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Old Apr 02, 2012, 01:19 AM
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kayvannouri's Avatar
United States, TX, Dallas
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Motor for Fast Funjet ?

I am looking for the fastest motor I can put on my funjet with a 4s setup (2200mAh 40c), I am using an 80 amp esc with 100 amp burst. Currently running this setup with Turnigy 2350 motor with 6x4 prop and very happy with the speed and performance,
SO WHICH MOTOR DO YOU RECOMMEND ?
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Old Apr 02, 2012, 05:57 AM
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Darron's Avatar
London
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Why don't you just change the prop?
The 4" pitch will be holding your speed back and the 6" diameter eating power.

Try the APC 5.25 x 6.25. That should take you from your 100mph to 150mph with less power. If you need even more speed, just try a motor within your budget with a higher Kv say 2800Kv which could get you about 180+mph at 1kW (same prop), but you'll only get 90 seconds or so on full power - depending on the airframe.

To be honest, you'd be better off posting this on the foamie forum
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Old Apr 02, 2012, 11:38 AM
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San Fernando Valley, California, United States
Joined May 2003
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Search for tue funjet thread. Tons of info on setups. How fast do you want to go? It takes monster power to make these things fast.
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Old Apr 02, 2012, 11:52 AM
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good idea, I gotta change the prop, but where can I get APC 5.25 x 6.25 ???
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Old Apr 02, 2012, 11:59 AM
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Darron's Avatar
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Quote:
Originally Posted by kayvannouri View Post
good idea, I gotta change the prop, but where can I get APC 5.25 x 6.25 ???
From your LHS or direct from APC
http://www.apcprop.com/v/index.html
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Old Apr 02, 2012, 12:09 PM
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got it
thanks
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Old Apr 02, 2012, 12:50 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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If you want to go real fast, cut up the FunJet and use it for insulation. The get yourself something made of Kevlar
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Old Apr 02, 2012, 02:44 PM
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San Fernando Valley, California, United States
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Quote:
Originally Posted by kayvannouri View Post
good idea, I gotta change the prop, but where can I get APC 5.25 x 6.25 ???
That would be much faster in a f5d airframe, but the funjet is much draggier. Check the funjet thread, most feel that the smaller props don't provide enough thrust in high power setups. The really fast guys are running 7" props, but you'll need a much larger controller and packs.

How many amps are you drawing now?
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Old Apr 02, 2012, 03:10 PM
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i would say about 68 amp
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Old Apr 02, 2012, 11:49 PM
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Canada, SK, Prince Albert
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kay - I'm running a Scorpion HK2221-8 on 3S with a 5.2x5.2 about "70ampsWOT static" and it is screaming fun with a stock airframe. Batts don't last to long though
It is a thumb duster offer for my fast planes
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Old Apr 03, 2012, 12:33 AM
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haha, thats a very nice motor and expensive !
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Old Apr 03, 2012, 04:54 PM
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United States, CA, Torrance
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Quote:
Originally Posted by kayvannouri View Post
haha, thats a very nice motor and expensive !
Speed costs $$$$. Especially trying to push such a draggy airframe though the air. Sometimes you will need near double the power just to add another 20mph once you start seeing 120mph+ speeds. This is not an exact example, just making a point.

Expensive power system and heap air frame....or....expensive air frame and budget power system for the speed. It' when you put both quality AF and PS together when things get exciting
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Old Apr 03, 2012, 05:33 PM
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nieuw vennep, the netherlands
Joined Feb 2010
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I fly with a Turnigy T3648-1450 on 4S with a APC7x10 sport,~94A static, ~65A inflight.
The flight time at WOT will be around 100sec's but speed will be around 150mph.
You can also stuff a 4S 3300 LiPo in it, then you have >2min WOT.
For me thats long anough.

