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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › "Home Machined" Blade Extensions
02-25-2010 12:08 AM  10 years ago
classic

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Juan,
I have seen a metal blade grip give out at the main bolt because of increased force from using longer blades then it was designed for. {840mm on a miniture aircraft metal blade grip}

I would reccomend drilling another bolt hole for the extension/grip but I have to admit, those look like some beefy blade grips...
Which is worse, ignorance or apathy? I don't know and I don't care!
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02-25-2010 12:31 AM  10 years ago
AirWolfRC

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If you can tow a car with the original blade grip, then it's probably OK
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02-25-2010 02:10 AM  10 years ago
JuanRodriguez

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The Villages, Florida

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Thanx for all of your comments, guys.........
Please keep them coming.

CJames...... I'll make sure that Mark reads your comments... Safety is paramount..... that's part of the reason why I started the thread (with by bud's OK), to see other's comments, including the safety aspect of the modification.... The blade grips ARE very beefy....

Mark goal is to achieve more lift at a reduced head speed while using the same blades.....

Perhaps I should have included that statement in my original post....
Been there, done that and old enough to know better.....
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02-25-2010 02:14 AM  10 years ago
classic

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Juan,
I don't know if this helps with Mark's math or not, but we were at 1400 H.S when the grip failed, and it was a longer, and heavier blade to boot then what he is currently using. Personally, the more I think about it, I bet the way he has it now will probably work just fine.

One thing I would recommend is after the first flight, check the bolt to see if it has bent.
Which is worse, ignorance or apathy? I don't know and I don't care!
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02-25-2010 02:57 AM  10 years ago
helicopter nut

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pleasanton, ca usa

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I agree that it should work fine. The centrifugal acceleration is not greatly enhanced if the blade speed is held constant at the tip as has been suggested. The blade dynamics, short of possible aero-elastic effects, should be fine. Cyclic might be a bit less brisk owing to the very slightly increased gyro effect of the blades. Keep the joints clean and wobble free and go flying.Lord hear our silent prayers to Thee
For those who fly from ships at sea.
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02-25-2010 03:10 AM  10 years ago
Avropilot

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Murfreesboro, Tennessee

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Good Gawd! Just go fly the dam thing.Waiting for parts
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02-25-2010 03:34 AM  10 years ago
Ace Dude

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USA

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I would have to say that you indeed increased the Disc Diameter, but not the Disc Area!!
The math doesn't lie. The formula to calculate the area of a circle is:

A = Pi * r^2 or simply Pir^2

r is the radius of the circle which is 1/2 the diameter.

If you increase the diameter the area has to increase as well.
  
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02-25-2010 03:55 AM  10 years ago
rchelichop

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seeya

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//..
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02-25-2010 04:07 AM  10 years ago
VooDooX

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Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-25-2010 12:56 PM  10 years ago
GyroFreak

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Orlando Florida ...28N 81W

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Interresting modification. I may try that and try to define what diff it makes with my data logger.
as so well put by jphilli
Disk area of a 1m blade:
pi*(1m)^2 = 3.14 m^2
Area of a 1m blade spaced out .1 meters:
pi*(1.1m)^2 - pi*(.1m^2) = 3.76m^2
Paul
I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?
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02-25-2010 02:23 PM  10 years ago
red_z06

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Dumont, NJ

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I'm sure most are familiar with the disc area formula Area = pi x radius squared.

Some of the common mistake made for a disc with a hole is in the process of subtracting the inner radius before vs after squaring.

Common mistake:

R2 = outer radius
R1 = inner radius

Area = pi x ( r2 - r1 )^2
Above seems logical but no matter how much you pull the blades out, you end up with the same area.

Correct subtraction:

Area = pi x (r2^2 - r1^2)
www.JustinJee.com
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02-25-2010 02:26 PM  10 years ago
AirWolfRC

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Of course the disk area will increase if you increase the radius. The center of lift is out at about 75% of the radius. <edit>
I have seen a metal blade grip give out at the main bolt because of increased force from using longer blades then it was designed for. {840mm on a miniture aircraft metal blade grip}
If That's the case then it was running way too close to design margins to be safe in the first place.

