McDonnell XF-85 "Goblin" is a jet aircraft created in the USA as an escort fighter capable of being based on the Convair B-36 bomber.
XF-85 at Edwards Air Force Base
The first thoughts of creating a strategic bomber that could, having taken off from the territory of the United States, cover a considerable distance to enemy positions, and, after completing a combat mission, return back, the American military appeared in 1941. The reasons for the appearance of these thoughts were the first defeats in the Pacific War, as well as the likelihood that Great Britain would fall. This is how the terms of reference for the six-engine strategic bomber B-36 appeared. The development of the machine was delayed so much that it did not have time to take part in the war. When the construction of an aircraft with a range of about 9 thousand km came to an end, it turned out that it did not fit into the concept of using bomber aircraft adopted at that time: there was no escort fighter capable of following the bomber throughout the flight. The existing aircraft, as well as those that could have been designed to accompany the Convair B-36 with a simultaneous launch, were not suitable: the existing ones - due to insufficient flight range, projected - would have turned out to be very heavy and unable to effectively reflect interceptor attack. In addition, the pilot of the escort fighter, being in constant tension throughout the entire flight, is very tired by the time the need to conduct an air battle arises. Representatives of the US Air Force considered that these problems could be solved only with a non-standard approach.
In December 1942, the US Air Force announced a competition under the designation "Project MX-472" - escort of a heavy ultra-long-range bomber. A special commission for two years considered a number of projects, but the choice was stopped on the project of a fighter of the so-called "parasitic" type, which for most of the flight would be inside the bomber, and, if necessary, would be released outside. This solution was not completely new - long before the Convair B-36 there were airships of a similar design.
The only company that presented a fairly well-developed project of this type of fighter was the recently created "McDonnell". Despite the problems that arose, the company's engineers, under the leadership of Barkley, who previously worked for Curtiss, in a short time presented several projects that met the requirements of the Air Force. The proposed options differed in the types of fastening: internal or semi-recessed suspension. By the beginning of 1945, representatives of the US Air Force had chosen a project that provided for an internal suspension. In the company, the car received the designation "Model 27D".
An order for the development of prototypes (military designation XF-85) from the American Air Force was received in March 1947, and the first independent flight took place on August 23 of the following year. The fighter was launched from a Boeing EB-29B bomber. Flight tests have shown that turbulence around the bomber creates severe control problems. Coupled with the fact that such a miniature aircraft could not have the maneuverability and speed of fighters with which it was to collide in the air, this led to the termination of development.
The dimensions of the bomb bay of the carrier bomber (4.88 x 3.0 m) also limited the dimensions of the XF-85 itself. Fuselage length - 4, 32 m (full length of the aircraft - 4, 5 m) width 1, 27 m, height 2, 0 m. The plane was to be equipped with four large-caliber machine guns. According to the specification, a fighter at an altitude of 10-12 thousand meters could be fired and adopted in one and a half minutes. The fuselage is an all-metal semi-monocoque made of aluminum alloys. Equipment, fuel tanks and weapons were installed inside the fuselage, since the wing was thin, had a folding unit at the very root and a complex structure. Wingspan 6, 44 m, sweep along the leading edge 37 degrees. The aircraft did not have a landing gear - only auxiliary runners intended for an emergency landing. The tail unit is six-plane.
The XF-85 Goblin cabin had a volume of 0.74 m3. Despite such small dimensions, heating, pressurization and pressurization were provided in the cab. In addition, the designers managed to "squeeze" a high-pressure oxygen supply system, as well as a can of oxygen for the pilot to breathe after an emergency exit from the aircraft (this was necessary, since the practical ceiling was 15 thousand meters). The pilot's rescue system was a T-4E ejection seat with a 33-degree back inclination. The tightness of the cockpit led to the fact that the machine gun sight and pedals, and not the chair, were made adjustable in height. In addition, the selection of pilots for this aircraft was also determined by the small dimensions: height no more than 172 cm, weight (including the suit) - up to 90 kg.
The fuel system consisted of a single 435 liter, protected horseshoe-shaped fuel tank encircling the engine. This volume at full engine power provided 20 minutes of flight, in cruise mode - 32 minutes. During the tests, it was possible to achieve a flight duration of 1 hour and 17 minutes. It was assumed that a 95-liter tank and two wing-compartment tanks with a capacity of 113 liters each would be installed in the gargrotta on production aircraft. All tanks were equipped with an inert gas filling system. In addition, the aircraft was supplied with a carbon dioxide fire extinguishing system.
