The low pressure turbine failed in the Pratt & Whitney Geared Turbo Fan engine on Bombardier’s CSeries, reports investment bank UBS, citing Bombardier.
BBD confirmed that recent GTF engine failure was in the low-pressure turbine and that the airframe (FTV1) was damaged in the incident, but downplayed the impact to the program schedule. While root cause analysis is ongoing, BBD emphasized that the failure was unrelated to the gearbox, and also suggested that a manufacturing defect (rather than a design flaw) may have been the cause. The subject engine was known to have problems, and BBD had considered sending it back to Pratt prior to incident on 5/29. Engine was instead repaired at BBD and the failure occurred during subsequent ground-testing. Root cause expected by end of week, corroborating message from our meetings with UTX on Monday.
The LPT is at the rear of the engine. A BBD official told us previously that FTV 1 was equipped with prototype engines, and that the production engines are first installed on FTV 4, the airplane that is designated to validate engine performance.
Engine failures during test programs are rare but not unknown. Rolls-Royce experienced a test-stand engine failure of the Trent 1000 for the Boeing 787 in which components blew apart.
Separately, a GEnx engine spit parts out of the back of the engine while a 787 was taxiing at Boeing’s Charleston 787 plant. Neither incident has serious impact on the program.
Some rumors coming out of P&W’s Connecticut plant, where the damaged engine has been sent for tear down, say it was an oil problem in the LPT.
The LP Turbine is what I had suspected in the first place and I mentioned it in a previous post: https://leehamnews.com/2014/06/01/cseries-setback-as-pw-gtf-has-reported-uncontained-failure/#comments
Here is the key excerpt from that post:
“Initially I thought this CSeries incident might have something to do with the LP Turbine, which turns 2 1/2 times faster on this engine than on a more conventional one. But if indeed the incident does not require a redesign it would mean that my initial concern was probably unwarranted.”
Yet, I am still not sure that it would not require a redesign, at least a minor one, since we now know that indeed it is the LP Turbine that has disintegrated. Whatever the case may be this should fall under the responsibility of MTU in Germany which, if I am not mistaken, is the designer and manufacturer of the LP Turbine on this engine.
When I first heard that one of the CSeries engines had had an uncontained failure I immediately discarded the fan as the culprit since this part of the engine is designed and tested to be containable. That left the core, and more specifically the LP Turbine and its unusual rotational speed.
That LP Turbine is directly connected to the gearbox which until now had been the focus of all the attention. But it looks like we may now have to divert our attention to the LP Turbine, which on this engine turns at 250% the normal speed. In fact we are entering a new territory here for a commercial engine.
Can anyhone cinfomrm the LP is faster? First reference I have come across it.
Also of interest “it wea repaired at BBD” Was that P&W that repaired it there or did they repair it themselves (sound unlikely but…)
cue GTF as in geared turbo fan 😉
You want a large fan to run as slow as possible ( pref. subsonic ).
You have similar limitations for the LP turbine.
thus a regular ( same upm ) lp spool has a turbine diameter in a fixed ~.5? relation to the fan diameter. Introduce a reduction gear and you can scale up LP upm while LP diameter shrinks towards the same blade tip speed. Gearbox weight is compensated by reduced mass ( and number of airfoils ) in the LP turbine.
No free lunch? Or is it better for the LP to run faster?
I know the general concepts but not specifics of those relationships.
the large fan makes sense as I read all the reports of propellers limitations due to the ends going supersonic (WWII fighters etc). Add more blades and shorter.
If it was discussed I missed the LP situation, but not looking for it as the emphasis was on the geared end.
You get a smaller, lighter LP section and a significantly reduced airfoil count.
Weight and complexity gains from the gearbox must be smaller than
the gains from the faster LP spool.
GTF LPT rpm are certainly quite high compared to other modern jet engines with highish By Path Ratio.
But they were quite usual in older jet engines with lowish BPR
PRATT said some time ago that they were back to the designs of some of their old classics
LPT with highish rpm are much easier to design, and much more efficient.
Which is also one reason for the 3 spool RR design
Looks like I need a primer on the whole engine. Interesting.
I really need to see the graphics of it all, hurts my head to think of all of those varous things moving at different speeds. A shaft hooked to a gear I understand, cars, boats etc.
Anybody care to check second source? Who sez that UBS got it right? Rumor has it that it was the LPC.
I believe another aviation website/publication, not sure which one at the moment, stated the fuselage suffered a fair amount of damage as well as the engine.
This was actually acknowledge by Bombardier not too long after the incident. But since the fuselage is made of aluminium-lithium it should be relatively easy to repair. Fortunately the composite wing was not affected, like it was in the case of Qantas Flight 32 for example.
Now the big question is will the CSeries be back in the air soon enough to make an appearance at Farnborough next month. Even before this incident its presence at the show was already questioned.
But what is the most important at the moment is that they find a quick fix for the anomaly so that it does not repeat itself. In the meantime I assume that they will want to install a pair of brand new engines on FTV1. I also assume that all the engines already manufactured, installed or not, will have to be modified to a certain extent.
All this could be a relatively long process that could keep the CSeries on the ground for a while.