NOT AHEAD OF THE SOUND

DO NOT OVERTAKE SOUNDExperimental aircraft D-558-I. In late 1944 the Douglas firm received an order to develop an experimental aircraft with a turbojet engine. The main goal of this project was to obtain information about the aerodynamic loads, stability and controllability of the aircraft at transonic speeds. These data were to complement the information obtained in the course of implementation of the programme of tests of a supersonic aircraft X-1. In accordance with the specification developed by NACA (national Advisory Committee for Aeronautics) the aircraft was to take off from the aerodrome, to gain height from 6000 to 10,600 m, within 10 minutes to fly at transonic speeds and then return to the airfield.

 
The project received the designation Douglas Model 558 High Speed Test Airplane, or just D-558. Work on the project was led by the legendary Edward Heineman, the designer of the famous cars A-26, A-20 and A-1 Skyraider, Douglas turned the name into a global brand.
 
Two months later, Heineman and his longtime assistant, Leo Devlin gave the NACA and Navy aircraft project with a combined power plant of the turbojet and rocket engines, representing not only a purely experimental machine, but the prototype fighter. The sailors approved the idea, and PASS it dismissed as not relevant to the research nature of the program. Heinemann then proposed to split the development into three stages.
 
The first stage involved the construction of six aircraft D-558 with turbojet engines TG-180 for research flights at speeds corresponding to the numbers M from 0.75 to 0.85. All the planes were supposed to have wings with different profiles and air intakes.
The second phase involved equipping two additional rocket engines for aircraft could achieve the speed corresponding to the number M=1.
 
And the third stage was to build on the basis of the best aircraft carrier-based fighter.
 
This compromise was acceptable to all, and may 9, 1945, construction began on the layout of the aircraft.
 
Experimental aircraft D-558-I
 
The machine had a small size — its length was 10.8 m and a wing span of 7.62 m. Almost the entire volume of the fuselage was occupied by the turbojet engine. Air intakes placed at the sides of the fuselage, freeing the nose part to embed the cockpit and equipment.
 
A straight wing with the relative thickness of 10 percent attaches to the bottom of the fuselage. With this arrangement, any big problems with the placement of the struts the main landing gear. The fuselage is fully occupied by the engine, and place the fuel tanks could only be in the cavity of the wing. The only place to accommodate the retracted landing gear was a relatively thin center section. To avoid the appearance of unwanted sagging, engineers had to develop a very thin wheels and Pneumatics to them.
 
The plane was calculated for a maximum speed of horizontal flight corresponding to the number M=0.9 and the achievement of number of M=1 was assumed in a dive from a height of 10 688 m at an angle of 25 degrees.
 
In July, the layout of the aircraft with the name Skystreak presented to customers. Meticulous examination and discussion of the layout lasted for two days. The representatives of the PASS, criticized the plane. Again they saw in the project an attempt Heinemann ignore research purpose machine. This clearly told the side air intakes, which reduced the thrust of the power plant, freeing due to this nose portion for mounting guns. Available free volumes suited only for placement of ammunition boxes, and not to bulky scientific equipment.
 
The Commission recommended to remodel the cockpit canopy, to increase the volume of the instrument compartments, to provide for the installation of the afterburner turbojet engine and replace the side air intakes front, with smaller losses. The Navy has concurred with these sentiments and recommended that the Heinemann alter the plane in accordance with the specifications NACA. The head of the Bureau of aircraft fleet (BuAir main customer of combat aircraft for the Navy) Emerson Conlon went further and stated that it would approve the project only after its approval by scientists.
 
Heinemann had to give up and proceed to the alteration of the project. Wing, empennage and most of the fuselage except for the air intake remains the same. The cockpit and instrument compartment with equipment located in the middle of the air channel in the extended Central partition. To reduce drag, the designers tried to make the cockpit as small as possible. To do this, they lowered the pilot’s seat so that above the surface of the fuselage were only one of his head. Teardrop lantern was made of double Plexiglas, which prevented its condensation at high altitudes.
 
The layout of the aircraft D-558
 
The layout of the aircraft D-558
 
The first sample D-558-I on the factory airfield
 
The first sample D-558-I on the factory airfield
 
First, D-558 was supposed to equip the ejection seat for the pilot, but the calculations showed that the required energy of the powder charge of the catapult needed to transport the chair in Kiel at transonic speeds exceed the physiological limit of the human body. Then Devlin proposed to apply a unique for its time, a recovery system with detachable nose piece. In an emergency, the pilot first use the explosive bolts separated from the aircraft nose, and after removing her from the car at a safe distance with a parachute jumped from the cab.
 
