Second Law = "The net force is equated to the product of the mass times the acceleration" If you're pulling more power from the exhaust gas, you'll reduce velocity through the turbine, but then you'll be moving more air with that power through the larger bypass Fan.

I feel this would be the major reason it F135 is sited as "NOT designed for supercruise"; it just won't have as much exhaust velocity at MIL as the F119 :2c:

dwight is right about the inner spool and the clutch too.
:cheers:

Here is the further info I talked about above...

Two-stage Low Pressure Turbine with more shaft horse-power than the single-stage LPT of the F119. The LPT torque is transmitted through the fan and a dry-plate clutch to the LiftFan drive shaft, the turbine power being shared by the two driven items,

As for blade construction, here is what one public source says:

high-strength powder-metallurgy (heated without melting) high-rotor blades of second-generation single-crystal Nickle-based alloy, with advanced outer air seals

They are also said to have twice the cooling of the previous generations turbine blades.

That_Engine_Guy · by **That_Engine_Guy** » 09 Feb 2008, 04:38

More LiftFan info I've found...

JSF119-SE611S was equipped with a vectoring nozzle and a powered clutch on the front of the LP (Fan) shaft, which, could transmit shaft power to the remote LiftFan. The power extracted was about 25,000 HP. The engine needed to operate at an increased turbine temperature, with a larger turbine for additional power. This power was needed to drive the engine fan and LiftFan together when engaged.

The clutch sounds amazing!?

High power rapid-action closed-loop dry-plate clutch. This massive clutch unit incorporates drive surfaces provided by Goodrich, based on carbon-brake technology. It has to accept a near-instantaneous input of some 21,600 kW (29,000 HP), and accelerate the large counter-rotating fans up to maximum speed in about two seconds

29K Horsepower in 2 seconds!? WOW! :shock:

EDIT: I forgot the pic :doh:

LMAggie · by **LMAggie** » 11 Feb 2008, 14:01

Update:

http://www.star-telegram.com/business/story/463056.html

tmofarrvl · by **tmofarrvl** » 11 Feb 2008, 17:13

LMAggie wrote:Update:

http://www.star-telegram.com/business/story/463056.html

I'm gratified to see that common sense has prevailed, and there will be to delay in the CTOL portion of the first F-35B's flight test program. There is no reason why this problem shouldn't be worked in parallel.

All of this is typical of what we should expect to see in a development program. The F-35 will be the first lift-fan equipped aircraft to reach production, and we should expect to see development hurdles commensurate with any new technology.

I must confess, however, that I am not a fan of the Star-Telegram's journalistic standards. "turbine compressor blade"? If this is where most of the public gets their news from, it's no wonder that the capabilities of the F-22 and F-35 are so misunderstood by the general population.

There is a more complete article on the flight test and engine test recovery program under this week's issue of Aviation Week (Feb 11, 2007, pages 35-36). The redesigned vane is expected to complete a back-to-back engine testing by "mid-year".