from here: http://www.eaa.org/experimenter/articles/2009-07_phantom.asp
THE PROP
Using the data collected by Tom while flying Phantom with Paul?s surplus two-blade prop, Paul used his computer program to design the planform and twist for a custom propeller, optimized for high speed and high rpm. A hand-carved, wood-laminate, composite-covered three-blade fixed-pitch ELIPPSE design was specified, and Mr. Catto was then engaged to carve the race prop.
As you may remember from the Paul Lipps article in the February issue, the ELIPPSE propeller makes thrust from the tip to the spinner. Unlike conventional props that make no thrust or even negative thrust at the root, Tom?s ELIPPSE propeller makes enough thrust at the root to increase the ram air effect on manifold pressure from the previous 1-1/2 inches over ambient with a conventional prop to a phenomenal 3 inches over. That?s 1-1/2 inches of additional manifold pressure free, which could easily translate to several extra horsepower, considering that it translates to approximately a 5 percent increase in power.
This article was written by John B. Moyle and Pat Panzera, NOT Paul Lipps himself. 3" over ambient ram air is a BOLD statement and seems to contradict Paul Lipps'(Elippse) own statements regarding the issue.
http://www.vansairforce.com/community/showthread.php?t=27921&highlight=ram+air post #6
At 200mph TAS, my three-blade prop imparts about a 5-7 ft/sec avg. velocity increase to the air in the rearward direction; that is nowhere near enough to give any appreciable pressure increase. At 8000' dalt and 200 mph TAS, stagnation pressure is 1.136". With an added 6 ft/sec, it would be 1.183".That is the increase that goes on all around the prop arc, not just during the small fraction of the arc when the prop is in front of an inlet, which is only a short part of the total inlet valve opening time. Plus, my blade design exerts much more velocity increase in the root area than does a typical design. In Jack Norris' book on prop design, he has a section in which he calculates the slow-down of air ahead of the cowling on an RV; he shows a very dramatic velocity decrease in the vicinity of the prop hub. I have always felt, but have never measured, that there is a definite free-stream velocity increase into inlets that are close to the base of the spinner since the spinner definitely displaces and speeds-up the air flowing over it on a continuous basis, not a pulse into the inlet as from the prop passing. Unfortunately, the spinner-cowl interaction is not covered in Jack's book. Whether the spinner would give an appreciable pressure increase is something that needs to be measured or calculated. You don't say whether you have a carb or FI; that's important since the carb gives much more pressure drop than does the FI throttle valve. The formula for ambient pressure vs pressure altitude is 29.92[(1-PA*6.88E-6)^5.256]. For your 7000' PA I get 23.083" which is about the same as your 23.09" Navy source. In all the tests I've run with my plane my MAP is always what I would get considering the stagnation pressure and the carb pressure drop, and I've got lots of flight data to back that up. What's it all mean, Alphie?
Always interested in learning more....
George
THE PROP
Using the data collected by Tom while flying Phantom with Paul?s surplus two-blade prop, Paul used his computer program to design the planform and twist for a custom propeller, optimized for high speed and high rpm. A hand-carved, wood-laminate, composite-covered three-blade fixed-pitch ELIPPSE design was specified, and Mr. Catto was then engaged to carve the race prop.
As you may remember from the Paul Lipps article in the February issue, the ELIPPSE propeller makes thrust from the tip to the spinner. Unlike conventional props that make no thrust or even negative thrust at the root, Tom?s ELIPPSE propeller makes enough thrust at the root to increase the ram air effect on manifold pressure from the previous 1-1/2 inches over ambient with a conventional prop to a phenomenal 3 inches over. That?s 1-1/2 inches of additional manifold pressure free, which could easily translate to several extra horsepower, considering that it translates to approximately a 5 percent increase in power.
This article was written by John B. Moyle and Pat Panzera, NOT Paul Lipps himself. 3" over ambient ram air is a BOLD statement and seems to contradict Paul Lipps'(Elippse) own statements regarding the issue.
http://www.vansairforce.com/community/showthread.php?t=27921&highlight=ram+air post #6
At 200mph TAS, my three-blade prop imparts about a 5-7 ft/sec avg. velocity increase to the air in the rearward direction; that is nowhere near enough to give any appreciable pressure increase. At 8000' dalt and 200 mph TAS, stagnation pressure is 1.136". With an added 6 ft/sec, it would be 1.183".That is the increase that goes on all around the prop arc, not just during the small fraction of the arc when the prop is in front of an inlet, which is only a short part of the total inlet valve opening time. Plus, my blade design exerts much more velocity increase in the root area than does a typical design. In Jack Norris' book on prop design, he has a section in which he calculates the slow-down of air ahead of the cowling on an RV; he shows a very dramatic velocity decrease in the vicinity of the prop hub. I have always felt, but have never measured, that there is a definite free-stream velocity increase into inlets that are close to the base of the spinner since the spinner definitely displaces and speeds-up the air flowing over it on a continuous basis, not a pulse into the inlet as from the prop passing. Unfortunately, the spinner-cowl interaction is not covered in Jack's book. Whether the spinner would give an appreciable pressure increase is something that needs to be measured or calculated. You don't say whether you have a carb or FI; that's important since the carb gives much more pressure drop than does the FI throttle valve. The formula for ambient pressure vs pressure altitude is 29.92[(1-PA*6.88E-6)^5.256]. For your 7000' PA I get 23.083" which is about the same as your 23.09" Navy source. In all the tests I've run with my plane my MAP is always what I would get considering the stagnation pressure and the carb pressure drop, and I've got lots of flight data to back that up. What's it all mean, Alphie?
Always interested in learning more....
George
