It would be difficult to find a more unique or odd-looking machine than the Italian Stipa-Caproni experimental aircraft. The plane, with its barrel or tube-shaped fuselage, was an experimental prototype model that made several successful flights. As strange as the Stipa-Caproni was, it might be possible to call it the first jet aircraft.

Design Based on Venturi Effect

In 1927, Italian aeronautical engineer Luigi Stipa was interested in improving aircraft performance. He devised the idea for his barrel-shaped aircraft based on his knowledge of the venturi effect. This thermodynamic principle states that the velocity of fluid will increase and its pressure will decrease when it flows through a constricted section of a pipe or tube.

Stipa speculated that a plane using the venturi effect in its design would be able to fly faster and with better performance than other aircraft flying at that time. He built a small-scale working model and tested it in a wind tunnel between 1928 and 1931. Based on these tests, he made some modifications to the design and concluded that it would be feasible to build and test a full-size model.

Support for Prototype from Italian Government

To do so, he needed to gain support for his design, which some called the Flying Barrel. In July 1933, he published his findings and data on the aircraft in the Italian Revista Aeronautica journal. Next, he contacted the Italian Ministry of Aviation, asking for help to build the prototype.

The 1930s was a time of much innovation and experimentation in aircraft designs. The Italian government was especially supportive of researching and testing new aircraft. General Luigi Crocco, director of the Air Ministry, saw potential in Stipa’s design and approved the project.

The next step was to build a working prototype. From the beginning, both the Air Ministry and Stipa only planned to use the prototype to test his concept for the aircraft. They knew there would likely not be any further development or additional models. Also, Stipa stated he felt the design would be best suited for larger aircraft such as bombers and cargo carriers.

Stipa-Caproni Had Unique Design Features

A key design feature was for the fuselage to have two large wooden rings and a series of smaller rings acting as spars. Horizontal ribs connected the rings, forming the basic shape. The large rings became attachment points for the wings and cockpit. Fabric covered the wings and fuselage. Metal braces and steel wires connected the wings to the fuselage.

Stipa positioned the tail so the slipstream from the tube would impact the control surfaces, hoping to improve flight performance and maneuverability. The aircraft had three landing gear, two in front and one in the rear.

Stipa and the engineers at Caproni installed a 120 HP de Haviland Gypsy III engine inside the tube and suspended it by stiff metal bars. The propellor was also inside the tube.

Stipa included the dimensions for his design in his initial report. It was to have a wingspan of 46.92 feet, a length of 19.8 feet, a height of 10.63 feet, and a wing area of 204.5 square feet.

He also planned for it to take off with a weight of 1763 pounds and require a takeoff and landing run of 590 feet.

First Flight of Stipa-Caproni Mostly Successful

They contracted with the Caproni aircraft manufacturing company from Milan Taliedo to build the prototype, and they completed it in October 1932. Two pilots took off in the Stipa-Caproni for the first time that same month. Their initial review was that it “flew without any major issues.”

During that first flight, the Flying Barrel experimental aircraft reached a maximum speed of 83 mph and reached an altitude of 9842 feet, although it took 40 minutes to get that high.

The pilots also reported the elevator, positioned in the slipstream, worked  “excessively well,” producing sudden changes in pitch. Interestingly, they also said the rudder was very stiff, requiring considerable force to move the stick.

Doubts About the Future of Design

After the first one, they conducted several other test flights. So, with proof that the Stipa-Caproni could fly, the Italians had to decide what to do with it. After reviewing the flight data, the Air Ministry concluded that the aircraft “did not exhibit superiority over conventional designs.”

It was, in fact, slower than similar-sized aircraft. Stipa, however, had predicted this when he first designed it, repeating that it was better suited for larger aircraft. His initial report discussed a future with larger aircraft powered by multiple tube-shaped fuselages. He even included images of what these designs might look like.

