Sig Sundancer 50 Biplane electric conversion?

[JUSS10]

Thanks for the tips everyone.

Now, here is your opportunity to learn a new skill. It's not hard to make a home vacuum forming setup to make small parts out of plastic. MAke magazine had a good writeup of how to make one in your kitchen:
https://makezine.com/projects/make-1...vacuum-former/

you can then just tape over the original cowl's hole, and then vacuum form a new cowl out of plastic. If you crash and destroy the cowl, you can then make a replacement part. this is a good skill for modelers flying obsolete planes.

I actually have a vacuum former at work so I do plan to make a "buck" to form another cowl. It'll have to be a two piece cowl though as it widens at the nose and you wouldn't be able to remove it from the form.

I was thinking of making a 2 piece negative mold of it and then lay light fiberglass in that and split the mold when done. We'll see.

As for a contour gauge, I do have one. I am a model maker of sorts by trade so I plan to model the whole plane up in cad so I can duplicate parts in the event of a crash. Already have the airfoil drawn up and the dihedral angle found out. May actually build a 75% size model out of DTFB for fun.

rockyboy, thanks for that chart. I think the motor I am picking up is somewhere in the 900 to 1100 watts range dependent on how its set up. I would think the 90-110 watts per pound sounds like a safe place for me to be, if thats the case, I think I'll be ok to get it off the ground. We'll see.

Got a buddy with a pile of standard futaba servos that I think I'll use for this. Likely the type of servos that were on the market when this plane came out!

 

[JUSS10]

just did some rough math and came up with 5lbs 10oz on total weight with the running hardware I know I'll have. I didn't add a BEC but I Think I may run a separate BEC from the ESC for safety. Will likely also add the voltage module for the taranis receiver to monitor voltage. Also will likely take the wheel pants off as the club I joined is a grass field. So worse case lets say 6lbs all out. That weight will liekly go up if I run 6s but so will the wattage...

 

[Geeto67]

I actually have a vacuum former at work so I do plan to make a "buck" to form another cowl. It'll have to be a two piece cowl though as it widens at the nose and you wouldn't be able to remove it from the form.

I was thinking of making a 2 piece negative mold of it and then lay light fiberglass in that and split the mold when done. We'll see.

Why not just saw your buck in half and then vacuum form two sides of the cowl, then plastic weld or fiberglass them together? you could probably do both sides out of the same sheet of plastic. From personal experience fiberglass for small pieces tends to be harder to work with in tight spaces, where as vacuum forming keeps the detail and keeps it light and thin.

If you are a "pro" model maker then you probably have access to a 3d printer to make your buck.

 

[JUSS10]

Why not just saw your buck in half and then vacuum form two sides of the cowl, then plastic weld or fiberglass them together? you could probably do both sides out of the same sheet of plastic. From personal experience fiberglass for small pieces tends to be harder to work with in tight spaces, where as vacuum forming keeps the detail and keeps it light and thin.

If you are a "pro" model maker then you probably have access to a 3d printer to make your buck.

Yup that was one of my thoughts also. I do have a 3D printer both FDM and SLA so I plan to model the cowl and then form it at some point. Especially if I make a foam version of this. Just can't have a nice biplane without a formed cowl!

 

[JUSS10]

Got my motor and ESC last night. Going to work on drawing up and cutting out a motor mount today.

Also, since i have been measuring and blueprinting the airframe I decided to try and make a wing half yesterday out of foam. Pretty happy with how it turned out. It uses 8 ribs per side with a double foam spar down the middle. removed the paper on the inside of the wing so it forms nicely. I know this has nothing to do with balsa but it turned out pretty cool and I might just have to make a foam one in the midst of bringing this old plane back to life!

Justin

 

[JUSS10]

So whats the normal way to mount a brushless motor in a conversion? make a box to mount it to out of ply? Stand offs? I was thinking of drawing up a box and laser cutting cutting, gluing and using that as a spacer. I guess I'm just curious how beefy the mount needs to be.

 

[JUSS10]

Sorry, one more question. I am still questioning if the 3300 4s I have will be enough. Numbers say yes but if i wanted to go 6s, could I just run two 3s packs in series as long as they are the exact same pack? I feel like I had to go out and buy a battery for this, I could get more use out of buying two 3s packs that I could run in other smaller planes when I'm not using this big one.

Justin

 

[rockyboy]

Yes, and yes



Size the box spacer as needed to get the cowling / prop alignment to work out right.

Running two batteries in series to double the voltage is a common practice among those of us too che... err... frugal to buy monster batteries at crazy prices. Just make sure they are the same mah capabity and charged within one or two tenths of a volt to each other (measured per cell) when you hook 'em up so they don't fight each other. I'm sure there is a more precise description of why that's important, but I think of it in simple terms and haven't burned anything up yet

 

[JUSS10]

Thanks rocky.

one more question, what C rating and Mah are you guys running on bigger balsa planes? HK has half price on a slew of their nanotech packs. Wrong connector but thats an easy fix...

 

[rockyboy]

For single motor scenarios, I feel like anything over 30C is overkill - but since I do double duty with my quads on my 3s2200 and 3s1800's I usually get them with with a higher C rating. Less than 30C on a quad can be a noticable drop in performance, even with my poor piloting skilz I've used quite a few of the smaller nanotech packs with 25C ratings and found them to be perfectly fine for my park flying.

