Stability

Creating Stability Between Supersonic Dive and Subsonic Level Flight

Here is the problem. During the supersonic dive, the weight is ideally forward to ensure that, as an airflow is felt by the aircraft, the drag of the tail keeps the craft oriented in vertical dive. That is assisted bythe drag across the aircraft and a low centre of gravity near the nose. During level flight below supersonic speeds the centre of gravity must be further back and ideally between the wings.

Jet fighter design has all sorts of tricks to alter the centre of gravity (or appear to) to make he changes needed. This can be as simple as changing wing shape or even extend more wing during lower speed flight. Some aircraft even have had swung wings. It is hard to control the major variations between the lift and drag that changes dramatically between subsonic and supersonic flight. None the less they do not need the dramatic changes in the centre of gravity that we are engineering.

ThunderStruck will be essential a poor flier as we are, at this stage, proposing symmetrical wings. The problem is that nothing is perfect and even the subtle differences between the wings can give on more lift than the other and create spin. Because of Bernoulli’s law, you might have supersonic flow on the wings, nose, or any other curvature way before you reach Mach 1. Battling with supersonic airflow below mach 1 is difficult and de-stabilising. We will be experimenting with dropping light airframes with a camera at the nose. Before we reach controlled airspace, we will deploy our parachute and have a reserve one for safety. We will watch carefully to see the effects on stability.

The diagram below is one solution to moving the mass required for stable flight in both modes. The pump must be fast and the liquid must stay “thin” and not become viscus. We will need baffles to slow the sloshing around during the changeover. These divide the tanks into chambers with some small holes joining the chambers to allow them to fill.

Centre of gravity adjustment transitioning from dive to level flight

There are other solutions such as screw thread that will shift the battery and electronics forwards or backwards. Since the flight is short the transition only needs to be one way, the design is thus simplified. I am not a fan of shifting the battery and electronics around. It will take a large movement to have the desired effect and it could cause wired t break if they get caught on something. I personally favour pumping the fluid from forward to back as shown above. Moving it down during horizontal flight creates even more stability by creating dihedral effect between the wings on an otherwise symmetrical aircraft.

Dihedral in aircraft is the inclination of an aircraft’s wing from the horizontal, especially upwards away from the fuselage. in this case it is the centre of gravity that I am measuring it against and this indicates that the weight is below the wings and the aircraft will be easier to fly.

Below is another thought on using systems, but this time we vent the fluid without the need for a pump.

gravity does the work for us and we remove the liquid away from any potential problems within the aircraft. Making it lighter will also make it more controllable once out of the dive.

gravity does the work for us and we remove the liquid away from any potential problems within the aircraft. Making it lighter will also make it more controllable once out of the dive.

Whatever system we chose, we will be writing it up here. we need to fly the craft and we also have access to a wind tunnel for subsonic tests.

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