Will I be able to get 25+ minute flights with a J250 on a 26" wing? - RC Groups
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Jul 13, 2004, 06:45 AM
Hogster's Avatar

Will I be able to get 25+ minute flights with a J250 on a 26" wing?

Subject says it all really. I'm currently using a 7.2v CN12-R-XC motor on my Miniwing, spinning a GWS 3x2 prop on a 2s1p pack of 1200mAh Kokams. I'm getting at least 25 minutes from this setup of nice docile flying (after that flight only 60% of the packs' capacity was put back in, ie. there's more fun to be had!), and it's very relaxing to fly, and I find it's good for winding down after flying more energetic models.

Now the thing is, I want more power! Hehe don't we all! I've got a J250 motor here and some 4.5"x4 props (can be cut down to 4"x4) and I want to know from all you J250 fanatics out there whether I'll still be able to get such long flight times from the same pack. I'm not looking for ballistic performance - I still want to keep the current docile...ness of this plane, but have the ability to climb steeply when required (to get up to a super height for example). Will it still fly slowly(ish) with a J250 on a 4x4 at a low throttle %? Will I still get long flight times? Or would I be better off going for something like a 3x3 prop on the CN12-R-XC motor? Here're some pictures:

Any thoughts are much appreciated.
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Jul 13, 2004, 12:41 PM
Lookin' Good. Real Good.
larsy87's Avatar
I have a scramblur, 20 inch with with J250 and 4x4 prop. I get abou 13 minutes at WOT with a 2s 1500 kokam. If I throttled back, I could squeeze 20, but I don't want to

I think the average draw with a 4x4 prop is 7 amps, so:

1.2/7 = 0.171 h, which is 10 minutes. This is at WOT, and makes sense because I get 13. Since you have a larger wing, you could throttle back and still get 20 minutes.

Jul 13, 2004, 01:08 PM
Hogster's Avatar
That's encouraging!

I like the way it flies at WOT on the 3x2 .... which is at around 19,000 RPM. If someone could work out the thrust from that and see how it compares with the thrust from a J250 on a 4x4 at the same voltage, that may prove informative.

Thanks Cam!

Anyone else?
Aug 09, 2006, 05:31 AM
Striving to Rip the Bring
raptor22's Avatar
Aug 09, 2006, 01:17 PM
It's been a while.
Daniel G's Avatar
He's got lipos.
I'd say brushless.
That wing would be perfect for a higher kv cd motor.
Unfortunatly, I've never used any brushed motor besides a sp400 so I can't really say how the j250 will perform.
However, using Webocalc: http://flbeagle.rchomepage.com/softw.../webocalc.html and assuming that your wing is around 10 oz, it should fly fine.

Edit: Raptor, why on earth were you up at 2:30!
Aug 10, 2006, 06:43 PM
Registered User
I have flown a 24" speed wing with the johnson 250 many many times. Youll never get 25 mins on a 4x4 prop. Id say more like 12-15 mins if your easy on the throttle. I tend to fly mine at WOT all the time and id get aroudn 10 mins.

you might want to try a feigo brushless and keep the same 3x2 prop. it will be more effecient then your brushed motor but still keep the longer flight times.
Aug 10, 2006, 09:21 PM
Make 'n Break!!
roosevelt's Avatar
or use the j250 w' a 4x2.5 prop. You should have plenty vertical. I did it on a 16" delta wing and it hauled w' almost unlimited vertical that plane was 7 oz w a 850 2s pack. I think if your plane is over 10 oz it might have a hard time. The 4x4 might end up frying the motor. Mine drew about 5-6 amps w' above prop, a little less w a 3x3 and it would barely fly w a 3x2.