OV-10 Bronco Replica- Redux

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Terrh

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I am thinking though that it will be closer to 3000#. I figured roughly 1020 f^2 wetted area, and that is a single engine pusher. There will be a lot of structure and systems in the booms and tail, and the forward fuselage will have a lot of structure as well, as it is cantilevered far forward of the wing. Not to mention all of the complexity and weight involved in making it twin engine.

I think I will probably stick with the single engine pusher idea, although it would be awesome to have twin engines.

Twin engines might be lighter. All things being equal, The wing, booms, etc can all be lighter if the engines are on them then if they aren't, because the load is cantilevered less. With all the heavy stuff being in the middle of the airplane, you need a stronger wing structure to support it, both in terms of lift, and landing gear loading.

If you are wanting a single pusher, you're going to probably need something like a GM LS2/3 based powerplant, which is realistically 500# and then eats up your entire cargo bay.

The cockpit is substanitally cantilevered compared to, say, a 172, but it still isn't cantilevered that far. at 80% scale the pilot seat is only about 4 feet ahead of the leading edge of the wing. That's less load than your standard single engine airframe would have up there.
 

Staggermania

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I see your point on the cockpit.
As far as doing twin engines, I see packaging as the main issue. It will be tough to find an engine that will fit and not ruin the lines.
I think the Rotax Rick twin idea has promise, but I think it would be underpowered. I think that a parallel hybrid design could work pretty well. Put an electric motor between prop and rotax for takeoff and climb. Could even fit the batteries in the nacelles.
 

Riggerrob

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Note how far forward pilots sit in the original Bronco and how short the engine nacelles are.
NAA faced the same dilemma as Ted Smith did when designing Aero Commander and Aerostar twins. Smith installed pilots just forward of propellers, a maxim adopted after Northrop P-61 Black Widow crew were killed by broken propeller blades during gear-up landings. Smith solved balance problems with short nacelles and forward swept wings. Yes, Aerostars have straight leading edges, but main spars are swept forward a bit and the trailing edge is swept forward a lot (ala. WW2-vintage Mosquito bomber).

Safety, weight and balance favour a single pusher engine.
Compare your scaled-down Bronco with a two-seater sailplane or Advanced High Performance Light Attack and Recce. Both simplify weight and balance by installing the rear seat back against the wing spar. This position simplifies weight and balance calculations. Both types also sweep wings forward to help balance. As long as forward sweep is kept to less than 10 degrees, it has little effect on structure or aerodynamics. Because the rear pilot’s eyes are so close to the leading edge. The second pilot only loses a little down-wards vision.
With a single engine mounted in the aft end of the central gondola, you might even be able to balance a pseudo-Bronco replica without sweeping wings.

As an aside, most of my recent sketches include a half-scale Blohm und Voss 141 assymetric airplane.
 

bmcj

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Stagger, you mentioned And post#1 that the verticals were oversized. One thing you have to take into consideration is that when you have a twin services like that, they tend to act more like a single surface because the area between is somewhat neutralized by the play of low and high pressures.

And a (not so realistic) suggestion for fixing your weight and balance problem... two small turboprop engines. It plays hell on the checkbook, but it gives you buku points for realism!
 

Terrh

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at 80% scale you've got something like 20" of nacelle width staying exactly to scale (Windows 10 just broke sketchup or I could look it up exactly)

A little bump or two wouldn't change the lines if it had to be there.

There are a TON of inline 4's that would fit within the nacelles and easily make the power needed. Short enough to fit within the height as well, or at least real close.

Doing a part electric will make things much heavier for minimal gains, unless you used maybe an auto engine w/ integrated electric assist, like the honda IMA system or whatever.
 

rv6ejguy

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Suzuki 1.3 putting out 194hp? That's nearly 150hp/liter.

Not without a turbo or some extreme rpms- like 9500+. Longevity at this output wouldn't be good for aircraft use.

You'd probably want at least 180 hp per side so it had a rate of climb on one engine (220+ if the props don't feather).

That leaves you with aluminum turbocharged inline fours or really narrow 60 degree atmo V6s if they are to fit inside the scale cowlings.

I think empty weights would be at least 1800 pounds with this sort of recipe.
 

Terrh

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The mazda rotaries are exceptionally reliable and compact, though they are thirsty and require substantial cooling. And while they're very light by 1980's standards, they're not that light by today's standards. Still, not a bad option. But I think there are better ones.

The suzuki 1.3 (hayabusa engine) does make 194HP at 10K RPM. But when I figured it out at 2500# you'd only need ~160HP which comes at a subsantially more reasonable 7000 RPM. And that's just for climb. They will absolutely handle 7000 RPM all day long reliably. I'm not sure if I'd push one to 2000+ hours TBO but I'm assuming that anyone that tried using one in an airplane would likely do some testing first. In the event of a single engine failure, there's no reason why you couldn't run it up right to 10K if you needed to. The redline is 11k, and while big numbers sound scary, they aren't really. The rotax 912's sit at 5000+ RPM cruising with a WAY longer stroke and a much heavier piston/rod combo.

