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Home✈️Aircraft🚁HelicopterBeginners Corner › Measuring head speed
03-22-2002 04:31 PM  19 years ago
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Captain Scarlet

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South Wales.

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Measuring head speed
Bit of a silly question,this.When measuring head speed,is it measured at rotor tips,or at root,or what?
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03-22-2002 04:34 PM  19 years ago
Doug

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Port Saint Luice Florida....

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Head speed it in RPM, Hopfully the tips and the roots are at the same RPM
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03-22-2002 04:36 PM  19 years ago
kovar

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West Chester, Ohio

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How do you measure it? Is there like a tach or something you hook up to it?
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03-22-2002 04:41 PM  19 years ago
Doug

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Port Saint Luice Florida....

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The best way is with the Min Air optical tach which spins a shutter, an assistant looks through and "freezes" the blades then just look at the RPM on the Tach. "Aircraft" tach's can be used as will either on the TR blades or main but not in flight. Ther are a couple that mount on the TB and can be seen in hover. Or you can fit a GV1 and not worry about it
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03-22-2002 04:44 PM  19 years ago
BladeRunner

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Ontario Canada. Member of "some sort" s

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Head Speed?
You can measure it with an airplane tach-but I wouldn't recommend it.
You have to get right under the spinning rotors. The better way would be to get a M.A. heli tach, you can measure the head speed(rotor) from across the field if you want to, even during flight well out of harm's way.

Be advised that it takes two people (well, a helper) to use this tach. The tach has a window that you look through (similar to a camera view finder) and a rocker switch that you use to adjust the tach until the rotor blades appear to be "stopped". Then you read the rpm on the LCD screen.
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03-22-2002 11:30 PM  19 years ago
gnichola

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Santa Rosa, CA. USA

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There is another optical tach that has a button on it. When you get the blades frozen in the display you push the button. The button holds the current number and then you can read it yourself.

Sorry, don't know the brand.

Later, Guy
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03-23-2002 02:26 AM  19 years ago
BladeRunner

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Head Speed?
Gezz Doug, you slid in there 3 min. ahead of me! Hehehe---good one.
It must have been that second paragraph I typed!
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03-23-2002 07:15 AM  19 years ago
Virtual1

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Waterloo, Iowa - USA

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Or the bicycle tach option. Install a magnet on the main gear (and a counterbalancing weight on the other side) and install a bicycle computer that can remember max speed. Set it to read in km/hr and then program the wheel circumference as 1667mm. (530mm diameter, 20.7 inch) The display will read in 10's of RPMs, so like 185.0 for a headspeed of 1850rpm. Cost is around $25, much cheaper than an optical, and you won't need a helper. Make sure you get one that can read high enough. (at least 200km/hr) Several brands can register up to 300km/hr.
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03-23-2002 03:12 PM  19 years ago
Sceadu1

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Rochester,Minnesota

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Measuring head speed
Virtual1

Do you have a link of a place to purchase the bicycle tach? Or a name
of a online store? Thanks , Jerry
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03-23-2002 05:13 PM  19 years ago
Hockeytown

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Highland, Mi. U.S.A.

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Heres the place...
The one most people try is from VDO....

http://www.bikeworld.com/vdo.htm

You can also Goto:

http://www.rcheliweb.co.uk/

then click on the link that says "DIY Headspeed Tach"

Hope this helps
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03-23-2002 07:45 PM  19 years ago
Virtual1

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Waterloo, Iowa - USA

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You should be able to find a good selection of bike computers at your local sports / bicycle shop, just look through their documentation until you find one that works. It needs to support wheel diameters down to 20 inch and speeds up to 200km/hr. I have a Sigma Sport "Targa" and it goes to 300. (all the Sigma Sports go to 300)
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03-23-2002 10:18 PM  19 years ago
Heli-Driver

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Arlington, TX

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The VDO works great.
I have the VDO Cytec 08 and it works great and is quite affordable. I have it inside my scale H500E with Raptor 60 mechs.

