Airflow blanketing, or "blanking", "shielding", etc. refers to an upstream disturbance that disrupts normal airflow and reduces the effectiveness of an aerodynamic flight surface. ## Deep Stalls Stall-induced blanketing of the horizontal tail surfaces is known as a "deep stall", and is of particular concern to t-tail designs. On some models, as a stall progresses and wing airflow separation occurs, blanketing of the horizontal tail surfaces will compromise pitch control authority. With aft center of gravity loading, natural nose-down pitching moments can be reduced to the point where this situation is unrecoverable. Particularly in jet transport designs, engine nacelle location can also contribute to a blanketing of the horizontal tail surfaces. ![[NASA deep stall.png]] ## Vertical Tail Surface Blanketing During Spins During a spin, the flight path and relative wind can become nearly vertical. Depending on the design of the tail, this may cause a significant portion of the vertical tail surfaces to be blanketed by the horizontal tail surfaces. On some models, this reduces or eliminates yaw control authority to the point where a **developed spin is unrecoverable.** ![[NASA rudder blanketing spin.png]] ## Fuselage-Wing Blanketing During Sideslip When an airplane is flown in a sideslip condition (ie directionally misaligned with the relative wind), the fuselage may blanket an inboard portion of one of the wings. This reduces that wing's lift, and results in a rolling moment in the direction that the airplane was yawed. ![[A4NA sideslip fuselage blanketing modified.png]] ## Other Types of Blanketing Airflow blanketing is not limited to the types described above, and is highly dependent on the design of the aircraft and the circumstances involved. For example, MD-80 series aircraft are known to experience a rudder blanketing effect when using reverse thrust during the landing roll: [[Runway Excursion During Landing, Delta Air Lines Flight 1086, Boeing MD-88, N909DL, New York, New York, March 5, 2015](https://www.ntsb.gov/investigations/accidentreports/reports/aar1602.pdf)]() ## Additional Information For additional information, see *T-Tail* (pgs. 6-6 to 6-7) in the *Pilot's Handbook of Aeronautical Knowledge*, and *A Systematic Study of the Factors Contributing to Post-stall Longitudinal Stability of T-Tail Transport Configurations* and *Summary of Spin Technology as Related to Light General-Aviation Airplanes* in the *NASA Technical Reports Server*. # References - [[faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf](https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/faa-h-8083-25c.pdf)]() - [[A Systematic Study of the Factors Contributing to Post-stall Longitudinal Stability of T- Tail Transport Configurations - NASA Technical Reports Server (NTRS)](https://ntrs.nasa.gov/citations/19660017791)]() - [[Summary of spin technology as related to light general-aviation airplanes - NASA Technical Reports Server (NTRS)](https://ntrs.nasa.gov/citations/19720005341)]() - [[Runway Excursion During Landing, Delta Air Lines Flight 1086, Boeing MD-88, N909DL, New York, New York, March 5, 2015](https://www.ntsb.gov/investigations/accidentreports/reports/aar1602.pdf)]() ### By Kevin Sakson