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kitplane01
Posts: 1622
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Re: GE9X Record Breaker

Sun Jul 14, 2019 7:02 am

Starlionblue wrote:
kitplane01 wrote:
If the engine can clearly produce more than rated thrust .... why is that not allowed during emergencies?

Example: If some particular flight is weight limited because of engine-out concerns, and the engine had an extra bit of thrust just for emergencies, then one could increase weight. (Assuming enough rudder, strong enough pylon, etc.)

I would assume there are some emergencies where an extra 10% of thrust for 5 minutes would make things better/easier. And it's availability would help with some operational restriction.


There are a couple reasons:
- ...
- The take-off and go-around calculations assume an engine failure at the worst possible time, with the thrust level on that day (including any flex/derate). In other words you don't need more.


I don't think that makes sense. If you have extra thrust for the emergency, then your take-off and go-around calculations would allow for a shorter runway and better climb-out. There are flights where this would allow extra payload/range.

Starlionblue wrote:
- Wear and tear increases significantly at the top end of the thrust range. Which is why almost all take-offs use some sort of reduced thrust.

Sure, and keep doing that. I was proposing extra thrust only in an emergency, which almost never happens.

Starlionblue wrote:
That being said, on A330 and A350 the TOGA limits are different with an engine out. 10 minutes at TOGA, as opposed to 5 minutes with both engines. Are the engines different with an engine out? Of course not. However, in normal operation, you're extremely unlikely to need TOGA for more than a few minutes, so I'm guessing RR simply limits wear and tear by imposing a 5-minute limit. On the other hand, with an engine out, wear and tear take a back seat to safety.


Didn't know that ... good to know. That's very similar to what I'm asking about.
 
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Starlionblue
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Re: GE9X Record Breaker

Sun Jul 14, 2019 7:49 am

It comes down to what operators want to pay for, which is why many engines have different thrust options. Sure, you could give the engine a higher thrust, and get more payload/range capacity. But that has to be weighed against the additional cost of maintenance. As I said, you don't "need" more because the engine you bought had the thrust required for your particular operation.

Furthermore, the manufacturer might not want to give you all that performance, because they can't guarantee the engine will perform at that thrust in an emergency without an unacceptable risk of failure.

There's a big difference between a new engine on a test bench in laboratory conditions, and real world operations.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
flipdewaf
Posts: 3789
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Re: GE9X Record Breaker

Sun Jul 14, 2019 11:05 am

Maybe the triple redline test for the GE9x is higher than that for the GE90-115b so they the GE9x can be put on to the 778F whilst leaving the old wings in place...

Fred


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JayinKitsap
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Re: GE9X Record Breaker

Sun Jul 14, 2019 9:03 pm

I believe there are hot and high considerations, flying out of Denver at 105F or Dubai at 120F the light air requires more thrust from the engine at the same time the engine produces less thrust because of the light air. Changing the condition to a -20F at sealevel the air is far denser. The larger frontal area would increase the effect between the 90X and the 115. I could easily see the triple redline thrust rising by 5 to 10% between the two.

I am sure there are some nice log curves showing endurance at specific thrusts, backing off from the triple red line condition to 90% of that might change the engine life from 100 hours to 5,000 hours. Then keeping it 5% lower than that might extend the life on wing by 10,000 or so hours. Red line is really that point where the engine is eating itself up.
 
stephanwintner
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Re: GE9X Record Breaker

Tue Jul 16, 2019 10:36 pm

kitplane01 wrote:
stephanwintner wrote:
Cold weather, alone, allows for quite a bit more thrust than, for example, a hot day takeoff. I'm not sure what precise values are used for a rating, but keep in mind that the rated thrust is not what the average engine makes. Every single engine in the fleet, worn or not, should be capable of exceeding that value.


That's not true for the part 91 fleet (Cessna Piper Mooney). Is it really true for the airliner fleet?


Which part do you mean ? According to the performance data at my current employer, temperature can certainly add thrust, yes. I can't share that data but it's in the 10% ballpark. The engine makers can and do use software to throttle the engine appropriately, so that gain may not be available to the pilots - but for a one time ground test they can reprogram the control module. They do that anyway fo certain tests.

(For example, one might use software to flat rate an engine at colder temperatures to avoid overtorqueing the shaft, but ignore that limit for a one time test)
 
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Matt6461
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Re: GE9X Record Breaker

Wed Jul 17, 2019 2:00 am

kitplane01 wrote:
I don't think that makes sense. If you have extra thrust for the emergency, then your take-off and go-around calculations would allow for a shorter runway and better climb-out. There are flights where this would allow extra payload/range.


Another consideration: If the 777X, for example, wanted its takeoff run calculated based on the theoretical triple-red-line thrust of a GE9X, then its vertical stabilizer would have to be sized much bigger. As is, it is sized to generate sufficient lift to counteract the yaw moment of 105k lbs-T. Increase that by 30% and you need a 30% larger tailfin or else the plane loses control when you pump the emergency-only power - obviously not a viable option. A 30% larger tailfin is no small matter - we're talking thousands of pounds of added weight and a significant parasitic drag delta.

