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Dave ,
From what I have read, flattening the pitch will get you RPM and power, but your forward speed will suffer.
Same like revving your engine in 1st gear. Prop with diameter like ours should be spun at around 3K RPM for best performance
on takeoff. With my reduction drive 2.17 this prop RPM also brought my engine at it's best power RPM at 6.5-7000 RPM
I may be wrong, but it worked well for me.
3 blades used to bring down my engine RPM to 5200 and the prop to around 2400. which was not that good?
Again, I'm just an eyeball engineer and not a guru on the subject.
Buly
Still hang'n around :)
On Aug 3, 2007, at 6:53 PM, David Staten wrote:
Lugging? Was this full fine? or at a coarser setting?
I'm all for 3 or more blades because there is more surface area to impart thrust from. Since we have a prop disc limit of 66 inches on our airframe, adding blades is the way to go to improve thrust. There is a limit to the amount of HP a given blade can absorb and transmit. I wouldnt necessarily be opposed to trying a 6 blade variant either, provided we are making full power with our engine, or later with the turbo.
Dave
Bulent Aliev wrote:
I used to have the same prop as Chris IVO Magnum 68" Diameter inflight adjustable. I felt the 3 blade configuration used to lug the engine down. Changed it to two blade (did not want to cut the blades). My takeoff RPM was 6,500-7000.
Buly
On Aug 3, 2007, at 4:15 PM, Mark Steitle wrote:
On 8/3/07, Al Gietzen <ALVentures@cox.net> wrote:
Al,
I think Chris B. brought this up earlier today. I didn't respond, but you mentioned it, so then couldn't resist the urge to comment. To refresh everyone's memory, I have a 20B with a 76" 3-blade constant-speed M/T prop. So, I can dial in the prop speed desired and the prop controller does the rest. With it set to 2500 rpm, I'm seeing 7000 engine rpm on takeoff rolls. (What a sweet sound! It makes those Lycosaurus' sound like farm tractors.) It will turn about 6700 - 6800 during static runups. But this is a c/s prop, so your mileage may vary.
Mark S.
I have found that with my 66" dia – 80" pitch prop my Velocity doesn't move until engine rpm is somewhere upward of 1500 rpm.
I get about 5500 static with my 20B, and about 5600 on takeoff. With adjustable pitch you will want to get some higher numbers.
Hope you find this helpful,
Al
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