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tip weight to the blades?

Old 12-23-2006, 11:00 PM
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Default tip weight to the blades?

OK. I'm make my owe blades/ Should I add tip weight to the blades? And if so how much?I'm think my blades will be 34 or 35 with a 2 1/2 Cord, Clark Y.
Old 12-26-2006, 12:43 PM
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Default RE: tip weight to the blades?

Hello Toyman....
Here's a couple of cents worth of thoughts:
The blades should be attached at about 25-30% of the chord. The blades should have their chordwise center of gravity at or forward of the attachment point. So it may be appropriate to add weight at the leading edge of the blades to achieve this relationship. There is a company in Oregon (I think) that sells lead wire of various diameters that can be buried in the LE very easily. Steve Tilson of Arizona Autogyros uses steel wire for this purpose.

As far as tip weight is concerned, if you decide to go that route, make sure the weights move the CG to the correct relation with the mounting bolt location. One feature of tip weights is that they can be used to make the total weight of each blade equal and, put the the spanwise CG of the blades at exactly the same spanwise location in each blade.

I suspect that you'll hear from some of the other guys with their suggestions.

BillF
Old 12-26-2006, 04:47 PM
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Default RE: tip weight to the blades?

So If I got it right.At attachment point should bal front to back?
Old 12-26-2006, 05:49 PM
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Default RE: tip weight to the blades?

No. Attachment point should be 25% of the blade chord.
Add tip weight in the leading edge until the whole blade balances at the 25%
chord point.
Details here:
http://www.rcgroups.com/forums/showp...8&postcount=18
Old 12-26-2006, 05:59 PM
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Default RE: tip weight to the blades?

OK. I just got to ask. In the pics of blabes. What one should it be. y1 y2 y2?Whan done.
Old 12-26-2006, 07:21 PM
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Default RE: tip weight to the blades?

y3
Old 12-26-2006, 10:20 PM
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Default RE: tip weight to the blades?

Hey Micky...
The "Following Rate" is a new term to me. Does it apply to flybar rotors or does it also apply to rotors that have flexing blades as do all of my gyros. And, just what is Following Rate??

Bill
Old 12-27-2006, 09:56 AM
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Default RE: tip weight to the blades?


ORIGINAL: billf

Hey Micky...
The "Following Rate" is a new term to me. Does it apply to flybar rotors or does it also apply to rotors that have flexing blades as do all of my gyros. And, just what is Following Rate??

Bill
Following rate applies to all rotors. It is a measurement of a rotors behavior.
Stan Hiller (of Hiller helicopters) used it to characterize rotor control behavior.
What you do is tilt the rotor 15 degrees left, then put in full right and measure
how long it takes to go 15 degrees to the right. Hiller found out that
a rotor had to do this between 1/4 and 2 seconds or it is unflyable by
a human being. Faster that 1/4 second and it's too fast for a human to
keep up, longer than 2 seconds and the pilot is always chasing the
aircraft.
Following rate increases with RPM, decreases with rotor
mass and increases with blade area, the reason model rotors have a very high following rate.
Flybars are used on model helicopters specifically to reduce the following rate to a human
flyable amount. A flybar is essentially a very small area rotor with a relatively large mass and
small diameter. This makes the following rate slower. When you slave the main rotor to the
flybar the main rotor adopts the (slower) following rate of the flybar. This is how a flybar
is used to make a model helicopter or gyrocopter rotor controllable by a human.

Additional comments here:
http://www.rcgroups.com/forums/showp...6&postcount=16

mickey
Old 12-27-2006, 11:46 AM
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Default RE: tip weight to the blades?

I also make most of my blades. They are foam filled fiberglass or carbon fiber. A 16" blade, 2" wide weighs about 27 grams and a 25.5" blade 2.5" wide weighs 115 grams. I have tried with and without extra tip weights. I used to balance them cordwise but found it doesn't make any difference, at least for me. If you use three blades find the heaviest one and mark the CG length wise. Mark the other two blades in the same location and add weight to either the hub or tip end until they all weigh the same and have the same CG. Mine are usually close enough that I just add a little 5 minute epoxy to the ends of the blades for balance. Works for me.

If you have a real light weight blade it will spin up faster and it will have a greater coning angle. If I'm flying in real windy gusty condition, I'll use a heavy blade. It adds stability and on a calm day I'll use a light weight blade.

Phil
Old 12-27-2006, 12:52 PM
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Default RE: tip weight to the blades?

Phil,
Your hollow blades are probably not that tail heavy to begin with so this is a good thing.
Also the carbon blades are very stiff torsionally (in twisting) and this prevents many
of the problems with tail heavy blades.
mickey
Old 12-27-2006, 03:21 PM
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Default RE: tip weight to the blades?

