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Jan 11, 2010, 09:37 PM
A&W
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cessna 310 twin electric conversion


I have plans from the early seventies for a gas powered (.10 - .15 size) 36" wings span cessna 310.
I am planning to build it lighter, with dual brushless motors, and the new Horizon electric retracts, not trying for scale, just building a nice bird. Considering flaps but that will probably be too heavy.

I have built planes before, however this will be my first truely scratch built from plans only. I do have a few questions to ask, before I begin this adventure. So pardon my inexperience, I have used the search fuction and will continue to research, as well as solicit information through this tread. Thanks in advance to anyone who is willing to shed light on my confusion.

So here in the first question? I know I need seperate speed controller's for each motor, and I read somewhere the the leads should be about the same from the motor to the speed control as the speed controller to the battery. Is it best to used one battery to controll everything? ( I already use Lipo's and am aware of the advantages and the dangers) I have looked at the diagrams but not quite sure of the wiring for the use of two BEC's, there seems to be two view points, one suggests to use both while the other suggest disabling one of the two. And if I use the same motor and speed controller for both sides do I need to worry about motor sync ?

Second question? Plans show no information about any thrust angle, so It is it correct to put in some down and slightly to the center or just leave it as is? Are Pusher props and regular props from APC ( 7x4 ) exactly the same, (same amount of thrust) to use them as counter rotation? If so then should the right motor or the left get the counter/ pusher prop?

As I scale out the retracts/ wheel bay requirements, It looks like I will most likely scale the project up to 110% or 115%, I wish to keep it smaller but I know weight of the gear will add up quick. My desire will be to keep it below 4 lbs so as not to overload the retracts. Any suggestions on Watts/ lb for a twin motor aircraft? I plan to use construction technique of light weight open formers and stringers, plywood only for the firewall/motor mount and wing saddle formers, D tube wing construction balsa sheeted leading edges, I know how to build light ( been flying gliders as well as heli's a few years).

If anyone can point me to a thread for a similar build I would appreciate learning from someone who has been there already....


I look forward to learning from this wonderful forum, been reading and learning here for a few years, but now that I sold my business, its time to build some of those dreams. Never had the time before, but that's changing slowly as I get finished with all the CPA's and Attourney's. Never knew it would take so long to get out of business.

Hope everyone's new year is off to a great start.

Alan

I thought I would start here in sport planes, but if this needs to be elsewhere I guess I'll figure out how to move it. thanks
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Jan 12, 2010, 10:18 PM
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Hi Alan, I can't answer all your questions but I do have some experience with one electric twin. I'm not saying I have THE answer but here's how I set up mine and it works just fine.

I use a single lipo to power both ESC's and motors. The 3S battery is connected to a Deans Ultra "parallel" connector for two the motors and ESC's. I used a Y-connector to the throttle channel for the 2 ESC's and disabled the BEC on one by removong the red wire from one of the ESC connectors. It's an easy process with a male connector, just push in the tab on the exposed metal part and push it out of the connector with a pin, fold it back and wrap it with some electrical tape, that way you can use that ESC in another project simply by bending the tab back up a little and re-inserting it back into the connector.

At first I tried using 2 channels to power the ESC's by mixing the auxillary channel to the throttle but I couldn't get the mix right. One motor would start first and and I couldn't get both motors to run at the same rpm at any particular throttle setting. So I went with using the Y connector to the throttle channel. KISS, (Keep It Simple Stupid)
Jan 12, 2010, 11:11 PM
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Wiring diagram


Howdy Alan,

Hopefully the diagram below will help you out some. It's basically the same as what I use when using a single lipo.

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SJ
Jan 12, 2010, 11:45 PM
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I'll try to answer the 1st question(s) for you. When setting up a Twin use the same equipment on both sides such as using the same brand & same size ESC's. The wires should be close to the same length on each one but if not you can cut the longer ones down to match the other ESC. Same goes for the motors you will use. I try and buy my motors for a Twin at the same time as well as the ESC's. IMO you'll have a better chance of getting items that closely matched. I've never had a problem with motors being so out of sync with each other that something needed to be changed. Not saying it doesn't happen but that's why I buy 2 of what I need at the same time when building a Twin. For the size model your planning on building one lipo should be able to do the job.
As to how you need to set up your motor...I always use a firewall mount & set the motors a -0- thrust angles. With a firewall mounted motor you can always adjust the motor angles if needed by using washers between the motor mount & the firewall. On a electric motor I see no reason for side thrust because we rarely deal with a motor out situation.
CR props on the size plane your planning on really won't make a big difference so you really don't need them to CR. As to whether a "pusher prop" is the same size/weight as the same dia/pitch of their tractor prop I would contact the manufacturer and ask them. Hope I was able to answer your questions without further confusing you more.

