NACDeC III
National Aerospace Conceptual Design Competition III
Contents
- Introduction
- Overview
- The Problem Statement
- Mission Requirements
- Evaluation Criteria
- Stages of the Concept Design
- A Learning Experience
- References
Introduction
I and four teammates, a group of 5, participated in the third edition of NACDeC, representing IIT Kharagpur, from October 2019 to around September 2020. We reached Stage II, but unfortunately could not qualify for Stage III, the finals. In this article, I will talk about the overall journey through the various rounds and reviews, and give a brief overview of the technical aspects involved, such as the software used, the iterations done, and the results obtained.
Overview
The Design Division of Aeronautical Society of India was set up in 2017, to act as a torch bearer for aerospace design professionals, and to help them scale professional heights by offering a platform for inter-organizational exchange of ideas, to report professional contributions and to augment professional knowledge. With this in mind, the Design Division decided to conduct a yearly National Aerospace Conceptual Design Competition (NACDeC) for students of Aeronautical or Aerospace Engineering department from CFTIs or AICTE approved institutions in India.
The Problem Statement
For the year 2019–20, the problem statement revolved around HALEAPs.
Design a High Altitude Long Endurance Aerial Platform (HALEAP) for station-keeping at four fixed locations, and moving between them, while carrying a dedicated communications payload.
Mission Requirements
Along with the problem statements, the specific mission requirements were-
- The HALEAP must be able to maintain its position over a Metro city for three months, and the relocated to another Metro city within five days.
- The HALEAP may be deployed at any altitude between 15 km and 20 km AMSL, but it should be able to maintain its location within a ground footprint of 5 km x 5 km during the entire period of deployment above the Metro city over which it is deployed.
- The system should be able to generate adequate power to maintain station, and to relocate to the next location within five days, without the need to bring it down.
- The HALEAP should be able to cater for a continuous power consumption of 1000 W by a payload weighing 100 kg.
- The HALEAP should be able to take-off and land within 2 km @ ISA sea level.
Evaluation Criteria
Stage-I -Initial concept review with ten teams shortlisted.
Stage-II -The second stage would consist of a mid-term review, and a final review. The mid-term review would be in the form of evaluation of a report, consisting of a summary of work done so far, and the proposed plan of action. The final review would also be in the form of an evaluation of a report, followed by a detailed presentation. The review of the report would be based on the following criteria-
- Technical Content
- Application and Feasibility
- Originality
- Organization and Presentation
Stage-III
Based on a scrutiny of the final reports, five teams would be shortlisted for Stage-III, and would be invited to make a detailed presentation on their project.
Stages of the Concept Design
After receiving the problem statement, studying the mission requirements and criteria, we came up with a detailed set of steps which we followed through the program duration -
- Existing Literature Survey
- Design Driving Requirements
- Initial Sizing
- Configuration Selection
- Constraint Analysis
- Structural Layout and Sizing
- Aerodynamic Analysis
- Powerplant Selection and Sizing
- Performance Estimation
- Sensitivity Analysis
1. Existing Literature Survey
In a conceptual design competition, it does not make sense to begin a design from scratch and do everything on your own. Existing designs or aircraft that are as close to the requirements as possible are taken, and modifications and iterations are made to those designs. These included both heavier- and lighter-than-air vehicles and had a variety of propulsion systems. Out of all such designs, 14 were identified as more likely candidates.
A common trend observed in all of these aircraft was that their wing areas were very large. This is because since their operating altitude is very high, the air is less dense and the wing loading of all these vehicles are very low. Several parameters such as payload, range, cruising altitude, endurance, takeoff weight, wing aspect ratio, wingspan, engine type, etc. were considered when comparing the designs.
Based on the literature survey, the HeliPlat model was chosen as the initial target model to make design modifications on.
2. Design Driving Requirements
In this section, the range of some important parameters was decided, factors that would drive the constraint analysis and the design were identified, types of suitable configurations were shortlisted, a list of software like XFLR5 and Ansys and books such as Aircraft Design, by Raymer, to be used and studied was created, tasks were distributed amongst the team members, and a preliminary schedule of the entire procedure was made.
The Reynolds’ number based on the altitude requirements of the problem statement was found, factors such as turning radius were found to drive the constraint analysis and the LTA and fixed-wing aircraft designs were shortlisted.
