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GLENCOE 1:32
MCDONNELL XV-1 CONVERTIPLANE
'INBOX Review'
Alternative Scale
Reviewer: Michael Johnson (rec.models.scale)
During the late 1940s, the rotorcraft industry began looking for ways to defeat the blade stall barrier and by the early 1950s; a cornucopia of experimental Vertical Takeoff and Landing (VTOL) aircraft had taken wing. Some of those experiments closely resembled helicopters but others looked like contraptions that escaped from the set of Cold War science-fiction films.
Several of these concepts demonstrated real potential to break the retreating-blade stall limit on higher speeds. Planners in the U. S. Army also saw potential for new types of aircraft to mobilize infantry and support units in numbers, and at speeds, hitherto impossible.
In 1951, the Air Force announced a competition to develop an aircraft that could take off and land vertically like a helicopter, then fly horizontally at speeds comparable to fixed-wing aircraft by using stub wings to augment lift from the main rotor. Bell, McDonnell, and Sikorsky responded, but Sikorsky had to excuse itself due to more pressing commitments to build and service military helicopters for the Korean War. The McDonnell and Bell proposals differed greatly. The Bell XV-3 mounted two rotors at the tips of small wings. For takeoff, the rotational axis on both rotors pointed straight up but once airborne, the rotors tilted forward for transition to horizontal flight. The rotors functioned more as propellers fitted to fixed-wing aircraft. A single engine mounted in the fuselage drove both prop-rotors via a complex transmission and drive shaft system.
In contrast to the complexities of the XV-3 drive system, McDonnell engineers used a single rotor for vertical lift and a pusher propeller for forward thrust on the XV-1. They designed this aircraft to operate in helicopter, autogiro, and airplane modes, depending upon the vertical or horizontal speed. The pilot of an XV-1 took off vertically and transitioned to forward flight, all in helicopter mode. As forward speed increased above the stalling speed of the stub wing, the pilot shifted the rotor to autogiro mode. He moved the rotor blades to shallow pitch (still generating lift but with less drag) and he disengaged the engine from driving the rotor. Now the rotor spun automatically (autorotation)-the XV-1 was an autogiro. During autorotation, air moving through the spinning disc of the rotor actually maintained rotation and provided some lift. The stub wing picked up its share of generating lift and the engine power diverted from turning the rotor now drove the pusher propeller, driving the XV-1 forward.
At higher speeds, the pilot moved the blades to an even lower pitch setting. They generated less lift but the stub wing compensated. This lower setting pushed the retreating-blade stall speed well beyond the maximum speed of other conventional helicopters of the time. At cruise speeds greater than 222 kph (138 mph) the stub wings provided 85% of the total lift, the remainder contributed by the auto-rotating blades. Even at maximum speed, the wings were not large enough to generate all lift. Engineers probably restricted their size to reduce drag.
This XV-1 design concept was promising but the engineering team had to surmount a major challenge. A single power plant and transmission had to drive both the main rotor and the conventional pusher propeller. Two transmissions would impose an unacceptable weight penalty. The solution seemed simple and elegant but it could not be bench-tested. McDonnell had to build and fly a manned, test-bed. Tip jets thrusting from the ends of each rotor blade (there were three) required no mechanical transmission, nor even an anti-torque tail rotor, according to the theory. The main engine drove two compressors. High-pressure air travelled from the compressors down piping to combustion chambers on each rotor tip where a burner ignited fuel to produce jet thrust.
Friedrich von Doblehoff had pioneered the first successful tip-jet helicopter in Austria during World War II and he provided expert guidance to the McDonnell team as they designed and built the XV-1 tip-jet rotor propulsion system.
To take off, the pilot increased rotor blade pitch collectively, exactly as he would do in a conventional helicopter; only the rotor propulsion system differed. Once airborne, and as speed increased above the stub wing stall speed, the pilot pulled a 'control shift' lever, transferring main engine power from the compressors to the pusher propeller, and reducing rotor blade pitch to the autorotation setting. As the XV-1 accelerated into airplane mode, the pilot again moved the control shift lever to transfer aircraft pitch and roll control from the rotor (cyclical changes in blade pitch in helicopter mode) to the elevator, ailerons, and rudder control surfaces that control conventional, fixed-wing aircraft.
McDonnell built the XV-1 entirely from aluminium and other metals. Twin tail booms supported the empennage clear of the pusher propeller. The aircraft took off and alighted on metal skids. The cabin was a streamlined tube covered almost entirely with Plexiglas windows. Seated in tandem, the pilot and co-pilot, or pilot and three passengers, enjoyed a spectacular view. Even at rest in front of a hanger, the XV-1 conveyed a sense of streamlined speed and elegant simplicity.
