SATPC0034588 Tab 04 SOW redacted.pdf

UNCLASSIFIED//FOUO/NOFORN

NASA LANGLEY RESEARCH CENTER

Independent Coaxial Rotor Drive System

STATEMENT OF WORK

March 20, 2024

1. INTRODUCTION

This Statement of Work (SOW) describes the design and development of a prototype system to test the concept of a model-scale direct-drive coaxial-rotor power system. The

Government is developing a testbed for model-scale wind-tunnel testing of coaxial-rotor helicopter designs. Based on technology developments in electric-motor technology, the government wants to test the concept of directly powering each rotor with its own electric motor and maintaining matching speed and relative position using encoder feedback. There are a number of motors on the market currently that operate at the much lower speeds typically used for model-scale helicopter rotors. Traditionally, coaxial rotors are linked through a transmission or gearbox such that identical speed and fixed phasing is mechanically enforced. When the rotors are counter-rotating, this phase can be thought of as the relative angle where the blades pass by each other. When the rotors are co-rotating, this phase can be thought of as the relative angle between the blades of each rotor.

Unfortunately, gearboxes introduce undesirably vibrations in the testbed. Also, an important area of research for coaxial rotors is testing how the phase angles between the rotors affect their behavior. When the rotors are linked by a gearbox, changing this phase angle becomes difficult. Eliminating the gearbox and operating each rotor independently means that the motor controllers must enforce the speed and position constraint between the rotors, because this constraint is critical to ensuring that the testbed behaves in manner similar to a full-scale aircraft.

Prior to designing and building the wind-tunnel testbed, the government desires to design, purchase and test the drive system using this independent direct-drive motor concept. The goal is to first identify the motors, controllers, hardware and software required for this concept. Then the components will be purchased and assembled into a prototype test stand for performance testing. Once the drive system has been satisfactorily tested, the components can then be incorporated into the future wind-tunnel testbed.

2. Scope The proposed work will be split into two phases. During the first phase, the Contractor shall evaluate existing motor and controller products and identify a specific combination of motors and controllers for an independent direct-drive motor system that is capable of satisfying the requirements presented in Section 3. Upon satisfactory completion of

Phase 1, the Government may optionally begin Phase 2, in which the Contractor will assemble the controllers into a mobile cabinet, design and build a human-machine interface

(HMI) for operational control of the motors, and assemble the motors into a test stand for operational testing. Because the specific motors and controllers cannot be accurately estimated prior to completion of Phase 1 of this work, the Government will decide whether to purchase the motors and motor-drives based on the recommendations produced during

Phase 1. If the Government decided to move onto Phase 2 then the motor and motor-drives will be provided to the Contractor as Government-Furnished Equipment (GFE) during

Phase 2.

3. REQIREMENTS

3.1 Coaxial-Rotor Requirements

The nominal rotor system for the coaxial-rotor testbed is a 57-in-radius rotor with a nominal speed of 700 RPM. However, as a research testbed it needs be compatible with a range of rotor sizes and hold constant rotor speeds. Analysis by the Government has identified two different speed and power ranges for the motor drive system. For the primary speed range, each motor shall be capable of operating at 100% duty cycle at the loads specified in Table 3.1. For the secondary speed range, each motor shall be capable of operating at 50% duty cycle at the loads specified in Table 3.2. It is recognized that meeting high-power requirement of 1460 rpm / 528 ft-lb / 146.8 HP, may not be practical.

Thus, the Contractor may, with Government consent, relax that requirement in order to achieve a cost-effective and practical drive system design.

Table 3.1 Primary operational speed range.

Rotor Speed (RPM) 852 802 757 718 682

Torque (ft-lb) 154 185 219 258 301

Power (HP) 25 28.2 31.6 35.2 39.0

Table 3.2 Secondary operational speed range.

Rotor Speed (RPM) 1733 1632 1541 1460

Torque (ft-lb) 316 378 449 528

Power (HP) 104.1 117.6 131.8 146.8

3.2 Motor Requirements

The selected motors shall be capable of directly spinning the rotors at the speeds presented in Tables 3.1 and 3.2 without the use of a gearbox or other transmission system. They shall be coaxial with the rotor shaft and must have a through hole that is sufficiently large enough for the upper rotor to be driven by the lower motor, as illustrated in Figure 3.1.

Figure 3.1 Coaxial-rotor configuration

The motors shall be electric motors capable of being operated with a traditional Variable

Frequency Drive (VFD) Controller Contractor shall assess the requirements for the motor that would be used to individually control rotors. Motors shall be identified that produce sufficient torque with maximum efficiency. The motor must be able to withstand operation for an extended period of time at nominal torque levels and dissipate heat produced during operation. Water cooling of the motors is preferable to reliance on air colling.

