Tag Archives: Fighter

15 May 1918

Packard Lepère L U.S.A. C. II in flight.

15 May 1918: The prototype Packard Lepère L U.S.A. C.II made its first flight.

The Packard Lepère L U.S.A. C. II was a single-engine, two-place, two-bay biplane chasseur which was designed by a French aeronautical engineer, Capitaine Georges Lepère, who had previously designed the Section Technique de l’Aeronautique Dorand AR.1 reconnaissance airplane for the Aéronautique Militaire, the military air service of France. The new airplane was built in the United States by the Packard Motor Car Company of Detroit, Michigan. It was a two-place fighter, or chasseur, light bomber, and observation aircraft, and was armed with four machine guns.

A contemporary aviation publication reported:

Flying Qualities—The machine exhibits excellent flying qualities, with ready response of all controls. Longitudinal, lateral and directional stability of the machine is good. In taxying, starting and landing it is entirely satisfactory, and on landing it does not roll more than 300 or 400 ft. [91.4–121.9 meters] All stunt maneuvers can readily be performed, and in general, from a pilot’s point of view, the machine is excellent.

The range of vision is very good, the controls well placed, and instruments so arranged that the pilot need only move his eyes.

AVIATION AND AERONAUTICAL ENGINEERING, Vol. VI, No. 8, 15 May 1919, at Page 426, Column 1.

Packard Lepère L U.S.A. C. II, P 54, S.C. 42138 (U.S. Air Force)

The Packard Lepère was 25 feet, 3⅛ inches (7.699 meters) long. The upper and lower wings had an equal span of 41 feet, 7¼ inches (12.681 meters), and equal chord of 5 feet, 5¾ inches (1.670 meters). The vertical gap between the wings was 5 feet, ⅝-inch (1.527 meters) and the lower wing was staggered 2 feet, 15/16-inch (0.633 meters) behind the upper wing. The wings’ incidence was +1°. Upper and lower wings were equipped with ailerons, and had no sweep or dihedral. The height of the Packard Lepère, sitting on its landing gear, was 9 feet, 7 inches (2.921 meters). The Packard Lepère had an empty weight of 2,561.5 pounds (1,161.9 kilograms) and its gross weight was 3,746.0 pounds (1,699.2 kilograms).

The fuselage was a wooden structure with a rectangular cross section. It was covered with three layers of veneer, (2 mahogany, 1 white wood) with a total thickness of 3/32-inch (2.38 millimeters). The fuselage had a maximum width of 2 feet, 10 inches (0.864 meters) and maximum depth of 4 feet, 0 inches (1.219 meters).

Packard fuselages under construction. (NARA)

The wings were also of wooden construction, with two spruce spars and spruce ribs. Three layers of wood veneer covered the upper surfaces. Heavy bracing wires were used. These had an airfoil cross-section and actually provided additional lift. The interplane struts were unusual in that they were fully-framed units.

The Packard Lepère was powered by a water-cooled, normally-aspirated, 1,649.336-cubic-inch-displacement (27.028 liter) Liberty L-12 single overhead cam (SOHC) 45° V-12 engine with a compression ratio of 5.4:1. The Liberty produced 408 horsepower at 1,800 r.p.m. The L-12 as a right-hand tractor, direct-drive engine and it turned turned a two-bladed, fixed-pitch wooden propeller. The Liberty 12 was 5 feet, 7.375 inches (1.711 meters) long, 2 feet, 3.0 inches (0.686 meters) wide, and 3 feet, 5.5 inches (1.054 meters) high. It weighed 844 pounds (383 kilograms).

The engine coolant radiator was positioned horizontally in the center section of the Lepère’s upper wing. Water flowed through the radiator at a rate of 80 gallons (303 liters) per minute.