Eventually, the Italian Air Ministry lost interest in the Stipa-Caproni experimental aircraft and scrapped the design. Later, in 1935, the French government showed some interest in the plan and purchased a license for it. They discussed building a two-engine variant. However, they gave up on the idea after some basic design work.

Similarities With Modern Turbofan Engines

Some have noticed that the tube design of the Stipa-Caproni was basically the same as that of turbofan engines on modern aircraft. The major difference is that modern engines have turbojets instead of piston-driven engines.

Aaron Spray of SimpleFlying.com has referred to the Stipa-Caproni as “nearly the first jet.” Others have called the aircraft a type of proto-jet engine, and there are similarities.

Possible Link to German Design

It is a bit ironic that several years after the Stipa-Caproni flew, Italy became an ally of Nazi Germany in the Second World War. During the war, the Germans deployed the first jet aircraft in combat, the Messerschmitt Me 262A Schwalbe. While Stipa was not involved with the Me 262, he suggested the Germans used his designs.

He went as far as claiming that the Germans stole his idea for the Stipa-Caproni and that the pulse engines on the V-1 flying bomb violated his in-tube propellor patent. According to some reports, he felt his work was overlooked and remained bitter about it for the rest of his life.

That wasn’t the end of the Stipa-Caproni story. In 1996, aviation enthusiast Guido Zuccoli began working on a small-scale replica. He passed away in 1997 before completing it. Another owner took on the project and finished it in 2001. One of the differences in this model was a different engine, a 72-hp Simonini racing engine. They made several flights in the aircraft. Today, it is on display at an exhibit in Toowoomba, Australia.

Australian aviator Sidney Cotton was known for developing innovative aerial reconnaissance methods and equipment before and during World War II. He also lived an adventurous and nontraditional life, never being one to accept authority. What some don’t know about Cotton is that author Ian Fleming based his character of James Bond on Cotton.

Sidney Cotton Begins Flying in World War One

Cotton was born on 17 June 1894 in Queensland, Australia. His ancestors had faced several betrayals from the British and Russian governments, which led them to move to Australia. Based on these experiences, Cotton may have learned the concept of challenging authority at an early age.

Cotton’s first experience doing things his way was in 1914, at the start of World War I. His father told him he could not join the war effort with the Australian Imperial Force. In 1915, following the German sinking of the RMS Lusitania, Cotton enlisted anyway and headed for England.

Always looking for adventure, Cotton signed up for pilot training with the Royal Naval Air Service at Chingford Aerodrome near London. The unit was training on the French Farman Longhorn, a 1912 model reconnaissance and training plane. It had a Renault 51kW and flew at a maximum speed of 56 miles per hour.

Cotton Makes First Solo Flight with Almost No Training

In Cotton’s autobiography, Aviator Extraordinary: The Sidney Cotton Story, he describes his first solo flight.  His instructor mistakenly thought Cotton had enough training to be ready to solo. With almost zero experience and training, Cotton climbed into the cockpit.

“It was make ‘em or break ‘em alright,” wrote Cotton. “There was nothing I could do but open the throttle and go to my death.”

Cotton completed the flight and landed safely. He enjoyed it so much that he wanted to take off again that same day.

Sidney Cotton’s First Invention

During the war, he flew aerial reconnaissance patrols over the English Channel and bombing missions over France and Germany. During these war patrols, he also developed his first invention, the “Sidcot” flying suit, to keep pilots warm. The Sidcot was a one-piece cotton outer liner with a rubberized inner liner. According to some reports, the famed German pilot Baron Von Richthofen, the “Red Baron,” was wearing a “Sidcot” when he was shot down. There was no proof regarding whether he got the suit from a downed British or American pilot or another source.

In the years following the First World War, Cotton continued to fly and also started several businesses. Some succeeded, and more failed. He became interested in aerial reconnaissance and, in 1933, purchased part of a company called Dufaycolor that produced color prints. After some initial success, he got into trouble for unpaid British taxes and needed money. Also, during those years, he divorced his first wife and gained a reputation as someone often seeking casual affairs with women.

