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Main Discussion > Easy function to get equal performance headspeed from all helis.
 
 
wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		I was pretty bored during class today so I made a function, using the tipspeed as a reference to estimate the perfect headspeed! Here it is, its really rough and dosn't really work on smaller helis but type it in and fill in x for your blade length in mm. It is just for fun!!! Also substitute 343 for the divisor and you will get how fast something has to be spinning in rotation per minute to reach the speed of sound.

headspeed =125.6637061436/(2*(pi)*.x)*60 in rpm to same perfomance at 2000 rpm headspeed on 600 mm blades with proportional chord

For tipspeed to break sound barrier it would be 343/(2*(pi)*.x)*60

Have fun!
11-06-2009 03:09 AM
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Ots
Heliman
Location: Glendora, CA - USA

My Posts This: Topic  Forum		[quote]...using the tipspeed as a reference to estimate the perfect headspeed![quote]

So the "perfect headspeed" is then that headspeed which yields a tip speed just at the speed of sound?
11-06-2009 05:23 PM
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VooDooX
Key Veteran
Location: San Francisco Bay Area CA, US (San Mateo)

My Posts This: Topic  Forum		i want a heli head that breaks the speed of sound BAM BA BAM BAM BAM when it blade farts hahahah

99.9999999999999% of an atom is empty space
11-06-2009 05:33 PM
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wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		no the first function, was the one for a proportional headspeed.
11-07-2009 01:39 AM
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emag remrofni
Elite Veteran
Location: Santa Clarita CA

My Posts This: Topic  Forum		Sweet, my optimal headspeed is 1.685943234 rpm on my 90! Time to pull out my multigov pro programming screen!

Team Avant
Lightning Power Batteries
11-07-2009 02:23 AM
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Warney
New Heliman
Location: Melbourne, Australia

My Posts This: Topic  Forum		Equaled exactly 2000 for 600mm blades (well, 2000.000000000013162848 to be precise)
11-07-2009 03:30 AM
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TipSpeed
Veteran
Location: Glenside, PA

My Posts This: Topic  Forum		What about tipspeed Lol.

-Dave
11-07-2009 03:46 AM
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eggmcmuffinplz
Elite Veteran
Location: Los Angeles, CA

My Posts This: Topic  Forum
Quote 
Sweet, my optimal headspeed is 1.685943234 rpm on my 90! Time to pull out my multigov pro programming screen!

What are you talking about?

According to the function, with 700mm blades, 1715 is what I got.

Scott D
Logo 500 3D V-bar
11-07-2009 04:28 AM
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wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		yea to get same performance! but this dosn't take into account chord so its not perfect
11-07-2009 05:24 AM
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T-Rex-Flyer
Key Veteran
Location: Panama City, Fl

My Posts This: Topic  Forum		How did you come up with 125.6637061436 as the divisor?

Edit:
Wouldn't the number abover be the Dividend?

Quote 
Arithmetic operation of division: if a / b = c then a is the dividend, b the divisor, and c the quotient.

Stuff like this make my head hurt.

If the wings are traveling faster than the fuselage, it's probably a helicopter.
11-07-2009 02:33 PM
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ErichF
Elite Veteran
Location: Odessa, FL 33556 (Tampa Area)

My Posts This: Topic  Forum		Just what exactly is your idea of a "perfect headspeed"? This whole thing makes no sense.

Erich
11-07-2009 03:23 PM
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wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		Its just a product of boredom. The divisor is that way due to the tipspeed of 600mm blades spinning at a little over 2000 rpm. thought it would be fun to see what people think. Its mathematically perfect not with all the real world variables.
11-07-2009 05:55 PM
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AirWolfRCrrProfessor - Location: 42½ N, 83½ W - My Posts This: Topic  Forum
You should re-examine your numbers.

Your calculation which uses 125.7 meters per second tip speed for "equivalent" performance does not take into account the distance between the blade bolts.

A 600 size has about 6" between blade bolts.
Use 0.6 + 3" = 676mm or 0.676 for your "X"
That puts a 600 size with 2000 rpm at 141.58 Meters per second tip speed.

125.7 M/s (or 141.58 M/s) is on the low side anyway from an aerodynamic perspective. That's only 0.37 Mach (or 0.41 Mach). Full size helis have a tip speed of 0.60 to 0.65 Mach. Our models don't even come close to that.

For a 600 size to have similar tip speeds (0.6M), the head speed will be up at 2907 RPM
- - - Good luck on the blade bolts holding at that speed.


The following is an excerpt from one of my home pages,

Rotor tip speed is where it's at.

For "nimble" flight characteristics, you want a relatively high rotor tip speed. 0.5 Mach is a good hi-ish number. For 710 blades and a 6.5" rotor hub, the rotor disk diameter is 5.2 ft. The head speed comes out to 1116.4 * .5 * 60 / 3.1416 / 5.2 = 2050 RPM.

Now the centrifugal force for 710 SAB blades at 2050 RPM -- that's 850 lbs trying to pull the blades off the rotor hub. You just need to verify that everything will hold together at that speed. At 1800 RPM it's only 660 lbs.

Before you say that's too high, keep in mind that the typical full size is 20% higher yet on the tip speed.
- - The Robinson R22 has a tip speed of 0.60 Mach on it's 25ft-2in rotor disk running at 510 rpm.
- - The CH-47D Chinook has a tip speed of 0.63 Mach on it's 60 ft diameter rotor disks running at 225 rpm.
- - The H-60 Black/Pave/Sea Hawk has a tip speed of 0.65 Mach on it's 53ft-8in diameter rotor disk at 258 rpm.
- - The Bell 222A (AirWolf) has a tip speed of Mach 0.65 on it's 42ft diameter rotor disk at 348 rpm.
- - The V-22 Osprey has a tip speed of Mach 0.59 on it's 38ft diameter rotor disk at 333 rpm.
- - - or depending where you look
- - The V-22 Osprey has a tip speed of Mach 0.70 on it's 38ft diameter rotor disk at 397 rpm.
11-07-2009 06:48 PM
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Ots
Heliman
Location: Glendora, CA - USA

My Posts This: Topic  Forum		Now we're making sense!
11-07-2009 07:31 PM
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wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		Yea, just a bored function but if we can make a usable function outta this that would be awesome. How could we account for blade chord? after that we could make a very efficient blade sized heli. Does anyone know the math to get a functions closest place to the origin?
11-07-2009 08:06 PM
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AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

My Posts This: Topic  Forum		If all you want is a relative performance comparison, just compare tip speed squared times blade area divided by weight.
11-07-2009 08:10 PM
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wws2010
Senior Heliman
Location: La Cresenta, California - United States

My Posts This: Topic  Forum		yea, lets make it an equasion! How to find blade area too. Oh and lets make a unit for it. lol open to ideas!!!
11-07-2009 10:29 PM
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T-Rex-Flyer
Key Veteran
Location: Panama City, Fl

My Posts This: Topic  Forum		AirWolfRC... You're making my head spin, I LIKE IT!

If the wings are traveling faster than the fuselage, it's probably a helicopter.
11-08-2009 01:30 PM
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Main Discussion > Easy function to get equal performance headspeed from all helis.
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