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.