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Old Sep 18, 2011, 05:29 PM
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Hastings, Hawkes Bay, New Zealand (Aotearoa)
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What prop for my Backfire?

Hi,

I am running a Kontronik FAI10 motor with 6.7:1 gearbox in a Backfire with a 3s-4200 Hyperion Lipo. ESC is a Kontronik Jive 100LV.

Currently using an Aeronaut 15x13 prop and have just installed a Unilog to see what was happening. My static current peaks at about 210A but rapidly drops to around 150A once it gets moving. I feel like I might need more pitch to get a bit more top end and keep the power level up.

Not sure as to to go Slim or not?

RFM do a 15x15 & 15x16 slim.

Any suggestions what would work better without popping my ESC? (The Jive 100LV seems quite happy at 200A bursts even though its continuous rating is only 100A)

I do have a set of RFM 16x16 (not slim) but have been too chicken to try them for fear of turning ESC into a crispy wafer..

Heather
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Old Sep 19, 2011, 11:41 AM
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If was my plane I would run a GM18x21, but, probably have to change your motor.

Andre
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Old Sep 19, 2011, 04:51 PM
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So the next step has now arrived, cool.

Hi Heather,

Nice to see someone else enjoying the Backfire here on groups.

I have a Kontronic 500-48 but with a 5.2:1 gearbox in my Backfire.
I am running it with a CC 125, and power from a 4s Thunder Power 3350 45c cells. and I am spinning a set of RFM 16 x17 slims.

I once worked out from seconds run and mah needed to charge my pack that it was drawing about 275 -285A. please remember this is with a 5.2 :1 gearbox and 4s.

It goes very well with this setup, about 60 ms straight up.
from first toss to 1000 ft/ 300m it takes 3.5 seconds. Each pass after that is about 2 sec for 1000 ft /300m so it is not word class but it is definatly a solid and fun setup with out pushing things to much.
But be sure to do the NACA duct and the wing outlet. I was using an RFM holed spinner and have left the tail come off but no other cooling, on the last flight, on the warmes fling days yet mine got rather warm and did puff my TP 4s pack slightly, I have now done the cooling and waiting for the next flights.

I don't have a Unilog but thinking about getting one in the spring.

Pcalc shows 3000w for this setup, for what it is worth, I know it is not real numbers but thought I would add as reference. I like things I can quantify.

I had run this same set up on 3s Hyperion 4500mah 30c-50c cells and was spinning a RFM 16 x17 reinforced wide blades and it was about 2/3 the power I believe it was about 185 -195 A, drawing around 2000w.

As for your Kontronic speed controller. my knowledge and experience is limited. Early on with this motor (10 years ago) in an converted E- Tsunami I used a Kontronics 80a esc with 10 NiMh cells and RFM 16 x16 wide prop it would thermaly shut down as I purposly did not have it in FAI mode to keep it from popping. It was drawing about 125-135A and I once put it on a watt meter and saw 1050w ( yes weren't we all young and foolish once)

So being a bit cautious myself I would beg borrow or buy 2 props, the 15 x16 and the 16 x17 slim. I think that both will be under 200a but the 16 x17 will be just bearly less with high C packs. when and if the time is right with a good esc and a 4s pack your Backfire will realy rock, and the motor will take it.
As for trying your 16 x 16 if you have good reports that the esc can take 200 but no more I would be quite cautious..... but I might still try a 1 sec birst with the Unilog on a brave day.

Cheers,
wetcoast
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Old Sep 19, 2011, 05:41 PM
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Hastings, Hawkes Bay, New Zealand (Aotearoa)
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Well I've gone and ordered 15x15, 15x16 & 16x16 slims to play with.

My motor has a Kv of around 6400 so I think 4s would be too much for it. Don't want to fork out for a new motor quite yet so will try these props first.

Heather
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Old Sep 19, 2011, 09:45 PM
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Quote:
Originally Posted by Heather View Post
Well I've gone and ordered 15x15, 15x16 & 16x16 slims to play with.

My motor has a Kv of around 6400 so I think 4s would be too much for it. Don't want to fork out for a new motor quite yet so will try these props first.

Heather
Heather, the bf has such a big span, I don't like the idea of a thin prop at launch on it. I always fly mine with the neu 17.5-17.5 prop, and it's a beast!
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Old Sep 20, 2011, 01:52 AM
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Yell out if ya wanna borrow a 16x16 or 16x17 slim to try Heather.
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Old Sep 20, 2011, 01:56 AM
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Quote:
I always fly mine with the neu 17.5-17.5 prop, and it's a beast!
What motor/Esc/Batt are you running?
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Old Sep 20, 2011, 05:35 AM
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Heather,

It's obvious you want more power in your Backfire.
Now would be a good time to consider selling of your current drive and to find a new setup which can cope with more power. Otherwise it's not inconceivable that you blow up the current drive while trying to find it's maximum, accidentally crossing the line. You'll then end up with worthless parts and still have to buy a new drive. Better to sell while it's still in good nick and get yopurself a robust drive which can nicely cope with more power.

Regards,
Gerben
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Old Sep 20, 2011, 07:57 AM
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Heather,

It's obvious you want more power in your Backfire.
Now would be a good time to consider selling of your current drive and to find a new setup which can cope with more power.
...or sell me your BF I have the complete setup here for her.

Try a 8S or 6S setup playing with some Neu 1512/XX...
I'm flying a very well know and "safe" setup Neu 1512/1.5D/6.7 on 6S with 17.5x17.5 or 18x21 (actual prop) on CC ICE LITE 200, good for 320amps and 6KW. I think Rich flys a 8S Setup reaching 6KW too, but current reamins 200amps

Andre
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Old Sep 20, 2011, 03:10 PM
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Quote:
It's obvious you want more power in your Backfire.
Yeah I know... you first fly it and think WOW, then it doesn't take long before you start thinking.. if only I had a bit more power...

I have a Kontronik Fun600-32 on a 5.2:1 gearbox that I might be able to fit. That on about 5s would be good.

But first I will experiment with a few more prop changes and try to not let the magic smoke out.

Heather
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Old Sep 21, 2011, 04:13 PM
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Yeah I know... you first fly it and think WOW, then it doesn't take long before you start thinking.. if only I had a bit more power...

I have a Kontronik Fun600-32 on a 5.2:1 gearbox that I might be able to fit. That on about 5s would be good.

But first I will experiment with a few more prop changes and try to not let the magic smoke out.

Heather
5s? That fuse is not very accomodating; I run 8s in mine, and it fits nice, two 4s packs back to back. But for a nice sized 5s pack, I have no idea what would fit
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Old Sep 21, 2011, 08:57 PM
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My Turnigy 6S 40C 2650 has 37x37x135mm
I know I know... everybody is gonna say 2650mah????
Well... after 9 cycles the pack is ok delivering 300amps, I fly 30s and land, charging back 1800mah. Maybe you can fins a 5S 3000mah that fits your BF
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Old Sep 21, 2011, 09:18 PM
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Of course the 5s number jumped into my head way before I even considered if one would fit... maybe 6s would be doable with two 3s packs... See I'm doing it again!

Ill play with props first and see where that takes me. Its just the Kontronik FAI10 is such a nice motor it would be a shame not to use it and I know I would get nothing much for it if I sold it.

Heather
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