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HomeAircraftHelicopterHelicopter Main Discussion › >>> Heli Speed Limit <<<
06-11-2013 05:42 AM  5 years agoPost 1
HeliOCD

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San Diego, CA

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Watch at YouTube

Its all earth!

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06-11-2013 05:53 AM  5 years agoPost 2
RogerRabbit62

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Nice video !

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06-11-2013 03:48 PM  5 years agoPost 3
VinceY

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Newnan GA

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I enjoy all his videos. My kids watch them too. Very educational!

Team Synergy/ Rail Blades

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06-12-2013 02:33 AM  5 years agoPost 4
Volcano

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chicago

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So what headspeed can a 700 run until rotortips goes faster than sound?

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06-12-2013 03:06 AM  5 years agoPost 5
Retired2011

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Lee's Summit, MO

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I don't even want to think about the formula for figuring the headspeed needed.

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06-12-2013 04:09 AM  5 years agoPost 6
RM3

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Killeen, Texas - USA

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So what headspeed can a 700 run until rotortips goes faster than sound?
well lets see I hope I did this right?...

4157 is the HS

.781 is meters distance from center to end of rotor tip (Trex700)

((2pi*4157)/60)*.781 = 339.98 m/s angular speed (which is a tiny tiny bit under the speed of sound at sea level of 340.29 m/s)

so if you can find a 700 that can manage to hold the blades onto the grips at just under 4,157 RPMs...just make sure your in a ballistic suit during testing

showing a preference will only get you into trouble, 90% of everything is crap...

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06-12-2013 04:27 AM  5 years agoPost 7
RaymondJ

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edmonton ab canada

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Edit- I need to double check what I was trying to figure out, I'm not converting a couple things properly. I'll just stick with head speed

Or 67560FPM X 3.82 (constant) /61.5 = 4196.41 Blade Rpm I got that one close to RM3's answer so maybe I'm on the right track lol

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06-12-2013 04:49 AM  5 years agoPost 8
RM3

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Killeen, Texas - USA

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8.96MPH forward speed needed to hit the sound barrier?
...holy crap!

that means Ive been doing MACH 6.14 everyday to and from class in my car!

The SR-71 ain't got nothin on me

showing a preference will only get you into trouble, 90% of everything is crap...

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06-12-2013 04:54 AM  5 years agoPost 9
Santiago P

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South West, Ohio

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So what headspeed can a 700 run until rotortips goes faster than sound?
they just cannot get there with conventional 3D blades.

even before a model's blade speed reach M 0.7 the drag become enourmous, and so does the power require.

They would need much, much thinner blades to even consider it possible.

To calculate the speed just take the rotor span (ft) times pi, times the RPM divided by 60, that gives you tip speed in ft/sec.

Speed of sound @ sea level is about 1120ft/sec.

I come up 4314 RPM for a 700 's tips to reach M= 1.0 (bout the same as Raymond) at zero forward speed.

Count on the bearings/grips to peel off the spindle a few rpms before it can get there.

S

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06-12-2013 04:56 AM  5 years agoPost 10
RaymondJ

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edmonton ab canada

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That sr-71 is 47 years old, couldnt stay ahead of the game forever haha

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06-12-2013 05:04 AM  5 years agoPost 11
Santiago P

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South West, Ohio

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BTW,
From observing the fastest guys of the speed runs last years, it appeared to get nasty at about 150mph and 2300 RPMs.

I think the limit (for a model) is still closer to 170 or even 200mph, but lots of variables like the total helicopter drag, CG and RPM play a part into it.

There will be much faster machines competing at the IRCHA speed cup this year including purposed made speed TDRs, couple of Banshee s, SRF and who knos what.

S

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06-12-2013 07:58 AM  5 years agoPost 12
Taipan

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Sydney, Australia

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I find it pretty crazy that the full-size record is only 249mph/400kmh by a Westland Lynx. Our models aren't that much slower!

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06-12-2013 03:35 PM  5 years agoPost 13
lejon

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Las Vegas, Nevada

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Full size becomes more impressive when you consider the rotor diameter is 42' for the Lynx. Something on the order of 19' blades.

Lejon

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06-12-2013 07:13 PM  5 years agoPost 14
Santiago P

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South West, Ohio

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+1

Full size rotor tips operate below Mach 0.7 to avoid shock waves and compresibility effects, and even use swept tips with M critical airfoils to retard/avoid formation of shock waves. Transonic speeds is not a good home for rotors.

As luck happens our RC models blades are far away from getting anywhere near those speeds.
And that is a good thing

S

Team Minicopter - PeakAircraft.com
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06-13-2013 09:37 AM  5 years agoPost 15
KC

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WA

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Cool video, we're getting closer to 200mph.

The busy area of the blade is about 80% out to the tip and is accurate if you limit advancing blade calculations to Mach 0.75

700mm size 2300rpm:

0.8^0.5 x (1600mm / 25.4mm / 12" x 3.14159 x 2300rpm x 60 min / 5280' ) = 380mph

Mach 0.75 = 0.75 x 760mph = 570mph

570mph - 380mph = 190mph

800mm size 2000rpm:

0.8^0.5 x (1800mm / 25.4mm / 12" x 3.14159 x 2000rpm x 60 min / 5280' ) = 375mph

570mph - 375mph = 195mph

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