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Electric B-17? - 2/22/2013 3:32 PM   
mattnew


 

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From: Haverhill, MA, USA
Status: offline 		 In the 70's my father built a B-17....





its a  ~77inch wingspan, designed to take 4 x  .19 size 2 strokes.....
Growing up I always thought it would be really cool to finish... Dad wouldn't have any of that mainly because at the time getting 4 .19 size engines to run together was near impossible.... we tried... Since he couldn't power it he never finished it. 
Its not finished yet...

But now I have it... and I'm an adult... and we have electric power now!
so whats the holdup? I know next to nothing about electrics... have always been gas/glow my whole life....I'm doing a ton of reading on the subject but I thought I'd put this project out there to see what people would say about it... Your advice and comments are appreciated...





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RE: Electric B-17? - 2/22/2013 3:38 PM   
mattnew


 

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RE: Electric B-17? - 2/22/2013 5:16 PM   
iFLYrc_Vic



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Status: offline 		That is absolutely gorgeous. I would love to have a plaane like that. I am sure you won't sell it so I will try to provide some advice on converting it to electric. there are several steps to the conversion process:
1. Determine the weight of the plane.
2. Use the weight of the plane to determine the amount of pwer required for the model. A good rule of thumb is 100-120 Watts per pound for this type of aircraft (warbird). for example, if the plane will have an AUW (all up weight) of 12 pounds, you should set a target of 1200 to 1440 watts of power from your power system.
3. Choose your motors that will supply the required power. In this case you have 4 motors so each motor should be capable of 360 watts minimum. Most modelrs now use "outrunner" type motors. In short, outrunner motors are more efficient and have a higher power to weight ratio than inrunner motors. On an out runner motor, the out case spins around (motors are an enitre topic in itself).
4. Most manufacturers will specify the power produced by the motor with a specific propeller. Choose a motor that will produce the desired power (360 watts) with a propeller diameter that will be suitable for the plane. This plane looks like it would look scale with 9-10 inch propellers. the motor must also be capable of handling the voltage of the battery you sellect.
Now it gets a little complicated:
6. Select a battery that willl produce the desire power for the expected flight duration. Batteries are rated in volts and mAh(s). The voltage is determined by the number of cells in the battery (listed as 3S, 4S, 5S etc.). A 3S battery has 3 cells with a nominal voltage of 4.2 volts per cells when fully charged. So, a 5S battery will have a voltage of about 21 volts. The mAh rating stands for milli amp hours. This determines how much current the battery can produce in an hour. So, if your power system draws 1200 watts, that results in a current draw of 57 amps from a 5S battery. If you do the math, a 5000 mAh 5S battery will provide 5.3 minumes of flying time at full throttle.
5. Select an ESC (electronic speed controller) that can handle 360 watts minimum. Most ESCs are rated for current draw (AMPs). Each of the 360 watt motors will need a separate ESC. The maximum current draw will be about 17 amps each at 21 volts (5S battery). So you should select 30 amp ESCs to allow room for error.

Now you have a power system that consists of four 360 watt motors that can handle a 5S battery, four 9-10 inch propellers, four 30 amp ESCs and one 5S 5000 mAh battery. This all will change if you change either of the components (motor, battery or ESC). I think I am a little small on the propeller but this is just an example of how to select the power system for your plane.

Hope this helps....

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RE: Electric B-17? - 2/22/2013 8:12 PM   
mattnew


 

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Status: offline 		I'll get some weights shortly for it... need to pull out the bathroom scale.

The funny thing is this has been up on ebay off and on for the past 5 years with no bites :-) I'm not sure what my father was asking though. 


Thanks for the advice, One of the things I'm trying to understand is if I have 4 motors, can I run them off of 1 speed control and 1 large battery? or do I need 4 ESC's and 4 batteries... There is certainly room for the latter since the gas tank compartments would be empty.


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RE: Electric B-17? - 2/22/2013 9:00 PM   
iFLYrc_Vic



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Status: offline 		Are you sure you don't want to sell this plane? If you are thinking about it, send me a private message with your price.

As for motors, batteries and ESCs, you need one ESC for each motor. The ESCs can be powered by one battery (just run the ESCs in parallel - all red wires together and all black wires together). The same applies to 2 batteries. OR, you can run one battery per ESC - pain the butt to discnnect and recharge. I would go with one big battery or two smaller batteries (2 motors per battery).

Some of the newer motors are numbered just like the glow motors. For example, a Rim Fire .10 is equivalent to a .10 size glow motor. Just look around the Internet and you will see a lot of motors numbered with glow equivalent numbering.

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RE: Electric B-17? - 2/23/2013 12:20 AM   
mattnew


 

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Status: offline 		 As she sits right now she is exactly 5 lbs having been already sheeted and fiberglassed.
 
So figure paint radio and motor system, you'd hope you could keep that under 10lbs...
 
so by your math thats about 1200 watts / 4 motors or 300 watts per motor. I was actually looking at e-flights power-25's... But I'm guessing those now would be overkill.

As for selling... Dad was trying to sell it... me ... I want to see this thing fly... 


