Team Dashpot

 

In association with:

 

 

 

 

PROJECT TITLE:               Design and Testing of an Active, Open-Loop Vibration Isolator for Vibration control of a Helicopter Tail-boom

 

 

SUBMITTED TO:                Sikorsky Aircraft Corporation

 

 

ADDRESS:                           Stratford, CT

 

 

CONTACT:                           Bill Welsh      (WWelsh@sikorsky.com)

                                                Dr. Ed Smith  (ecs@rcoe.psu.edu)

 

 

TEAM MEMBERS:              Adam Long

                                                Patrick Farabaugh

                                                Hagan Baturay

                                                Mike Kienzle

 

 

TEAM CONTACT:               Adam Long

 

 

TELEPHONE:                      814-883-2378

 

 

EMAIL:                                  adl138@psu.edu

 

 

DATE:                                    February 9, 2004

EXECUTIVE SUMMARY:

 

Sikorsky Aircraft Corporation is a leading company in the design and production of advanced helicopters for commercial, industrial, and military use.  For the past few years Sikorsky and The Pennsylvania State University have been working together to reduce the vibration that occurs in the tail-boom section of a helicopter.  A one-third scale vibration absorber was developed in a previous semester’s Senior Design Project to control the first bending mode of a one-third scale model of a helicopter tail-boom.  In this phase of the research, the new objective is to design, fabricate, and test an open loop active augmentation to the existing prototype.

 

In order to solve this problem the team first searched through patents and vendor websites and discussed different approaches with professors and team sponsors.  After researching different ideas, four possible approaches were considered.  Using a decision matrix it was determined that adding a force actuator in parallel with the damper was the best approach to solve the problem. To improve team efficiency, specific responsibilities were assigned to each team member. 

 

TABLE OF CONTENTS: 

 

Topic 
    Page
 
   
1. Introduction and Problem Statement
4
2. Objectives
5
3. Technical Approach
5
4. Project Management
10

4.1 Decription of Task Phrases
10
5. Deliverables
11
6. Budget
11

7. Communication and Coordination with Sponsor

12
8. Special Topics
12
9. Team Qualifications
13
10. References
14
11. Appendix
15

11.1 Gant ChartSpecial Topics
15

11.2 Resumes
16

 

1.  INTRODUCTION AND PROBLEM STATEMENT:

 

Sikorsky Aircraft Corporation is a leading company in the design and production of advanced helicopters for commercial, industrial, and military use.  In their continuing desire to improve product quality, Sikorsky Aircraft is looking for a way to reduce mechanical vibration in their aircraft[1].

 

Several attempts have been made to reduce the vibration that occurs in helicopters.  The main focus of this Senior Design project is the vibration that occurs in turbulent air flow over the fuselage which can cause excessive vibration, damage, and/or affect the flight of the aircraft.  The Pennsylvania State University has been working with Sikorsky to alleviate this problem for several years.  To aid the research of this problem, a one-third scale model of a tail-boom (Figure 1) was constructed about three years ago.  A damped passive vibration absorber (Figure 1) was previously developed in an earlier Senior Design project to reduce the first mode of vibration at the fundamental natural frequency[2].

Figure 1: One third scale tail-boom model and initially proposed active absorber[2]

 

The purpose of this project is to design, fabricate, and test an open-loop active augmentation to the current prototype. The proposed active element (labeled in Figure 1) is expected to reduce the overall mass of the absorber and give a broader frequency bandwidth at which the absorber will be effective in reducing vibrations.

 

2.  OBJECTIVES:

 

Our objective is to successfully add an open-loop active element to the existing Passive Vibration Absorber prototype.  The assembly is then to be thoroughly tested and modified as needed to create a final workable prototype. 

           

Constraints based on full scale tail-boom:

  • At least a 5lbf of output for every 1 lbm.
  • Max force of 50lbs. at 6 Hz.
  • Total weight of 10 lbs.
  • RMS power consumption of 300 watts, either electrical or hydraulic, with a 1kW peak.
  • Approximate dimensions of device not to exceed 5 inches in diameter and 4 inches in height.

 

Since we are testing using a 1/3rd scale model of the Apache tail-boom, it is assumed that all of the above values should be a third of the full scale constraints.

 

3.  TECHNICAL APPROACH:

 

In order to solve the problem of tail boom vibrations, an organized nine-step process was followed:

 

  1. Recognizing the Need:  Sikorsky found that in an Apache helicopter, tail boom vibrations can transfer through the entire helicopter and lead to many problems, such as damaging certain fragile equipment, and making it hard for the pilot to read gages and operate the helicopter.  Therefore, they determined that there is a need is for something to cancel out or reduce the vibrations in the tail boom. 

 

  1. Defining the Problem:  Specifically, the goal is to design and fabricate a light and small active open loop device to cancel out the tail boom vibrations over a range of frequencies.  The constraints based on a full scale tail-boom are that there needs to be at least 5lbf of output force for every 1lbm, a max force of 50 lbs at 6 Hz, a total weight of no more than 10 lbs, a RMS power consumption of 300 watts, either electrical or hydraulic, with a 1kW peak, and dimensions not exceeding 5 inches in diameter and 4 inches in height.  For the 1/3 scale model that is available for testing, the device should weigh approximately 3.33 lbs, and be manually adjustable for the range of frequencies between 10 and 30 Hz. 

