Prop speed RPM

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JAMES
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Prop speed RPM

Postby JAMES » Tue Jun 13, 2017 10:13 pm

All my power to this motor is 500+ on the DYNO
come in at 5400 RPM's I have a 79 in EX What I want to know and I forgot how to do it is where do I want that tip speed WW says 2000 to 2500 max how do I figure out my Tip speed i'm turning 5000 on ground set on 17 -17-1/2 I just want to make sure I'm in that speed range
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Re: Prop speed RPM

Postby Coastslider » Tue Jun 13, 2017 10:38 pm

With your reduction you have listed it puts your prop rpm at 1865 at 5000engine rpm I believe

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Re: Prop speed RPM

Postby digginfool » Tue Jun 13, 2017 10:42 pm

Circumference is pi times diameter. So, 79" x 5400/12 = feet per minute. Divide again by 60 gives you feet per second. Or, multiply by 60 then divide by 5280 gives you mph. Pi = 3.14.

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Re: Prop speed RPM

Postby Coastslider » Tue Jun 13, 2017 10:43 pm

Ps tip speed is a totally different equation. WW is referring to propeller rpm

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Deano
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Re: Prop speed RPM

Postby Deano » Wed Jun 14, 2017 12:03 am

Here ya go James:

Image

5400 Engine rpms is only turning the prop 2015 rpms. Got plenty of room.
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Re: Prop speed RPM

Postby SWAMPHUNTER45 » Wed Jun 14, 2017 7:51 am

It appears that you may benefit from a 2.37 ratio

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Re: Prop speed RPM

Postby digginfool » Wed Jun 14, 2017 7:54 am

Coastslider wrote:Ps tip speed is a totally different equation. WW is referring to propeller rpm


You're correct. I did not figure in his gear ratio. You would have to divide RPM by gear ratio to get actual tip speed.
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JAMES
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Re: Prop speed RPM

Postby JAMES » Wed Jun 14, 2017 3:18 pm

I guess the big question is my prop is supposed to be 2000 to 2500 max in between that I guess is ideal correct ... too low I'm losing performance too high I'm taking a chance on catastrophic failure ? Also to high means a lot more noise I guess setting my motor at 5400 would be ideal I making over 500 hp at 5300
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Re: Prop speed RPM

Postby One Eyed Gator » Wed Jun 14, 2017 4:20 pm

Sent ya a PM

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Re: Prop speed RPM

Postby SWAMPHUNTER45 » Wed Jun 14, 2017 8:26 pm

5300rpm / 2.37 = 2236 rpm at prop

5400rpm / 2.37 = 2278 rpm at prop

Clearly that puts you in the props prime performance range

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Re: Prop speed RPM

Postby Coastslider » Wed Jun 14, 2017 9:23 pm

SWAMPHUNTER45 wrote:It appears that you may benefit from a 2.37 ratio

X2

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Re: Prop speed RPM

Postby One Eyed Gator » Fri Jun 16, 2017 12:14 pm

Just my 2 cents. Has more to do with tip speed than prop RPM.
To put the tip speed around 500mph which seems to be a good spot for R blades and other med width props

2.68 with a 79" prop takes 5700 motor rpm to be at the 500mph mark
2.55 " 5400 "
2.37 " 5050 "

2.68 with a 82" prop takes 5500 motor rpm to be at the 500mph mark
2.55 " 5200 "
2.37 " 4850 "

So get either a 2.55 box or an 82" prop set around 5400 and ride out. tweak it from there. Also I would more concern where it made its peak torque.

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Re: Prop speed RPM

Postby CarMotorBarge » Fri Jun 16, 2017 7:15 pm

One Eyed Gator wrote:Just my 2 cents. Has more to do with tip speed than prop RPM.
To put the tip speed around 500mph which seems to be a good spot for R blades and other med width props

2.68 with a 79" prop takes 5700 motor rpm to be at the 500mph mark
2.55 " 5400 "
2.37 " 5050 "

2.68 with a 82" prop takes 5500 motor rpm to be at the 500mph mark
2.55 " 5200 "
2.37 " 4850 "

So get either a 2.55 box or an 82" prop set around 5400 and ride out. tweak it from there. Also I would more concern where it made its peak torque.


So let's assume the peak torque is at 4500. How would this change your recommendation above on the gearbox ratio and prop length?
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Re: Prop speed RPM

Postby Coastslider » Fri Jun 16, 2017 9:32 pm

Manufacturers prop rpm has a lot to do with tip speed. Not to mention width and pitch. How does this change your theory ? The more width and pitch the more drag and vibration. This changes rpm recommendations. Propeller theory is deeper than this argument

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Re: Prop speed RPM

Postby kwanjangnihm » Sat Jun 17, 2017 6:55 am

James here's a visual of the prop speed 2000-2500 (for the EX) with 3 different ratio's.

Image
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Re: Prop speed RPM

Postby JAMES » Sat Jun 17, 2017 5:20 pm

2.55 not gonna happen i think im gonna try 238! 255 more for racing ive been told and noone ive seen really likes it compared to 268
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Re: Prop speed RPM

Postby ffjpowell » Sun Jun 18, 2017 9:18 pm

www.hoverhawk.com

Try this site. I went with a 84" R series and a 2.7 belt and am very happy with the results. U can teeek ur #'s accordingly. Out site temp is in Celsius so just figure out ur average temp for ur area and convert to C*.

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Re: Prop speed RPM

Postby Prototype » Thu Jun 22, 2017 9:04 pm

James,
I don't have a excel spreadsheet for you like some. That's what you asked for but since you seem lost with tip speed v performance of a ww blade, I can only imagine your still lost?
If not post what you did or bought to kick that sucker in the ass!
Normally I would never post to a ex 220 guy because they are a hint below a stock dd caddy!
I know you have the answers to your question but is that question correct? Is tip speed your major concern over performance or gear or number of blades? Of course you could be feeling out the census for what they know to a vague question? I highly doubt your power comes in at 5400 unless your looking for a 3 gear and have about 40 k into that motor

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Re: Prop speed RPM

Postby JAMES » Sun Jun 25, 2017 10:18 pm

Prototype wrote:James,
I don't have a excel spreadsheet for you like some. That's what you asked for but since you seem lost with tip speed v performance of a ww blade, I can only imagine your still lost?
If not post what you did or bought to kick that sucker in the ass!
Normally I would never post to a ex 220 guy because they are a hint below a stock dd caddy!
I know you have the answers to your question but is that question correct? Is tip speed your major concern over performance or gear or number of blades? Of course you could be feeling out the census for what they know to a vague question? I highly doubt your power comes in at 5400 unless your looking for a 3 gear and have about 40 k into that motor

Unless the dyno lied it does i was their we changed cams multiple times and went with different lifts and Grinds im making @4700 490.7 and 440.1 my boat will break free at 36-3700
With 3 adults its a well built engine
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