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Scratch Build Design: Swappable Rockwell Bronco OV-10

#1
I was a scale model airplane builder as a kid, not RC but your standard plastic models. While walking down the isle at the hobby shop I caught my first glimpse of the Rockwell Bronco and I HAD to build that plane. Something about it made an impression, with it's twin prop, twin rudder, high tail, and a central fuselage with it's high, bubble cockpit. It looked like a mash up of a P38 Lightning and a Huey Cobra, so ugly with so much visual attitude.

In a cold war age dominated by the screaming air superiority platforms of the F14,F15, and then new F18&F16 this was a small, close support fixed wing that was designed to use roads for runways if it had to (20ft wide road). Versions of it were used for everything from Air-to-ground attack, night attack, paratrooper insertion, air ambulance, reconnaissance, and it's currently used by California to fight wildfires.

ov10a.jpg
bronco 4.jpg

My own personal encounter with a Bronco in Pima AZ
2 AroSpace Center Outside_05.JPG

While watching the FT Cruiser supplemental video I realized that here was an awesome twin engine platform that might be able to be packed into a swappable dollar store foam core Bronco!

So I'm going to try and design/build/test fly my own design of a Bronco, what could possibly go wrong?

I'm starting out with google sketch up and I'll try and document as much as I can. I'm using a very precise technique called "iBalling-IT".

I located a good three view of the aircraft and pulled it into Google Sketchup and applied it to a rectangle. I've also built a virtual power pod to scale and I'm sizing the plans to fit the power pod into one of the nacelles.
Setting-up-scale.png

I then drew the outline of the wing...
Drawing-wing-shape.png

...and then drew the center fuselage profile shapes.
Creating-fusalage-profile.png

I followed this up with the nacelles, rudder, elevator and top view of the center fuselage.
Created-nacelle--rudder--and-elevator-profiles.png

I pulled up copies of my geometry and extruded them 3/16th of an inch to give myself some virtual foam board shapes to work with.
Mirrored-and-Angled-fusalage-panels.png

I continued this technique of building up a simple 'cut out' shape and then extruding the thickness. Once I get the whole thing worked out I'll have to go back and plan out my 50% cuts, A&B folds and where some panels will meet when the real foam core is cut out.

Here I've pulled in a virtual power pod to continue my super precise "iBalling-IT" and work on the nacelles.
Poping-out-sides-of-nacelle.png
Test-fitting-nacelle-with-powerpod.png

For giggles I wanted to see how a KF airfoil would look but I'm going to redo the wing to be closer to the FT Baby Blender airfoil.
Blocking-out-KF-wing-for-gut-check.png
That is as far as I've got but I'll update this as I go along. In the end I hope I'll have a fairly good approximation of the Bronco that (hopefully) flys with many of the STOL characteristics of the full size aircraft.
 
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earthsciteach

Moderator
Moderator
#3
Looking great in the CAD world, Jason! I need to familiarize myself with Sketchup. I really like this extrude technique you are using.
 
#6
Looking great in the CAD world, Jason! I need to familiarize myself with Sketchup. I really like this extrude technique you are using.
It helped me realize a fatal flaw in my thinking of how to do a twin nutball.
Double-Nutball---SketchUp.png

I'll either need to go with smaller props or a larger body but imagine 'Crazy Mode' on a nutball.

Come to think of it... the more I look at that nutball the more I think a 'pod racer' type design could be built off of the nutball idea. (I'll look into that after the Bronco)
 
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#8
Utilitarian it may have looked but it was never intended to have a STOL performance and at it maximum take off weight of 14,000 lbs it certainly wasn't.
Indeed in Vietnam it was considered to be seriously under powered for close support duties being unable to climb out of a steep terrain which resulting in several fatalities.

Nice design so far but a pity you could not use true scale sections. ;)
 
#9
Swapped out the KF for a baby blender wing.
Bronco wing.png

I'm going to curve up the wingtip to match the Bronco but this just feels like a much better wing for this.
Bronco_wing2.png

My plan is to get the whole plane built virtually, discovering and fixing any problems with the foam thickness and intersections. Once I'm confident with it I'll basically unwrap the shapes and lay them flat in in Sketchup to create a printable plan. Once I have these shapes I'll tile/print them and cut out a physical prototype. I'll add in the electronics and test fly this first prototype.

As I assemble and fly the prototype I'll note any revisions on my prototype printed shapes and then transfer these back to my Sketchup plans. Rinse and repeat until I feel I have a solid set of plans. Once I have a solid build and fly I'll put the plans together in a public ready format, maybe even a build video.
 
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#15
any updates on this project?
It's been on the shelf for a while while I was getting my first plane ready to fly. Now that I've got that under my belt I'm going to be picking this back up. I've even found a plugin that I hope will help automate the 'flattening' of the model out to printable plans.
 
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#16
Dude, if you get this thing going, you are my hero! My dad flew these in the early 70's. I got to sit in one. I still remember him telling me "Don't touch anything!" This was his squadron, VMO-2, at the time. I know I have some photos somewhere. OV-10A_Bronco_VMO-2_parked.jpg
 
#18
Dude, if you get this thing going, you are my hero! My dad flew these in the early 70's. I got to sit in one. I still remember him telling me "Don't touch anything!" This was his squadron, VMO-2, at the time. I know I have some photos somewhere. View attachment 12790
Funny thing, my mom used to work on the A4 Skyhawk back in the 70s, like the one in the background of your photo. T-A4-J actually. I'm pretty stoked. Still trying to figure out the best way to do the rudder linkage. I'd like to only use one servo to drive both rudders.