Lightning - delta wing

[fdr]

Originally Posted by nzhills

Hi
On the Lightning, does anyone know why Petter, (the designer of the initial LIghtning), go for what amounted to a delta with a notch taken out of it and a tailplane? Would much be gained from a Skyhawk or Mig 21 like setup, i.e. a complete delta with a tailplane? There’d be more wing area, the wing close to the root would be thicker thus giving more possibilities for undercarriage stowage and putting fuel in the wings and he could of added some sort of flap. Conversely by putting the notch into the rear of the wing the total drag would have been less in a turn than the unnotched one, (aspect ratio would be lower on the non-notched example and thus the induced drag would have been higher). What are your thoughts?
Mark

• The lightning did have flaps....
• the angled (swept) flaps are effective at high deflections, there is a vortex structure that develops due to the crossflow, and that is stable, and can increase CL at high flap deflection angles, where otherwise CL is only marginally increased, but drag increases... The flaps on the lightning are quite effective. The MiG-21 had a nice fowler flap design, the A-4 had a split flap which is OK for CL but comes with lots of drag. The Mirage, no flaps, the constraint of having a tailless delta.
• the aspect ratio of the notched delta was substantially greater than the other deltas, and drag at high alpha is far better. The notch still achieves a vortex lift at high alpha from a vortex formed immediately behind the LE, that gives a greater alpha capability than a straighter wing would have, common to all deltas.
• Petter designed a neat MLG that was a clean installation and which had an efficient structural mass fraction.
• fuel volume was restricted by the design, and that also misses out on wing bending moment relief, but the plane was built for fairly high g anyway, so the structural penalty of having fuselage fuel only for clean config is not that great.
• Having 2 big bunsen burners made the plane work for it's intended task, that of being a point defence interceptor, short range, rapid response, high rates of climb, and fair turn rates for operating inside an ADIZ environment. Similar brief for the MiG-21 and Mirage, but the 21 could do a fair ground attack, and the Mirage had some capability. The scooter was predominately a ground attack aircraft, and had a very good load carrying capability for its tiny size.
• Petter designed a neat plane. The change of the outer sweep and its twist improved the handling at low speeds, but many British aircraft went through similar wing LE changes to improve handling.