Thanks Mickey...
Your explanation is quite clear. However, another question now arises: How does one decide upon the amount of tip weight (especially for a flapped blade rotor like I use) to achieve the right following rate?

Bill
Old 12-27-2006, 03:53 PM
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Default RE: tip weight to the blades?

Phil.

Care to make me some? My frist time. And I need them big. 35 by2 1/2.
Old 12-27-2006, 05:51 PM
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Default RE: tip weight to the blades?


ORIGINAL: billf

Thanks Mickey...
Your explanation is quite clear. However, another question now arises: How does one decide upon the amount of tip weight (especially for a flapped blade rotor like I use) to achieve the right following rate?

Bill
I'll find you the formula, But you can probably get there by experimentation pretty
quickly.
I'll hunt down the equation, might take a day.
Old 12-27-2006, 06:49 PM
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Default RE: tip weight to the blades?

Hi,
I have only made two different size molds and I think they do perform better than the wood blades, but I can buy them cheaper than I can make them. Unfortunately for me it's cost prohibitive to produce these blades as the material is just too expensive. Someone in the molding business that buys the material in bulk could probably produce them for a fair price.

What is the weight of the gyro that requires a 35" blade? My largest gyro weighted about 14 lbs and I flew that with 30" blades.

Phil
Old 12-27-2006, 06:52 PM
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Default RE: tip weight to the blades?

16 lbs
Old 12-27-2006, 07:09 PM
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Default RE: tip weight to the blades?

thtoyman,
Send us a picture of your 16# Monster Autogyro..Although I have had a 12# Autogyro I like the 3 & 4 # Autogyro's the best.

Jim
Old 12-27-2006, 07:27 PM
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Default RE: tip weight to the blades?

Hi,

Aerobalsa has great blades and the price is right. Let's see those pictures of the 16 pounder.

Phil


http://www.aerobalsa.com/pages/order.htm
Old 12-27-2006, 11:04 PM
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Default RE: tip weight to the blades?

Hi all. I will do 2 posting. I will add some pics. Any way. here the frist one. Yes a does have a 74in blades. If you like check the web site on it.Oh ya is a 1937 kellet.
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Old 12-27-2006, 11:18 PM
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Default RE: tip weight to the blades?

here the other one. I like to make it a autogyro. I'm just getting of it. Yes is a big club. Its got 5 -1/4 scale servos and one 148. Run on a big gas and old mix..also Its got 5 D size cells in it. I'm thinking its 15 or 16 lbs
So I'm looking for info how to.But also Kellrt needs new blades to.

Ps Jim I still want the AD DC . let me know how and when.
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Old 12-28-2006, 08:25 AM
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Default RE: tip weight to the blades?

thtoyman,

That Kellet should only weight about 12# at most. I have built 2 and I don't think they should weight 16#. They came with 36" blades but could fly on 25" Aerobalsa blades, which are far superior to the blades that came with the kit.

Jim
Old 12-28-2006, 08:33 AM
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Default RE: tip weight to the blades?

Jim. Its not the kellet. That one ataround 11lbs I think. Its the other one I like to make a autogyro out of.Also I'm looking in to getting new blades for kellet from Aerobalsa.
Old 12-28-2006, 11:21 AM
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Default RE: tip weight to the blades?

Hi,

Here is a video of my 1/3 scale cub, about 14 lbs with four 30" blades. My blades were only about 25" long so I cut off the ends of some other blades and glued them on the ends to get the 30" blades. The video was taken before I finished painting it.

http://web.tampabay.rr.com/pploof/cub.html
Old 12-28-2006, 11:29 AM
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Default RE: tip weight to the blades?


ORIGINAL: billf

Thanks Mickey...
Your explanation is quite clear. However, another question now arises: How does one decide upon the amount of tip weight (especially for a flapped blade rotor like I use) to achieve the right following rate?

Bill
Here's the math.
http://www.rcgroups.com/forums/showp...6&postcount=37
I think you would want to add tip weight to get to something you want. I think you can
ignore the fact that tip weight makes the blade not a uniform density and just use
the overall blade weight including the tip weight.
mick
Old 12-28-2006, 11:30 AM
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Default RE: tip weight to the blades?

Hi,

Just a couple of other things. You must add extenders to your rudder as the fuselage is wide and blocks the air from the prop. If you try and fly it with out the extenders it will almost certainly crash. I used the conventional elevator and till on the rotor head. The hub was solid with no flexing, however, with this size and weight the blades do flex.

Phil

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