Secret Aerial Reconnaissance Missions During Buildup to World War II

A new opportunity came to Cotton in 1938. As the UK saw the growing threat from Nazi Germany, they needed photographs of German installations and troop movements. Fred Winterbotham, Chief of British Air Intelligence, asked Cotton if he would perform aerial photography for them. This arrangement would include giving him the use of a plane, a 1936 Lockheed 12A Electra Junior, and a large budget to cover his expenses.

The plane is an eight-seat, six-passenger twin-engine transport aircraft designed by Lockheed for small airlines, companies, and wealthy individuals.

Cotton immediately accepted the assignment. His mission was to pose as a civilian photographer and secretly fly to and from Germany, taking photographs. For the next two years, he flew all over Europe, focusing mainly on photographing German and Italian operations.

Cotton Customizes Plane with Cameras

Once Cotton received his plane, he customized it for his secret missions. He installed two cameras in the plane’s belly and others in the side windows. He also said he put cameras in the wing leading edges. Constantly innovating, Cotton also modified the plane to direct warm air at the camera lenses to prevent fogging.

Some of the cameras were mapping designs that provided images of German territories. Despite some inconsistent reports, Cotton provided a very useful service to the UK military. According to some accounts, his work may have saved thousands of lives.

Outrageous stories from Cotton

Cotton also told several outrageous stories about his aerial reconnaissance missions. He claimed to have taken Luftwaffe Chief of Staff Albert Kesselring on several flights. According to Cotton, while Kesselring was preoccupied looking outside the plane, he reached under his seat and secretly operated the cameras. Cotton added that this allowed him to photograph key German positions like the Siegfried Line.

One verified story is that Cotton was in Germany in the days before the beginning of the Second World War. He was about to fly Nazi Party leader Herman Goring to England for negotiations, but the Germancanceleded the plan. Cotton made the last flight out of Berlin before the war started.

Stories like this helped give Cotton the reputation of a somewhat unconventional aviator willing to take risks. They also created some doubts. In 1940, a German parachute bomb struck the hangar in Heston, UK, containing Cotton’s plane.

Renovations Cast Doubts on Modifications to Plane

The plane ended up in the United States for repairs and renovations, and it still flies today. During the renovations, crews discovered things that cast doubts on some of Cotton’s stories. For example, he claimed that the belly cameras sat under the floor, unseen by passengers. Crews discovered this was impossible due to the size of the cameras.

Cotton had also stated that he had installed windshield wiper motors that could uncover the cameras in the wingtips during flight. Again, this was not true. There were no motors or even mounts for any cameras or components to open covers. In fact, Cotton would have had to open the covers manually before flight, which the Germans would have seen.

Cotton Assumes Command of Photographic Unit During the Second World War

Once the war began, Cotton took command of the RAF Photographic Development Unit. It had his Lockheed Electra and four Spitfire fighters. Along with the Electra, Cotton fitted the fighters with cameras, and they achieved some impressive results. On one aerial reconnaissance mission, the Spitfires flew at 30,000 feet and photographed 400 German tanks parked under trees and other camouflage.

In the first few months of the war, the Royal Air Force lost 40 aircraft while trying to photograph 2500 square miles in Europe. At the same time, Cotton’s Spitfires photographed over 5000 square miles with no losses.

Despite Cotton’s successes, he never handled authority very well. Some called his unit the “Cotton Club,” and a memo from that time referred to it as “a law unto itself.” In 1940, the RAF relieved him of his command, and he resigned his commission.

Inspiration for James Bond

One of the most interesting parts of Cotton’s wartime experience was his friendship with author Ian Fleming, creator of James Bond. Fleming was a naval intelligence officer at the time. He later credited Cotton as one of his inspirations for James Bond. With Cotton’s strong interests in adventure, gadgets, and women and his disregard for authority, this is not surprising.

