(12) United States Patent (10) Patent No.: US 8,991,744 B1 Khan (45) Date of Patent: Mar
USOO899.174.4B1 (12) United States Patent (10) Patent No.: US 8,991,744 B1 Khan (45) Date of Patent: Mar. 31, 2015 (54) ROTOR-MAST-TILTINGAPPARATUS AND 4,099,671 A 7, 1978 Leibach METHOD FOR OPTIMIZED CROSSING OF 35856 A : 3. Wi NATURAL FREQUENCIES 5,850,6154. W-1 A 12/1998 OSderSO ea. 6,099.254. A * 8/2000 Blaas et al. ................... 416,114 (75) Inventor: Jehan Zeb Khan, Savoy, IL (US) 6,231,005 B1* 5/2001 Costes ....................... 244f1725 6,280,141 B1 8/2001 Rampal et al. (73) Assignee: Groen Brothers Aviation, Inc., Salt 6,352,220 B1 3/2002 Banks et al. Lake City, UT (US) 6,885,917 B2 4/2005 Osder et al. s 7,137,591 B2 11/2006 Carter et al. (*) Notice: Subject to any disclaimer, the term of this 16. R 1239 sign patent is extended or adjusted under 35 2004/0232280 A1* 11/2004 Carter et al. ............... 244f1725 U.S.C. 154(b) by 494 days. OTHER PUBLICATIONS (21) Appl. No.: 13/373,412 John Ballard etal. An Investigation of a Stoppable Helicopter Rotor (22) Filed: Nov. 14, 2011 with Circulation Control NASA, Aug. 1980. Related U.S. Application Data (Continued) (60) Provisional application No. 61/575,196, filed on Aug. hR". application No. 61/575,204, Primary Examiner — Joseph W. Sanderson • Y-s (74) Attorney, Agent, or Firm — Pate Baird, PLLC (51) Int. Cl. B64C 27/52 (2006.01) B64C 27/02 (2006.01) (57) ABSTRACT ;Sp 1% 3:08: A method and apparatus for optimized crossing of natural (52) U.S.
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