Analytical Methods

Honeywell Engine Testbed

Honeywell manufactures a variety of engines for the aircraft industry. In order to properly test and certify their engines, Honeywell operates a modified Boeing 757 as a testbed aircraft. This aircraft has been modified to carry a test-engine on a pylon mounted to the forward fuselage. In this analysis, the HTF7000 turbofan engine was being tested.

Stark/AMI was responsible for the following tasks.

  • Determine a suitable location for the test engine such that the engine wake would have a minimal effect on downstream structure and on handling qualities.
  • Create an engine pylon fairing that would minimize interference drag and vibration.

Engine Placement

Choosing a location for the test engine was dependent on several factors. The test engine installation had to be placed in a region with air coming in at near freestream conditions. In addition, the installation could not have negative impact on the aircraft itself. Stark/AMI investigated various characteristics of several potential installation locations. The results of the study were instrumental in choosing the right location.

Some of the characteristics which went into making the decision were impact on static pressure port, exhaust plume location, and aircraft stability. Any impact on the static port would affect the aircraft’s ability to determine altitude, and if the effect was severe enough, the aircraft would not be able to fly under RVSM rules. The exhaust plume from the test engine could not impact any part of the aircraft. Any plume impact on the aircraft skin would lead to overheating problems. Because the engine was mounted on the side of the fuselage, the plume had potential to strike the horizontal tail. The optimal location was found to be forward of the wing and on the upper portion of the fuselage. This location minimized the impact of the installation on static port pressure and reduced the chance of plume impingement on the tail, but an investigation into stability showed a need for changes to the c.g. range.

Pylon Fairing

CFD analysis of the initial engine pylon showed unfavorable flow conditions near the join between the fuselage and the engine pylon. At transonic speeds there were indications of strong shocks and the potential for flow separation. A fairing was rapidly designed in order to mitigate the potential problem. As part of the design, Stark/AMI calculated the aerodynamic loading on the fairing and provided NASTRAN load inputs to the structural analysis engineers. The Stark/AMI fairing is seen on the final aircraft.