Dumas L-19: Walnut scale!

[DarkFire]

I recently saw an email from the website Tower Hobbies in my inbox. I opened it up and saw a gleaming blue banner promoting a sale on all Dumas rubber powered kits. I clicked on the link, scrolled down a bit, and saw the crown jewel. A bright orange, dorky looking beaut of a plane, the L-19 Bird Dog. Quickly clicking on it, I saw the thing I most wanted to see: 18 inch wingspan (perfect for my 2 foot by 2 foot building board). After that it gets hazy from the excitement, but I do remember putting Titebond glue in the virtual cart too.

This thread will be where I hope to document my build process and ask/answer questions along the way. Also I might make an article based on this thread later on. It will move quite slow though, as the increased homework this year just hit like a semi full of bricks, along with other things.

Anyway, the kit arrived in a very safe package, a thing I've noticed with Tower Hobbies. It was well protected, and someone smart put a bulkhead of bubble wrap in between the heavy glue and the kit itself.

The box was colorful and had large print saying 'Made in the USA' prominently displayed (always a good thing). It had a nice little display explaining the kit contents and a HUUUUGE list of what to build next from Dumas.

On to the pictures!!!!



Full size plans to build on with little reminders and helpful hints



All contents arrived safe and sound!




The laser cutting is excellent, with the parts cut all the way through and well placed "bridges" to hold the parts in for now.




The kit comes with the material for the windscreen, orange tissue paper, and decals, all to make it look like on the box!



The box wasn't really glued together, but the plastic wrapping help the tabs in place. I thought this a bit short-sighted until I realized it unfolded to make a nice container for parts!



The instruction has a really nice diagram showing the labels for all the laser cut parts, and refers to them as A1, A2, and so on in the step-by-step instructions. The only thing I don't like is there are no pictures in the instructions, but they are very well written.


All in all this kit looks exciting, and I can't wait to start! Oh.... I'll have to wait....darn homework

 

[rockyboy]

Awesome!! Welcome to the Balsa Breakers - the fuzzy wood grained side of the FT Forums :applause:

(At least I think a welcome is due - I don't recall seeing other balsa builds in your posts, but I might have missed them)

Are you planning to stay in the native rubber power zone with this one, or has the idea of a UMX style receiver brick conversion caught hold of you yet? Or is that plan being saved for build number 2?

 

[DarkFire]

Thanks for the welcome! This is indeed my first balsa build, and since it is I am debating the rubber or RC question. I've heard some people say that converting a stick and tissue plane is a lot harder than it looks, something to do with the reinforcements needed. I do have the guts from a UMX spacewalker and a micro champ that I can take apart. Do you have any experience with these conversions?

 

[rockyboy]

Just one - and it was a little bit frustrating at times, but really awesome to see it fly on the fifth or sixth rebuild when I got it right

I'd probably recommend you'll have a less frustrating experience if you do your first kit by the recommended instructions to learn the techniques and have a success to tide you over through the rough spots of the first conversion build. But if you are the kind of person who loves tough building / engineering problems and enjoy figuring out seemingly inexplicable problems then by all means go for it!

 

[DarkFire]

Update #1

I have decided to go with an RC conversion of this plane with the electronics from a Hobbyzone Champ. That will include a tray for the ESC/Servo/Receiver brick thing and a mount-ish for the motor. Those tiny UMX style motors are really easy to install though, so it might not even need extra bracing.

Anyway, here's a pic from my first evening of building.



Other than a few moments of asking 'how the heck do I unstick this from the plans?', the two fuselage frames and 4 formers went together really well. I've only done this much and I'm already hooked!

 

[DarkFire]

Alright, a couple questions based on the RC conversion. When I make the tail feathers, is it worth it to make them stock (the tail is right below the fuselage frames in the last post's pic) or out of solid balsa? Also, what should I use as hinges on the control surfaces?