Grtz René

ps you will need nose weight with that lite 2200 4S pack!
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Old Apr 04, 2012, 05:37 AM
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Here is something I came across in one of the forums about the " the cubic power-to-airspeed rule"
Something to think about next time we consider a power system for our plane

""" the problem with getting fast through the air.

The cubic law (like when calculating volume, then you have to multiply lenght x width x height, and for a cube that's just a^3 with all three sides equal to a, that is where the name cubic comes from) can easily be understood as follows - I will have to do a little bit of basic physics first:

If you lift an object of mass m up (against gravity) you have a constant force (F = m x g, g=gravitational acceleration, value is around 10 on earth). To lift it up, say, 10 meters, you can calculate the necessary work W = energy E = m x g x h (energy ist just stored work, or the potential to do some work).
Power is defined as energy divided by the time required to do it. You can do the same work slower or faster, in the absence of any drag forces, the work will be the same - but the required power is rising with the velocity: The faster you do something, the more power you need. In the example lifting an object, the power needed will be rising with the velocity, and since you will be up quicker, this effect cancels with the decreased time, and work/energy is the same.
So just doing work against the SAME force quicker needs more power, it rises linearly with the velocity.

Now comes air drag: The force needed to overcome air drag, unsurprisingly, rises with the velocity. So, unlike the gravitational force, it will not be the same regardless how fast you move. The extra-bad news is now that - as you know already - drag resistance not only gets bigger, it gets bigger with the square of the velocity. So twice the speed, 4 times the air drag.

Just from doing something faster we already had a linear dependency on speed (that factor ist often forgotten), and now we have to add a square law with the drag force - in total velocity comes in threefold, and that might be called a cubic law.

Easiest to see is : you want to go twice as fast you need 2 x 2 x 2 = 8 times the power. And that is true in the real world, e.g. a Funjet needs just 100W to go 100km/h, but it will take 800W to get it up to 200km/h

A law of diminishing returns, indeed

cheers """""
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Old Apr 04, 2012, 05:31 PM
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United States, CA, Torrance
Joined Nov 2005
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Quote:
Originally Posted by Adrian_M View Post
Here is something I came across in one of the forums about the " the cubic power-to-airspeed rule"
Something to think about next time we consider a power system for our plane

""" the problem with getting fast through the air.

The cubic law (like when calculating volume, then you have to multiply lenght x width x height, and for a cube that's just a^3 with all three sides equal to a, that is where the name cubic comes from) can easily be understood as follows - I will have to do a little bit of basic physics first:

If you lift an object of mass m up (against gravity) you have a constant force (F = m x g, g=gravitational acceleration, value is around 10 on earth). To lift it up, say, 10 meters, you can calculate the necessary work W = energy E = m x g x h (energy ist just stored work, or the potential to do some work).
Power is defined as energy divided by the time required to do it. You can do the same work slower or faster, in the absence of any drag forces, the work will be the same - but the required power is rising with the velocity: The faster you do something, the more power you need. In the example lifting an object, the power needed will be rising with the velocity, and since you will be up quicker, this effect cancels with the decreased time, and work/energy is the same.
So just doing work against the SAME force quicker needs more power, it rises linearly with the velocity.

Now comes air drag: The force needed to overcome air drag, unsurprisingly, rises with the velocity. So, unlike the gravitational force, it will not be the same regardless how fast you move. The extra-bad news iOs now that - as you know already - drag resistance not only gets bigger, it gets bigger with the square of the velocity. So twice the speed, 4 times the air drag.

Just from doing something faster we already had a linear dependency on speed (that factor ist often forgotten), and now we have to add a square law with the drag force - in total velocity comes in threefold, and that might be called a cubic law.

Easiest to see is : you want to go twice as fast you need 2 x 2 x 2 = 8 times the power. And that is true in the real world, e.g. a Funjet needs just 100W to go 100km/h, but it will take 800W to get it up to 200km/h

A law of diminishing returns, indeed

cheers """""
That's what I said in post #12.........................sorta
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