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Old Jan 15, 2006, 10:05 PM
EDF rules... :)
AirX's Avatar
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CofG,

I posted the math on the rotational stress/tensile strength in my previous post.

Eric B.
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Old Jan 15, 2006, 10:16 PM
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Chris Nicastro's Avatar
Post Falls, ID United States
Joined Feb 2004
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Sweet, thanks for that. I'll try it on the Vasa rotor as much as I can, limited on info.

BTW I thought the tach he was using only reads up to 3 blades.....he should just get an Emeter! lol

Chris
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Old Jan 16, 2006, 02:54 AM
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Bishops Stortford, UK
Joined Dec 2005
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Quote:
Originally Posted by bmiller
Sorry you crashed your MiG. Sounds more like you smoked the motor rather than the ESC just cutting out. Suggest you see if it still runs and if it does you need to check the ampdraw(use 3S to test)My last himax shorted the windings so on 3S it ran but was pulling 35amps instead of 22amps! ie. no good...
I've no experience with the miniACs so can't comment on that.
Not sure if the Astro (in a alfafan) can spin at 50-60,000 continously without throwing a magnet. It is a very good motor in the minifan.(30,000rpm or so.)
Saw the flightpowerEVOs at the show yesterday, They look awesome!
Bruce
Thanks for that Bruce.
The Mini AC still runs, the ESC was red hot. I'm gonna try a Castle Creations 45 amp ESC, this sounds a good move as I believe you are using one of these with your Mega 16/15/2. I have that motor too, and was thinking of going down that combo route . I don't know what Amps the Mini Ac/ womotec fan is pulling, but guess it is quite a bit.( I will be buying an Ammeter soon !) There are more fan blades with a bigger pitch ie more work needed from the motor. Think you said in one of your quotes the Mega has a greater torque output so that maybe the route I will take.
I know you guys have been playing with cut down fans on the bench, but have you flown anything yet ? The Wemotec Minifan 480 was easy to cutdown and balance and does appear to chuck out alot more thrust ( again a pair of scales are on my shopping list !) See you managed to pick up a couple at the show. Hope you are gonna chop one up, I'll be REALLY intersted to see what you come up with.
Regards
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Old Jan 16, 2006, 03:12 AM
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Bishops Stortford, UK
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Mig #2 fitted with Nav lights and modified canopy (cockpit area removed) to take the larger EVO 20 batteries
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Old Jan 16, 2006, 02:51 PM
SoCal, Year Round Flying!
bmiller's Avatar
Newport Beach, CA
Joined May 2002
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You still need to check the ampdraw on the motor just to be safe...
My mega is only drawing 25.1A right now and has unlimited vertical.
I have the kyosho rotor to try next as the hub is the same size as the alfa.
The hub on the mini480 rotor is huge by comparison and masks alot of the swept area.
But it works for you so I may have to try it!
The Mig looks good! I'll build mine one of these days!
Bruce
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Old Jan 16, 2006, 08:23 PM
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mode101's Avatar
Wellington, Florida
Joined Oct 2005
702 Posts
Quote:
Originally Posted by AirX
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.

How did you calculate 10% loading? Did you perform an ash test? I never seen a Wattage fan in person but it appears the Alfa fan is mostly likely PP with a small loading % of something other then glass, I would say carbon black but this is speculation on my part. I would flame test it, but I don't have a spare laying around.
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Old Jan 16, 2006, 09:53 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,517 Posts
Hi Mode101,

I used 10% glass fill as my plastics reference only has that as its lowest reference for glass fill. The difference between this and PET is small. If you think you want to dig this material up it is relatively easy to run the calculation.
I contacted Alfa for thier rotor, and thier reply was that it is a polyamid molding.

