Hello all ! It's been a while since I last posted, it's mostly because I've been busy brushing up on Aircraft controls and dynamics so that I can create an autopilot for the VTOL design. We re-iterated our previous design which was a flying wing to a fixed wing aircraft because no matter how much we tried to optimize it, the performance was always below what is achievable from fixed wing UAVs. So we decided to make the switch and moved to a twin boom inverted V-tail design with three motors.

We got a very efficient forward flying characteristics with the design at a cruise speed of around 20 m/s it can fly for an hour and MTOW is 6.2kg. With the design procedure that was almost similar to my previous post where I talked about Flying wing tilt rotor design, we moved to bigger challenges. The first was to control the aircraft during the three flight regimes : hover, transition and take off. To get the control and stability, derivatives the UAV was modeled in USAF DATCOM+ and the required parameters were obtained. But since the software was written in 1976 it doesn't provide support for V-tail. However, after posting on online forums I was told there's hardly a difference in the stability derivatives and hence, the following model was used to get the results.The vertical stabilizer can be seen in the above image which is the drawback of outdated software. However, AVL can also be used to generate control/stability derivatives. I plan to use it in future iterations of the design to get more accurate model. The next step was dynamic modelling of the aircraft in MATLAB. It was started with designing a GUI for visualizing the effect of various input parameters on the UAV. Below is the GUI that was created in MATLAB for the aforementioned purpose.

Once this was done the rigid body equations were modeled (PS debugging in MATLAB is a pain) and the following window was created. This is a screen-grab of the second version of GUI with control gains that allowed me to change the parameters while running the simulation.

So that's a quick update of what I've been up to. The next step would be to model the aerodynamic equations over the rigid body dynamics skeleton. I plan on first implementing decoupled 3 DOF equation model which I'll later extend to a 6 DOF model of the UAV.

Cheers,

Karan

A big hello to all the intelligent lifeforms everywhere and to everyone else out there, the secret is to bang the rocks together.

I just want to update you all on my current project work. The design started by deciding the performance objectives for the UAV which are as follows:

1. 30 min cruise endurance + 10 min VTOL + 5 min take off landing
2. Around 15 m/s cruise speed and a flying altitude of 150 m
3. An operational radius of 30 km
4. A payload capacity of >2 kg which will include thermal/IR cameras etc.

The UAV configuration will comprise of 2 tilt-rotors which will be active during all of the flight phases and also one main rotor which will be just active during the VTOL and hovering phase. In the cruise mode, tiltrotors will be turned to the flight direction using simple servo motors and the power of the coaxial central motor will be boosted to provide necessary lift. Once the transition is completed, the central motor will be slowly turned off so as to maintain constant altitude and the duct will be closed to reduce drag.

The above image is the result of trade studies that were performed to estimate thrust and weight loading for the UAV.

After running initial weight estimation algorithm and performing the trade studies, T/W and W/S were decided along with the thrust distributions for the rotors. The image shows the weight estimation algorithm that was used along with trade studies for determining thrust and wing loading.

After preparing concept sketches for the UAV, blended wing configuration was selected by keeping in mind the portability and efficiency. Flying wing configuration has a minimal wetted surface area which reduces profile drag significantly. The absence of stabilizing surfaces induces higher maneuverability, which is essential to the UAV. Use of commercially available autopilots will greatly ameliorate the dearth of stability in flight dynamics. Once this was completed we moved to selecting airfoils for the flying wing VTOL tilt-rotor. Different reflex airfoils were analyzed in PROFILI so as to enhance the maximum lift coefficient while limiting the maximum drag. In addition to the flying wing design, blended winglets will be used to enhance the aerodynamic efficiency. Winglets will house the rudder controls for the UAV. 

This image shows the UAV in VTOL mode with the central open hub which we plan to close in cruise flight. Eppler 334 was selected for the central plank section, NACA34112 for the wing plan-form and NACA0012 for the winglet. The next step was to perform preliminary iterations in a basic software like XFLR5 so as to get some results for number crunching.

The above image is the result of aforementioned XFLR5 analysis showing the air stream flow around the UAV at trimmed flight of 4 degrees along with the pressure contours. A CL/CD of around 20.5 is achieved which proves the initial guess of superior flying wing efficiency as compared to conventional configurations.

This image shows the side view of the mesh that was generated for CFD analysis. 

This is flow field around the UAV in cruise flight with the flap open, the drag penalty can be seen clearly in the form of vortices.  

This brings me to the end of my blog post. I'll update you guys on more once I get some substantial results. 

Looking forward to your expert opinions in the comments below. 

So long and thanks for all the fish.

-Karan 

Flying Wing for Search and Rescue

Hey Guys,

I've been working on designing a flying wing UAV since 2 months now. Human search and rescue using an autonomous drone is the prime objective of this project.

First Prototype.

One of the major aim of our project is to show how a visual human detection system that uses images from a normal camera can be implemented in software. The system would fit into the larger context of disaster management and more specifically how it can benefit search and rescue operations. 

So the first prototype was made but it couldn't fly all that well. The tips stalled while rolling(probably because of no twist and less sweep) and led to a disastrous crash. As soon as our first prototype failed we got down to designing the second version.

I need some advice with the design of the second air-frame. 

So I'm pretty satisfied with the numbers Xflr is churning up for the second prototype. But I'm unhappy with the kind of performance I'm getting. 

Also I'm a bit skeptical about the amount of twist I've to give to prevent my wing tips from stalling. I'm using the Pankin twist formula and it gives approximately -9 degrees of twist. I'm not sure if this is usual for flying wings or not. I was told anything between 4-15 is normal. 

So my doubts about the design are : 

1) Is the twist alright or should i reduce it a bit ? 

2) What can I do to improve my max Cl/Cd ? 

3) Any other design faults you guys see in the design ? 

Also some updates on the Image processing part. 

HOG detector was successfully tested on a sample camera feed.

Thank you for your time and consideration.

Cheers,

Karan

Hey everyone,

I'm Karan from India and have been involved with drones for around 3 years now. 

I have worked extensively in Aircraft CFD analysis and control systems (way point navigation). I have been working on these domains exclusively since the past 3 years. 

I have worked on multiple autopilot systems and have designed completely autonomous multi-copters. I have also worked on aircraft design and completely constructed a 4-axis CNC machine for foam cutting (airframes) and test rigs with my mates here. 

I've been in talks with Wayne Garris and hopefully we'll soon be working together on the next techpod along with the complete drone community. (if the design becomes open source)

Really excited about this, would be a great learning opportunity working withprofessionals like Wayne.

Looking forward to working with you Wayne.

Do check out the attached pictures.