Jan 11, 2006, 10:42 PM EDF rules... :) Joined Nov 1999 13,725 Posts Hi guys, Just to throw fuel on the fire on the use of the Wattage rotor, what rpm do you think your turning and if you dont have a tack reading that is reliable it wont do us much good to haggle over any of this. I ran the numbers on the rotor blades and here is what I find assuming that the blades are fiber filled PE or worst case scenario. The shroud is the alfa so the blades are shortened to fit. The area at the root of the blade is 0.00465in2. The volume of one blade is 0.011in3. The weight of the blade is 0.214gr. The centroid(cg) of the blade is 0.91" from center of rotation. The shear strength of Polyethylene with 10% glass fill is 5800 psi. The ultimate tensile strength of polyethylene wiith 10% glass fill is 14.5 ksi(14500 psi) The rotational speed in the calculation is 60,000 rpm. The rotational g force at the centroid is 141500 g. The rotational weight at centroid is 67.6 psi. The area at root multiplied into the ultimate strength of the material = 67.4 psi. This maps out the ultimate rotational speed of the rotor assuming that the material is polyethylene reinforced with 10% glass fibre. This is just a little math and physics applied to the rotor. As for me, I dont think we are reaching this kind of rpm with this rotor probably more in the 40,000-50,000 rpm which should be good for 21oz thrust. Cheers, Eric B.
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 Jan 11, 2006, 11:39 PM Pro Horder upland CA Joined Dec 2004 7,983 Posts he is back working again! Well if I can improve my machining skills I will have the walkura ready.I keep drilling the shaft hole off centre.Picked up a new lathe so should be better! Scott
 Jan 12, 2006, 01:57 AM Watts your motivation San Bernardino, CA Joined Aug 2003 6,512 Posts Yep, back to work. At least I have 3-4 day weekends with these never ending shifts. I have cleared my bench and am focusing on the cutdown rotors before I start or finish any other project. (Unfortunately honey-do list is not an "optional project") Weather is starting to look great again. Justin
 Jan 12, 2006, 02:56 PM SoCal, Year Round Flying! Newport Beach, CA Joined May 2002 5,745 Posts You guys going to the big AMA show out in Ontario somewhere? I believe it runs friday thru sunday. Bruce
Jan 12, 2006, 03:06 PM
SoCal, Year Round Flying!
Newport Beach, CA
Joined May 2002
5,745 Posts
Quote:
 Originally Posted by AirX Hi guys, Just to throw fuel on the fire on the use of the Wattage rotor, what rpm do you think your turning and if you dont have a tack reading that is reliable it wont do us much good to haggle over any of this... I ran the numbers on the rotor blades and here is what I find assuming that the blades are fiber filled PE or worst case scenario... This maps out the ultimate rotational speed of the rotor assuming that the material is polyethylene reinforced with 10% glass fibre. This is just a little math and physics applied to the rotor. As for me, I dont think we are reaching this kind of rpm with this rotor probably more in the 40,000-50,000 rpm which should be good for 21oz thrust. Cheers, Eric B.
Thanks Eric!
No rpm #s on the wattage rotor yet....
Is there a mathmatical way to compare the load of the alfa rotor to the load of the cutdown 6blade wattage rotor and state it as a percentage?
ie: The wattage is 20% more load than the alfa...
Regards,
Bruce
 Jan 12, 2006, 03:09 PM Registered User Long Beach Joined Jan 2004 1,432 Posts I'll try to go...I've going for the past 14 years kinda getting burnt out..it used to be in Pasadena....Its near the Ontario Airport...Between the 60 and the 10 fwy @the convention center. Henry V
Jan 12, 2006, 04:01 PM
Registered User
Post Falls, ID United States
Joined Feb 2004
4,460 Posts
Quote:
 Originally Posted by AirX Hi guys, Just to throw fuel on the fire on the use of the Wattage rotor, what rpm do you think your turning and if you dont have a tack reading that is reliable it wont do us much good to haggle over any of this. I ran the numbers on the rotor blades and here is what I find assuming that the blades are fiber filled PE or worst case scenario. This is just a little math and physics applied to the rotor. As for me, I dont think we are reaching this kind of rpm with this rotor probably more in the 40,000-50,000 rpm which should be good for 21oz thrust. Cheers, Eric B.
I like all of the the data you presented. How are you getting this info together? Are you using a software or are you actually taking measurements and doing the math?
I would like to see this applied to a Vasa rotor and see what we get since its all composite materials and not plastics.
I'm turning the Vasa rotor in the 40K+ rpm range and I need to get a static thrust figure but I bet its in the 21-24oz range. I'd like to predict it then test it. I would also like to add this rotor to a comparison table like Bruce mentioned.
Using the calculations, including the plactic, can you predict the breaking point of the GWS rotor? As I mentioned before I tried one on the Alfa fan and it did pretty well considering what it is, its advantage is its light weight. I was surprised it held up to the Mini AC motor on 3S.

Can you share how you are working this out?