A Westinghouse J34-WE-7 turbojet engine (thrust 1361 kg) was installed in the forward fuselage. This location was chosen to shift the center of gravity of the fighter forward. Thanks to this, the shoulder of the tail unit has increased. A 1320-mm exhaust pipe was connected to the nozzle exit from the engine; the pipe and motor were covered with a layer of fiberglass wool and aluminum foil to reduce heat transfer. In addition, the air coming from the air intake blew outside the engine. If the freestream speed exceeded 250 km / h, the engine turbine autorotated, which made it possible to exclude the scrolling of the turbocharger when starting from the carrier aircraft. The Willard BB 206 / V accumulator was used for ignition.
In the course of the design, several options for attaching a fighter were considered, including the use of a long cable with a loop at the end. The fighter, after the capture of which, was drawn into the bomb bay. However, due to the laxity of the cable, there was a possibility of a collision between the carrier and the fighter being pulled up. To avoid such situations, a rigid trapezoid of complex design was chosen as a hook-up device, which took the parasitic fighter away from the carrier's fuselage, minimizing the risk of collision.
The hook-up device that was installed on the fighter is a retractable steel hook equipped with a spring-loaded safety bracket. To detach from the carrier, the head of the hook was rotated. The cleaning drive is electric. The suspension system was designed on the basis of a similar device previously used on the Makon and Akron airships. The head of the hook in the extended position was in the pilot's field of view above the front of the canopy.
The tightness of the cockpit is also reflected in the configuration of the dashboard. The required minimum of instruments was installed on it: navigation - indicators of a gyrocompass and an automatic radio compass (ARC); aerobatic - airspeed indicator, accelerometer and altimeter; engine control devices - indicators of turbine temperature, turbocharger speed, fuel pressure and fuel gauge. There was also a cockpit pressure gauge. In order for the pilot not to injure his legs during the ejection, the instrument panel was fired back together with the cockpit canopy. The radio equipment of the serial "parasitic" fighter was supposed to consist of an AN / ARC-5 VHF radio station and an AN / APN-61 radio compass. The radio station antenna was planned to be placed at the tip of the upper left keel. There was no radio equipment on the prototypes.
To ensure fire safety, the wiring of the aircraft was retracted into fireproof boxes and sleeves. There were connectors in the air intake shell and in the suspension hook for connecting an external power supply.
The roll control system did not have hydraulic boosters. Ailerons are of the usual type, with trimmers adjustable in flight and aerodynamic compensation. Control over the pitch channel, in contrast to it, was organized in a very peculiar way - due to the differentiated deflection of four steering surfaces located crosswise. The law of deflection of steering surfaces was based on the same principle as for aircraft with V-shaped tail: when pedaling, they deflected in different directions, and when giving a handle - in one direction. An original differentiating mechanism was installed in the control channel of the tail surfaces. The rudders were also equipped with trimmers adjustable in flight. The adjustments were especially important because the alignment of the fighter changed a lot as the fuel ran out.
The XF-85 Goblin's armament consisted of four 12.7 mm Colt Browning M-3 light machine guns. Ammunition - 300 rounds per barrel. On prototypes, the embrasures of the weapons were closed with overlays. The installation of a cinema-photo machine gun was also provided. It was planned that the machine guns would subsequently be replaced by Ford-Pontiac M-39 cannons of 20 mm caliber. The reloading of the weapon was carried out using a pneumatic system for which air was taken from the engine compressor.
Before the start of flight tests, due to a clearly small shoulder and insufficient vertical tail area, a pair of additional fixed keels was installed on both prototypes - below and above the tail cone. This solution made it possible to increase the track stability. Under the fuselage there was an aerodynamic brake made in the form of a hydraulically deflected flap. The control was carried out by a slider located on the throttle. When exceeding the speed of 900 km / h, the flap was automatically deflected. When the speed dropped below 297 km / h, the automatic slats were deflected. The drive is via a worm gear, electromechanical.
At the request of a representative of the air force, primitive landing devices were installed on the plane, which, when landing on the ground, were supposed to prevent damage. They consisted of a strongly protruding ski-spring, bent from a steel strip, and two small steel heels installed at the ends of the wing.
On June 2, 1946, the wooden model of the fighter and the suspension trapeze for it were demonstrated to the representatives of the customer. On June 8, the Air Force ordered 2 prototype aircraft and a glider for static tests. All of them did not have electronic equipment and weapons. At the end of 1946, the first prototype of the Goblin, built with great care and in the shortest possible time, was delivered from the McDonnell pilot plant in St. Louis, Missouri to Moffett Field AFB (California) for purging in a NASA wind tunnel … However, during transportation, the prototype suffered a big setback - when loading onto a trailer due to poor slinging, the airplane fell off and fell on the concrete from a height of three meters. The fall severely damaged the nose, engine and fuel tank. The first Goblin was returned to St. Louis for refurbishment. The tests continued on the second prototype.