Eric B.
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Last edited by AirX; Jan 16, 2006 at 09:56 PM. Reason: Spelling
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Old Jan 17, 2006, 01:48 AM
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Post Falls, ID United States
Joined Feb 2004
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I purchased the BNB flight data recorder today, the 100A model and twin temp sensor and temp sensor with LED. So now I will answer my all-time nagging question; What happens in the air, during a flight to the amp draw/voltage/temps? I want to compare static to dydnamic loads on the system so I can anticipate the performance a setup will do. The next thing is the new Medusa Research power analyzer pro deluxe with load cell and rpm and temp sensors, all PC compatible. They also have a smaller less expensive 4min. data logger for under $30. Later I'll be able to post a chart of the flights for comparison.

If anyone has experience with these let me know please, I would like to understand what you have experienced with these products.

Chris
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Old Jan 17, 2006, 02:10 PM
SoCal, Year Round Flying!
bmiller's Avatar
Newport Beach, CA
Joined May 2002
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Cool Chris!
post a link please!
Definitely would like to know the difference between static test ampdraw and inflight ampdraw. And rpms for sure.
Bruce
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Old Jan 17, 2006, 02:39 PM
turbonut's Avatar
upland CA
Joined Dec 2004
7,185 Posts
Hey Guys! Looks like I missed a bunch..Went to death valley(furnace creek) for our annaversery.Took the huck so I could see how she flies below sea level but the winds where too high..O well. Did talk the wife into waiting to leave fri. So I could go to the ama show..I picked up a set of mini retracts from larry and chris from JHH.Very nice stuff..Larry is also going to ARF his A7..Wonder if some one will e power it!
Scott
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Old Jan 17, 2006, 03:53 PM
SoCal, Year Round Flying!
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Newport Beach, CA
Joined May 2002
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Wondered where you went! Now you can finish the F-104?
and get that walkura rotor going!
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Old Jan 17, 2006, 05:40 PM
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Post Falls, ID United States
Joined Feb 2004
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www.bnbproducts.com

I have wondered the same thing and when I ask the "experts" I dont get an answer sooo here we go, I'll log it and see!

Chris

BTW there is Medusa Research and Eagletree as well so I picked BNB for starters on price/performance. Shipped already and will arrive the 23rd.
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Old Jan 17, 2006, 07:48 PM
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Henry V's Avatar
Long Beach
Joined Jan 2004
1,402 Posts
Got a chance to fly the mig today twice and I am happy with my set-up with the shorter wattage impeller w/ AON 2415/4900...unlimited vertical also before the LVC kicks in. I really wish I knew how fast I'm going but diffenitly a big difference!
Unfortunatly the Mig's luck ran out today...My instinct told me to go home and put my 35amp ESC, but instead I went and flew it and ended up frying my CC25 at full throtte into the ground at 45 degrees ...im thinking of picking up another Alfa Mig because I love the way this plane flys...
Henry V
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Old Jan 17, 2006, 08:31 PM
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mode101's Avatar
Wellington, Florida
Joined Oct 2005
702 Posts
Quote:
Originally Posted by AirX
Hi Mode101,

I used 10% glass fill as my plastics reference only has that as its lowest reference for glass fill. The difference between this and PET is small. If you think you want to dig this material up it is relatively easy to run the calculation.
I contacted Alfa for thier rotor, and thier reply was that it is a polyamid molding.

Eric B.
I was thinking that was a possibility, PP and Nylon (Polyamide) have similar specific gravity when you add glass fibers to PP at least. Did a float test and it sank.

I'm surprised they didn't make the rotor stiffer, safety factor I guess?
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Old Jan 17, 2006, 08:56 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,517 Posts
Hi Mode101,

I dont think they were thinking in terms of safety factor(Alfa of Wattage for that matter), for that it just needs more area at the root. It would be stiffer as a benefit from more material. Moving the air thru the fan is where some stress on the blades, but it is only going to be as forceful as the thrust out(23-25oz) and that is not enough to shear a blade, the rotational loading is far greater and there is more than enough area for strength in the blades stock for the rpms our motors will generate.

Eric B.
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