SOO Atch 1 - Actuated MPS.pdf

Distribution A. Cleared for Public Release. AEDC IRA-26-1262.

Technical Requirements: Actuated Model Positioning System and Internal Balances

1. Introduction

This document outlines the requirements for the procurement of a freestream Force & Moment

(F&M) measurement system for the AFRL-operated supersonic wind tunnel. A two degree-of-freedom (DOF) actuated model positioning system (either pitch-roll or pitch-yaw) will provide precise control of test article orientation within the facility test section and will interface with contractor-supplied 6-DOF internal force and moment balance instrument(s).This document specifies the required articulation range, control, interfaces, and other critical parameters for the model positioning system (MPS), along with expected operating environment and maximum load for the internal balances. The values in this document are estimates; the performer shall work with the Government to revise and confirm these values prior to final fabrication.

2. Scope

This document covers the functional and performance requirements for the F&M balance and MPS, including:

• Maximum balance load

• Operating environment and conditions

• Physical dimensions and mounting interfaces

• Data acquisition and output requirements

• Calibration requirements

• Articulation range and control

3. Requirements: Internal Balance

3.1 Functional Requirements

The force and moment balance shall measure the six components of aerodynamic forces and moments:

• Normal force (Fn)

• Axial force (Fa)

• Side force (Fs)

• Pitching moment (Mp)

• Yawing moment (My)

• Rolling moment (Mr)

3.2 Performance and Environmental Requirements

• Maximum Aerodynamic Loading: Maximum loading experienced by a test article and its support structure in the tunnel occurs during the unsteady, chaotic, asymmetric flow breakdown at the end of every tunnel run.

As an upper bound, the differential pressure experienced by a test article is theoretically largest when flow is “unstarted” (subsonic, with high static pressures behind a normal shock at test Mach number) and fully started (supersonic, with low static pressures) on opposite sides of the test article.

Practically, the maximum loading experienced by test articles during breakdown are shown via experiment to be less than this and can be predicted empirically from Eq. 4 of Maydew

(“Compilation and Correlation of Model Starting Loads from Several Supersonic Wind

Tunnels”, 1962) as N = CN*S*P0, where

N = maximum unstart / blockage / breakdown load (lbf), CN = empirical force coefficient (unitless), S = cross-sectional area (in2), and

P0 = upstream pressure at breakdown (psia).

For the tunnel, the maximum breakdown loading occurs at the end of a maximum-duration run at a Mach number of 2.6, where CNc = 0.262 and P0 = 60 psia. Thus, N = (17.3 lbf/in2) * S

As an upper bound example, consider as a large test article an 18-inch long delta wing model with a maximum span of 6 inches at the base, having a planform area S = 54 in2. For this example geometry, the maximum starting load on the test article, N, is 933 lbf. Note any side-loads generated by the model positioning system and sting must also be considered.

It is well-understood that maximum design load is a driving factor for balance and mechanism design, and that high loads required for survivability are in opposition to a desire to optimize balance sensitivity and uncertainty. The maximum design load for the combined test article and support system may require tailoring, in coordination with the government, to provide an optimal compromise of balance survivability, balance sensitivity, maximum model size (S) and tunnel runtime (i.e., P0 at unstart). This requirement should be clearly defined and agreed upon early in the effort such that any operational and/or experimental-design limitations may be fully understood.

• Operating Temperature Range: The typical total temperature within the facility is less than 200ºF, with adiabatic wall temperatures close to ambient (i.e. 70ºF).

• Operating Pressure Range: Operating static pressure in the test section during operation at high Mach numbers can be assumed to be at vacuum (~0.1 psia). The balance must be designed to operate under these conditions.

• Operating Duty Cycle / Conditions Exposure Duration: The tunnel is an intermittently operated blowdown facility. Test run durations are typically less than 5 minutes each at operating conditions, occurring typically fewer than 20 times per shift. Pre- and post-operational procedures may require the test section to be at stagnant vacuum conditions for longer (typ. 30 minutes), during which time balance tares and/or checkouts may be performed.

3.3 Physical Requirements

• Dimensions: Balance diameter is anticipated to be 0.5” – 0.625”, but this value is open to revision to meet other requirements (e.g. Maximum Startup Load).

