Seduced again! One look at the K & A Models ad in the magazine, showing a picture of a twin-motored Bronco, and I had to get one. I remember that ‘other’ Bronco kit – the one that could be converted to electric. This one has nearly the same wing area, but was designed as an electric for two Speed 400’s. It just couldn’t be as heavy as that other one, I thought. ..and it’s not.

Built pretty much ‘stock,’ the ready-to-fly weight is 44.3 ounces (1255 grams). That gives a wing loading of 18.8 ounces per square foot of wing area, with two props spun by 750 SHP turbos pulling this little beauty into the wild blue yonder …oops…that’s the prototype specs! Imagine, though – you are in a de-militarized bronco: No gun pods, no combat radios, no armor, nothing on the hard points so your flying weight is around 10,000 pounds – and you have 1,500 shp on command. "Hot" seems a fitting description of this Fireboy’s Flyer!

 

Flying qualities

So how does it fly? Quite well! Very stable, and the control throws recommended are tame so that there were no surprises. Well, except for the speed. It is slower than my Zagi 400! Now, that is not a problem - it moves around the sky with authority, and with good control. But this is not a highly-loaded model (under 19 ounces per square foot) and with the recommended 6x4 props and 16 cells in series, it just isn’t a speedster. Hey, on the first flights – slower is good! I intend to try different props, though. I want just a bit more speed.

Incidentally, landings are like a fast walk – the Bronco did not slide even 20 feet on our slick nylon-belt runway, at the end of the flight. Oh – the 6x4 props, even windmilling, didn’t touch the runway on landing due to the angle between the bottom of the fuselage, and the wing-tips. No broken props upon landing!

 

Color and Markings

The color scheme I chose is one used by the California Department of Fire, where they use a fleet of 14 Bronco’s for fire spotters. The scheme is well-documented by Bob Banka, of Scale Model Research, with the best set of photos I have yet seen for a scale modeler.

I first saw this color scheme in the back of the "OV-10 Bronco in action" book from Squadron Signal, #154. If you don’t like the CDF color scheme, take a look at the Squadron book, as it has ten military color schemes – all of them eye-catching. The Squadron Signal book also has great detail shots of the cockpits, weapons systems, cargo area, and gear shots – and the only photos I have seen of the OV-10B(Z). This last variant was developed by North American for the Germans, who wanted more power to tow target tugs. They mounted a jet engine on top of the wing! No color shots of these, but several black and whites.

If you want a red, white and black Bronco as wallpaper for your computer, go to: www.fire.ca.gov/cdf_fp_airfight.html (those spaces between cdf, fp, and airfight are really Underlines). Scroll down the page to the Bronco; then rightclick on your mouse and select Wallpaper from your drop-down menu (assuming you have Windows 95). Another great site for Bronco info, or PC wallpaper, is: www.ov-10bronco.net   Gentlemen, click your mice!

Building the Kit

You will like this kit – premium balsa, selected for each application. And the canopy! Very scale, clear, and thick! The plans are minimal, but since it is a war-bird (well, depending on the color scheme) and a twin-boom model, chances are than anyone building it will have plenty of building skills. If you don’t, hook up with someone who does in your club.

If you have any questions while building the model, you will appreciate the customer support from K & A Models. I emailed Ken Williams at K & A Models several times during my building of the kit, and he always responded immediately to my questions. After completing the model, I emailed him the below issues and comments. He notes that over 120 kits are now amongst us, and most of the issues have been addressed in the later runs of the kit. Your plans and kit should be great, but you might like to see how another modeler went about building an early kit. If so, read on.

 

Wing

Reading between the lines of an email from the manufacturer, I guess I spent unnecessary time on this mod, but I did not want to have two wing-spar glue-joints in the center of the wing – even on a 44-ounce model. So, I took the 4 spar pieces and cut two of them in half, and scarf-joined two pieces to each end of the other two pieces, creating two spars. That gives three pieces for the top spar, and three for the bottom spar. I had to be very careful to keep the scarf cuts accurate (sand carefully with 250 grit paper and an aluminum sanding bar), but I got what I wanted: no center glue joints on the spars, and no need to fiberglass the middle of the wing (and have covering hassles from that).  It should be obvious, then, that I  built the entire wing in one piece. I always prefer that when the wingspan will allow it, since it reduces the sanding I always seem to have to do to get the trailing edge even.

The ribs for the part of the wing between the two booms have a hole drilled in each one, permitting passage of the servo and motor wires. Before gluing any wing ribs I drilled another hole in each rib, about an inch closer to the spar, for the motor wires. I wanted some separation (even one inch is enough with Speed 400’s) between servo wires and motor wires.

Wait - don’t glue any wing ribs, yet. Check carefully to ensure that each rib seats completely over the bottom spar, touching the bottom sheeting. Some of my ribs had to have the slots enlarged. Do a similar check with the top spar, before gluing. Ensure that the spar seats fully into each rib - check with a straight-edge (ruler) to be sure that the top spar is flat across the top.

