ASYMMETRICAL OR TWIN-BOOM?

ASYMMETRICAL OR TWIN-BOOM?

Logical heresy in aeronautics

(by X.Toff)

– updated 2015, June 29th –

VERSION FRANCAISE (référence)
New features in this update
Links
Going back to the main site about twin-boom projects 39-45
Introduction
  Looking around the dreamy dahu-ibex of the mountains, Patrick Leroy found peculiar animals: among those abnormal asymmetrical ones, there were not only walking animals, but also swimming creatures, and a point which struck me: flying animals (the whirling vulture Vautahu). I would like to add to this collection: flying machines, because some of these asymmetric metal-birds were twin-boom (like the DaU-0, opposite), and drawing twin-boom planes is my hobby...
  For an overview concerning the true History of asymmetrical aircraft, from 1915 until the present day, see Igor Shestakov's website. Without duplicating this superb catalogue of strange models, built or proposed by manufacturers and modellers, here I will just present a minor addition, trying to understand and daring to dream, simply...
The Da-U of Jacques Lecarme
  The Da-U was an asymmetrical plane, named in honour of the small legendary goat. Its cabin and its tail were on the left and its engines on the right. To start with, I present here a single-engined derivative (DaU-1), which explains even better the main advantage of such a drawing: with this odd asymmetrical configuration, the airline staff could disembark passengers without shuting off the engine. Indeed the rotating propeller, being completely hidden by the fuselage, was not likely to kill a child moving away from the proper path, running below the wing for example - which would have been a mortal danger with a traditional layout (Clas-1 sketch). However, as the child could turn all around the plane, it would be even better to have a twin-fuselage layout, with a completely hidden pusher propeller (BiP-1). Moreover, this layout would provide 4 exit directions, making easier (or quicker) the disembarkation of passengers. Simpler would be an asymmetrical vertical layout rather than left/right: a raised up engine (Clas-0) would not have threatened anybody, even if it is not very aerodynamic...
  Switching off the engines had been the simplest solution, so such strange ideas were not considered seriously. They could have made an improvement for short-distance shuttles in cold climates: in which cases passengers join and leave every ten minutes of flight, and turning on the engines again is a time-consuming and difficult process.
  The Da-U was in fact a journalistic hoax, published in Aviation-Magazine on April 1st, 1968. The article presented silly technical-commercial arguments, like the possibility of left-handed pilots being able to buy, at a slightly higher cost, a reversed model, with engine on the other side... what reminds the adventures of the left-sided and right-sided dahus, turning in opposite direction around the same mountain.
  Regarding my choice of name & colour, neglecting vertical asymmetry, let me explain:
- When I say that a peculiar animal is asymmetric, I mean that it has a very rare difference between its left and right halves. At the same time, it is judged very normal to have a head on top and none at the bottom, even if (speaking geometrically) this is also some lack of symmetry...
- In the same way, we are so much used to have eyes facing forward and not seeing backward that we forget the involved lack of balance. Winged aircraft having a thick leading edge and sharp trailing edge, I am not either speaking of front/rear difference when I refer to odd asymmetric aircraft (all of us mean: laterally).
- Other detail: the asymmetry mentioned here concerns only the visual aspect - external features. We do not mind having a port heart and starboard liver, but having two left arms and none on the right would be weird. In the same way, a single aisle airliner may have seats on the port side and an aisle on the starboard side, but this is not what is described here.
The anti-torque principle
  In the Da-U article, there also appeared a judicious reflection: the public may be unaware that pilots are accustomed to manage an asymmetrical behaviour during take off with propeller-planes (only those having contra-rotating propellers being actually balanced). Indeed, an engine driving a propeller undergoes a force making it turn to the opposite direction. That force is compensated by the reaction of the ground as long as the wheels are in contact. As soon as the plane takes off, the force is perceptible and dangerous as there is a risk of the wingtip touching the ground, resulting in a crash and victims...
  I thus propose to use an anti-torque rotor on traditional plane (DaU-1½), as are used on helicopters. Here it would be an horizontal propeller at the wingtip. This asymmetrical device would, paradoxically, return us to a symmetrical state, and safety would improve. On the drawing, the solid arrows represent the air flow, the dotted ones show the force exerted on the plane (even before the invention of the jet, planes were pushed forward by reaction...).
  However, it is clear that this anti-torque rotor would not contribute to plane performance. The safety factor did not prevail, here. In fact, learning to be a pilot includes this management of take-off imbalance, and with the assistance of asymmetrical aerodynamic adjustments, normal planes are very safe. Economic considerations could, someday, replace the talented expensive pilots by unqualified cheap-employees, though the future seems rather to point towards piloting by cheap-machines, and if electronics are good, then perhaps they will not be dangerous...
  I could have installed a rotor pushing down at the port wingtip instead of a rotor pushing up at the starboard wingtip, but I have not, because in this approach the power lost for balance provides lift, allowing the use of a smaller wing, thus less weight and better performance (DaU-½). If classical airplanes with 1 propeller do not have a wing bigger than the other, it is because the imbalance is not constant: high at full power for take-off, low in cruising flight. With a variable rotor, I can have different wings...
  For a free lift setting, a rotor is not necessary: another way is variable geometry: having for instance a half-wing that can use different span (or chord), small for take off at full power (DaU-GV).
Other ways towards balance
Instead of countering propeller torque by increasing lift on one side, or decreasing it on the other side, it is possible to manage the weights that these lifts are supporting. There are several ways - for instance:
- add an extra weight on the side going up (DaU-Dp)
- move the main weight (of the pilot?) to the side of the fuselage into a separate nacelle (DaU-Dn).
A slight unbalance can also be cured: the tendency for the plane to turn due to the airflow vortex on the fin. [This phenomenon is light, as an airflow acting much on the tail would counter enough the torque, while it is not enough by far]. Usually, for ground clearance or nose-up take-off, the fin is located above the fuselage, without a counterpart below (this is a classical vertical-asymmetry); the airflow from a single propeller pushing in only one direction (for the above part) is pushing on the directional fin-area which makes the airplane turn, rotating over its center at mid-length. Adding a little wing-tip tractor propeller, for instance without an extra engine (through gears and shafts from the central axis), a force is countering the turning tendency (DaU-F).
