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Posted for Ken Welter <rotary.coot@verizon.net>:
Hi Marv
What is this moly-coating on the side housing and who did it for you.
Ken Welter
[Hi Ken,
The moly coating was applied to the faces of the side and intermediate housings and the gears in an effort to reduce friction and thereby reduce some of the cooling load. The coatings were done by Darus Zehrbach, an engine builder out of Morgantown, WV. He does lots of interesting things and has some really wild projects underway... he has 3 customers that he's built inverted 650ci turboed V-8's for who are presently installing them into their Lancair IV-P's (pic attached). They're designed to operate without a PSRU... I'm pretty sure the big bell housing on the front is strictly a bearing housing to tame the gyro forces of the prop and to get it forward enough to fit the cowl.
Anyway, there's an interesting story behind the evolution of these coatings... the Israeli military has been using a UAV called the Harpy for the last 30 years, a single-rotor prop-driven missile that launches from under the wing of a strike fighter, and which is tasked to destroy surface-to-air missile and anti-aircraft sites. They had a problem with these things, though, that being that about 1/3 of them would fry the engine as soon as they left the rack, and they would simply crash and explode. The problem was that the the engine was pull started by a lanyard attached to the weapons rack, with momentum to get the missile out of the rack provided by a short-burn rocket motor. The prop starts out folded against the sides of the missile, and is direct driven by this little rotary through a clutch... centrigual force opens the prop and away it goes. The engine has no throttle control, it simply starts up at full throttle and engages the clutch almost instantaneously once its running. Even though the clutch put a load on the engine in less than a second, these little rotaries would spin up to about 12,000 rpm instantaneously and fry the side seals or seize up the rotors completely due to a lack of lubrication before the oil would start to flow. It seems that some years ago Darus was building marine racing engines that were using ceramic and moly coatings and winning lots of races with them, and somehow the Israelis heard about his success. Subsequently they contacted him and he worked with them to incorporate these super-slippery coatings into these Harpy missiles... lo and behold the failure rate due to the lack-of-lube problems went to just about zero. He's still putting this coating on these things for them to this day. And that's the name of that tune <g>. It has been suggested that these coatings could well turn out to be completely sacrificial, and that they would gradually wear away and be consumed during the combustion process. Only time will tell. <Marv>
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