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Jan 13, 2010, 11:00 AM
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Cessna 310


Thanks guys for the input. I did more research on wattflyer last night. Another great site with a wealth of information that SlowJohn pointed me to.

I am supprised there is not more postings regarding twins out there.(Motor Setups that is)

I have a set of Castle Creations 35's but will need to pick up the motors and bench test I guess, are the turnigy motors from HC dependable as far as Rpm ranges?

Sounds like the thrust angles will be better left as the plans call for, so that is what I will do. Still on the fence about wether to upsize the plans, looks like a call to Staples will be on my list for today to see if they can enlarge only 10%, My office copier would only do as low as 25% and wow that was big.

Holding off on ordering anything till I get the size worked out.

Again Thanks for the help, I'll keep you posted with update as I learn, experiment, make mistakes. Well that is part of the fun!!!


Alan
Jan 13, 2010, 11:40 AM
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Just in case...to locate similar threads look below the Quick Reply at the end of the last post on each page to the "Similar Threads" section.

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Jan 14, 2010, 06:45 PM
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Cessna 310


Well I e-mailed APC and this is the reply.


"Hi Alan,
Yes, our 'pusher' props (of which many are counter rotating tractors) are designed to the exact same specs as the standard tractor props.
You are welcome to post a link to our website (www.apcprop.com) in your thread".

Regards,
Robert APC


So at least for APC any pusher prop should have a matching regular prop, example 6x4.5 EP is the counter rotations for the 6x4.5 E ( E = electric, P = Pusher) At least it is easy to remember! ha ha

I guess I will shoot the Large scale 310 guy's the question about which side gets the counter prop.

To all those looking in feel free to express any thoughts, hope to have some build pic's next week, W-2"S are almost comlete should have time to start build after this weekend. Tax man doesn't wait.

Till next time
Alan
Jan 14, 2010, 11:10 PM
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Alan,
Here's a link to an electric conversion I did on a Twinstar a few years ago:
https://www.rcgroups.com/forums/show...light=twinstar
The counter rotating props were exactly the same. The motors had out-thrust and down-thrust built into the motor mounts so thats how I left them. The out-thrust helps during a motor out by directing some prop blast over the rudder. I also used switch enabled differential thrust to help taxi the plane and to spice up the aerobatics (spins and snaps were wonderful). I could switch it off when I didn't need it.
McD
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Jan 15, 2010, 07:55 PM
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kingsflyer


kingsflyer: Just got hold of a royal cessna 310 set of plans ( .40 size) it also show 3 1/2 degree's of out thrust, but with no down. Wow that's opposite of what I expected. But your description makes sense. Can you tell me, looking at the front of the plane did you put the counter on the left or the right? I reviewed the royal plans & instructions, and also went to the Tower Hobbies site and looked at the giant Top Flite 310 online manual but still cant find a reverence to an answer to this one. Sorry if I missed is it in your review, very nice job by the way. Thanks for the link. I saved it in my reference file.

So, now I get to choose betweeen enlarging the plans I have to 120% (I know that's larger than I said in previous post but 36" at 120% will give me 43.2 inch wing span), or reducing the Royal plans to 90%. I like Royal construction technique better so I may have them print both. I found a local pack & ship that can enlarge/reduce in 1 degree increments up to 36" and 12' long. (Wow) was not expecting that.

Trying to stay with 42" to 44" wingspan, however need the depth in the wing to handle the retracts.

I think I have the power setup straight now, waiting on plan decision in order to calculate wing/load and Watts. Seems like most common estimate is 150 watts/ pound although thats probably overpowered for scale type flying.

Here's a new question for you guy's, do any of you have experience in forming the canopy's out of Soda Bottle plastic. I beleive SJ mentions it in one of his post's or maybe I read it on wattflyer, can seem to remember at this moment.

I'll post a decision on the plans most likely on sunday. Till next time.

