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| The twin engined Caudron G.4 at the Smithonian’s UdvarHazy museum. At the Silver Hill facility the aircraft was suspended from the ceiling. Now it sits at ground level, in plain view. |
Once upon a time, in the days before Marcel Dassault created his Ouragans and Mysteries, you could count on the French. Ah yes, without exception, and year after year, they produced the homeliest, most inelegant flying machines in the world. Well, now and then they slipped up and produced a good performer like the SPAD 13 that was also a classic beauty, but always you could count on them to follow up with something strange like the SPAD S.A-4. In the last year before World War I, it was the brothers Caudron who stepped up and, with unmatched élan, seized the title of creators of the homeliest production machine of 1913. Consider their G.3 and its sister ship, the G.4.
Actually, the G.4 is quite easy to consider, if you tour the Smithsonian’s UdvarHazy facility, because it holds possibly the best location for viewing in the entire museum. And it’s about time. For years, the G.4 could be seen at the Silver Hill facility, hanging overhead. It was tantalizingly close, but not even the most sympathetic docent could have granted enough access to really comprehend this strange critter. Now, thanks to its placement in a corner of the World War I collection at Udvar-Hazy, where both catwalk and ground-level walkway get you some choice three-dimensional views, it is possible to really enjoy one of the more creative aeronautical oddities of its time.
This is an interesting machine to write about, but I could hardly send off an article to the Styrene Sheet unless there were a modeling connection, could I? Ah-hah! There is one! Some time ago Formaplane produced a vac-u-form kit of the G.4. One can still be found on e-bay now and then, but the selling price typically reaches $40 or more, and that is a bit beyond what I can bring myself to offer for 65 grams of polystyrene, no matter how well done (and the Formaplane kits of this vintage are typically exceptionally nice) so I have never actually laid hands on one. Just to keep the pot boiling and make this short story longer, the twin-engined G.4 has a sister design, the single-engine G.3, a design so similar that the two can be discussed together. Best of all, there is a currently available vacform in 1/72 by Roseplane, and I have one! It is, as of now, uncut and reserved for fondling and contemplating because this is one challenging-looking model! Let’s begin with this kit and bring in the G.4 later.
Roseplane’s G.3 is an absolutely beautiful kit, with about 35 vac-u-form parts (16 of which may actually be intended for use as cutting and assembly jigs for the boom structures and struts, but which may be used as molded), metal wheels (four), metal rotary engine and prop, and about five feet of extruded rod and strut. Five feet of struts? In 1/72, that is a scale 360 feet! See why I haven’t started it? Surface detail is very nice: there is just the right touch of fabric sag between wing ribs, and the engraved panel lines are fine and consistent. The interior, consisting of five pieces plus two seats, offers a satisfying beginning, though I can’t attest to its accuracy. Very complete drawings in Windsock International magazine for May-June 2003 show a conventional plain joystick for the aft position, extending high enough to place the grip above the cockpit sides. Possible details not provided included a small set of engine control levers high on the left and a cylindrical air pump on the right to pressurize the fuel tank. Overall, Joe Chubbock, the kit designer, has made an exceptionally nice job of it. Decals are furnished for a French aircraft and two Finnish ones, plus serials for an Italian ship.
The wings are what initially put me off. Uppers and lowers are each molded in two spanwise sections. For the upper wing, both forward and aft sections are about three scale feet in chord. For the lowers, the sizes are three feet and one foot. The drawing shows them being pieced together, but with no clue as to exactly what they should represent when done. Do I apply enough filler to make a smooth upper contour? Does the whole aft portion of each hinge for roll control? What? Thanks to the UdvarHazy display, I now understand what I’m seeing, though I don’t understand the logic behind it all.
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| The Smithsonian Caudron G.4’s odd layout and bat like wings can be viewed from the ground and from the museum’s catwalk. |
The airfoil of NASM’s G.4, is quite unusual. The forward three feet is a typical thin WWI-era section, built around two spars, the front one forming the leading edge. Abaft the rear spar, however, the upper surface tapers sharply downward, and joins the lower surface, leaving exposed ribs on top to hold the shape. This results in a smooth and continuous lower surface with a rather badly disrupted upper. In the various collections of wing-section data I have seen, I don’t recall ever encountering this curious shape. And with some good reason: wing performance is much more sensitive to upper surface quality than lower surface. So WWII designers felt free to clutter their lower surfaces with exposed hinges, coolant radiators, bomb and rocket mountings, and uncovered wheel wells, so long as they kept the upper surfaces clean. Nonetheless, here’s the Caudrons’ solution, and it presumably worked reasonably well: I have seen references that claim the Caudrons’ aircraft were good climbers, and since climb is a direct function of amount of power left over from the task of dragging the airframe through the air, the wings must have been acceptably efficient (I would very much like to see a comparison of the drag contributions of the various parts, though). The kit wings are modeled with only top surface being correct, the forward portions being too concave on the underside. In my opinion, the under-surface should be filled or covered to replicate the smooth contour of the actual thing. Also, notice, before we leave this part of the discussion, that the ribs at the forward section don’t match the exposed ones aft. Yup. For whatever reason, different ribs form the top and bottom contours.