An all aluminum turbo inline 4 is a great idea too, especially with there being so many fantastic examples of them these days. Cobalt SS/pontiac solstice and the new hondas both popped into my mind.

What I'd personally love to try (but can't seem to find the ideal engine so far) is an aluminum turbo 4cyl diesel. Apparently some year Chevrolet Cobalts have them, and I'm told they are a variant of the fantastic european honda 1.6 I-DTEC. But i've never seen one with my own eyes.
 

rv6ejguy

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Ok, talking bike engines. Then you'll need to spend some time on redrive design and torsional vibration testing with the large rev range required.

Diesels are all too heavy to be practical here and again some different issues with TV and the gearbox.
 

MadRocketScientist

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An experimental air frame and experimental engines are a bad combination, there must be some proven engines that are a suitable size that would make the project safer? Even if the looks weren't quite right, once the air frame was proven they could be exchanged for less well known units?
 

Staggermania

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And a (not so realistic) suggestion for fixing your weight and balance problem... two small turboprop engines. It plays hell on the checkbook, but it gives you buku points for realism!
Yes, turboprops would be awesome! I agree it would play hell on the checkbook, but that's okay because we can use yours;)
 

Staggermania

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With a single engine mounted in the aft end of the central gondola, you might even be able to balance a pseudo-Bronco replica without sweeping wings.
It has been a while, and I appear to have lost all of the data, but I was able to balance without sweep. I think I may have needed some ballast on the booms, though.

As an aside, most of my recent sketches include a half-scale Blohm und Voss 141 assymetric airplane.
That is a wild looking plane!
 

rv6ejguy

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They are still rare, but there are more and more lightweight all aluminum diesels. Subaru even makes one that's only about 20lb heavier than their gasoline engine.
The EE20 Subaru diesels had some issues with broken cranks. Not sure they've solved that issue yet. They are still almost 75 pounds heavier than an EJ SI engine of similar power.
 

Riggerrob

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Not folding, but rather slide outboard wing sections into and out of the center section. If booms are no wider that 102” outside to outside, then it would be trailerable. Might need to drop it down on its gear some for height, but certainly doable.
————————————————————————————————

Simpler to simply fold (outer) wing panels inboard so that they lay on top of the fuselage. This reduces folded width to 8’ 8”.

Alternately, you could build aft booms as single-layer profiles and install hinges at the (main wing) trailing edge. This will retain 26’ wingspan, but reduce (folded) length to. .
 

autoreply

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Why not electric? Have two powerful electric motors (geared) turning big props and a generator behind the pilot? This would solve both the CG challenge and the small nacelles. Add a small (5 min power) battery and you have twin-engine reliability for EFATO.
 

Staggermania

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Why not electric? Have two powerful electric motors (geared) turning big props and a generator behind the pilot? This would solve both the CG challenge and the small nacelles. Add a small (5 min power) battery and you have twin-engine reliability for EFATO.
Thanks for chiming in AR:) Don't know if you saw my previous post about a Parallel Hybrid using the Rotax Rick engines?

Anyway, I have thought about going with a serial hybrid configuration just as you suggest. If I were to do a faithful replica, I think that this would be more affordable than the twin turboprop.

I think, though, that my ultimate goal is to have an airplane that is unmistakably Bronco inspired, but is relatively simple to build and operate, and relatively inexpensive. I think that a single engine pusher, maybe with a Lycoming 540 putting out 300 plus HP, would be "fastest to the fun":)
 

Tiger Tim

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Simpler to simply fold (outer) wing panels inboard so that they lay on top of the fuselage. This reduces folded width to 8’ 8”.
With the long gear legs of a Bronco, the high wing and the short span, you might even be able to fold the wings down. There would be no mistaking if the locking pins got missed on the pre-flight and if they somehow came unlocked in flight it should give a much safer failure mode.
 

Toobuilder

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...I think, though, that my ultimate goal is to have an airplane that is unmistakably Bronco inspired, but is relatively simple to build and operate, and relatively inexpensive. I think that a single engine pusher, maybe with a Lycoming 540 putting out 300 plus HP, would be "fastest to the fun":)
There was a time when I too was looking at doing a "Bronco inspired" design. Probably a bit more abstract than even a stand WAY off scale, but it captures the chunky look of the OV-10. Think Long Eze fuselage (no canard) shoulder mounted hershey bar wing (three, 10 foot sections with polyhedral), the characteristic Bronco booms and tail, and a direct drive V-8 pusher.

Maybe someday.
 
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