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Another prop question?

Old 08-25-2005, 11:17 AM
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Flyboy76
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Default Another prop question?

Can you put a 9X8 APC prop on a .46 size p-51 and get away with it safely?

Thanks,

Geoff
Old 08-25-2005, 11:54 AM
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Dr1Driver
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Default RE: Another prop question?

a 9x8 will run on a .46. That's getting into pylon racer size, though. If the model is heavy or draggy, it will take forever to get up to speed, and it might be VERY fast. For that plane and a .46 engine, I'd go with a 10x6 or 11-6. It'll be plenty fast for swcale-type flying.

Remember: GIVEN THE SAME RPM - more diameter/less pitch = more pulling power, less top end. More pitch/less diameter = less pull, more top end.

Dr.1
Old 08-25-2005, 12:19 PM
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Default RE: Another prop question?

thankyou very much.


Geoff
Old 08-25-2005, 12:43 PM
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britbrat
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Default RE: Another prop question?

The 9-8 will also notably increase the landing speed of the model, increase the take-off run, reduce vertical capability & reduce its closed-throttle aero-braking capability.

Lots of negative trade-offs for a modest increase in level-flight speed.
Old 08-25-2005, 01:40 PM
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Dr1Driver
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Default RE: Another prop question?


ORIGINAL: britbrat

The 9-8 will also notably increase the landing speed of the model, increase the take-off run, reduce vertical capability & reduce its closed-throttle aero-braking capability.

Lots of negative trade-offs for a modest increase in level-flight speed.
I doubt it will increase the landing speed since, at idle, this prop will produce very little practical thrust for this heavy, draggy plane.

Correct - It will increase the takeoff run since it will take a while for that little prop to pull that plane up to speed.

Correct - It will reduce vertical and braking capabilities.

Good bottom line - lots of negative trade-offs.

Dr.1
Old 08-25-2005, 07:33 PM
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britbrat
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Default RE: Another prop question?

ORIGINAL: Dr1Driver

I doubt it will increase the landing speed since, at idle, this prop will produce very little practical thrust for this heavy, draggy plane.

Dr.1
At idle, the slipstream discharge velocity for a 9-8 is still ~1/3 greater than that for a 10-6, regardless of the thrust. It has the same effect as raising the idle speed by 33%!! That, plus the lack of aero braking will definately result in a higher landing speed.
Old 08-25-2005, 07:48 PM
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Default RE: Another prop question?

That may be true, but the 9-inch prop is 23.4% less in swept area than the 10-inch prop. THAT'S where the pull is. The thrust must overcome the drag. What you might gain in airspeed at idle, you lose because the prop can't overcome the drag.

Dr.1
Old 08-25-2005, 07:54 PM
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britbrat
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Default RE: Another prop question?

Not to get into a pi$$ing contest here -- try it & watch what happens.
Old 08-25-2005, 08:07 PM
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Dr1Driver
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Default RE: Another prop question?

I have.

Dr.1
Old 08-25-2005, 08:18 PM
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Default RE: Another prop question?


ORIGINAL: Dr1Driver

I have.

Dr.1
Me too --- we disagree

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