Rotor Weights

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Mohanakannan

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Feb 6, 2013
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Chennai, Tamilnadu, India
Hi all

I've built a set of wooden rotor blades with NACA0012 airfoil and I added noseweights. Since the density of wood is constant through out the blade it balances at about 40% of the chord. In order to make the blade balance chordwise at about 25% we attach nose weights. I tried having these noseweights at the spanwise location given in the plans of Hobby Choppy helicopter, it worked perfectly fine and was able to lift the craft (The craft was teathered to ground by the way). When I changed the nose weight location by bringing it towards the inboard (The static chord wise balancing will still be achieved where ever the nose weight stays along the span) the blades doesn't seem to cross certain RPM, I know it is because the blade nolonger balances at 25% of the chord (dynamic balancing) and of the large moment arm twisting the blade increasing its pitch creating more drag. It aslo leads to blade slapping at about 70% of the design RPM. I would like to know how the nose weight location (Span wise) has been calculated for this application so that I can make modifications to it. Can any one please help me out by providing any proven calculations for nose weights if you have. I have attached a picture of a set of bensen blades with nose weights.

Regards
Mohan

images.jpg
 

don january

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Average aspect ratio (span/cord) is about 18 to 1. Exterior weight approx. 85% span from root, Trim tab approx. 85% span from root
 

TFF

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Don't have a scientific explanation, but weights need to be out not in. Blades need the centrifugal weight to stiffen the blades. Moving weight in probably makes everything outward of it not stay as straight as it should, or sets up some kind of spot where outboard is not in frequency of some sort and is trying to dampen. .
 

henryk

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Don't have a scientific explanation, but weights need to be out not in. Blades need the centrifugal weight to stiffen the blades. Moving weight in probably makes everything outward of it not stay as straight as it should, or sets up some kind of spot where outboard is not in frequency of some sort and is trying to dampen. .
-I dont know....

file:///C:/Users/xxx/Downloads/PreprintDesigningtheOrnicopterATaillessHelicopterwithActiveFlappingBlades_revised.pdf

https://www.researchgate.net/publication/288056751_Designing_the_Ornicopter_a_tailless_helicopter_with_active_flapping_blades_A_case_study

https://www.youtube.com/watch?v=XXDjqgnewQo

http://ovirc.free.fr/Alain_Hairie.php
 
Last edited:

Swampyankee

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If you're making a helicopter, vs an autogyro, one issue you may want to consider is that the greater the rotor's mass moment of inertia, the longer the pilot has to reduce the collective pitch when transitioning to autorotation.
 

henryk

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If you're making a helicopter, vs an autogyro, one issue you may want to consider is that the greater the rotor's mass moment of inertia, the longer the pilot has to reduce the collective pitch when transitioning to autorotation.
-auer goal is to build autogyro-like device,much moore energyefficiant(permanent rotor
prerotation) with possibility of VTOL,simple,gearless construction...

=on the 1.5 m modell we have got >10 kG/kW thrust force!
 

stuart fields

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Inyokern California
If you're making a helicopter, vs an autogyro, one issue you may want to consider is that the greater the rotor's mass moment of inertia, the longer the pilot has to reduce the collective pitch when transitioning to autorotation.
And the longer it takes to recover from a low rotor rpm. The more you lean toward needing hydraulic boosted controls.
 

stuart fields

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The early Benson gyrocopters had wooden blades with a weight mounted on the leading edge. You might try to find someone with a set and try the same dimension.
 

dino

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I believe the wooden Benson blades had their mass balance bullet located at 70% span.
 

BBerson

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I would use a long steel round bar from say 60% to 80% or more of blade. Most helicopters are 100% of blade.
 

henryk

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BTW= who know this formula, for rotors efficiancy comparation

(коэффициент летучести, качество Ренара или число Эверинга)

(fly coefficiant,Renard finesse,Evering number)=

K=q√p

q=F/N

F=thrust force ,N=power

p=F/s

s=rotor surface
 

pictsidhe

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They are likely fluttering. Having them evenly balanced at 25% all the way along likely makes it hardest for them to flutter. Having the balance inboard will tend to encourage it. The suggestions of 70% and 85% should be listened to.
 

rotax618

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Oct 31, 2005
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Location
Evans Head Australia
Benson blades had a tapered 1/8” mild steel(Boiler Plate) spar the full length of the blade, it was attached to the ply spar using countersunk screws. The noseweight was attached at 70% span and was weighted to give the blade a 25% chordwise balance or the blade would flutter. I still have a plan somewhere amongst my stuff, I re-designed the Benson Gyro in the 1960’s to suit the local materials (here in Australia) for submission to the then DCA (equiv. FAA).
 
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