I have some questions for those who would know. On air cooled aircraft engines, shock cooling is a important issue. Is it also an issue on liquid cooled engines? (P-51)? How about combat aircraft normal procedures? Such as the P-47 WW II fighter on the overhead break to landing pattern?
Last Edit: Oct 30, 2008 11:32:06 GMT -5 by cptdail
Post by Dee the man on Oct 29, 2008 22:32:57 GMT -5
I only have one brief experience flying a liquid-cooled engine. That was on a RAM modified twin- Cessna 414 with TCM LTSIO-550 engines. It was a nice airplane and shock-cooling was not a factor in the engine performance. Strangely, it took some getting used to! After many years experience of needing to care about shock-cooling, I just couldn't bring myself to brutishly push the throttles around!
I don't know anything about how WW2 pilots were taught to operate those round engines on fighters. But it is my understand (from listening to stories) that those engines had incredibly short TBOs (Time Between Overhauls). There might be a connection...
Dee Waldron Tokyo Japan HJG charter member, Sr model designer, retired.
On the R2800 and other related engines, shock cooling is only an issue during high speed descent and rapid movement from high power to no power. Once entering the pattern (at a fairly level pitch and at high ambient temps) it's not nearly as much of a problem, especially as you typically carry some power until round-out (flare). I know that from 1100HP cruise, a single reduction of power is all that's needed to setup for a constant descent to landing on a CV240, so it's obviously not too big of a deal.
As for TBO, much of that was due to the use of the engines at high altitude for prolonged periods of time and high power settings. This puts a lot of wear on the engines with the air as thin as they are and the required power changes, however I doubt shock cooling was too much of a problem as you usually didn't need to chop it that much to cause a problem. I know the TBO on the Merlins and Allisons weren't much better than the radials, so whatever was causing the short TBO on the radials was doing it on the "inlines" too.
Interesting, I have not heard anything regarding the inlines. Perhaps that is why the fighter pilots pulled so hard overhead to get it slowed down without chopping the power all the way back to get all the dirty stuff down.
1) To minimize the time needed to land. 2) To allow power to be held on as long as possible. The second was because many of the high HP aircraft like the fighters had some nasty habits when "firewalling" the engine on a go-around (think Corsair - the P-51 and P-47 can do it too). By keeping the power up, you're already partially trimmed against that condition. In addition, when jet engines came in, the overhead allowed you to keep power into the band where response from the engine was much more "crisp" (as low speed response was horrible).
Basically, the idea was - you keep as much power as you can to give you as many options as possible. The more options you had, the less likely the result of ending up dead in a smoking hole.