Those 2 measures combined on the DaU-FD: the pilot is moved to the side that was tending to raise up, the engine is pulling on the side that was tending to move more slowly. Increased force balance with decreased shape balance.
The Gyrodyne
  Anti-torque devices on traditional planes are never encountered, but they are routinely used on helicopters (classical ones like the Clas-H drawing). Engineers have proposed, in this field also, an unusual optimisation by asymmetrical means: instead of pushing laterally, at the rear, why not pushing forward, laterally (DaU-H)? Thus, countering the imbalance created by the main rotor would increase speed. Good idea.
  Until now, however, the very complicated force adjustment has not allowed a satisfactory development of this clever configuration.
Rotors without torque
  To avoid torque of the rotating wing, the best solution is having two of them, rotating in opposite directions. Their axis could be separate (port/starboard, as on Clas-H1, or front/rear, as on Clas-H2) or else could be the same (simply above/below, as on Clas-Hc).
  Then, it is possible to turn to the world of the autogyro, half helicopter and half airplane: adding to the helicopter a propeller in the proper direction for speed. Counter-rotating propellers could be used there too, in order to decrease the length of the blades that need staying below the lower rotor. A little wing provides lift when speed is high enough, and real tailplanes are providing control in fast moving slipstream. If the propeller and engine were located in the nose, the helicopter's wonderful forward visibility would be lost, so they should be somewhere else… for instance laterally (DaU-Hc). This layout is reminiscent of the DaU-H, but here the propeller is not fighting torque but creating it… Without asymmetry, a simple solution is pusher propellers, with for instance two booms to carry the tail (BiP-Hc).
  There is also the combination of Clas-H1 and H2 layouts into a 4 rotor aircraft: BiP-H4, which obviously requires lateral booms. The triplex-rotor layout BiP-H3 is enough to require a twin-boom layout (while the asymmetric DaU-H3 may be unstable).
Vertical without rotor
  The tilting-propeller principle is another way towards vertical take off. For the airflow not to be blocked by the wing area, the best solution is using a tilting-wing also. Before trying to drive simultaneously 2 distant propellers with shafts and gears, the simplest approach is a counter-rotating coaxial double-propeller, located at the centre of gravity. That results in lateral twin-fuselages: BiP-Dv. Nevertheless, if the intended use of the aircraft is to carry a single big device, it is impossible to have such half fuselages, and the single one must be lateral, in an asymmetric arrangement, with a counterweight on the other side: DaU-DV.
  For a lighter aircraft, the BiP-D2 twin-boom design is also possible: the central engine, aft of the cockpit, does not move, but the propeller tilts horizontally for take-off and landing. A similar device is used with tilting jet pipes (BiP-Dj) blowing down when necessary; as the hot downward airflow can reflect dangerously upwards off the ground, twin-booms and external tailplanes are appropriate.
Almost vertical
  Airplanes with "fan in wing" device take off almost vertically, but there is not enough support for the tail (Clas-Wi), unless two booms are used (BiP-Wi). Between them there is the asymmetric unstable possibility (DaU-Wi).
Improved flying boats
  One danger for seaplanes, whilst on the water, is rolling so much that one wing goes under waves, the machine could turn completely and sink. In order to keep the wing tips a safe distance above water, the standard solution is using lateral extra floats (Clas-W). These appendices are heavy and create drag in flight. Moreover, with the nose being just over the water, it is impossible to have the engine and propeller installed in that position, the standard solution being to install them on a pylon above the wing, which is not very aerodynamic.
  Moving the hull laterally, it is possible to remove one lateral float, the engine and big wing weights having no equivalent on the other side. Moreover, the engine may be brought down to the wing (DaU-W). Safety on taking off and touching down was nevertheless judged poor and this layout was not successful (nor even built, in the 20th Century)…
  Less daring, the twin-hull layout (BiP-W) is a derivative of the twin-float on which are put many landplanes: two middle-size lateral floats are often preferred to one big central and two small lateral stabilizers. The removal of the pylon and one of the 3 dragging bodies are featured like with the asymmetric layout, but without dangerous unbalance. The main drawback is the need to separate the load in two.
Twin-pod details
  The family of twin-hulls itself (or twin-pods more generally, sometimes called twin-fuselages) splits into single-boom with central tail (Clas-W2), asymmetric with unique lateral tail (DaU-W2), double-tail (BiP-W2) separated or linked, double-tail with asymmetry (BiP-DaU-W2). And there are also models with several booms, less harmonious.
Twin-engine and push-pull principle
  In terms of safety, it should be understood that planes fly in the same way that bicycles stay upright, i.e. only due to forward speed. So if the engine stops in flight, the danger is high: it is necessary to glide downwards to avoid slowing down to the point of losing all forward momentum (which would cause a fatal vertical fall). When most of the altitude is lost, it is necessary to make an emergency landing - and if the available area is forest everywhere, the impact may kill most of the passengers. Thus, since the beginning of aviation, designers proposed to install several (small) engines rather than only one (large enough). If the frequency of failure is 1 out of 1,000 flights, 2 engines will fail simultaneously only 1 time in 1,000,000, and 999 failures among 1,000 will lead to a safe flight, completed at reduced speed but without loss of life.
  However, multi-engined planes have not always won the commercial race, because the price of maintenance and purchase are increased, and customers often prefer a cheaper service even if it is theoretically a little less safe... In the cases where twin-engines were selected, there was another drawback to manage: aerodynamic drag, and for that part, improvements were proposed by the adoption of asymmetrical ideas. I will try to explain.
  Classically, a single-engined aircraft (Clas-1') presents only one body facing airflow: the fuselage, which, of course, includes the engine; however on a traditional twin-engine design (Clas-2), it is no longer one body but three: left engine + fuselage + right engine (aerodynamic obstacles consuming power, leading to decreased payload or lower speed). So a solution was to join together in only one body: nose-engine, fuselage, tail-engine - in a push-pull layout (Clas-3). However, the nose engine would have meant losing the advantage of good visibility of the traditional twin-engined (Clas-2) and pusher single-engined aircraft (Clas-4). For military pilots escaping from their plane (perhaps in fire), the propeller behind the cockpit was very frightening on the push-pull twin-engined (Clas-3) and pusher single-engined aircraft (Clas-4): they could be cut into slices by this atrocious circular saw! That led to the proposal of the aerodynamic compromise of a structure with 2 bodies (worse than 1, but better than 3) with a free nose and without propeller behind the cockpit, the push-pull engines being separated from the fuselage. Two approaches were possible:
