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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › "Home Machined" Blade Extensions
02-24-2010 09:07 PM  10 years ago
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JuanRodriguez

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The Villages, Florida

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"Home Machined" Blade Extensions
A friend (whose name shall remain anonymous to protect the innocent ) came over to use my mill and whipped out a set of blade extenders (or extensions) as seen in the pic below. The blades on the ship are 800's...... not sure what they are now, I'll post the new "dimension" later.

Reason for doing it ? To enlarge his disc size (that's DISC ! )without the expense of buying longer blades...... and for the "tinkering factor" ..... They were made from 6061 grade aluminum to fit a Bergen gasser camera ship.

My bud is a professional mechanic and has some aviation in his background. I believe he holds a commercial/instrument/multi-engine rating and in the past has worked at Rotorway Aircraft/Vertical Lift Technologies and a lot of his work had to do with rotary blades.

The machine has been test hovered and it is as smooth as before the extensions were installed.

Looking for comments...... good, bad or indifferent !!

Been there, done that and old enough to know better.....
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02-24-2010 09:13 PM  10 years ago
nitrojunkie

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N.C

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I gotta ask.Is that not a good potential future lead or lag problem?The task was met but I don't know about the extra joint and possibility of it loosening up.I love the smell of nitro in the morning..
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02-24-2010 09:14 PM  10 years ago
Wingman77

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Pulaski Tennessee

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I don't see any issue as long as it is a good snug fit and your tail blade clearance is still good.
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02-24-2010 09:17 PM  10 years ago
VooDooX

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San Francisco Bay Area CA, US (San Mateo)

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i think as long as the overall disc diameter remains lower then the size allowed by the manufacturer and theres no risk of a boom strike no harm in itVelocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-24-2010 09:22 PM  10 years ago
JuanRodriguez

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The Villages, Florida

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I gotta ask.Is that not a good potential future lead or lag problem?
Good point.....don't know the answer to that. We need someone like Wolfgang to come up with some calculations on that !
Been there, done that and old enough to know better.....
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02-24-2010 09:44 PM  10 years ago
VooDooX

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I just realized there may be additional concerns. You can drill a second hole in the original grips, and the extenders, and then bolt another bolt in there. That will stop any lead/lag issues, although moving the hole outward may induce additional torsion stresses on the blades during high pitch maneuvers.

This due to the increased blade tip speeds. There's a higher chance of blade failure as the diameter increases so does the tip speed the blades may not be able to handle this additional stress Because as speed increases so does the G Load on the blades and also as this increases it may also strip out the Feathering shaft and sling a blade...

Good luck tho i would recommend at least reducing the blade speed the same percentage as the increase in diameter so if you increased the disk size 10% reduce RPM 10% should help a little at lease so if blade speed was 1800 reduce it to 1620
Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-24-2010 09:46 PM  10 years ago
eSmith

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Edmonton, Alberta, Canada

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I think that pretty cool, but wonder, as the others did, what lead lag issues might come out of the double jointed blade grips.

As I see it, without 2 mount points, it is not as much an extension as it doesn't just make it longer but adds a second pivot point as well. So what do you call that?

-eSmith.
http://www.edmheli.ca
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02-24-2010 09:55 PM  10 years ago
buzzsaw

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Southeast USA

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uh?Oh!
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02-24-2010 10:18 PM  10 years ago
Flying Tivo

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Monterrey,NL,Mexico

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Disc Area
I would have to say that you indeed increased the Disc Diameter, but not the Disc Area!! It would not lift more, the wing loading will remain the same. If you where having problems with the heli vibrating then its something else.

Felipe
If life throws at you lemons......Squirt some lemon juice in the eye of your enemy!!!!
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02-24-2010 10:20 PM  10 years ago
eSmith

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Edmonton, Alberta, Canada

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He didn't increase the disk area but he did move the lift area of the blade out further which WILL result in faster tip speeds which should make it so he can have more authority with less head speed. No???

