Although the concept of Natural Laminar Flow (NLF) has existed for many years, only recently have modern aircraft fabrication techniques and airfoil design technology reached the level of maturity necessary to permit the achievement of significant amounts of NLF on production aircraft. Current design trends toward turbocharging and pressurized cabins are pushing new aircraft into higher altitude regions where low unit Reynolds numbers are more conducive to the achievement of NLF. Extensive use of composite materials is providing the smooth surfaces necessary to permit NLF. Recent experimental designs have demonstrated 70% chord runs of NLF on upper and lower wing surfaces, as well as significant NLF on fuselages, empennages and propellers.
A consequence of achieving highly laminar boundary layers, however, is that an aircraft may then be susceptible to large performance losses when environmental or operating conditions result in early transition of the boundary layer. Further, if the NLF airfoil sections are improperly designed, stability and controllability problems can result.
The FAA is currently working with NASA and the industry to evaluate the adequacy of existing regulations and procedures for certifying highly laminar aircraft designs. This paper will cover some of the FAA concerns about the potential effects of loss of NLF on aircraft performance and handling qualities. The paper will also discuss what the FAA is doing to help address these concerns and interim guidelines that are being used to certify a current project that is expected to achieve large amounts of NLF.