LowNSlow,
You asked about radials. It's not a _big_ radial, but the M14P in the Yak takes quite a bit of warming and has to be treated very gently in terms of revs until the CHT and oil temps reach certain levels. I try to do the actual start at low revs (around idle, which is around 750 rpm (around 25%), and as soon as I confirm oil pressure I let it gradually pick up to around 1200 (40%, a little more as time goes by). (It often does this semi-automatically as additional cylinders chime in.) It is especially important not to rev too hard when the oil is cold in the winter as this tends to promote cavitation of the oil pump, with the pressure falling as the revs rise.
In most M14P installations the pilot has the considerable benefit of being able to close and open the cooling gills in front of the engine, and open / close the oil cooler. After start you can shut off the cooling to encourage the CHTs to start moving into the green in reasonable time, and thereby help to get the oil warmed up as quickly as possible. The CHTs come up quicker than the oil, so once the CHTs are up you start opening the gills again while you wait for the oil to come the rest of the way. On the Yak I fly, on a temperate autumn day or cooler, opening the gills all the way on the ground at 1200 rpm will make the CHTs drop back out of the green, so ithe intermediate settings are not just for show. In the winter, all of this can take a lot of ground running, 15 mins or even more. Pre-heating would be nice to have!
On really big radials there are usually controllable cooling gills at the rear edge of the cowling. From conversations and observations at Duxford over the years, getting big radials to stable core temperatures before flight is a major deal for the operators. There's a lot of metal in those very large engines and the sheer size means it takes longer to get all the temps nice and even, and all the internal clearances and tolerances in the best ranges. The Blenheim folk, and probably others, go to great trouble to pre-heat both the oil and the Pegasus engines themselves before starting, actually pumping hot oil all around the lubrication system, as cold starts are the time when almost all engine wear takes place in normal use.
With Merlins, Allisons and other liquid cooled engines you have the advantage that the coolant heats up quickly and then rapidly carries the heat around the engine, so even temperatures can be achieved much more quickly.
(edited for silly spelling)
Last edited by Lowtimer; 29th December 2003 at 16:27.