mattnew

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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...

mattnew

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iFLYrc_Vic

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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....

mattnew

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

iFLYrc_Vic

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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.

mattnew

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As she sits right now she is exactly 5 lbs having been already sheeted and fiberglassed.

iFLYrc_Vic

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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.

guamflyer

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 correctabout 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 knowingthe 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.....




SLOPE FAST - SOAR DEEP

guamflyer


P-40 brotherhood #5 and #6

iFLYrc_Vic

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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...

guamflyer

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

mattnew

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

iFLYrc_Vic

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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.

guamflyer

I like that wiring diagram for your B-25...My Dad's been hinting about one for awhile...LOL

mattnew

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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.

iFLYrc_Vic

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Mathew, if the Power 25 is too big, try a Great Planes Rim .15 motor. It has a rating of 500Watts continuous and 650 burst and runs on 3S or 4S Lipos. With four of these you would have 2000 watts at your disposal. Assuming an AUW of 10 lbs (guessing), that would give you 200 watts per pound! That is way more than what you would need to fly this model.
Vic

BTW - what is the estimated flying weight (AUW) of this model? I have seen reports of 10-12lbs for the Royal B-17.

Dr Kiwi

try a Great Planes Rim .15 motor. It has a rating of 500Watts continuous and 650 burst

Rimfire outrunners have seriously optimistic ratings! [I tested quite a few of the range some years ago]. At 102g that Rimfire 15 should be rated for about 300W continuous (3W/g)... 500W/650W will cook it.

mattnew

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oooooooohhhh blech. I'm in Kv hell I think...

My main hangup is my attempt to run scale props or close to scale props. Scale for this B-17 would be 8.5 inches on the radius, so either a an 8x6 or 9x5 3 blade would be ideal. It would seem the engines though that are good for that size prop aren't going to put out the power that I want.... so we went with buying a cheap test setup so I can mount a set of ESC's and motors to a board and do a bit of hands on learning.

I bought:
4 x Turnigy 3548-4 1100Kv motors, on a 9x5 three blade eCalc shows them producing 50oz of thrust, on a 10x6 that goes up to 75oz. Its bigger than I need, but it also seems to show that flight times should be on the order of 10-15 minutes depending on props.

4x Turnigy plush 80amp speed controllers. Way more than needed, but they get good reviews and are cheap....

I'm taking the wing to my local hobby shop today to see what size battery we can shoehorn into the former gas tank bays.

once I have a full setup I'm going to hook things up on a testbench and see what sort of real world results I get.
I feel like with this setup being a bit of overkill, I'd be stressing the components less and have better long term results. We shall see...
I have mixed feelings about buying the chinese stuff, on one hand they have good reviews, and are dirt cheap...and where I'm mainly using this as a learning exercise I'd rather go with the 15 dollar motor instead of learning on the 80 dollar o.s. or eflite motors. I may or may not fly the plane with these.... I really don't know at this point....

mattnew

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I started doing some panel line work as well on the plane



you'll note the primer is still drying and the chartpack tape is still on the elevator.

And had to create an access panel on the bottom of the wing in order to make modifications for the electric conversion.





One thing I haven't been able to find yet is a set of electric retracts that can handle a 12lb or so plane that retract forward as the B-17's do. Dad had put fixed gear in the model back in the 70's, but I'd really like to swap those out for a set of electric retracts.

Dr Kiwi

Here is what DriveCalc says for the Turnigy 3548-1100 with 3-blade 10x6 GWS HD on 3s. Close to the motor's limit (a realistic limit of perhaps 400-500W, not the idiotic 910W max. given by HK). Other brands of 3-blade 10x6 will draw more. 9x5 GWS HD 3-blade would draw closer to 30A/320W

mattnew

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Thats what I saw as well, I think my thoughts here were, at 16 bucks a piece its at least giving me something to play with and cut my teeth on. they may never make it into the plane itself. or maybe they will.... I need something to mess with, hook up to my oscilloscopes and really learn what I'm doing when it comes to electric.

I'm taking the wing in tuesday to figure out how big a battery we can squeeze in there.. Once I have the battery figured out I'll know a lot about what I can/can't accomplish with the plane.

mattnew

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real world….

Turnigy 3549/4 1100Kv, 80 amp speed controller, 2200mah 3s Eflite battery, 9x5 3 blade prop.

5 minutes at 12000 rpm and we sucked down 820ma of juice from the battery. This is at about 3/4 throttle, I think I need a bigger prop. All in all though, not really sure how to interpret these results. This makes me think I could likely get a 10 minute flight out of a 2200mah battery fairly easily.

mattnew

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This post here is a bit of "thinking out loud"...

I've been trying to figure out how to handle the .50 caliber machine guns on bomber… 1/16 scale is a bit difficult as you don't see a lot of kits for browning 50 calibers in 1/16 and similarly not a lot of other model airplane companies are doing 1/16 scale bombers.

Tamiya has 1/16 scale tanks though, and the sherman's had browning 50 calibers on them, turns out you can get parts for Tamiya's sherman tank line. The barrels of the tank 50 calibers are different, but I'm looking at experimenting using the body of the gun with either a brass barrel or possibly stirene ( sp? )… I'm not loving the brass as its a bit hard to get the drill bit to center properly for drilling… the pictures following are first attempts where I'm really just messing around with practice pieces...


by no means the final product… just trying to think and figure out how to make this work.

mattnew

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the brass rod is 3 pieces fitted inside each other… the soldering to keep them together is easy.. trying to figure out how to center the rod and get the middle sized piece drilled properly has me hung up at the moment. I've built a jig to mount the brass rod on my drill press, however the bits are so thin that they flex when lowering the press.. no matter how slowly. I've "choked" up on the bit as much as I am able to to limit the flex… its still more than I've deemed "acceptable"...

[email protected]

Hey, how about some updated photos of the plane and the remodelled room too !

Bro

mattnew

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Nothing done really yet, I've been working mainly on trying to figure out how to get some of the details into the plane that make a B-17 a B-17. trying lots of new things...

Here is a mockup of the motor nacelles with an idea I was trying out.


Props are 9x7's off of a starmax B-17 and the dummy radials I found a place that makes 9 cylinder vacuum formed dummy engines, these are 2 5/8" in diameter, a tiny bit small but the closest I could find


I made a jig to create the gun barrels… its similar to the fretting jigs I've used in the past to make guitar fretboards...

basically the round gun barrel will go inside the square styrene piece. This component will get slide along another flat piece with a pin sticking out of it to catch the notches. What this accomplishes is it makes each drill hole occur in the exact spots I want them too. The two sides are offset for each side of the gun barrel for the holes. We should see how it works tomorrow…I think… This jig will make 4 gun barrels in a row, which can be separated later. The square tubing is just because its easier to drill through a square tubing than a round tube. I found the drill wandered to much on the round tube by itself. I also switched to styrene for the outer tube, with the inner still being brass.

The B-17 landing gear is set at about 70 degrees for scale. I wanted to figure out how to get a set of retracts to work with this plane and I thought I could get electric retracts to stop at 70 degrees fairly easily…Fortunately hobby king sells cheeps' ( $6-7 bucks a piece ) to play with. A little tweaking and tada….



Ignore the bent landing gear.. this was mainly for proof of concept. Turns out they are pretty easy to modify. I think I may keep the actuators and build my own set to go around them.. they seem to work pretty well.


The only other thing was that the plastics were a bit messed up, and quite a few missing pieces, so after a ton of searching I dug up a new canopy set, a new interior kit and a new set of plans… since the plans are gone and its doubtful if we'll be able to find them.