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Oct 28, 2017, 10:43 AM
Registered User

Electrifying a Scratch built 79" WS 2-33

I'm building a 2-33 foam and balsa hybrid and looking for suggestions on motor/prop/ ESC size recommendations. I found the great thread and info on the MotorSpatz by Kiwikid and the Parkzone Ka-8 with Folding Prop thread by PJpjpj for inspiration..

This is my first attempt at getting into building a glider. I have been flying gas r/c for many years since I was a younger lad. But completely new to the world of the electric stuff, so still need to do some more learning and reading on everything.

I live in Atlanta so no slope flying here for a glider, my initial idea was to build a semi-scale 2--33 and use a hi-start system for launching. But, i'm building it with a foam wing wing and concerned about the launch. So that is why my interest in making it a electric motor assist and going that route.

I'm making it a 79" inch wingspan. The fuselage is a hybrid of square stock and balsa with foam filled in for stiffening and shaping of the final surface. Then using the newsprint and TiteBond glue method that I found on RCG here as well. Very surprised at the durable hard shell finish that the newsprint creates when fully cured. To my surprise it is actually coming out very sturdy, and pretty light. No idea of all up weight yet.

Kiwikid in his MotorSpatz thread suggested a ..... based on a 79 " wing, ... suggest a 3 cell set up generating around 300W with a 40amp ESC would be ideal for this? What size prop / motor / ESC based on your experience would you suggest...

Just curious if anyone else has done such a conversion with a 2-33 build and how it turned out. I'm concerned that i may not have enough nose room area for a battery location. I will have to doing some more design work.

Thanks to all!!
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Oct 28, 2017, 12:23 PM
Sagitta Fanboy
A good starting point is the power system for the E-Flite Radian.

That uses a 960Kv 480-sized motor, a 9.75x7.5 folding prop and a 30A ESC to give a quite spirited climb (ALES-capable, so 200m in 28-29 seconds) for a 78" 30oz plane off a cheap 3S 1300mAh pack
Oct 28, 2017, 01:03 PM
B for Bruce
BMatthews's Avatar
Keep an eye on the weights of the parts. To allow for thermal flying you don't want to see the weight climb up much past 400z If it does it might still soar but it'll require a strong thermal.

Within that 40oz some reasonable targets are radio, battery and motor at around 10oz. That leaves you 30 for the model itself. Wings should not be much over 6oz total. Tail surfaces all together another 3. That leaves a lot for the fuselage. But still try to keep it light. You could easily require a big lump of lead in the nose if you're not careful with how heavily constructed the rear portion is.

By all means use layers of the paper to increase durability of higher stress areas like the tail surface mounting points and the wing saddle and in particular to the fuselage sides around the trailing edge of the wing.

If you go with the Park 480 size motor I can assure you that it'll still provide a HEALTHY climb angle to a 40 oz glider.

Of course if it turns out you come in closer to the mid or low 30 oz range you'll have a superb model. And from the pictures you posted it does look like you are well on the way to that sort of success. And in truth it's a very interesting combination of wood and foam you're using.

I've done a bit of foam and newsprint myself. So I'll be watching this develop with great interest.

Note too that the weight of the pink foam does add up. Don't be afraid to hollow out the blocks you use to something like 3/8 or 1/2" thickness. Especially again in the tail. The nose blocks I'd leave fairly thick for a little more crush durability.
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Nov 02, 2017, 05:51 PM
Registered User
Hi mawz & Bmatthews... Thanks for the great input and advice on everything. I'm brand new to the world of electric, I've been flying since the 80's but it has always been gas.

I just picked up a used Maxford Storch that came with a Futaba FP-T7UAF radio. It was a great deal and also came with 3 batteries that are 2200mah, 3S and 25C.

The plane has a Turnigy 3532 with a 11x5.5 prop on it. I also picked up a used triton EQ charger that now I have to figure out how to use. I have a extra computer power supply that I pulled from a old PC and going to see how the guys on here and at my local field are setting charging systems up now these days.

thanks for the ideas on power mawz. I'm going to use your size requirements here and pick up some different size motors, props, and ESC to have around and play with. I picked out a couple below as possible choices from Hobby King..
Turnigy Park450 Brushless Outrunner 1200kv.. it weighs 66 g
Turnigy Park450 Brushless Outrunner 890kv

Great reply matthews.. Those are all great target weights that you provided and are right on. I started building this and did not have any PPO foam or what ever the designer had in mind to build this with so I departed and designed the fuselage around my concept of combining the foam with a somewhat typical balsa and spruce stick structure.

I have only covered the tail surfaces with the newsprint so far but was very much amazed at what it did after finally curing out. Yes, I have been whittling away at the foam as I noticed it was much heavier than I initially thought it would be.

The fuselage as of now even without any newsprint covering is very light and very durable,I have been checking the strength as I am moving along.. I did like you said and kept the nose and bottom area solid for durability.. I have to pick up a better weight scale for measuring everything.

