Dr. Iscold defies gravity and time in the Red Bull Plane Swap
What can you do in 45 seconds? Could you skydive between two planes that are in a 140 mph vertical dive, regain control, and avoid the rather final stop at the end?
That’s the premise of Plane Swap, the latest and perhaps craziest world premiere from the Red Bull Air Force aviation team, and 45 seconds really is how much time pilots have to do it. . It seems impossible, so Digital Trends spoke with Dr. Paulo Iscold, the engineer responsible for modifying the plane that will be used in the company, to make it a reality.
Slow down, not speed up
“It’s a pretty tough challenge,” said Dr Iscold, in what sounded like a serious understatement, before continuing with a laugh. “When Luke [Aikins, the Red Bull Air Force pilot who came up with the Plane Swap concept] put the problem in front of me, I thought, ‘What are we doing here?’
Iscold is exactly the type of person you want on this kind of project. Not only does he have a PhD in Mechanical Engineering, but he’s been designing and building airplanes since 2001. His expertise was evident in our conversation, as was his enthusiasm for Plane Swap and aviation in general. However, it is very different from what he has done before.
“My background is in racing planes and breaking records, but it’s the opposite, it’s about how we to slow down the plane. From an aerodynamic point of view, it was a challenge. When you see the big picture, it’s two people swapping planes during the flight and it’s very scary. But we don’t see that big picture, we see the little pieces that get us there. That’s what this project is, that’s how you make this crazy thing not crazy.
There are two main engineering challenges that stand out among all these small parts: the development and installation of a special speed brake and a custom autopilot system. These are the aspects that we explored during our conversation.
Do the speed brake
“When we first spoke I thought the speed brake would be much smaller than what we have, and I thought it would be on the wing like a glider,” Iscold explained, before smiling and added, “That’s probably why I said let’s do it because I thought it would be easy, then later found out it wasn’t!
The planes used are two Cessna 182s, and the speed brake is essential for the planes to have a controlled dive, not only to maintain the target speed of 140 mph, but also for stability. Although speed and air brakes are commonly used in aviation, from planes landing on aircraft carriers to the side of a SpaceX rocket when it lands, it’s uncharted territory here.
“It’s at least five times bigger [than what I thought it would need to be],” he explained. “I thought it would be 4 feet by 12 inches above the wings, and now it’s 6 feet by 5 feet and on the belly of the plane. It is attached to the landing gear and another hard point in front of the fuselage, and it uses hydraulic actuators to operate.
Although this is a large extra part added to the plane, it has been cleverly integrated into the body. “It’s a very clean modification of the plane, the landing gear works normally and we don’t need to cut or drill any holes. It simply attaches to it with a mounting point, and in 30 minutes the entire section could be removed and the plane would be back to standard.
Installing a giant flat structure at the bottom of the plane created some additional challenges. Iscold fixed the buffeting issue by adding holes to the speed brake, which allow air to pass through it and break up stability-threatening vortices, but an unexpected issue required a bit more work. He explained that the speed brake is actually made up of four pieces, and during the first flight tests, no matter how many sections were used, the aircraft would not pass a 70 degree dive, and it had to be at 90 degrees.
“It took a while to figure out what was going on, even with more test flights and simulations,” Iscold said. The team finally made a crucial discovery. “The speed brake has a low pressure area right behind it, and it turns the airflow. The tail of the plane is in that flow, and that was forcing the plane nose up. The two were fighting.”
The solution turned out to be simple (if you’re a mechanical engineer): “We created a space between the fuselage and the airbrake, so that the air passes through it, and this jet of air protects the tail from the flow of air. created by the brake.
Iscold compared this to the operation of the drag reduction system (DRS) on a modern Formula 1 car, where a section of the rear wing lifts up to reduce drag. On an F1 this increases top speed, but on Plane Swap aircraft it means that a 90 degree dive can be achieved safely and reliably.
