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Old Jun 09, 2002, 10:11 PM
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S. IL.
Joined Feb 2002
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Need advice on what to power scratch Air Tractor with?

I'm going to ramble about 2 posts worth , so bear with me.

I am scratch building a 44" ws Air tractor (no, not up to certain other peoples superb standards) and I have been thinking of going dd sp-400, or dx-d and possibly 3 bladed gws prop.


I have built the airframe pretty darned light, but used huge tires and lg wire because of my flying fields actual status as a hay field!

If I go speed 400, I'm not sure about the airframe, may have to beef up the elevator a tad, plus the long nose is going to put that heavier motor way out there, I may have to install the battery in the tail to compensate. If I go gws dx-d, I'll have to ditch the heavy duty gear and go for light and ineffectual.

Maybe a speed 280 and gearbox compromise? My goal is to be able to do some scale like low and slow passes, then pull up and around nicely. Don't know how slow I can go with a dd 400.

I'm planning on using a bottom airscoop for cooling, and leave the side windows open for cooling. The bottom wing center, cockpit, and whole upper front 'tank cover' will be removable for access.

Ive been flying my poor old goldberg "Gull" to death (I think I'll call it 'patches') with a DX-A, and I'm wanting to try a low wing (with ailerons) configuration. I may save the speed 400 for a hotter foam (easier repaired) ship.

Thoughts?
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Old Jun 09, 2002, 10:16 PM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
I'd go for a GWS EPS-300. Check out thier website or AeroMicro for the thrust, etc numbers, or try EZcalc. I realy like these 370's.... You can use AAA NiMh 720's with that motor.
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Old Jun 09, 2002, 10:21 PM
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Mike Hall's Avatar
Albany, GA
Joined Jun 2002
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I just bought a EPS-300C for my 44" turbo porter I built and this thing put out some thrust. From what I have read this motor with 10" 7 prop puts out almost 14 oz of thrust. Be careful when playing with these motors. I pluged it up and hit the throttle and it almost flew out of my hand. By the way my porter will only weigh about 10 oz so it should be very powerful.

Mike
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Old Jun 09, 2002, 10:24 PM
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S. IL.
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wow, 14 oz thrust and 10 oz weight..that ought to do it!
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Old Jun 09, 2002, 10:28 PM
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yeah I think its going to be real fun. Here is a pic on the project.
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Old Jun 09, 2002, 10:30 PM
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Albany, GA
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Forgot to attache
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Old Jun 09, 2002, 10:33 PM
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S. IL.
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What kind of LG is that using? Carbon fibre with foam wheels?

ROG in about 2 feet?LOL
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Old Jun 09, 2002, 10:39 PM
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Albany, GA
Joined Jun 2002
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Well thats bambo i got from the super market. those are foam wheels I made up. The bambo seems to be very flexable so I dont think I will have any problems with it. I will see soon.

Mike
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Old Jun 09, 2002, 10:41 PM
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S. IL.
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http://www.toddsmodels.com/gwsmotordata.htm

Looks like my 10A ESC will be ok. Anyone know what compares to a 1047 prop in a 3 blade? Or am I just dense? I like the looks of the 3 blade on an air tractor, plus it gives me another inch of ground clearance (I hope).
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Old Jun 09, 2002, 10:46 PM
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Albany, GA
Joined Jun 2002
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I bought a 10 amp ESC with my motor. I think the 5 amp will work but I went with the 10 so I can get all I can out of the motor.

Mike
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Old Jun 09, 2002, 10:53 PM
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Indianapolis, IN
Joined Sep 2001
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I found the 5A to be a little light for the 370. It shut down after ~ 1 minute WOT...
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Old Jun 10, 2002, 06:59 AM
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Raleigh/Durham Intl, North Carolina, United States
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Looking good! I second the idea of using the gws 370.I have a hobby lobby cub designed for a speed 400 and I swapped everything for the GWS gear.It went from 20+oz to 15oz and flies quite a bit better.What does yours weigh?Wing area?The cub is a little over 300 sqin and empty airframe is 8oz.On your 3 bladed prop,general rule of thumb on the gas stuff I used to fly was to drop down 1 in in diameter from whatever the appropriate 2 bladed prop was.If there isn't one the right size,you can cut one down.
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Old Jun 10, 2002, 07:17 AM
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S. IL.
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Well, it's practically the same right now. 308 sq in, and 7.5 oz with 25% of the airframe covered, no servos or cowling yet, I figure about 10-12 oz, though I can eliminate an oz or two with lighter LG.
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Old Jun 24, 2002, 10:03 AM
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S. IL.
Joined Feb 2002
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D'uoh

got my DX-F yesterday (Yes F...9:1. Wanted to try the 3 & 4 bladed GWS props to see how they work.) All I can say is ACKK! I totally ignored the size of the gear when the ratio is this low. I was thinking of having plenty of thrust at a low speed. The gear is big enough that I will have to center the shaft in the cowl, dropping the motor past the bottom of it. The good thing is, this will put it right out in the airstream where I can cover it with a scoop, tha bad thing is, its not supposed to have a scoop that far forward, and it will be the first part to hit in a crash. (not Like it is scale anyway)

Oh yeah, I think it will work like that ...but I was wondering just how far back I was going to have to mount the battery with this long snout anyway to get the proper cg...Has anyone ever mounted the motor back a ways and used a shaft extention? 1 1/2 " or more would get it all under the cowl. have to support it with bearings..
Hey, I'm turning at a slower rate,(though more torque) than an A or B ratio... The fuse on my model is fat as a whale anyway, plenty of room...and I did make that whole "hood" removeable...am I crazy? Or just silly. (and should go to a higher ratio)

Should I be concerned about the torque rolling the plane at full power? (with the big prop)
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Old Jun 24, 2002, 03:23 PM
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Raleigh/Durham Intl, North Carolina, United States
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CG shouldn't be a problem.On mine I was able to balance it with the batteries just ahead of the wing spar.You should have plenty of room in there. You can make a shaft extension out of a piece of carbon tube. The GWS shaft fits nice and snug inside 3/16 tube if memory serves.Glue the shaft in the tube and then wrap it with thread and apply some thin CA to keep the tube from splitting.Make a front bearing carrier out of balsa and use a bearing from an extra gearbox.It works good but it will make getting the motor out a pain in the butt.I would avoid the complexity if possible.Good luck!
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