Category Archives: Aircraft

Hughes XF-11 no1 taxi

Hughes XF-11 Photo-Reconnaissance Aircraft

By William Pearce

In the early World War II years, the Hughes Aircraft Company (HAC) worked to design and build its D-2 aircraft intended for a variety of roles. However, the United States Army Air Force (AAF) was not truly interested in the twin-engine wooded aircraft. To cure design deficiencies and make the aircraft more appealing to the AAF, HAC proposed a redesign of the D-2, designated D-5.

Hughes XF-11 no1 front

The Hughes XF-11 was an impressive and powerful aircraft intended for the photo-reconnaissance role. The eight-blade, contra-rotating propellers were over 15 ft (4.6 m) in diameter. Note the deployed flaps between the tail booms. (UNLV Libraries image)

The initial D-5 design was an enlarged D-2 and employed Duramold construction using resin-impregnated layers of wood, molded to shape under pressure and heat. The proposed aircraft had a 92 ft (28.0 m) wingspan, was 58 ft (17.7 m) in length, and weighed 36,400 lb (16,511 kg). The D-5 was powered by Pratt & Whitney (P&W) R-2800 engines and had a forecasted top speed of 488 mph (785 km/h) at 30,000 ft (9,144 m) and 451 mph (726 km/h) at 36,000 ft (10,973 m). A 4,000 lb (1,814 kg) bomb load could be carried in an internal bay. The AAF was still not interested in the aircraft and felt that HAC did not have the capability to manufacture such an aircraft in large numbers.

In early August 1943, Col. Elliot Roosevelt, President Franklin Roosevelt’s son, was in the Los Angeles inquiring with various aircraft manufacturers to find a photo-reconnaissance aircraft. Col. Roosevelt, who had previously commanded a reconnaissance unit, was hosted by Hughes and taken on a personal tour of the D-2. At the time, the aircraft was undergoing modification to become the D-5 and was not available for flight, but Col. Roosevelt was sufficiently impressed.

Hughes XF-11 no1 taxi

Howard Hughes taxies the first XF-11 out for its first and last flight. The nose of the aircraft accommodated a variety of camera equipment. Note the cowl flaps and the large scoops under the engine nacelles. (UNLV Libraries image)

General Henry “Hap” Arnold of the AAF was put under pressure from the White House to order the D-5 reconnaissance aircraft into production. To ease the AAF’s concerns about the D-5’s Duramold construction, the design was changed to metal wings and tail booms and only the fuselage built from Durmold. Arnold made the decision to order the D-5 aircraft “much against [his] better judgment and the advice of [his] staff.” The AAF issued a letter of intent on 6 October 1943 for the purchase of 100 examples of the D-5 reconnaissance aircraft. An official contract for the aircraft, designated F-11, was issued on 5 May 1944. Two aircraft would serve as prototypes with the remaining 98 aircraft as production versions.

As contracted, the Hughes XF-11 prototypes were of an all-metal construction and powered by two P&W R-4360 engines. The aircraft had the same layout as the Lockheed P-38 Lightning but was much larger. The fuselage consisted of a streamlined nacelle mounted to the center of the wing. At the front of the fuselage were provisions for photographic equipment. The cockpit was positioned just before the wing’s leading edge, and the cockpit was covered by a large, fixed bubble canopy. The pressurized cockpit could maintain an altitude of 10,500 ft (3,200 m) up an aircraft altitude of 33,500 ft (10,211 m). Entry to the cockpit was via a hatch and extendable ladder just behind the nose wheel landing gear well. The pilot’s seat was offset slightly to the left. Behind and to the right of the pilot sat a second crew member, who would fulfill the role of a navigator/photographer. The second crew member could crawl past the pilot and into the aircraft’s nose to service the cameras while in flight. The nose landing gear retracted to the rear and was stowed under the cockpit.

Hughes XF-11 no1 first flight

One of the very few images of the first XF-11 in flight as it takes off from Hughes Airport in Culver City, California on 7 July 1946. Note the rural background that is now completely developed. (UNLV Libraries image)

The XF-11’s wings had a straight leading and trailing edges, with the leading edge swept back approximately 6 degrees and the trailing edge swept forward around 3.5 degrees. Mounted to each wing about a third of the distance from the fuselage to the wing tip was the engine. The engine nacelle was slung under the wing and extended back to the aircraft’s tail. A large flap was located on the wing’s trailing edge between the tail booms. Each wing had an addition flap that extended from outside of the tail boom to near the wing tip. Relatively small ailerons spanned the approximate 66 in (1.68 m) distance from the flap to the wing tip. The aircraft’s main source of roll control were spoilers positioned on the upper surface of the outer wing and in front of the flap. Each wing incorporated a hardpoint outside of the tail boom for a 700 gallon (2,650 L) drop tank, and 600 gallon (2,271 L) jettisonable tip tanks were proposed but not included on the prototype aircraft.

Each 3,000 hp (2,237 kW), 28-cylinder R-4360 engine was installed in the front of the wing and was housed in a streamlined cowling. Cowl flaps for engine cooling circled the sides and top of the cowling. Under the engine nacelle was a scoop that housed the oil cooler and provided air to the intercooler and the two General Electric BH-1 turbosuperchargers installed in each tail boom. Air that flowed through the oil cooler exited at the back of the scoop. Air that flowed through the intercooler was routed to an exit door on top of the engine nacelle, just above the wing’s leading edge. Exhaust from the superchargers was expelled from the sides of the engine nacelle, just under the wing. The turbosupercharger on the inner side of each tail boom could be shut down during cruise flight to take full advantage of the remaining turbosupercharger operating at its maximum performance. The main landing gear was positioned behind the engine and retracted to the rear into the tail boom. Attached to the end of each tail boom was a large, 11 ft 8 in (3.56 m) tall vertical stabilizer. Mounted in the 25 ft 8 in (7.82 m) space between the vertical stabilizers was the horizontal stabilizer. The left tail boom housed additional camera equipment behind the main landing gear well.

Hughes XF-11 no1 cockpit crash

The cockpit of the crashed XF-11 illustrates how lucky Hughes was to have survived. Hughes crawled out through the melted Plexiglas and was aided by residents who had witnessed the crash. Note the armored seat. The XF-11 had 350 lb (159 kg) of cockpit armor and self-sealing fuel tanks. (UNLV Libraries image)

The XF-11 had a wingspan of 101 ft 4 in (30.9 m), a length of 65 ft 5 in (19.9 m), and a height of 23 ft 3 (7.09 m). The aircraft had a top speed of 450 mph (725 km/h) at 33,000 ft (10,058 m) and 295 mph (475 km/h) at sea level. The XF-11 had a service ceiling of 42,000 ft (12,802 m), an initial climb rate of 2,025 fpm (10.3 m/s) and could climb to 33,000 ft (10,058 m) in 17.4 minutes. The aircraft had an empty weight of 39,278 lb (17,816 kg) and a maximum weight of 58,315 lb (26,451 kg). With its 2,105 gallon (7,968 L) internal fuel load, the XF-11 had a 5,000 mile (8,047 km) maximum range.