Major Rudolph W. Schroeder flying P 53, a Packard Lepère L U.S.A. C. II,  A.S. 40015, over McCook Field, Ohio, 24 September 1919. (U.S. Air Force)

The Packard Lepère had a maximum speed of 130.4 miles per hour (209.9 kilometers per hour) at 5,000 feet (1,524 meters), 127.6 miles per hour (205.4 kilometers per hour) at 10,000 feet (3,048 meters), 122.4 miles per hour (197.0 kilometers per hour) at 15,000 feet (4,572 meters), 110.0 miles per hour (177.0 kilometers per hours) at 18,000 feet (5,486 meters) and 94.0 miles per hour (151.3 kilometers per hour) at 20,000 feet (6,096 meters). Its cruising speed was 112 miles per hour (180 was kilometers per hour). The airplane could climb to 5,000 feet in 4 minutes, 24 seconds, and to 20,000 feet in 36 minutes, 36 seconds. In standard configuration, the Packard Lepère had a service ceiling of 20,200 feet (6,157 meters). Its range was 320 miles (515 kilometers).

The fighter’s armament consisted of two fixed M1918 Marlin .30-caliber aircraft machine guns mounted on the right side of the fuselage, synchronized to fire forward through the propeller arc, with 1,000 rounds of ammunition, and two M1918 Lewis .30-caliber machine guns on a flexible mount with 970 rounds of ammunition.

The Air Service had ordered 3,525 of these airplanes, but when the War ended only 28 had been built. The contract was cancelled.

The third Packard Lepère, S.C. 42130, under construction at the Packard Motor Car Co., Detroit, Michigan. (NARA)

Six Packard Lepères were used for flight testing at McCook Field, Dayton, Ohio, assigned project numbers P 44, P 53, P 54, P 65, P 70 and P 80. One of these, flown by Major Rudolph W. Schroeder, set two Fédération Aéronautique Internationale (FAI) World Records for Altitude at 9,455 meters (31,020 feet), 18 September 1918.¹ On 6 September 1919, Schroeder flew a Packard Lepère to 8,616 meters (28,268 feet) while carrying a passenger. This set two more World Altitude Records.² Flying P 53, A.S. 40015, he set a fifth FAI altitude record of 10,093 meters (33,114 feet), 27 February 1920.³ On 28 September 1921, Captain John A. Macready flew P 53 to an altitude of 40,800 feet (12,436 meters). On 13 October 1922, 1st Lieutenant Theodore J. Koenig flew P 53 to win the Liberty Engine Builders’ Trophy Race at Selfridge Field, near Mount Clemens, Michigan. Koenig completed ten laps of the triangular racecourse in 2:00:01.54, at an average speed of 128.8 miles per hour (207.3 kilometers per hour).

The only Packard Lepère in existence, serial number A.S. 42133, is in the collection of the National Museum of the United States Air Force, Wright-Patterson Air Force Base, Ohio.

Packard Lepère L U.S.A. C. II, S.C. 42133, at the National Museum of the United States Air Force. (U.S. Air Force)
Packard Lepère L U.S.A. C. II, right profile

¹ FAI Record File Numbers 15463 and 15671

² FAI Record File Numbers 15464 and 15675

³ FAI Record File Number 8229

© 2019, Bryan R. Swopes

6 May 1941

Republic XP-47B 40-3051 prototype in flight. (Republic Aircraft Corporation)

6 May 1941: Just eight months after a prototype for a new single-engine fighter was ordered by the U.S. Army Air Forces, test pilot Lowery Lawson Brabham took off from the Republic Aviation Corporation factory airfield at Farmingdale, New York, and flew the prototype XP-47B Thunderbolt, serial number 40-3051, to Mitchel Field, New York.

During the flight, oil which had collected in the exhaust duct began burning. There was so much smoke that Brabham considered bailing out. He stayed with the prototype, though, and when he arrived at Mitchel Field, he exclaimed, “I think we’ve hit the jackpot!”

Alexander Kartveli

The prototype was designed by Alexander Kartveli, a Georgian immigrant and former chief engineer for the Seversky Aircraft Corporation, which became the Republic Aviation Corporation in 1939.

Alexander Kartveli (née Kartvelishvili, ალექსანდრე ქართველი) was born in Tbilisi, in the Kutais Governorate of the Russian Empire, (what is now, Georgia). After World War I, during which he was wounded, Kartvelishvili was sent to study at the Paris Aviation Higher College of Engineering in France by the government of the Democratic Republic of Georgia. He graduated in 1922. Kartvelishvili did not return to his country, which had fallen to the Red Army in the Soviet-Georgian War. He worked for Blériot Aéronautique S.A. until 1928, when he was employed by the Fokker American Company (also known as Atlantic Aircraft, or Atlantic-Fokker) which was headquartered at Passaic, New Jersey, in the United States. In 1931, he became chief engineer for the Seversky Aircraft Company in Farmingdale.