The rigging is a bit perplexing, also. Wing-warping is used for roll control but the logic of the warping rigging is not really shown on the plan. Adding to that problem is a subtle question of the strut arrangement outboard. These are actually sesquiplanes, with the area of the lower wing only half of the upper. French designers seemed to favor this style up through the Nieuports of the 1920s. The Caudrons consequently used a large overhang on the top wing, which they braced with struts that combine with the outboard vertical struts to form triangles. Nice solid strut braced triangles, at that. Triangles are famously rigid, so why did they combine rigid triangles with a flexible warping wing? This forces the rear upper spars into shallow S-curves when a roll command is applied, not the uninflected single curves we might expect. Given the rather modest maneuverability needed for the observation and bombing roles, it evidently worked all right, but it makes the roll-rigging a little different, if you are accustomed to thinking of that of the pylon-braced Eindekkers or the Deperdussin racer. In the Caudron’s case, the roll control consists of an extension forward of the joystick gimbals to a pair of bellcranks in line with the lower rear spar, and a pair of redundant cables running just above the top surfaces of the lower wings to the mid-wing interplane struts, where they turn upward to the tops of the outboard vertical interplanes. So the entirety of the lift loads of the outboard 2/3 of the wings passes through the pod, attaching to the stick in the middle, without being anchored otherwise. The ground (or anti-lift) rigging wires for the outer bay are similarly replaced by a cable that runs from the bottom of the outboard strut, turns at the top of the middle interplane, and passes across under the top wing to the opposite outer bay. In keeping with the needs for wing-warping, there’s no criss-cross diagonal bracing between the outboard struts, as is common among biplanes. None of this is obvious from the kit plans. I might note here that, in contrast with many later biplanes, none of the rigging other than the roll-control lift wires is doubled, not even the front spar lift wires.
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| Bob’s sketch shows the unusual layout of the G.4 wing. While the forward portion of the wing is conventional for WWI, the aft portion exhibits features not common to other aircraft. |
The wing is not the end of the oddities of the Caudron G.4. How about that configuration? This is the only example I can think of with a twin-tractor-engine, twin boom and pod configuration to reach production until the Dutch air force’s WWII Fokker G.23 “Reaper” of 1939, and then, of course, the P-38. The usual configuration for the smaller WWI aircraft that needed the nose clear for bomb-aimer or observer was a single pusher engine. If the plane needed more than the 100 or so horsepower available from one rotary, or the 160 from an inline, designers commonly went directly to a larger design with single fuselage and inline engines in nacelles. But not rotaries. How did the G.4 arise? It appeared to have been the natural development of the Model A, 1912 sport/trainer design. It appears to have had a single tractor 6-cylinder Anzani radial. So the brothers Caudron seemingly began with one of the common early configurations and made it more comfortable by seating the occupants in an enclosed nacelle. A couple of easy steps of evolution produced the mildly militarized G.3, with which France entered WWI. Still a pod and twin-tailboom tractor, this one had either the 80 hp rotary or an Anzani radial of 100 hp. This was hardly an airplane that would survive in the air when pilots started shooting at each other, and since the French seemed to view the pilot as little more than a chauffeur operating in three dimensions, the commander rode up front, where he was surrounded by engine, wings, struts and wires. This was fine for observing in a permissive environment, but where to from here? Needing more power than one engine could deliver, they essentially took the same aircraft, extended the upper wing span from 43 ft 11 inches to 56 ft 4 inches, mounted a pair of the same engines on nacelles, still in tractor configuration, moved the observer forward, then gave him a bomb-aimer’s window and a choice of formidable-looking gun mounts. NASM’s aircraft has a track on which a gun can be traversed forward and down. It looks intended to attack ground forces from above. Though the notion of attacking trenches from above in an unarmored aircraft seems appalling in retrospect, remember, this was the war of Paaschendale and the Somme, where 50,000 men died in a day. What’s one aircrew, in comparison?
Still, despite all this weaponry up front, you have to have sympathy for the chauffeur. He sat at the absolute rear of the pod, and by simply looking over his shoulder, he would find that the “blind spot” that worried most pilots was totally nonexistent. He could readily scan the entire hemisphere behind him. Should he (Sacre bleu!) look back and discover the agile three-gun Eindekker of Max Jmmelmann overtaking from below... well, Merde! He still had a pistol to brandish.
The Roseplane kit offered no clues about armament, though the only thing that could possibly be attached to a G.3 airframe might be a small bomb or two. The French withdrew them from combat by 1916 and used their G.3s for trainers, as hinted by the alternative “E.2” subtype, for, perhaps, Ecole, so unarmed is appropriate for this one. I have no information on the armament Formaplane may suggest for the G.4.
