New prop

[elippse]

Well, I finally got to take my plane up with the new three-blade Elippse prop. It was designed to give me 3000 rpm at best power mixture at 14,500 dalt at 204 mph TAS, and 221 mph TAS at 3250 rpm and 1000' dalt. With it I got 2550 rpm static vs 2210 rpm for my first three-blade. I only got to do a few circuits around SMX so I throttled back to 2650 rpm at 3000', 4500' dalt, and got 171 mph TAS avg GPS GS at 5.6 gph. Climb was sensational; I got 1700 fpm average at 3500' dalt at 105 mph IAS and 1320 lb vs the previous 1550 fpm, 105 mph IAS, and 2420rpm! Not too bad for only 125 Hp O-235. The prop was clocked so that when it stops, one blade either points straight up or straight down and it runs very smooth; Catto did a nice job on it and its paint scheme. After I get some more time on the prop and venture further, higher, and more rpm, I will also try the prop in the other two positions to see if I feel any roughness from the prop position relative to TDC as I said I would do in a previous post. When I get my loaned two-blade modified prop back I will test it for roughness also in all three positions. I loaned it to a fellow who had a three-blade Ivo on his Lancair 235 that had one of the two 5/8" bolts holding the blade to the special flange come off and dent the inside of the spinner. The two-blade increased his ROC from 800 fpm to 1300 fpm and his TAS from 167 mph to 188 mph at the same rpm. He has a three-blade Elippse on order which he should get this month, so we'll see how much more performance he gets with it.

[Mike S]

Photos???

[pierre smith]

...you're running a Catto three-blade? With improved climb and cruise speed?

Or is it one of your designs that Catto built?

Thanks,

[hevansrv7a]

From the data Paul supplied, his THP in climb increased by 6 HP. ((1700-1550) x 1320 / 33000). If his static increase can be taken as meaningful (not a solid assumption) the BHP should have increased by around 15.4% (2550/2210). It's a 125 HP engine turning at or above rated RPM's at 3500 DAlt, so 6 HP is closer to 5%. These are very rough comparisons, but they suggest that prop efficiency did not improve.

The friend's climb THP increased by 20 HP. (500 x 1320 / 33000) plus or minus the error in my weight assumption of 1320. The cruise speed change was 12.6% at the same RPM. If we ignore that about 10% of the cruise drag is induced and just cube the speed difference we get over 40% more THP needed for that cruise increase. How does that work for you? (1.126^3)

I'd rather just have directly comparable data in sufficient depth to make good comparisons. How about you?

[rvmills]

Originally Posted by pierre smith

...you're running a Catto three-blade? With improved climb and cruise speed?

Or is it one of your designs that Catto built?

Thanks,

Pierre, Paul will confirm, but I'm pretty sure Craig builds his Elippse designs, so its that latter.

Paul, I'd also love to see pix!

Cheers,
Bob

[elippse]

Originally Posted by pierre smith

...you're running a Catto three-blade? With improved climb and cruise speed?

Or is it one of your designs that Catto built?

Thanks,

It's an Elippse design, Pierre, built by Craig.
The efficiency of this prop in climb and cruise should be about the same as my previous three-blade, about 82% in climb and over 90% in cruise; the climb efficiency based on the number of blades, diameter, and forward speed. The increased climb rate is solely accounted for by the increased HP due to rpm. This was my design goal! I wanted it to turn 3000 rpm at 14,500' dalt at best power mixture. That way I'll have more rpm and power for takeoff and climb. I then intend, once I reach design altitude, to reduce power and rpm at WOT by giving it maximum carb heat to increase the engine's thermal efficiency and have better fuel atomization, so that I can lean it even more and increase ignition timing more. The increased induction temperature will also decrease the volumetric efficiency, the fuel-air charge density, to further reduce the power. If I can get 100F increase it will reduce power by 10% and speed to 196-197 mph and rpm closer to sea-level rated 2800. Since the engine will still be at WOT to minimize pumping losses, I am hoping by this method to get even better fuel consumption specifics. I shall see when I make my trip to Carson City for the Reno air races and Phoenix for Copperstate.
As soon as I get an interface cable from my cell-phone to the computer I will send some pix.
We tested an Elippse IF1 test prop on an IF1 racer last week and we picked up 20 mph IAS over his Hill Twisted-Composite IF1 prop! The owner and crew were astounded by the speed increase and reduced prop noise. Unfortunately at Reno, if you start back in the pack, your lap speed will be about 10 mph less than your qualifying speed, 'cause you've got to follow other planes and their vortices. Im always surprised at "Phantom" 'cause Tom gets a little slower start off the line and usually gets overtaken by the 2nd and 3rd planes on takeoff. He then passes them after the first turn, and then catches up and passes the last five planes before the end of the 6 laps, so even though he must pass on the outside and so fly a longer course than in qualifying, he still equals or exceeds his qualifying speed! It must be the old competitive juices at work!