Delivery of the first XF-11 (44-70155) was originally scheduled for November 1944 with peak production of 10 aircraft per month being reached in March 1945—an ambitions timeline for any aircraft manufacturer. Delays were encountered almost immediately and gave credence to the AAF’s belief that HAC was not up to the task of designing and manufacturing aircraft for series production. By mid-1945, the XF-11 had still not flown, and the war was winding down. It was clear that the XF-11 would not be involved in World War II, and there was much doubt as to the usefulness of the aircraft post-war. As a result, the order for 98 production examples was cancelled on 26 May 1945, but the construction of the two prototypes was to proceed.

Hughes XF-11 no2 front

With the exception of its propellers, the second XF-11 was essentially the same as the first aircraft. The bulges on the nacelles under the wings were the exhaust outlets for the inner turbosuperchargers. (UNLV Libraries image)

The first XF-11 prototype was fitted with Hamilton-Standard Superhydromatic contra-rotating propellers. The front four-blade propeller was 15 ft 1 in (4.60 m) in diameter, and the rear four-blade propeller was 2 in (51 mm) longer at 15 ft and 3 in (4.65 m) in diameter. The impressive aircraft was finally finished by April 1946 and began taxi test. With Howard Hughes at the controls, an aborted high-speed taxi test on 15 April resulted in some minor damage and the need to rework some of the aircraft’s systems.

Once repaired, Hughes decided to make the XF-11’s first flight on 7 July 1946. The AAF had stipulated that the XF-11’s first flight should be no more that 45 minutes, the landing gear should not be retracted, the aircraft should stay near the airport and away from populated areas, communication should be established with the chase plane, and the flight should follow the plan discussed beforehand. While the flight was discussed with some, many involved with the aircraft were unaware of Hughes’ plans. Had his intentions been better known, someone may have reminded him about the propeller seal leak on the right engine. Hughes request 1,200 gallons (4,542 L) of fuel to be on board, which was twice as much as should be needed for the scheduled 45-minute flight. HAC’s Douglas A-20 Havoc would serve as a chase plane for the flight, but radio issues prevented communication between the two aircraft.

Hughes XF-11 no2 top

Top view of the second XF-11 illustrates the aircraft’s layout, which was similar to that of a Lockheed P-38. However, the XF-11 was a massive aircraft. Note that the rear of the fixed canopy has been removed. (UNLV Libraries image)

At around 5:20 PM, Hughes took the XF-11 off from Hughes Airport in Culver City, California on its maiden flight. Shortly after takeoff, Hughes retracted the gar, and the right main light remined illuminated, indicating a possible issue with the retraction. Hughes and the XF-11 flew out over the Pacific Ocean and turned back toward land. The landing gear was cycled several times during the flight in an attempt to resolve the perceived issue on account of the illuminated light.

After about an hour and 15 minutes, the oil supply in the right propeller was exhausted and the rear set of blades moved into a flat or reversed pitch. Had Hughes stuck to the 45-minute flight as the AAF ordered, the oil supply would not have been depleted. The reversed pitch propeller created a massive amount of drag on the right side of the aircraft. To the A-20 chase plane, it appeared that Hughes was maneuvering to land back at Culver City, some distance away. The chase plane broke formation to return to the airfield on its own. Had the two aircraft been in communication, the situation could have been discussed.

Hughes XF-11 no2 top rear

The trailing edge of the XF-11’s wing had a flap between the tail booms. Long flaps extended from the outer side of the tail booms almost to the wing tips. Note the relatively small ailerons at the wing tips. The wing spoilers are visible just in front of the outer flaps. (UNLV Libraries image)

Hughes, now alone, believed that the right main gear had deployed on its own and was causing the drag. Had Hughes left the gear down, he would have known the drag was a result of some other issue with the aircraft. Trying to keep the XF-11 straight resulted in the deployment of the left-wing spoilers, which further slowed the aircraft. Low, slow, and over a populated area, Hughes tried to make it to the open space of the Los Angles Country Club golf course in Beverly Hills. Landing short, the XF-11 crashed into four houses, broke apart, and caught fire. Hughes managed to pull himself from the wreckage, where he was helped further by neighborhood residents and arriving paramedics. Hughes suffers major injuries, including severe burns, at least 11 broken ribs, a punctured lung, and a displaced heart. Remarkably, he made a near-full recovery, but the incident started an addiction to codine, which would cause Hughes problems throughout the rest of his life.

Construction of the second XF-11 prototype (44-70156) continued after the accident. The second prototype used single rotation, four-blade propellers that were 14 ft 8 in (4.47 m) in diameter and made by Curtis Electric. Despite all of the new rules implemented because of his crash, Hughes was adamant that he pilot the first flight of the second XF-11 prototype. The AAF initially refused, but Hughes pressed the issue and made personal appeals to Lt.Gen. Ira Eaker and Gen. Carl Spaatz. Hughes also offered to put up a $5 million bond payable to the AAF if he crashed. With the posting of the bond, the AAF gave in. On 4 April 1947, Hughes flew the second XF-11 on its first flight, taking off from Hughes Airport. The flight was a personal victory for Hughes.

Hughes XF-11 no2 flight

The second XF-11 on an early test flight. The aircraft was later fitted with spinners. Note the turbosupercharger’s exhaust just under the wing and the oil cooler’s air exit at the end of the scoop. (UNLV Libraries image)

The second XF-11 was later delivered to the AAF at Wright Field, Ohio in November 1947. After further flight tests, the aircraft went to Eglin Air Force Base in Florida. The XF-11 was noted for having good flight characteristics, but in-flight access of the camera equipment was extremely difficult and some of the aircraft’s systems were unreliable. In 1948, the aircraft was redesignated XR-11 in accordance to the new Air Force designation system. The XF-11 was tested at Eglin from December 1947 through July 1949.

Other, existing aircraft, mainly Boeing RB-29s and RB-50s, were serving in the reconnaissance role intended for the XF-11. These aircraft proved much less expensive than the XF-11, making the impressive and powerful XF-11 irrelevant. While the XF-11 probably could have done the reconnaissance job better, money was tight in the post-war years and there were other, more-promising projects to fund. The XF-11 was transferred to Sheppard Air Force Base in Wichita Falls, Texas on 26 July 1949 and subsequently served as a ground training aid, never flying again. The aircraft was struck from the Air Force’s inventory in November 1949 and was eventually scrapped.

Hughes XF-11 no2 1948

The second XF-11 sometime in 1948 with the revised (red stripe) Air Force insignia. The aircraft has recently taken off and the very large nose gear doors are just closing. Note the underwing pylons. (UNLV Libraries image)

Sources:
World’s Fastest Four-Engined Piston-Powered Aircraft by Mike Machat (2011)
R-4360: Pratt & Whitney’s Major Miracle by Graham White (2006)
Howard Hughes: An Airman, His Aircraft, and His Great Flights by Thomas Wildenberg and R.E.G. Davies (2006)
McDonnell Douglas Aircraft since 1920: Volume II by René J. Francillon (1990)
“A Visionary Ahead of His Time: Howard Hughes and the U.S. Air Force—Part II” by Thomas Wildenberg, Air Power History (Spring 2008)
https://en.wikipedia.org/wiki/Hughes_XF-11

Williams Mercury Racer

Williams Mercury Seaplane Racer (1929)

By William Pearce

In 1927, Lt. Alford Joseph Williams and the Mercury Flying Corporation (MFC) built the Kirkham-Williams Racer to compete in the Schneider Trophy contest. Although demonstrating competitive high-speed capabilities, the aircraft had handling issues that could not be resolved in time to make the 1927 race. Williams, backed by the MFC, decided to build on the experience with the Kirkham-Williams Racer and make a new aircraft for an attempt on the 3 km (1.9 mi) world speed record.