- vertical asymmetry (Clas-5): engines on pylon above the fuselage
- lateral asymmetry (DaU-2, Da-U): engines on the left, fuselage on the right (or opposite).
Alternate push-pull proposals
  As the DaU-2 sketch looked fragile, I could turn it solid with a twin-boom layout, staying asymmetric to keep a perfect view forward (DaU-2b).
  The variant DaU-2c is similar, with less aerodynamic drag. For weight balance with heavy engines and light crew, it is better to have a starboard push and port pull (DaU-2d). A twin-boom derivative would feature a longer cabin (DaU-2e).
  Still with push on one side, pull on the other, it is possible to have propellers side by side (DaU-2f). On a normal airplane, with central fuselage, this brings a double asymmetry, front/rear as well as port/starboard.
Push-push and pull-pull
  The classical push-pull layout, coaxial (Clas-3/5, DaU-2/2b/2c), discussed previously, had two propellers behind one another. Was this a good thing (by synergy, the rear propeller being more efficient than the front one) or a bad thing (by disturbance, the rear propeller being less efficient than the front one)? As well, the rear propeller was discussed: good for aerodynamics (avoiding a violent airflow on the structure thus decreasing drag) or bad (by “tail-drag” phenomenon)? Besides the classical push-pull layout were thus considered the push-push (PP1) and pull-pull (PP2).
  Coaxial propellers, distant as well as near, were judged rather bad, but the tremendous success of turbojets, with coaxial compressor rotors, had to be taken into account. Maybe with a duct to direct the airflow (PP3), synergy would be favoured for coaxial propellers... Adding a fuel injection in the airflow with firing, this was even inventing again the turbojet somehow. Anyway, it was more easy (and secure in case of bailing out) to install the fuselage laterally, asymmetrically, rather than at the centre of the machine from Hell…
Pulling with twin-bodies
  Without coaxial propellers, there is another compromise of a twin-engine with 2 bodies: the fuselage is hidden behind one of the engines, simply (DaU-3). An alternative is possible: hiding the cockpit behind an engine, and the beam supporting the tail behind the other engine (asymmetrical DaU-4). That provides an excellent view backward, as on a tail-less aircraft (DaU-5) - best formula theoretically but difficult to balance. Note: the long tailplane on the port side of DaU-4 is not a mistake, even if the extra weight to lift is on starboard: usually taiplanes do not act as extra wings to lift but exert a downward force to balance.
  From there, it is possible to use two fuselages (BiP-2), in order to manufacture fewer different parts.
  This simplified manufacturing leads to creation of symmetrical twin-fuselage aircraft by twinning laterally 2 single-engined mass-produced aircraft (BiP-3). This way provides, with reduced times and costs, a model of double capacity (in payload), and the performances are higher because, for a doubled power there is not exactly a doubled drag (the central wing is common) nor a double weight (reduced landing gear, and wing).
  Even without this advantage in twinning, the twin-fuselage layout is good for large models: weights are dispatched on the wing thus improving solidity. Having the cabin separated in two is usually regarded as bad, but that may provide the passengers with 3 panoramic view points, without disturbing the pilot (BiP-3').
Double visibility
  We have seen that a good view forward justified the push-pull asymmetrical planes, and that a good view backwards justified the very asymmetrical twin-bodies, now it is necessary to supplement that by the ideal: a plane having a perfect view both forward and backward. That may be rather simple on a large traditional twin-engine (Clas-6), with lateral engines allowing a glazed nose, and a large rear fuselage continued aft of tail-planes, but the drag is high (3 bodies), 2 engines are expensive, and the distance between front and rear posts may be a problem if this is for a crew of observers rather than separate passengers.
  Distances can be reduced by choosing a flying-wing layout, but if there is a central engine with lateral gears (Clas-7) to avoid expensive twin-engines, the rear and front posts remain separate. It was thus proposed, since the very beginning of aviation, an asymmetrical single-engined aircraft, in 2 versions:
- vertical asymmetry: engine and tail on pylon, above a pod (Clas-8)
- lateral asymmetry (DaU-6): engine and tail on the left, pod on the right (or opposite)
  This reason justified the first aeronautical patent for asymmetrical aircraft, and almost reached success a few decades later, but it was not considered sufficient, twin-engines being at last selected for aerial observation despite their higher cost.
  After accepting such a principle of lateral asymmetry, it is possible to come back to a flying-wing principle with one engine in the cabin (to be repaired in flight) and remote propeller (DaU-6B). Many other combinations are possible, as the twin-boomer with high push-pull engines BiP-22, and the classical twin-pod Clas-21, etc.
Free angle
  On small airplanes, weight balance does not allow to have a rear post, and the rear view uses a central turret. Alas, the fin is disturbing (Clas-Tu). Moving this fin lateraly, with a boom to hold it, solves this problem twin-boomly (BiP-Tu). For "balance", it is possible to move as well engine and tailplane (DaU-Tu). Alas, this was not necessary, as a double fin was enough (Clas-Tu²)...
Safety with a single engine
  To improve safety without a second engine, it is wise to have a mechanic aboard, with full access to the engine, while the pilot stays at the controls. On a little plane with perfect view forward (thus a pilot in a glazed nose) and a tractor propeller, this leads to place the engine and mechanic on one side, the pilot on the other (see the asymmetric twin-fuselage Da-BiU-2M).
  In normal, problem-free, flights the mechanic is free for another task, like observer/photographer. His fuselage needs only to be truncated to get a tail canopy (asymmetric pod DaU-2M).
  Of course, a more classical vertical asymmetry gives a similar result, but with fragility and difficult access (Clas-2M).
  Even without mechanic aboard, a single-engine plane may be asymmetric for safety reasons (tractor DaU-2S, pusher DaU-1): in case of a crash landing, the cabin will not be crushed nor burnt by the motor.
  But, in the best way, if the pilot suffered a heart-attack, a mechanic-photographer may save their lives trying to take the controls, which needs some physical communication between the 2 posts, for instance through a lifting fuselage, with a wing profile (Da-BiU-2P). A simpler solution would be an aft engine and a pusher propeller, and this is discussed below.
Pusher propeller