Republic XP-47B Thunderbolt prototype 40-3051 at Farmingdale, New York, 1941. The pilot standing in front of the airplane gives a scale reference. (Republic Aviation Corporation)

Kartveli submitted his design proposal for the XP-47B to the U.S. Army Air Corps, 12 June 1940. The prototype was ordered 6 September, and a week later, 13 September 161 production P47Bs and 602 P-47Cs were ordered. The contract was for $56,499,924. The company named the new fighter “Thunderbolt,” which had been suggested by C. Hart Miller, director of the military contracts division of Republic Aviation.

The XP-47B was the largest single-engine fighter that had yet been built. The production P-47B was 34 feet, 10 inches (10.617 meters) long with a wingspan of 40 feet, 9-5/16 inches (12.429 meters), and height of 12 feet, 8 inches (3.861 meters).¹ The wing area was 300 square feet (27.9 square meters). At a gross weight of 12,086 pounds (5,482 kilograms), it was nearly twice as heavy as any of its contemporaries.

Republic XP-47B Thunderbolt 40-3051 at Wright Field, Dayton, Ohio.(Ray Wagner Collection, San Diego Air & Space Museum Archives )

The XP-47B was powered by an air-cooled, supercharged and turbocharged, 2,804.4-cubic-inch-displacement (45.956 liter) Pratt & Whitney R-2800-21 (Double Wasp TSB1-G) two-row, 18-cylinder radial with a compression ratio of 6.65:1 had a normal power rating of 1,625 horsepower at 2,550 r.p.m., to an altitude of 25,000 feet (7,620 meters), and a takeoff/military power rating of 2,000 horsepower at 2,700 r.p.m. at 25,000 feet (7,620 meters). The engine drove a 12-foot, 2 inch (3.708 meter) diameter, four-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction. The R-2800-21 was 4 feet, 4.50 inches (1.340 meters) in diameter and 6 feet, 3.72 inches (1.923 meters) long. The engine weighed 2,265 pounds (1,027 kilograms). Approximately 80% of these engines were produced by the Ford Motor Company. It was also used as a commercial aircraft engine, with optional propeller gear reduction ratios.

A large General Electric turbosupercharger was mounted in the rear of the fuselage. Internal ducts carried exhaust gases from the engine to drive the turbocharger. This supercharged air was then carried forward through an intercooler and then on to the carburetor to supply the engine. The engine’s mechanical supercharger further pressurized the air-fuel charge.

Republic XP-47B 40-3051. The pilot enters the cockpit through a hinged canopy segment. (Ray Wagner Collection Catalog, San Diego Air and Space Museum)

During flight testing, the XP-47B Thunderbolt demonstrated speeds of 344.5 miles per hour (554.4 kilometers per hour) at 5,425 feet (1,654 meters), and 382 miles per hour (615 kilometers per hour) at 15,600 feet (4,745 meters). Its maximum speed was 412 miles per hour (663 kilometers per hour) at 25,800 feet (7,864 meters). The test pilot reported that the engine was unable to produce full power during these tests. It was determined that it had a cracked cylinder head, resulting in a loss of 2.5–4% of its maximum rated power. Also, the XP-47B was painted in camouflage, resulting in a slight loss of speed.

It could climb to 15,000 feet (4,572 meters) in just five minutes.

The Thunderbolt was armed with eight Browning AN-M2 .50-caliber machine guns, four in each wing, with 3,400 rounds of ammunition. It could also carry external fuel tanks, rockets and bombs. The structure of the P-47 could be described as “robust” and it was heavily armored. The amount of damage that the airplane could absorb and still return was remarkable.

 

Republic XP-47B Thunderbolt 40-3051, 4 May 1941. (U.S. Air Force)
Republic XP-47B Thunderbolt 40-3051, 4 May 1941. (Republic Aviation Corporation)

During a test flight, 4 August 1942, the XP-47B’s tail wheel was left down. The extreme heat of the turbocharger’s exhaust set fire to the tire, which then spread to the airplane’s fabric-covered control surfaces. Unable to control the airplane, test pilot Filmore L. Gilmer bailed out. The prototype Thunderbolt crashed into Long Island Sound and was destroyed.

