F-22 (Prodeign) PDF Manual and build thread

http://www.youtube.com/watch?v=zM8YoRvV01Y

It's promising but you will need to test the sapacs with the edf to see if they give adequate thrust. The MB1 can supposedly run with 5S.

You will find that your 4S lipos are too small. You will be lucky to get more than 1-1.5 minutes flight time.

Around 4000mah would be better.

Whalleyboy,

No matter what you are looking at 100+feet of take-off roll. Jets have relatively poor static thrust (even when generously powered) and struggle with take-off. The trick is to keep the roll to less than 300 ft! I hope you are flying off a smooth sealed surface. If it's grass you're looking at 300 ft roll. Fit the biggest wheels you can find.

As for power systems, you want POWER - a combination of voltage and current, delivered efficiently. Your target power loading should be 300W/lb. Assuming you hit 7lb, you therefore want 2100W+ total, or 1050W+ per motor. This is at the high end of 70mm fans, but it's achievable. I have a Wemotec 70mm with a 3650Kv 2W-20 motor (old version with higher Kv than the currently marketed 2W-20) pulling 1300W on 5S.

As for cell count, you want to maximize voltage and minimize current - this is the key to efficiency. Efficiency is lost through resistance losses, calculated by I^2 x R (I=current, R=resistance) - note it's I squared, therefore it's very important to keep I LOW. Therefore it's a no brainer to go 6S. 6S should achieve a working voltage of 21+V under load, so the 1000W from each motor will require ~50A each.

However, if you supply 6S to a 3700Kv hot wind motor attached to a Wemotec 70mm fan, the motor will pull a LOT of current (WAY more than 50A!!!). You will far exceed the rated power of all components. Higher Kv doesn't mean more performance. The Kv must be aligned with the cell count to achieve the target current, and 3700Kv is simply too high on 6S. If you are set on this Kv then you will be limited to 5S max (my set-up), and the motors will need heat sinks to handle the scary power draw (my 2W-20 is heat sinked, and I am careful not to spend too much time at full throttle).

There is no weight penalty from going 6S - you will need a lower Kv motor (the HET 2W-25 has a Kv of 2500 and is well matched to 6S performance on a Wemo Mini fan) to get the 50A. If you went 4S each motor would need to draw nearly 75A (33% less voltage needs 50% more current to get same power - see how it works?). The higher current draw on 4S would need more cell capacity. E.g. 6S 3000mAh would become 4S 4500mAh - no significant weight difference. Required mAh depends on your flight time requirements and how reserved you are with throttle. I can help you with this requirement too if you wish.

As for the ESCs, it depends if you take my advice and go 6S with 2500Kv motors, or a lower cell count with higher Kv and higher current draw. Note that each motor must have its own ESC. There are lots of good ESCs at Hobby King, and even at 6S you've got no issues with high voltage. I like the Turnigy DLUX ESCs - the heat sink cases work well, and the 6S capable type have switching BECs. ESCs are all much of a muchness in this low voltage range - you won't necessarily get more power from a "quality" ESC. Paying more dollars is also not necessarily indicative of quality, especially at HK. I'd steer clear of the Super-simple ESCs, but the Plush range, K-Force, DLUX, etc. are all good. Select one with a current rating that is a a good margin higher than your peak, e.g. if you go 6S, select a pair of 70A+ ESCs, whereas if you go 4S go 90A+. I hope you see the light and go 6S.

I hope this helps and you don't feel I was "talking down" to you. Based on your questions you were not aware of what I've discussed here.

Cheers,
Straight Up.

Straight up, Your absolutely right. I had been looking at the weights and dimensions of the Turnigy 40c in both 4s 3700's vs and my latter alternative 6s 2650's. It appears there is no real weight difference and in some cases the 6s are smaller in dimension and weigh less. Time I reconsider. Thanks.

Thanks... that was my next question. So my current plan is to use 2900 kv Velocity motors on 6s for 1900w peak power. I am thinking I should pair them with Castle Ice 100A esc's that can burst at 170A. This would provide more than enough power and allow me to use my 6s 40c 5000mah Gravity Lipo's from my 90mm F18. I should have the room hopefully for the one battery and wont need to worry so much about using two lipos.(I'm getting tired of buying different size batts every time I get a new plane)