  On a single-engined plane, combining good forward view with an engine that can be repaired in flight, is possible using a pusher propeller. The best solution is a flying-wing (Clas-9), but other possibilities result from getting more balance with a tail: rear tail-planes with a shaft from the central engine (Clas-10) or front canard foreplanes (Clas-11).
  As far as I are concerned, I prefer the twin-boom layout (BiP-4) or asymmetrical (vertical, Clas-12, or lateral, DaU-7), which leads to the same efficient result, but with a touch of fantasy...
Weird oddities...
  Even if the twin-boom and asymmetrical layouts were alternatives to the canard layout, this is not an universal truth. Many proud professional experts defined the French twin-boom word (bipoutre) as requiring beams aft of the wing, but there is no reason, this is only lack of imagination... see my twin-boom canard BiP-4c and its asymmetrical equivalent DaU-7c. The DaU-67 is another possibility, difficult to classify...
  Awaiting punishment for crimes of heresy and resistance against the experts, let me dream: it is possible to also have aircraft featuring 3 sets of areas (BiP-4t and DaU-7t), they are not much worse than corresponding traditional versions (Clas-11t), which existed at the beginning of aviation, which were condemned as stupid, before reappearing for other reasons on the best supersonic planes of the 21st century...
  More original would be high tailplanes and low foreplanes (Clas-11v), which can be installed on a biplane as well, and a twin-boom asymmetrical version of it (BiP-4v) is a further challenge for stability…
Other peculiar pushing designs...
  In the catalogue of aircraft with a pusher propeller, there are also cases with a pod and 1 boom. The simplest is the classical Clas-Pb with a pusher propeller above a low wing. The version with high boom, Clas-Ph, is richer, as it leads to derivatives with a nose propeller and rear canopy. A special variant uses a propeller shaft inside the boom: Clas-Ph-2.
  Still more original, adding high boom and low boom creates a vertical twin-boom layout. The best solutions are using double propellers of reduced diameter (BiP-Phb), or a shaft-high-boom and a structural low boom (BiP-Phb-2).
  But to be really pleasing, some asymmetry must be introduced... The 4-engined twin-fuselage BiP-DaU-Phb uses a starboard push-pull layout with low boom, a port double-pusher layout, with a shaft-high-boom above a propeller...
Big jets
  Far from propeller dreams, it would be wise to come back to modern planes, jet powered. Well, the parts of a turbojet include several ducted fans looking like propellers but, seen from outside, a jet is a clean and narrow unit. The basic principle was simple: the air intake and jet exhaust should be straight and short. For a twin-engined model, there was no problem: jets were fitted below the wings, but for a single engined aircraft, it was less easy to put this big unit upon the centre of gravity. Above the fuselage (Clas-J) or below (Clas-J'), there was a risk to burn the rear fuselage and tail. So it seemed more simple to have lateral tails (BiP-J) or lateral fuselages (BiP-J'). The latter layout could be simplified in an asymmetric version (DaU-J). As a jet engine (early version, without fan) is narrow, it could be close to the fuselage, with a very slight asymmetry, and the lateral position was the best if there was no room above (rotor or radar disk) nor below (risk of sucking in debris from a poor runway): DaU-J'.
Nuclear hypothesis
   At the beginning of the atomic era, nuclear engines were also considered for aircraft. The main issue was radiation endangering the crew’s safety, so designs needed to provide the greatest distance between the cockpit and the big engine – the asymmetric airplane DaU-Nu seemed the best. To work on the big engine, removed and brought to a security zone, the aircraft needed to stay stable, and for that the asymmetric twin-boom Da-BiU-Nu was interesting. The BiP-Nu twin-boom layout seemed also pleasant, despite its uneasy access.
Area rule
  Near the sound barrier, in the transonic zone, the cross-sectional area (including wing) should change progressively, without accute shock (creating much drag). For that, a fuselage local enlargement may be used (Clas-LA), even if there is nothing to put inside, but it is more elegant to have a port wing then a starboard wing, staggered (DaU-LA, BiDaU-LA).
Cargo function and mother-plane
  All that has been said about visibility applies to other roles: throwing huge loads (DaU-R1, BiP-R1 – on the ground or in flight, without hurting the tail) or baby-planes (DaU-R2, BiP-R2 – without a width above the runway dimension), or else "flowers" the military would say…
Other functions as launcher or transporter
  The same way towards twin-boom (BiP) and asymmetric (DaU) occurs with slightly different situations: instead of dropping loads downwards or releasing airplanes taking off upwards, it is possible to launch upwards rockets-satellites (-L) or releasing downwards parasite aircraft (-P, -P').
Canard lifting body
  The "Burnelli" aircraft layout, with a flat and profiled fuselage could include canards as well, but aerodynamics and visiblility would lead to choose the twin-boom way (BiP-Bc) or even better: asymmetric (DaU-Bc).
Weird comfort
  Sometimes an unusual airplane (Clas-E4) features a pilot sitting on a hot lateral engine. By removing this engine, for comfort reason, engineers (would) get an asymmetric aircraft (DaU-E3).
  The same genesis may happen from a twin-boom layout (BiP-E4), giving birth to an improved version, asymmetric, a little less powerful (BiDaU-E3).
Over-symmetric dead-ends
  If designing an asymmetric airplane would be condemned as heretic, we could also prohibit front/rear asymmetry, weird examples being BiP-4tt and 4ttt. The panoramic view-points could be replaced by engines and propellers.
  But the same is possible without even twin-boom fantasy (Clas-11ttt), and it is almost surprising that this has not become the mandatory way in aeronautic design...
  Thinking about it, there are 2 different ways to build a front/rear symmetry: either a mirror effect (keeping port and starboard unchanged) or a 180 degree rotation (inverting port and starboard). Somehow, the DaU-180 would be 'very symmetric'.
Extreme variations
  An unusual approach of the twin-fuselage layout with nose-propellers (BiP-3 and 3') was also possible, installing engines asymmetrically, with coaxial counter-rotating propellers. For a twin-engined plane, that gives the BiP-2/3 sketch, which provides a perfect view forward & backward and only one fuselage to be pressurised for high altitude. With 3 engines, the layout BiP-2/3' is less optimal, unless imagining 3 coaxial propellers on the same side...
  Such a principle can be applied without double-tail (DaU-2'), with panoramic front & rear canopies. Cabin and engines could be reversed (DaU-2"), but this results in no advantage over the push-pull DaU-2.
  If the twin-engined DaU-2' and BiP-2/3 are compared, there is no need for having a twin tail, but that changes if there is a requirement to carry a heavy weight aft, for instance on a simple 6-engined push-pull (BiP-2/6)... This is a good reason to be a twin-boomer, and surprisingly, it has not been tried yet!
From mountain aviation to room aviation