On the front of Aviator Extraordinary, Cotton includes a quote from Henry David Thoreau, which provides a clear hint regarding his personality: “If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music that he hears.”

Beginning in World War II, air forces around the world have been interested in developing human-carrying external pods for aircraft. These ideas have ranged from advanced concepts, such as pods designed for modern aircraft like Harrier Jump Jets and Apache Attack helicopters, to simple ideas like bags strapped to airplane wings.

One key reason for developing external pods for military aircraft has been to rescue downed pilots and wounded service members. Other possible missions include transporting special forces personnel, spies, and support personnel like crew chiefs and relaying others between locations.

Weight of Human-Carrying External Pods No Problem for Fighters

Fighters are actually well-suited for these tasks. They often carry external fuel tanks and ordinance that weighs more than pods containing people. If pods or containers have aerodynamic shapes, the fighter’s performance will not be impacted more than those carrying tanks or missiles.

EXINT Pod System Designed for Harriers and Apaches

One of the most modern external pod designs is the EXINT system, which was designed in the late 1990s by the British company AVPRO UK Ltd. The company developed the human-carrying external pods for British Sea Harrier GR5 fighters and AH-64 Apache helicopters. The pods were intended for special forces insertion and extraction missions and for transporting wounded personnel.

AVPRO UK initially made the pods 13 feet long and could carry two people, along with medical and other equipment. The pods had oxygen and heating systems, which enabled use at high altitudes and speeds. In addition, they had parachutes and a satellite-assisted rescue system. Following testing. The company converted the EXINT to a one-person design.

Despite some success in testing the EXINT pods, they never made it into the British inventory; however, they are still certified for Israeli AH-1 Cobra attack helicopters. There were some significant problems with the design.

People Inside Pods Experience Extreme Decibel Levels

The underwing pods were exposed to extremely high noise levels from the Harrier’s Rolls Royce engines. When close up, they produce 165-170 decibels. Besides hearing loss, exposure to extremely loud noises can damage the heart, raise blood pressure, reduce concentration, and affect other cognitive functions.

The pods’ position in relation to the center of the fuselage exposed them to very high G forces and other effects while flying at Mach 1.

British Spitfires Carried People Inside Bags Strapped to Wings

During the Second World War, the U.K. considered carrying people externally on aircraft. Their first version of a human-carrying external pod was the “Spitfire Body Bag.” This was a canvas bag, similar to a sleeping bag, that could fit one person. Two straps attached the bag to the cannon and wing trailing edge. Aircraft with the bags installed could not maneuver as sharply as they normally could.

The idea behind the “body bags” was to transport squadron personnel to remote locations that lacked maintenance or support facilities. While the U.K. considered using them during the D-Day invasion, there’s no record of them being used in actual missions.

American Mounted Human-Carrying External Pods on P-38s

The Americans also experimented with their own version of human-carrying external pods on the P-38 Lightning. They developed modified drop tanks to carry people under the wings. These pods had a plexiglass nose cap.

On 13 and 15 June 1945, US Marine Corps Photographer David Duncan climbed inside the modified drop tank of an F-5, the reconnaissance variant of the P-38. He took photos of USMC Corsairs attacking Japanese positions on Okinawa. Later, he wrote that the pod had no air vents and was “very uncomfortable.”

Russian Pods Could Carry 16 People

In the 1930s, during the Spanish Civil War, the Russians tested their own versions of human-carrying external pods. They designed paratrooper compartments that hung under the lower wings of Polikarpob R-5 biplanes. There were four compartments, each carrying four paratroopers.

The Russians found that the pods created excessive drag, so they added an additional wing below the pod. The increased drag from the pods lowered the plane’s speed from 124 to about 81 piles per hour.

During World War I, the Russians fitted pods under the wings of their Polikarpov Po-2 aircraft. They devised a very unusual or radical mission profile. Once the planes reached a planned destination, they descended to a very low altitude, and soldiers exited the pods without parachutes and aimed for the deepest snowdrifts they could see.

