David McCandless asked:

Hi Paul, since the injectors are now on the 'hot side', would the
magnesium further increase the fire risk? BR,Dave McC

"Kent, Russell" wrote:

The ignition point of cast magnesium is 1153 deg F (623 deg C).  I

don't

know what Mg alloy Mistral is using, but it's solid-form ignition

point

is unlikely to be far different.  If the cowl temps are that high,
you've got other issues...

Reference:
http://www.eh.doe.gov/techstds/standard/hdbk1081/1081tab2.html

Russell Kent

It?s a non-issue.  We didn?t do any high-tech test, but we suspended a

piece

of that Mg alloy over a big oil pan full of at least half a gallon of
gasoline and ignited it.  The gasoline burned out and the magnesium

had

not

ignited.  Furthermore, remember that the manifold is internally cooled

by

cool intake air blowing at 60-70 mph on average.

It won?t ignite unless you use a welding torch on it!

The problem with Mg is machining.  The part will not ignite, but the
scrapings may.  Machining speed has to be considerably reduced vs Al,

hence

the higher costs.  Casting is also much trickier and few foundries

master Mg

casting real well.

Francois

Francois,

    It looks like a very nice unit. I don't know how realistic your test

is

though. My concern, based on experience would be an in flight failure of

the

exhaust system, which is in very close proximity. With the rotaries very

high

exhaust temps, a high pressure fuel system (shrouds would not last long)

and

relatively high cowling temps it could turn a bad situation much worse
quickly. I would consider an aircraft engine installation to be more

likely

to have a fire than a 72 VW microbus, I have seen a couple of them go up

and

there is no putting them out. Could they be made of Al ? at least then you
could shut of your fuel and glide in. Nothing scares the shit out of me
(sorry Paul) like smoke in the cockpit.

John

I think you could just put a relatively thick sheet of 421 SS (say .065)
between
the exhaust manifold and the intake manifold and you would be OK.

Paul Lamar

Yes, the air intake manifold on the "hot" side of the engine may well end-up
being made of Al, while the one on the "cold" side would remain Mg.  It only
adds a pound or so to the engine weight.  But you know, it's so easy to add
a pound here, an ounce there, etc and to end up with an engine which weighs
20 lbs more!

BTW, Mg parts are not new to aircraft engines, even certified ones.

Francois

 
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