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Tiger Tim

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For civilian sport aircraft unconcerned with tail gunner firing arcs or the view straight down for reconnaissance or bombing, I think the approach of a fuselage housing the pilot (and passengers if any) and a single engine nacelle has a lot going for it.
I’d be inclined to stick with the engine on the fuselage and a nacelle for pilot/passengers as Dr. Vogt did. Just imagine if the rearmost seat(s?) in the passenger nacelle could be installed backwards what a view that could give or the incredible air-to-air photography vantage points that would become available. Field of fire but applied to civilian undertakings...
 

Jay Kempf

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Always liked Topaz asymmetric. Engine on back of pilot pod and front of tail boom. That's out of the box.
 

Riggerrob

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Dear Tiger Tim,
Great point about visibility for aerial photography!

If I ever built a two-seater replica of an asymmetric B&V 141, rear-sear passengers would only be able to sit looking backwards, but would have a choice of two machineguns!
Hah!
Hah!
Seating the rear-seater facing backwards also helps balance because his/her butt/centre-of-gravity ends up closer to the wing spar (ala. White Lightning 4-seater, kitplane).

My last sketches were of an ultralight that could fold into an ISO 20 shipping container. It started as a twin-boom pusher with both the engine and pilot in the gondola/nacelle.
Sketches soon lost the right-hand tail-boom, but I still struggle to make the gondola/nacelle less than 8 feet long. ... not did I want a loud, gasoline engine roaring that close to my ears.
The third set of sketches have only the pilot in the gondola/nacelle. The engine pulls from the front end of the left-hand tail-boom with tail-feathers bolted to the rear end of the LH tail-boom.
 

Topaz

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Like any red-blooded wannabe homebuilt airplane designer, I've looked at a lot of configurations, being drawn to "unusual" ones because they're just so "cool."

I happen to think Dr. Richard Vogt is probably one of the most un-sung aircraft designers we've ever had, who should be right up there with Kelly Johnson and Burt Rutan. His designs were often "odd", but always for a usually innovative and brilliant reason.

The BV-141 has always fascinated me as the basis for a homebuilt design, but when you dig into the details, it doesn't scale down small very well. The realities of the sizes of people, propellers, engines, and the unique packaging of this asymmetric design kind of pushes it bigger than an equivalent "conventional" configuration. That's not necessarily a problem, but it's something to be aware of.
 

cluttonfred

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To my mind, the question of putting the pilot and passenger(s) in a pod vs. putting the engine in a nacelle in an asymmetric comes down to relative mass. For low-powered light aircraft, the pilot in the cockpit with seat/harness/controls/instruments represent a significantly larger mass than the engine and prop, an effect that is even more pronounced with both seats occupied in a two-seater. From a handing perspective, it seems better to concentrate the mass as much as possible and move only what you have to move to gain the benefits of an asymmetric layout. Clearly a 200 lb Rotax 912 installation is going to be a very different animal than a 2,000 lb BMW 801 radial. There's certainly nothing wrong with the pilot pod if all-around vision is the specific asymmetric benefit you are seeking, it just seems more natural in a high-powered application where the engine far outweighs the pilot.

Keeping in mind that every aircraft is vertically asymmetric, here's another favorite of mine, the David Thurston-designed Patchen Explorer. The one and only prototype was bought but South Africa (pre-embargo) and evaluated as a FAC plane but never produced. It has been restored by the South African Air Force Museum and is flown regularly. It's hard to imagine better visibility in the forward hemisphere in a single tractor engine design but engine access and maintenance seems a little awkward. Still, that could sorted with built-in hand- and footholds and a reinforced wing walk area. The Explorer was a pretty big plane with a 200 hp Lycoming, but I would love to see a little 100 hp design along the same lines taking advantage of liquid cooling (Rotax, Aeromomentum, etc.) to flip the engine around as a pusher to move the prop further from the cabin for less noise.