Williams Mercury Racer model

R. Smith, chief draftsman of the wind tunnel at the Washington Navy Yard, holds a model of the original landplane version of the Williams Mercury Racer. Lt. Al Williams was originally not focused on the Schneider Trophy contest but was later convinced to enter the event.

Although there was no official support from the US government, the US Navy indirectly supported Williams and the MFC’s continued efforts to build a new racer. Williams’ previous racer was designed and built by the Kirkham Products Corporation. However, Williams felt that Kirkham lacked organization, and he was not interested in having the company build another aircraft. Williams had already shipped the previous racer to the Naval Aircraft Factory (NAF) to undergo an analysis on how to improve its speed. With the Navy’s support, the NAF was a natural place to design and build the new racer, which was called the Williams Mercury Racer. The aircraft was also referred to as the NAF Mercury and Mercury-Packard.

In mid-1928, a model of the Williams Mercury Racer landplane was tested in the wind tunnel at the Washington (DC) Navy Yard. However, the decision was made to design a pair of experimental floats and test them on the aircraft, since there was a pressing need to explore high-speed seaplane float designs. It appears all subsequent work on the aircraft was focused on the seaplane version. Williams did not originally intend the Williams Mercury Racer to be used in the 1929 Schneider race. But the US had won the Schneider Trophy two out of the last four races, and another win would mean permanent retention of the trophy. With the Williams Mercury Racer now a seaplane, Williams relented to pressure and agreed to work toward competing in the 1929 Schneider Trophy contest and to attempt a new speed record.

Packard X-2775 NASM

The Packard X-2775 engine installed in the Williams Mercury Racer was actually the same engine originally installed in the Kirkham-Williams Racer. It has been updated with a propeller gear reduction, new induction system, and other improved components. This engine is in storage at the Smithsonian National Air and Space Museum. (NASM image)

Under the supervision of John S. Kean, work on the racer began in September 1928 at the NAF’s facility in Philadelphia, Pennsylvania. On first glance, the Williams Mercury Racer appeared to be a monoplane version of the previous Kirkham-Williams Racer. While some parts such as the engine mount and other hardware were reused, the rest of the aircraft was entirely new. The Williams Mercury Racer was powered by the same Packard X-2775 engine (Packard model 1A-2775) as the Kirkham-Williams Racer, but the engine had been fitted with a .667 propeller gear reduction, and its induction system had been improved. The 24-cylinder X-2775 was rated at 1,300 hp (969 kW), and it was the most powerful engine then available in the US. The X-2775 was water-cooled and had its cylinders arranged in an “X” configuration. The engine turned a ground adjustable Hamilton Standard propeller that was approximately 10 ft 3 in (3.12 m) in diameter. A Hucks-style starter driven by four electric motors engaged the propeller hub to start the engine. Carburetor air intakes were positioned just behind the propeller and in the upper and lower Vees of the engine. The intakes faced forward to take advantage of the ram air effect as the aircraft flew.

The Williams Mercury Racer consisted of a monocoque wooden fuselage built specifically to house the Packard engine. The racer’s braced mid-wing was positioned just before to cockpit. The wing’s upper and lower surfaces were covered in flush surface radiators. A prominent headrest fairing tapered back from the cockpit to the vertical stabilizer, which extended below the aircraft to form a semi-cruciform tail. A nine-gallon (34 L) oil tank was positioned behind the cockpit. The wings and tail were made of wood, while the cowling, control surfaces, and floats were made of aluminum.

Streamlined aluminum fairings covered the metal struts that attached the two floats to the racer. The underside of the floats had additional surface radiators, which provided most of the engine cooling while the aircraft was in the water at low speed. However, the radiators were somewhat fragile and required gentle landings. The floats housed a total of 90 gallons (341 L) of fuel. Some sources state the fuel load was 147 gallons (556 L). The Mercury Williams Racer had an overall length of approximately 27 ft 6 in (8.41 m). The fuselage was 23 ft 7 in (7.19 m) long, and the floats were 19 ft 8 in (5.99 m) long. The wingspan was 28 ft (8.53 m), and the aircraft was 11 ft 9 in (3.58 m) tall. The racer’s forecasted weight was 4,200 lb (1,905 kg) fully loaded. The Williams Mercury Racer had an estimated top speed of around 340 mph (547 km/h). The then-current world speed record stood at 318.620 mph (512.776 km/h), set by Mario de Bernardi on 30 March 1928.

Williams Mercury Racer Packard X-2775

Lt. Al Williams sits in the cockpit of the Williams Mercury Racer during an engine test. The Hucks-style starter is engaged to the propeller hub of the geared Packard X-2775 engine. Note the ducts above and below the spinner that deliver ram air into the intake manifolds situated in the engine Vees.

The completed Williams Mercury Racer debuted on 27 July 1929. On 6 August, the aircraft was shipped by tug to the Naval Academy in Annapolis, Maryland for testing on Chesapeake Bay. Initial taxi tests were conducted on 9 August, and a top speed of 106 mph (171 km/h) was reached. The first flight was to follow the next day, and Williams had boldly planned to make an attempt on the 3 km (1.9 mi) world speed record on either 11 or 12 August. To that end, a course had been set up, and timing equipment was put in place. However, it was soon discovered that spray had damaged the propeller. The propeller was removed for repair, and the flight plans were put on hold.

Although not disclosed at the time, the aircraft was believed to be 460 lb (209 kg) overweight. Williams found that the floats did not have sufficient reserve buoyancy to accommodate the extra weight. The spray that damaged the propeller was a result of the floats plowing into the water. Williams found that efforts to counteract engine torque and keep the aircraft straight as it was initially picking up speed made the left float dig into the water and create more spray. Williams consulted with retired Navy Capt. Holden Chester Richardson, a friend and an expert on floats and hulls. Richardson recommended leaving all controls in a neutral position until a fair amount of speed had been achieved. As the aircraft increased its speed, the water’s planing action on the floats would offset the torque reaction of engine and right the aircraft.

Williams Mercury Racer rear

The racer being offloaded from the tug and onto beaching gear at the Naval Academy in Annapolis, Maryland. The rudder extended below the aircraft and blended with the ventral fin. Note how the fairings for the lower cylinder banks blended into the float supports.

Weather and mechanical issues delayed further testing until 18 August. Williams lifted the Williams Mercury Racer off the water for about 300 ft (91 m) while experiencing a bad vibration and fuel pressure issues. After the engine was shut down, the prop was found damaged again by spray. Like with Williams’ 1927 Schneider attempt, time was quickly running out, and the racer had yet to prove itself a worthy competitor to the other Schneider entrants. Three takeoff attempts on 21 August were aborted for different reasons, the last being a buildup of carbon monoxide in the cockpit that caused Williams to pass out right after he shut off the engine. Attempts to fly on 25 August saw another three aborted takeoffs for different reasons.