Germans Also Tested Their Versions of Pods

The Germans also tested pods on the Ju-87D-3 Stuka bomber. These pods carried two people, one in front of the other. The pods could be launched in flight and descend under parachutes. Like most other designs proposed by other nations, the German concepts never made it into production.

Most recently, British and Israeli air forces devised a much simpler method for carrying personnel externally on Apache helicopters. This technique is to seat people on the Apache stub wings with seatbelts securing them. British Apache crews used this method several times in Afghanistan to carry wounded soldiers.

The US Army has recently made a significant investment in the development of an ultra-STOL (short takeoff and landing) aircraft. Under development by Electra, the aircraft has a hybrid-electric powertrain, power, and propulsion system. The design has several unique features and capabilities that promise clear advantages over other short takeoff and landing aircraft.

Electra Receives $1.9 Million to Develop EL9 Ultra-STOL Design

On 1 July 2025, Electra received a $1.9 million Small Business Innovation Research (SBIR) contract from the US Army to research and develop hybrid-electric powertrain, power, and propulsion systems (HEPPS). This agreement allows Electra to develop and test its EL9 ultra-short takeoff and landing (Ultra-STOL) aircraft design.

“This work gives the Army a clear path forward in understanding how hybrid-electric technologies can support real operational demands while enabling entirely new logistics capabilities,” said Donn Yates, Vice President of Government Programs at Electra.

Aircraft Will Have Eight Electric Motors Mounted on Wings

Electra is currently flight-testing its EL2 Prototype. It has eight hybrid electric motors and propellers mounted under and just forward of its high wing. The EL2 can carry just two people in the cockpit, while the larger EL9 can carry nine passengers.

The gross weight of the EL2 is 3,100 pounds. Electra plans for the EL9 to be able to carry more than 1000 pounds over 1000 miles.

EL9 to Takeoff in Less Than 150 Feet

Perhaps the EL9’s most impressive feature will be its ability to perform takeoffs and landings from airfields of less than 150 feet, which is shorter than a soccer field.

“Electra’s hybrid-electric ultra-STOL aircraft redefines what is possible for Army aviation with its ability to operate from small, rugged sites, reduce fuel demand, and increase flexibility for the commander,” said Yates.

Blown-Wing Technology the Key to Ultra-STOL Performance

A feature known as “blown-wing” technology will give the EL9 its Ultra-STOL performance. Blown-wing, or blown-lift, is an aerodynamic effect produced by accelerating air over the top of a wing. The electric motors move the air much faster over the top of the wing than air moving under it. This feature produces lift at much slower aircraft speeds than standard designs.  With this configuration, the aircraft doesn’t have to rely on its forward speed alone to generate lift.

The electric motors, smaller and lighter than other powerplant types, make the blown-wing effect feasible. The idea of blown-wing technology came about in the 1960s, but it required shafts or ducted gas linked to turbine or piston engines to produce the airflow over the wing. These ideas were complicated and expensive, requiring extensive design modifications. These early concepts never made it past the prototype or low-production stages.

Electra tested this concept in a wind tunnel on a scale model 20 percent the size of the EL9. The company found that the blown wing lift was seven times as effective as an unblown wing.

EL9 to Be Quieter Than Traditional Designs

Another advantage of the Electra Ultra-STOL design is that it will be very quiet. Electra recently tested the EL2 and found that it produced about 55 decibels flying at 500 feet, while a conventional turbine-powered aircraft puts out 75 decibels. A quieter aircraft could be valuable to the Army for quiet intelligence, surveillance, and reconnaissance (ISR) missions.

Electra Ultra-STOL Aircraft To Generate Electricity in Remote Locations

A unique feature of the Electra EL9 Ultra-STOL aircraft, which could be especially important for the Army, will be its ability to function as an electricity power source when operating from remote or undeveloped locations. The EL9 will serve as a generator, producing more than 600 kilowatts of continuous power and even more than 1 megawatt for short bursts. This onboard capability will allow it to recharge mission-critical equipment like communications systems and drones.