 

  1. Planning the Project:  In order to complete the project in a timely and efficient manner, a Gantt chart was constructed to organize the tasks and divide the work among the members of the team according to their strengths and weaknesses (Appendix A).  Special consideration was given to try and organize as many tasks as possible simultaneously to conserve time.

 

  1. Gathering Information:  Many references were utilized to better understand the problem and the theories behind the possible solutions. Text books were used to understand the basic design and vibration principles [3] [4].  A search of patents [5] and published works was done to find any previous designs or ideas that could be helpful in finding the best solution.  Also an internet search of was done to see what types of actuators were available that may be applicable [6].  Finally, many people including the sponsor, Bill Welsh, the main contact, Ed Smith, the cooperating TA, Joe Szefi, and professors Dr. Lamancusa, Dr. C.D. Rahn, and Dr. Carpino were questioned to gather more information on the project and possible solutions. 

 

  1.  Conceptualizing Alternative Approaches:  Before a final solution can be chosen, many possible solution alternatives need to be analyzed.  After talking to some of the contacts, professors, and peers, and after gathering a lot of information (Step 4), the team brainstormed to come up with any and all possible solution alternatives.  At this point, the ideas were not evaluated. 

 

  1. Evaluating the Alternatives:  Once a list of the possible solution alternatives was created, the team used their engineering background to evaluate them based on the estimated performance. Cost was not as much of a concern as actual performance, weight, and complexity.  The initial list of all possible solutions was narrowed down to 4 possibilities (Figures 3-6) which were all based on the previous passive design (Figure 2).

Figure 2:  Original Passive Design

         Contains a damper (C), spring (K), and mass (M).

 

Figure 3:  Design A adds a force actuator in parallel with the damper. 

The Force actuator is a device that exerts a force on a mass.  Different types of force actuators include: electromagnetic, inertial, and hydraulic.  Figure 7 below shows an actual electromagnetic inertial force actuator.

 

Figure 4:  Design B adds an electric motor with an offset mass to the spring arm.

The electric motor with the offset mass creates a vibrational force to counteract the vibrational forces in the tailboom. 

 

Figure 5:  Design C adds a reaction mass actuator to the spring arm.

This design is semi-active, and would be controlled by changing the C and/or K values. 

 

 

 

Figure 6:  Design D replaces the mass with an electric motor with an offset mass

     Similar to Figure 3 except that here, the motor is also used as the mass.

 

Figure 7: SA1 Force actuator produced by CSA Engineering (www.csaengineering.com)

 

  1. Selecting the Preferred Alternative:  A decision matrix was used to choose which alternative should be pursued.  Table 1 was used to rank the importance of the criteria that were used to evaluate the solutions.  In Table 1, the criteria were charted against each other.  If the criterion on the left was more important then the criterion on the top, then it was given a one.  If it was not then it was given a zero.  The row totals were calculated by summing the number of ones in the rows, and then the normalized weights were calculated by dividing the row totals by the sum of the row totals.  The normalized weights were then used in Table 2 to rank the four design possibilities.  Each criterion was ranked on a scale of 1-5 for each design.  The weight was multiplied by that rank, and then the values were summed.  The resulting net scores show how the designs fair against each other based on the criteria and the importance of each criterion.  From the decision matrix, Design A was chosen, but the other Designs were not far off and could still be considered if Design A ends up being rejected.

 

 

Table 1:  Ranking of Criteria / Weights

 

Size

Light Weight

Reliability

Ease of Fabricatrion

Ease of Testing

Performance

Cost

Simplicity of Design

Row Total

Normalized Weights

Size

N/A

0

1

0

1

0

0

0

2

0.071

Light Weight

1

N/A

1

1

1

0

1

1

6

0.214

Reliability

0

0

N/A

1

1

0

0

0

2

0.071

Ease of Fabrication

1

0

0

N/A

0

0

0

0

1

0.036

Ease of Testing

0

0

0

1

N/A

1

1

0

3

0.107

Performance

1

1

1

1

0

N/A

1

1

6

0.214

Cost

1

0

1

1

0

0

N/A

1

4

0.143

Simplicity of Design

1

0

1

1

1

0

0

N/A

4

0.143

 

 

 

 

 

 

 

 

Sum

28

1.000

 

Table 2:  Concept Selection Matrix

Decision Matrix

Weight

Design A

Design B

Design C

Design D

Size

0.071

5

5

5

5

Weight

0.214

4

3

3

3

Reliability

0.071

5

4

4

4

Ease of Fabrication

0.036

5

5

5

5

Ease of Testing

0.107

4

4

4

4

Performance

0.214

5

4

5

4

Cost

0.143

3

5

3

5

Simplicity of Design

0.143

5

4

5

4

 

Net Score

4.39

4.04

4.11

4.04

 

Rank

1

3

2

3

 

  1. Communicating the Design:  To communicate the final design, detailed drawings, plots, and calculations will be made.  Also, an explanation of what the device actually does and how it works will be written.

 

  1. Implementing the Preferred Design:  To produce a prototype, parts will be purchased based on the calculations and the design.  An initial prototype will be developed and tested, and will then be modified, if needed, according to the test results,

 

4.  PROJECT MANAGEMENT: 

 

 Team responsibilities:

 

Members

Tasks