The general consensus was that the aircraft’s excessive weight and insufficient reserve buoyancy prevented the racer from flying. With time running out, one final proposal was offered. The Williams Mercury Racer could be immediately shipped to Calshot, England for the Schneider contest, set to begin on 6 September. While en route, a more powerful engine and new floats would be fitted. It is unlikely that the more powerful engine incorporated a supercharger, as supercharger development had given way to the gear reduction used on the X-2775 installed in the Williams Mercury Racer. The gear reduction was interchangeable between engines, but it is not clear what modification had been done to the second X-2775 engine at this stage of development. Regardless, the improved Mercury Williams Racer would then be tested before the race, and, assuming all went well, participate in the event. However, given all the failed attempts at flight and the very uncertain capabilities of the aircraft, the Navy rescinded its offer to transport the racer to England.

Williams Mercury Racer

The completed racer was a fantastic looking aircraft. A top speed of 340 mph (547 km/h) was anticipated, which would have given the British some competition for the Schneider race. However, the speed was probably not enough to win the event.

The Williams Mercury Racer was shipped back to the NAF at Pennsylvania. Williams wanted to install the more powerful engine, which had already been shipped to the NAF, and make an attempt on the 3 km record. The Williams Mercury Racer arrived at the NAF on 1 September 1929, but no work was immediately done on the aircraft. The Navy had not decided what to do with Williams or the aircraft. At the end of October, the Navy gave Williams four months to rework the racer, after which he would be required to focus on his Naval duties and go to sea starting in March 1930.

Studies were made to decrease the Williams Mercury Racer’s weight and improve the aircraft’s cooling system. It was estimated that the suggested changes would lighten the aircraft by 400 lb (181 kg). When the four months were up on 1 March 1930, Assistant Secretary of the Navy for Aeronautics David S. Ingalls felt that enough time, effort, and energy had been spent on the racer and ordered all work to stop. Ingalls also ordered Williams to sea duty. This prompted Williams to resign from the Navy on 7 March 1930. Williams had spent nearly all of his savings on his two attempts at the Schneider contest and knew that the MFC and the Navy had also made a substantial investment in the racer. He wanted to see the project through to some sort of completion, even if it did not result in setting any records.

No more work was done on the Williams Mercury Racer. In April 1930, Williams testified before a subcommittee of the Senate Naval Affairs Committee regarding the racer, his resignation, and other Navy matters. During his testimony, he stated that he wanted another year to finish the aircraft. This time frame would have made the racer ready for the 1931 Schneider Trophy contest, but even in perfect working order it probably would not have been competitive. Williams said the aircraft was 880 lb (399 kg) overweight and that this 21% of extra weight was the reason it could not takeoff. The racer actually weighed 5,080 lb (2,304 kg), rather than the 4,200 lb (1,905 kg) forecasted. Williams said he was initially told that it weighed 4,660 lb (2,114 kg), which was 460 lb (209 kg) more than expected. But Williams thought they could get away with the extra weight. It was only when Williams requested the aircraft to be weighed upon its return to the NAF that its true 5,080-lb (2,304-kg) weight was known.

Williams Mercury Racer Al Williams

The Williams Mercury Racer being towed in after another disappointing test on Chesapeake Bay. Williams stands in the cockpit, knowing his chances of making the 1929 Schneider contest are quickly fading. Note the low position of the floats in the water.

Williams stated that he wanted to take the Williams Mercury Racer to England even if it was not going to be competitive or even fly. Williams said, “I felt we should see it through no matter what the outcome was. If she would not fly over there—take this, to be specific—I was just going to destroy the ship. It could have been done very easily on the water. I intended to smash it up; but I did intend and [was] determined to get to Europe with it. It made no difference to me what the ship did.”

Ingalls also testified before the committee. He had been involved with the Williams Mercury Racer, was a contributor to the MFC, and had friends who were also contributors. Ingalls said that Williams had informed him about the possibility of crashing the Williams Mercury Racer in England if it was unable to fly. Ingalls said that it was ridiculous to send an aircraft to England that may not be able to fly just so that it could be crashed. It was this consideration that led him to withdraw Navy support for sending the aircraft to England. Ingalls also said that of the aircraft’s extra 880 lb (399 kg), around 250 lb (113 kg) was from the NAF’s construction of the aircraft, and around 600 lb (272 kg) was from outside sources, such as Packard for the engine and Hamilton Standard for the propeller. Ingalls reported that Williams supplied the engine’s and propeller’s weight to the NAF, but those values have not been found. Perhaps the original engine weight supplied to the NAF was for the lighter, direct-drive engine and smaller propeller—the combination installed in the Kirkham-Williams Racer.

On 24 June 1930, the Navy purchased the Williams Mercury Racer from the MFC for $1.00. Reportedly, $30,000 was invested by the MFC with another $174,000 of money and resources from the Navy to create the aircraft. It is not clear if the Navy’s investment was just for the Williams Mercury Racer, as the Packard X-2775 engine was also used in the earlier Kirkham-Williams Racer. The Navy stated they acquired the racer for experimental purposes, but nothing more was heard about the aircraft, and the Mercury Williams Racer faded quietly into history.

Williams Mercury Racer taxi

Williams taxis the racer in a wash of spray, most likely damaging the propeller again. Note how the floats are almost entirely submerged, especially the left float. The aircraft being very overweight severely hampered its water handling.

Sources:
Schneider Trophy Seaplanes and Flying Boats by Ralph Pegram (2012)
Wings for the Navy by William F. Trimble (1990)
Master Motor Builders by Robert J. Neal (2000)
Racing Planes and Air Races Volume II 1924–1931 by Reed Kinert (1967)
“Lieut. Alford J. Williams, Jr.—Fast Pursuit and Bombing Planes” Hearings Before a Subcommittee of the Committee on Naval Affairs, United States Senate, Seventy-first Congress, second session, on S. Res. 235 (8, 9, and 10 April 1930)
“Making Aircraft Airworthy” by K. M. Painter, Popular Mechanics (October 1928)

Kirkham-Williams Racer no cowl

Kirkham-Williams Seaplane Racer (1927)

By William Pearce

Lt. Alford Joseph Williams was an officer in the United States Navy and a major proponent of aviation. Williams believed that air racing contributed directly to the development of front-line fighter aircraft. In 1923, Williams won the Pulitzer Trophy race and later established a new 3 km (1.9 mi) absolute speed record at 266.59 mph (429.04 km/h). In 1925, Williams finished second in the Pulitzer race, but his main disappointment was not being selected as a race pilot for the Schneider Trophy team. Williams was also not selected for the 1926 Schneider team. That year was a particularly bad showing from the United States despite its advantage of hosting the Schneider contest.

Kirkham-Williams Racer front

The Kirkham-Williams Racer was built to compete in the 1927 Schneider Trophy contest and to capture the world speed record. Note how the large Packard X-24 engine dictated the shape of the aircraft.

