The idea is that a single blade would be more efficient than multiple blades because the single blade is always travelling through undisturbed air. The propeller is counterweighted and mounted eccentrically on the hub to keep it balanced. It also has fore-aft pivot so the prop pitch self-adjusts to the most efficient angle – you can move the tip of the blade forward and back several inches with your hand.
Apparently the design worked; in 1939 the Everel prop was tested on a Taylorcraft in a race and won by quite a bit. However, shortly after the introduction of the prop, powerful 50HP engines were developed which rendered the efficiency gains of the single blade moot. Considering that the balance of the prop was very fickle in changing weather, the already mechanical complex prop just wasn’t worth the effort, so the design never caught on. It’s a nifty bit of engineering and a cool piece of history.
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One of two flying single blade J-2 Cub
By: Slipstream - 19th October 2013 at 15:16
There a number of issues to consider when designing propellers, power delivered by the engine, weight, diameter wrt tip speed, ground clearance and gyroscopic effects, aspect ratio of the blades and probably more I haven’t thought of. A single blade may be more efficient but totally impractical.
By: Baldeagle - 19th October 2013 at 05:29
http://www.youtube.com/watch?v=fqiBb98o1D8&feature=c4-overview&list=UUWb5Y5B_JfGQwLJi6Vc-Q4w
By: TonyT - 15th October 2013 at 21:17
Some gliders have used them for years, see
http://youtube.com/watch?v=l1-xSq6uaIQ&desktop_uri=%2Fwatch%3Fv%3Dl1-xSq6uaIQ
By: Graham Boak - 15th October 2013 at 13:27
The relative efficiency of multi-bladed props is linked to the maximum diameter available, which in turn is limited not just by the aircraft configuration but by tip speed. This does tend to suggest that the theoretical superiority of the single blade is indeed limited to lower thrusts. I’d have thought that the larger it gets then balance problems would come to dominate, but that may just be an assumption open to discussion.
By: flyernzl - 15th October 2013 at 10:09
Wasn’t one of those tested on an Auster somehere in the UK, back in the early 50s?
By: HP111 - 15th October 2013 at 09:42
Interesting to see a fullsize example. Strange then that 4, 5 and even 6-bladed props are considered very efficient. I suspect it is more a case that apparently improved effectiveness of the 1-blader really comes from the greater diameter/chord or whatever needed to absorb the power available when using only one blade, and that as a potential solution it is only applicable to low powers. An interesting aerodynamics question though. I suppose for two approaches to propulsion one could contrast the Osprey and A400M, but that sounds like the wrong forum.
By: Deskpilot - 15th October 2013 at 02:00
A case of where theory doesn’t quite work in practice.
By: CIRCUS 6 - 15th October 2013 at 01:44
Cool! I’ve seen and done this on model planes, but never seen it full size…
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October 14, 2013 at 11:37 pm