The Government has identified motors by EMRAX (https://emrax.com/e-motors/emrax-

348/) and YASA (https://yasa.com/) as potentially meeting these requirements. The

Contractor shall consider these motors, and also identify other motors that meet the specified requirements.

3.3 Drive/Controller Requirements

The motor drive system used to drive and controller the motors shall be a commercially available VFD. Available input power shall be assumed to be 450V 3-phase AC service.

The drives shall use A/B/Z encoders to identify rotor speed and position. Since the motor position is also an important measurement signal, the system shall include an output

Upper Rotor

Lower Rotor

Motor 1

Motor 2

Coaxial Rotor Shafts https://emrax.com/e-motors/emrax-348/ https://emrax.com/e-motors/emrax-348/ https://yasa.com/ connection that passes through the A/B/Z signals from both encoders, so that these signals can be used by a separated data acquisition system to analyze motor speed and position.

3.4 Control Requirements

The developed control/drive system shall use closed-loop control to synchronize the phasing between the motors based on rotor angle. The system shall support both co-rotating and counter-rotating operation. It must be able to maintain matching rotor speed and maintain phase between the motors to within 1 degree during steady operation and to within

3 degrees during changes in rotor torque induced by the rotors. The term phase in relation to counter-rotating rotors is defined to be the relative angle between the two motors when motor 1 crosses its zero-azimuth defined by its encoder. The term phase in relation to co-rotating rotors is defined to be the relative angle between the two motors during the entire revolution, as defined by its encoder. If this requirement cannot be achieved with current technology, it may be relaxed by the Government upon advice of the Contractor. It should be noted that this phase requirement is only applicable during steady operations at a specified rotor speed. During startup, shutdown, and other rotor-speed changes the rotors are expected to not have a constant phase.

The phase angle between the motors must be able to be changed in software. Ideally, it is also desirable that the phase be able to be controlled by an external signal. This external signal would be a programmatically controlled command signal a Government data acquisition system that would permit the phase angle to be incrementally varied during rotor operation, thus enabling efficient measurement of rotor performance as a function of phase angle.

In addition to operating with both drives synchronized, as described above, the motors shall also be able to be operated independently with separate RPM control for each motor. This applies to both co-rotating and counter-rotating operation. This includes one-motor operation, with the other motor secured.

The controller/drive shall fit into a mobile NEMA cabinet with a maximum footprint of 39

in. by 58 in. The maximum cabinet height is 72 inches. The cabinet shall be on wheels/casters to permit transport between testing locations. The enclosure shall include the ability lockout the motor drive system for safety during maintenance. The drive cabinet must be capable of interfacing with facility power and meet the safety requirements of

NASA Langley Research Center.

3.5 Test Stand Requirements

Since there is currently no wind-tunnel model available to attach the new motors to, a simple test stand will be made to mount the motors to for bench testing. This bench testing will not involve any rotor systems and is merely intended to demonstrate the accuracy of the developed system at controlling speed and phase angle. The test stand shall mount the motors side-by-side rather than coaxially. The test stand shall accommodate the encoders, cabling and motor cooling. Ideally, the test stand shall accommodate a means of applying an external torque to the motors, possible through a dynamometer.

3.6 HMI Requirements

The HMI shall consist of a graphical touch screen at least 12-in in size. This screen shall be mounted into a desktop box that can be easily moved to accommodate different pilot configurations. The primary means of controlling motor speed shall be a large, easily manipulated dial encoder mounted to the face of the desktop box and capable of changing rotor speed in no more than 1-rpm increments. The desktop box shall include any required power supplies and shall be powered through a standard 120V AC electrical connection.

The HMI software shall display typical motor parameters for each motor, such as speed and current. The HMI software provide access for changing phase angle and all tuning parameters required achieving the control requirements of Section 3.4. The desktop box shall include a resettable Emergency-Stop button that will secure all power to the motors in the event of an emergency.

4. Phase 1 Tasks

4.1 The Contractor shall identify a cost-effective combination of electric motors and a motor drive system capable of meeting the requirements of Section 3.

4.2 The Contractor shall document the capability of the proposed components to meet the specified requirements and the drawbacks to alternative motors and drives.

4.3 The Contractor shall identify all supporting hardware required to produce a functional independent direct-drive motor system, including encoders, cabling, and HMIs.

4.4 The Contractor shall identify costs and obtain quotes for the specific motors and motor drives to be used in Phase 2.

4.5 The Contractor shall produce a preliminary design for the mobile cabinet used to house the motor drive system. This design shall be documented and presented to the

Government so that it can be evaluated prior to Phase 2.