Not sure if this is mentioned already but current regs don't allow you to "flex" your thrust in the middle of an emergency - i.e. OEI after V1. IIRC Boom is trying to convince regulators to allow for this change. The Boom plane would take off at something below max thrust and be programmed, presumably, to jack up to max thrust in the event of OEI. So in order to use your emergency thrust under the current regulations, it wouldn't be emergency at all - you'd have to start at that 3-red-line thrust or forget about using it.

IDK about whether Boom has formally applied for this regulatory change. Anyone know?
 
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kitplane01
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Re: GE9X Record Breaker

Wed Jul 17, 2019 4:27 am

Matt6461 wrote:
kitplane01 wrote:
I don't think that makes sense. If you have extra thrust for the emergency, then your take-off and go-around calculations would allow for a shorter runway and better climb-out. There are flights where this would allow extra payload/range.


Another consideration: If the 777X, for example, wanted its takeoff run calculated based on the theoretical triple-red-line thrust of a GE9X, then its vertical stabilizer would have to be sized much bigger. As is, it is sized to generate sufficient lift to counteract the yaw moment of 105k lbs-T. Increase that by 30% and you need a 30% larger tailfin or else the plane loses control when you pump the emergency-only power - obviously not a viable option. A 30% larger tailfin is no small matter - we're talking thousands of pounds of added weight and a significant parasitic drag delta.

I agree, you might need a bigger tail. But depending on the benefit, it might be worth it. I'm saying it should be a tool that designers can use when needed.

Some engines have a 5-minute extra thrust possibility, and it gets used for takeoffs when needed. But "when needed" could mean "when there's an emergency".

Matt6461 wrote:

Not sure if this is mentioned already but current regs don't allow you to "flex" your thrust in the middle of an emergency - i.e. OEI after V1. IIRC Boom is trying to convince regulators to allow for this change. The Boom plane would take off at something below max thrust and be programmed, presumably, to jack up to max thrust in the event of OEI. So in order to use your emergency thrust under the current regulations, it wouldn't be emergency at all - you'd have to start at that 3-red-line thrust or forget about using it.

IDK about whether Boom has formally applied for this regulatory change. Anyone know?


Question about that. Could one just write a flight manual that says "takeoff is at 80% thrust. If an engine quits, go to 100%"? It's not a flex, it's a normal operational thing.
 
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Starlionblue
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Re: GE9X Record Breaker

Wed Jul 17, 2019 4:57 am

kitplane01 wrote:
[

Matt6461 wrote:

Not sure if this is mentioned already but current regs don't allow you to "flex" your thrust in the middle of an emergency - i.e. OEI after V1. IIRC Boom is trying to convince regulators to allow for this change. The Boom plane would take off at something below max thrust and be programmed, presumably, to jack up to max thrust in the event of OEI. So in order to use your emergency thrust under the current regulations, it wouldn't be emergency at all - you'd have to start at that 3-red-line thrust or forget about using it.

IDK about whether Boom has formally applied for this regulatory change. Anyone know?


Question about that. Could one just write a flight manual that says "takeoff is at 80% thrust. If an engine quits, go to 100%"? It's not a flex, it's a normal operational thing.


Given most take-offs are at reduced thrust, we already do pretty much that. However, the assumption is that TOGA is not needed if we lose an engine. It is needed for a windshear warning.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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enzo011
Posts: 1919
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Re: GE9X Record Breaker

Wed Jul 17, 2019 9:45 am

Is there also not just a little bit of ego involved here for GE? That they broke their own record for thrust and is able to get publicity from it, when the engine that achieved it will be used on a design that needs less thrust than the predecessor?
 
flipdewaf
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Re: GE9X Record Breaker

Wed Jul 17, 2019 12:13 pm

Starlionblue wrote:
kitplane01 wrote:
[

Matt6461 wrote:

Not sure if this is mentioned already but current regs don't allow you to "flex" your thrust in the middle of an emergency - i.e. OEI after V1. IIRC Boom is trying to convince regulators to allow for this change. The Boom plane would take off at something below max thrust and be programmed, presumably, to jack up to max thrust in the event of OEI. So in order to use your emergency thrust under the current regulations, it wouldn't be emergency at all - you'd have to start at that 3-red-line thrust or forget about using it.

IDK about whether Boom has formally applied for this regulatory change. Anyone know?


Question about that. Could one just write a flight manual that says "takeoff is at 80% thrust. If an engine quits, go to 100%"? It's not a flex, it's a normal operational thing.


Given most take-offs are at reduced thrust, we already do pretty much that. However, the assumption is that TOGA is not needed if we lose an engine. It is needed for a windshear warning.


Doesn't the A220 already have a feature that automatically changes thrust during the roll to help the transition between nose-wheel steering authority and rudder based steering authority?

Fred
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olle
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Re: GE9X Record Breaker

Mon Jul 29, 2019 7:41 pm

Stitch wrote:
Pudelhund wrote:
I am not very familiar with engines, so why would you need a GE9X if it carries the 777-9 with less thrust than the GE90 for the 77W?


As AirKevin notes, the GE9X will be significantly more fuel efficient (especially at cruise) than the GE90 so it will contribute greatly to the 777-9's overall fuel efficiency improvements over the 777-300ER.



How much more efficient is GE9X compared to RR XWB for 350-1000?

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