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Dec 18, 2013, 10:59 PM
team sleprock
whiskykid's Avatar
providing you have enough wing area, ( not knowing what style of wing you plan on using)

with todays props, say an 8x8 on those Os's should get you well over a hundred!
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Dec 18, 2013, 11:22 PM
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lukes221's Avatar
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the wing shape will be like a spitfire wing cut in half. how i mean is looking at it from the top the LE will be straight and the TE will be a curved taper from the root to wingtip. im not sure what the wing area will really be as i still have to draw it up. but good to know its at least possible.
Dec 18, 2013, 11:42 PM
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For easier controll with the CA, you can use special tips like these:

Tower sells them as well, but I can't find the link right now! Really, really helps.
Dec 19, 2013, 12:16 PM
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Citabria Pro - Electric conversion

Lukes 221,

I just saw your post from a few days ago. I have not decided which power system I am going to use, but this is roughly what I have in mind:

1000 Watt System:

AXI 4130/16 16oz
5 S battery 18-20 oz (4000 - 5000 mah)
Prop 16x12 or 17x12

If the plane comes in around 10 lbs or so, this system will give the plane about 100 watts/lb which should equate to very nice performance. No unlimited verticals, but better than scale performance. If it comes a litte heavy at 12 lbs or so, I will be closer to 80 w/lb which should be more than adequate. If need be, I can go to either a 8S (1500 watt) or 10S (2000 watt) power systems.

In terms of balancing the plane, you need to keep in mind that the electric motor is more compact than its glow or gas counterpart. Therefore, the motor will be placed further foward within the cowl. If it ends up being tail heavy, using an aluminum spinner is always an option.

I will make some minor changes to the model in order to save weight. The 1/4" sheeting used in the forward fuselage will be replaced with 1/8" sheeting. I will probably also use a thinner firewall or at the very least, it will have a few holes poked into it. Finally, the ribs will get some lightening holes and I might replace the wing sheeting with 1/16 rather than using the 3/32 the design call for. On a plane of this size, I am not sure if this is a good idea, so that is what it is at this time. In the end, I think that most of the weight savings will come from the power system being used. We will see.

Last edited by viva_peru; Dec 19, 2013 at 12:27 PM.
Dec 19, 2013, 09:33 PM
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lukes221's Avatar
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Sounds good Teo, I'd love to see it be built as an electric. You'll have to keep us updated!

And thanks Aaron those look pretty handy, well see if I end up going for one, I was doing pretty good towards the end and for the higher stress tacks (the curves from the capping) needed a little heavier tack but they would definetly help in some areas!
Dec 19, 2013, 09:45 PM
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I have built for years without them, so you can move forward without them but once I picked them up, I will never go back!

Loving your build. Makes me want to build mine. Looking forward to how you craft the cage; I am no good at soldering and you have to nail the incidence with this one
Dec 19, 2013, 10:04 PM
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lukes221's Avatar
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Originally Posted by 4075aaron
I have built for years without them, so you can move forward without them but once I picked them up, I will never go back!

Loving your build. Makes me want to build mine. Looking forward to how you craft the cage; I am no good at soldering and you have to nail the incidence with this one
I'm fairly decent at soldering and the little method of wire wrapping them and then putting a drop of CA to hold them while its done sounds pretty straightforward, so we shall see I suppose. I'm probably going to make the tail feathers removable in the case of ease if repair if I damage them which shouldn't be too bad. I'm still trying to figure out a good way to stabilize the pilot cam, not that its an integral thing.

Also, without really thinking about it I bought a Du-Bro soft mount. I read something after about these and found some dont like them. I would imagine they help with airframe vibration but the engine can move which would mean larger clearances. Is there anything else I should take into consideration with a soft Mount?
Dec 21, 2013, 06:20 PM
Neophyte hacker
portablevcb's Avatar
Going to electric and your method of losing weight seem counter to each other.

I would not worry about any wood forward of the CG. And cutting holes in ribs is one of the most non-productive ways to lose weight. I would try to lose as much weight in the tail as I can, since you will probably be tail heavy. The electric motor will be much lighter than the IC motor. Figure out how to move the batteries forward.

Remember it is more efficient to add tail weight to a nose heavy model than to add nose weight to a tail heavy model.

Dec 21, 2013, 11:58 PM
Registered User

The rear structure on the plane is quite light. I was a little surprised because it relies on 4 1/4 balsa longerons with the proper cross bracing. The other thing that is a little odd is the cg location which is at about 1/3 of the cord. That might be a little agressive. In the end, the nose moment is quite long because the wing is relatively far back.

