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Model Aviation: The Aviator XF-11

August 2005 Volume 31 Number 8

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(Editors Note: Last month we presented the first article in a three-part series about how Joe Bok and his company Aero Telemetry produced the model Hughes H-1 racer for director Martin Scorsese and the blockbuster hit movie The Aviator. This month we'll present the story behind the XF-11 that was made for film.)

XF-11 Background

The Aero Telemetry XF-11 – the world's largest and fastest scale model of the Hughes XF-11 aircraft - and ten other airplanes they provided for The Aviator have made their way into Hollywood history in the film's much acclaimed flight sequences. The airplanes flew so realistically that they were featured prominently in the TV and theatrical trailers for the movie, which is a tremendous honor considering the limited amount of content presented during a typical 1-minute or 30 second commercial. Film trailers always strive to put their best footage in front of the audience.

Just days after completing what was, at the time, the most strenuous and difficult part of the project - the flights of the H-1 Racer - Joe and his team were preparing for what was to become the most challenging and renowned radio-control-airplane project in history: building and flying a Cessna-sized scale model of the Hughes XF-11 Reconnaissance Airplane.

The original airplane was built by Howard Hughes in 1946 and was intended to be a reconnaissance-photographic, twin-boom, high wing monoplane. Gross weight for take-off was roughly 58,000 pounds. The XF-11 had a wingspan of approximately 101ft. Power for the first XF-11 was provided by two Pratt & Whitney R-4360 28 cylinder engines with contra-rotating propellers. The nose area carried several cameras and four more cameras were carried in the rear of the twin fuselages. The XF-11 had a ceiling of over 44,000ft with a range of over 5000 miles and a speed well in excess of 450 mph.

Howard Hughes decided to pilot the XF-11 on its first test flight and after about 2 hours, the starboard contra-rotating propeller failed and sent Hughes careening into a residential area in Beverly Hills, California. The crash was devastating and nearly killed Hughes. Some say he never really recovered from this accident. Although the crash would have serious debilitating effects on Hughes’ health for the rest of his life it never deterred his courage and pioneering spirit. Within a year Hughes took to the air once again as the test pilot on the second XF-11. This flight went as planned and Hughes was pleased with the performance of his new airplane.

The Aviator XF-11

The Aviator Executive Producer, Chris Brigham and Academy Award winning visual effects director Rob Legato, turned to Joseph Bok and his company Aero Telemetry Corporation to design, build, and fly one of the largest scale model airplanes ever to be filmed for a Hollywood epic movie.

The biggest challenge was to provide a flyable model that was large enough to realistically simulate the flight characteristics of the real Hughes XF-11 while maintaining an unprecedented margin of safety in the design. The proposed 12-week schedule made it extremely difficult to accomplish the task.

Joe Bok explained:

“The XF-11 was a very difficult airplane to design, duplicate, and scale down. From a performance and reliability standpoint it was off the chart in terms of challenging. We had to come up with entirely new ways of building hydraulic landing gear, coordinating complex flight control systems, and integrating all of them seamlessly to overcome the aerodynamic stresses of high speed and heavy payload. Most importantly it had to be safe and it had to look perfect through the film camera lens”

Aero Telemetry's first job was to create a roughly ¼ scale flyable and historically accurate version of the original XF-11. Its wingspan would be roughly 30 feet long. It had to take-off under its own power and fly at distances of up to 5 miles while performing many different flight maneuvers. It would require the use of custom hydraulic retractable main landing gear and a steer-able nose wheel that also had to retract. These had to be designed, built, tested and fully operational in less than 12 weeks!

XF-11 Design, Build, and Flights

Joe said, “Based on our load calculations we knew where the airframe was going to see the most of its stress. Because of the sheer size and anticipated weight of the payload, I made sure to take extra care in certain areas so we wouldn’t have to come back later and add heavy internal structures to keep the plane strong. I decided early to forego some of the smaller weight saving issues in favor of an airplane that would be very rugged. It would be flying over hundreds of peoples’ heads and millions of dollars of equipment. Safety was my primary concern throughout this entire project.”

While the large airframe and wings were being built, the Aero Telemetry engine shop was again in full gear. The engines were given first priority for testing. The location where the plane would be flown would necessitate that the XF-11 have as much power as possible to climb-out under full load at higher than normal density altitudes. The density altitude is defined as the pressure altitude corrected for non-standard variations. Joe said, “Very simply the Density altitude affects the take-off distance and the rate of climb, so from a design standpoint for the XF-11 it was important to factor that into the engine and propeller integration.”

To counteract any unexpected flight behavior or tendency for the XF-11 to yaw (left or right movement) due to gyroscopic precession, each of the engines and propellers turned in an opposite rotation to each other so as to cancel out the energy created by the rotating masses (pistons, connecting rods, and propellers). The counter-rotating propellers worked perfectly and minimized any yaw induced by prop and engine torque.