3. Initial Sizing
To decide the initial values of the size of the final aircraft, the first iteration was done by taking the initial parameters the same as those of the target aircraft, the HeliPlat. Using the relevant equations and tailoring the values according to our chosen altitude, the initial planform area, weight, power, and empty weight were calculated in the loiter as well as the cruise phase.
The initial concept review took place after performing the initial sizing calculations, and our team was shortlisted for the Stage II of the competition.
4. Configuration Selection
This section dealt with determining some parameters related to the configuration of the platform, viz. wing loading and design lift coefficient. A few quantities related to the wing geometry, viz. span, sweep, taper ratio, were then found out along with root, tip, and mean aerodynamic chords. The operating Reynolds number was also obtained and an airfoil for the wing was selected.
Based on the calculations performed, the A18 smoothed airfoil was found to be the optimum one, and was chosen for further calculations.
5. Constraint Analysis
In this section of the report, the wing loading and power-to-weight ratio of the platform were calculated. From the mission profile, various related constraints were formulated. A constraint analysis is then done to obtain the optimum values of the aforementioned parameters by selecting the design point. The second iteration was performed, and the design values and parameters were re-calculated using the design point.
6. Structural Layout and Sizing
The wing loading was used in this section to recalculate the wing geometry that was initially estimated during the configuration selection. The length of the platform was found out, followed by the geometry of the tails. Then the materials for various parts of the platform were determined.
7. Aerodynamic Analysis
In this section, the airfoil lift and airfoil drag curves were drawn to find the required angle of attack for various stages of flight. Then, the wing lift and wing drag curves were drawn for the cruise phase. The tail lift and tail drag curves were also drawn. The wing geometry was iterated and the convergent Reynolds’ number was calculated. The maximum efficiency and other parameters were found. XFLR5 was the software used for all the plots.
8. Power Plant Selection and Sizing
This section focused on finding the power output required from the propulsion system using the power-to-weight ratio obtained from the constraint analysis. The geometry of the propellers was then determined, along with the speed at which it should rotate. Finally, details about the placement of the fuel tanks were decided.
The Hydrogenics HyPM HD 50kW power module was chosen for our aircraft. It produces 50 kW of continuous power, with an operating voltage of 220VDC.
The Stage II mid-term review took place after performing the power plant selection and sizing. The second iteration of our aircraft design parameters passed the review, and we were chosen to go ahead with our work for the final review.
9. Performance Estimation
Performance parameters such as thrust, angle of attack, operating envelope, etc. were determined for various stages of flight operation. The aerodynamic coefficients and available power obtained from previous chapters were used for these calculations. The steady level flight envelope was also plotted. The third iteration was performed to converge the design parameters according to the performance estimation and the constraint analysis.
10. Sensitivity Analysis
Sensitivity analysis is the study of how the uncertainty in the output of a mathematical model or system can be divided and allocated to different sources of uncertainty in its inputs. The influence of various design variables on the final design was investigated. This provides us with a specific range of operation according to our requirements, and also the expected change in performance if some parameters were changed.
The Stage II final review took place after we performed the sensitivity analysis. We submitted the final report, but unfortunately, could not make it to the final stage, Stage III.
A Learning Experience
Overall, NACDeC was a huge learning experience, where I got to learn the art of conceptual design, and dabble in aircraft structures, flight mechanics, interact and efficiently work with an amazing team, attend webinars from Prof. Rajkumar Pant, the professor-in-charge of the entire competition, and gain valuable insights from him. I would like to thank my teammates Apurv, Jasmine, Mohit, and Aditya, Athrey for all his guidance, and the organizing committee for this experience. It was a pleasure working with you all. I look forward to innovating, learning, and discovering more in Aerospace Engineering. Cheers!
References
- NACDeC -Mumbai Chapter
- Aeronautical Society of India
- Aircraft Design: A Conceptual Approach, Daniel. P. Raymer
- Performance, Stability, Dynamics and Control of Airplanes, Third Edition, Bindu. N. Pamadi
- HELIPLAT: Design, Aerodynamic, Structural Analysis of Long- Endurance Solar-Powered Stratospheric Platform, Guilio Romeo
- Horizontal Wind Model (HWM) 1993, A. E. Hedin