The electric motor is quite light compared to the 4 stroke 120 engine and even lighter when compared to a 20 cc gas. The system I picked is roughly equivalent to .90 sized engine which is on the low end of the recommended range. However, the motor does hang quite a ways in front so the lever arm from the motor cg to the airplane cg is quite long. If cg is an issue I have a 20 oz weight (the battery) which can be shifted around. If more is needed, the I might use an aluminum spinner.

Structurally, the plane is a little odd. The fuse is quite beefy up front and a little delicate in the rear. The wing is built in 3 sections, but the dihedral braces only extend 1 rib bay into each panel. The struts are made from spruce so they are structural but don't tie to the spars. Instead, the are anchored by a ply plate which runs from the front to the rear spar. The cabane structure ties into grooved blocks which has me a little nervous as all of the glue joints are in tension, not shear. Also, the flights loads are transferred to the groove blocks by simply sliding the cabane wires into the slots. It works, but it is not the best design.

You are right, the holes in the ribs will only save about 2 oz, but I think that the make structure look more "engineered".

Finally, the cowl and wheel pants weigh a ton. I might replace them with fiberglass parts.

In the end, we will see. This is not my first conversion and if I end up tail heavy I might just use a heavier motor and battery.

Last edited by viva_peru; Dec 22, 2013 at 08:26 AM.
Dec 22, 2013, 10:18 AM
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hmm i hadnt considered the cabane mounts until you mentioned it, yes in tension alone might be indesireable. however, what if instead of solely gluing them, how about putting a bolt (or 2, nylon perhaps? not sure as i dont know how big they go) through the mounts and the piece they are glued to as a failsafe, as the place the mount is glued to would rely on sheer, maybe even add a couple little gussets under that piece at the sides if needed. i would think that would be sufficient would it not?

i can see how you mean the cabanes "just slide in" although, i think most of that was for ease of removal for transport as they would be a pretty easy thing to hit just sticking up if they were permanant, although they could be altered that way, the old ones could be used as a tamplate to create new ones or the plans. i will probably end up not doing much to them as it would be good if they were removable (i am somewhat clumsy and i would totally smack one off something, which is why i also want the tail feathers to be removable.) I dont think them being mounted in that fashion would be bad because it would be unlikely that they would ever be subjected to enough side pressure to push one out/pull out the blind nuts/mounts on the wing that would facilitate that happening. From what i see from the measurements on the plan the plane will most likely remain assembled for me most of the time for me because it will fit sideways in my small suv fairly well.

i think over all the tail would not be too weak, i can see it would be much weaker than the front by comparison but the construction looks pretty well braced in all directrions from twisting and oscillation, although if i end up having troubles with it the covering will come off and it will be fixed. but i dont think it will come to that.

i plan after a couple flights on doing a couple "engine failures" to get comfortable with that so ill find out the CG pretty fast that way so we shall see if that is right.

as for the plastic, could it not be done as using the old ones for a template to Vac form new thinner ones or would that be more work? Ill probably use the stock ones as i could always go back and change those.

Either way, they way ive been looking at it for some of it, is if the first flight was achieved with such simple materials why cant one with better materials also fly.

i really hope it to be on the lighter end of things in the end and the heaviest one i believe i heard of was 15 lbs so i think i definetly dont want to be that heavy.

In either confinguration whether it be electric or gas or glow, im sure it will be a nice flying plane.

Have you already thought of a color scheme Teo? will you be using the scale look or a different one?
Dec 22, 2013, 11:33 AM
Registered User
Hello Lukes,

I built a Sig Smith MiniPlane a little while ago and it used a similar system to anchor the cabane struts; however, the wires would fit into brass tubes which are held in place using landing gear straps or hooks. Could probably use something similar in the Citabria Pro.

The issue I have with using the wooden blocks is that in normal flight, the wires within the blocks are putting a load along the grain direction which made me think that in principle the wires could split the blocks and come loose. The rear cabane attachment is set up for two wires next to each other, so you would probably have to trim the diagonal wire so that only the main cabane wires go into the fuse. The you could use a brass tube or carbon fiber tube to receive the wire and anchor the cabane. Either way, I am going to epoxy the wires in place simply to make sure they have nowhere to go. If I bend the cabane in a mishap, chances are that I have probably more significant damage elsewhere.

In the end, the structure is reasonably light as it is. You could argue about the thickness of the material used here and there, but without a major re-design I doubt you could save more than 6oz, maybe 8oz.

