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Old Jan 03, 2007, 12:01 AM
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Joined Nov 2004
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House of Balsa 1/12 scale - Motor question

I am sure that this has been discussed on a thread before.

What is a good power system to use with the House of Balsa 1/12 scale stand-off kits.

They make a P-51, ME-109, FW190, P-47, Bonanza, and a Chipmunk.

I am building the chipmunk and here are the stats.


Wing area: 216 sq. in.
Wing span: 36 in.
Length: 28.5 in.
Weight: 20 to 28 oz.
Engine: TD .051 to.10
Wing loading: 14.6 - 18.6 oz./sq. ft

Input is greatly appreciated.
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Old Jan 03, 2007, 05:04 AM
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manuel v's Avatar
Mexico, BC, Mexicali
Joined Aug 2004
5,422 Posts
You stall speed for 20,24,28oz is 19,20.22mph.
for 50 mph. Max speed.
APC7x5e, 10600revs. 81watts out., 17.3oz thrust. For 60% eff. you need a motor with 10.5v, 12.9A, 135W. in. and 1300Kv. for 70% ef. maybe 1150-1200Kv.

APC8x6e, 8800revs. 102watts out., 22oz thrust. For 60% eff. you need a motor with 10.5v,16.3A 170W. in. and 1100Kv. for 70% ef. maybe 1000Kv.

For 66 mph. Max speed.
APC6x5.5e, 12700revs. 76watts out.,12oz thrust For 60% eff. you need a motor with 10.5v, 12A,126W. in. and 1400Kv.

All motor Outruners, 1.6-2.5oz.
Calculated with. motor xl, motocalc and drivecalc.

you frame = 15.8Oz. and you setup with battery 3s 1p 1200=8.2 oz.

Manuel V.
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Last edited by manuel v; Jan 03, 2007 at 05:12 AM.
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Old Jan 03, 2007, 06:02 AM
It's a Great Day to Fly
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Melbourne Beach, Florida
Joined Jan 2002
3,869 Posts
AXI 2217/16 would be one option with a bigger prop, 9x7 or 10x6.
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Last edited by LenBFP; Jan 03, 2007 at 06:21 AM.
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Old Jan 03, 2007, 06:26 AM
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In my home
Joined Jan 2006
775 Posts
A friend gave me the 1/12th Bonanza kit. I guess I need to break it out as well.
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Old Jan 03, 2007, 06:50 AM
Dr John
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Lake Placid, Florida
Joined Dec 2001
2,712 Posts
Here is a couple of pics of my HOB 1/2A P51 "Miss America".

AUW=28oz
AERT
3s 2100 lipo
CC Phx25
Astroflight 19 inrunner direct drive
APC 8-6 8-8 7-9
Hand launch belly flopper
Straight and level 60-70 mph

John
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Old Jan 16, 2007, 02:39 PM
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Joined Nov 2004
111 Posts
E-power for HOB 36"-ers

One of my first efforts at e-power was to convert my existing HOB P-47 (MPJet .06 diesel powered) to electric. E-powered, my P-47 weighs 24.1 ounces, and is set up with all four flight functions plus Robart 1/2A retracts (which is why it's a bit heavy for that much wing) [BTW, all the HOB 36" kits use essentially the same wing at about 220 SqIn]. On an APC 8x4 E prop, it was a missile--far too fast--, so it flies now with tamed authority on a regular ol' 8x3 wood prop. 10+ minute flights on a 950 mah 23C LiPo pack. Full throttle pulls 12amps, which is 88 (input) Watts/Lb, and is PLENTY for this much airframe. It will cruise (maintain level flight) at about half that much juice. I ended up with about 3 degrees of downthrust and 2 degrees of right thrust to keep the trim changes from power on to power off at a minimum. All the HOBs will be pretty much the same, since they all use the same moments, same wings, same tail volumes--they just fudge the outlines. Mine is also converted from bubble canopy to razorback.

My power setup is this: KMS 31/21 bell-type outrunner and matching KMS 18A ESC. The P-47 was such a success that I immediately turned around and bought another combo set for some other similar project or a twin. You can buy both as a combo for under $50 at http://www.hobbypeople.net/combos/999841.asp. The only thing that was confusing for me was the setup for 2- vs 3-cell selection. There is no programming to the ESC; to set for 3-cell use, you simply remove the "jumper" attached to the extraneous lead. I thought this was odd, since when you do that, you leave two pins exposed, so I covered/insulated them with a bit of tube and a piece of tape. It works fine, with no fuss. I've had no issues with pulling the current needed for all 4 servos thru the ESC. I'd post some photos, but I don't have them available here at my office; if you reply to this and request that I do, I'll post some next time I'm online from home. It's pretty fun watching this little thing tuck its undercarriage up after takeoff. The airframe is getting a bit tired these days, but it's still presentable.

One other thing: if you build the Bf-109, the stab setup will not be correct, and you'll have to shim the trailing edge of the wing (or do something at the tail during the build) to get the decalage correct and eliminate "pitch-twitch." I avoid these kinds of issues by converting these "sort-a-scale" projects to a flying stab setup, which avoids any such issues. I would recommend this modification for all of them, as it sure makes things better.

And in case you're interested, HOB had more than just the kits available now. My memory is that originally, they had a P-40, P-39, Macchi 202, and maybe some others, but this trivia is taxiing my memory. Maybe plans for those others are still available somewhere.

The power setup I described above will work fine for any of the HOB 36" kits. I would keep the weight down to below 24 ounces, if you can. Mine is no big deal to fly, but you don't do much "floating" or "stretching the glide" with it at that weight!!

And, no, I have no connection with Hobby People--I just went shopping for a cheap setup and I think I got lucky with what I bought, so thought I would pass the info along.

JGO
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Old Jan 16, 2007, 02:40 PM
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Don't forget the retracts!!!
JGO
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Old Jan 16, 2007, 03:30 PM
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Canada
Joined Nov 2000
7,270 Posts
Having owned a few of these things when they were new :_) The power requirement was (in real life) a TD .09 .. Otherwise they were just hi speed misiles onna .051 no power for aerobatics.
Basic problem is the things were built like bricks .. way overkill in '75 . Just plain laughable on '07 Way toooo much weight. Best advise is to use the plans and build a much lighter model use 1/6 for the fuse, substitute light balsa everywhere else and discard all the light ply, it only adds weight. .don't.. sheet the wings and only use the actual canopy part of that goofy vac formed upper bit. Try for a sub 10 ounce , painted ready to fly (sans all Electrics) model.. THEN it will perform in a style befitting what it is a Model of.
G'luck.
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