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Size zero

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Nigel Davison06/03/2009 11:29:47
37 forum posts
really like the design but would like to convert to electric as i am based on a remote island in the canaries ic isnt an easy option . anyone any thoughts on motor size etc .
Tim Mackey06/03/2009 13:01:48
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more info on the model please...AUW  weight etc
David Ashby - Moderator06/03/2009 18:00:51
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Nigel, four years ago when we were on a cruise, the ship stopped at La Gomera for the day. We went on a coach trip and passed down a ravine and through a small village where I was astounded to see a group of R/C flyers flying from what looked like 2-3 tennis courts.  
 
Were you there?   As Tim says, bit more info required .  
Nigel Davison06/03/2009 18:32:13
37 forum posts
almost certainly not many of us flying here ,alot more on tenerife though ,if not we would have been racing i mtr sail boats in the harbour , we live on the other side of the island from the harbour its a lot less windy over here.next time youll have to drop in for tea !
 
size zero auw 39 3/4 oz 43" span  16.6 oz loading designed for a .15 , . would  a 250 watt / 1000kv motor be about right. or is it a bit much .
Tim Mackey06/03/2009 19:47:30
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seems about right I would think - on a 3s lipo for reasonable pitch speed
Nigel Davison06/03/2009 21:43:18
37 forum posts
thanks Tim .what prop would you suggest  i have a 10 x 7 apc would that be ok ,  im not sure if its an electric or slow fly prop and im not sure i understand the difference , is there one ?  i use 3 cell lipo on the helis i have so i was going to use one of those .
Tim Mackey06/03/2009 22:25:14
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You really ought to use a wattmeter to assess the current draw with different props - and also to ensure that you use the correct ESC. Electric props are generally lighter than IC props... but slow fly props are different again being as the name suggests, suited to lower revving slow flying machines - they are too bendy for high RPM
If you find the specs for the actual motor you plan on using - they should tell you the prop range.
David Ashby - Moderator07/03/2009 07:28:29
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I will do that Nigel, lovely place you fly from there
Nigel Davison07/03/2009 08:08:58
37 forum posts

tim wattmeter on order but was oos at smc when my last parcel arrived should be on next one , checked out the spec and mine very similar so i guess my prop is ok . there is so much i dont understand so sorry if the questions are never ending , i understand kv /rpm etc from your article and therefore type of prop etc but what  detemines the choice of motor kv for a particulat type of model  is it simply slower model bigeer prop lower rpm , faster model small prop higher rpm. have you seen the size zero plan i guess you would describe it as a sport model but with a suggested 16.6 oz  wing loading im not sure what sort of design speed it would have , am i making things too complicated .

 

Nigel Davison07/03/2009 08:18:49
37 forum posts
gosh david your an early bird too. yes i live on the side of one of those ravines planty of air space but small landing strip  hence diven to thinks that fly slowly ,
Tim Mackey07/03/2009 08:23:19
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Hi Nigel - I usually start by assessing the required flying characteristics of the model as you surmised., coupled with the likely power required. The other consideration is battery size ( cell count ) and in orer to keep the amps sensible, once you start getting up around the 30 - 40A mark, you need to consider higher volts and lower current to achieve your target watts IYSWIM.  These higher volts will, in turn, produce higher RPM, and the following formula ( which you may already be familiar with ) will give an idea ( estimate only of course ) of likely pitch speed. Ina perfect world with zero airframe drag and 100% efficient props etc, the model speed in MPH can be found from ( RPM X PITCH) / 105
EG: 8000 RPM X 7" Pitch / 1056 = 53MPH
These factors should help you decide on the motor you need.
 
Of course many suppliers are now helpfully recommending the correct motor ( as an IC equivalent ) for particualr models / model types.... E Flite being one example.
 
Nigel Davison07/03/2009 09:53:52
37 forum posts
thanks tim , no i didnt know the formula for the est airspeed  it makes it alot clearer thats really helpful . ive noticed a lot more manufacturers going down this road but its nice to know why your doing something though as i know you appreciate. i am getting there .
 
thanks again
Peter Miller10/03/2009 08:46:09
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Isn't it a shame that electric motors do not seem to have consistant form of classification.
 
Any .15 would fly Size Zero but every electric mot0r has a different number an no indication of what it really means.
Nigel Davison10/03/2009 18:43:00
37 forum posts
yes it is peter , i wish sometimes i had access to ic fuel etc but im so far down the electric route its too late now .
i like the design and hope to start in the next few weeks when ive finished a couple of others im working on , ill let you know how it goes . after that its time to start my own design  thanks to the inspiration of your modellers world series book .  
Doug Ireland11/03/2009 21:03:56
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I agree with you Peter. I think they do it deliberately to keep their "black arts" away from us oil burners!
Peter 'Ivanna Crashalot' Savage12/03/2009 00:25:25
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well electrics are normally referred to as 400s or 280s etc, however with the advent of brushless that has kinda gone down the toilet
Peter Miller12/03/2009 08:44:11
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I think a lot of the trouble is the infinite variations you can have with electric motors. Magnet strength, number of windings, guage of wire and so on.
 
With ic motors you have the capacity which is always a good guide. All right, some are more powerful than others but generallay a .15 will fly any model designed for that size of engine, with some it might be sluggish and with another it might go like stink but they both will fly it.
Tim Mackey12/03/2009 09:17:24
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The " trouble" can also be its advantage, and not withstanding matters such as maximum efficiencies etc, one advantage of the electric motor is the ability to swing diffrent props at diffrent revs for different models. Not infinately flexible of course, but certainly more latitude than IC. The same motor, propped differently can be used between several different types of model, using different battery voltages ( cell count ) and differing prop sizes.
PS this is NOT an attempt to lecture to petrolheads about the joys of electric flight - although I like electric, you can never accuse me of this crime - I enjoy both, and see the merits of both. In fact, if anything, I hear more IC diehards  be-littling electric than the other way around.
Peter Miller12/03/2009 12:11:28
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I was not saying one was better than another. I was trying to say why it is so hard to tell what electric motor to use for a given size of model because there is no system whereby you can look at the motor number and tell what power it is.
 
I just looked through some adverts and I see that a few shops are now including the i.c. equivalent beside many of their brushless motors. That is good but many do not. The J.Perkins website doesn't for a start.
 
With so many people converting models to electric power I feel that all motors should have the equivalent given.
Tim Mackey12/03/2009 12:23:20
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But thats kinda my point Peter- the flexibility of the complete powertrain is higher than simply saying "this is the equivalent of a 30 2 stroke" or whatever. Yes it might be with certain props and batteries, but then play around a bit with a few other props and cell counts, and suddenly  its maybe more like a 50 four stroke. besides, which 30 2T do they mean ?  -the cooking plain old OS LA or the blistering rear induction 30% nitro guzzling Rossi on the oversquare prop?
I know you were not saying one is better than the other, and I also know that many people find it difficult to grasp the whole electrci flight thing but it doesnt have to be that way.
I happen to like fiddling and experimenting, but have plenty of clubmates who happily just buy the setup recommended by the model manufacturer and fit and forget.
They havent a clue how it all works , but fly on in blissful ignorance and enjoy it tremendously - thats absolutely fine.
They probably do far more actual flying than a sad old geeky type experimenter like me

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