The third production Republic P-47B Thunderbolt, 41-5897, at Langley Field, Virginia, 24 March 1942. The door-hinged canopy of the XP-47B has been replaced by a rearward-sliding canopy, requiring that the radio antenna mast be moved.(NASA)
A Republic P-47B Thunderbolt in the NACA Full Scale Tunnel, 31 July 1942. (NASA LMAL 29051)

A total of 15,683 Thunderbolts were built; more than any other U.S. fighter type. In aerial combat, it had a kill-to-loss ratio of 4.6:1. The P-47, though, really made its name as a ground attack fighter, destroying aircraft, locomotives, rail cars, and tanks by the many thousands. It was one of the most successful aircraft of World War II.

¹ Data from Pilot’s Flight Operating Instructions, Technical Order No. 01-65BC-1, 20 January 1943

© 2018, Bryan R. Swopes

6 May 1935

Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)

6 May 1935: At Buffalo, New York, the prototype Curtiss-Wright Model 75, X17Y, serial number 11923, made its first flight.

Donovan Reese Berlin. (Niagara Aerospace Museum)

Designed by Donovan Reese Berlin, the airplane was a modern design of all metal construction, with fabric covered control surfaces. The Model 75 was a single-seat, single-engine low-wing monoplane with retractable landing gear.

Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)

In its original configuration, the Model 75 was powered by an air-cooled, supercharged 1,666.860 cubic inch displacement (27.315 liter) Wright Aeronautical Division GR1670A1 two-row 14-cylinder radial engine. The GR1670A1 was a developmental engine with a compression ratio of 6.75:1. It was rated at 775 horsepower at 2,400 r.p.m. at Sea Level, and 830 horsepower at 2,600 r.p.m. for takeoff, burning 87-octane gasoline. The engine was 3 feet, 9 inches (1.143 meters) in diameter, 4 feet, 4–25/32 inches (1.341 meters) long, and weighed 1,160 pounds (526 kilograms). The GR1670A1 drove a three-bladed Curtiss Electric constant-speed propeller through a 16:11 gear reduction.

The GR1670A1 was also used in the Seversky SEV-S1, NR18Y, a record-setting experimental variant of the rival Seversky P-35.

The United States Department of Commerce, Bureau of Air Commerce, registered X17Y to the Curtiss-Wright Corporation, Kenmore & Vulcan Street, Buffalo, New York, on issued 1 June 1936. This registration was cancelled 26 April 1937.

Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
Curtiss-Wright Model 75, X17Y. (Ray Wagner Collection, San Diego Air & Space Museum Archives)

The Curtiss-Wright Model 75 would be developed into the P-36 Hawk fighter for the U.S. Army Air Corps. France ordered it as the H75A-1, and in British service, it was known as the Mohawk Mk.I.

The tenth production P-36 was modified with a liquid-cooled Allison V-1710 V-12 engine to become the prototype XP-40.

1st Lieutenant Benjamin Scovill Kelsey in the cockpit of a Curtiss-Wright P-36A Hawk, circa 1938. (U.S. Air Force)
1st Lieutenant Benjamin Scovill Kelsey, Air Corps, United States Army, with a Curtiss Wright P-36A Hawk, Air Corps serial number 38-2, at Wright Field, Ohio, circa 1938. (Ray Wagner Collection/San Diego Air & Space Museum Archives)
Curtiss-Wright P-36B 38-020. (U.S. Air Force)
Curtiss-Wright P-36B 38-020. (U.S. Air Force)
Curtiss-Wright P-36C camouflage test, Maxwell Field, 1940. (Ray Wagner Collection, San Diego Air & Space Museum Archives)
Curtiss-Wright P-40 Warhawk, 55th Pursuit Squadron, Oakland, CA, 1941 (IWM FRE11437)

© 2019, Bryan R. Swopes

2 May 1957

McDonnell F-101A-1-MC Voodoo 53-2418, first production aircraft, parked on Rogers Dry Lake, Edwards AFB. (U.S. Air Force)

2 May 1957: The United States Air Force accepted the first production McDonnell Aircraft Corporation F-101A Voodoo supersonic fighter.