The following mock-up Committee arrived in El Segundo (the headquarters of the company Douglas) on August 14, 1945. After seeing the layout, the members of the Commission came to the unanimous opinion that all the comments NACA considered.
 
A few days before this was one, at first glance, an insignificant event — servant of the firm Douglas A. Smith returned from a business trip to Germany. But what it brought, had a serious impact not only on the program D-558, but also on the development of the entire high-speed aircraft of the United States. In his Luggage were microfilms of German documents from the research center of DVL in göttingen, where he was doing research on swept wings. Guide by Douglas appealed to the military and scientists from NACA, requesting permission to use the German experience in the program D-558.
 
The proposal was supported, and the program of studies immediately included purging models of aircraft with swept wings and at the same time planned the establishment of the instance of the D-558 with swept wings. This aircraft received the designation D-558-II, and already developed, the project became known as the D-558-I.
After approval of the project Orthoptera D-558-I, the firm has started construction of the first copies of the aircraft. The full cost of the program amounted to almost $ 7 million. The sailors such money was not, and the Bureau of aviation of the fleet had in reducing by half the order, paying for the construction of only three planes.
 
The fuselage is of the monocoque type of aluminium alloy with protective coating was calculated at the maximum overload 13D. Research equipment with a mass of 288 kg was placed just behind the cockpit, and across the wing span set the air pressure coming through 400 holes drilled in the hull.
 
The power plant consisted of a single turbojet engine Allison J35-A-23 thrust 1820 kgs. The engine was designed by General Electric and formerly designated TG-180.
 
Built plane has made an indelible impression. The casing it was covered in red paint and carefully polished. April 14, 1947, test pilot by Douglas Eugene Mei picked up the first copy of the plane in the air — it was the aircraft with serial number 37970 designed to fly in the company Douglas and the Navy. But for scientists NACA built the second and third D-558-I numbers 7971 and 37972.
 
Douglas D-558-1 Skystreak
 
Douglas D-558-1 Skystreak
 
 
After the flight, the pilot noted the strange behavior of the turbojet engine. After submitting the Ore forward of the engine very slowly gained momentum and developed insufficient thrust. April 21, after checking the power plant was the second flight, however, the situation repeated itself. Flight tests had to be interrupted and to contact the experts from the company General Electric. Those have carefully examined the engine and found no defects. One of the engineers suggested that the culprit might be fuel system, or rather — the lack of pressure in the fuel supply system. The pressure in the tanks decided to increase at the expense of air flow. On the wing tips installed two rods, via which the air is fed into the cavity tanks. The revision took about a month.
 
Later flight revealed that the engine performance improved, but the troubles did not end there — once the flight aboard was on fire. Immediately after opening the machine, may lead D-558-I on the landing. On the run he went down the brakes, and only super-long strip on the basis of Muroc (at the bottom of the dry lake) saved the plane and pilot. The engineers again went to work. The causes of the incident were revealed immediately: improper connection of electric wires and a malfunction in the hydraulic system of the drive wheel brakes.
 
After repair D-558-I made five successful flights, and this ended the first phase of flight tests.
 
The program began to connect and other pilots. In their reviews, the machine was well managed and had an amazing climb rate — altitude 3048 m (10,000 ft), she gained in just one minute. All comments of test pilots belonged to the features of the cockpit layout. The main drawback they considered a bad review on the landing to see the runway, the pilot had struggled to pull the neck and assessing the situation, to literally “dive” into the cockpit and see the instruments. Moreover, the width of the cabin was only half a meter, which is also not added optimism to the pilot during the flight: the tightness could even cause an attack of claustrophobia.
 
Fuel capacity 870 l was only half an hour flight. When the entire programme needed more time — to the ends of the wing were suspended additional fuel tanks with a capacity of 190 liters, which pilot dropped after the climb.
 
The main trouble began with the transition to high-speed flight. As soon as the D-558-I exceeded the speed corresponding to the number M=0,75, it started to shake, and loads of controls repeatedly increased. The head of the pilot, clad in steel helmet, fighting-o-lantern, with the plexiglass there were numerous scratches. After several such flights, the pilots began to hang the helmet with pieces of thin leather.
 
Despite all the difficulties, the research agenda of flow of the wing at transonic speeds moved pretty quickly. Within four months after the first flight, August 20, 1947, the Navy pilot Turner Caldwell set a new world speed record — 1030,95 km/h. the Previous record belonged to a pilot from the air force to albert Boyd, who was able to overclock the XP-80R Shooting Star to 1003,6 km/h. the Result of Caldwell lasted four days and was closed once the flight of the second D-558-I # 37971. This time was different Volumetric Karl of aviation of the Marine corps. His record — 1047,33 km/h stayed more then a year. Before performing a record flight of the Douglas designers had replaced on the aircraft lantern. For increased strength the frame it is made of metal. The cockpit view has become even worse.
 
