[rdeis]

I have a 24" shockflyer-like SU-27, and a 3200Kv mamba motor.

Can someone reccomend a Cell count prop combination that would work well?

All-up weight should be in the 8-10 oz range, and the max prop diameter is 6". I was using a 3 blade 6-3 with a 1320Kv outrunner, which was fine, but I'm hoping to keep up with the little 17" guys and their Feigao's...

[Kai_Shiden]

Originally Posted by rdeis

I have a 24" shockflyer-like SU-27, and a 3200Kv mamba motor.

Can someone reccomend a Cell count prop combination that would work well?

All-up weight should be in the 8-10 oz range, and the max prop diameter is 6". I was using a 3 blade 6-3 with a 1320Kv outrunner, which was fine, but I'm hoping to keep up with the little 17" guys and their Feigao's...

Hi rdeis,

I've been doing quite a bit of research into the 6" prop sizes, however I haven't found specs on a 3200kv mamba motor I only know of 3600kv (I think it's discontinued), 4200kv, 5400kv, and 6800kv. If you know the motor constants for your motor I can probably come up with a good combo to try out. Additionally I don't know what battery chemistry you wish to run (NiMh or Lipo)

I've been playing with this page: Chuck Gadd's Electric Flight Calc (if someone has motocalc and can run some numbers for you their results should be closer real world numbers)

I ran some numbers for the 3600kv (since Azarr has them on sale). If you run a GWS EP4025 DD, then it should give close to 10.7oz of thrust, at 26k rpm, at 61.7mph pitch speed, at 10amps on 3cell lipo (10v under load).

Any 6" prop I know of would over amp it direct drive on 3 cells, but if you wished to use a gearbox you could use a GWS EPS400C-A (2.14:1) gearbox with a 3600kv Mamba, and APC 6x4E thin, for 13.8oz of thrust, 12,700rpm, 48.3mph pitch speed at 9.1amps (same 3cell and 10v).

These numbers are not real world tests, but simply estimations run from a calc page.

-Kai_Shiden

[rdeis]

4x2.25 and 3 cells, I'll try it- thanks!

Can you run a 3x3 as well?

[Kai_Shiden]

If it is the Mamba 3600kv, the 3x3 (measured is more like 3.25x3), 7.2amps, 9.2oz of thrust, 86mph pitch speed but a risky 30k RPM (10.5v under load, from 11.1v resting).

On my feigao 12mm 4100kv DD on 3 cells, I sometimes blew up GWS 3x2 props at 25k RPM, so I'm not sure I would trust running a larger motor direct drive on them over 30k (which the above combo would do with a full battery pack). The pack I'm simulating is close to what my Etec 1200HP's do under load (tweaked with the settings in the calc until they matched what my medusa power analyzer shows, based upon my Razor400 in different configs).

If your motor is equivalent to the Himax 2025-3200 (which I believe was what you said in your post in the "flying wings" forum), then the numbers come out pretty close, 6.4amps, 9.3oz of thrust, 86mph pitch speed, 30k RPM (10.6v under load). But, the Himax 2025 is a heavy motor (over 2oz), the reason the numbers come out similar is that the Mamba is a lower amp motor than the 2025, so it ends up with it's rpm dropping under the load more. The 2025 is a 15amp + motor so it's not even really working hard under this setup.

-Kai_Shiden

[rdeis]

Originally Posted by Kai_Shiden

If your motor is equivalent to the Himax 2025-3200

That is my understanding, but I could be wrong. I got it as part of a sale package at NSP last December. That current fits my battery better, but I don't want to blow up a prop..

[Kai_Shiden]

I think you'll probably be fine at 30k rpm, my props were pretty abused. I ran them on a 16.5" SU-37 with fixed landing gear off of a concrete parking lot, so it used to suck up small debris and chip the props (weakening them a little bit).

Just make sure to test it off the plane first, the prop will unload in the air but I've heard of people using gws 3x3s on Razor 400s on 90mph wings without significant problems (probably pushing 40k RPM in flight). Also keep a watchful eye on the condition of the props (check the center hub for signs of stress cracks).

If 6amps is what your battery packs are happy with, then the voltage depression will probably keep you under 30k static.

-Kai_Shiden

[jumpinj]

I'm thinking of purchasing a brushless motor and am looking for something
that would work direct on my SU-27 and also in a GWS gearbox on
my SS. Would the Mega 16/7/8 work in both of these situations?

Thanks,

Jon

[rdeis]

Originally Posted by Kai_Shiden

If 6amps is what your battery packs are happy with,

They're rated to 9, just under the 4x2.5 predicted draw. I'll grab some 3x3 and a 4025 and see what the wattmeter says-- many thanks!

[Kai_Shiden]

Originally Posted by jumpinj

I'm thinking of purchasing a brushless motor and am looking for something
that would work direct on my SU-27 and also in a GWS gearbox on
my SS. Would the Mega 16/7/8 work in both of these situations?

Thanks,

Jon

Hello Jon,

Jurgen is running a Mega 16/7/8 on his SU-27XXL

Originally Posted by Jurgen Heilig

Hi Rich,

Mine uses a lighter brushless motor, a lighter ESC, a much lighter battery pack, lighter RC gear and weighs just 320g - with 550g of static thrust.

My MEGA 16/7/8 draws just over 15A static from a 3s1p Kokam 740 and an APC-E 6x4".

Jürgen

I would be wary of running that particular MEGA in the configuration that he is, the motor is a 10amp motor (see specs at edogfight), he is only seeing 15A because his batterys are the amp limiting factor, he doesn't mention that at 15A his battery pack is probably voltage depressing to about 2.7v per cell. If he were running large packs with better voltage retention, it would run up to over 20A (admittedly producing over 700g of static thrust, but also burning out quite quickly). The 740 20C kokams would burn out if full throttle were used for too long in his config, but for indoor flight the throttle couldn't be pegged for much time so the bursts should be short enough to allow the cells to recover.

For use in the SU-27XXL I would suggest the APC 4.7x4.2, it should produce 18oz (510g) of thrust, 81.7mph pitch speed, at 10.2A, 10.3v, and 20,500RPM, a much more comfortable config for the motor, in all flight regimes. Ideally, finding a motor that would comfortably be able to run a prop that fills the prop slot on the SU-27XXL would be best, theoretically the larger the prop, the better potential efficiency it has.

For your Slow stick, if you have the 400C gearbox, then the E gearset (3.4:1), with a 10x7 prop, should produce around 25.8oz static thrust, 40.6mph pitch speed, at 9.2A, 10.4v, and 6100RPM. You could go to a D (3:1) gearset at the expense of higher amps with the same 10x7 (about 12A static), with the slow stick you will always be moving (except for takeoff) so the amps at static are going to be higher than what the motor will see in flight.

-Kai_Shiden

[Kai_Shiden]

Originally Posted by rdeis

They're rated to 9, just under the 4x2.5 predicted draw. I'll grab some 3x3 and a 4025 and see what the wattmeter says-- many thanks!

rdeis, you're welcome.

That's very good, running under the rated amp draw significantly improves cycle life of lithium cells. Plus it's always nice to have decent flight duration.

-Kai_Shiden