Williams could see that racing was not a priority for the US military and decided to take matters into his own hands. In late 1926, Williams sought the support of investors to build a private venture Schneider racer. Since the US had won the Schneider Trophy two out of the last three races, another win would mean permanent retention of the trophy. Williams received further support from various departments in the US Navy, and the Packard Motor Car Company (Packard) was willing to design a new engine provided the Navy paid for it. On 9 February 1927, the US government officially announced that it would not be sending a team to compete in the 1927 Schneider race, held in Venice, Italy. The plans that Williams, the Navy, and Packard had implemented moved forward, and a syndicate to fund the private entry racer was announced on 24 March 1927. The Mercury Flying Corporation (MFC) was formed by patriotic sportsmen for the purpose of building the racer to compete in the 1927 Schneider Trophy contest, with Williams as the pilot.

Although the US government was not directly supporting MFC’s efforts, the US Navy was willing to lend indirect support by transporting the racer to Italy and providing a Packard X-2775 engine for the project. The X-2775 (Packard model 1A-2775) was a 1,200 hp (895 kW), water-cooled, X-24 engine that had been under development by Packard since 1926. The engine was a result of the talks initiated by Williams for a power plant intended specifically for a race aircraft. Ultimately, the engine was covered under a Navy contract. The X-2775 was one of the most powerful engines available at the time.

Kirkham-Williams Racer wing radiator

The racer had some 690 sq ft (64.1 sq m) of surface radiators covering its wings. Fluid flowed from a distributor line at the wing’s leading edge, through the tubes, and into a collector line at the wing’s trailing edge. Tests later indicated that the protruding radiator tubes doubled the drag of the wings.

Williams had decided that the racer should be designed along the same lines as previous Schneider racers built by the Curtiss Aeroplane and Motor Company (Curtiss). MFC contracted the Kirkham Products Corporation (Kirkham) to design and construct the racer. Kirkham’s founder was engineer and former Curtiss employee Charles K. Kirkham, and a number of other former Curtiss employees worked for the company, such as Harry Booth and Arthur Thurston. Booth and Thurston had been closely involved with the racers built at Curtiss. The aircraft was named the Kirkham-Williams Racer, but it was also referred to as the Kirkham-Packard Racer, Kirkham X, and Mercury X.

The Kirkham-Williams Racer was constructed in Kirkham’s faciality in Garden City, on Long Island, New York. The biplane aircraft consisted of a wooden fuselage built around the 24-cylinder Packard engine. The engine mount, firewall, and cowling were made of metal. The upper and lower surfaces of the wooden wings were covered with longitudinal brass tubes to act as surface radiators for cooling the engine’s water and oil. The specially-drawn tubes had an inverted T cross section and protruded about .344 in (8.73 mm) above the wing, creating a corrugated surface. The tubes were .25 in (6.35 mm) wide at their base and .009 in (.23 mm) thick. Around 12,000 ft (3,658 m) of tubing was used, and the oil cooler was positioned on the outer panel of the lower right wing. The water or oil flowed from the wing’s leading edge to a collector at the trailing edge. The aircraft’s twin floats were also made from wood and housed the racer’s main fuel tanks. The floats were attached by steel supports that were covered with streamlined aluminum fairings. The forward float supports were mounted directly to special pads on the engine. The cockpit was positioned behind the upper wing, and a headrest was faired back along the top of the fuselage into the vertical stabilizer. A framed windscreen protected the pilot. A small ventral fin extended below the aircraft’s tail.

Kirkham-Williams Racer starter

The Packard X-2775 engine barely fit into the racer. The engine cowling mounted to arched supports running from the cylinder banks to a ring around the propeller shaft. The Hucks-style starter, powered by four electric motors, is connected to the propeller hub. Note that the forward float strut is mounted to the engine’s crankcase.

The Kirkham-Williams Racer had an overall length of 26 ft 9 in (8.15 m). The fuselage was 22 ft 9 in (6.93 m) long, and the floats were 21 ft 3 in long (6.48 m). The upper wing had a span of 29 ft 10 in (9.09 m), and the lower wing’s span was 24 ft 3 in (7.39 m). The racer was 10 ft 9 in (3.28 m) tall and weighed 4,000 lb (1,814 kg) empty and 4,600 lb (2,087 kg) fully loaded. The aircraft carried 60 gallons (227 L) of fuel, 35 gallons (132 L) of water, and 15 gallons (57 L) of oil. The direct-drive Packard engine turned a two-blade, ground-adjustable, metal propeller that was 8 ft 6 in (2.59 m) in diameter and built by Hamilton Standard. A Hucks-style starter driven by four electric motors engaged the propeller hub to start the engine. Carburetor air intakes were positioned in the upper and lower engine Vees and were basically flush with the cowling’s surface.

Packard was involved with the aircraft’s construction, and Williams was involved with the engine’s development. The Kirkham-Williams Racer was finished in mid-July 1927 and transported later that month to Manhassest Bay, on the north side of Long Island. Weather delayed the first tests until 31 July. Taxi tests revealed that the float design was flawed and caused a large amount of spray to cover the aircraft and cockpit. The spray resulted in damage to the propeller during a high-speed taxi test. In addition, the aircraft was around 450 lb (204 kg) overweight.

Kirkham-Williams Racer launch

Lt. Al Williams prepares the racer for a test on Manhassest Bay. The cockpit was designed around Williams, and he was the only one to taxi or fly the aircraft. Note the support running between the vertical and horizontal stabilizers.

With the Schneider race just over a month away, little time was left to properly test the aircraft and transport it halfway around the world. Williams requested a postponement of the Schneider race for one month, but the British contingent declined the request. To make matters worse, Williams had been very optimistic about the aircraft’s test schedule and repeatedly promised an attempt on the world speed record. Issues with the Kirkham-Williams Racer resulted in a continual push-back of Williams’ proposed speed flights.

With a repaired propeller and new floats, the Kirkham-Williams Racer was ready for additional tests on 16 August. An oil leak and air in the water-cooling system caused Williams to cancel the day’s activities before any real testing had been done. On 17 August, high-speed taxi tests were finally sufficiently completed. Williams announced that the Kirkham-Williams Racer’s first flight would be the following day, but unfavorable weather caused that date to be pushed back. The racer’s first flight was on 25 August, and it should be noted that this was the first flight for the X-2775 engine as well. Some sources state that Williams made two speed runs at an estimated 250 mph (402 km/h). However, Williams stated that no speed runs were attempted on the first flight. While 250 mph (402 km/h) is an impressive speed for the time, it was most likely an estimation made by observers and not achieved over a set course. The second flight that day was cut short because of engine cooling issues caused by air in the cooling system.

Kirkham-Williams Racer runup

Williams is in the cockpit running up the X-2775 engine. The registration X-648 has been applied to the tail. The fuselage was painted blue, with the wings, floats, and rudder painted gold. Note the rather imperfect finish of the fuselage, just before the tail.

Unfavorable weather resulted in more delays, and it was not until 29 August that Williams was able to take the Kirkham-Williams Racer up for another flight during a brief break between two storm fronts. Williams made a high-speed run, and the racer was unofficially timed at 275 mph (443 km/h). Later, Williams would say the speed was probably around 269 mph (433 km/h), but he and others felt the aircraft was capable of 290 mph (467 km/h). Weather again caused delays, and three takeoff attempts on 3 September had to be aborted on account of pleasure boats straying into the aircraft’s path and causing wakes.

