Aircraft Design Changes

ThunderStruck mk2ThunderStruck Design on the “Fly”

We now have 2 major changes to the ThunderStruck aircraft. The first is shown in the image to the right. Winglets. The second is a square-ish cross-section to the fuselage rather than a round fuselage – this is under consideration to aid in landing the craft.

The image to the right still shows the aircraft with a round fuselage, but it is obvious that we will miss out on some lifting ability from the body at landing by making the fuselage round. A flat surface on the underside if the craft will provide more lift at the right angle of attack.

winglet_effect_Winglets

The image right is from Wikipedia:

Line drawing of wingtip vortices behind a conventional wingtip (on the left) and a blended winglet (on the right).

This is important as it reduced the vortices behind aircraft that cause so many dangerous incidents at airports when aircraft get too close to each other. It also reduced drag and thus efficiency in aircraft.

The ThunderStruck craft will certainly use the winglets to reduce drag by reducing vorticies, but this will have no impact at supersonic speeds because we will be using symmetrical wing. Normal wings have a flat bottom and a rising leading edge and a trailing edge on the top surface.  This makes the air flow faster over the top compared to the steady flow over the bottom. This reduces the pressure on the top pushing the wings up. This would be nice for the cruising stage after the dive, but bad for holding the craft in a supersonic dive. Any air flow over any asymmetrical surfaces may produce drag or lift that could pull the craft out of a supersonic dive early. The effects could be catastrophic.

Many high altitude model aircraft dropped from high altitude balloons (usually illegally) follow a roller coaster ride due to the thin air and lift in the wings. We don’t want that so the wings will be symmetrical – no lift. We do not need them for the supersonic dive. What we also need is symmetry in the aircraft at any cross-section, vertical or horizontal. The closer to total symmetry, the more likely that ThunderStruck will reach speeds of near 2,000kph. So if we have winglets, they need to extend top and bottom.

So Why the Winglets?

Simply we need wheels. The winglets hide the wheels and any need to lower wheels for landing. We may use a retractable wheel for the front, but not the rear wheels.

The Winglets will also house twin rudders, making a dedicated rear stabiliser (top and bottom) unnecessary. The rear cross-section looks like the picture below:

ThunderStruck Cross-section

Lifting Body (at Landing).

In the cross-section above the flat surface of the lifting body is obvious. This will only be important when landing as the craft assumes a significant nose down attitude during the gliding phase. Since we have no lift from the wings, the craft needs strong elevators to redirect the airflow at the rear of the aircraft to keep control. We will stay aloft by having speed due to a high angle of attack (nose down). Large elevators will keep the aircraft flying at this high angle of attack. It will be a poor glider – but so was the space shuttle – for different reasons – more to do with the delta wing configuration. A round fuselage cross-section would not aid the lift of the craft at landing. A square fuselage will increase the drag as the surface area is greater, but it will help fly the craft at lower speed when landing. It will have little effect during the glide phase. We may add canards to the front of the craft to increase the lift at the front during low speed flight, but they will pop out after we go subsonic. Delta wing craft work well at supersonic speeds, but are poor performers at low speeds. In the picture at the top of screen, the craft does not have a supersonic spike. We will need this for the Transonic tests, but not for return from a sounding rocket or re-entry from orbit.

Below is a closer look at the Winglets. We have yet to show the square cross-section in an image, since this is still under test. It is felt that the flat surface will help drive a higher pressure under the craft (between the ground and the craft) allowing it to land at a slower speed. This is a form of “ground effect” making the need for a long runway important to drop off speed until the effect lessens and the aircraft eases to the runway. Tests may find little difference in the landing speed and thus we may revert to a cylindrical fuselage. Time for some wind tunnel testing.

ThunderStruck mk2 closeup

 

One comment on “Aircraft Design Changes

  1. It was mentioned on our Facebook page that the design is looking like a small version of the B-70 Mach3 craft. 2 were built by the US and tested as fast bombers. The project was abandoned and one craft survives in a US museum. (Not shown in this image are the pop-out canards that will have lift).

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