If you have a Raptor 60, the VDO is a perfect for that heli. The magnet replaces the nut on the lower Jesus bolt under the main gears. Mount the sensor on the side, clip the computer on the boom, program the wheel size (1667mm) and you're done.

It comes with a spiffy mounting bracket that mounts to the boom and is held in place with a half looped O-Ring. It looks very clean on the heli, much cleaner than the larger factory heli tachs that are optical tachs.


Raymond

Predator Gasser SE/231 X 2
Century Helicopters
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03-23-2002 10:20 PM  19 years ago
Captain Scarlet

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South Wales.

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Ok guys,thanks for the input.Think a GV-1 is the way to go.
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03-24-2002 01:33 AM  19 years ago
Sceadu1

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Rochester,Minnesota

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Measuring head speed
RaptorDriver

Would I use these same settings on my Sceadu 30? Would the set up be the same? I ordered one and should get it next week.
Thanks , Jerry
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03-25-2002 01:33 PM  19 years ago
mash

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Stratford-on-Avon, UK

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Here's how I do it for hovering RPM, cheap and cheerful...
I use a bog standard optical tacho meant for plank props (Thunder Tiger brand but there are many similar). I then make a divot in the grass with my heel and place the tacho vertically within the rotor arc while the heli is idling. I then spin up the heli to just before hover and take a glance at the tacho.
This tells me that my Sceadu 50 is overspeeding at 2k RPM and that I need to invest in some 600mm blades but that story is well told elsewhere on this forum!
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03-25-2002 05:58 PM  19 years ago
NEM3

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New Lenox, Il

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Now see I have tried using an airplane prop tach. And it kept telling me that I was flying at 1100rpm. The way that I did it was to wire tie the tach to the boom. I does add a bit of weight but you can trim that out if need be. But the bike speedo is a much easy and lighter set-up.

I did try to do the bike speedo deal but the one that I bought does not go up to 200km/h nor does it have a setting for the right size. And I though I was buying a good one. Pffff.
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03-25-2002 06:09 PM  19 years ago
ed vega

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nyc, queens

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my approach is - by the way it responds at the required stick positions , or the pitched sound of blades at lower / higher speeds ..

I stop using pitch indicators a long time ago .. it's that easy .. but my system is not for the entry level flyer - stay with the pitch gauge and get a MA rotor speed indicator initially - it's good equip, you'll progress from there
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03-25-2002 09:55 PM  19 years ago
Virtual1

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Waterloo, Iowa - USA

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Nem3: I spent about 20 minutes at the bike shop, digging through the bike computer boxes, reading their documentation until I found the ones that would work, and then I bought the cheapest. ($25) Price didn't seem to have much of an impact on max ranges, it only seemed to give you more featuers you won't need for this use. (like settings for multiple bicycles, extra menus, etc)
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03-25-2002 10:14 PM  19 years ago
Captain Scarlet

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South Wales.

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Yes.I have a cheapy Thunder Tiger tacho,and the guy at the local heli shop(who used to fly for a model company) told me that this was the one he used.He said,tie it to a tent peg,and go hover over it.
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03-26-2002 02:34 AM  19 years ago
Safe_Cracker

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Chicago, IL

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I have one too.
For all the ones getting false readings off there handhelds here's a couple of tips.1.)Make sure if your mounting it to the boom that it's either before or after the paddles.It cannot recognize the flybar it'self but will think you have a 4 rotor system if you are under the paddles and cause an error reading.2.)Must make sure there is enough light over head of the rotor and the optical eye.3.)Make sure it isn't flourescent light either or it will read the power cycles of the light pulses and YES flourescents aren't a constant light source they are made up of pulses.I use mine duct taped to the boom after the the flybar in heavy sunlight or taped to a paint stir stuck in the ground with the same light.Oh one other thing,I use a 6' ladder as my run-up stand!!Don't laugh!!!!Weighted of course with bungie cords holding the chopper.
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