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Old Jan 20, 2015, 06:12 PM
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Australia, VIC, Melbourne
Joined Nov 2006
12,220 Posts
Maybe the Efflux Speed changes then.
Thrust alone does not seem to be a way to measure the total energy out. It is not a 'pure' way to measure energy.

High Blade Swept Area fans (like Taft, CS, XRP) build a more solid 'wall' of air.
Wemo, 5, 6 blade - which have Low Blade Swept Area (bigger space between the next blade coming) - send out a 'thinner' weaker wall of air... but can do that faster for the same total load/Power.
Efflux pushing out into "air" (just air behind the jet).... a 'solid wall' has a different ability level to 'push', versus the case of higher speed of less air.
It is a lot like Torque (ft/lb) versus BHP.... HBSA fans are like a V8 or truck, versus Wemo,5,6 being like a Turbo engine result.

So if you are getting the same Power used, you are probably getting the same energy, but just in a different form/balance of Efflux Speed to Thrust.
The "Thrust" you think you see on a scale is not that same thrust.... maybe there should be different words. The scale measured one is the 'final result in weight it can lift, in that specific static state'. Once flying it is different. Different than a system deriving that static Thrust from higher Efflux Speed.
eg BOTH had the same static thrust on your scales - one was derived more via Efflux Speed, which does not excel at static state.... but excels once moving faster. (again like the V8 versus turbo car)
When the Taft is 'a bit more starved' (it is probably not 100% fed for any inlet you have anyway) its output could be that bit higher efflux instead. (some change at least) as there was less air to 'ram' down the exhaust now, so it has that bit more freedom to have speed instead. And 'speed', Efflux Speed, is poorer at converting to thrust than a 'solid wall' is.

That is what all the cases I have come across seem to add up to.....
I like Wemo EVO, Jetfans WAY more now!! And a bit of a growing dislike for CS/Taft etc. Their power cost per return is not as good. But nice sound!! So if you are willing to throw that bit of cost onto the sound return, that is fine!
But I still have quite a few CS/Taft lying around, and I hate wasting stuff.... so, they still will be used anyway.
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Last edited by PeterVRC; Jan 20, 2015 at 06:32 PM.
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Old Jan 20, 2015, 07:42 PM
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
23,236 Posts
you will find that once in the air you will recover any if the lost thrust at speed
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Old Jan 20, 2015, 11:05 PM
Fly it like you're in it
microlyn's Avatar
Canada, ON, London
Joined Nov 2012
715 Posts
Good stuff Eric, glad you've got it sorted out!
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