Last March 21st theOffice of Scientific Research (AFOSR) of the US Air Force launched its project Boundary layer transition and turbulence (BOLT II). The aim of the initiative is to create a jet powerful enough to make hypersonic travel a reality.
The flight test was recorded by NASA with the aim of obtaining concrete data on the difficulties of the hypersonic flight.
The company has been working for years on developing a vehicle powerful enough to travel at hypersonic speeds. Above all, NASA aims to build a lightning-fast passenger jet, capable of moving from one point to another in a short time. Vehicles such as the Dragon capsule of SpaceX and intercontinental ballistic missiles have demonstrated that reaching these speed levels is possible. Scientists just need to figure out how to insert humans without causing harm.
Imagine what kind of revolution passenger jets would face. Flight time would be dramatically reduced, making travel easier and accelerating everything.
Christopher James, NASA engineer
The problem of hypersonic travel
Despite the fascinating possibility of accessing the world of hypersonic travel, many airlines have faced many technical problems. Creating vehicles that are so fast and, at the same time, accessible for passengers is not that simple.
Secondo Scott Berry, one of the collaborators of the project BOLT II, the main problem is to predict the “boundary layer transition position”.
What is it about? During a flight, a thin layer of air wraps around the vehicle, moving with it. This “boundary layer” is very important, because it plays a fundamental role in identifying the drag forces that slow down the vehicle.
The boundary layer has one thickness different throughout the vehicle. Its flow tends to be "laminar" in the upper area, and "turbulent" at the base. When it is laminar, the layers of air flow past each other in parallel without incident. Conversely, when the flow is turbulent an increase in flight drag may occur. In hypersonic travel, this drag would increase further, because the vehicle travels at a higher speed and “displaces” more air.
The goal of BOLT II scientists is to predict the position of the flow; predict when it goes from “laminar” to “turbulent”, minimizing the risk of turbulence.
Dr Sarah Popkin, AFOSR High Speed Aerodynamics Program Manager, explained: “Turbulence can cause heat to evolve over almost the entire surface of the vehicle. This means that you need to be able to protect the vehicle's internal system from heat and, at the same time, be able to predict turbulence associated with heating. Heat is the mother of all problems for hypersonics”.
New designs for hypersonic vehicles
Hypersonic travel is difficult to manage and design. As expected, to be able to predict turbulence, it will be necessary to carry out several more flight tests. The first BOLT flight test was launched in June 2021 byEsrange Space Center, in the north of Sweden. Unfortunately, it failed due to problems with the launch mechanism. The error, however, allowed us to create a more precise model: the BOLT II.
Christopher James, an expert from the University of Queensland, explained that the BOLT II has a complex geometry with a concave surface capable of facilitating the achievement of hypersonic speeds. The current fully autonomous vehicle is equipped with over 400 sensors needed to acquire data on the flow environment during experiments.
The launch was streamed on the YouTube site of Wallops. And it can be considered a success.
Meanwhile, China is also working to get closer to the goal of hypersonic travel. The space company Space Transportation has announced a bold plan for a hypersonic plane capable of flying from Beijing to New York in an hour. Scientists predict it will be ready for flight by 2024.
We'll see!