McDonnell spent twenty-two months building the XV-1.
When project test pilot John R. Noll began hover tests on February 11, 1954, he had more experience piloting helicopters than most other test pilots. Noll was among the first helicopter pilots to evacuate men wounded in combat during World War II. In the first series of XV-1 test flights, ground technicians loaded the aircraft with lead to keep it from flying out of ground-effect, about a wingspan's height above the runway. Problems with the tip-jet rotor propulsion system delayed free flights with safety weights removed until July 14, 1954. Meanwhile, McDonnell completed the second XV-1 prototype. Engineers modified the new test vehicle to test several significant design changes. Engineers lowered the rotor pylon and added tiny tail rotors at the end of each tail-boom to boost directional control when the XV-1 flew as a helicopter during takeoff and landing. Technicians also retrofitted tail rotors to the first XV-1. Noll's initial flight tests had dashed the design team's hopes of eliminating the inefficient and lift-robbing tail rotor altogether. Noll also recommended that stouter legs replace the spindly landing skid struts, but McDonnell did not make this change until after an XV-1 suffered damage when one of these struts failed on landing.
Noll first transitioned from helicopter to airplane mode on April 29, 1955, but the highlight of the XV-1 flying test program came on October 10, 1956 when the second prototype became the first VTOL aircraft to exceed 322 kph (200 mph) in level flight. This speed was 71 kph (44 mph) faster than the conventional helicopter speed record at that time. By 1961, improved rotor systems gave conventional helicopters the speed to match the XV-1 record, and then surpass it by a wide margin several years later. This doomed the convertiplane concepts that employed fixed, rather than tilting, rotor systems. Bell Helicopter and Boeing's rotorcraft division continued to develop the tilt-rotor variation of the convertiplane.
While I was undertaking more on-line research on the Fairey Rotodyne, I stumbled across the XV programmes that were being undertaken by United States aircraft manufacturers during the same period. By far the most attractive and similar to the Rotodyne was the XV-1 Convertiplane developed by McDonnell. The XV-1 was much smaller than the big 40 passenger Rotodyne by Fairey but looked similar, employing the rotor tip jet system that made the Rotodyne so noisy.
Well, this plane was a feast to my eyes and I quickly found that Glencoe made a 1:32 version of the kit (re-boxed from the 50’s) via a review in SAMI magazine from 2000 I was re-reading one night. I showed my lady wife (she who paints miniatures, figures and builds the occasional model) bounded out of bed, raced to the PC and checked ebay, nothing……at which point my wife smiled and told me to come get some sleep!
A quick post the next day on Aircraft Resource Centre’s wanted forum yielded almost instant results and within a fortnight I was the proud owner of an unopened kit from a fantastic Canadian modeller for the grand total of $18 including postage, Joy!!
Opening the box reveals a bag of light greys and larger parts, separate bag with the clear canopy inserts, instruction sheet and small decal sheet.
The instruction sheet consists of only one A3 page printed both sides. The sheet is certainly more than adequate as the kit only has a few pieces to it.
The small decal sheet by Scalemaster is excellent with all images thin, sharp and in register. No problems there I would not imagine.
On the whole, parts are relatively crisp, with only small amounts of flash on most parts. Details are raised and consist of rivets and raised panel lines. Nothing out of the ordinary as this kit heralds from the same era that Airfix released its Rotodyne kit. Like the Rotodyne kit, I would recommend a light application of 1200 grit wet and dry to tone down the raised detail.
It is great to see the transparencies bagged separately, so avoiding most of the scuffs and scratches that we modellers have to deal with most kits we build.
The reviews I have read indicate some fit issues, which is something to be expected for a kit which was first produced in the 1950’s.
Glencoe provide a detailed interior for the XV-1, which lends itself to further detailing even to just adding an etched harness for the pilot and co-pilot’s seats and lap belts for the rear passengers.
Unfortunately there is very little information available on the XV-1, so I will have to rely on a couple of images I found on the internet to assist with detailing.
Well, what a neat kit, which should, with care, build up nicely and look great next to my Revell 1:32 AH-64A Apache.
I have since found out that a limited run company based in Hong Kong called Anigrand produce a series of 1:72 scale resin kits of the XV series including the XV-1. At US$32 + postage they are not exactly cheap but I am hoping to purchase one to sit next to my completed Rotodyne’s.
It is ironic that the USAF is currently expecting delivery of the V22 Osprey, a tiltrotor transport that owes much to the XV-1 Convertiplane for its development.
Recommended for those experienced modellers like myself who love esoteric aircraft, helicopter lovers or anyone wanting to build something a little different.
SMAKR
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