Patchen Explorer in flight in South Africa.jpg
 

Topaz

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To my mind, the question of putting the pilot and passenger(s) in a pod vs. putting the engine in a nacelle in an asymmetric comes down to relative mass. For low-powered light aircraft, the pilot in the cockpit with seat/harness/controls/instruments represent a significantly larger mass than the engine and prop, an effect that is even more pronounced with both seats occupied in a two-seater. From a handing perspective, it seems better to concentrate the mass as much as possible and move only what you have to move to gain the benefits of an asymmetric layout. Clearly a 200 lb Rotax 912 installation is going to be a very different animal than a 2,000 lb BMW 801 radial. There's certainly nothing wrong with the pilot pod if all-around vision is the specific asymmetric benefit you are seeking, it just seems more natural in a high-powered application where the engine far outweighs the pilot. ...
Putting the "heavy stuff" together in the pod gets you about the smallest, lightest, easiest asymmetric possible. You essentially end up with a pod-and-twin-boom airplane with one of the booms removed. The width of the pod/wing root segment/boom makes for difficult trailering and the pusher prop confines it to paved or grass runways, but it's a nice solution of those two things aren't an issue in the design mission. You still pay a bit of a weight penalty for the two extra 90° load-path direction changes, and complexity with the direction changes for the control system to the rear tail surfaces, but again, relatively minimal and "livable" if you're not looking for the absolute lowest weight and complexity. In return, you gain spectacular visibility and a relatively simple airframe in an easy-to-analyze and design package.
 

cluttonfred

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Sorry, I don’t follow your logic, Topaz. Presumably the fuselage (boom) itself and the junction with the wing are also heavy bits so why not put everything together except the engine and prop?
 

Topaz

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It has to do with the real-world geometry of the parts. If the engine is on the front of the boom (BV-141 style), the prop is adjacent to the forward part of the pod. You need a good 8" to a foot clearance between the prop tip and the pod side for reasons of cockpit noise and vibration. The prop arc tends to fall somewhere between the pilot's ankles and knees in most reasonable arrangements. That section is about 80% of the width of the widest portion of the pod, which forces the centerlines of the pod and boom farther apart. The wider the pod, the worse it gets, with a side-by-side seating pod being the worst case. The farther apart the centerlines are, compared to the span, the more aileron power you need, and the longer the tail boom has to be, to preserve lateral control power.

If the engine is, instead, a pusher installation behind the occupants, the width of the boom is the limiting factor on the spacing of the centerlines of the pod and boom. Since the boom can be relatively narrow in plan view, the centerlines can be relatively close together compared to the BV-141-style case. Everything gets smaller as a result. It's just lighter and easier.

Do some scale drawings of both configurations, including pilot and passenger, and you'll see what I mean.

The BV-141 configuration also has another issue when applied to small airplanes: As I said earlier, the prop arc tends to fall between the pilot's ankles and knees, and that presents a danger in the case of a thrown blade. You either need to reinforce the pod against a blade strike, or accept the danger and odds that the blade will actually hit the pod.
 

cluttonfred

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OK, I understand now that we were talking about different things. I was comparing fuselage + nacelle vs. pod + single boom asymmetric *tractor* engine configurations.

IIUC, you are talking about a pusher engine behind the pod and a single boom. I get the packaging advantage, but honestly at that point why not just go with a pusher twin boom?

It’s the tractor engine visibility issue that drives the asymmetric configuration choice. With a pusher, why bother?
 

Topaz

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... I get the packaging advantage, but honestly at that point why not just go with a pusher twin boom?
One less boom to build, and the boom ends up being a little bigger diameter, making it useful for things like a fuel tank at the forward end.

...It’s the tractor engine visibility issue that drives the asymmetric configuration choice. With a pusher, why bother?
One less boom to build, and you get "pusher" visibility without having to resort to a canard or a long driveshaft.
 

cluttonfred

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Sorry, Topaz, I don’t buy it. The single boom makes everything harder thantwin booms in terms of bracing, torsion, cantilever surfaces, etc. I still think that the asymmetrical approach makes more sense with tractor than a pusher when it comes to single engines.
 