  While Mr Lecarme's Da-U had only asymmetry in common with the slope-animal, it is pleasant to propose a plane much nearer to the small goat, with legs (i.e. landing gears) of different lengths... Stupid? Maybe not. It is well known that landing in mountain areas is difficult: how to find a large flat zone? If the ground goes down, you'll have a very long roll, if the ground goes up, you will have a hard landing! A transverse level way may be better, and this one would be inclined because of the slope. As the plane needs to be horizontal while approaching, for lift balance, touching the ground would need an inclined track, with one leg shorter than the other. However, mountain planes are usually shuttles linking mountain and plain, so they cannot be as specialised as dahus. Fortunately, technique provides more flexibility than Nature, through variable geometry - in this case, it would be a variable elongation (DaU-8). That would make a plane symmetrical or asymmetrical at will, left-sided or right-sided as required.
  Elsewhere, a dreamer suggested that a small mountainous country produces a supersonic aircraft with circular flight not to exceed the borders... With normal wings ensuring a safe takeoff, this variable-geometry aircraft (DaU-8s, Superdahu) would retract one wing in flight to transform itself into a mechanical vautahu. An amusing idea, more original than my DaU-GV whose goal was balance... As for the mountain landing-gear, technique could provide left-sided and right-sided options by simply pressing a switch.
  At low speed, circular flight could also be the goal, for flying around a tourist spot to be admired from every direction (there is a less poetic military variant of this), with passengers on a single side, balanced by the weight of an opposite engine (DaU-8t).
  Finally, a friend building flying models taught me that Control-Line models, as intended for circular flight, are often drawn as asymmetrical (only one wing, for example - DaU-8m). This is optimisation for their use, without playing to look like transcontinental planes while they are intended for circles at 30 feet distance... And I must apologise not to have included this major chapter earlier. My aeronautical culture was desk-model making and book reading, therefore I discovered weird aircraft through the ones that marked History (asymmetrical Bv 141 and twin-fuselage He 111Z, which had interesting silhouettes, pleasant somehow, but which may have made the dreadful Nazis win, alas), and I regard as better than myself aviation-enthusiasts focusing on gentle toys for the pleasure of flight, without any connection toward the past atrocious slaughters...
  There is an asymmetric approach which is specific to model kits for home shelves, as these 'planes' are not at all intended to fly, just to look pretty. As only one side will be seen, there is no need to paint back areas, to include hidden details as opposite landing gear… This DaU-8k layout is not absurd, this is saving useless efforts, which is a logical way to appreciate aircraft for the enthusiasts focusing on visual appearances.
Aviation on bookshelves
  For modellers, the main problem of aircraft is the size. This practical issue may be cured with an oblical position, with asymmetry or twin-fuselage, or both.
Landing-gear affair
  A pilot friend told me a little known fact: some rare planes have a swivelling landing gear to ensure a stable takeoff even with side wind (DaU-Wh). It is the same principle as my anti-torque device: intentionally countering an asymmetrical force by an asymmetrical mechanism.
  After all, it is possible to mix both ways: anti-torque countering through landing gear asymmetry instead of auxiliary rotor. The goal would not be safety (danger happening only when the airplane takes off and landing gear has no effect then) but weight saving: using a tiny wheel where there is less work to perform, resisting weight only and not torque moreover. This created the classical DaU-T1 and monotrace T2, the DaU-Tr with asymmetry increased by landing gears, the double-plane BiP-Tr with 2 landing gears instead of 4...
Weird simplification
  Classical airplanes have straight wings (Clas-d), or to achieve more speed: rearward-swept wings (Clas-f) or forward-swept wings (Clas-i) to counter-balance the fragile torque of rearward swept wings. I can bring more structural simplicity with handling asymmetry and using a skewed single wing (DaU-i). This wing, rearward-swept on one side, forward-swept on the other side, brings great solidity, not great stability...
  Such a layout would ease a lot variable-swept wing devices, and would bring security without imbalance risk anymore (the sweeping of one half-wing cannot be delayed).
Crazy wings
  To smile again, let us imagine the mixing of delta-wing and inverted delta (DaU-delta)...
  As well, it is possible to increase speed by optimising half of the wing, swept, the other half staying straight for landing control (DaU-f2). The same logic, a long time ago, could have produced a half-monoplane, half improved for speed keeping one half at its best for turn-rate (DaU-m2).
  Reminiscent of the famous TV-plane with W-wing (Baa Baa Black Sheep's Corsair), and knowing the gull M-wing planes, I will invent another solid freak: DaU-WM V^ - with a corresponding tailplane, half butterfly-V and half inverted-V (^): a simple slope plan...
  Of course, I could also have built (and crashed?) a flying test-bed of the canard layout, keeping carefully one half classical (DaU-c). Mixing rearward/forward swept wing with front/aft position of half-canard, I get the weird DaU-n & k.
  Another possibility: wings swept rearward inboard and forward swept outboard, or opposite (W or M seen from above, nose up). This also can be imagined in an asymmetrical form (half-W & half-M): DaU-fif, or its twin-boom counterpart: BiP-fif.
Asymmetrical twins
  We have seen that twin-fuselages and asymmetrical planes were in competition in several cases, but instead of imagining a war between these layouts, I may wish their union, generating nice half-breed children, like the Bi-DaU-2, 6 and 7.
  These twin children are of course only one option among several combination possibilities, as my mixed DaU-0 and BiP-2/3 were at the same time asymmetrical and twin-boom, without twinning.
Twins becoming asymmetric
  In order to enrich my collection, it is amusing to double traditional twin-engines (Clas-1) or single-engined (Clas-1) aircraft, including a little asymmetry for fun: Da-BiU-1 and 2.
  The same is possible with old biplanes (Clas-12) and tandem-wing planes (Clas-13), doubled with originality as Da-BiU-3 and 4.
Twins loosing asymmetry
  With asymmetric swept wings (DaU-i' & i), joining opposites can paradoxically restore a perfect symmetry (BiP-i).
  Joining asymmetric single engine aircraft which are opposite (DaU-1m & 2m) also creates a well-balanced model (BiP-3m).
  Anyway, mixing both ways, with opposite swept wings and engines (DaU-fm & fm') does not always give a symmetric result (DaU-fm")…
Simplified or complicated asymmetry
  Variable Geometry was mentioned because it is difficult for a wing to be at its best for both take-off and cruise; anyway, I have said that very-short distance shuttles could be optimised for taking off only, so they may have a big half wing counter-balancing torque: DaU-S. The double version Bi-DaU-S is similar.
  Not to be boring, let us consider an oblique pair: Bi-DaU-B.
Better and better (or worse and worse...)
  The passenger view point may be improved further, not reserving it anymore to front and rear seats. A high wing provides huge windows to everyone (DaU-6H).