The McDonnell outboard fighter program aroused such great interest among the customer representatives that Convair was instructed to equip all production B-36 bombers (starting with 23 machines) with a trapeze for the Goblin. In addition, 10% of these bombers were to be produced in the version of "clean" aircraft carriers capable of carrying three or four "parasitic" fighters. The first series of "Goblin" was supposed to consist of 100 cars. In addition, there was a project to convert it into a portable reconnaissance aircraft (it was embodied in the FICON system, the F-84F Republican reconnaissance aircraft based on the GRB-36 carrier). The purges were completed in early 1948. According to their results, it became clear that the slats are ineffective, and in the released state, the hook reduces track stability by 75%. This is because the high speed open pit hook acts like a plate across the flow. The angle of deflection of the slats was increased, the hook was fixed in the released position, the well of the hook was closed with a fairing. After completing the improvements, the car was delivered to the Muroc Dry Lake airbase. There, the EB-29 bomber, bearing its own name "Monstro", was already waiting for him, converted into a carrier.
This aircraft was in service, but did not take part in hostilities. By the time it was converted into the XF-85 carrier, it had flown 180 hours. The main alteration was the expansion of the rear bomb bay and the installation of the McDonnell folding trapeze. In addition to the suspension loop, this design had a lifting collar, which in the lowered state covered the bow of the "Goblin", preventing it from swinging. The trapezoid in the extended position went down by 3.2 meters. In the rear bomb bay was also equipped with a pressurized trapeze control post, and near it a "waiting room" - the place where the Goblin pilot waited for the signal.
The operator kept in touch with the pilot of the XF-85 "Goblin" using a low-power VHF radio during the uncoupling-pickup. For filming and photographing the process of launching and receiving the "Goblin" on board, cameras and cameras were installed on the lower surface of the carrier's wing. The tail section of the Monstro was painted bright yellow to enhance visibility, and wide yellow and black stripes were applied to the bottom and top of the wing. So that during takeoff, the fighter, hanging under the tail bomb bay in a semi-recessed position, does not accidentally hit the surface of the runway, the Monstro's tail support was lengthened. Since the clearance of the former bomber was insufficient, the "Goblin" was loaded through the pit. First, a fighter was driven into the pit on a cart, then the carrier ran into it from above, lowered the trapezoid and carried out the pickup. The only test pilot recruited into the Goblin's test program was Edwin Skosh, Chief Pilot of the McDonnell Company, a former US Navy pilot.
At the beginning of June 1948 the Monstro made its first flights with the XF-85 Goblin on board. After the first ascent, Ed Skosh insisted on a detachment and an independent flight, he literally fell in love with the new fighter, and it seems that the plane reciprocated; none of the many emergency situations that occurred during the tests ended tragically. During the first flights, the Goblin engine was checked and tested. In addition, a pre-flight procedure was developed: first, the "Goblin" descended on the trapeze, the pilot had to leave the sealed "waiting room" through the airlock, go along an unenclosed narrow metal path to the cockpit of the fighter, which was again pulled into the compartment, climb inside without any stepladder, close the lantern, and only after that was he in relative safety. The situation in the bomb compartment of the B-36 would have been somewhat easier, because it was closed from below by flaps, but they were absent on the Monstro, and the way to the cockpit from the “waiting room” was difficult and dangerous.
On August 23, 1948, the Goblin made its maiden flight. The uncoupling was carried out at a speed of 320 km / h at an altitude of 6.1 km. The pilot turned the head of the suspension hook, the XF-85 sank 40 meters while the engine was on mode. After that, the fighter went into active flight. Ed Skosh spent 10 minutes checking the flight data of the Goblin in the speed range of 290-400 km / h. after that, he made an attempt to moor to the trapezium, but it was unsuccessful. It turned out that the engine control system was too insensitive for accurate speed control. Also, the turbulence created behind the lowered trapezoid squeezed the airplane down. In addition, it was difficult for the pilot to determine the distance to the ear of the trapezoid. Skosh himself admitted that the eye meter failed completely, and sometimes it seemed to him that he closed one eye. Attempts to navigate the stripes on the tail and wing of the "Monstro" also did not help. During the second run, due to the large difference in speeds, the "Goblin" hit the trapezium with a lantern and smashed it. The pilot, who lost his helmet and oxygen mask, sat down on a spring ski in the desert with almost completely depleted fuel. The mileage was 400 meters, while landing the car was not damaged. Based on the results of this flight, it was concluded that there was insufficient controllability in the pitch channel.
