Hi All,
 I've seen in a number of posts that target RPM should be in the region of 70-80% of the rated Kv*Pack Voltage. I've always based the battery voltage on nominal voltage. Is this correct? I was reading the thread on the Imitation conversion and Igor mentioned 2.8v per cell (A123) at the end of a flight. I'm still rattling my E-Streak around (AXI2820/08 [1500kv], CC45, 3s1pA123) and was wondering if I should really be running a smaller higher pitch prop, or just a higher pitch at less revs than I am. I'm currently turning an APC E 10*5 at 9600, which is actually about 65% [nominal] but I needed a bit more duration so slowed it down a bit until I was still able to keep control in the overheads.

Alternatively should I really be basing my calculation on 8.4v (2.8v per cell)? This gives me ~8800 and then go for more pitch (I can't really get more than a 10" prop on the streak and still have clearance for take off's).

If I should be basing my calcs on end of flight condition what would be the base voltage for a Lipo cell as I'm also running an old Goldberg Buster but this time with Scorpion 3014/16, CC45, 3s1p 2500Mah. For this I have arrived at ~9500 again with an APC E 10*5. Should I perhaps be running a 10*7 at lower RPM to allow for end of flight conditions?

Sorry if this is all a bit basic, but every new thread answers questions and then poses a few more.   

Thanks in advance

TTFN
John.

Hi All,
 I've seen in a number of posts that target RPM should be in the region of 70-80% of the rated Kv*Pack Voltage. I've always based the battery voltage on nominal voltage. Is this correct? I was reading the thread on the Imitation conversion and Igor mentioned 2.8v per cell (A123) at the end of a flight. I'm still rattling my E-Streak around (AXI2820/08 [1500kv], CC45, 3s1pA123) and was wondering if I should really be running a smaller higher pitch prop, or just a higher pitch at less revs than I am. I'm currently turning an APC E 10*5 at 9600, which is actually about 65% [nominal] but I needed a bit more duration so slowed it down a bit until I was still able to keep control in the overheads.

Alternatively should I really be basing my calculation on 8.4v (2.8v per cell)? This gives me ~8800 and then go for more pitch (I can't really get more than a 10" prop on the streak and still have clearance for take off's).

If I should be basing my calcs on end of flight condition what would be the base voltage for a Lipo cell as I'm also running an old Goldberg Buster but this time with Scorpion 3014/16, CC45, 3s1p 2500Mah. For this I have arrived at ~9500 again with an APC E 10*5. Should I perhaps be running a 10*7 at lower RPM to allow for end of flight conditions?

Sorry if this is all a bit basic, but every new thread answers questions and then poses a few more.   

Thanks in advance

TTFN
John.

John,
Basing the target rpm on the nominal voltage is probably fine. The reason is that you need to have maneuvering power at the end of the pattern when you hit the overhead 8's and clover on a nice windy day! At least with my setups, the peak power is about 30% higher than my level lap power needs (450 watts vs 300 watts for my Nobler setup. At that time my 4s pack output voltage is running about 13.8V. I note that using the nominal voltage gives 14.8V!

On my Nobler setup, the target rpm (70%) would be 0.70*14.8V*880 rpm/V=9117 rpm. I actually fly at 8000 rpm with my 12-6 prop. On my Vector, the motor kV is 780, so here the target rpm would be 8080 rpm , and in this case, I also fly at 8000 rpm with the 12-6 prop and it seems to work without the rpm sagging in the overhead 8 or clover.

I see that my Phoenix Ice has shipped ( ), so once I have it, I plan to put it in the Vector, and see how close I am actually getting to full throttle. That will be interesting.

Anyway I find that I still have enough overhead to have the needed power to keep the rpm constant.

Thanks for the replies, and clearing that up. I definitely am going to get some of the pusher props to give them a go, I've not heard anyone say anything but good things about them but I had always been put of as (at least in the UK) choice seems limited, there seems to be nothing between a 9*6 and a 12*6, plenty in the smaller sizes, I guess because of all the small pusher foam ARF RC Jet types available. I'm currently putting 1450->1480Mah back into my Lipo at the end of a Buster flight (33oz) and getting a full 5 mins flight time for that.  The E-Streak is pulling about 1850-1900Mah out of the A123's for 4:25 but field repairs over the past year means that's now become a porky beast at 36oz and I do throw it around the sky a lot for that.

I've been messing around learning the OTS schedule and was thinking of campaigning an electric model next year. I really fancy a Jameson Special but it looks like it has a very thick wing section and I'm not sure it would be happy in the winds we seem to get over here. One of the other club members has suggested a Barnstormer. I want a reasonable size 48"+ and Flapless. Power train is open to suggestions. Any thoughts on an ideal model?

TTFN
John.

Doh, 2nd post and it's a sticky thread as well 32 oz RTF sheesh!  I'm hoping to get some plans in a week or so I'm willing to bet mine will end up a bit heavier than that though.

TTFN
John.