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Old Jan 25, 2005, 05:39 PM
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Skaneateles, New York
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Question
e-flight outrunner w/ (?x? prop.) on a 28" wing and 3 cells=FAST?????

Hi all, I have a 28" wingspan flying wing with a clark Y airfoil and a 3 cell 1320 lipo or a 2 cell 730 lipo. My motor choises are a brushed J250 or a eflgiht outrunner 1360KV. This is my second wing, im more of a 3d guy but I want something fast, What settup will be fastest and what prop. I would like something that would work with both batteries.
thanks Sammy
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Old Jan 25, 2005, 09:33 PM
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Old Jan 26, 2005, 06:06 AM
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Bump .o.o.o.o. ^^^^^^^^^^^^^^^^^()()()()()()()&&&&&&&&%%%%%%%%
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Old Jan 26, 2005, 12:39 PM
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Airdrie, AB Canada
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I don't have this outrunner. But it is pretty close to an axi 2208/26.

Here is some data that will get you in the ball park on props and speed:
http://www.flyingmodels.org/motortes...xi_2212-26.htm

I'd start with a 7x6 and keep cutting it down until I got the rpm and amps I was looking for. 12300 will get the pitch speed up around 70mph. Which is possible on 3s.

The j-250 is a different animal 4x4 is the biggest prop and probably only decent for 2s. On 3s take a 3x3 and cut it until you are satisfied with the amps and rpm. You'll need to get both props around 20k to get over 50mph.

I have a j-250 I bought for a 24" wing. Tested it on 4x4 and 3x3 and it was working very hard. I cut the prop significantly to get the amps right. Never bothered installing it... went with a himaxx 2015-4100 on a 4x4 instead. Way out of spec it will do around 100mph when flown hotliner style. That feels quick on a tiny wing. ;D

Mike
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Old Jan 26, 2005, 01:30 PM
Fly, Crash, Build, Fly!!!
Sammy B's Avatar
Skaneateles, New York
Joined Mar 2004
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Hey thanks, I am looking for a 100 mph settup with my 3 cell battery....
My choisses are:
the outrunner
a razor 300 with a 4.4:1 or DD
or the J250
what do you think?
thanks, Sammy
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Old Jan 26, 2005, 03:25 PM
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I don't know if you can get the outrunner to 100mph. On 3s lets say 10.5v under load you can theoretically get 14280rpm. You'll need 13200rpm on an 8 pitch prop. You can get more thrust with the outrunner, likely have better launching and flying characteristics, but it won't be as fast.

The j250 can't handle the power levels of the brushless motors. It is cheap, but will suffer in both top speed and thrust.

The razor 300 is probably a little hot (4900kv) to run with a DD set up. It might be perfect on 2s. Stick a 3x3 on it and measure the current and rpm. I've seen the 350 (4200kv) used DD on a 24" wing 4x4 prop. It'll unload to over 25k in the air which gets you to 95mph.

I cut down a 4.7x4.7 till it would hit about 23k static. This was on a tiny wing designed to fly at 4oz. Stapped on my Gen 2 tp2100's. Doubled the weight and let it rip. Funny thing was it didn't mind the weight at all. Launched like a rock, but didn't do anything crazy.

NOTE: this is 200w on a power system designed for 100w. Understand that these tiny motors can NOT take this kind of power for long. Airframes don't tend to last long with this kind of wingloading and power either. Pushing the limit will eventually cost you money.

The outrunner will probably be an excellent choice. Great thrust and good speed. Anything over 50 with a tiny wing down low and tight will keep your heart rate up. I would certainly see what kind of prop the razor will swing.

Go slow. Check temps and current. Work up to the extreme slowly and you'll save the equipment. You've got all the necessary ingredients for a good time.

Mike
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Old Jan 26, 2005, 04:23 PM
Fly, Crash, Build, Fly!!!
Sammy B's Avatar
Skaneateles, New York
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Hey thanks man! I apretiate it! So what would you reccomend stsrting with? The razor 300 or the outrunner? And with what prop for 3 cells. I will start big and cut it down. You said that you cut a 4.7x4.7 dowwn? On what motor? Thanks Sammy I appretiate this man, I am more of a 3d guy so I don't have to much experience with wings.
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Old Jan 26, 2005, 04:30 PM
Fly, Crash, Build, Fly!!!
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Hey, I think that I would like to use the outrunner on this. do you think That I could trim down a 10x4.7 with the outrunner on 3 cells?would that pitch be slow?
thanks Sammy
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Old Jan 26, 2005, 04:58 PM
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You won't have much pitch with the 4.7, but you'll likely have very easy launches and good vertical. Some guys have run a 7x8 on the equivalent axi outrunner. Parkflyermotors has a spreadsheet with some direct drive numbers as well.

I ran the cut down 4.7x4.7 on a himaxx 2015-4100 to keep from burning it up. Also worked great on a cheap gws 4x4 hd. Your razor is hotter and will require less prop or less voltage.

Wings are easier to lauch and fly with more thrust. So starting with something like a cut down 10x4.7 should make life easier, after that you just keep cutting down the prop until it is too tough to launch, or you hit the speed limit of the airframe.

Mike
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Old Jan 26, 2005, 05:03 PM
Fly, Crash, Build, Fly!!!
Sammy B's Avatar
Skaneateles, New York
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So if I start with lets say a 10X4.7 on the outrunner on 3 cells, the more I cut it the faster it gets and the harder it is to launch? is that right? What about amps? Will WOT be under 15 amps?
thanks Sammy
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Old Jan 26, 2005, 06:14 PM
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Airdrie, AB Canada
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Yep. Just like on a 3d plane. As you decrease the diameter you lose thrust, but it takes less power to spin so you gain rpm and speed. It's always a trade off.

The wing may not slow down enough to be happy on a 10x4.7. Depends on the design and wing loading. 8x6, 9x5 etc might be better, but try a few. The idea is that you don't start off with the ultimate speed prop, as it will be much harder to launch due to severly decreased thrust (acceleration) and possible severe stall when static.

Mike
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Old Jan 26, 2005, 06:56 PM
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Ok thanks! SO If I start with a 10X4.7 on the outrunner, as I cut it down the wing will have a higher top speed but it will be harder to launch right? Again thanks for yuor paitients.
thankls Sammy
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Old Jan 27, 2005, 10:28 AM
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If you cut the 10x4.7 down very far, you'll probably hit the rpm limit of the outrunner do to the low kv. On 3s you won't get much more than 14k. You may need to go to a prop with higher pitch. Depends on the airframe.

It should fly like your 3d planes on the 10x4.7. Lots of vertical and slow forward speed. As you decrease the diameter you'll gain more speed to a point. The outrunner will probably swing a 8x4.7 as fast as a 4.7x4.7 it will just use more amps, but the top speeds will be similar.

You need a certain amount of speed for the wing to fly well. After that you will be trading thrust to add more speed (if watts are constant.) More thrust will always make it easier to launch and give you better uplines.

Mike
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Old Jan 27, 2005, 10:34 AM
Fly, Crash, Build, Fly!!!
Sammy B's Avatar
Skaneateles, New York
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Thanks! So how fast do you think the outrunner will go on 3 cells with a prop somewhere in the range of 4-8x4.7? My 3d planes are slow but they 3d well with a 10X4.7.
thanks Sammy
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