Prop sizing
Posted: Fri Feb 17, 2012 11:02 pm
I've got my engine decisions pretty much completed. The only things I have
yet to figure out are which carb and I would like to find a way to have
redundant ignition. My first look at ignition was to put a mag in the
distributor hole. I know I could use dual electronic with a second small
battery for backup but I like the idea of a mag that will run without
external power. I just can't figure out how to have two with a single set
of plug wires. I really don't want to deal with dual plugs.
I was thinking about giving the three bladed in-flight adjustable IVO-Prop
with the electronic constant speed prop governor a try. It's only 26.7
pounds and $2130. Supposed to be good up to 700 HP. Can anyone tell me how
to size and pitch the blades? Here are the ranges possible according to
their website.
30"- 90" or 45" to 105" pitch range
58"-76" diameter
I keep hearing that the biggest blade I can run and have good ground
clearance is what I want. That being the case, then I guess I would go with
the 76" diameter which I think should have plenty of ground clearance in a
level attitude rolling down the runway. What pitch range would I want?
Using a prop tip speed calculator I found on the web a 76" diameter prop
needs to turn 3000 rpm to develop the desired tip speed between .88 and .92
mach to produce maximum thrust. (Only works between about 30-70 deg. F). I
want to limit my max engine rpm to about 5000 rpm so that means I will want
a gear reduction ratio of about 1.7. Then again, I also keep hearing that a
big slow turning prop is what we want on a Super Rebel. Perhaps 76" just
isn't big enough?
Mike Kimball
SR #044
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yet to figure out are which carb and I would like to find a way to have
redundant ignition. My first look at ignition was to put a mag in the
distributor hole. I know I could use dual electronic with a second small
battery for backup but I like the idea of a mag that will run without
external power. I just can't figure out how to have two with a single set
of plug wires. I really don't want to deal with dual plugs.
I was thinking about giving the three bladed in-flight adjustable IVO-Prop
with the electronic constant speed prop governor a try. It's only 26.7
pounds and $2130. Supposed to be good up to 700 HP. Can anyone tell me how
to size and pitch the blades? Here are the ranges possible according to
their website.
30"- 90" or 45" to 105" pitch range
58"-76" diameter
I keep hearing that the biggest blade I can run and have good ground
clearance is what I want. That being the case, then I guess I would go with
the 76" diameter which I think should have plenty of ground clearance in a
level attitude rolling down the runway. What pitch range would I want?
Using a prop tip speed calculator I found on the web a 76" diameter prop
needs to turn 3000 rpm to develop the desired tip speed between .88 and .92
mach to produce maximum thrust. (Only works between about 30-70 deg. F). I
want to limit my max engine rpm to about 5000 rpm so that means I will want
a gear reduction ratio of about 1.7. Then again, I also keep hearing that a
big slow turning prop is what we want on a Super Rebel. Perhaps 76" just
isn't big enough?
Mike Kimball
SR #044
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To unsubscribe from this list go to:
http://www.dcsol.com:81/public/code/html-subscribe.wcx
Archives located at http://rebel:builder@www.dcsol.com:81/default.htm
To contact the list admin, e-mail mike.davis@dcsol.com
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Unsubscribe: rebel-builders-unsubscribe@dcsol.com
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