The McDonnell F-101 Voodoo was originally designed as a single-seat, twin-engine long range bomber escort, or “penetration fighter,” for the Strategic Air Command, but was developed as a fighter bomber and reconnaissance airplane. 53-2418 first flew 29 September 1954, and it was the first production F-101A to be delivered to the Air Force.

mcDonnell F-101A-1-MC Voodoo 53-2418, right front quarter view. (U.S. Air Force)
McDonnell F-101A-1-MC Voodoo 53-2418, right front quarter view. (U.S. Air Force)
McDonnell F-101-1-MC Voodoo 53-2418 (U.S. Air Force)
McDonnell F-101A-1-MC Voodoo 53-2418, right profile. (U.S. Air Force)
McDonnell F-101A-1-MC Voodoo 53-2418, right rear view. (U.S. Air Force)
McDonnell F-101A-1-MC Voodoo 53-2418, right rear view. (U.S. Air Force)

The F-101A was 67 feet, 5 inches (20.549 meters) long with a wingspan of 39 feet, 8 inches (12.090 meters). It was 18 feet (5.486 meters) high. The total wing area was 368 square feet (34.2 square meters). The wings were swept 36° 36′ at 25% chord. The angle of incidence was 1°, with no twist or dihedral. The Voodoo weighed 25,374 pounds (11,509 kilograms) empty and had a maximum takeoff weight of 51,000 pounds (23,133 kilograms).

The standard F-101A was equipped with two Pratt & Whitney J57-P-13 turbojet engines. The J57 was a two-spool axial-flow turbojet which had a 16-stage compressor (9 low- and 7 high-pressure stages), 8 combustors and a 3-stage turbine (1 high- and 2 low-pressure stages). The J57-P-13 was rated at 10,200 pounds of thrust (45.37 kilonewtons), and 15,800 pounds (70.28 kilonewtons) with afterburner. The engine was 3 feet, 4.3 inches (1.024 meters) in diameter, 17 feet, 7.0 inches (5.359 meters) long, and weighed 5,025 pounds (2,279 kilograms).

The Voodoo had a maximum speed of 876 knots (1,008 miles per hour (1,622 kilometers per hour) at 35,000 feet (10,668 meters). Service ceiling was 45,700 feet (13,929 meters). It carried a maximum of 2,305 gallons (8,725 liters) of fuel internally. With external tanks, the fighter bomber had a maximum ferry range of 1,898 nautical miles (2,184 statute miles/3,515 kilometers).

McDonnell F-101A-1-MC Voodoo 53-2416 in flight, bottom view. (U.S. Air Force)
McDonnell F-101A-1-MC Voodoo 53-2416 in flight, bottom view. (U.S. Air Force)

The F-101A was armed with four 20mm Pontiac M39 single-barreled revolver cannon, with 200 rounds per gun. It could carry a Mark 7, Mark 28, or Mark 43 “Special Store” on a centerline mount.

McDonnell built 77 F-101As for the Air Force. 29 were later converted to RF-101G photo reconnaissance airplanes by Lockheed Aircraft Services.

F-101A 53-2418 was transferred to General Electric for testing of the J79 afterburning turbojet engine which would later power the McDonnell F-4 Phantom II.

General Electric returned the Voodoo to the Air Force in 1959. Now obsolete, it was used as a maintenance trainer at Shepard Air Force Base, Texas. It was next turned over to a civilian aviation maintenance school and assigned a civil registration number, N9250Z, by the Federal Aviation Administration. The airplane was sold as scrap, but was purchased by Mr. Dennis Kelsey.

In 2009, Mrs. Kelsey had the airplane placed in the care of the Evergreen Aviation and Space Museum, McMinnville, Oregon. After being partially restored by the Evergreen Air Center, Marana, Arizona, 53-2418 was placed on display at the Evergreen Museum.