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| The center nacelle of the twin engine Caudron G.4 with its gun track. The pilot sat in the rear while the observer rode up front. |
There is a G.3 at the RAF museum at Hendon with much the same sort of comments applying, but with another interesting twist. The Roseplane kit included the LeRhone rotary but the example at Hendon has a ten-cylinder Anzani radial, entirely uncowled, and with a pair of half-ring exhaust collectors at the front, each exiting downward. The engine is as curious as all the other aspects of this bird. It appears to be a single-row radial with an even number of cylinders. Impossible! At closer inspection, it turns out that it is a twin-row, even though the offset in the second row of cylinders is so small as to be easily overlooked. Anzani dispensed with the center crankshaft bearing and used an offset crank throw that allowed the second bank to be displaced perhaps three inches from the front bank. This is a 100 hp engine, and the solution probably wouldn’t work for anything with much more power, but it is just one more item in the list of curiosities in these strange aeroplanes. The British version differs in another respect from the French design in Roseplane’s kit. Instead of the wide-open “bathtub” cockpit of French aircraft, Hendon’s has a short top deck separating the two positions. This did little for its looks and couldn’t have done much good except to slightly decrease the wind blast hitting the back-seat guy, but considering they trundled about the sky at 60 mph or so, this hardly seems worth the trouble.
In regarding colors, Roseplane calls for the French G.3 to be painted aluminum on top, with clear-doped linen on the bottom surfaces. This surprised me, but the NASM on the Mall has a Voisin painted overall aluminum so (assuming the Garber Facility folks got the Voisin right) this scheme was apparently at least occasionally used. In a guidebook Jim Lund brought back from the French Museum of Air & Space, their G.3 appears to be painted in a color that approximates clear-doped linen but looks too opaque to actually be that. The kit plan similarly shows Finnish machines in aluminum overall, while the Italian were in clear-doped linen, with outer wing panels painted red and green, approximating the Italian flag. The British example at Hendon is in clear doped linen. I once came upon a Royal Aero. Soc. paper discussing the damaging effects of solar UV on clear-doped fabric (and, for that matter, on the lozenge-dyed fabric the Germans used), which could reduce the strength of a fabric cover by half over the progress of a summer of sun exposure. They knew this in 1916. So why no sunblocking pigment on this aircraft? Did the British anticipate the lifetime of their Caudrons to be so short that they would never last long enough to make loss of fabric strength significant? In the slaughter of World War I, was this trivial, not worth the price of another coat of dope?
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| Please put your seat back and tray in the upright position. A vintage photo of the Caudron G.3. |
The G.4 is hard to interpret. It is apparently painted overall in a khaki color (I had no color standards with me when I was there) as the surfaces are too opaque to look like clear-doped fabric. The color has a sort of grimy look that one might expect from something that had hung for years at Silver Hill, but earlier photos of the G.4 hanging overhead show some tattered wing fabric that has been repaired or restored for the aircraft as it now appears. Is it possible that the crisp, attractive khaki we apply for WWI SPAD camouflage jobs should actually be shaded toward a dull grey? If anyone goes back to D.C. take along some color standards and write us some answers, OK?
Although they are strange, the Caudrons have to be described as successful. Over 3800 G.3s and G.4s were built. First flying in 1913, there were G.3s in service at the beginning of WWI, and they were still working at the end, though, as combat types, only with the British RFC. They went to Finland (for which decals are included), the USA, Belgium, Russia, and were widely used for private flying after the war. The Caudron brothers went on to build a G.6, a design similar to the G.4 but with the span increased from 13.4 meters to 17.21 and the LeRhones raised from 80 to 110 hp. Their final WWI design was the conventional but very attractive R.11, a design that would have looked good in a 1929 flying review. (Sierra Scale produces a 1/72 scale kit of the R.11, and most Sierra Scale kits are very good.)
So what did I think of the Caudrons? An aircraft is a sort of living creation. At their best, they entice you to come closer, like a pretty girl that you can’t help looking at and soon find yourself drifting toward (if you’ll pardon the sexist language.) Who wouldn’t love to be invited to climb into a Spitfire or Macchi 202, and just sit there and dream, or, in the ultimate fantasy, hear someone say “Go ahead, take ‘er around?” The Caudrons are intriguing, but, sorry, they don’t entice nor seduce me. Down the WWI line from the G.3 at Hendon is a BE-2b, universally reviled as “Fokker Fodder”, as “flimsy” or “rickety”. But it’s kind of cute, and absolutely right for 1913. I can’t remotely imagine being over the trench lines in it in 1915, with people shooting at me, but offered a ride today in my choice of the two, it’s the plain-vanilla-looking BE-2 that somehow wins. Wouldn’t I jump at the chance to take that one up for a couple of turns around the pattern?
