ELIPPSE-Felix prop on RV-6

[Bob Axsom]

The only way to really know of course is to refly the test at 6,000 ft. density altitude and validate the 1.6% assumption. The 4kt subtraction from my speed for the cooling drag mod is probably OK but the drag is not constant at different velocities - it probably is a higher figure at the 177.8 KTAS value but close enough. A confidential chart I was given with predicted cruise efficiency comparison between my prop and the Hartzell blended airfoil prop with 7496 blades across a speed range of 140-200 KTAS shows a rapid drop off of my prop above 165 KTAS. At my max cruise speed (minus the 4kt cooling drag improvement) 173.8 KTAS the efficiency is 85.4%. At this same airspeed on the chart the blended Hartzell is at 87.8 and climbing with cruise airspeed. I have been reeding Jack Norris' book "Propellers, the First and Final Explanation" and I have seen photos of your propellers on the winning biplanes at Reno for the past few years so I know that the blade area distribution appears to conform to his rule and the speed at Reno validates their effectiveness for obtaining high cruise. I can believe that 90% efficiency at this speed is achievable with your prop.

Bob Axsom

[David-aviator]

Originally Posted by elippse

Jim Smith of Wichita, KS has been doing TAS testing of his ELIPPSE-designed, Fred-Felix-made, three-blade propeller on his stock 150 HP, auto-fuel RV-6. His best speed was at a density altitude of 7000' where the four-run, GPS-derived, TAS average was 191.6 mph at 2741 rpm, with high and low speeds of 193 mph and 189.5 mph. His average ROC from takeoff at 1350' to 10,000' was 800 ft/min at 95 mph IAS and 1440 lb., and a recent ROC test yielded an average of 1032 ft/min from 2000' to 10,000' at rpm ranging from 2300 at 3000' to 2175 at 10,000', 1440 lb and 95 mph IAS.

Paul,

In reading about the ELIPPSE design, I've wondered if it is related to the Felix bi-camber design and it would appear it is. I've had 2 Felix props, one a 2 blade pusher on the Cozy MKIV and the other a 3 blade fixed pitch experiment with the Subaru engine, both of a bi-camber design.

[IMG][/IMG]

I really liked the idea of a simple fixed pitch prop with this engine but it did not work out. For lack of a starting point of pitch and diameter, I asked Fred Felix to design it as if it were an O360 180HP engine. Ha, the thing turned up at 1900 rpm and made for quite a long take off roll with the Subaru. In flight engine cooling was terrible so after just 2 flights I sold the prop to a friend with an 0360 RV-4 and he is most happy with it.

Question, is it possible to design a fixed pitch prop to work with a 2:1 reduction and the Subaru engine? Fred Felix said he could have repitched the prop to perhaps turn up 2000 or 2100, but I thought I needed at least 2300 to get it to work for take off, and even at that was inclined to believe it would over speed quickly in flight.

By the way, I sat in on Klaus Savier's talk on props and other things at OSH last summer. That was a very interesting seminar and he touched briefly on why the MT seems to run out of steam on the high end of the performance envelop. It is all in blade design and I'm curious as to why Mt hasn't done something about it.