On 4 September, a good, extended flight was made, after which Williams reported the aircraft was nose-heavy and became increasingly destabilized at speeds above 200 mph. The issue was with the orientation of the floats. Modifications were made, and the aircraft flew again on 6 September. Williams reported improved handling, but some issues remained. The Navy had held the cruiser USS Trenton at the Brooklyn Navy Yard with the intention of transporting the Kirkham-Williams Racer to Italy in time for the Schneider contest, which was to start on 23 September. However, Williams cancelled any attempts to make the Schneider race on 9 September, citing the nose-heaviness and also float vibrations.

Kirkham-Williams Racer no cowl

Williams stands on the float, with work going on presumably to clear air from the cooling system, which was a reoccurring issue. The copper radiators covered almost all of the wing’s surface area. Note that the interplane struts protruded slightly above the wings.

During the time period above, it was felt that the Kirkham-Williams Racer may not have been competitive, and Packard was asked to build a more powerful engine. In the span of 10 weeks, Packard designed, constructed, and tested a supercharged X-2775 engine. The Roots-type supercharger was installed on the front of the engine and driven from the propeller shaft. Liberal tolerances were used because of the lack of time, and the supercharger generated only 3.78 psi (.26 bar) of boost. The supercharged engine produced 1,300 hp (696 kW), which was only a slight power increase. The engine was not installed, because the minor gain in power was offset by the added weight and complexity of the supercharger system.

With the Schneider race out of reach, the Kirkham-Williams Racer was converted to a landplane with the intent to set a new world speed record. The floats were removed, and two main wheels attached to streamlined struts were installed under the engine. A tail skid replaced the small fin under the aircraft’s rudder. In addition, the X-2775 engine was fitted with a new cowling and spinner that gave the aircraft a more streamlined nose.

Kirkham-Williams Racer landplane front

Williams reported making four emergency landings in the racer at Mitchel Field, but the causes of the forced landings have not been found. The aircraft was fitted with the same direct-drive X-2775 engine as the seaplane. The intake of the upper Vee engine section can just be seen above the cowling.

The modifications to the Kirkham-Williams Racer were completed by late October 1927, and the aircraft was taken to Mitchel Field on Long Island, New York. Williams’ initial tests found the plane heavy with a landing speed of around 100 mph (161 km/h). Williams felt Mitchel Field was not an ideal place for experimental work with the aircraft, but the MFC did not have funds to seek a better location. Williams ended up making four forced landings at Mitchel Field in the Kirkham-Williams Racer.

On 6 November, Williams flew the aircraft over a 3 km (1.9 mi) course and was unofficially timed at 322.42 mph (518.88 km/h). This speed was significantly faster than the then-current records, which were 278.37 mph (447.99 km/h) set by Florentin Bonnet on 11 November 1924 for landplanes, and an absolute record of 297.70 mph (479.10 km/h) set by Mario de Bernardi on 4 November 1927. Some were skeptical of Williams’ speed, especially since it was achieved in only one direction and with the wind reportedly blowing at 40 mph (64 km/h). Williams announced that an official attempt on the record would soon be made, but no further flights of the Kirkham-Williams Racer were recorded. Later, Williams stated that the racer’s still-air speed on the 6 November 1927 run was around 287 mph (462 km/h), which was much lower than anticipated.

Williams had the aircraft disassembled and shipped to the Naval Aircraft Factory (NAF) in Philadelphia, Pennsylvania to further evaluate ways to improve the racer’s speed. A section of the wing was removed and tested by the National Advisory Committee for Aeronautics in their wind tunnel at Langley Field, Virginia. The test results indicated that the corrugated surface radiators decreased lift, doubled drag, and slowed the aircraft by some 20 mph (32 km/h). While at the NAF, the disassembled Kirkham-Williams Racer was used as the basis for Williams’ 1929 high-speed aircraft—the Williams Mercury Racer.

Kirkham-Williams Racer landplane

In landplane form, the Kirkham-Williams Racer had a more streamlined nose and an added tailskid. The machine looked every bit a racer and was one of the fastest aircraft in the world, even at only 287 mph.

Sources:
Schneider Trophy Seaplanes and Flying Boats by Ralph Pegram (2012)
Schneider Trophy Racers by Robert Hirsch (1993)
Master Motor Builders by Robert J. Neal (2000)
Racing Planes and Air Races Volume II 1924–1931 by Reed Kinert (1967)
Full Scale Investigation of the Drag of a Wing Radiator by Fred E. Weick (September 1929)
“Lieut. Williams’ Racing Seaplane” by George F. McLaughlin, Aero Digest (September 1927)
“Lieut. Alford J. Williams, Jr.—Fast Pursuit and Bombing Planes” Hearings Before a Subcommittee of the Committee on Naval Affairs, United States Senate, Seventy-first Congress, second session, on S. Res. 235 (8, 9, and 10 April 1930)

Vickers Type 432 in flight

Vickers Type 432 High-Altitude Fighter

By William Pearce

In March 1939, The British Air Ministry issued Specification F.6/39 for a 400 mph (644 km/h) two-seat fighter. The aircraft was to carry four 20-mm cannons, with the possibility of later mounting two 40-mm cannons. Under a design team led by Rex Pierson, Vickers-Armstrongs Ltd. (Vickers) had been working on a fighter with a single flexibly-mounted 40-mm cannon installed in the aircraft’s nose. The twin-engine aircraft was powered by Rolls-Royce Griffon engines and met the requirements of F.6/39, aside from its armament. Vickers met with the Air Ministry in April 1939 to discuss the aircraft’s potential. The Air Ministry was sufficiently impressed and issued Specification F.22/39 that covered the Vickers fighter, which carried the internal designation Type 414. Specification F.6/39 was subsequently cancelled in November 1939.

Vickers Type 432 front right

The Vickers Type 432 prototype DZ217 appears shortly after its completion at Foxwarren. The bystander gives some indication to the aircraft’s size. Note the bubble canopy.

Two Type 414 prototypes were ordered on 30 August 1939, and they were assigned serial numbers R2436 and R2437. After inspection of the Type 414 mockup in early February, the Air Ministry inquired about the possibility of installing several 20-mm cannons in place of the single 40-mm cannon. Vickers responded with aircraft proposals incorporating eight 20-mm cannons or two 40-mm cannons.

Vickers designated the fighter with 20-mm cannons as the Type 420. Two cannons were positioned in the aircraft’s nose, and three were on each side of the cockpit. Vickers and the Air Ministry discussed the Type 420 in June 1940, and Specification F.16/40 was issued for the aircraft’s development. The Type 420 was given a high priority, and an order for two prototypes was expected. The order for two Type 414 prototypes was still in place. However, the Type 420 took precedence, and work on the Type 414 slowed substantially.

In early January 1941, the Air Ministry requested a design change to reduce the number of 20-mm cannons to six. At the same time, Vickers had designed a high-altitude fighter that used many components from the Type 420. The high-altitude aircraft was armed with four 20-mm cannons and powered by two Rolls-Royce Merlin engines. The Air Ministry was interested in Vickers’ proposal, as they felt there was an urgent need for a heavily armed, high-altitude fighter aircraft to intercept high-altitude German bombers that were expected in the skies over Britain. However, high-altitude German bombing raids were never undertaken en masse and did not present a significant threat to Britain during World War II.

