It seems I'm the happy recipient of this beautiful 1/6 scale airframe. The previous owner/builder (Dr. Joe Makovich) wasn't able to complete her & so she sat for many years. When I heard she was just gathering dust I happily volunteered to take over the project. As you can see she's been masterfully crafted...
All balsa/plywood construction (note the side windows haven't been cut out yet)...
She's a nice size at 72" (1828mm)...
Love the scale corrugation work on the control surfaces...
Beautiful functional fowler flaps...
Beneath the fiberglass cowl lurks a gas motor mount...
So technically this is a kit built airframe (someone built her from the plans up) but for my purposes, she's ARF. From what I've read about Jack Stafford's kits, this was no easy build. Even though I enjoy kit building, its nice to have the bulk of the work done, especially as it appears to have been done well.
So what are my intentions for this Bird Dog?
As an avid RC sailplane pilot I spent last Summer learning the finer arts of being towed aloft by an RC tow-plane. This year I'd like to return the favor & do my share by aerotowing with my own tug. So I'm entertaining the idea of outfitting this bird-puppy as an aerotowing workhorse.
Ben Diss' L19 Bird Dog tow-plane
Its high-wing layout should make for a nice stable platform. Its 72" wingspan, 1/6th scale should allow me to tow everything from an Easy Glider to a three meter glass-slipper. As a noob tug pilot I don't want to tow anything larger or should I say more expensive, until I have more experience. The big fowler-flaps should come in handy for diving back to the field after release. And lastly she's scale so should be a welcome addition at many of the scale aerotowing events I attend.
Gas Vs Electric
Yeap there's no doubt Gas rules when it comes to hauling sailplanes up, up & away. You can tow all day with just a couple gallons of the smelly stuff. With a line of eager glider-jockeys waiting to fly you don't want them waiting around while you're charging batteries.
I'm not a gas kinda guy though. I have not-so-fond childhood memories of my father having to start my 0.49 cox engine for me. I was afraid to stick my fingers anywhere near that thing, hated everything about it, the prop, the noise, the smell, did I mention the prop? 35 years later I still feel uncomfortable around gas planes which makes no sense, as electrics are just as likely to lob off a few digits *shrug*
Irrational phobias standing, this will be an electric aerotow tug
Several of my club mates have electric tugs & as long as there's extra batteries, they work out just fine. We've been averaging around five or six tows per battery, at say five to ten minutes per tow, all together that's enough time to fast-charge a second pack while towing with the other. Theoretically an electric tug should be able to tow non-stop with only minimal downtime while swapping out batteries.
One of the concerns with this airframe is the weight. The fuselage is primarily 1/4" balsa planking. The wing is fully sheeted top & bottom. She seems pretty hefty so I ran the numbers...
33 oz fuselage
28 oz wing
5 oz tail
13 oz aprox .60 sized brushless motor
15 oz 4S 4000mAh LiPo
3 oz 100a ESC
11 oz 8 standard servos
16 oz odds & ends
24 oz fiber-glass, paint, covering
148 oz or 9.25 lbs total (4.19 kg total)
With 714 sq/in wing area that equates too...
30 oz/sq.ft (91 g/sq.dm)
27 mph stall speed (43 Km/h)
Coming from a glider background those numbers scare the heck out of me. Then again if I run the full scale Bird Dog's numbers I get the same cubic wing loading.
Do I need to find ways to lighten her up?
I'm somewhat loathed to go hacking up the fuselage cutting lightening holes all over the place but maybe that'd what I need to do. I was also thinking about maybe removing some of the wing's sheeting, maybe cut lightening holes in the ribs. Leave the wing as a partial open structure & recover with Ultracote instead of sheeting. Basically put her on a diet. What do you guys think?