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Old Jun 02, 2014, 02:51 PM
mopetista is offline
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no performance w/ 10-blade fan: exhaust too small

Quote:
Originally Posted by Phaedra View Post
...
Lots of stuff to think about now.
1. How comes this EDF combo doesn't have more power? It should fly like a rocket on this setup.... I'll check throttle range, but maybe ESC timing could have any influence?
...
the exhaust is too small for a Change Sun fan - either you open up the rear end to at least 58mm so it will at least work decently in flight (for better static thrust choose 60mm), or you install a different fan - of the multibladers, only the Wemo Mini Evo will handle the small 55mm efficiently
cheers
Clemens
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Old Jun 02, 2014, 02:53 PM
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Belgium, Flemish Region, Duffel
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Ok, thanks, I'll have a look at that!
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Old Jun 02, 2014, 03:11 PM
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Diverted by planks
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Woot! Hey, she got up, flew, and returned to earth in one piece -- that's the definition of a successful maiden!

Now it looks like you just have some issues to work through.

As to the late rotation, I have heard a lot of people blame bottom cheaters, only to eventually find another issue (CG, thrust angle, incidence, elevator throws, etc) so I would check it out thouroughly before hanging my hat on that one.

In any event, you are over the big hurdle!
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Old Nov 08, 2014, 02:03 PM
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Really nice.

I always thought this model had no retract mounting options, and have never purchased it as a result (already have a funjet). I noticed recently pictures of retracts! Has this model always had retract 'mounts', or is there a new version?

Cheers
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Old Nov 08, 2014, 03:38 PM
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Mine had retracts provisions, and I bought it two years ago...
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Old Jul 17, 2015, 02:59 PM
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Belgium, Flemish Region, Duffel
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It's been quite a while, but I picked up the Epic again to try and get it to fly properly.
The first and critical problem to tackle is the lack of thrust.
And so I decided to take this step by step, and review my choice of motorisation.

At the time, I opted for the CS 10-blade fan with the 2855 2300kV motor, and powered this combo with a 4S4000mAh via a 60A ESC.
According to the specs this should give me 900g of thrust.

So I took out the kitchen scales, and put the model nose-down on it.: 1600g ready to fly.
Powered up the model, and gave it WOT: the scales read 2400g. So I had about 800g of thrust, for a weight of 1600g, meaning a 1/2 thrust-to-weight ratio. Just enough to fly at WOT. Opening up the exhaust duct might increase this to something closer to 900g, but that is still a bit marginal for safe operation.

Reading back this same thread, I discovered an error I made: when I chose this motor-fan combo, I intended to use it on 5S! On 5S it should produce a decent 1,3 kg of thrust, for an increased weight of 1700g, which would give me a more comfortable margin to fly.

According to the specs, the 2300kV motor can only be operated on 4S, but I have read multiple stories of people operating them (reliably?) on 5S.

So now I'm confronted with a whole new problem:
- the 5S Lipo is about 100g heavier, and larger, so it won't fit in the battery compartment.
- my ESC is rated 60A; a linear extrapolation of the current at WOT would yield 50A+...leaving less than 20% of margin on the ESC.

An alternative is to switch to Wemotec fans, but that would cost me around 120 Euro for a whole new combo....

So I need to do some more research about running this combo on 5S.
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Last edited by Phaedra; Jul 18, 2015 at 03:12 AM. Reason: got the numbers wrong....
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Old Aug 06, 2015, 08:44 AM
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I have been doing some tests and experiments lately, and it isn't looking really good.
First, I tried to open up the exhaust tube a bit, trying to get a better FSA. Result: no real measurable difference.
I then bit the bullet, and bought myself a 5S battery. When I ran the EDF combo with this 5S lipo, I could feel that it generated quite a bit more heat, so I'm not really comfortable with this situation. And what is worse, I did get a 200g increase in thrust, but that still is far away from the thrust I'm looking for.
It might be that the inlet channel is too long now because of me moving the EDF to the tail of the engine.
So I have two options:
- move the EDF back to the center of the model
- buy a different (Wemotec) EDF that handles these kinds of inlet/outlet channels better.

But right, now, I'm really a bit fed up with this model, and about to throw the towel into the ring. Thniking a bout selling it, cutting my losses. I have other models to fly with, and I intended to use this model as an EDF trainer, but never got to use it for that purpose. Meanwhile, I've flown a couple of EDFs, so I don't really need this model anymore.
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