L-19 Bird Dog, Balsa Scratch Build

Joker 53150

Mmmmmmm, balsa.
Mentor
Finally something to mention on this build! Nothing major, but an update is an update. Back in late December I sent a check for the L-19 cowl and the plans for the T-28 (gotta have more planes in line for construction!). A new job and life in general got in the way of building and I forgot about the order until a few weeks ago when I realized I didn't get the cowl yet.

So I called a few weeks ago and was told that the check must have never arrived or the cowl & plans would have been sent out. I decided to skip plans for the T-28 and instead get the L-19 cowl and plans for the Microwave (see pics), and sent another check. Again I forgot about it again until today, when I called to see if check #2 arrived. I was promised a call back once they looked into it. When I got home from work today, a box was waiting for me. I figured it was order #2, but turns out it was order #1!

Weird timing, and a bit annoying having to wait just over 3 months for a simple order to arrive... I'll probably let Order #2 go as planned so I have a second L-19 cowl. The Microwave would probably go into the build order before the T-28, but there are other planes also waiting patiently to be built. Eventually...!

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Joker 53150

Mmmmmmm, balsa.
Mentor
A new job has kept me pretty busy, but I finally got back to work on the L-19. I'd like to have it finished in time for Flite Fest 2014, but we'll see how that goes.

The servo tray was cut to match the plans, but the servo cut-outs were much larger than the 9-gram servos I'm using so I had to add a little support for the servos. Supports for the wing hold-down bolt were also added. There is a lot of detail work needed now, so updates will be a little slow.

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Joker 53150

Mmmmmmm, balsa.
Mentor
FINALLY getting back to work on the L-19! The cowling was cut to size, the motor mounted with the recommended 5 degrees down-thrust, etc. I started off with the wing to see how the finishing method would work out. Sanding sealer was applied, sanded lightly, and re-applied before paint was sprayed. I haven't finished straight balsa like this before so this was new to me. The pieces I tested before moving to the wing all worked out well, so I gave it a shot. There is minimal grain showing through but it isn't really noticeable.

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Since the wing turned out well I did the fuselage in the same manner. This surely adds some extra weight, but the plane is so light I'm not too concerned. The top of the nose was painted black. It's really screaming for some graphics right now, so I'll have to get started on making those soon.

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Last, I finally got to the tailwheel work. Too much epoxy was used so it started running on me after I set it down and walked away - lesson learned on that one! It'll be hidden pretty well under the elevator and will disappear pretty well once I paint it, so no big deal. A control horn still needs to be added for the rudder. Some creativity will be needed to make it all work properly.

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Joker 53150

Mmmmmmm, balsa.
Mentor
I'm still slowly chipping away at the work needed to get the L-19 in the air. The wing struts really slowed things down, as I wasn't sure how I wanted to do them. For a light park flier I'm not sure they're absolutely necessary, but visually they help complete the look.

I've also been trying to figure out how I wanted to mount the battery. The original plan was to simply slide a 1000mAh 3S in through a side window which would allow easy access without removing the wing. However this would leave the plane very tail heavy in part due to the sheeting I used on the tail instead of lighter weight film covering. There is a small amount of room under the instrument panel which would let a batter sit far into the nose so I'm going with that option. A 1000mAh will just fit and may be enough weight to balance it out.

I also did some trimming of the elevator as the rudder didn't have a lot of travel in the stock size. With the trimming done I think there should be plenty of travel for both elevator and rudder.

Front and rear canopies were cut from clear plastic and installed. This was my first attempt at making them from scratch and I'm happy enough with the results. Not perfect by any means, but they're good enough for now.

Still to come: painting the struts and touching up other details, hooking up the servos, and a few other details so it's ready for flight.

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Joker 53150

Mmmmmmm, balsa.
Mentor
Thanks!

It looks like the L-19 is ready for a maiden flight. There are still finish details to take care of, but I'll see how it flies before I spend the time on finish work. Assuming all goes well I'll make my own vinyl graphics for it. I have all the equipment at work available to me, all I need to do is find the right font and work on my creativity.

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Pics 2 and 3 show the mounting of the wing struts so they're removable. I wasn't paying attention and installed them on the wrong sides for these pictures. Swapping them around will make it less likely that the top piece can slip out of the plywood "donut" (the donuts are prop washers that came with my Flite Test tri-copter camera/battery mount).

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The last picture shows how tight the area is for control horns and linkages. It'd be easier if the rudder were about 1/2" longer at the bottom.

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I'm still kicking myself for sheeting the entire fuselage, although I like how it looks. That much extra weight in the tail required 3/4 ounce of lead in the nose to balance it.

Once I finish the programming on the radio to limit the throws, set dual rates and expo, etc it'll be ready for the maiden. Weather for the next few days appears to be questionable, so I've got plenty of time.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Oh, my goodness, this thing is beautiful! Fantastic work, Joker! Coming to FTFF, by chance?

Yes, I convinced my dad to take a short vacation with me over his birthday, and might also bring my son for 3 generations of Jokers.

Thanks for the compliment, I'm happy with how it's coming along and hope it flies as well as Uravitch planes are rumored to fly.
 

Joker 53150

Mmmmmmm, balsa.
Mentor
Joker 53150
What is its all up weight ready to go?

All-up weight including a 1000mAh 3S is 17oz/480g, which is an ounce or two less than the plan designer's description. Possibly because electronics are lighter than when he drew up the plans?
 

quorneng

Master member
Joker 53150
The 'open' wing under surface gives in effect a high under camber wing section. This will indeed create generous lift (the WWI aircraft designers knew all about that) but it does rather become a single speed wing. Too slow and the stall is dramatic yet the drag will rise rapidly with speed.
In addition as it speeds up the centre of pressure will move forwards requiring ever more down elevator to keep the nose down, assuming you have the necessary power. ;)

However I am sure within its limits it will fly fine. Do let us know how you get on.
 

SnowRocker88

Amateur pilot and builder
Couldn't you just skin from the root out and leave a section of the wing, near the tip, open? So it would have the extra lift and resist tip-stalls but wouldn't have the drag issues as bad? ...or would this create a poor wing-loading situation?

Great build btw. I love the craftsmanship that comes with a balsa plane.
 
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Joker 53150

Mmmmmmm, balsa.
Mentor
Well, it flies! Here's a quick video of the maiden take-off. It pulls hard to the side right now, possibly due to some warping on the wing, but that is being fixed now before additional flights. I think the CoG listed on the plans is a little far back, maybe 1/4" or so, but I'll know for sure once the wing warping is taken care of.

Also, I think I've over powered it with the current motor/prop combination. It'll take off easily at 1/2 throttle and cruises at around 1/3 throttle. That is being adjusted as well since this plane doesn't need a ton of power.

Even with the less-than-perfect flight, I'm happy that it's back on the ground in one piece. A little tweaking and some vinyl stickers and it'll be done.

 

Joker 53150

Mmmmmmm, balsa.
Mentor
The plane has been flown a few times now. The wing warp has been a headache but I might finally have it cured. I had to cut and re-glue 4 of the ribs to get most of it out. I also steamed it and weighted it to force some more of it out. Last, shimming the trailing edge took care of the rest.

The vinyl decals are coming along for my first attempt. The lettering is all done, so next up will be the stars & bars. Letters are easy but the multi-color pieces will be trickier, but it's a good chance to learn the software. Lucky for me, I've got all the equipment to do this at work.

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