Design, fabrication, test, and evaluation of small-scale tiltrotor whirl flutter wind tunnel models

Guillermo J. Costa, Sandilya Kambampati, Samuel C. Johnson, Edward C. Smith

Research output: Contribution to journalArticlepeer-review


Three generations of small, semispan, subscale tiltrotor wind tunnel models were designed, fabricated, and wind tunnel tested. The goal of this project was to develop a series of flutter tests at small scale and low cost that would experimentally validate a series of analytical models developed in-house; this required a wind tunnel model that had as low a flutter speed as was feasible, in order to permit it to be tested to the point of instability within the operating limits of the current facility. The first-generation model consisted of a hollow plastic wing rapid-prototyped from ABS plastic, with a three-bladed rotor consisting of constant-chord wooden blades. Five different configurations of this first-generation model were tested, but only one configuration exhibited whirl flutter within the test facility, at a speed of 115 ft/s; however, this configuration was only able to exhibit whirl flutter through the use of a one-pound steel mass mounted aft of the wing trailing edge. For the unstable configuration, the center of gravity (e.g.) of the aft-mass was located 5.5 in. aft of the wing elastic axis. The second-generation model used the same wing, but featured composite rotor blades; this second-generation model exhibited whirl flutter at a tunnel speed of 113 ft/s, but was also incapable of experiencing an instability without the use of the aft-mass. The third-generation model consisted of a composite wing and composite rotor blades, with an integrated wing spar that acted as a flexure; two configurations of this third-generation model exhibited whirl flutter within the test facility, at tunnel speeds of 95 and 105 ft/s, and showed excellent correlation with the analytical model.

Original languageEnglish (US)
Pages (from-to)2596-2611
Number of pages16
JournalAnnual Forum Proceedings - AHS International
Issue numberJanuary
StatePublished - 2015

All Science Journal Classification (ASJC) codes

  • Engineering(all)


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