On 06/06/2010 11:56 PM, rparigoris wrote:
> **Ask any Rotax distributor in the know, they want a 914 to run well
> below edge of redline for longevity. Not too cold, but near the lower
> end is preferable. I think we can agree on this.
I don't necessarily agree with this. There is a practical reason to
limit the temperatures of the cylinder heads: above a certain
temperature the aluminium softens. But you can't reverse this reasoning:
there is no additional benefit to get further away from this redline
than necessary. In fact, a lower temperature worsens the efficiency of
the engine, causes worse fuel atomization, etc.
The same with the oil temperature. The red line is there because above a
certain temperature the oil starts breaking apart. But you shouldn't
stay further away from this red line as neccessary. I think we all know
that colder oil is not working well, that is why we have a lower limit
on the oil temperature after all.
I wouldn't see why running well below the edge would increase the
longevity. The heads melt or they do not.
> **Now here is where I don't agree with you.
You have some points here. It is just that I think that having to rely
on electrical fans is not elegant, and electrical fans can fail. I
prefer to make the best use of the air flow we already have by the
nature of flying, but there is no real wrong or true here.
> I disagree
> that heating cowl air is a good thing.
I didn't say that. I said: "heating up the air before it leaves the
airplane is a good thing".
With other words: you should try to heat the air up on its way to the
exit... but make very sure that it exits indeed and doesn't linger
around in the cowling. With a proper airflow from top to bottom, the
turbo and muffler are the very last things the air will encounter. It
could be beneficial to pick up heat from it as much as possible, to
increase the air volume and have something to offer to the void behind
the cowling or cowl flap. The more volume of air you exit, the less drag
you have... until at some point you even get propulsion from the hot air
exiting the cowling (but true, we aren't likely to achieve this stage
with an Europa).
BTW, thanks for the information you sent!!
Frans
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