Props, Pictures and PDF's

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Postby TreetopFlyer » Thu Feb 26, 2009 1:23 pm

Hello everyone, my name's Neil. I'd joined the forum a year or so ago but got pulled away by other demands on my time. Though I'm still not a pilot or owner of a Lazair, I'm still very much an enthusiast of the aircraft and have been enjoying reading many of the posts here again. Anways, on to a couple of questions...

First, I've noticed that a number of Lazairs have adopted a double prop arrangement, with a pair of propellers mounted in tandem on the same crankshaft on each engine with the idea of increasing the effective thrust from each engine, but doesn't having two props mounted so close together on the same shaft with the rear one embedded in the turbulence of the front prop's propwash render it less effective? Wouldn't a cruciform arrangement of the two props work better, or using a single 3- or 4-bladed prop?

My other question has to do with items posted to the forum itself. I've tried to look at the larger versions of various photos posted here, as well as open the PDF file on the February 2008 KITPLANE magazine but all I get are pages of symbols and webding gibberish. I'm using the latest version of Firefox for my browser and have the current version of Adobe acrobat running. Do I need to change some settings?

Cheers & Blue Skies,

N.
TreetopFlyer
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Postby TreetopFlyer » Thu Feb 26, 2009 10:51 pm

Ok, figured out my viewing problems with photos and pdf's lies with my Firefox browser so I'll resort to Explorer when I want to check out those things here.

N.
TreetopFlyer
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Postby Shannon » Thu Feb 26, 2009 11:01 pm

Hi Neil

The doubled "Bi" props were a standard factory set-up on the Rotax 185 engine. The original small 6hp Pioneer engines used on the planes used the same prop but only one. In any case factory testing showed that no appreciable difference in thrust was gained with the Bi-props mounted differently. For ease of mounting the props were "stacked" in the unusual configuration. This arrangement should have never been adopted as standard for the planes as it was not understood and not efficient. Eventually conventional props better suited for the engine (Rotax 185) were tested. As much as a 17% increase in thrust was reported using a more conventional custom 2 blade prop on the Rotax 185.

http://lazairforce.central5.com/
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Shannon
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