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Old Timer
01-02-2006, 02:44 AM
I have a Balsa Products Eng "replica kit" of the Brooklyn Dodger Old Timer free flight model that I would like to make my "first" electric model airplane. This kit was re-designed for R/C and is 30% larger than the original.

Wing Span 71 INS.
Wing Area 788 SQ. INS.
Length 52 INS
Weight 3 to 3 1/2 LBS.

It's a three channel model.

I was looking at the Hobby Lobby web site but I'm not sure what size motor I should buy. I'd like to order from Hobby Lobby as I have had good service from them in the past and I can buy "matched" components.

This is a Big Floater so I would rather have a longer run time over vertical performance.

Any help that you can give me would be greatly appreciated.
Thanks in Advance.
John

Rugar
01-02-2006, 02:56 AM
I would think a Axi 2826 with a Jetti 40 ESC on a 3S2P would do the trick for what your wanting to do. Im not sure if the 10 or 12 would be the best for you.

Old Timer
01-02-2006, 03:19 AM
Well, I figured out what the Axi 2826 motor and Jetti 40 are...What is a 3S2P? And what does the 10 or 12 dilimter mean? Smiles

This is my first electric so...it's a bit over my head.

Rugar
01-02-2006, 04:20 AM
The 10 turn will be a little hotter motor producing a little more power but at the expense of having to use a higher amp draw on your batteries. 3S2P is two 3 cell batteries wired in parallel which gives you more battery capacity for longer run times, and the ability to use a higher amp draw then just using one 3 cell battery.

Old Timer
01-02-2006, 05:24 AM
So either will work but the 12 turn isn't as "Hot" a motor meaning it doesn't rev as fast? Which would use the smallest propeller?

What would you estimate the weight of a system like this to be? Best Guess...

I appreciate your help.

Thank you for your time.

ragbag
01-02-2006, 10:44 AM
John,
Here is a thread that I started using the 2826/10 in a Kadet LT 25 conversion. It has some input from other people that have used this motor also.
Might give you somethings to think about.

http://www.wattflyer.com/forums/showthread.php?t=1012

I won't go into all the data I have but I have gotten over five pounds of thrust from this motor on 3s2p4200 Polyquest 12c packs, 13x8.5 MAS.

The LT came in a 4#8oz all up weight. Ready for a test flight as soon as my buddies get theirs finished and we do it together.

I will be following your thread, lots of pictures please.

By George

Ben
01-03-2006, 07:53 PM
Seems everyone feels that vertical is what we all need - impressive, but not exactly casual sports style. The Brooklyn Dodger conversion looks like a .40 wet candidate or?? My problem also. Some assumptions: a .40 wet will deliver ~1 hp, or ~760 watts(!?), a 3c lipo @ 11 v, supplying 70 amps (70!!!) will perform similarly, with appropriate (?) motor - that's 7000mah from a 1s with a 10C discharge, or 3500 from a 2s - where have I made a mistake? Where does one find a table that shows amperage ratings of available motors, the efficiency of same with various props, the limitations of available battteries, etc? I know the answers are relatively complex and appreciate where Old Timer and his Brooklyn Dodger are coming from, but where is the book "electrics for dummies" that most of us need??

Old Timer
01-03-2006, 09:25 PM
Ben, the kit/instructions doesn't list a recommended engine size but I figure that a Schnerle(?) ported .25 or an old by-pass port .40 would probably work as it was an old Free-Flight model at one time.

The plans don't even call out a C/G. there is a note that says;

In the 1940 era the CG location generally was not shown on the plans. Models with lifing stabs were commonly balanced to as much as 70% behind the leading edge. We recommend starting out with a safe CG of 30% behind the leading edge. For optimum glide the CG may be moved aft untill it is achieved.

I'll have to purchase the motor and batteries prior to construction of the fuse to see if I can make them fit.

I'd like to go electric on this model because "to me" it's so cool looking and I'd like to hang it on the wall in my house when I'm not flying it. Something I really don't like to do with my glow powered planes. I'd also like to cover it using silkspan and give it an "Old Timer" look.

I think I'll call Hobby Lobby and see what they recommend and go from there.

Rugar
01-03-2006, 09:29 PM
I think I'll call Hobby Lobby and see what they recommend and go from there.
Good idea. Please let us know what they recommend.

BradT
01-04-2006, 06:21 AM
Old Timer, and Ben:
Your "Electric for Dummies" book exists in the form of a performance prediction program called "Motocalc", found at www.motocalc.com (http://www.motocalc.com) . You get a 30 day free trial, then an unlock key for $39US to keep the program thereafter. Upgrades are free for life; I originally bought V3.0 years ago, and just upgraded to V8.0 yesterday, at no cost.

The program has a huge database of motors, gearboxes, props, cells, and airframes, constantly being added to by users and the author, and also allows you to input any airframe that you build, or plan to build.

Ben, your comparison to a .40, based on the h.p./watts ratio sounds good, but doesn't pan out in practice. Glow/gas engines produce their h.p. figures at high rpm with a relatively small, low pitch prop (if they ever do reach the advertised h.p.), while e-motors can be matched to a much more efficient large dia., higher pitch prop, at much lower rpm, to effectively fly the same model at much lower h.p./watts. I've been told that the 75" D VII in my avatar would need a .90 to 1.20 with a 16" to 18" prop to fly well on glow; that would be 1500W or more, while it actually flies very well on a 20 cell (24V), 30A setup (720W), turning a 22x12 Zinger at 4000 rpm max. In flight, I am usually at about 35% throttle, so power used is actually much less than the system's capability.

When you first enter e-flight, all the possible combos of motor/gear-no gear/cell count/prop size can be daunting. Start off by copying what works for someone else with a similar model to yours, and you'll get a feel for it all as you build and power more planes, and as you read and ask more questions on this forum.

Hope that helps,
Brad.

qban_flyer
01-04-2006, 03:41 PM
I think I'll call Hobby Lobby and see what they recommend and go from there.

Good call. Ask the receptionist if L. A. Johnston is available for technical advice. He won't steer you wrong. Been dealing with him since '99!:)

cebola
06-13-2006, 02:40 AM
In the 1940 era the CG location generally was not shown on the plans. Models with lifing stabs were commonly balanced to as much as 70% behind the leading edge.

Hello

Old Timer

In http://www.wattflyer.com/forums/showthread.php?t=7495, I am talking about my BD, in fact this is n2, I mean the big one.

On my first BD, the CG location was at 75%, and the nose was a litle bit heavy, the engine for the small one (60") was a Komodo KH 283 V2, and the model climbs very fast.

On my new Dodger, the engine will bee a Hyperion Outrunner Z3025-10 (http://www.asaseletricas.com.br/loja/product_info.php?cPath=8_24&products_id=430) , very powerfull.

But, the CG location I will put on 65%.

Regard's

Cebola
Brazil

Twmaster
06-13-2006, 04:16 AM
I think that AXi 2826 will be more than enough. I have an old Buzzard Bombshell here that is of similar size and weight. When I got it it was powered with a geared car motor. Prolly making ~250W.

On the Glow Conversions page at H-L they show a lot of '40' sized birds with that AXi under the cowl.

My BB, airframe without motor/radio gear weighs exactly 2 pounds.