The Aero Telemetry team encountered several problems “early-on” that were related to negligent and untimely contractors. John Keefe, chief machinist for Aero Telemetry, said, “negligence on the part of one company required that we redesign major portions of both the wing and fuselage sections of the XF-11” said John, “We lost precious time and money, but as result we came through it smarter and more capable of doing our own wing manufacturing and composite mold design and development.

Another major problem was the poor fuselage mold supplied by another company. Added John, "Crooked molds make crooked parts and the vertical stabilizers and rudders on the XF-11 were so flawed that we had to cut the verticals off, then redesign and rebuild the entire back end of both fuselage sections in order to get them straight. We wouldn’t have even gotten down the runway with those. The fuselage mold provided by the other company didn't have to be straight because their version of the model didn't have to fly, and the additional castings they provided like the rudders were even worse. We had to take those apart and start over too!”

"Thankfully, we turned an otherwise disastrous situation into a positive thing. Since we didn’t have time to dwell on their incompetence during that phase of the project, we just threw their parts in the garbage and started over until it was right,” added John, “That’s something that Howard Hughes would have done also, he never accepted less than perfect on any of his airplanes and neither did we,” he exclaimed.

Despite the temporary setbacks and having to do work over again, the XF-11 was beginning to look like a formidable machine. The engines were mounted and fuel tanks installed. The big XF-11 was getting close to being ready for its own date with destiny at the Norton Air Force Base in San Bernardino, California on November 21, 2003.

Joe’s flight crew arrived the night before on Thursday, November 20th and followed a semi-tractor trailer carrying the huge airplane along several Los Angeles area freeways. “Needless to say, the trip to the air force base was a spectacle all by itself,” remarked Butch Fleck “so many people were amazed at what they were seeing, they were honking and flashing their lights at us, they must have thought we had some kind of new Air Force spy plane.”

The Aero Telemetry XF-11 was a very fast airplane and it had just enough fuel to run for approximately 20 minutes. Due to the substantial flight envelope it was critical that the uplink control system was reliable and trustworthy.

The heart of the Radio Frequency (RF) system consisted of a commercially available radio coupled to the bulletproof Aero Telemetry uplink command and control system. Joe said, “our ATC uplink system was absolutely critical in the success we had at keeping the XF-11 in-control at all times during the flight, especially in the crowded airspace around Los Angeles,” he added, “we never had so much as a glitch at any point during the flights.”

For this flight, Joe decided to call on the piloting skills of Bill Hempel. He had experience flying heavy twin-engine drones for the military. It took real skill and teamwork to concentrate on flying the airplane while so much activity was going on around them and Bill’s professional demeanor had a calming effect on Joe. Also, due to the complexity of all the systems on the XF-11, Joe decided to simplify responsibilities during the flight by adding a separate control uplink for all non-flight critical items such as landing gear and gear door operation. As co-pilot and flight engineer, Joe handled those.

The first flight was dramatic as usual with the XF-11 taking every bit of an 1800-foot runway to get airborne. With the chase helicopter in close pursuit, the XF-11 carefully found its way into the overcast sky that morning, making history on several levels but certainly as one of the largest and heaviest scale model aircraft to ever fly.

The plane flew extremely well for its first flight and considering all the pressure on the flight crew it was a real accomplishment. After a few touch-and-go’s and low passes for the ground cameras it was finally time to come home. Bill set up for a perfect landing with wings level. The historic XF-11 settled in and once on the ground it continued on quite a ways from the forward momentum. A tremendous cheer went up from the hundreds of personnel who had just witnessed the amazing flight.

A real sense of achievement and pride were apparent on the faces of the Aero Telemetry team members present. “We knew what we had just done was one for the record books,” said John Keefe, “the plane flew perfectly and did exactly what they wanted it to.”

The second flight of the day went well and the plane performed on cue. Following close directions from the helicopter pilot, Billy guided the XF-11 through its paces flawlessly. Just before the order to land, Joe requested an impressive full-power wingover. In what was to become its’ signature maneuver, the big XF-11 was brought out of a diving left hand turn and the engines increased to full power with the wings just feet from the ground. “It was a spectacle to behold as the big plane thundered past us,” said Roger Thornton, who was watching from a large airplane hanger nearby, “It looked so completely real that everyone here was cheering wildly as the XF-11 started its turn-out and soared upward! It’s a moment that I will never forget.”

It was indeed a moving moment for many of the flight crew when the XF-11 finally landed and came to complete stop.

