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Old Aug 05, 2010, 01:41 PM
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TEXAS
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Any reason why a fan unit is not mounted all the way back?

If room and design allows why is the fan unit not mounted all they way back with using the fake ehxuast covers to cover and channel air. Or has any one tried using the MKII 400 pusher and the cone it has fo the exhaust tip? Trying to use some highber mAh battheris and out of room still tail heavy...
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Old Aug 05, 2010, 03:04 PM
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Taos, NM
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I don't think there's any reason why the fan jet motors are mounted midsection instead of way back in the tail other than the obvious balancing concerns. If you put it way back there, then you could end up with a very tail heavy condition, and most planes end up tail heavy anyway. So why put all that ballast in the nose if you can mount the motor midships and avoid all that? I think that's probably the main reason.
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Old Aug 05, 2010, 03:13 PM
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Most fans don't do well with really long intakes either which you would have if the fan was all the way back.
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Old Aug 05, 2010, 04:47 PM
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Also keep in mind the length of the wires and the gauge needed which adds weight and sometimes strain the planes electrical system. That is in regards to motor/fan placement.
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Old Aug 05, 2010, 05:25 PM
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http://www.rcgroups.com/forums/showthread.php?t=1184716
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Old Aug 05, 2010, 05:42 PM
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Like jdlilfan said; you can loss what you gain by putting the battery so far away from the ESC. Max length on wires is 20cm either side. You can go more but your performance goes down or needs larger battery and ESC to push it. You can up the gauge which increases the weight also.
Not that it can't be done but talk to Claus. He's shown diagrams etc placing the EDF somewhere in the middle.
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Old Aug 05, 2010, 07:41 PM
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CoG and wire lengths concerns aside, You can mount it where you like but an (optimal) exit length of 3-4 inches allows you to squeeze the exit smaller (typically 90%)and increase the efflux speed. Just like sticking your thumb over the end of a waterhose to increase its velocity.
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Old Aug 05, 2010, 08:20 PM
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Here is a picture of the tail cone of an F-35 being sold by Nitro planes. looks like the brushless motor/fan are at the very rear of the tailpipe.

http://www.nitroplanes.com/93a35-f35...o-rtf-24g.html

C of G must be tricky.
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Old Aug 06, 2010, 01:10 PM
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Has this understanding changed much? http://www.rcgroups.com/forums/showt...6#post10837456
He reps the Velocity fan so h may be able to help you with optimal.
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Old Aug 06, 2010, 02:03 PM
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I was thinking furgther back to accomidate heavier batteries,

On the test stands if you use a cone to channel the exhuast 10 or 20% do you see a loss in thrust and a gain in velocity?

If this is a true statement then and I wanted plane that could do the alfa or cobra manuever I woild give up some speed but have a lot of tbhrust to achieve the beter than 1 to 1 ratio, plus if I got introuble I would. Have the extra thrust to save my azz easier. So I probably would do no chaneling?
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Old Aug 06, 2010, 07:05 PM
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Quote:
Originally Posted by 320pilot View Post
Here is a picture of the tail cone of an F-35 being sold by Nitro planes. looks like the brushless motor/fan are at the very rear of the tailpipe.

http://www.nitroplanes.com/93a35-f35...o-rtf-24g.html

C of G must be tricky.
Naw man! 95mm from wing joint. I added a pound to mine and it flys well and really fast
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Old Aug 07, 2010, 02:19 AM
Foam bounces...
Turbs's Avatar
SA, Australia
Joined Aug 2007
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The shorter the discharge side of the fan, the more turbulent the air leaving the plane.
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