I looked up the Evolution engine you intend to use and my power system weighs just about the same, so I would save weight by not needing an engine mount, gas tank, throttle servo and a receiver pack (although I might use one in this plane just because of its size). The plane is not meant to be super fast either and with the lack of vibration coming from a gas or glow engine, I can probably use standard digital servos on it. Properly trimmed, most of my planes require relatively small surface movements to be aerobatic: +/- 15/14 degrees on the ailerons, +/- 15/16 degrees on the elevator and +/- 35 degrees on the rudder. I always set up the systems so that the servo has a mechanical advantage over the surface....

Finally, I have not decided on the colors yet. Unfortunately, there was only one example of the plane built, so if you want it to be scale you have no choice. I really like the old Navy colors of the 30's, so I might go for a non scale finish. We will see.

Good luck,

Dec 22, 2013, 11:37 AM
Neophyte hacker
portablevcb's Avatar

OK. If you've done this before then please ignore the comments.

FWIW, IC models are always built heavy up front to withstand engine starting and running forces. Electric doesn't need all that structure and it looks like a great place to save weight. But, the motor weighs less, so reducing the structure weight is counterproductive unless you can get the batteries up there.

Dec 22, 2013, 12:03 PM
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Thread OP
Hi Teo,

Actually yes i can totally see the concern there with the Wires being along the grain, maybe i will do something like your brass tube idea since it will be hidden within the covering anyways. Yea i also saw its not supposed to be a blazing fast plane or anything which is fine, i really only wanted something i could have a little more fun than my trainer with, i want to learn some more advanced aerobatics, not 3d and i would be amazed if it ended up being under the 10lbs the evo 20gx calls for to be good for 3D anyways.

Maybe i will even try a little fpv on it but who knows and i have yet to take that dive yet and i probably wont for a while.

I will probably go for a LiFe Reciever Pack and a Lipo Ignition Pack, or would that be not necessary? I have the 2S lipo (800mah) kicking around already and i heard LiFe packs were a little safer for the electronic systems. I have seen it can also be done where the electronics could be powered lets say from a LiFe and the ignition could be run from the balance port or a splitter. although i also read that having the same battery for both could be bad for the reciever/servos as the impluse from the spark affects them through the battery, that was my reason for separating them.

A Navy scheme could look great! i rather like the original so ill be doing that look, and i even saw a pink one while poking around.

Im sure an electric version will be great, im going gas because i like big gas planes, and nitro is way to expensive for a plane this large in my opinion and i will be flying it a lot so itd be nice if its cheaper to fly and i always have gas around.

Thanks, Luke
Dec 22, 2013, 02:02 PM
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So in the last couple days up to now i was installing the aileron servo which i may have mentioned before is a Hitec 645MG. Having never had a servo that strong it really is pretty amazing how strong something so little is, and i know there are MUCH stronger ones out there.

So in the plans it showed the way it originally wanted which was to have it open top out the bottom of the wing on rails (picture below). I did not really like this method as it really doesnt look very nice. Then they also included the "optional" method which is laying on its side on a little door with just the servo arm coming out, which looks infinetly better, so i of course went that route. I put a couple bass rails on the wing ribs and epoxied them on (probably could have used regular glue but i wanted it to be strong as it is a working part), cut off a little piece of Birch Ply i bought and made up the little door and slot. Is there an easy way to create that slot?? maybe i was using over thick material (5/32) but it was REALLY annoying to make that slot. i somewhat half sawed half knifed it in there and marked the length of it with drill holes to start but it wasnt overly pleasant. but its in there and looks pretty good and isnt too long or short at all so im happy with it.

i screwed the servo on and just have to make the holes for the screws to fasten it to the wing. it looks pretty nice and i just have to sand it to the profile to the shape of the wing when i sand it all.

I also played with the idea of making the cowl 2 piece (since it already is). what i mean is for ease of engine access leaving it split and mounting each half separately (probably a little differently than on the plans) and having one side be easy to remove for this reason but i may not do that as from what i see gas is less fussy than nitro for tuning all the time so i probably wont have to take it off very often anyways.

I ordered my aerobroach slotting tool from their website on Thurs. so ill probably see that sometime in the new year (or at least one would hope ) and hopefully that makes hinge slots a little nicer. After im done the aileron servo and saw the excess on the root im done at this point with the wing and will probably slap the center section together as i imagine it will be fast and maybe build the rudder alongside as they will probably both fit on the glass.
Last edited by lukes221; Dec 22, 2013 at 02:07 PM.

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