One problem I've seen is getting low away from a landable area following
flight in very cold air, e.g., wave. Whereas my Stemme has very little
increase in drag during engine start, and it starts quickly and
reliably, there's a requirement not to use much power until the oil
temperature reaches a certain level. Even with cowl flaps closed, that
can take 5 minutes or more to achieve. Fortunately, with power just
above idle, the Stemme has little to no decent.

Having flown turbojets in Alaska and turbofans in the lower 48, I don't
recall any cautions about oil temperature, though good sense should
prevail. There should be enough temperature for oil to circulate. The
jets would start and run just fine at -40 deg F.

On 1/7/2017 11:31 AM, Paul Ruskin wrote:
On Wednesday, January 4, 2017 at 3:48:53 PM UTC, Dan Marotta wrote:
Jets are cool, no doubt, and highly reliable, but they're very noisy
and, at the speeds gliders fly, very inefficient. I don't know how they
cost compared with a Wankel or piston engine, but I wouldn't have one.
The novelty will wear off.

Noise can certainly be an issue, and you wouldn't want to use them much near your home site. But for us glider pilots, efficiency is not a big issue (we don't use it enough to worry). However, they have a very distinct advantage over a piston or wankel, and that's the lack of drag when you extend them.

That means that your commit height is much lower - people I know with conventional engines have to start them above 1000 ft AGL (some use considerably higher) and be downwind on a suitable landing area in case they don't start. With a jet, there's effectively no extra drag, so waiting until 500 ft AGL is perfectly feasible - or you can be further away from the field. That's the difference between completing a flight and not doing so, surprisingly often.

For me, at the moment it's a toss up between jet and FES - though I suspect within a few years FES will win out as battery technology gets better.

Paul


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Dan, 5J