Topaz

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Sorry, Topaz, I don’t buy it. The single boom makes everything harder thantwin booms in terms of bracing, torsion, cantilever surfaces, etc. I still think that the asymmetrical approach makes more sense with tractor than a pusher when it comes to single engines.
Okay, and that's fine, because I'm not "selling" it. I've just done multiple comparisons of BV-141-like designs, asymmetric pusher-engine-on-pod designs, and twin-boom pusher designs.

The first, for me, always ends up being the biggest airplane of the three types for a given mission and payload, for the reasons I've stated. The second being the smallest with the lowest parts count, plus it's got a very convenient place for a fuel tank that most pushers lack. The last is the easiest to design, but has more parts and few places to put fuel if you're going to take the wings off for trailering, which is always a requirement in my particular case.

Again, I would encourage you to do some scale drawings. See how it works out for you.
 

rbarnes

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Here's my current dream. Mini-Aerostar.

Everything in yellow is an off the self Velocity XL fuselage. The spar runs thru the fuselage in same place. Then design wing and tail. Re use Velocity doors, windows, windshield, interior, front landing gear and possibly the rear as well.

Pair of 200+hp turbo Apex engines. 70-80gallson fuel. 200++kts in the 8-15k msl range.

VelocityTopView9.jpg
 

Sockmonkey

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Here's my current dream. Mini-Aerostar.

Everything in yellow is an off the self Velocity XL fuselage. The spar runs thru the fuselage in same place. Then design wing and tail. Re use Velocity doors, windows, windshield, interior, front landing gear and possibly the rear as well.

Pair of 200+hp turbo Apex engines. 70-80gallson fuel. 200++kts in the 8-15k msl range.
Looks a little nose heavy. I'd stick a canard on that.

Everyone remember this bad boy.
 

rbarnes

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Looks a little nose heavy. I'd stick a canard on that.
that's what I was thinking as well, but somehow the Aerostar makes the configuration work. I'm teaching myself OpenVSP, so I'm interested to see how the CG and pitching moments work out.
 

billyvray

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Nice thinking Mathew,
I've thought an updated VJ-22 would be pretty slick. Bigger balloonish tires, wing mods (slats and flaps) ala some of the STOL racers, and a Yamaha turbo'ed and pushing about 200hp would make a fine little backwoods amphibian. Maybe add side sponsons to eliminate the wing tip floats and have a place to suck the tires in. Who needs an Icon?

1603654897490.png



The Explorer was a pretty big plane with a 200 hp Lycoming, but I would love to see a little 100 hp design along the same lines taking advantage of liquid cooling (Rotax, Aeromomentum, etc.) to flip the engine around as a pusher to move the prop further from the cabin for less noise.
 

Pilot-34

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I am pretty sure you do slightly better than that with a lake buccaneer. Or perhaps anything by David Thurston?
 
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WarpedWing

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I am more interested in applying the asymmetric approach to new original designs than in creating a replica. The traditional tractor-engine monoplane layout has the huge disadvantage that the engine blocks the view forward and downwards during the most critical phase of flight operation...landing! I would love to see an otherwise straightforward design like my conceptual asymmetric Jodel D.9 to really put the approach to the test.

For civilian sport aircraft unconcerned with tail gunner firing arcs or the view straight down for reconnaissance or bombing, I think the approach of a fuselage housing the pilot (and passengers if any) and a single engine nacelle has a lot going for it. Check out this Aeroprakt A-28 four-seat light twin and then squint your eyes and imagine an asymmetric two-seater with the engine on the right side only and the engineless left wing a little shorter.

View attachment 103359View attachment 103360
You can't beat Burt Rutans solution for asymmetrical thrust, I think the Boomerang is gorgeous..
 

Pilot-34

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No need to get asymmetrical just put the engine behind you.
The propeller can go wherever you like
 
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