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From: n295vv
Susan, you have sent an excellent reference for the Lancair builders. The level sensor itself that Pillar Point sells is what I described several weeks ago--It consists of an emitter and collector, and when the end of the optical rod is wetted by liquid, it bounces the beam back to the collector. It is virtually foolproof.
I hope this firm carries this concept several steps further--it is possible to put several of these optical detectors in a fuel tank and give very exact fuel levels. They are very cheap to make, and are extremely reliable. Of course, one of the sensors could be used to trigger a low level warning sequence, as their current system has.
Interestingly, as I mentioned in my previous post, these sensors will detect the flame of a match from as much as 15' away. Some of you people may want to build your own fire detection system in your engine compartment. I think they might also be able to detect IR levels of less than a complete flame, but I am not sure. If so, this would warn of approaching combustion conditions before actual fire happens. It would depend on the specs of the detector you inserted in the fitting. To use the existing Pillar Point detector as a fire detection device, simply grind off the point of the glass rod so the end is flat instead of pointed. Then polish the flat surface with a diamond grit lapping paper so it is optically transparent.. You can also increase the scanning angle to be a cone of several degrees by making the end of the rod somewhat rounded. I have done this by heating the glass rod (I used quartz glass rod in the old days) until it melts and forms a convex lens shape to the end of the rod. If you melt the glass sufficiently, you will not have to polish it.
Glass is not the only material that can be used in the detector. Several optical plastics can be used, if their chemical and mechanical properties are acceptable. But glass is readily available and cheap. And, if quartz glass is used, it is tougher than hell. In any event, the Pillar Point system is excellent, and if I were building a plane now, I would jump at the opportunity to incorporate it.
David Jones, Pecatonica, Illinois
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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