-eSmith.
http://www.edmheli.ca
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02-24-2010 10:28 PM  10 years ago
VooDooX

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I would have to say that you indeed increased the Disc Diameter, but not the Disc Area!!
absolutely wrong.. lengthening it in this way DOES increase disk area the outside of the blade travels farther (the circumference is larger) thus more lift is produced..and the disk is also larger.. do the math if you don't believe me also the speed at the tip is higher producing more lift
Velocity 50 "99.9999999999999% of an atom is empty space." also 01001000 01001001
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02-24-2010 10:44 PM  10 years ago
Flying Tivo

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Monterrey,NL,Mexico

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Speed
Voodoox:
absolutely wrong.. lengthening it in this way DOES increase disk area the outside of the blade travels farther (the circumference is larger) thus more lift is produced..and the disk is also larger
I did not mention speed nor lift, the original post was about enlargeing the Disc or larger blade length without the longer blades.
Please explain in simple terms, how can the extra blade grip contribute to the disc area?????? This is a no lift area that includes from the main shaft to the blade bolt(aprox). In this case to the second blade holder bolt.

There is no need for math when logic prevails! But i may be wrong in the lifting area!

Felipe
If life throws at you lemons......Squirt some lemon juice in the eye of your enemy!!!!
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02-24-2010 10:57 PM  10 years ago
JasonJ

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North Idaho

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While it would seem like the true disc area used for lift hasn't changed, the blades being farther out might produce a more clean disc. The air would be really jumbled and "dirty" close it to the helicopter from the muffler and so on, so the extensions would seem to make better use of the available lift from those blades.

Guess the only way to know would be a max payload lift comparison between the setup with and without extensions.
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02-24-2010 11:06 PM  10 years ago
Flying Tivo

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Monterrey,NL,Mexico

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Faster tip speed
It also applies that at faster speeds more drag, so the math
will prevail on this concept! So you would have to look up the
most efficient speed for that specific blade.

Felipe
If life throws at you lemons......Squirt some lemon juice in the eye of your enemy!!!!
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02-24-2010 11:06 PM  10 years ago
AWittleWabbit

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O.C., CA

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You guys' argument has thinking why props have twist in them. Sound like your both kinda right, or wrong. I think posters new rotor will lift more at a given rpm. I dunno about the double lead lag hinge. There's also more bending moment at the spindle. Neat project, but be careful.Heli-itis sufferer.
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02-24-2010 11:07 PM  10 years ago
jphilli

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Atlanta, Ga.

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The disk area definitely increased.

Simple example to see this:
Disk area of a 1m blade = pi*(1m)^2 = 3.14 m^2
Disk area of a 1m blade spaced out .1 meters: pi*(1.1m)^2-pi*(.1m^2) = 3.76 m^2.

The actual proof is extremely straightforward and almost trivial so I won't bother typing it up.
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02-24-2010 11:20 PM  10 years ago
AWittleWabbit

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Jphilli, your right. Heli-itis sufferer.
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02-24-2010 11:52 PM  10 years ago
AirWolfRC

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The blade is still required to produce the same lift (the heli still weighs the same), so the only diference is the center of spanwise lift is further out by about 7% of the span by the looks of the photo.

There is little bending force on the blade roots. The lift is the result of the coneing angle. Consider that the blades are trying to leave the hub with a centrifugal force in the neighborhood of 600lbs. 600lbs force out and only 7-8 lbs (lift of one blade) up makes for a coneing angle of less than 1º.

I doubt there is any problem with lead/lag. Blade lag can also be calculated. The lag angle will show only at the position of the original blade bolt because from there to the main shaft is solid. Assume the blade bolt span is about 7.5", Motor HP in hover is 2 and rpm is 1600. That's 6.6 ft lbs torque on the main shaft and 10.6 lbs of "lead force" at the original blade bolt position. Again with 600 lbs centrifugal and 10.6 lbs of "lead force", you get about 1º of blade lag.

Any body care to check my numbers ?
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02-25-2010 12:01 AM  10 years ago
ttsingram

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Lincoln, Ne

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Just a thought. He moved the tip of the blade x amount. But didn't he move the inner point of the blade x amount also. The lift produced by the inch or two of the inner part of the blade moved out an inch or two. To me this did not increase total lift, it just moved it outward.

And as for the curved prop idea, look at the Osprey, its the same there. The inner part of the blade is moving slower so to have the twist it provides the same thrust at lower speed.
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02-25-2010 12:06 AM  10 years ago
Flying Tivo

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Monterrey,NL,Mexico

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I will eat my words
JPhilli:

You are correct, the disc area does increase.

Felipe
If life throws at you lemons......Squirt some lemon juice in the eye of your enemy!!!!
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