nassio%cfassp12@harvard.harvard.edu (George Nassiopoulos) (07/29/89)
From: nassio%cfassp12@harvard.harvard.edu (George Nassiopoulos) I have gone to two airshows this summer and have noticed a slight modification to the F/A-18 Hornets. At the first airshow, i noticed the modification on the Blue Angels' jets and thought that it was probably applied only to those aircraft, but then at a second airshow i saw the mods. on two fleet (i.e. combat) F/A-18's. The modification i am speaking about is the addition of two identical canard-like objects (winglets?) to the ``chines'' of the aircraft. (I don't know if ``chines'' is the correct term -- i mean the parts of the fuselage which begin at the canopy and extend out towards the roots of the wings. They provide a sort of ``hood'' over the engine intakes and give the F/A-18 a cobra-like appearance.) The ``winglets'' are bolted onto the ``chines'' almost directly above the engine inlets and they stick outwards almost at the same angles as the aircraft's twin tails. Does anyone know what these additions are? They could conceivably be antennae/sensors, but my hunch is that they were placed there for aerodynamic/stability reasons. Anyone know for sure? George Nassiopoulos nassio@cfa.harvard.edu
jlo@ames.arc.nasa.gov (Jeff Lo) (08/01/89)
From: elan!jlo@ames.arc.nasa.gov (Jeff Lo) In article <8673@cbnews.ATT.COM> nassio%cfassp12@harvard.harvard.edu (George Nassiopoulos) writes: >I have gone to two airshows this summer and have noticed a slight >modification to the F/A-18 Hornets. At the first airshow, i > >The modification i am speaking about is the addition of two identical >canard-like objects (winglets?) to the ``chines'' of the aircraft. There was a bit of discussion on these additions in a recent AvLeak in the story on the high angle of attack F/A-18 at Dryden. They are aero devices, not antennae or some such. The story as I remember it is that they are there to move vortices away from the vertical stab. I heard (fourth hand or so, so don't trust the accuracy of this) that there was a problem with cracks in the tails of some Hornets, and apparently this little tab solved the problem by moving turbulence away from the tail. Any more confirmation or details from M F Shafer? -- Jeff Lo, Elan Computer Group, Inc. jlo@elan.com, ..!{ames,uunet}!elan!jlo 888 Villa Street, Third Floor, Mountain View, CA 94041, 415-964-2200
shafer@elxsi.dfrf.nasa.gov (Mary Shafer) (08/01/89)
From: shafer@elxsi.dfrf.nasa.gov (Mary Shafer) In article <8673@cbnews.ATT.COM> nassio%cfassp12@harvard.harvard.edu (George Nassiopoulos) writes: >I have gone to two airshows this summer and have noticed a slight >modification to the F/A-18 Hornets. >The modification i am speaking about is the addition of two identical >canard-like objects (winglets?) to the ``chines'' of the aircraft. >(I don't know if ``chines'' is the correct term -- i mean the parts >of the fuselage which begin at the canopy and extend out towards the >roots of the wings. They provide a sort of ``hood'' over the engine >intakes and give the F/A-18 a cobra-like appearance.) >The ``winglets'' are bolted onto the ``chines'' almost directly >above the engine inlets and they stick outwards almost at the same >angles as the aircraft's twin tails. >Does anyone know what these additions are? They could conceivably >be antennae/sensors, but my hunch is that they were placed there for >aerodynamic/stability reasons. Anyone know for sure? They're strakes added to reduce the buffet loads on the vertical stabilizers. (Yes, I know they aren't really vertical :-)) The leading edge extensions (LEXs), which are what you're calling "chines", generate a vortex which impinges on the verticals. The buffet from the LEX vortes at high angles of attack is damaging the verticals by fatiguing them. The strakes keep the vortex burst point off of the verticals. If you want an idea about the LEX vortices and their impingement on the verticals, try to find the AvWeek with the NASA Dryden F-18 on the cover (Sometime in May, I think). We inject smoke into the LEX vortex, making it visible, and you will readily see where these vortices are and why they're so hard on the vertical. Just a quick (and probably tedious) note on nomenclature--the tail of an aircraft is just the back end. The rudder is on the vertical stabilizer and the elevator/elevon is on the horizontal stabilizer. An elevon is a control surface which provides both pitch (elevator) and roll (aileron) commands. If the entire horizontal stabilizer is a control surface, it's a stabilator (combination of elevator and stabilizer) or, particularly for larger airplanes, a flying tail. Also on larger airplanes, an elevon is sometimes called a rolling tail. However, the flying and rolling tail terms are older terms and not very common. -- M F Shafer shafer@elxsi.dfrf.nasa.gov NASA Ames Research Center arpa!elxsi.dfrf.nasa.gov!shafer Dryden Flight Research Facility Of course I don't speak for NASA