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gliderx5
Joined: 30 Jun 2008
Posts: 203
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 Posted: Mon Aug 11, 2008 2:21 pm Post subject: static thrust question |
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gliderx5
Joined: 30 Jun 2008
Posts: 203
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| Posted: Tue Aug 12, 2008 2:34 pm Post subject: static thrust question |
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Sorry, it's another test
-------------- Original message ----------------------
From: gliderx5(at)comcast.net
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gliderx5
Joined: 30 Jun 2008
Posts: 203
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| Posted: Tue Aug 12, 2008 2:46 pm Post subject: static thrust question |
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Sorry for all the empty emails on the list. My signature was causing problems.
I just got back from measuring thrust on my MKII 503 SCSI, 66 inch IVO 3 blade.
Using a 300 lb hanging type scale hooked to a truck the Rotax bulled just past
the end of the marking (I'm guessing 305 lbs). I did a quick check on the scale
by hanging from it and it got my 200 lbs correct. The Kolb was on level ground
with the wheels on plywood during the test. My MKII has a top level speed of
just over 65 mph and I cruise at 50 to 55 mph. Climb solo is 600-700 fpm.
We also measured two other aircraft. One with a 45 hp Zenoah, 2 blade 62 inch
(not IVO) and it measured 195 lbs. The other was a Hirth 40 hp with a 68 inch 2
blade IVO and it peaked at 190 lbs. Later we installed my 3 blade IVO on the
Zenoah
and measured 225 lbs thrust
Last year, using a 200 lb hanging scale and a pulley to allow measuring 400 lbs,
we measured my Corvair powered Pietenpol at 280 lbs static with a wood 66 inch,
35 inch pitch, homemade prop. It's very interesting that the 46 hp Rotax
produces more thrust!
-------------- Original message ----------------------
From: gliderx5(at)comcast.net
| Quote: |
Sorry, it's another test
-------------- Original message ----------------------
From: gliderx5(at)comcast.net
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jb92563
Joined: 23 Mar 2007
Posts: 314
Location: Southern California
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| Posted: Tue Aug 26, 2008 11:47 am Post subject: Re: static thrust question |
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Yep, its all in the prop.
The more blades you drive the more static thrust you get but as the prop starts moving forward through the air at greater flying speeds the thrust starts to drop off rapidly.
In general 3 blades will produce a lower top end speed than 2 blades, but 2 blades produce less thrust during takeoff.
Its always a tradeoff, but most slow planes (under 100mph) are more safe with 3 blades due to the higher takeoff and low speed thrust.
My other plane with feathering prop (Grob 109) actually can not safely take off with the pitch set in "Cruise" pitch, but the "climb" pitch is lower and produces more thrust & rpms for takeoff and climbout.
If you like doing XC trips a lot you could save some fuel buy getting an IVO inflight adjustable pitch prop and adjust your own cruise economy.
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_________________
Ray
Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider
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