Douglas O-2H by Ardpol Resin
Kit No. 72-015
Decals: One version – U.S. Army Air Corps, 91st Observation Squadron, 1930
Comments: Nicely detailed resin kit; difficult windshield assembly; interplane struts may need replacing; quick drying cyanocrylate adhesive a must; some scratchbuilding skill required
The Douglas O-2H entered service with the United States Army Air Service in late 1928, and was one of the later versions in a long series of observation biplanes that were among the most important American military aircraft of their era, with nearly 900 machines built. The O-2 series originated in late 1923, when the U.S. War Department issued a series of contracts for prototypes of new observation aircraft to replace the First World War era license-built de Havilland DH-4Bs and DH-4Ms then in use with the Air Service. Douglas Aircraft Company received two of those contracts, each for one aircraft – the first to be powered by the 420hp Liberty V-1650-1 engine and the second by a 510hp Packard 1A-1500 engine. Apart from the engines, the aircraft were identical. Both were given the designation XO-2.
The Liberty powered XO-2 was the winner in its competitive trial, and on February 25, 1925 Douglas Aircraft was awarded a contract for 75 aircraft. The XO-2 was a conventional biplane with a welded steel tube fuselage and wooden wings, all covered in fabric with aluminium panels on the forward fuselage. The wings were of equal span, un-staggered and connected by a mix of struts and bracing wires. It had a tunnel radiator mounted under the engine, a divided main landing gear and rear tail skid. The horizontal tail plane was strut braced. Two sets of wings were tested on the Liberty powered aircraft, a 39 ft. 8 in. long span wing and a 36 ft. 3 in. short span wing. The long span wing was more successful, with better handling, lower landing speed and a higher ceiling, and was used on the production aircraft.
Later O-2 variants including the O-2H had a more streamlined fuselage and a two-blade metal propeller instead of the earlier wooden propeller. Some were modified as basic trainers by adding flight controls and instruments to the rear cockpit. During the 1920’s and early 1930’s, the reputation of Douglas observation planes was such that during the 1934 airmail emergency, when President Franklin Roosevelt directed the Army Air Corps to take over from private contractors because of suspected improprieties in awarding contracts, Douglas biplanes flew the U.S. airmail routes for 78 days, leading to the manufacture of a civilian version for the mail service. Between 1923 and 1936, the company sold 879 in the series, one as a civil aircraft, 108 to foreign air forces and 770 to the U.S. military services.
The Douglas O-2H saw such a major redesign of the aircraft that it really deserved an entirely new designation. The fuselage and tail were both modified, and a new streamlined main undercarriage, with a single main leg and bracing, replaced the tripod arrangement of earlier aircraft. Most dramatically, the wings were totally redesigned. The equal span un-staggered wings of the original O-2 were replaced with unequal span staggered wings (with a 40ft 10in span on the upper wing and 38ft 6in span on the lower wing).
The inter-wing struts sloped forward and the third strut introduced on the O-2E was adopted as standard. The O-2H was powered by the Liberty engine, with the vertical radiator above the engine as used on the O-2C. The wing mounted fuel tanks were removed and a new tank was installed in front and below the pilot’s cockpit. The O-2H had a two-blade metal propeller, replacing the wooden prop used on earlier models. These changes meant that the O-2H was lighter than the O-2, 6 mph faster, had a slightly better service ceiling and a much improved range, up from 360 miles to 512 miles.
The O-2H was produced in large numbers for the period, with 90 built for the Air Corps and 50 for the National Guard, for a total of 140 aircraft. Later in the production run the vertical tail surface was made shorter and wider, and the horizontal tail surfaces were also modified. All 140 aircraft were delivered in 1928-30.
First flight: Autumn 1924
Wingspan: 39 feet
Length: 29 feet 7 inches
Height: 10 feet 6 inches
Ceiling: 12,275 feet
Range: 400 miles
Weight: 4,985 pounds
Power plant: 435-horsepower Liberty engine
Maximum Speed: 103 mph
Armament: Two Browning .30-caliber machine guns, 100 pounds of bombs
Maximum speed: 128 mph (206 km/h)
Cruising speed: 103 mph (166 km/h)
Range: 360 miles (579 km)
Service ceiling: 16,279 ft (4,960 m)
Rate of climb: 807 ft/min (246 m/min)
A key difference between this kit and my first resin aircraft kit (see XP-67 Moonbat by Anigrand in the WWII Section), is that Ardpol’s Douglas O-2H is injection molded resin, while the XP-67 was solid cast resin. Injection molded resin can offer superior detail, but has less density and can be far more brittle than resin cast in solid pieces. The latter will hold up to any abuse short of being dropped on a hard surface from three feet on up, but injection molded resin can break from ordinary handling, as I discovered early on when I cracked one of the O-2’s fuselage halves while sanding down the resin blocks it was attached to.