4.6 The Contractor shall produce a preliminary design for the human-machine interface

(HMI) that will be used to control motor speed during testing rotor operation. This design shall be documented and presented to the Government so that it can be evaluated prior to Phase 2.

4.7 The Contractor shall assess the need for a filter on the output of the motor drive with regards to minimizing motor temperatures and electrical noise. If filtering is needed, the Contractor shall provide a detailed recommendation regarding a suitable filter design.

4.8 The Contractor shall evaluate the installation location of Buildings 647 and 648, NASA

Langley, to assess compatibility of the proposed electric motors and a motor drive system. This includes evaluating line-length issues and power requirements. The

Contractor shall document this evaluation and make recommendations regarding any facility upgrades that may be required.

4.9 The Contractor shall produce a preliminary design for a simple test stand as described in Section 3.5. The contractor shall evaluate the possibility of incorporating an external torque or dynamometer and provide recommendations on cost and feasibility.

5. Phase 2 Tasks

5.1 The Contractor shall design and build a complete Independent Coaxial Rotor Drive

System based on the design and evaluation of Phase 1.

5.2 The Government shall provide the require electric motors and motor drives to the

Contractor as GFE for the Independent Coaxial Rotor Drive System.

5.3 The Contractor shall design, purchase hardware, and assemble the mobile cabinet housing the motor drive components.

5.4 The Contractor shall design, purchase hardware, and assemble the HMI that will be used to control motor speed during testing rotor operation.

5.5 The Contractor shall produce all software required by the HMI to interface with the motor controller display required information to the operator.

5.6 The Contractor shall test the completed system to ensure that it meets the requirements specified in Section 3.

5.7 Contractor shall provide a full set of drawings and instructions for operation.

6. DELIVERABLE ITEMS

The Contractor shall provide the deliverables in Table 2. The Contractor shall propose a milestone payment schedule.

Table 2: List of Deliverables

SOW Deliverable Dates

6.1 Kick Off Meeting Within 2 weeks of award

6.2 Status Reports and Meetings Monthly

4 Phase 1 Tasks 30 days after task starts

5 Phase 2 Tasks Within 90 days of start of tasks or within 30 days motor/controller delivery

(whichever is longer)

6.1 Kick Off Meeting:

Kick-Off Meeting to be held within 1 weeks of delivery order award.

6.2 Status Reports and Meetings

The Contractor shall provide bi-weekly status reports and notification of meetings via e-mail Andrew Kreshock (Andrew.R.Kreshock@nasa.gov), Robert Thornburgh, Technical Representative/Engineer (robert.p.thornburgh@nasa.gov).

The first report shall be submitted (2) weeks after the kickoff meeting and each Month thereafter until final delivery of all deliverable items. Reports shall include progress towards the milestones.

The Contractor shall provide the written status reports and host the meetings listed in

Table 3. The final conceptual design shall be accompanied by a conceptual design presentation.

Table 3: List of Status Reports and Meetings

SOW Meeting Estimated

Duration Due Date Planned Location

All Written Status

Reports n/a Monthly E-mail

6.1 Kick-Off 4 hrs.

Within 2 weeks of

Award

Contractor’s Facility and/or virtually via

TEAMS or WebEx

6.2 Status Meetings 1 hr. As needed

Contractor’s Facility and/or virtually via

TEAMS or WebEx

4.0 Conceptual

Design Report 4 hr.

Conceptual Study

Completion

Contractor’s Facility and/or virtually via

TEAMS or WebEx mailto:robert.p.thornburgh@nasa.gov

6.3 Electronic Data

The Contractor shall deliver electronic data through file transfer to easily access the data.

Delivery upon completion of the conceptual study to the TR. The electronic data shall include:

• Documentation of the conceptual design study

• All design data and data files

• Any drawings in PDF format.

7. PLACE OF DELIVERY

The Contractor shall contact technical representative for pick up or deliver to the following address:

National Aeronautics and Space Administration Langley Research Center

218 Dodd Blvd (Bldg. 648)

Attn:

Hampton, VA 23681-2199

8. NASA TECHNICAL REPRESENATIVE (TR):

The TR will serve as the task technical liaison between the Contractor and the COR and will assist the COR in performing his/her duties.

Name:

Org Code: D308

Phone Number:

E-Mail Address:

9. GLOSSARY

CF - Centrifugal Force

MSCRAT – Model Scale Coaxial Rotor Aeroelastic Testbed mailto:Robert.P.Thornburgh@nasa.gov

RPM - Revolutions per minute

SOW- Statement of Work