Mark Drela Tail Airfoils
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Home > Articles & Tips Index > Aircraft Design (Airfoils section) > Mark Drela Tail Airfoils

[Courtesy of Mark Drela, drela "at" MIT.EDU, July 2001]

The HT12,13,14 airfoils are specifically designed for RC glider tails. If constructed accurately, they will have complete absence of deadband even on the smallest HLG tails. They also have fully laminar flow for the lowest profile drag possible. At zoom and penetration speeds a "slab" tail will have nearly twice as much drag in comparison.

ht121314.gif (7496 bytes)
Click the small image above for a graphic of these airfoils

The thinnest airfoil should be used consistent with structural requirements. The recommendations are: 

  • 5.0% HT12 for HLGs and light 2M gliders (ht12.dat - 4 kB coordinates file)
  • 6.5% HT13 for heavier 2M and light Open gliders (ht13.dat - 4 kB coordinates file)
  • 7.5% HT14 for large heavy gliders (ht14.dat - 4 kB coordinates file)

The airfoils can also be blended across the tail span, e.g. HT14 at root for structural merit, HT12 at tip for low core weight and minimum drag.

Thinning of the HT12 is not advised... max control power will start to degrade. Thickening of the HT14 is not advised... deadband will start to creep in.

For built-up tails, the TE can be made blunt by rotating each surface about the LE point to get the TE to the right thickness. Drag will increase slightly, but the nice control characteristics will be unaffected.

These airfoils favor a very wide control surface. The hinge is ideally at 40% chord, although a 50% hinge is almost as good. The max thickness locations are quite far forward, so using such wide flaps does not significantly reduce the bending strength of the fixed part of the tail.



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