To improve handling, the pitch trim and elevator deflection have been increased. For an additional check of the systems "Monstro" on October 11 and 12, twice lifted the "Goblin" into the air without uncoupling from the trapezoid. The second independent flight took place on October 14. Skosh After uncoupling, he made a whole cascade of evolution on the fighter, checking the rate of climb, maneuverability, course stability and acceleration characteristics. The Goblin was superior to any fighter of that time in terms of its flight performance. The main advantage of the new fighter was its high thrust-to-weight ratio - about 0.8 with ½ fuel capacity. One could only dream of such a thrust-to-weight ratio in the 1940s, since the then jet engines had a large mass, low thrust and significant fuel consumption.
Thus, the XF-85 Goblin surpassed all its contemporaries in acceleration and climb rate. However, the plane began to show its temper: the car was quite difficult to pilot, which made it inaccessible to pilots with average qualifications. In addition, even after the addition of two large keels under and above the aft fuselage on the course, stability remained insufficient because both keels were in the aerodynamic shadow of the fuselage, which caused oscillations of the "Dutch step" type during the dive of the aircraft.
At the end of the second flight, the skosch successfully moored the fighter to the trapezoid from the first approach, but this procedure can be compared with the "Russian roulette", only thanks to luck the pickup was successful.
The next day, they made two more flights. "Goblin" both times docked to the "Monstro", but Skosh noted in the report that the vortex track, which stretches behind the lowered trapezoid, interferes with the pickup. On October 22, after the flight, Skosh, after 3 unsuccessful attempts to dock, sat down in the desert.
To neutralize all negative factors, theoretically calculated and well thought out measures were required. The second prototype "Goblin" at the Washington Institute was blown in a wind tunnel. Based on the results of the purges, it was decided to modernize both prototypes in St. Louis. There, fairings of the lower part of the hook were installed on the machines, which, according to calculations, should have neutralized the effect of the release of the hook on track stability. The hook ear length was increased by 150 mm. Swept keels were installed at the ends of the wing. The aircraft returned to the Muroc Dry Lake base at the end of the winter of 1948/49.
The second Goblin prototype made its eighth flight on March 8, 1949, after which the first prototype was connected to the program. During the first flight, he suffered a failure - a strong side wind led to the fact that the plane yawned at launch, broke off the hook and severely damaged the trapezoid, which they could not remove. The Skosh landed in the desert without any problems, as usual. The pilot's opinion of the upgraded fighter was positive.
It took about a month more to restore the trapezium, and on April 8, the XF-85 Goblin made its last flight. The attitude of the air force towards the program at this time was already quite cool. Ed Skosh tried to squeeze the maximum performance values out of the aircraft during the flight. However, the pickup failed again, and the tester had to land the plane in the desert again. The XF-85 program was canceled in May 1949. It was in vain that the company representatives and the test pilot argued that during the tests the portable fighter had fewer flaws in comparison with any other prototype of the combat aircraft.
The main troubles were caused by an inconvenient truss trapezoid, in the wake of which a small plane was mercilessly thrown in different directions. On a proactive basis, McDonnell quickly presented the Air Force with a draft trapezium with a telescopic exhaust rod, which grabbed the Goblin's hook 20 meters under the carrier outside the turbulence zone and then pulled it to the main grip. In addition, options for the development of the XF-85 Goblin were being worked out - an aircraft with a swept wing and a speed of M = 0.9, as well as a transonic aircraft with a deltoid wing. However, these projects did not progress beyond the drawings. Also known are other attempts to create an airborne "parasitic" fighter, but unlike the McDonnell project, not even prototypes were created.
After air refueling systems appeared, there was no need for such fighters. Goblin spent $ 3,211,000 on the XF-85 program, and even the most die-hard skeptics had to admit that McDonnell was the best at handling the problem. The weak point was not the plane, but the conditions for the launch and landing of the fighter. Both "Goblins", unlike most prototypes, survived, probably due to their original and good looks. In 1950, they were bought from the company by aviation museums: the first prototype was acquired by a private museum, which later transferred the aircraft to the American Air Force Museum in Dayton (Ohio), the second got to Offut airbase (Nebraska) and is exhibited at the Museum of Strategic Air Command …
Flight technical characteristics:
Length - 4.53 m;
Height - 2, 56 m;
Height with folded wing - 3, 32 m;
Wingspan - 6, 44 m;
Wing area - 9, 34 m²;
Empty weight - 1696 kg;
Normal takeoff weight - 2194 kg;
The volume of the fuel tanks is 435 liters;
Engine type - 1 Westinghouse J34-WE-22 turbojet engine;
Unforced thrust - 1361 kgf;
Cruising speed - 689 km / h;
Maximum speed - 1043 km / h;
Climb rate - 63.5 m / s;
Flight duration - 77 minutes;
Combat radius of action - 350 km;
Service ceiling - 15520 m;
Armament - four 12, 7 mm machine guns;
Ammunition - 1200 rounds;
Crew - 1 person.
Prepared based on materials