  But still this is not enough: central passengers would be able to see the ground but not the stars. Such a discomfort! They may be moved externally, to the wingtip (DaU-6E). But if the central port passengers would protest, maybe the best would be the Clas-8' layout, so classical so sad...
  However, if this plane is an airliner carrying travellers and their suitcases, not tourists just wanting to admire landscapes, there is a need for a luggage-hold while glass everywhere is not appropriate. So a cargo pod may be on the other wingtip, and that improves balance even if asymmetry remains (DaU-6S).
  The former plane featured front and rear doors, and maybe this is more than necessary. The cargo pod may be hidden behind the engine, leaving a free rear door, and two booms would carry the long tailplane without inconvenience for the loading trucks: this adds to the collection an asymmetrical twin-boomer with external cabin (BiP-E).
  Another variant is possible: twin fuselage, twin-engined with propellers rotating in the same direction (imbalance to compensate with weight asymmetry): BiP-3E.
Improved Push-pull
  When presenting the push-pull principle, I did not include its very classical twin-boom version (BiP-PP) because it was not perfect as lacking view forward. Now the twin-fuselage planes have been introduced, so I can present a great panoramic variant (BiP-P3)...
  A pod below the wing is another way to create a panoramic push-pull twin-boomer (BiP-PH). But that would make 4 dragging bodies, and some asymmetric layout with 2 bodies (DaU-6P) seems better, if balance is achieved.
4-engined freaks
  I have started with single- and twin-propeller planes, as this was enough to introduce many interesting layouts, but obviously the range of usual aircraft is far wider. For instance, big airplanes were often 4-engined, for a practical reason different from safety: simply, twice the power of the most powerful (& reliable, cheap) engine was not enough. So many aircraft had 5 dragging bodies (4 engines + fuselage). It was rather easy to improve aerodynamics, keeping classical: 3 bodies (port push-pull + fuselage + starboard push-pull) or 1 body with coupled engines and double propellers (double-tail-push / fuselage / double-nose-pull).
  If, with those 4 engines, one wants a panoramic cabin, with for balance a tail (far aft), that leads to more original designs (illustrated here). A first solution is based on the 3-body-plane mentioned above (port push-pull, starboard push-pull), carrying tail with lengthened push-pull pods (BiP-P4) or an extra boom, moved from the passenger part, vertically (classical) or laterally (DaU-P4).
  Other possibility: take the 1-body shape (double-push, double-pull) as a basis, putting passengers elsewhere, vertically (and with 2 booms to be compact: PiP-Q4) or laterally (DaU-Q4).
  And dreaming, a few fantasy ones: a twin-boomer with vertical steps (BiP-X) and a tandem-wing model with asymmetry both vertical and lateral (DaU-X)... This might be dangerous for real, but for a paper dream, it is just funny, absurd...
  The DaU-Y deals differently with the push-pull layout, separating the engines. On starboard, they are located on different surfaces; on port, the propellers are brought together, the engines being moved at the ends of a boom. Crazy...
Three-engined logic
  Even if all intermediate engine powers are available, using the most powerful engine of all may lead to be under-powered with 2 engines and over-powered with 4, the best choice being 3.
  Classically, the two engines to complete were lateral and the third was fit in the nose, but the panoramic frontal canopy was lost (Clas-3p), a tail propeller being theoritically better. Vertical asymmetry then became common: the central engine was fit in the fin or on a pylon, unless the whole wing was parasol – a purely axial variant was possible (Clas-3v), a jam on any engine providing no lateral asymmetric unbalance.
  Among oddities, the BiP-3' and BiP-2/3' models were already three-engined, but it is better to start the analysis again from the best twin-engined layout: the asymmetric push-pull DaU-2. Adding a third engine on the other side is very simple, even improving balance (DaU-3p1). The third engine could also be installed in the tail (DaU-3p2), on a pylon (DaU-3p3) or on the fin (Dau-3p4). Many variants are possible, changing the tractor propeller into a pusher (DaU-3p1', 3p3', 3p4') or inverting the push-pull group and the single engine (on DaU-3p3, 3p4, 3p3', 3p4'). Miror copies are also to be counted, as well as variants with biplane wings or parasol wing (DaU-3p5 etc.). At last, related twin-boom versions would be more solid (as BiP-3p1 for DaU-3p1).
Vertical way
  Previously was mentioned that vertical asymmetry is too common to be included. However, to complete the overview, it is necessary to realize that vertical twin-boomers are rare, linked tails (one above the other) providing solidity to float-planes (BiP-Fp).
  Anyhow, it is possible to add an asymmetric plane in both ways: vertical and horizontal, or asymmetric above on one side and below on the other side (DaU-Fp).
Weighing unbalanced shelf models
  Apart of true flying aircraft, there are "aeronautic" models or toys, that have their own problems: for instance, with a tricycle landing gear and a nose wheel, unbalance is common, with an aspect "sitting on its heavy tail, nose up, ugly"... Adding lately a "radar" (lead weight) under the nose is a classical cure, but only one radar may be not enough and two radars would not look true; so, having 2 noses (BiP-Lt) seems a godsend, and that may elect the twin-boom layout as "favorite in the collection". But... if a single-fuselage model has been chosen, this is not desperate: giving up realism (towards "what-if modelling"), it becomes possible to add a second fuselage with nose weight, for a creative result, "well-balanced" concerning weight, maybe not mental sanity... (DaU-Lt).
Stretched between two
  In the field of unrealistic fantasy, there are several "reasons" for additional twin boom configuration. A cartoonist (Philippe Abbet, site Phloxtoon and book Luftgaffe) has invented a twin boom "net" interceptor of missiles (with pilot or not): BiP-Do. This was reported to me when I invented as dangerous in reverse: a twin-fuselage BiP-Ne2 with net to intercept the terrorist bomb falling on Hiroshima, to carry it back home to explode on the sender's city. The same is possible with a stretched picture instead of the net, for aerial advertising: BiP-Fo. Of course, an absurd equivalent is "possible" in the asymmetric way : DaU-Ne or even classic double: Clas-Do.
Familial and civilian peace
  The what-if modeller Captain Canada, in 2015, invented a new reason to be twin-fuselage : stop the fight between brothers in a single cabin (BiP-Fa). This recipe could apply also on airliners for enemy fans of football/hockey teams (BiP-Fa2 : Madrid-Berlin plane for the final of european football Real Madrid vs. Atletico Madrid). However, the same principle could concern an asymmetric plane (DaU-Fa), a single pilot being able to manage the flight and being not "enemy". Or even in standard version, twin-cabin-pod (Clas-Fa), to convey tigers or naughty humans...
Counting explosion
  Are there some forgotten possibilities up to now? Of course! There are millions of possible layouts, and most of them are asymmetric.
