WWC snapshot of http://www.dfrf.nasa.gov/Projects/ERAST/APEX/APEX.html taken on Sat Jun 3 19:40:59 1995
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Background

Interest in ultrahigh altitude aircraft for atmospheric sampling and military surveillance has been increasing every year. Several aircraft are currently in the process of proving the feasibility of extended duration flight near 80,000 ft, and eventually other aircraft will fly even higher. More information is needed about the aerodynamics of this previously unexplored flight regime if those aircraft are going to be successful.

Research into low Reynolds number, high subsonic Mach number aerodynamics has produced some promising, if somewhat limited, results (references). However, some questions remain unanswered, and flight testing offers an attractive means of acquiring some of those answers.

A preliminary design study was undertaken several years ago to find a satisfactory method for achieving trimmed flight at (or near) 100,000 ft altitude. The study identified several possible techniques which allowed an aircraft to achieve trimmed flight beginning between 95k and 100k ft (depending on the launch method used.)

Objectives

The objectives of the APEX project are:

Experiment Description

The test vehicle will be a remotely piloted, highly modified commercial sailplane. It will be towed to an altitude in excess of 100,000 ft by a high altitude balloon, released vertically and maneuvered to achieve horizontal flight (figure). Flight testing will begin at an altitude between 100K and 95K ft. The unpowered craft will collect aerodynamic data all the way down to a lakebed landing at Edwards AFB. The wing will be custom designed to incorporate an airfoil suitable for low Reynolds number flight at high subsonic Mach numbers (less than 0.65). A portion of the unswept/untapered wing will serve as a test section. The wing instrumentation will be imbedded during construction. The following measurements will be used to satisfy the stated objectives:

  1. Measure boundary layer profiles at several locations streamwise.
  2. Measure chordwise pressure distribution.
  3. Measure boundary layer state with hot-films or microphones.
  4. Measure section drag with a fixed wake rake.
  5. Measure local angle-of-attack as well as freestream airdata information.

The experiment will use a PCM and telemetry system to send the signals to a ground-based recording system. Flight test maneuvers will consist of limited duration push-overs to lower than trim angles of attack, and stabilized turns to achieve higher than trim angles of attack. Other maneuvers could include constant alpha descents, constant qbar descents, or constant Mach number descents.

Frequently Asked Questions (FAQ's)

Due primarily to the extraordinary flight conditions that APEX is being designed for, there are several questions that come up on a regular basis. The project has compiled a list of some of the most frequent questions and answers to them. If more in-depth information is needed on a particular topic, please contact the appropriate discipline on the project team.

Project Status

The APEX project team has been assembled and is currently in the process of designing the aircraft and experiment systems, selecting suitable hardware, and working out operational details. The team has a preliminary design including a baseline airfoil, measurement locations, quantity, and accuracy, system architecture, operational plans, and a preliminary flight test plan.

Milestones:

Robert Geenen
APEX Principal Investigator
NASA Dryden Flight Research Center/D-2033
(805) 258-2265 (geenen@cs1.dfrc.nasa.gov)
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Curator: Robert Geenen - geenen@cs1.dfrc.nasa.gov

Modified: April 3, 1995