Demonstration of the first two aircraft D-558-I representatives of the Navy and the NACA
 
Demonstration of the first two aircraft D-558-I, representatives of the Navy and NACA
 
Pilot Eugene P. May, the aircraft D-558-I
 
Pilot Eugene P. May, the aircraft D-558-I
 
After a record flight Eugene Mei continued to study high speeds. He was given the task to create the maximum possible load on the structure. Mei reached the altitude of 12,000 m and swooped down to 9000 m angle 2 — 3 degrees, gradually getting to the number M=0,85. Only there were about 10 such flights. Five of them used external fuel tanks.
 
29 Sep 1948, may on the D-558-I # 37970 broke the sound barrier in a dive at an angle of 35 degrees. It was the first and last supersonic flight D-558-I. Flight of the first prototype of the aircraft continued until April 1949, after which the car was written off and used as a source of spare parts for the third prototype. All in all it made 101 flight. Currently, it is restored glider on display at the National naval aviation Museum USA.
 
The second instance of the D-558-I, equipped with a large number of control and measuring apparatus, intended for research in the interest of NACA. In November 1947, after 27 flights, performed by pilots of the company Douglas and the Navy, the aircraft was transferred to the airbase Muroc. November 25, 1947, NACA pilot Howard Lila circled the plane. Lila took an active part in the program X-1 and was the third pilot to break the sound barrier in this plane. Subsequent testing of the machine was rife with numerous failures and malfunctions of various systems. The most serious incident at this stage there was a fire in the air April 14, 1948.
 
3 may 1948 Howard, Lila had to make another nineteenth flight. Shortly after take off, at a height of 45 meters, collapsed the compressor of the engine. Fly away compressor blades interrupted traction control and fuel system piping. Observers from the ground reported that the car stretched a black plume of smoke. Lila lost control and at the speed of 400 km/h crashed into the ground. Recovery system with detachable cabin was not calculated on such a small height, and the pilot had no chance to stay alive.
The Commission investigating the disaster, demanded from the company Douglas to improve the design of the first and third instance with the aim of improving safety. Mainly, these requirements are related to the reservation control rods and piping in the engine, replacement of the obsolete engine more modern and alteration of canopy pilot. Attempts by engineers to improve the emergency rescue system was not successful, and left it in its present form.
 
New engine J35-A-11 had more thrust ( 2270 kgs) and afterburner. It was slightly longer than the old turbojet engine, and its exhaust pipe was made for the edge of the rear fuselage.
 
The system was changed the opening of the lantern. Now he opened earlier, and velocity head only helped this process. Previously to open the flashlight in flight was almost impossible.
 
In addition to these design improvements, NACA demanded repainting your D-558-I in white color. The fact that services ground visual accompaniment was not able to catch the red plane in their telescopes. This wish was fulfilled, but to repaint the rudders on the firm refused. Engineers feared that the additional layer of paint will increase their mass and change the dynamic characteristics.
 
Testing of the third aircraft after all the modifications conducted Eugene may. The flight was successful, and on 22 January 1949 adopted a modified NACA D-558-I # 37972 in operation.
 
Research fly this machine lasted four and a half years, the last of them — the 78th was done June 10, 1953. Currently, the aircraft is recovered and the aviation Museum of the Carolinas in North Carolina.
 
Despite the fact that three aircraft D-558-I managed to get a lot of research information, which concerned the problems of the structural strength and control at high transonic speeds, the value of these machines in the history of high-speed aircraft is small. D-558 already in his time looked anachronistic against the background of high-speed jets F-86 and b-47. The plane was clearly late with his appearance. However, his story full of dramatic events, worthy of respect. Especially because it started his career with famous American test pilots.
 
Here is the complete list of pilots who flew on this plane. From the firm Douglas: Eugene P. May, George Jansen, Larry Peyton, Johnny Martin. From US Navy: Carl Marion, Turner Caldwell, Frederick Trapnell. NACA: Howard C. Lilly, John F. Griffith, Scott Crossfield, Joseph A. Walker, Stanley P. Butchart, Robert A. Champine, John B. McKay, Walter P. Jones.
 
Flight performance experimental aircraft D-558-I
 
Length, m………………………………………..10,87
Wing span, m……………………………….7,62
Height, m………………………………………..3,68
Wing area, m2……………………………..14
Normal takeoff weight, kg………..4423
Maximum takeoff weight, kg…….4583
The maximum number of M
at high altitude…………………………..0,99
Maximum speed
at sea level, km/h……………………….1050

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