Chris
 Jan 12, 2006, 07:10 PM EDF rules... :) Joined Nov 1999 13,725 Posts CofG, I gathered the data and did the math, the calculations are in a high school physics book. I would do the vasa but dont have one available to work with. The GWS will take more than the wattage or at least the 55 will. I dont have a 64 to measure the blades. Give me a little time in the next day or so I will publish the math for this so you can work it. On the Vasa I need the blade geometry to figure the "volumetric output" and the thrust. On thrust I posted a writeup on that already. http://www.rcgroups.com/forums/showp...&postcount=227 Bruce, The Alfa rotor is a lot stronger than the Wattage, we cant turn the Alfa high enough on a 20mm motor to do it harm according to the numbers I ran on the Alfa. The wattage does have an upper limit. If it is only made of polyethylene then the upper limit rpm numbers are arround 40,000. I know the rotor is fiber filled but I dont know how much is the ratio. my numbers are on 10% glass fibre mix to HDPE or worse case materials and the rpm limits are over 50,000 which might be able to be reached on 3 blades. The rotor problems I have heard about are mostly problems cause in putting it together or from not letting the blades seat enough before jamming power to it with a high powered setup. Eric B.
 Jan 12, 2006, 07:40 PM Registered User Post Falls, ID United States Joined Feb 2004 4,460 Posts Thanks, I'm looking forward to it. I have always wanted to do this but no real direction to get it done or time to get in to it so this will be interesting. I was interested in how you got the area at the root of the blade. Is this the actual airfoil area or minimum dia. of the rotor? I thought it was the first one because you go into describing the volume of the blade itself. Do you know what airfoil is used on that rotor blade to get such a value or have you basically measured the airfoil in several places and averaged it out? Thats what prompted me to ask the first question about how you calculated this and if you used software or a database of airfoil info. I have closely compared the 64mm and 55mm GWS rotors and they use the same hub. The bades are different, thinner chord, looks like the same pitch as the 55. The 75mm fan has even thinner blades but they all seem the have the same pitch when compared side by side. I cut down the 65mm fan to 59 and it works fine in the Mig. The Vasa blade is very simple, its a rectangle twisted. I can measure it for you. The hard part would be predicting the materials strength. The hub is cast from a white resin that has a tooling material quality to it if your familiar with those materials, it cuts very nice and clean but it can chip. The carbon is, well, carbon, maybe 6K, but the epoxy resin used could be anything, West Systems maybe? So the other data might be more useful then and we will just have to wait for one to explode to find the limits! On my Hyperion meter I tached the Alfa rotor at 60400rpm and there where no signs of rubbing in the housing. Thanks in advance Eric, Chris
 Jan 12, 2006, 07:56 PM Suspended Account Utica Il. Joined Dec 2002 4,222 Posts This Is Gettin' Technical Keep it comming. Good things to learn here Randy
 Jan 12, 2006, 08:39 PM SoCal, Year Round Flying! Newport Beach, CA Joined May 2002 5,745 Posts Thanks Henry, It'll be my 1st one! I think I'll go either Sat or Sun. It depends on the weather(rain predicted on saturday) . Thanks Eric, I think you misunderstood my post alittle though... I was not very clear on it. What I meant to say is load on the motor. ie:the wattage rotor places 20% more load on the motor? What I'm really interested in however is, How much more load will a cutdown mini480rotor place on the motor in an alfafan? My 4S mega16/15/2 needs to know! Regards, Bruce
 Jan 12, 2006, 09:40 PM EDF rules... :) Joined Nov 1999 13,725 Posts Hi Bruce, On the existing motors(20mm) is it maybe 5-10% more load, the 16/15/2 on 4s would see somwhere arround 600watts 40amps if you can hold the voltage as WAG. Definitely faster. Eric B.
Jan 12, 2006, 10:33 PM
SoCal, Year Round Flying!
Newport Beach, CA
Joined May 2002
5,745 Posts
Quote:
 Originally Posted by AirX Hi Bruce, On the existing motors(20mm) is it maybe 5-10% more load, the 16/15/2 on 4s would see somwhere arround 600watts 40amps if you can hold the voltage as WAG. Definitely faster. Eric B.
Thanks! Thats very good to hear!
Hopefully I can get a mini480 rotor at the upcoming AMA show!
And maybe a 40A capable pack too!
I'll try my best to blow up the alfa fan! lol
Jan 12, 2006, 11:13 PM
EDF rules... :)
Joined Nov 1999
13,725 Posts
Cof G,

Does the Hyperion tachometer work with 6 blades? If not how did you go about calculating the rpm?

Here is a measurement pic of a rotor for illustration of how to get the angles for calculating the pitch.

Eric B.

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 Jan 12, 2006, 11:31 PM Pro Horder upland CA Joined Dec 2004 7,983 Posts Bruce, I have a 480 fan and the problem I see is the hub is too large. You will loose a lot of the FSA due to the cone size.I dont think it will work well..But then again? You going to the ama? I will be there tomarrow when they open at noon! Scott

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