HAMMERHEAD AND NOSE-CYLINDER-FLARE AEROELASTIC STABILITY REVISITED

The flow mechanism responsible for the recently discovered buffet-prod ucing critical cylinder length for hammerheads is discussed. For short cylinder lengths, the upstream effects of the hammerhead wake are abl e to affect the terminal shock location, driving now separation to the nose-cylinder shoulder. This has the potential to cause aeroelastic i nstability leading to structural failure. A similar critical-cylinder- length effect exists for cone-cylinder-flare configurations. This too involves an upstream flow effect. In this case the flare-induced press ure rise drives the shock-induced flow separation to the cone-cylinder shoulder. Neither of these effects is recognized in the existing NASA guidelines for elastic vehicle design. Some currently proposed design s for heavy lift launch vehicles incorporate dangerously blunt noses, in violation of the NASA aeroelastic design criterion. A reexamination of these nose effects indicates the possibility of aeroelastic instab ility and structural failure. It is the conclusion of this study that it is imperative to consider aeroelastic stability effects early in th e design process in order to avoid the possibility of a flight failure or a costly redesign later in the development cycle if the presence o f an aeroelastic stability problem is discovered.