Team Vision for System-Level Design Phase
This phase concerns the concept selection of aircraft components to meet the engineering and customer requirements, as well as the constraints obtained in the problem definition phase. With a strong focus on the overall mission requirement of the competition, which is to carry the highest payload possible, the following selections have been made:
1. Wing planform and geometry
2. Empennage configuration
3. Horizontal stabilizer planform and fuselage station location
4. Vertical stabilizer planform
5. Fuselage configuration
6. Engine-propeller location
7. Landing gear configuration
We have determined, at this early phase, the size of our wing. This size is subject to change, and was determined by CFD using XFLR5 and Fluent. We have also made an initial study of our aircraft performance requirements, the propulsion system, materials selection, and budget/cost analysis. The flight conditions and atmospheric properties were defined. Overall, a very conventional aircraft configuration is chosen.
There are two images below which document our functional decomposition. They are the same decomposition, but the image becomes too wide and unwieldy if they are combined.
We have continued to benchmark moving into this phase. At the present, our collection of benchmarking documents are summarized in this PDF.
Comparison with Previous Competition EntriesBenchmarking efforts have continued in this phase. Primarily, we have reviewed already discovered design documentation for the SAE Aerospace Regular class competition in greater depth. Now that we are more fully aware of some of our design challenges we have extracted more useful information from reviewing those sources. We have also procured several more regular class design reviews. The full collection is located in the directory here.
University of Illinois Low Reynolds Number Airfoil DataThe design and manufacture of airfoils meant for low Reynolds numbers is a challenge that was firmly met by Michael S. Selig and others at the University of Illinois. Their data will be invaluable for the design of the airfoil and comparison and validation of our CFD analysis. The directory of PDFs is located in this directory
Preliminary Material BenchmarkingWhile it will be necessary to test materials in order to determine the most effective option for each of our needs, we have begun to compile available data so as to make some early estimations. The chart containing this data is located here as an excel worksheet.
Morphological Chart and Concept Selection
Solution 1 (Best Solution)
Runner Up Solutions
Pugh Selection ChartThe Pugh selection chart was utilized in order to determine which of the frontrunner concepts was the best. The datum aircraft was chosen because of its success in the 2014 competition as one of the top three lifters and the design documentation is available. For this reason we are benchmarking against very effective design. This should work out in our favor performance wise but may present design challenges.
Statement of IntentionMuch of our concept selection will be related to the stability of the aircraft and our ability to control it. For this reason, we are going to begin paying attention to some of our design details at this early phase so that we can make an effort to quantify what concepts will produce more desirable results in terms of these factors. MIT's open course initiatives have resulted in the documentation for a graduate level course in aircraft stability and control being posted Here. The lecture notes for this class are located within the directory here.
Overall Dynamic Architectural Diagram
The diagram below demonstrates the flow of forces and information (either as observation or electrical control signal) through the complete system. It does not identify all of the subsystems we will need to address, but it does illuminate the importance of our electrical system and demonstrates the indirect route of feedback to the pilot.
Feasibility: Prototyping, Analysis, Simulation
Preliminary Flight Conditions
Preliminary Wing Design: Iteration 1
Takeoff and Landing Distance Analysis
Takeoff and landing offer the largest challenge to the aircraft. Marc developed a matlab script which performs the necessary calculations to determine our takeoff and landing distance.
Battery SelectionWe have determined that we should be able to proceed comfortably using an off-the-shelf battery. Our time envelope of maximum power will be limited, but at steady flight our battery should be under a lower load than calculated here. Batteries are classified by the energy stored in mA*h (milliamp hours), the voltage, and the rate of discharge. We are presently not sure of our needs in terms of discharge rate, but we are aware of our voltage due to competition requirements. We predict that we need a capacity of 4688mAh to accomplish our mission objectives. We will size a battery larger than this.
Propeller Thrust Analysis
Thrust is an ongoing challenge that will dictate many of our design decisions in the future. It has important implications for lifting capacity of the aircraft, and so the determination of our capabilities at this phase is essential to guide future endeavors. Our efforts to calculate the thrust generated by our propeller are located in this pdf. The calculator is a spreadsheet.
When completing our initial risk assessment in the problem definition phase one of our largest concerns was not having enough initial funding to complete the project. As a result a cost analysis feasibility was conducted. This feasibility analysis is simply just a preliminary Bill of Materials (BOM) with current estimates of required materials, quantities and costs. This preliminary document can be found here. Looking at the document it is obvious that we will not be able to meet the budget constraints. As of the Systems Level Design Review, the total cost comes in at roughly $170 dollars over the $500 budget. This is including use of donated materials that save the team well over $600.
Current donated materials include an electric motor, motor control, and a variety of propellers from Professor John Wellin. Assuming we are able to utilize these parts for our application they would total a cost savings of over $500. Professor Wellin has also allowed us to use a 6-axis force meter to test the thrust of different motor/propeller combinations. We are very thankful for this contribution.
In discussions with the RIT Aero Club it appears we will have more potential parts available for us to use throughout the duration of the project. Such parts include a radio transmitter, battery charger and a variety of propellers for use in thrust testing. This could save the team around $150 or more. The RIT Aero Club continues to be very helpful in not just use of parts, but also general knowledge for model airplane construction.
Designs and Flowcharts
Our combined use-design flowchart is located below. We expect it to change in coming phases.
As discussed in the feasibility section, meeting the budget constraint is one of our largest concerns. Every attempt will be made to alleviate this risk by using cheaper parts and parts available to us free of charge through donations. However, as of the Systems Level Design Review we are still significantly over budget. Because of this we have updated the Risk Assessment document to reflect the increased likelihood of being over budget.