Laminar Flow Considerations

[remove, for Hazen letter only]  Homebuilders now have access to adhesives which can replace rivets, bolts and welds in aluminum wing construction.  The temperatures and pressures for curing have all fallen into the DIY range, and to values that will not change aluminum alloy properties.  Any of them: VHB tape, aerospace epoxies,  AFxxx welding films, Prepreg honeycomb adhesive, and Brazing can also repeatedly withstand the temps and pressures needed for the others (and of powder coating), so the logistics of  progressive construction are simplified.] 

Its Holy because it promises >5% lower drag over a wide operating range.  Its the Grail because it can't be found (in  the aluminum world of small planes -  actually not much of anywhere except model airplanes & composite airplanes very carefully made).  That's because of these groups of problems:

  1. Military and Commercial environments: very long distances, unlimited environmental variation, extreme flight regimes (forces), hurried maintenance, hurried departure, swept wings, large complex flap systems, icing boots, leading edge slats, wing pylons, wing engines, large wings requiring many plate boundaries, frequent operational damage, workers on wings.  Paint.  And sometimes gun barrels, gun vibration, debris & smoke, battle damage.
  2. Imperfections: local and larger distortions of wing from discrete fastenings, rivet heads, dimples and countersink "valleys",  and  unfair foils due to imprecise rib fabrication, vibration, air leaks, lateral skin plate boundaries, inspection ports
  3. Dirt, dust, bugs, oil, fuel
  4. Gadgets: lights, instrument sensors, gas caps, drains, breathers, no-slip strips 
  5. Underway: dents, oil-canning/rippling on compression side of wing - becoming permanent 
 
A small aluminum airplane already has several advantages: no necessity for all that in 1., no (necessary) sweep, no non-slip necessary, no paint needed, fewer vibration sources, short chords permit single plate wrap of wing along a few ribs,...

Without discrete fasteners, skin alloys can be chosen without concern for what sort of rivets are best if any.  So oil-canning and fatigue ripples are easier to avoid - with no weight penalty.  Conformal foam tape would virtually eliminate vibration, and make up for small imperfections in rib fairness.

Continuous fasteners would also facilitate the use of cored sandwich skins, which are greatly superior for dealing with (ripple-making) compression forces (i.e. particularly on the upper wing surface), even while saving >35% of the weight of a single skin.  (Somewhat unbelievably, the current practice is to let compression buckling failure happen, because of the necessity of using relatively thin skins, and "hope" its in the elastic range.)  Fabricating such sandwich skins is easier homebuilder because he is working with developable surfaces so the sandwich cores need not accommodate complex curvature and applying pressure is easier.  A possible core is aramid honeycomb with adhesive pre-applied.  It does require low temp baking (with the box already built for the VHB tape and any Welding Film), and some pressure.  A homebuilder can apply the pressure by putting high aft tension on each skin - which wrap most of the wing surface with a single plate "along" 2 or 3 ribs.

If a suction scheme is necessary (as Boeing has researched on the 737), the wing is air-tight in whatever divisions you decide, a suction system would not be unduly difficult to set up as in an airliner wing.

What happens if we fail?  The plane is still quite low drag (and somewhat higher lift) with all those negative factors missing.  The Grail is still there, closer than before and this project will have helped focus on what remains to do to get there.  And for consolation, many laminar airfoils are quite low drag for high speeds even without any extensive laminar flow, and there are quite a few GA airplanes happily flying with laminar flow wings and little laminar flow.

Problems if one Does Succeed
  1. Stall ...
  2. Ground Loops
  3. Failure consequences
  4. Inconvenience
  5. Repair complexity
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