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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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 Posted: Wed Jul 09, 2008 1:53 pm Post subject: 2 blade vs 3 blade, was: Gyrocopter intercept |
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At 03:41 PM 7/9/2008, jb92563 wrote:
| Quote: |
Dana,
My logic behind the 2 blade, faster airspeed for best rate of climb is:
The 2 blade produces more thrust at greater airspeeds than a 3 blade so
more speed equals greater lift from the wing up to some optimum point and
hence a greater rate of climb.
In practice you would probably notice a flatter initial climb with a 2
blade but a greater rate of climb after your speed has increased up to
that magic best climb rate speed.
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Again, it's not the number of blades but the pitch and blade
area. Increasing the diameter (if possible) of a 2 blade prop has a
similar effect to adding a third blade but is more efficient. In either
case you'd have to reduce the pitch or increase the redrive ratio.
"Greater lift from the wing"... actually the lift from the wing is the same
whether you're climbing, flying level, or gliding. It's always equal to
weight (minor differences due to the angles aside, or maneuvering flight,
which is a whole different situation). If lift exceeded the plane's
weight, you'd _accelerate_ upward, and climb at an ever increasing
rate. Climb comes from excess power, not greater wing lift.
| Quote: | If you want to go touring/cruising a 2 blade is the way to go.....or get
an inflight adjustable 2 blade and have the best of both worlds.
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In a fast plane with a wide variation between climb and cruise speeds, an
adjustable prop makes a lot of sense. Our Kolbs have a narrow enough speed
range that an adjustable prop is unlikely to be worth the added weight and
complexity.
-Dana
--
"If yew ain't livin' on th' edge, yer takin' up too much room!"
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planecrazzzy
Guest
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| Posted: Wed Jul 09, 2008 3:52 pm Post subject: Re: 2 blade vs 3 blade, was: Gyrocopter intercept |
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Hey Guys,
I wasn't following the other thread....
But , this is how it worked for me....
I had my 3 blade IVO set - level flight 6500 rpm.....
My cruise at 5900 was around 60 ASI
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I changed to 2 blade... I bought the "Blocks" , and took off one of my blades....
I set my pitch for 6500 - level flight....
Now, my cruise is 70 -75 ASI at 5900 rpm
Simple....The 2 blade set-up gives me faster cruise....
Longer take-off distance....less rate of climb....
"I" like it this way.....
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Gotta Fly...
Mike & "Jaz" in MN
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http://groups.yahoo.com/group/Buttercup-STOL/
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