2003-2004 Rochester Institute of Technology
Micro Air Vehicle Team


Concept Development/Feasiblity

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Concept Development/Feasibility

Airframe - Vehicle Configuration

A conventional aircraft design consists of a fuselage, wing and tail, while a tailless flying wing design consists of only a wing and control surfaces. The main drawback to the conventional configuration, when considering the unique application of MAV's, is the minimal wing area due to the addition of a tail. A flying wing configuration will maximize wing area within a maximum linear dimension constraint, and was therefore chosen as the vehicle configuration for RIT's MAV.

Conventional tail configuration

Flying wing "tailless" configuration

Airfoil

Selection Criteria

  • Flight Regime - 70,000 < Reynolds Number < 200,000
  • Thickness to Chord Ratio < 10%
  • CL and CD
  • Stability Effects - CM > 0

Using the above criteria, the list of potential airfoils was narrowed down to three.


Planform Shape

The primary consideration when determining body shape is the need to maximize wing area while minimizing the largest linear dimension. This suggests that to maximize the available lifting wing area, the aspect ratio should be near one.

An extensive literature search of low aspect ratio wings led to four basic shapes; rectangular, Zimmerman, inverse Zimmerman and elliptical.

Materials and Fabrication

Many concepts for the design and construction of the airframe were considered, including:

Molded Carbon Body

Carbon-Rod Frame covered with Mylar

Lightweight Polystyrene Foam


Propulsion

Three different concepts were evaluated for the MAV's propulsion system. The major considerations for a successfully propulsion system are the thrust produced, power consumption, and overall system weight. The three types considered are rocket propulsion, and two motor - propeller combinations; one utilizing an internal combustion engine, the other using an electric motor. Two possibilities for the propeller selection are commercially available propellers or custom designed and manufactured propellers.


Rocket Propulsion


Internal Combustion Engine

Electric Motor


Commercially available propellers

Six criteria were used to narrow down the propulsion type selection:

  • Thrust Available
  • Reliability
  • Weight
  • Ease of Integration
  • Multiple Usage
  • Ability to Control

Using this criteria a weighted evaluation showed that the electric motor/commercial propeller combination was the best option to pursue further.

Weaknesses of other options:
Rocket Propulsion - Difficulty of integration, cannot be used on multiple flight attempts, unable to control thrust output
ICE - Unreliable, high weight penalty, difficult to integrate, difficult to control thrust output
Custom Propellers - Difficulty in design and fabrication.


Electronics

Control System

Numerous control receiver units were considered, taking into consideration the amount of current drawn, the physical size, the mass, and receiver range. An design decision was made based on the knowledge that the base station would have unlimited transmission capability and the control signal can be boosted if necessary with the use of a signal amplifier. All of the receivers considered operate in the 72MHz band and are five volt compatible. The HFS-04MG and 92515Z were rejected based on weight considerations despite superior range characteristics. The Feather was also rejected due to the benefit in weight and size reduction realized by choosing the R4P-JST.


Control receiver options


Wes-Technik control receiver


Speed control modules are required to increase or reduce speed of the motor as necessary by varying the voltage and duration of the time that the motor is supplied. The YGE-3 was chosen over the MX9104 because of its compatibility assurance with the R4P-JST receiver. It was chosen over the YGE-6 because the motor (eventually chosen by the propulsion group) should not draw more than two amperes, making the YGE-3's continuous current rating sufficient.


Speed controller options


Wes-Technik YGE-3 Speed Controller

Video System

All image acquisition and transmission equipment that was initially considered was supplied by Black Widow Audio-Video. The camera considered is the Panasonic CX161. This CCD camera was chosen because of its superior image quality compared with CMOS cameras despite its weight disadvantage. The camera runs in the five volt range at 160mA, increasing its ease of integration into the rest of the system. The camera weighs 11.6 grams and has a 52 degree field of vision.

Panasonic CX161

 


To receive the video imagery in real time, a transmitter/receiver system is necessary. The standard commercially available miniature five volt transmitters all send data in the 2.4 GHz band. Transmission range is doubled with a quadrupling of transmission power. The transmitter eventually chosen was picked based strictly on weight and power consumption considerations. The issue of improving the range is addressed in the choice of the receiving antenna at the base station.


Video transmitter options


Core5 video transmitters


Four different 2.4GHz band antennas from Hyperlink Technology are considered to increase the range of the video signal. Desired attributes are high gain and wide beamwidth. High gain is most important, however. Antennas considered are the HG2414P Patch antenna, the HG2414D Backfire Reflector antenna, the HG2416P Directional Panel antenna, and the HG2424G Parabolic Grid antenna. The antenna selected as the correct antenna for the design was selected based on maximum gain and the a priori flight path information (general directional knowledge of the location of the target). Also, team members would be able to point the antenna manually in the direction of the aircraft at all times using the rotating antenna stand. An adapter/cable is required to properly interface the antenna with the receiver unit.


Video ground-based antenna options


Hyperlink HG2424G antenna


Batteries

The battery source to be used was decided to be lithium polymer cells due to their extraordinary power capacity to weight ratio. The decision process was implemented in deciding which of the available battery capacity would minimize weight, yet still supply sufficient current for a prescribed flight time.


Battery options


Kokam battery

The batteries will produce a 7.4 volt DC source. To provide the correct voltage to a majority of the electronics, a voltage regulator is necessary. It must source at least 1 amp continuously. The LM2940 is a logical choice because of its fixed voltage characteristics. The LM2940 can source one ampere at a constant five volts.



Launcher

Three basic concepts for launching the MAV were considered. The first is a simple hand launch. This very simple method requires no equipment and little time. Unfortunately, hand-launching can be difficult to do successfully and repeatability is hard to ensure.

Another method investigated was a handheld launcher mechanism. Several hand-held devices exist for launching small aircraft. These have incoporated pneumatics, cross-bow type drawstrings, and even rubber bands.

Finally, ground and table based launcher mechanisms were considered. These provide a stable platform from which to launch the MAV. However, they also lose a degree of portability because of their size.


Hand launch

Table launch concept (courtesy of U. of Florida)

Ground launch concept (courtesy of MLB Company)

 


Copyright · 2004
RIT Kate Gleason College of Engineering and the RIT MAV Team.