I've always been amazed at my dad's building skill.... very little filler and super tight joints on all balsa lines on this model. I'd like to pretend mine are half as good but.... :-)





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RE: Electric B-17? - 2/23/2013 3:11 AM   
iFLYrc_Vic



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Status: offline 		Your dad really did good work. You should have enough info to properly setup an electric power system for this plane. The Eflite power 25s would be a good choice since the plane was designed for .19 size glow engines. A little extra power is always good for in flight emergencies. Good luck on your build. Let me know how it turns out.

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RE: Electric B-17? - 2/23/2013 9:09 AM   
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Mattnew, vic is right on about how to power that bird...my Dad started me on the path of rc.. I clearly remember him building the guillows 51 and 40 for control line back in the 70's.. My dad always loved the P-40 so when I had the chance I got him one that we only fly when together.. again Vic is correct about the numbers changing when u decide what to power it with, or rather which outrunner..I'd definitly go out runner.. on my Dad's kyosho 55 p-40 for example , I put in a rimfire 55 motor at 480kv, 60 amp esc from electrifly running two 3300 3 cell lipos for 22.2 volts , 14X10 apc prop at an auw of 71/2 lbs the plane is no slouch for speed the esc I used allows me to run a 6.6 volt flight pack to RX so that I always have control  even if the motor batt runs low..I get honest 8 - 10 min flights this way on a full house bird..ail,ele,rud,flaps, and retracts..consider powering ur servos this way so that the motor batts are dedicated to motor...somewhat some peace of mind knowing the wheels will come down. thats if ya put retracts .But I must say that the 17 is a great looking bird even after 30 years in storage..fly it bro...oh yeah I almost forgot, I get about 1200 watts of power just in case..I rarely go past 3/4 throttle and thats only for the runway straffing runs .
25's would be excellent powerr..I actually found you on ur gp rv-4 page ,I got one nib next upp on the table...I'll keep checkin ur progress.....fly it bro.....




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RE: Electric B-17? - 2/23/2013 12:12 PM   
iFLYrc_Vic



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Status: offline 		gaumflyer, I also use a separate battery to power the receiver on my B-25 and Bonanza. The Bonanza has retracts and it is a good idea to power them from a separate source than the motor battery. I did not want to get into that in my discussion as I was just try to give Mathew the basics. That is more of an advanced topic.

Once again Mathew, that is a great looking plane that you should be proud of. Any other questions, just fire away...

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RE: Electric B-17? - 2/24/2013 1:22 AM   
guamflyer


 

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Status: offline 		yeah thats true Vic...the way your birds are set-up is the only way for me as well...a quick pic of my Dad's p-40 since we doing Dad's plane

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RE: Electric B-17? - 2/24/2013 9:37 PM   
mattnew


 

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Status: offline 		Love the P-40, was always one of my favorites as well. 

thanks for all the replies. 

As of right now... I'm thinking 4 power-25's with ESC's, a battery for the radio and I'd like to try to one run battery for the 4 engines... though it may be easier to run 1 battery per wing, so 1 battery for 2 engines. I'd probably use LiFe batteries so that I could have some safety with charging them in the plane... I don't think I'd want to remove 4 batteries after every flight, or even 2.

I have to get this on the workbench and get it finished before any of that can even happen though! I think this plane will be a lot of fun once done...


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RE: Electric B-17? - 2/24/2013 10:29 PM   
iFLYrc_Vic



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Status: offline 		Mathew, attached is my wiring diagram for the B-25. As you can see, I use two batteries. However, you will also see the "Jumper" wire that connects everything together. this results in the system appearing like there was one big battery powering the two motors. Since the baterries are in parallel, the ESCs and motors see only 16.8 volts (4S) and one side does not dischrage differently than the other due to differences in manufacturing of the motors and ESCs. I use Castle Creations 100 ICE ESCs that have a cutoff switch (no power to motors until switch is turned on - very safe). Therefore, I have three switches, one for the receiver and one for each motor. Again, this is not a simple plug-n-play setup.

As for charging the batteries inside the plane, that is a "noble" thought. If you are going to use a high mAh battery (e.g. 3000mAh to 4000mAh), it will take quite some time (30 to 40 minutes) to recharge the battery(s) after a flight. You will soon find it problematic to sit and wait for the batteries to charge at the field. I recommend at least two sets of batteries to reduce the "sit and wait" time between flights.

We have a limited membership (40) at my present flying club - see attached photo. Of that, only a handful fly regularly. Therefore, we normally only fly one at a time and therefore we can just about fly at will - no long waits between flights. I stopped flying at another field in the area because they had 150 members and the flight line was constantly full with 4 pilots in the air - not my idea of leasure flying.

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RE: Electric B-17? - 2/25/2013 6:42 AM   
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Status: offline 		I like that wiring diagram for your B-25...My Dad's been hinting about one for awhile...LOL

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RE: Electric B-17? - 2/28/2013 3:27 PM   
mattnew


 

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Status: offline 		Thanks for the info! I was asking around my new club last night but it doesn't seem that anyone is flying multi-engine electrics... The wiring diagram will definitely be useful as I continue to learn a bit more here.. This isn't going to be a rush job, likely a year or more before this sees its maiden... which is ok. I'm going to have fun with it. The B-17 was always one of my favorites... such a beautiful plane. I'll continue to post updates as things happen!

Keep the advice coming! All comments are welcome.


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