According to Bok, “There was an overwhelming necessity to collapse from the fact that several of us had been awake for more than 40 hours for the second time in the same week preparing for this flight, making sure it would be perfect for The Aviator people,” continued Bok, “that coupled with an overwhelming feeling of accomplishment for what we had just done and a tremendous feeling of relief knowing that the flight had been performed safely and successfully. It was positively spectacular to be able to bring to life something as magnificent as the XF-11 and have it flown in such a way that the plane really appears to be the manifestation of the real airplane and Howard Hughes himself….it was brilliant.”

February 29th, 2004, Film Flights XF-11, Catalina Airport

As fate would have it, the weather conditions and lighting on the day of the first XF-11 flight in November would preclude the use of any of the film footage shot that day. It was decided to try and get some shots of the XF-11 which included some “over-water” flying that more closely resembled the Los Angeles area and coastline as it looked in the 1940’s when and where the original one would have flown. Joe Bok suggested Catalina Island Airport as a flying location, since he had flown there several times as a full-scale pilot. “It was remote and provided an excellent background with outstanding ocean views, plus it was safe.”

Many changes were being made to the XF-11 for its next flight at Catalina Island. New paint was applied, pitch sensitivity issues were addressed, engine horsepower was increased, an Aero Telemetry downlink system was added, and the Aero Telemetry RF uplink control output maximized to accommodate the increased flight envelope and extended range at the Island. According to John Keefe, “Flying out over that stretch of ocean and rugged mountainous terrain at Catalina left us zero margin of error, any mistake out there and the plane and everything on it would be gone forever.”

The Aero Telemetry flight crew had the XF-11 ready to go at first light on Sunday morning. After the plane was rolled out of the hanger and onto the runway, the engines were warmed up and the XF-11 was ready for the first flight of the day. Wind direction and meteorological conditions were confirmed with the weather station at the island. It would be a perfect day for flying. Meanwhile the director and movie crew waited for the right lighting conditions before giving the OK for take-off. As the clouds and sun fought it out to see who would win, the Aero Telemetry flight team stood at the ready. Finally at about 9:00am Bok’s order to “take-off” rattled through the headsets and the engines were started. Take-off would be to the east end of the Island over the ocean and a 1000-foot steep drop-off the end of the runway.

With the film helicopter in close pursuit the XF-11 began its roll down the runway and into another chapter of aviation history. The plane climbed steadily upward and into an oval pattern out over the Pacific Ocean and high above the 26-mile mountainous expanse of Catalina Island. Right away Bill discovered that due to the increased power from the engines, the XF-11 was now able to operate at a lower throttle setting.

The XF-11 responded perfectly and once the cruising speed was established the cameras started rolling. “The director shouted “action!” and for the next 8 hours that is exactly what we had!” says Bok, “our XF-11 performed very well under the conditions up there at Catalina”.

The Aero Telemetry XF-11 made several flights that day and flew over several miles of scenic ocean coastline and rugged mountainous terrain. The helicopter camera got great footage and so did the film cameras on the ground.

As a dramatic maneuver on the last flight of the XF-11, Bill brought the plane around in a shallow dive towards a position below the runway off the west end of the Catalina. He kept the plane just about 20 feet off the side of the steep slope while flying at full power directly towards the film cameras located at the edge of the cliff. Approaching at high-speed and at roughly ground level the sight of the tremendous XF-11 made everyone brace themselves. Some people even crouched on the ground in anticipation of the rapidly approaching behemoth. All eyes were glued to the shadowy figure homing in on the cameras and the crowded crew flight station.

Tom Bok, who was helping with flight operations said, “The big XF-11 came over our heads so close - moving so fast that you could hear the air moving out in front of it. The entire area just shook around us. Because of the tremendous noise coming from the engines, airframe and propellers, it really looked and sounded like the real thing.”

“The platform we flew from was turned around and we headed back to position at the beginning of the runway so the pilot would have a better look." said Tom. " The last landing of the XF-11 was right on the white line of the runway, Bill even kept the nose-wheel off until the wings stalled; it was picture perfect.”

Joe said:

“The entire Aero Telemetry flight crew was proud to have accomplished this last mission with the Hughes XF-11 on Catalina.”

“In terms of the movie, our work on The Aviator was groundbreaking. By delivering safe, reliable, and convincing scale model airplanes on schedule and within budget I know we provided The Aviator with the best possible and most cost effective solution to delivering special effects that are really believable by and credible with their audiences."

“The proof is in the movie and in the rave reviews for the flight sequences. People need to go see the movie and try to see if they can tell the difference between our models and the real thing…” says Bok, “I’ll bet you can’t tell the difference!”

(Editor's note: Next month, find out how Joe Bok and the Aero Telemetry team designed, built and flew the world's largest flyable scale model of the legendary Hughes H-4 Hercules (Spruce Goose) and seven other World War I airplanes for the Hell's Angeles scene for Martin Scorsese's The Aviator.)

Note: Where applicable, excerpts of the article reprinted with permission from Model Aviation and the Academy of Model Aeronautics.


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