Alan
Jan 15, 2010, 10:22 PM
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I have one heck of a collection of plastic bottles saved just to make canopies, wingtips & cowls. The canopies can be made lots of the time w/o heating the plastic. I'd say that about 3/4 of my scratch built planes canopies are made by only cutting them out. Once you make a couple like that you'll find yourself looking at every clear & some tinted plastic bottles on the store shelves trying to find one with just the right shape. I've bought stuff just because the bottle had that great potential to make a canopy. There's a thread or two that cover the "how to" on heat forming plastic that I'll try to find & post here for you.

As for off setting electric motors I don't. I use -0- down & -0- L & R. If I need to I'll add washers between the motor mount & the firewall. The off-set engines on Twins were to help the pilot try & keep better control of his plane in case of an engine out situation. Larger tail surfaces are also employed for the same reason. I've read where some designs flew good on just one engine where another wouldn't fly at all on one engine. It's fairly rare to lose a electric motor once airborne on a Twin although it does happen. I've found that if I have the altitude I can usually throttle all the way back and then come back up slowly on the throttle enough to maintain enough airspeed to make it back for a safe landing. There's only been twice in 5 yrs. or so that I've had to walk aways to retrieve my plane and only once that it came home in a bag from losing power on one motor.

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SJ
Last edited by Slowjohn; Jan 15, 2010 at 10:29 PM.
Jan 15, 2010, 11:03 PM
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Hope this link below will help.
http://www.wattflyer.com/forums/showthread.php?t=36104

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Jan 16, 2010, 05:51 PM
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SlowJohn; Thanks for the link, I am also on Wattflyer under the same name "A&W", I have been posting on the E Scale Forum http://www.wattflyer.com/forums/show...682831Henry111 and Jeaton01 agree with you on thrust angle's and wether counter props are necesary. He also pointed me to his web-magazine which had the same article in it but more descriptive, the you-tube video was very informative on the soda bottle canopies. I spent forty minutes this morning watching his other video's on water proofing your electronics.

Well 120% is toooo big. The wing cord resembled that of a .40 size trainer, I don't think I can keep the weight down enough to build it that big, but I will keep the plans for "Later". Ha Ha Will see what 110% looks like. Do they make wheels "scale like" narrower than 1/2 inch? Have not found any yet except the light/ mico type that would not look right on a scale-ish plane. I did look at the Bonanza at HHhttp://www.horizonhobby.com/Products/Default.aspx?ProdID=EFL2575 Now that is some light ply constructin. WOW (look at the pics on there web site) Wish I had a lazer cutter. I have to admit I considered ordering the ARF and converting it to a twin, instead of doing all this work. ( Yes I know the word is spelled PLAY). Now I wonder if the entire Cabin could be made from a 3 liter soda bottle. Now that an idea, would save a lot of weight, sort of like a Herr model. Hmmmm.

Here is the answer to one of my questions: posted by jeaton01 on Wattflyer:

The convention for airplane left and right is always as the pilot sits, or looking at the airplane from the rear, not the front. Put the standard prop on the left, which will turn clockwise viewed from the rear. The reverse turning propeller should go on the right, and will turn counterclockwise when viewed from the rear. The main benefit I can see is reduced tendency to turn left on take-off or to yaw left in a slow airspeed high power steep climb. It would be more useful on a glow or gas powered twin where engine outs are more likely, not so necessary on an electric twin.

Wanted to put this here for any one else following the thread.

Till next time

Alan
Jan 16, 2010, 06:21 PM
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CR Props setup.


Looking from the front of the plane towards the tail, the RIGHT motor has the normal tractor prop rotating counter clockwise with the tip falling towards the fusalage. The LEFT motor has the "pusher" prop rotation clockwise with the tip falling toward the fusalage.
Jan 16, 2010, 08:12 PM
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Not all twin motors turn the same


Didn't the P-38 props turn opposite? Also the A-26 Invaders didn't counter rotate so not all twin powered aircraft turned the same. Just something else to research when trying to build scale like models.

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SJ
Jan 16, 2010, 09:22 PM
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Quote:
Originally Posted by Slowjohn
Didn't the P-38 props turn opposite? Also the A-26 Invaders didn't counter rotate so not all twin powered aircraft turned the same. Just something else to research when trying to build scale like models.

Standing By,
SJ
To determine the CR prop rotation, picture in you mind prop rotation in relation to torque. You want to rotate the props so that torque has the least effect on the airframe. We're not dealing with full scale airplanes, only models. ANY QUESTIONS?


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