McDonnell JF-101A 53-2418 with General Electric J79 engines, circa 1957
McDonnell JF-101A 53-2418 with General Electric J79 engines, circa 1957
The first production Voodoo, McDonnell F-101-1-MC 53-2418 on display at the Evergeen Aviation Museum (flickriver)
The first production Voodoo, McDonnell F-101-1-MC 53-2418 on display at the Evergreen Aviation Museum (flickriver)

© 2019, Bryan R. Swopes

26 April 1995

Roman Taskaev in the cockpit of a Mikoyan MiG-29 in flight over Canada, circa 1990. (Vintage Wings of Canada)

26 April 1995: Mikoyan test pilot Roman Petrovich Taskaev flew a MiG-29 to a Fédération Aéronautique Internationale (FAI) World Altitude Record of 27,460 meters (90,092 feet) at Aerodrome Akhtubinsk, Russia. This record still stands.¹

Роман Петрович Таскаев (Roman Petrovich Taskaev) was born at Khilok, Zabayaski Krai, Russian Soviet Federative Socialist Republic, 14 October 1954.

From 1967 through 1971, Taskaev was a member of the Chita aero club, where he participated in gliding and skydiving.

Taskaev entered the Soviet Army in 1971. In 1975, he graduated from the National University of Internal Affairs at Kharkiv, Ukraine Soviet Socialist Republic. He then served with several combat units of the Soviet Air Force. He was promoted to the rank of captain in 1981.

Роман Петрович Таскаев

Captain Taskaev attended the School of Test Pilots in 1983. He was then assigned to the Mikoyan Design Bureau as a test pilot in June 1983. He remained there through May 1998. he was a senior test pilot 1992–1997. He was involved in flight testing the variants of the Mikoyan MiG-23, MiG-25, MiG-29 and MiG-31. He flew a MiG-31 over the North Pole.

Taksaev has ejected from a MiG-23UB at very low altitude and maximum speed following an engine failure, and from a MiG-29M.

By decree of the president of the Russian Federation, 16 August 1992, Taskaev was named a Hero of the Russian Federation with Gold Star. In 1996, he was awarded the order of Courage, and in 1998, he was named an Honored Test Pilot of the Russian Federation.

Since 1998, Roman Taskaev has served as Deputy Director of Flight Testing at the Yakovlev Design Bureau.

Roman Taskaev holds his FAI record certificate. (FAI)

The Mikoyan MiG-29 is a fourth generation, single-seat, twin-engine, Mach 2+ air superiority fighter built by the Mikoyan Design Bureau. It entered service with the Soviet Union in 1983 and has been widely exported to many other nations.

The MiG 29 is 17.320 meters (56 feet, 9.89 inches) long, including the pitot boom. The wingspan is 11.360 meters (37 feet, 3.24 inches) and the overall height is 4.730 meters (15 feet, 6.22 inches). They have an area of 38 square meters (409 square feet). The wings’ leading edges are swept aft to 42°. They have approximately 5° anhedral. The two vertical fins are tilted outboard 6° and their leading edges are swept to 50°. The horizontal stabilizers are swept to 47° 30′.

The fighter has a basic weight of 15,775 kilograms (34,778 pounds) with full internal fuel and a centerline tank. Its maximum takeoff weight is 18,480 kilograms (40,741 pounds).

MiG 29 three-view illustration with dimensions

The fighter is powered by two Klimov RD-33 engines. The RD-33 is a two-spool, axial-flow, afterburning turbofan with a 13 stage compressor section (4 low- and 9 high-pressure stages) and a two-stage turbine (1 high- and 1 low-pressure stages). It has a military power rating of 49.43 kilonewtons (11,111 pounds of thrust), and 81.40 kilonewtons (18,298 pounds) with afterburner. The RD-33 is 1.040 meters (3 feet, 6.95 inches) in diameter, 4.229 meters (13 feet, 10.50 inches) long, and weighs 1,055 kilograms (2,326 pounds).

The MiG 29 has a maximum speed of Mach 2.25 and a service ceiling of 59,100 feet (18,013 meters). Maximum range with internal fuel is 1,430 kilometers (888 miles).

Armament consists of one Gryazev-Shipunov GSh-301 30mm autocannon with 150 rounds of ammunition, and a combination of air-to-air missiles, rockets or bombs carried on underwing pylons or fuselage hard points.

More than 1,600 MiG 29s have been built.

Mikoyan MiG-29SMT RF-92934 (“22 Red”), Russian Air Force. (Alex Beltyukov/Wikipedia)

¹ FAI Record File Number 2554

© 2019, Bryan R. Swopes