[NSRCA-discussion] Electric props

[Earl Haury]

Stuart

For a given voltage the motors we use will run (nominally) the same rpm 
within a reasonable range of props (load) with the current flow increasing / 
decreasing with load. However - the catch 22 - as more or less current is 
drawn from the batteries the voltage will vary accordingly (batteries aren't 
a constant voltage source). So while a charged pack is nominally 42v no 
load - voltage  will be considerably less with load, and motor rpm will vary 
accordingly. So max "throttle" rpm will be higher with smaller props than 
with larger, as the lighter load results in higher volts.

With the 14  Hacker any of the props you list will work - data I've 
collected indicate that the 20x15, 21x14, 21x13W, & 22x12 run about the same 
(volts / amps / rpm) with different flight performance for each - you'll 
need to see which works best for you. (I suggest trying the 21x14 first.)

I've observed that folks switching from glow to E and using the lower pitch 
(10 - 12) props tend to use a lot of their battery capacity for a flight in 
an effort to attain the speed they're used to with glow (flying E at max 
throttle a lot). For this reason it's probably better to start with the 
higher pitch props and work back (or simply use the stick) for slower speeds 
as one gets used to E performance.

Earl


----- Original Message ----- 
From: "Stuart Chale" <schale at optonline.net>
To: "'NSRCA Mailing List'" <nsrca-discussion at lists.nsrca.org>
Sent: Friday, June 23, 2006 6:44 AM
Subject: Re: [NSRCA-discussion] Electric props


>I am still a little vague on some of the electric stuff which is why I am
> starting with a known combination.
> The motor is the standard Hacker C50 14 XL with 6.7/1 gear box.  Hacker 
> acro
> 90 speed controller. I am going to run Falcon F3A packs.
> The plane is an E- Pinnacle and all up weight with the Falcon packs is 5
> kilos.  Actually about 5010 gms right now but that is a different tale :)
> The Falcon packs are about 5 oz heavier than the TP packs.
> I am starting with the APC 22 x 12 as that is what most seem to use.
>
> Putting on a bigger prop causing it to draw more current makes sense.  As 
> I
> understand it the motor wants to spin a set rpm based on the input 
> voltage.
>
> What about a smaller prop?  Does it still turn the same RPM at less 
> current
> and thrust?
> How do I determine which smaller diam/higher pitch prop is too much for 
> the
> system?  I am sure that some of you have already tried this?
>
> Do the calculators really help?
> Dave, which one?
> Pocono?  No haven't even flown the plane yet :)  You will not see me at a
> contest until I have a good bit of practice.  I have to get my son flying
> yet.  Maybe Sayre?
>
> Stuart
>
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Larry
> Sent: Friday, June 23, 2006 2:36 AM
> To: NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] Electric props
>
> Hi Stuart,
>
> We need more info. Unfortunately, electrics have more variables than IC
> setups.
>
> What plane is this going into? Specifically what is the all up weight of 
> the
>
> plane going to be and how much power do you think you need?
>
> What size battery pack are you going to run - ?S?P and what capacity?
>
> Also, what gear ratio?
>
>
> To start answering your question - every item in an electric power system
> has an effect on power output and amp draw.
>
> Larger diameter/higher pitch props will draw more current and produce more
> power than smaller ones. Assuming all other variables stay the same.
>
> However, you cant just arbitrarily increase/decrease the prop size. The
> total power system has to work together. The batteries need to be able to
> sustain the load and the motor needs to be able to handle the power 
> output.
>
>
> Larry
>
>
> ----- Original Message ----- 
> From: "Stuart Chale" <schale at optonline.net>
> To: "'NSRCA Mailing List'" <nsrca-discussion at lists.nsrca.org>
> Sent: Thursday, June 22, 2006 9:30 PM
> Subject: [NSRCA-discussion] Electric props
>
>
>> Rather than redo tests that others have done I thought I would question
>> the
>> group regarding the different sized electric props available.  It seems
>> like
>> there should be a much better consistency and less variability between
>> different electric motors compared to different IC setups.
>> I am going to run the Hacker C50 14 XL (not comp model) with the 90 amp
>> Acro
>> speed controller.  Seems as if most people are running the 22x12 APC E
>> prop.
>>
>>
>> Below is a list of potential props I found on the APC web site.
>> If you have tried any of them and found a reproducible difference from 
>> the
>> 22x12 I, and I am sure others would like your thoughts.  If any of the
>> props
>> are too much for the setup please let me know.  (No reason to waste money
>> on
>> an unusable prop)
>> Hat happens when you run less of a prop say the 20 x 11?  Does the RPM
>> stay
>> the same?  Will the current usually go up or down?
>> These seem to be the possible choices from APC
>>
>> 20 x 11
>> 20 x 13
>> 21 x 14
>> 20 x 15
>> 22 x 10 ( I would suspect a slower flight speed)?
>> 20 x 12 wide
>> 21 x 12 wide
>> 21 x 13 wide
>> 20.5 x 12 wide
>>
>>
>> Thanks
>> Stuart Chale
>>
>> E-Pinnacle should be ready to fly this weekend.
>>
>>
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>>
>
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