I really want to keep the power to a bare minimum so that I can generate a nice climb under power but not a lot more than that. Just like you said so that I can keep the weight low. What are good motor choices when moving to a size even smaller than a 450 size.

Have you tried using the news print with very thinned out epoxy? That might be something that I try, Not sure if there would be any significant weight or strength savings for that as compared to just using a light weight glass cloth.
Nov 02, 2017, 08:43 PM
B for Bruce
BMatthews's Avatar
I actually did make one small vacuum bagged wing just as a test using newspaper and epoxy. It was back when I was interested in moving into vacuum bagged glass and epoxy flying surfaces for gliders. But before I got to where I produced anything I lost interest in working with foam.

What I did was make 4 or 5 control line combat models for the local .15 powered fun class. These used thinned white glue and newsprint and worked out SUPERBLY well. In each case it took being hit in mid air to break the models. Crash landings didn't bother them at all as long as they were not straight in events. I'll attach the "plan" for these below so you can see how I built up the newspring in layers and gussets to harden the areas around the engine mount and tail boom exit. In one case I was testing a remnant to destruction and it required a full on overhand swing of the wing that hammered the maple engine mounts into the concrete floor to rip the newsprint and make the mount loose in the foam. And that was after about three ever increasing attempts and checks. To say I was impressed with the method and strength would be a gross understatement. This is a VALID way to build ! ! ! !

If were still doing glow powered models of this sort I'd try using the water based polyurethane. Might still be worth it anyway. I'd also dip the newsprint through a trough of water and let it drain somewhat before laying onto some fresh varnish and then brush it out with more varnish. And since the paper will shrink strongly you NEED to ensure good even airflow around all parts of the items.

A lot of that you likely already figured out from doing parts. But if there's anything there that's new then you're welcome to it.

Now onto power. A lot of folks don't seem happy unless they are powered up to the point where they can climb vertically. I can see the draw in some models but for a lot of my flying I actually prefer something more "normal". There's something "wrong" about a PT-19 that has enough power to look like an F18 on full afterburner in the climb...

Now when I posted that 40oz target I intended it as a realistic value that would produce a nice flying model. But hey, if you can hold it down to LESS than that it will only be better. Anything you can do to build down closer to 30oz will strongly enhance the thermalling ability of the model. And needless to say keeping the tail light as you can means you potentially need a LOT less nose weight... which would be part of sneaking in well under a 40oz cap.

Now as for power needed here's some figures that work for me and which seem to hold true from hearing and seeing models flown by other folks.

20 to 25 watt/lb- slow climb that resembles an uphill glide. Think of an ultralight and you won't be far off
30 to35 watts/lb- This give a reasonable climb of around 20 to 25 angle and at a reasonable speed.
40 to 45 watt/lb- This will give you a climb angle of around 30. Again not a slow "hanging on the prop" climb. An honest 30 at a reasonable flying speed.
55 to 65 watt/lb- Now you're pushing up to around a 40 to 50 climb and it's moving well.
70 to 80 watt/lb- More like a 60 degree climb or more.
90 to 100 watts/lb- approaching vertical climb. Might be a bit slow and wants to fall off at the lower end unless you correct it during the climb.
110 watts/lb and up- Unlimited vertical climb. Going over 110 just makes it climb vertically faster.

Now if you fly on some blustery days you want a little extra. So I feel that even if you want a fairly lazy climb and are willing to take a minute or so to reach up around 400 feet you are likely better off to use up around 45 to 50 watts /lb. Although for all that my early electrics back in the days of brushed motors and heavy battery packs flew just fine on 35'ish watts per lb and a bit of patience while they took something like 90 seconds to reach around 450 feet.

Sooooo.... where's that leave you? If you can save a few ounces by reducing the size of the motor and the battery and lighten the model so it doesn't NEED the nose weight and it all comes together and you end up at 30 or 32 oz then what do you need? Lets say 32oz which is two lbs even for easy math If you can live with 50 watts/lb and a roughly 30 to 35 climb angle then you need 100 watts of power. On the nominal 12 volts for a mid pack run from a 3S pack that means just 8.3 amps. Now it's best if you use a motor that is rated for a little more so you're not in any risk of "letting the smoke out". So I'd shop for motors that can handle 10A max continuous and which have a fairly low Kv value of around.

A quick look at the motors on HobbyKing suggests these as possible options;

Here's one with a little more than you need-

A touch lighter and closer to the power you need for how you want to fly.-

This would be spot on if you can hold the weight down closer to 32 oz-

Another good match. Maybe the best. This would work even with a 40 oz AUW.-

This is nice IF the weight comes in well under control and if you don't need nose weight-

There's others but that's the 5 minute tour for some options. And of course depending on the prop you want to use you may need to go up in Kv if you want to run a fairly small prop. Plus with a smaller prop not being as good for climbing you might need another 5 to 10% more power to reach the performances I gave earlier. Those were all based on moderately larger props for each range of motor size.

Oh, and to close things out here's that foam wing plan showing the newsprint layering....
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