Thanks,
Dark

 

[rockyboy]

I'd suggest staying close(ish) to stock and just doubling up the balsa spar at the hinge line so you have a solid piece on either side. For something this lightweight, a tape hinge - packing tape or 3M blenderm medical tape should work great

 

[DarkFire]

And i would assume that tape goes under the covering, right?

 

[rockyboy]

Over actually - as long as the covering is attached well it'll work just fine. Surprising, I know

 

[DarkFire]

Huh, glad I checked. Could have screwed that up

 

[rockyboy]

Been there, done that, got the t-shirt :black_eyed:

 

[Joker 53150]

+1 on the Blenderm tape by 3M. It's very sticky, flexible, and doesn't get brittle with age or temp. I've got some planes built 5 years ago with it, and the tape is still as good as the day it was applied.

 

[DarkFire]

Does Office Max sell this tape? Or maybe some similar store?

 

[Joker 53150]

I've only seen it online or at hobby shops. Hobby King sells it, I think in 1/2" and 1" wide rolls.

 

[rockyboy]

I've found it in the bandages section in both CVS and Wallgreens pharmacies

 

[DarkFire]

Ok, cool. Probably should have read this before passing Walgreens on the way home

 

[DarkFire]

Long Rambling Post

As a result of multiple factors *cough**cough* school *cough*, I haven't been able to post any updates in a few days. I have been working on the plane though, so this long post will be a combination of 3 days' work.

After I assembled the fuselage frames I glued them to the formers. I haven't put the stringers on just yet, but I'm almost ready to do so. The wing has been built and sanded to shape, along with the elevator and rudder. Up front, the fuselage has been modified to hold UMX Spacewalker electronics and is ready to be glued together.

Anyway, on to the pictures!



The two wing halves built and ready to be sanded.



Both the elevator and rudder assembled. If you notice, just to the left of the elevator you can see the plans for it. It only show one 'strut' if you will spanning the whole length of the surface. I doubled that up so I can make a tape hinge as per RockyBoy's suggestion.



The wings and control surfaces ready to go! When I built the wings, I followed the instructions by building the two outer sections first then the center section. But I noticed the plans said to sand the wing's leading edge and trailing edge after gluing the wing halves and center together. I found it easier to sand them when they were separate.





To install the motor, I cut a little piece of plywood to the shape of the cowling hole, then drilled a hole in that to stick the motor in. After some sanding it fit into the front nicely.





The stock cowling had to be drilled out a little to fit the gear on the prop shaft comfortably. It turned out to be just right



I also made a little tray for the receiver/ESC/servo brick thing. I thing the battery will go in between the bulkheads behind it.

 

[rockyboy]

Looking great!

Before settling in on the battery location and committing to the receiver mounting, it's a good idea to think about Center of Gravity. With a rubber powered model, the weight of the rubber motor is spread sort of evenly down the fuselage, but in the world of electrics you have a couple pieces carrying most of the mass.

If possible, it's best to center the receiver brick right at the center of gravity location so it's not impacting things. That takes care of the biggest weight. The control horns and rods going back to the tail are going to largely offset the motor being up front, and the battery bay should need to be pretty close to that center of gravity, maybe a little to the front - but this is also influenced by how heavy you are with the glue and the amount of surface to cover too

If you can get things close to balancing just loosely assembled before covering, and give yourself room to move the battery around by a good bit (1/2 to 3/4 of it's own length) I think you'll be in good shape post covering, and not need to add much dead weight to balance her out.

 

[DarkFire]

I can get the battery below and even behind the CG, but the receiver is pretty far up there. Do you know if there are any extensions for the motor connection?

 

[rockyboy]

Soldering together an extension would be pretty simple - but if you don't have a soldering iron yet we can get to that skill later

There are extensions available here:

http://www.rc-connectors.com/index.php?main_page=product_info&cPath=115_84&products_id=414

http://www.ebay.com/itm/Mini-Plug-E...hash=item35cb35b417:m:mA2dyRfJl_BeXYLb2Gw3N-A

https://hobbyking.com/en_us/mini-plug-extention-for-micro-battery-10cm-5pcs-bag.html (out of stock at the moment, but best price per piece)