Vickers Type 432 rear right

Rear view of the Type 432 displays the aircraft’s long engine nacelles and ventral pod for the six 20-mm cannons. Note how the aircraft’s tail resembles that of a de Havilland Mosquito. The completed aircraft was disassembled at Foxwarren and taken to Farnborough for flight testing.

In March 1941, work on the Type 414 was stopped completely, and discussions with Rolls Royce commenced regarding the acquisition of Merlin engines. In May 1941, Vickers detailed the specifics of the high-altitude aircraft, which it had designated as Type 432. Specification F.22/39 was cancelled, thus halting work on the Type 420. Design work on the Type 432 continued, resulting in the switch to a single-seat cockpit placed in the nose of the aircraft and six 20-mm cannons installed in a ventral fairing. Each cannon had 120 rounds of ammunition. The Air Ministry ordered two Type 432 prototypes on 9 September 1941, and the aircraft would be built to the new Specification F.7/41. The two Type 432 prototypes were issued serial numbers DZ217 and DZ223.

The fuselage of the Vickers Type 432 was made of stressed-skin aluminum panels that were flush-riveted to the closely-spaced circular structures that made up the airframe. The forward part of each wing was made of a similar stressed-skin construction. The thick skins and their supports created a torsion box of sufficient strength so that conventional wing spars and ribs were omitted. Fabric covered the aft section of the wings and the aircraft’s control surfaces. The wings had a unique elliptical planform with a slight forward-sweep outside of the engines. The wing leading edges between the engines and fuselage housed the coolant radiators.

The aircraft was powered by two-stage, two-speed Merlin 61 engines capable of 1,580 hp (1,178 kW) at 23,500 ft (7,163 m). The engines were housed in long, streamlined nacelles mounted to each wing. The main landing gear retracted rearward into the nacelle behind the engine. The cockpit consisted of a pressure cabin topped by a small canopy that hinged to the side for entry.

The Type 432 was a rather large aircraft with a wingspan of 56 ft 10 in (17.3 m), a length of 40 ft 7 in (12.4 m), and a height of 13 ft 9 in (4.9 m). Forecasted top speeds were estimated at 320 mph (515 km/h) at sea level, 435 mph (700 km/h) at 28,000 ft (8,534 m), and 400 mph (644 km/h) at 40,000 ft (12,192 m). Cruise speed was estimated at 400 mph (644 km/h) at 29,500 mph (8,992 m). The aircraft had a 2,750 fpm (14.0 m/s) initial climb rate and a service ceiling of 43,500 ft (13,259 m). The Type 432 weighed 16,373 lb (7,427 kg) empty and had a maximum takeoff weight of 20,168 lb (9,148 kg). With 506 gallons (421 Imp gal / 1,914 L) of fuel, the aircraft had a 1,500 mi (2,414 km) range.

Vickers Type 432 left side

During its initial taxiing tests at Farnborough, the Type 432 exhibited tracking issues and snaked from side-to-side. The landing gear was moved aft 3 in (76 mm) to improve handling. Flight tests revealed other undesirable characteristics, and modifications were made to the aircraft’s ailerons and tail to improve its handling.

The Type 432 mockup was inspected in late December 1941, and the first prototype, DZ217, was built throughout 1942. The aircraft was built at Foxwarren, a special Vickers dispersal site for experimental work near Brooklands in Surrey, England. The site did not have an airfield, so the Type 432 was disassembled and transported to Royal Aircraft Establishment Farnborough for its first flight. The Type 432 was first flown on 24 December 1942, piloted by Tommy Lucke. On 29 December, the Ministry of Aircraft Production cancelled the partially-built second prototype. This decision was not made official until 1 May 1943. The entire Type 432 program was cancelled at the end of 1943.

The sole Type 432 aircraft continued to fly occasionally until November 1944. Some efforts were made throughout the aircraft’s existence to improve its handling and flight qualities, as the Type 432 was noted as having heavy controls. Only 28 flights were made, and the aircraft was never submitted for official trials or tested to its maximum performance. Additionally, the 20-mm armament and the pressurized cabin were never installed. Although the Type 432 exceeded 400 mph (644 km/h) in a slight dive, the highest speed obtained in level flight was 380 mph (612 km/h), recorded on 14 May 1943. One of the factors that limited flight testing was that the Merlin engines installed in the Type 432 did not run well above 23,000 ft (7,010 m). Since the Type 432 had no future as a production aircraft, the performance issues of its Merlins were never fully investigated.

Aircraft observers were a regular fixture during World War II, keeping an eye out for any enemy action in the skies over Britain. The rarely-seen and oddly-shaped Type 432 was only listed as “AP1480” in the recognition handbooks. This non-descript designation led the spotters to dub the Type 432 as the “Tin Mossie” on account of the aircraft’s resemblance to the wooden de Haviland Mosquito. Some source list the aircraft as being referred to as “Mayfly,” but the origin of this name has not been found.

Vickers Type 432 in flight

The Type 432 made only 28 flights in its two-year life. The aircraft was noted as having some handling deficiencies that were never completely resolved, because the project was a dead end. Note the slight forward sweep of the Type 432’s outer wing panels.

Sources:
British Secret Projects: Fighters & Bombers 1935-1950 by Tony Buttler (2004)
Vickers Aircraft since 1908 by C. F. Andrews and E. B. Morgan (1988)
RAF Fighters Part 3 by William Green and Gordon Swanborough (1981)
The British Fighter since 1912 by Francis K. Mason (1992)
Aircraft of the Fighting Powers Volume VII by Owen Thetford (1946)

VEF I-16 Front right

VEF I-16 Light Fighter Aircraft

By William Pearce

VEF (Valsts Elektrotehniskā Fabrika or State Electro-Technical Factory, often spelled Valsts Elektrotechniskā Fabrika) was a large industrial manufacturer founded in Latvia in 1919. Kārlis Irbītis was an engineer at VEF during the 1930s and 1940s. Irbītis had designed aircraft since the 1920s and continued the practice in his spare time while employed at VEF. In 1935, Irbītis suggested that VEF should enter the aircraft manufacturing business, and VEF management was responsive.

VEF I-12 International Expo 1938

The VEF I-12 was a light sport plane and a follow-on to the I-11 aircraft. Powered by a 90 hp (67 kW), air-cooled, four-cylinder Cirrus Minor engine, the I-12 had a top speed of 143 mph (230 km/h).

VEF solicited a manufacturing contract from the Latvian government, but the request was denied. Frustrated, VEF decided to build Irbītis’ latest aircraft design, the I-11, as a private venture. The I-11 was the first in a series of fixed-gear, low-wing aircraft designed by Irbītis and built by VEF. The I-11 was a two-seat sport plane that first flew in late June 1936. Some aspects of the I-11 design were less than ideal, as aircraft components had to be made to fit out the workshop’s small door. After the I-11’s successful flight tests, an improved model was designed and designated I-12.

The I-12 was seen as a stepping stone to the design and construction of future military aircraft. VEF approved of Irbītis’ plan to build a military trainer after the I-12, and a light fighter would follow after construction of the trainer. The I-12 was first flown on 26 June 1937 and demonstrated good performance and handling. Ultimately, around 12 I-12 aircraft were built. Construction of the I-14 military trainer started in April 1937, and the aircraft made its first flight on 19 November 1937. The I-14 prototype was damaged beyond repair during an emergency landing on 23 April 1938. Undeterred, VEF authorized the design and construction of two new aircraft types: the I-15 trainer and the I-16 fighter.