If you want to calculate the forces, refer to one of my pervious posts for centrifugal force, https://rc.runryder.com/p2243030/
Full size use an absolute design margin of 50% for loads.
. . . . if a wing is rated for 6G's, it won't break until it sees 9G's
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02-25-2010 02:39 PM  10 years ago
red_z06

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Dumont, NJ

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The blade swept area is the same however.
Umm. See the post directly above yours regarding common disc with a hole calculation mistake.

Diameter/Radius is a linear function, while area is an exponential function.

Here is a simple way to think.

If a disc has an area of 1(unit does not matter).
Doubling the diameter will make the area equal 4.
Now, subtract the origial area and you end up with 3.
This is identical to disc area when the grip holes are connected together directly (no hole) and then you increase the grip hole distance the same amount as the blade diameter.
www.JustinJee.com
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02-25-2010 03:10 PM  10 years ago
AirWolfRC

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Yep, you're right, blade swept area is NOT the same. My bad.
. . . inadvertant release of CH4 from cranial housing . . .
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02-25-2010 03:42 PM  10 years ago
VooDooX

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Above seems logical but no matter how much you pull the blades out, you end up with the same area.
Wrong... Completely WRONG

wow Ok ok ...people just THINK OF IT THIS WAY its much more simple and maybe you can wrap your brains around it... take your hand... and then hold it close to your body and spin in a circle... see how much area if covered? not much right now take that same hand and hold it WAYYYY out from your body and spin in a circle... all you did was move the hand out but the hand still moved a lot further when it went out.. any distance out you go the amount of area covered by the hand increases SHEESH People seriously this is not a hard concept to grasp.... some people just like to argue without knowing wtf there talking about... end rant i may have misunderstood your post but if your saying disc area is less or the same then you are wrong..
Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-25-2010 03:53 PM  10 years ago
red_z06

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Dumont, NJ

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The other common mistake that pops up every now and then is "If I increase the blade length 5%, does the disc area increase 5%?"

See my previous explanation.
www.JustinJee.com
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02-25-2010 04:03 PM  10 years ago
VooDooX

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Does the outside Circumference increase... YES
Does the inside Circumference increase... YES
does the width change... NO
so in turn OBVIOUSLY the F*#&ING Area increases... please stop spewing your so called "knowledge" around you think your so smart that is the problem please go look it up more..

basicly your saying theres the same amount of pavement in a 1 mile circular track and a 1.1 mile circular track as long as the road is the same width..obviously that right there should tell you your WRONG i wish i could do such magic i would be rich

im not saying it increases the amount you move it out i AM saying it does increase i will not argue any further on such a stupid argument you might as well say mars and earth (almost the same size) travel the same distance around the sun
Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-25-2010 04:19 PM  10 years ago
broggyr

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Naugy, CT

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Good Gawd! Just go fly the dam thing.
+1
- Brian
irony [ay-ruh-nee', ay-er-nee'] adj.: Like goldy or bronzy, but made of iron
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02-25-2010 04:22 PM  10 years ago
VooDooX

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so the yellow circle has the same area as the grey circle on the outside .. surreeeee
Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-25-2010 04:34 PM  10 years ago
broggyr

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so the yellow circle has the same area as the grey circle on the outside
Sure it does! But the mass in the gray outer circle is less dense, and it was cheaply made with a cheap color, not like the quality yellow circle pigment. So, if we factor in the quality variable, plus the average velocity of a coconut-laden swallow, we should find that a pound of rocks and a pound of feathers still weigh the same, indicating that I have new socks on...

Wait, what?

- Brian
irony [ay-ruh-nee', ay-er-nee'] adj.: Like goldy or bronzy, but made of iron
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