This item seems critical. It sure changed how I assembled the tail booms, much later in the building process: The original plans and instructions say to plank between two ribs on each side of the wing, at the area where the tail booms will be glued. When I did that, I found that there was no wood extending out past the sides of the tail booms (on the bottom of the wing) to which I could iron on the covering. So - cut the planking for the bottom of the wing about ½ inch wider, where the tail booms will later be attached, so that the planking will extend about a quarter inch wider on each side of the ribs than the plans show.

You can save possibly 5 grams each side of the wing, if you hollow the wing tips. I was amazed to find that so much sawdust lightened the tips so little. This kit has good wood! Same result for the motor wire holes I drilled into the inner wing ribs: Not even 6 grams total savings.

I chose to block sand the wing before cutting the ailerons free, instead of following the instructions and doing it after the ailerons were free. I have had more consistency, this way, on my wings.

The plans did not show where the aileron servo wires run, or the motor wires, either – and more importantly, the plans did not mention to run the wires through the wing, before one is instructed to glue parts (miss this and you’ll have to fish the wiring through, later).

The two pictures of the fuselage pod sitting on the wing (with the tail-booms already glued on) show the orange and blue Sermos motor wire plugs, which will plug into the ESC in the fuse pod. The ESC is Velcroed to the side of the fuse pod, above. The blue blob with the white rod going to the right is the Dean’s antenna; the white rectangle above the blue blob is the Rx battery. The Rx in hidden inside the round cross-piece which the wing will butt against – you can see all the servo wires disappearing into the recess where it, too, is Velcroed. The vacu-formed rear of the fuselage is screwed onto four pieces of ply, one of which is visible just at the rear of the fuselage by the antenna, and another on the opposite of the rear of the fuselage.

Before covering the wing, ‘dry fit’ your motors and radio system. Ensure that your elevator, aileron and motor wiring has been completely thought out, extensions checked, and run all your wiring inside the tail boom and wing – to the center section, and out some holes – before you cover the wing. The plans don’t prompt one to do that, and I trust plans to tell me these things! (Check to ensure that your wiring comes out holes you cut in the bottom of the wing.)

 

Tail Booms

I had never built a twin-boom model, and I only decided to do the Bronco because a flying buddy has done twin-booms and I could always plead for help if my fears of misaligning overcame my desire to see the Bronco fly. (Translation: if I chickened out and quit.) Surprise for me: Although there was a lot of fiddling, blocking, weighing parts so they didn’t move, and measuring with my Robart incidence gauge – the booms came out so perfect that I can’t see any angular difference between them. All that worry for nothing!

I turned the elevator servo upside-down relative to the plan, for ease of future maintenance. I would rather cut in through the bottom of the boom, if I have to, than have to take the (glued) wing off the boom. I also used a Futaba S133 for that servo, instead of one half the price, because that elevator servo is buried in that boom.

 

Fins and Stab

I noted that the pieces for the fins are of different thickness, and emailed Ken Williams at K & A Models about that – he noted that the differences between the wood sizes creates a ‘step’ between the fin and the rudder, which he says looks great after covering – just be sure to get the Monokote sealed tight at that step. I chose to sand the step off, and the ‘rudder line’ you see in the photos is created by a 1/32 inch piece of Monokote…easy to do all the panel lines that way, and the color lines too. (Use a metal ruler and a new blade to cut the small pieces, and just cut carefully, holding pressure on the covering with the metal ruler so it doesn’t move. Scissors won’t give you as straight a cut. Tack the strips down with the iron on medium, with a sock on the iron. If you want them to stay on forever, put a little thin CYA on the edges.)

NOTE: There are no incidence references for the wing or the elevator. I measured carefully, and the horizontal stab to wing difference is 2 degrees, with the front of the stab being negative (down) relative to the wing. Because of the height of the stab relative to the wing, I thought it was much more, but an email to K & A confirmed this measurement. I used a Robart Wing Incidence rig to measure this, too.

 

Attaching the Wing to the Fuselage

This is not a hard step – but: The only error I made with this model was in the attachment of the wing to the fuselage. I decided that gluing the wing to the fuselage would save me half an ounce…and now if I ever want to get inside and swap ESC’s or Rx’s or anything else, I have to hire an elf to crawl in there – no room for even small hands. So - follow the instructions here, and make the wing removable, or you’ll have to pay the same price I will, in the future.

 

Overall Impression, and Ordering Instructions

What a model! I am going to order another Bronco from K & A Models, so I have one on hand should something nasty happen some flying day. This model is even nicer than my Kyosho Agwagon – since it has two motors.

If you like the looks of a Bronco, and like smaller models – you will love this kit. Order yours from your local hobby shop, or through K & A Models.  Email: kenwood(at)nmia.com.