3 ms·

I'm surprised they bothered providing that option for such a small benefit. Was there some specific enemy fighter model that this allowed them to outfly?

GuB-42 6y ago
I think it is cheap to add and it may safe your life so why not? It is just a matter of raising a limit. On the mechanical side of things each part has a certain lifetime, you can increase it by reducing strain and vice versa. So they probably already know how much the engines can be pushed if you only need a total lifetime of 1h instead of hundreds or hours. They most likely extrapolated that 2% from this.
sturmeh 6y ago
I assume that's why they restrict its use now, because the overhead of repair/stress isn't worth the 2% thrust. During WW2 there's a good chance they had no idea what they'd be up against whilst they were developing this jet, so they built in a theoretical 2% improvement switch with a large caveat incase the 2% improvement ever gave them the edge. I think the use of the VMAX switch is only warranted if the ship would otherwise be destroyed or lost if it were not used, which seems like a very unlikely scenario.
- vlasev 6y ago
  Reminds me of how the Space Shuttle Main Engines gained improvements over time so you could then set them to 104.5% thrust. Higher modes were later available. From Wikipedia on RS-25 engines: - Block IIA (RS-25C): First flown on STS-89, the Block IIA engine was an interim model used whilst certain components of the Block II engine completed development. Changes included a new large throat main combustion chamber (which had originally been recommended by Rocketdyne in 1980), improved low pressure turbopumps and certification for 104.5% RPL to compensate for a 2 seconds (0.020 km/s) reduction in specific impulse (original plans called for the engine to be certified to 106% for heavy International Space Station payloads, but this was not required and would have reduced engine service life). A slightly modified version first flew on STS-96. - Block II (RS-25D): First flown on STS-104, the Block II upgrade included all of the Block IIA improvements plus a new high pressure fuel turbopump. This model was ground-tested to 111% FPL in the event of a contingency abort, and certified for 109% FPL for use during an intact abort.

GuB-42 6y ago

I think it is cheap to add and it may safe your life so why not? It is just a matter of raising a limit. On the mechanical side of things each part has a certain lifetime, you can increase it by reducing strain and vice versa. So they probably already know how much the engines can be pushed if you only need a total lifetime of 1h instead of hundreds or hours. They most likely extrapolated that 2% from this.

sturmeh 6y ago

I assume that's why they restrict its use now, because the overhead of repair/stress isn't worth the 2% thrust. During WW2 there's a good chance they had no idea what they'd be up against whilst they were developing this jet, so they built in a theoretical 2% improvement switch with a large caveat incase the 2% improvement ever gave them the edge. I think the use of the VMAX switch is only warranted if the ship would otherwise be destroyed or lost if it were not used, which seems like a very unlikely scenario.

vlasev 6y ago
Reminds me of how the Space Shuttle Main Engines gained improvements over time so you could then set them to 104.5% thrust. Higher modes were later available. From Wikipedia on RS-25 engines: - Block IIA (RS-25C): First flown on STS-89, the Block IIA engine was an interim model used whilst certain components of the Block II engine completed development. Changes included a new large throat main combustion chamber (which had originally been recommended by Rocketdyne in 1980), improved low pressure turbopumps and certification for 104.5% RPL to compensate for a 2 seconds (0.020 km/s) reduction in specific impulse (original plans called for the engine to be certified to 106% for heavy International Space Station payloads, but this was not required and would have reduced engine service life). A slightly modified version first flew on STS-96. - Block II (RS-25D): First flown on STS-104, the Block II upgrade included all of the Block IIA improvements plus a new high pressure fuel turbopump. This model was ground-tested to 111% FPL in the event of a contingency abort, and certified for 109% FPL for use during an intact abort.