trying to figure out the "ata" gauge

[Voyager]

Originally Posted by Viper2000

[...]
an early Merlin just wouldn't be physically strong enough to stand up to the cylinder pressures produced for more than about 15 minutes or so [...]

Just a fun little nit-pick, that is not necessarily true. When an engine is rated for a specific output that just means that it has been tested for that power output without failure for a minimum percentage of runs. It does not necessarily mean that the engines have actually been characterized as to their true maximum strength.

It is analogous to the wing strength tests airliners go through these days. The max strength is predicted by modeling and small tests, then full up tests are done to show that it at minimum meets its spec. Generally it is close, because you want to get the most out of your things, but if you've estimated your design power too high, you'll get a string of bad test failures without getting your engine certified, and freaking out your regulatory body. I suspect this predict, test loop is why in WWII most engines tended to both be rated in multiples of 50hp, and increase in multiples of 50hp. That's not a natural thing.

During WWII there were a number of engine that were uprated simply because additional testing showed they could be run at the higher boosts, without any design change at all, beyond upping the boost limit.

That is also part of what War Emergency Power was all about. Proving that an engine can provide a continuous power setting is much harder than simply proving you can run it for 5-10 minutes at a setting, so for the demand of war, engine companies would run quick and dirty tests to show that an over-boost setting could be used for a little while, even when they had no idea if it was safe to use continuously, or even when it was known to be unsafe for constant use, while they worked on either proving that it was good for continuous use at that setting, or fixing why it wasn't.

This continues in modern unlimited air racing, where teams will often simply unlimit the boost entirely, to get those ludicrous power outputs they do. And sometimes their engines blow up.