For mah ratings, I view that as a balance with how much weight I want to carry. Personally, I'm not a guy in pursuit of long flight times - I'm plenty happy with 5 minutes in the air - so the biggest batteries I have now are a pair of 4s3000 that I use individually for my big foamies, and am planning to run parallel for a big balsa conversion I've been working on - but I haven't put that in the air yet or even tried to balance it, and might need to jump to something bigger.

But Joker probably has the most experience with big electric balsa of anyone I can readily think of - hopefully he or someone else knowledgeable in the field can chime in and set us both straight

 

[Joker 53150]

For your motor mount you could cut a plywood box - it works fine and I've done it a few times. Or you could go with an adjustable metal mount like Joshua did with his recent Spacewalker build. A little more expensive, but you can fine-tune the final motor position.

Regarding the batteries, I'm still not convinced 4S would be sufficient for this big of a plane, but I have been wrong before. Just ask my wife! If you've already got a motor and ESC that would handle it I'd go the 6S route with either 2 or 4 batteries. Assuming we're talking 3S 2200's, I'd just do 4 total since they're so common. 2 in series and 2 in parallel to give you a 6S 4400. For the first flight, assuming you don't need the extra battery weight to hit the proper CoG you could even just do a pair of 2200s to make a 6S 2200 and keep the flight short. One big advantage of using multiple batteries (other than 2200s are dirt-cheap) is that you don't need a high C rating, as multiple batteries are working together.

 

[rockyboy]

For your motor mount you could cut a plywood box - it works fine and I've done it a few times. Or you could go with an adjustable metal mount like Joshua did with his recent Spacewalker build. A little more expensive, but you can fine-tune the final motor position.

Regarding the batteries, I'm still not convinced 4S would be sufficient for this big of a plane, but I have been wrong before. Just ask my wife! If you've already got a motor and ESC that would handle it I'd go the 6S route with either 2 or 4 batteries. Assuming we're talking 3S 2200's, I'd just do 4 total since they're so common. 2 in series and 2 in parallel to give you a 6S 4400. For the first flight, assuming you don't need the extra battery weight to hit the proper CoG you could even just do a pair of 2200s to make a 6S 2200 and keep the flight short. One big advantage of using multiple batteries (other than 2200s are dirt-cheap) is that you don't need a high C rating, as multiple batteries are working together.

I think I'm going to be buying one more 3s2200 (only have 3 at the moment) and try this 2 batteries in series, and then those sets wired in parallel with my Kadet Senior restoration.

Also, for that harness I was thinking of using XT60's for the battery connections, and then an XT90 on the final harness to ESC connection (since I'm planning on an 80 amp esc, using a 60 amp connector when all the pixies are joined together seems foolish!)

 

[Joker 53150]

A 6S 4400 in a Kadet Senior should give you PLENTY of power! If you can get them far enough forward you may be able to get away without extra noseweight. I think I added about 1.25 ounce of lead to mine with the 5S 5000. Good plan on upgrading the connectors for the main plugs!

 

[JUSS10]

Alright, got my plywood box done, what do you think? Too many speed holes? Its double ply 1/8" front and back and single on the sides. all high stress joints are completely surrounded my solid materiel. Medium CA to set the whole thing up and thin CA on all open joints after the medium set up. Also used T nuts for the motor with 8-32 screws. Firewall of the plane already had T nuts with 3mm screws.

 

[Joker 53150]

Dang, that looks great!

 

[rockyboy]

Ahh the joys of having a laser cutter

Very nicely done!

 

[TexMechsRobot]

Very jealous of your access to a laser cutter. That's high on my list of things I want and can't afford!

 

[JUSS10]

Thanks everyone. I try not to flaunt it. I'm beyond blessed to run a shop and have access to the tools I do. I try and help out a lot of the local rc guys I fly with when I can as well pretty happy with how it turned out.

Got an elevator servo mounted up and hope to get the rudder servo in tonight as well.

Not a huge fan of the aileron servo mounts (old and cracking) I'll likely draw those up and print new ones.

 

[JUSS10]

Almost didn't fit under the hood!





Rudder servo is in and cables are adjusted. Kind of like the pull/pull cable setup. works well and looks scale!

Tomorrow I hope to get to the ailerons. Then to figured out the ESC and receiver mounting. I found a matched pair of 2750 3s packs I think I'll try the first time.

Justin

 

[JUSS10]

So HK has some stuff on sale and has me side tracked. Found this motor and ESC... I know the ESC is way overkill but the price isn't bad. Thoughts for tossing in big balsa planes? I know i just got a motor and ESC but while in my basement it hit me, literally, I have a big old Sig Kadet Senior hanging there that I got on an auction a long time ago, needs some work but would also be a fun big balsa plane to covert. May even be a better first balsa plane just to get the hang of a big plane in the air vs the foam I have been flying for the last few years.

ESC: https://hobbyking.com/en_us/hobbykingtm-ss-series-190-200a-esc-opto-only.html

Motor: https://hobbyking.com/en_us/propdrive-v2-series-4248-650kv-brushless-outrunner-motor.html