• Mounting Interface: The form factor for the balance is expected to be a cylindrical device mounted internally within the Government-supplied test article. Specific interfaces / tapers etc. are negotiable but should be suitable for application to a wide variety of test article geometries and support/interface adapters.

3.5 Calibration Requirements

• Calibration Process: Recommended calibration procedures and intervals should be supplied by the performer.

4. Requirements: Model Positioning System

4.1 Functional Requirements

The model positioning system shall provide precise control of the model's orientation (either pitch-roll or pitch-yaw) within the wind tunnel test section during facility operation.

• Number of Degrees of Freedom: 2 (pitch-roll or pitch-yaw)

• Minimum Angle Range: Pitch: -10° to +10°; Yaw: -5° to +5°. Actual range may be higher, and is subject to facility blockage calculations.

• Balance Integration: The model positioning system shall seamlessly integrate with the performer-supplied F&M balances. This includes mechanical mounting, wiring, and data handling.

4.2 Performance Requirements

• Angle Accuracy: < 0.1°

• Actuation Rate: > 0.5° / second

• Control Interface: Vendor shall supply positioning-system control software or a documented interface coordinated to be compatible with existing facility data and control systems (NI LabVIEW-based). Control shall allow for scheduling of programmed sweeps

(continuous or ‘pitch-pause’) and positioning shall be closed-loop. Pertinent time-stamped position feedback and status indications shall be available as logged output or available to the facility data systems.

• Data Handling: The actuator control system shall allow for synchronization/alignment of control and position feedback with data acquisition from F&M balances and other facility data systems. Data from all vendor systems should be time-synced (NTP, PTP, and IRIG-

B are available) and output in a clearly-documented format.

• Wiring: All wiring for the balances shall be routed through the actuated mechanism and terminated at a designated connection point outside the wind tunnel test section.

4.3 Physical Requirements

• Mechanical Tunnel Interface: System must mount via (and maintain seal of) the facility’s existing ceiling and floor modules, approx. 7 in wide by 35 inches long on the flow side.

External to the tunnel test section, the facility’s structural frame limits the space available for external mechanisms to a deep cavity approx. 9.5 inches wide by 38 inches long.

o Mounting via the ceiling only (i.e., a single-sided system) is highly preferred.

o See Figure 1, highlighted green ceiling module.

• Test Area: Model Position and Center of Rotation:

o The primary test core, preferred for F&M testing at all operating conditions, is centered approximately 20 inches forward of the leading edge of the ceiling module proposed to support the model positioning system. A sector-sting or multi-bar linkage system should accommodate this forward cantilever.

o The center of rotation of the model positioning system’s pitch axis should, if possible, be near the upstream edge of the indicated test area. It is desired that the position of the center of rotation be configurable, to the extent practical, either mechanically or via manipulation of one or more actuated degrees of freedom.

o See Figure 1, highlighted dotted region in “Forward Window (A Port)”.

• Handling: Attachment points (e.g. D-rings) should be integrated for overhead lifting with the facility crane.

• Operating Temperature: 20 – 200 F

• Operating Pressure Range: Operating static pressure in the test section during operation at high Mach numbers can be assumed to be at vacuum (~0.1 psia). The model positioning system must be designed to operate under these conditions.

• Operating Duty Cycle / Conditions Exposure Duration: The tunnel is an intermittently operated blowdown facility. Test runs are typically less than 5 minutes each at operating conditions, occurring typically fewer than to 20 times per shift. Pre- and post-operational procedures may require the test section to be at stagnant vacuum conditions for longer (typ.

30 minutes), during which time model positioning system actuation will be performed in support of balance tares and/or motion checkouts.

Figure 1 Simplified layout of the tunnel test section. Flow is left to right. Primary test area for test articles is in the “Forward Window (A Port)” region. Proposed mounting location for model positioning system (sector-sting, multi-bar linkage, or otherwise) is in the ceiling module highlighted in green.

Figure 2 Notional concept for model positioning system and test article in the tunnel, showing the facility nozzle

(left), test section, test article, and a notional sector-sting system (orange). This is for illustration only; the vendor-proposed solution need not implement this specific design/concept/architecture.