After a little research, I bought some quick drying cyanoacrylate liquid adhesive and repaired the damage. Applying just a little of this stuff to the crack did the trick, as it penetrated instantly and dried about a second later. If you ever have to resort to this, be sure the cracked parts are perfectly aligned, just as they were before the damage occurred, because quick drying cyanoacrylate works FAST — there will be little to no time to line things up once it is applied. It works with capillary action, enabling it to penetrate and then seal any crack or crevice within seconds. The fuselage repairs were completed after a little sanding to smooth away the last hints of the damage.
Assembling the fuselage interior and halves, as well as the lower wing, tail, and elevators proceeded smoothly, although some extra sanding may be required to ensure the elevators look symmetrical once cemented to the rear fuselage, especially from above. The real challenge comes, as with most biplanes, when it’s time to attach the upper wing, which brings me to the main defect of the kit. The upper wing is in three parts instead of the standard single piece. The three-part assembly made it extremely difficult to effectively correct the wing’s tendency to bow upwards; applying heat and pressure ran the risk of the wing breaking apart, and — since it was resin — not necessarily along the join seams where the three parts were cemented. Biplane kits are challenging enough without this added complication, even more so when you are working in resin.
Another challenge is in the major flaw category: The interplane struts provided are structurally too weak to hold the upper wing, and will have to be replaced. Even fast drying cyanoacrylate could not salvage them. I fashioned replacement struts from Evergreen strips that were sanded so that their angle allowed the upper wing to be positioned a bit forward of the lower one, as later O-2’s had this feature.
I then cemented the struts to the lower wing using BSI Insta-Cure, a super-thin cyanoacrylate adhesive. Properly sanded and positioned, once they were dry and securely attached to the lower wing, it was a simple matter to apply a drop or two of Insta-Cure to the top of each strut and carefully lower the upper wing into position, and allow it to rest on the struts as the adhesive dried. Surprisingly, I was able to cement the upper wing into the proper position without the use of a jig, which I had recently bought for that purpose.
While the main landing gear look spindly and troublesome, I was able to assemble them without incident, making sure to use only Insta-Cure, since the wheels attach to the main landing gear struts by only the smallest of contact points. But with Insta-Cure the main gear ended up having surprising structural strength. The part for the tail skid was missing, so I fashioned one from plastic card and painted it after cementing it onto the fuselage. The ring assembly for the rear .30 caliber machine gun consists of four parts, two of them quite small, but with patience, it builds up to look quite presentable. I replaced the kit’s .30 caliber gun with another from my spares box that was slightly larger, more detailed, and looked a bit more to scale.
The barrel for the forward machine gun must be handled with care — at several points, care and disciple with tweezers was essential given the number of small parts. The dozen tiny exhaust pipes for the engine are a case in point. They are not all of a uniform shape or size, and do no more than give a general impression of what the exhaust manifold looked like — I was able to cement 8 of the 12 into place without damage or loss. Other than this, the kit’s one major drawback is that the unorthodox shape of the coaming around the pilot’s bay makes it quite difficult to attach a windscreen, which must be fashioned from clear plastic (provided) but also bent in at least four places to have a stepped appearance, and cut assymetrically to be cemented atop the coaming without looking lopsided. After four attempts at this, I surrendered — this is one part it would have been a delight to have in injection molded form.
The O-2H is decked out in the standard colors for U.S. Army aircraft in the late 1920’s — a blue fuselage and yellow wings and tail. The challenge was in getting the right shade of both. For the fuselage I used GTW Blue, a Polly Scale railroad acrylic, which airbrushed on beautifully after being thinned with a little distilled water at a ratio of 5:1. To my eye, this was the perfect shade of blue. For the “Yellow Wings” I used Golden Yellow, an Akan acrylic (BS: 356) intended for propeller tips and the like, thinned with distilled water but at a ratio of 4:1. This paint looked brighter in the bottle than when airbrushed onto the wings, as it has a warm, almost orange hue, but I was pleased with it. The nose radiator is painted acrylic Gloss White, Tamiya’s X-2, and the propeller is airbrushed in Aluminum, a lacquer from AK Interactive’s Xtreme Metal series, AK 479.
The kit decals are excellent, and although I was highly skeptical about the stripes decals for the rudder, after painstaking trimming they went on beautifully, and responded well to decal solvent. Mysteriously, much of the rudder decal on the right side cracked and broke off well after the final treatment with Future, and so had to be painted over. For this I used Tamiya enamel-based Royal Blue, Model Master enamel Flat White, and Model Master acrylic Navy Red, all with a very fine paint brush. It came out well enough to pass muster, at least to the casual observer’s eye. The irony is that when it comes to tail markings, I greatly prefer paint to decals.
This is an interesting kit of a forgotten U.S. Army observation aircraft of the period between the World Wars, one of the first if not the very first contribution of the Douglas Aircraft Company to the American military, which set a standard of ruggedness and dependability. Highly recommended for those on the lookout for something unusual.