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From: argosy!freeman@decwrl.dec.com (Jay R. Freeman)
Newsgroups: sci.military
Subject: Re: SR-71 congealed oil
Message-ID: <1990Oct16.010951.11280@cbnews.att.com>
Date: 16 Oct 90 01:09:51 GMT
References: <1990Oct8.220953.7541@cbnews.att.com> <1990Oct10.000645.444@cbnews.att.com> <1990Oct11.051057.29887@cbnews.att.com> <1990Oct15.034029.13416@cbnews.att.com>
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From: argosy!freeman@decwrl.dec.com (Jay R. Freeman)

In article <1990Oct15.034029.13416@cbnews.att.com> ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) writes:
>*>    The "solid oil" problem crops up in more conventional aircraft in
>*>wintry temperatures.


>In the book about german ace Erich Hartmann, a captured
>russian pilot showed the germans how to keep their air-
>planes startable in the frigid temperatures. The technique
>was to mix gasoline with the oil! Apparently, after the 
>engine warmed up sufficiently, the gasoline boiled off 
>or evaporated. Do they make multigrade oil for airplanes?
>Or can you use Mobil 1?

I have heard of the gas-in-oil trick, somewhere.  I think possibly
that special, built-in hardware for this purpose is called an
"oil-dilution system", but I have an uneasy sense that I may
be applying a correct name to the wrong apparatus.

This flight involved a brand new engine in a brand new plane.  The
tendancy at such times is to run the beast on a simple grade of
uncompounded mineral oil, with no fancy additives.  I am not sure why.
Many lightplanes are regularly run on very simple oils -- I think the
idea is that many additives break down into things that gum up or
damage the engine, and high-reliability in *the* engine is of course a
paramount consideration.  Light airplanes used for hire get an oil
change at least every hundred hours of operation, in any case.

Lightplane engines tend to run somewhat hotter than (say) automobile
engines, and when they are run it is typically for several hours at a
time, at a high percentage of peak power.  One weight of oil is likely
sufficient for normal operation at equilibrium engine temperature,
without regard to ambient air temperature.  And given the relatively
widespread availability of (eg) preheaters, there seems to be no real
need to seek out multi-weight oils just for starting.

It has been twelve years since I have been active as a pilot; perhaps
there have been some changes in the technology since then.

                                               -- Jay Freeman

	  <canonical disclaimer -- I speak only for myself>