VEF I-14

The VEF I-14 was developed as a military trainer and was powered by a 200 hp (149 kW), air-cooled, six-cylinder Menasco B6S Buccaneer engine. The I-14 had an estimated top speed of 186 mph (300 km/h), but a crash prevented the completion of flight tests.

Irbītis continued to improve his aircraft designs. The I-15 and I-16 shared a very similar layout and employed the same construction techniques. Manufacture of the I-15 started in the summer of 1938, and two aircraft were built. The I-15a had a wooden, fixed-pitch propeller and gun camera, but it had no armament. The I-15a was powered by an air-cooled, 200 hp (149 kW) de Havilland Gipsy Six series I engine. The I-15b was powered by a 210 hp (157 kW) Gipsy Six series II engine and used a metal, constant-speed propeller. The I-15b could accommodate a single 7.7 mm machine gun, and its cockpit was moved forward slightly to improve pilot visibility.

The I-15a first flew in April 1939. The first flight of the I-15b was delayed because of the late delivery of its constant-speed propeller but finally occurred around November 1939. The Latvian Aviation Regiment decided to purchase the I-15a and I-15b aircraft based on the favorable experience with four I-12 aircraft given to the Aizsargu Aviācija (Aviation Guard) by VEF in late 1938. The I-15a had a top speed of 186 mph (300 km/h), and the I-15b had a top speed of 205 mph (330 km/h). Both I-15 aircraft had successfully completed flight testing by the time Latvia was invaded by Soviet forces in June 1940; the invasion stopped further development.

VEF I-15a

The VEF I-15a on skis to enable flight testing during the Latvian winter. The I-15A carried the Latvian military serial number 190, while the I-15b carried 191.

Design work on the VEF I-16 light fighter began in late 1938. The aircraft was a single-seat, low-wing monoplane with fixed undercarriage. The landing gear was covered in streamlined fairings, and a retractable gear design was to be incorporated on a later model. The I-16 was comprised of a wooden structure covered in plywood and had fabric-covered control surfaces. Each wing accommodated a 10.6 gallon (40 L) fuel tank, and a single fuel tank in the fuselage held 58.1 gallons (220 L). The I-16 had two 7.7 mm machine guns mounted in the upper cowling in front of the cockpit. Provisions were made for an additional 7.7 mm machine gun to be mounted under each wing.

The I-16 was powered by a Sagitta I-SR engine built by Walter in Czechoslovakia. The Sagitta was an air-cooled, inverted V-12 engine that had a 4.65 in (118 mm) bore and a 5.51 in (140 mm) stroke. The supercharged engine displaced 1,121 cu in (18.4 L) and produced 520 hp (388 kW) at 12,467 ft (3,800 m). Air was fed into the supercharger via two scoops on the upper cowling. Engine exhaust was discharged through ejector stacks positioned at the bottom of the cowling. The shroud around the exhaust stacks also allowed cooling air to exit the cowling after passing through the cylinders’ fins. Additional cooling air exited via a vertical slit at the rear of the cowling. The engine turned a two-blade, wooden, fixed-pitch propeller, but a three-blade, metal, constant-speed propeller was planned for future use.

VEF I-16 construction

The VEF I-16 was a continuation of Kārlis Irbītis’ light, sleek monoplane design. The aircraft was the only monoplane fighter designed and built in Latvia. The wooden, fixed-pitch propeller was considered temporary. The cockpit canopy hinged open toward the right.

The I-16’s wingspan was 26 ft 11 in (8.2 m); its length was 23 ft 11 in (7.3 m); and its height was 8 ft 10 in (2.7 m). With the three-blade propeller, the aircraft had an estimated maximum speed of 286 mph (460 km/h) at 13,123 ft (4,000 m) and 249 mph (400 km/h) at sea level. The I-16 had an initial rate of climb of 2,187 fpm (11.1 m/s), and its ceiling was 26,247 ft (8,000 m). The aircraft had an empty weight of 2,425 lb (1,100 kg) and a loaded weight of 3,417 lb (1,550 kg). The I-16’s range was around 497 miles (800 km).

Construction on the I-16 continued through 1939, and the aircraft made its first flight in the spring of 1940 at Riga, Latvia. The pilot for the first flight was Konstantīns Reichmanis, and the I-16’s engine quit after about 20 minutes of flight time. Reichmanis managed to get the aircraft back on the ground without any damage. Poor fuel distribution was thought to have caused the engine trouble, as similar issues had been encountered during ground runs. Reichmanis praised the aircraft’s handling during his short flight. Changes were made to the I-16’s fuel system, and a few more flights were accomplished before testing was halted by the Soviet invasion.

VEF I-16 rear left

The completed I-16 with German markings during an engine runup in 1941. The two intake scoops for the engine are visible on the top of the cowling, with the left gun port immediately below. Armament was never installed in the aircraft, but VEF did have possession of the Browning machine guns until they were removed by Soviet occupying forces.

The Soviets expressed some interest in the VEF aircraft, and the I-15a, I-15b, and other aircraft were shipped to the Soviet Union in March 1941. The I-16 remained in Latvia to resolve the fuel distribution issues. Before the I-16 could be sent to Russia, the Germans attacked the Soviets and took over Latvia in June 1941. Irbītis escaped deportation, but many of his colleagues, including Reichmanis, were not so fortunate and disappeared into the work camps in Siberia. Under German occupation, the I-16 was returned to an airworthy status and carried the identification code AW+10. The aircraft made two test flights before it was taken over by the Luftwaffe. Some accounts list the aircraft as being part of a training school in Toruń (in occupied Poland) until 1942, but its final disposition is not known.

In late 1939, Irbītis began designing a new fighter, the I-19. With a wingspan of 36 ft 1 in (11 m) and a length of 29 ft 6 in (9 m), the I-19 was larger than the I-16. The I-19 also featured retractable gear, two machine guns in each wing, and a top speed of 404 mph (650 km/h). Irbītis persisted with the wooden construction, but the lack of a suitable power plant led him to consider building his own engine comprised of three V-12 engine sections, with each engine section based on a Ranger V-770. The cylinder banks of each engine section were spaced at 120 degrees. The resulting 36-cylinder engine employed three crankshafts and three superchargers. Irbītis estimated that the engine would displace around 2,200 cu in (36 L) and produce 1,450 hp (1,081 kW) at 3,250 rpm. However, Irbītis switched to an Allison V-1710 engine when more serious design work was undertaken. The I-19 never proceeded beyond the preliminary design phase. After World War II, Irbītis immigrated to Canada and helped develop the tiltwing Canadair CL-84 Dynavert.

VEF I-16 Front right

The sleek I-16 aircraft resembled similar light fighters developed in France (Caudron) and Italy (Ambrosini) during the same period. Note the streamlined fairings covering the gear.

Sources:
Of Struggle and Flight: The History of Latvian Aviation by Kārlis Irbītis (1986)
Latvian Air Force 1918–1940 by Richard Humberstone (2000)
http://latvianaviation.com/VEF_I-16.html
http://airwar.ru/enc/fww2/i16l.html