Recommended Modifications to Laser-Arts Majestic All mods are roughly independent, so only a partial mod list can be selected from the list below. Mark Drela 14 Aug 01 (last modified 2 Nov 01) ================================ Wing layout modifications Original wing layout # span chord alpha z 0. 10.0 0.0 0.0 24.75 10.0 0.0 0.0 42.0 8.5 0.0 2.0 54.0 6.0 0.0 6.7 Modified wing layout # span chord alpha z 0. 10.0 0.0 0.0 24.75 10.0 0.0 0.0 42.0 8.5 -1.0 3.0 54.0 6.0 -1.0 7.5 | suggested 1-bay extension with 56.0 4.5 -1.0 8.25 | curved LE a'la Allegro-Lite where z is the height of the dihedralled-wing sections above the table Mid panel now has 1 degree washout twist (TE at 8.5" chord raised by 0.15"), while center and tip panels are still flat. - improves tip stall margin (stock Majestic is prone to tip stall during slow circling) - reduces CDi by 2% at low speeds - little adverse impact on penetration capability Effective dihedral has been increased from 8.3 to 10.2 degrees. - improves roll response - reduces the sideslip needed to hold a steady turn (and hence reduces drag) More dihedral burden is now carried by mid panels. - improves tip panel stall margin when in steady sideslip in turn Tip panels extended by 2" or more, with curved (swept back) leading edge like that on the Allegro-Lite. - reduces CDi by additional 8% on top of washout's reduction - cleans up tip flow during steady sideslip in turn In slow, tight thermal flying, the modified wing is expected to be more maneuverable, more docile, and give a 5-7% sink rate reduction. If the wingtip extension is deemed to be too much trouble, then just round off the last rib bay LE like on the Allegro-Lite. The stock end rib is not used in this case. -------------------------- Note (29 Sep 01): John Hayes has recently added the 1 deg washout to his otherwise stock Majestic, using a heat gun. He reports a major improvement in tight circling behavior -- the glider no longer tends to fall off onto the inside wing. -------------------------- ================================= Tail layout modifications Original tail layout # span chord alpha z 0.0 7.5 0.0 0.0 13.0 4.5 0.0 8.3 Modified tail layout # span chord alpha z 0.0 7.5 0.0 0.0 17.0 4.5 0.0 12.0 A 4" extension is added to the tip of each V-tail half, and the tail V-dihedral has been increased from 40 to 45 degrees. - Effective horizontal tail volume is increased from 0.40 to 0.44 + CG location can be moved back slightly from recommended position - Effective vertical tail volume is increased from 0.018 to 0.028 + Yaw damping rate will increase by about 60% + Rudder roll power will increase by about 90% (60% more rudder yaw power together with 22% more dihedral) A simple way to implement this is to increase the rib spacing to 2.4", and extend the spanwise wood via splices or just replace it. ================================= Wing airfoil modifications The SA7038 airfoil is somewhat overcambered for this glider. It penetrates OK, but not as well as it could with a lower camber airfoil. One of two modified airfoils is suggested: SA7038 mod 6 SA7038 mod 7 These differ in the severity of the LE upsweep modification. Both airfoils have the same TE modification. Specifically: a) The bottom LE upsweep is increased slightly (mod 6) or significantly (mod 7). b) On both modified airfoils, the slight undercamber of the SA7038 is flattened by removing the rear 5% of the chord, and straightening the downward-curved bottom surface to regain the sharp TE. This is simple to do with the Majestic's rib/TE structure. The airfoil is now flat behind the spar which should simplify construction and covering somewhat. The aspect ratio has also been increased by about 5%. Mods a) and b) are cumulative, and only one of these can be implemented for a partial improvement. The modified airfoils are quite similar to the MH32, but a bit thicker. Compared to the stock SA7038, at 50 mph they will increase L/D by 30% or 40% (mod 6 or mod 7), dramatically improving penetration. Float and winching performance will be only slightly degraded, but this can be easily more than compensated with a lower flying weight. A lower weight is highly desirable to take best advantage of the new airfoils. Consider using light radio gear and a carbon tube boom to eliminate any nose weight. The elevator is unnecessarily beefy at the tip. As you go out, use larger lightening holes than those shown on the plan. Move the elevator hinge to the bottom and shorten the horns by 1/4". ================================= Structural modifications As minimum, beef up the spar. My numbers indicate that to make it winchproof it wants 0.040" carbon on top, and 0.030" or 0.020" carbon on the bottom sparcaps at the wing center. These can taper in thickness outboard. CST's or ACP's tapered carbon would work well. Wrap this spar near the end of the joiner rod and at the root rib to prevent it from bursting apart at these point-load locations. The shear web wants to be at least 1/4" total thickness of 10 lb balsa in the center, this thickness tapering roughly linearly outboard. With the specified carbon strips, the spruce caps are largely superfluous, and could be replaced by hard balsa. The sparcap carry-though method which is used on the outer dihedral break of the Allegro-Lite could be used for both breaks of the Majestic. This is easy to install and vastly lighter than a ply joiner. Minimizing yaw inertia should be the #1 priority for getting the best turn handling possible. The wing structure looks kinda beefy towards the tips which doesn't help. I think you can progressively narrow the TE as you go out (lengthen the capstrips to reach it). A 3/4" wide TE should be fine at the tip. Narrow the outer capstrips, maybe down to 1/8" in the tip panels. Use the lightest sheeting possible for the tips. The extreme outboard spar can be whittled down. The beefy end rib can be replaced by the one-bay tip extension with a curved leading edge as described above, or just installing the curved LE in the last rib bay. Grams count at the wingtips!