Autopilot from a rocket
The speed brake is just part of what makes Plane Swap challenging. Since each aircraft will be left unattended for some time, the autopilot must take over. Normally a plane’s autopilot cares about keeping the plane level, but for Plane Swap it needs to do the opposite and maintain a vertical dive. Iscold explained that a normal autopilot is not suitable, as all his usual reference points lose their meaning in this 90 degree dive. The solution? “We went to the same system that rockets use, because they operate at 90 degrees.”
Once the system was chosen, the tight tolerances and pinpoint precision needed to make the plan successful had to be worked out, starting with the differences in speed and size of the objects involved. “Paratroopers fall vertically and can move sideways a little, but not much. It’s about 10 miles per hour. They are also subject to the wind and will move with it. However, in a plane going straight down at 140 mph, if you change the angle just four degrees, that’s already 10 mph horizontally. When the wind hits the skydiver, the surface level is small, but when it hits the wing of the plane, it is like a sail. This means that the autopilot must always be within three degrees of bank for the plane’s path to be stable enough for skydivers.
At this point, it’s also important to remember that there are two planes and two paratroopers who have to deal with all of this. “We have a formation flight and the two planes need to fly together, so you might think the natural solution would be to sync the two planes together,” Iscold told us. “We don’t do that. They are independent. We adjust them to behave the same, and when we do the dive the autopilot tries to maintain the correct pitch and heading. To prevent them from colliding, they dive in a diverging trajectory of a few degrees, but you won’t see this with the naked eye.
Because Plane Swap is a revolutionary company, there is no blueprint for aircraft design or set of guidelines to follow, which means there are always unexpected problems to solve. The day we spoke to Dr Iscold, the team had battled with one plane that behaved differently than the other. This was a surprise as the two planes are essentially identical.
“The blue plane dives straight down like an arrow to the ground. It’s perfect. The silver plane is a nightmare and never tracks properly,” Iscold revealed, adding that the two planes are exactly the same, at the except for a slight difference on the tail.
“We tried changing some things to replicate the blue plane, but that didn’t help,” he continued. “The team changed the size of the speed brake, and we noticed that if we reduced it a bit, the plane became more stable. Unfortunately, this makes the plane faster and it becomes more difficult for skydivers.
After further investigation, Iscold found the problem. “We knew that an airplane had a slightly different center of gravity, and what happens is when you’re vertical, the speed brake is like a parachute, and you want the center of gravity to be behind the parachute, if it’s on top it’s not stable so we play with that and it makes a difference It’s obvious when I say this but because the project is so big and so complex we we lost sight of it.
The silver plane was the first built, then the blue plane was developed to be identical. Problems like the one with the center of gravity are difficult to pinpoint, especially when flight testing is logistically complex, as a sufficiently large airfield is always required, along with the paratroopers and test equipment, and the fear that if something goes wrong, it could mean losing a plane. Solving problems takes time, and Iscold said it takes a steady, step-by-step approach to make things run smoothly.
45 seconds to success
Now that the complexity of the task is clear, let’s go back to that 45 second delay for skydivers to jump from plane to plane and regain control.
“Between the initial dive and recovery we have 45 seconds,” Dr. Iscold told us, but in reality that time gets even shorter when you break it down. “Paratroopers must operate all buttons and handles before exiting [of the plane], while they will lose about five seconds and they will need 10 seconds to recover,” he continued. “So they have 30 seconds to transition.”
So it actually only takes 30 seconds to parachute between two rapidly descending planes. However, although it seems far too short, Dr. Iscold is not concerned. “Now [that] we did a few test flights, I would say that’s a lot of time. To the point that if they miss the first, they have enough time for a second try.
Clever engineering and a passion for pushing the limits of what’s possible with an airplane suddenly made 45 seconds seem like a lot, at least to the two brave skydivers undertaking this thrilling feat.
You will be able to see the result of the hard work of Dr. Iscold and his team when the Red Bull Aircraft Swap takes place on Sunday, April 24. It exclusively streams live on Hulu in the US at 7 p.m. ET or 4 p.m. PT., and on Red Bull TV globally at the same time.