  The principle of the calculations opposite is combining the numbers of axles and kinds of layout per axis. The basis is a simple wing portion, with 2 tips, thus 2 axes - and a 6-engined classical planes has a central fuselage, 6 lateral engine pods, 2 wingtips, making 9 axes... On each axis, the number of possibilities may be 2 (nothing/something) up to above 10 (propeller push or pull, or push-pull, or none; front canopy or rear or both or central or none; elevator planes front or aft or both or none; etc...). From the list of whole figures 0 to 2500, changed from my 10-base into 2-base ("10" means our 2) up to 7-base ("10" means our 7), it was rather easy to automatically calculate the cases ratio asymmetric/total.
  The conclusion is clear: 'democratically', the asymmetric layouts must win, if 1 layout = 1 vote... However, if 1 built machine = 1 vote, they are a very small minority, neglictible. This is a law of Mother Nature: even if there are more ubnormal failures then successes, the failures disappear and the good-enough shapes are the only ones to survive, and they multiply almost unchanged.
The Hypothesis of a crazy biologist
  While technicians may have taken animals as a starting point to design machines (birds for Léonard de Vinci, dahus for Jacques Lecarme), the reverse is possible nowadays: laboratories could take as a starting point planes to create similar birds, by genetic engineering. It is not science-fiction anymore.
  It seems that raises ethical and religious questions: are humans allowed to become the Creator of beings? The violent revolts against GMO (Genetically Modified Organisms), and the absolute prohibition of human cloning show that this subject is a taboo. However, floral hybridisation is a practice accepted for many centuries, creation of canine or bovine races happened similarly, and making war against new tools that would just do the same further seems mainly connected to political reasons: resistance against scientist leaders.
  Anyway, let us imagine an insane researcher working as a recluse, in secrecy, after winning the lottery. His favourite hobby was aircraft modelling, but he was excluded from his club for heresy, because it was required to respect military History and the aviators that died for the national flag, while free invention was absolutely prohibited ("What-if" modelling is outlawed in many countries). Frustrated, this man took a revenge by inventing animals looking like old planes he loved.
  With eagle genes, his first creation was the asymmetrical Blohm-und-Eagle 141 (DaU-6 way): a bird with the body on the right and the head on the left… Poor animal.
  Then, he created the Lightn'Eagle 38 with 2 tails connected to wings (BiP-4 way), just as aberrant and not viable... Finally, he just made the Twin-Eagle 82 (BiP-3 way), which could have existed in Nature: simple Siamese-twin-brothers.
  Easier to create were the birds with 2 tails (2Q) or 2 heads (2T). Some swallows had already 2 tails, so it was not very inventive, and that resembled only very special twin-boomers, with beams carried by the fuselage (BiP-5). For the two headed ones, that did not have any relevance to flying, just like Siamese chickens; and aircraft with such a layout (Clas-2T) being excessively rare, there was no further reason to claim inventing a bird from an aircraft source.
  At last, the only successful creation of this researcher was the double bird, but the twins seldom flapped their wings simultaneously, and the poor couple was unable to fly. The biologist thus planned to apply the same principle to double flying squirrels and flying lizards, corresponding to double sailplanes (only 2 of the half-dozen that I know were fools' day jokes…). To jump synchronously would not have been easy, either, for the 2 separated brains… Other twinning tests considered: double dipterous insect, double-bee with 4 wings, double-butterfly, double bat, double flying fish, double ptérodactyl. Worse than Jurassic-Park!
  Creation was well made, finally, and to invent anything does not automatically work. The mad biologist decided to close his laboratory, to kill his poor monsters without pain, and to become a priest...
Optimisation logic
  The command to respect God's Creation led some American states to prohibit teaching Darwin's theses, as they do not follow an official biblical dogma. However the hypotheses of the heretic biologists were plausible: 1/ Variations would happen through the natural mechanism of "mutation" (copy error during embryo development); 2/ Natural selection, known as "survival of the fittest", sometimes would make abnormal shapes become dominant ones, even if they were very rare at the beginning. For example, during prehistory, 2 goats born with leg imbalance, that would have survived with difficulty, became far better adapted than average when their herd had been driven out towards the mountains, and after a famine leaving them as only survivors, would have generated the dahus family... More seriously, this principle would explain why microbes became resistant to antibiotics, without having to conclude that the Devil's power (magic evil) is the only available explanation. The principle of change could have been invented by God for His world to move, and to consider it is not insulting the Creator. But it is sometimes forbidden to find a logic, it is mandatory to obey the Law…
  Outside of the animal world, human society knows the same painful fight: those wanting stability are strongly opposed to those wanting constant improvement of performance (it is a difficult subject, polemic, and I will present only one humble personal opinion, which is not better than another).
  In the technical world, exploring unconventional ways (like asymmetrical or double planes) is involved in an optimisation called Progress, meaning that it is a good thing. But why travel always at higher speed and distance, beyond what is necessary? Why lowering the costs just to increase the profits for an immoral caste of lazy capitalists? A charitable answer is possible: thanks to progress, techniques will be cheaper, therefore they will not be restricted anymore to the rich in capitalist countries and to the leaders in communist countries…
  Between Capitalism and Communism, some European unions require a stabilisation on current comfort, but that does not seem fair either: 1/ in France, this comes mainly from Government employees, protected from effort to overcome concurrence but having high wages thanks to taxes (and police threat) on the private World creating richness with constant hard improvement to survive; 2/ the Western workers refuse competition with the poor immigrants (accepting to work more for less money), while after hours, as clients, they love the products and raw materials at minimum price, provided by the very hard international competition.
