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Old May 02, 2011, 06:13 PM
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United States, AZ, Yuma
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Build Log
24" foamy B17 build log.

i am planning a 4 engined plane. i am figuring on using 7mm motors turning GWS 2510, getting about 12g thrust each. looking at a 24" ws b17. what do you all think? am i smoking something?
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Last edited by nemoskull; May 06, 2011 at 12:10 AM.
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Old May 02, 2011, 06:29 PM
Gary
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USA, CT, Sandy Hook
Joined Dec 2009
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Well, I just finished a 24 inch span, two engine Skyvan, using two Champ gear boxes and smaller 4025 props (for clearance). (http://www.rcgroups.com/forums/showthread.php?t=1404259)

The AUW is 85 grams and the power was marginal. Measured thrust was only 43 grams. I have just tonight switched to cut-down 5030 three bladed props, cut to a 4 1/8 diameter. Thrust now measures 53 grams. I anticipate that this will serve my needs. My experience has always been that thrust needs to be over 50% of the model weight for successful flying. With other factors also being an influence, i.e. type of wing, wing loading, need for breaking free of ground (my issue with the skyvan), etc. My gut says that you may need to get a little more thrust or the ever popular - build lighter!
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Old May 02, 2011, 11:02 PM
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San Diego, CA
Joined Oct 2005
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direct drive 7mm motors? have you considered brushless? a 7mm pager weighs 2.7 grams and puts out 12 grams of thrust with a 2510 prop. With the 2gram outrunner using the 2510 prop You can get about 20grams of thrust per motor. You would need 4 of the 1 gram esc's but the total weight of four BL motors and four BL esc's is the same as four 7mm pager motors and one brushed esc. You just get about 30 grams more thrust. Might be able to do some ROG take offs with that kind of output.
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Old May 02, 2011, 11:11 PM
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yes, but i can get the whole system for 20 dollars. i would be looking at 50 dollars for the same. one day, but probly not today.
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Old May 02, 2011, 11:30 PM
Looking4Grass in AZ
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United States, AZ, Mesa
Joined Feb 2011
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I think if you use much less foam than that Skyvan had, you'll be able to pull it off. Roll some 2mm foam maybe?
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Old May 02, 2011, 11:43 PM
TheyreComingToTakeMeAway!
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USA, ID, Coeur D'Alene
Joined Dec 2003
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if you make the wing and fuselage out of eps foam, it will weigh probably 4-5 grams for the fuse and 3-4 for the wings, then use some 2mm depron or foam plates for the tail and it'l be light, real light.
i think its do-able but your going to need to watch the current in the brick, 4 of those motors would likely be to much for the brick. unless it was the new twin brick, it should work.
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Old May 03, 2011, 12:20 AM
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Singapore
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If you are using Aero Ace props for 7mm motor it will have 16-17g thrust and motor much cooler than with GWS 2510 prop
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Old May 03, 2011, 03:40 AM
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derk, i was going to use a 3 amp brushed ESC or the ar6400T i have. i havent done the weights yet, so i reay have no idea what i have left for the airframe.
burantio: do you have any hard data? if i could get even 12 g out of them, then i could scale down the plane.
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Old May 03, 2011, 06:38 AM
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Singapore
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You can check this out
http://www.rcgroups.com/forums/showthread.php?t=1413355

First I also don't think it possible so I did the test myself and got the same result.
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Old May 03, 2011, 08:58 AM
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hmmmm...... very intresting. i have a 7mm motor at and and some old AH props. i will have to see.
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Old May 03, 2011, 11:26 AM
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San Diego, CA
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wow that's impressive! Looks like All4smallrc was getting 14g thrust, which is still better than 12. The amp draw is probably lower as well. when you start multiplying it x4 things add up in a hurry.
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Old May 03, 2011, 12:19 PM
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Quote:
Originally Posted by nemoskull View Post
i am planning a 4 engined plane. i am figuring on using 7mm motors turning GWS 2510, getting about 12g thrust each. looking at a 24" ws b17. what do you all think? am i smoking something?
Err . Why not 4 x PKZ3916 Micro J-3 Cub Main Motors 6mm and 4 x Micro Cub Complete Gearboxs PKZ3928 .

The micro Cub 6mm motor and gearbox puts out allmost 20g thrust

4 x 20g = 80g thrust is that enough thrust for you????
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Old May 03, 2011, 12:32 PM
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UNGN's Avatar
Southlake, TX
Joined Jan 2008
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Quote:
Originally Posted by richos View Post
Err . Why not 4 x PKZ3916 Micro J-3 Cub Main Motors 6mm and 4 x Micro Cub Complete Gearboxs PKZ3928 .

The micro Cub 6mm motor and gearbox puts out allmost 20g thrust

4 x 20g = 80g thrust is that enough thrust for you????
The cub motor/gearbox/prop makes over 20g of thrust, but that's with a 4" prop.

With a direct drive 2.5" prop, a 6mm motor probably isn't going to generate 20g of thrust.

They should make 12g - 15g, though and have the best Power to weight ratio if weight is important.

If $ cost is important, the cheapest set up is the $2.25 Playmate/Albatros 7mm motors. These should make good direct drive motor with a 2.5" prop.
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Old May 03, 2011, 12:42 PM
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You must also consider which 7mm motor you want to use. The hottest 7mm (1.7ohm, SS Blue?, JS or Walkera) will give you 14g-16g thrust on a AH prop@1,1A-1,2A current draw. All others will obviously be less thrust, but also less Amps.

A DD 6mm will give you considerably less I think, 5g-8g would be my best guess.
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Old May 03, 2011, 12:50 PM
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Southlake, TX
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Quote:
Originally Posted by speedemo View Post
You must also consider which 7mm motor you want to use. The hottest 7mm (1.7ohm, SS Blue?, JS or Walkera) will give you 14g-16g thrust on a AH prop@1,1A-1,2A current draw. All others will obviously be less thrust, but also less Amps.

A DD 6mm will give you considerably less I think, 5g-8g would be my best guess.
The J-3 motor is pretty hot for a 6mm. It probably can make as much DD thrust as most old school 7mm's.

The Albatros 7mm motor likely makes as much thrust as an "SS Blue".

Nobody has really tested these new motors vs. the old motors, but from the weight of the planes they will fly, they are making more power than most of similar motors in the archives of RCG.
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