On the other board..Al has been showing his seafury build. I am asking here a quesion because I have not seen anyplace else with as much electric knowledge posted.
If a model like the Seafury was to be built for electric how much batter and prop would you expect to need for it.
It just a question? I have not noticed anybody to build any electrics that big though I may be wrong.
 

Jim, at the top of this section " gettin all amped up" there is a sticky thread labeled something like " post your setups here" I think you will find there are actually many airplanes that size listed along with the equipment used in them

What's it weigh*?

Multiply the weight in ounces by 11 -- that's the peak power you need from the motor, in watts.

Go shopping for a motor.

Divide 3600 by the motor kv, and round up to the nearest whole number -- that's the number of cells you need in the pack.

Take your peak power in watts, divide it by 3, then divide it again by your number of cells -- that's the current rating you need for your ESC.

Go shopping for an ESC.

Multiply the weight in ounces by 250, divide by the number of cells in the battery -- that's the battery capacity you need in mA-h.

Go shopping for a battery.

So, to check my math, for a 50oz plane you need a peak motor power of at least 550W.  

If you have a motor with a kv of 900, you need four cells.

550 watts, four cells, you need an ESC current rating of at least 46A

50 ounces, four cells, you need a pack capacity of at least 3130mA-h.

From memory, that's about in line with the 50 ounce planes that are in the "List your setup" thread -- feel free to check up on me, 'cause I'm too lazy!

People are flying 1/4-scale RC planes on electric -- there's motors and batteries available.  The prices may seem insane -- but they're out there.

Note: as others have pointed out, Jack's planes have larger fuselages.  I think they look fairly aerodynamically clean, so I suspect you won't get all that much extra drag.  But I could be wrong.  If I am then you'll drain the battery more, and will need more battery capacity and to a lesser extent more peak current.

* Be warned -- I haven't tried these design equations.  I'm just taking the advise of experts on this forum and trying to make the math easy.  Once you get expert at this, you'll have your own opinions.

What's it weigh*?

Multiply the weight in ounces by 11 -- that's the peak power you need from the motor, in watts.

Go shopping for a motor.

Divide 3600 by the motor kv, and round up to the nearest whole number -- that's the number of cells you need in the pack.

Take your peak power in watts, divide it by 3, then divide it again by your number of cells -- that's the current rating you need for your ESC.

Go shopping for an ESC.

Multiply the weight in ounces by 250, divide by the number of cells in the battery -- that's the battery capacity you need in mA-h.

Go shopping for a battery.

So, to check my math, for a 50oz plane you need a peak motor power of at least 550W.  

If you have a motor with a kv of 900, you need four cells.

550 watts, four cells, you need an ESC current rating of at least 46A

50 ounces, four cells, you need a pack capacity of at least 3130mA-h.

From memory, that's about in line with the 50 ounce planes that are in the "List your setup" thread -- feel free to check up on me, 'cause I'm too lazy!

People are flying 1/4-scale RC planes on electric -- there's motors and batteries available.  The prices may seem insane -- but they're out there.

Note: as others have pointed out, Jack's planes have larger fuselages.  I think they look fairly aerodynamically clean, so I suspect you won't get all that much extra drag.  But I could be wrong.  If I am then you'll drain the battery more, and will need more battery capacity and to a lesser extent more peak current.

* Be warned -- I haven't tried these design equations.  I'm just taking the advise of experts on this forum and trying to make the math easy.  Once you get expert at this, you'll have your own opinions.

pretty sure you can get away with less battery on a 50 plane Tim - I have flown 60+ oz planes on 3000mAh 4s packs at under 75% of capacity...

pretty sure you can get away with less battery on a 50 plane Tim - I have flown 60+ oz planes on 3000mAh 4s packs at under 75% of capacity...

Those numbers came about because I compiled a bunch of data from the "List your setup" thread, and came up with 11W/oz for peak power, and 7W/oz average (either that, or Dean Pappas said that and my numbers just confirmed it).  The rest comes from those numbers, and from targeting 75% capacity use, and derating the battery voltage by 75% for the kv (and assuming 10000 RPM).

So, I can believe that my numbers are high.  To some extent they're intentionally so:  Personally, I'd rather start with a plane that's a bit porky in terms of batteries and motor, then lighten it by getting lighter batteries.  In the other direction you're left trying to diagnose why the thing seems to crap out in the cloverleaf, etc.  And for a beginner to electric power, I think that starting out a bit conservative is good, too, for the same reasons.

Ultimately you have to start somewhere, and then tweak and tune from that point to where you are finding the most joy in your system.

Tim,
I agree with Will, that your equations are definately, very handy indeed, Thanks again.

James

yes a good base point,  but real world learning shows you can do better.

I've never had an electric plane that couldn't benefit from some post-build fiddling.  I say "couldn't" instead of "didn't" because there have been some sport RC jobbies that were good enough for floating around on lazy afternoons, but could have been improved.

Jim
The Brodak T Rex has a massive body also. An axi 2826/12 with a 4s pack (I use 3700 mah Rhino now because I found it gave me better braking than the 3000 mah packs I used to use ) with a 45 amp esc and apc 12X6 EP drives it with extreme authority. Empahsis on the extreme. Number of cells in the pack is largely dependent on the prop you want to turn and the kv of your motor. If you want to use a low pitch larger diameter prop with a lower kv motor like the 2826/12 then you would go to 5S and the 3000 mah pack would be fine. Since I have found the 12X6EP is ideal for me I fly 4S and higher mah pack. Weight of the packs are equivalent between the larger 4s and smaller 5S packs. If you go to a higher kv motor in the 900 plus range you will get higher rpm with a lower cell count pack but you will draw more amps doing it. Its all trade offs, just like in glow. I also fly an sv11 with the same setup. I could not handle more power in the plane than this setup. I did a build thread on the T-Rex and the sv-11 in this forum and they both illustrate the evolution of the power trains I currently use in them and the results of the testing I did. May be helpful to you.

bob branch

Just a note of interest, Al said the Sea Fury will weigh between 73-80 oz with IC set up. One of the reasons the 14" prop is used is the Plane is big and heavy, two the nose is 6" wide and spinner is 3.5 inches in diameter. I  believe John Calentine said he was going to build the Sea Fury with Electric.

I am building one that will have IC.

Picture is the Original Sea Fury hanging in Al Rabe's shop