  Americans have domestic raw materials thanks to their forefathers that stole the Native Americans' property before claiming a holy legality in ownership. Europeans had conquered the World to get those materials, but liberation of the crushed people broke their empires. Americans celebrate national selfishness called 'patriotism' while European speeches pretend to fight this nazi-like nationalism, all claim to make the democratic (Christian or lay humanist) logic win, but if a World democracy were really born, dominated by the numerous Asiatic, the Westerners would loose their privileges, what they refuse violently, with massive destruction weapons to threaten the poor. It is clear that terrorism and bloody wars would occur before a democratic whole World ever happens. Besides, the vertiginous progress of aviation during the twentieth century did not try to satisfy consumers or comrades, it was primarily a consequence of the Weapons race between hostile countries trying to dominate the World.
  This alarming mechanism is the animal logic of wolves: it is required to respect domination, and if there is rebellion, violence breaks out unbounded until rendering of one and victory of the other. Most moral speeches seem successful lies providing sinful comfort.
  In this context, the aircraft engineers will just take care of tiny details. The survival of the fittest logic will mean, concerning aviation: survival of bombers trying to slaughter the enemy, survival of employment against pitiless competition, survival of passengers in dangerous machines.
  That will not be Twin-boom in Heaven
Do not mix aviation and religion, you fool!
  Basing an aviation analysis on religion will be classified insane, as the flying priests visiting isolated people are just a very tiny detail… I must explain a little more: aviation and religion are not much linked, in this World, while they could have been.
  Remember Galileo, condemned as heretic criminal because he thought the Earth was rotating... our society could obey very severe religious commands, forbidding Science & Technique. Official Law, world-wide, would be: "if you want something, go to church/ temple/mosque/synagogue, buy holly candles and pray very hard - if you ever insult God's will to fulfil your need or not, by personally using technical inventions or drugs, you have a Devil state of mind, and you will be burnt alive, with generosity, to save your soul..." Religions would be powerful, rich, in a Middle-Age lasting forever, without aircraft... So extremist religious leadership could kill flying machines, yes.
  Other possible link: "God has chosen to create many animals with wings, and human-beings without. So making human-beings fly is insulting God's Creation. Yes, God created human-beings with brains enabling some invention of artificial-flying devices, but the Prophets have explained what brains are made for: reading and teaching the Holly Book and their own life description, admitting the proofs of God's love that the animals, stupid, are not able to see. The mandatory way is following the Prophets attitude and acts: they have not flown at all, so human flying is clearly a sin..." This is just a nightmare, maybe, but this could be the Law.
Do not mix twin-boom and terrorism, you stupid!
  As no twin-boom aircraft has ever been involved in a kamikaze attack, mentioning "terrorism" in an analysis about twin-boom principles seems COMPLETELY CRAZY, I know. But I disagree… Even mentally ill, I am not lacking logic, I just have a heretic forbidden logic, frightening:
  Historians have mentioned that the Porokhovchikov Bi-Kok twin-boomer was turned down by the officials of Russia in 1912 because it was "not like a right airplane must be", no matter its higher performances and lower cost. And the same system declared right that richness is not deserved by efficient hard-workers and genius inventors but will belong forever to the right families (commanding the police and the army). The result has been the Russian revolution, with honest poor people fighting for Justice - and also hateful criminals seizing this occasion to murder innocent rich-babies. The 1917 communists decided to forbid personal property, and this was doomed as there is not much work anymore if work is no more rewarded by higher personal comfort. That led to a severe police state and active brain-washing, with common misery as final result anyway. Thus communism has fallen down by itself (without nuclear War, fortunately), but the source moral problem is still the same: a hard worker or genius inventor deserves more, honestly, than a lazy stupid heir, king of the capitalist way. A revolution can happen again, for another system, rewarding fairly the merit of individuals, instead of protecting the rich families' ownership.
  I think this will not happen inside our countries, as the worse problem now is between countries: Christian or lay honesty should remove the borders - those guarded borders 'protect' the rich countries from rewarding fairly work and effort. This looks like Russia 1916, France 1788, and the result may be another revolution for Justice. With the West massive-destruction weapons, this cannot be a classical war between armies, and most of the crushed ones remain dominated up to now, angry, while a few ones attack us committing suicide. As Western civilian electors, we are not innocent, we are guilty of voting for this situation, only our rich-babies being innocent victims. The murderers and ourselves will go to Hell, I think, if there is a Final Judgement above. Concerning the dishonest crushing for material selfish comfort, Jesus-Christ has said "happy are the poor, for they will receive Eternal Life". Christian leaders have chosen to forget that to reach higher success: "follow us and you will have both the highest material comfort and after-death reward - crushing the others, that deserve no respect as being non-Christian, enemy of Liberty" (the Liberty to be richer without sharing)…
  Before the forthcoming War with the poor hard-working Asia, a War with the Arabic and Muslims may happen, as the Westerners protect the Zionists of right blood crushing the Palestinians. And that brings back to the twin-boom subject, somehow the very symbol of the double-tail aircraft is the mass-produced Lightning hero of 1942-45, killing the evil Nazis pretending to be the highest race, our teachers say (avoiding to mention this Lightning served in the army of USA 1939-49 where black people were not allowed to vote) and Westerners are educated to be proud of US History (slaughtering the Native-American, enslaving the Black people, were not faults towards God, as there was no victim among the Jewish people, the highest race said the Old Book written by Judaic leaders…). I am myself of Jewish descent, I am not condemning Jewish blood at all, just the racist leaders and their proud followers, making my disturbing voice shut down. I am mad, but the principle of dominating families (as the rejection of twin-boom & asymmetric planes - apart from unbalance, drag, weight, technical arguments) leads politics automatically to violent hate, terrorism and next World War… Too bad.

List of updates

June 29th, 2015 - adding paragraph "Familial and civilian peace"
2004-2013 - miscellaneous additions
January 3rd, 2004 - first English version on line
November 11, 2003 - first (French) version of this site
October 2003 - in the absence of positive answer from artists, personal drawing tries
September 2003 - idea to suggest to Patrick Leroy a fancy book Dahu Volume 3 devoted to asymmetrical planes, with also double-planes and Siamese birds

Friendly Sites

 Dahu-ibex of French mountains legend

 Catalogue of asymmetrical planes in History

 Principle Analysis

 Superdahu project

 Asymmetrical Blohm und Voss derivatives

 Forum of What-if modellers

 Twin-boom projects



 Phloxtoon air fantasy