The US Army is not the only organization interested in the Electra EL9 Ultra-STOL aircraft. Electra already has over 2,200 pre-orders for the EL9 from more than 50 customers worldwide. Customers are considering a variety of uses for it, such as medical evacuation (MEDEVAC) and casualty evacuation (CASEVAC).

Electra is planning for its first test flights of the full-scale EL9 in 2027.

There was a Spirit Airlines foam party in Detroit on Independence Day, and we weren’t even invited. 

A malfunctioning fire suppression system turned a routine evening at Detroit Metropolitan Wayne County Airport (DTW) into a frothy spectacle, flooding a maintenance hangar and its surroundings with corrosive foam. This was undoubtedly one July 4th celebration Spirit Airlines didn’t plan for, although we’re sure there were fireworks in CEO Dave Davis’ office that night. 

Cloudy with a Chance of Foam 

On the evening of 4 July 2025, a thunderstorm rolled through Detroit, and it seems Mother Nature had a mischievous streak. Around 1700 local time, a lightning strike is believed to have triggered the fire suppression system at one of Spirit Airlines’ primary maintenance facilities at DTW. 

Instead of dousing flames as intended, the system unleashed a torrent of foam, blanketing the hangar and spilling onto the tarmac. It is unclear whether the 126,840-square-foot facility’s hangar door was open throughout the debacle or if Spirit Airlines personnel opened it to let the foam spill out. 

First responders, unaware that there was no fire, rushed to the scene, ready to battle a blaze, only to find no flames—just a sea of Spirit Airlines foam engulfing everything in sight. The scene was less “Top Gun” and more “Ghostbusters” meets a bubble bath gone wrong. 

Foam’s Corrosive Conundrums 

Fire suppression foam is a lifesaver in aviation, designed to smother fuel-based fires, cool hot surfaces, and prevent reignition. It is composed of water, foam concentrate, and air, which combine to form a thick, flame-choking blanket. 

The foam is corrosive and can damage aircraft engines, avionics, wiring, metal, and even cabin interiors. Older formulations, like PFAS-based foams, can degrade materials and contaminate the environment, making cleanup a race against time. 

While a common practice in the early days of aviation, the use of foam in aviation, particularly to coat a runway before an emergency landing, has largely disappeared in recent decades. This article explains why. 

Five Spirit aircraft–two inside the hangar (an Airbus A320 and an A321) and three parked outside–were caught in the foamstorm. A fourth Airbus on the ramp escaped unscathed. 

Following the incident, Spirit Airlines issued a statement, claiming that operations would not be affected:

Whether that’s true or not remains to be seen. However, the removal of three aircraft from service is significant. The airline operates a 195-aircraft all-Airbus fleet and is already facing operational constraints due to Pratt & Whitney engine issues, compounded by the busy summer travel season. The foam’s corrosive properties could lead to extended downtime for inspections and repairs, as it risks damaging critical components and creating environmental concerns. The carrier has not indicated a potential dollar amount in damages, but it is likely to be significant. 

Cleaning Up the Bubbly Mess 

By 5 July, first responders and cleanup crews were hard at work, battling the Spirit Airlines Foam Flood of ‘25 to minimize damage. The foam’s ability to seep into sensitive components like engines and avionics means every minute counts. 

It is worth noting that this incident is not unique to Spirit. In 2020, American Airlines experienced a similar mishap at Chicago O’Hare International Airport (ORD), where two Boeing 787s were coated in foam due to an accidental fire suppression system activation. Other airlines have faced comparable sudsy sagas, too, proving that hangar foam parties are an occupational hazard in aviation. 

For Spirit, this Fourth of July was less about fireworks and more about fighting foam—a celebration they’d rather forget. Now, it’s all hands on deck to clean up the mess and hope the damage isn’t as bad as it looks.