Aero Club Make a Foam Plane - Centre For Innovation

Transcription

Aero Club
Presents
Introduction to RC Modeling
Module 5
Make a Foam Plane
Centre For Innovation
IIT Madras
Aero Club - Intro To RC Modelling – Module 5 - Making a FOAM PLANE
Table of Contents
Introduction: ...................................................................................................................................................... 3
About foam plane: ......................................................................................................................................... 3
Materials and Avionics ....................................................................................................................................... 3
Designing – plane parameters ........................................................................................................................... 4
Weight Estimation ......................................................................................................................................... 4
Wing parameters ........................................................................................................................................... 4
Optimization: ............................................................................................................................................. 5
Airfoil Selection .............................................................................................................................................. 5
Horizontal and Vertical Stabilizer .................................................................................................................. 6
Fuselage and other parameters ..................................................................................................................... 6
Building Steps:.................................................................................................................................................... 7
Shaping the wing............................................................................................................................................ 7
Making the fuselage....................................................................................................................................... 7
Fixing control surfaces ................................................................................................................................... 7
Reinforcements .................................................................................................................................................. 8
Attaching everything together ........................................................................................................................... 8
Avionics setup .................................................................................................................................................... 9
Finishing it up ................................................................................................................................................... 10
Fly through the sky........................................................................................................................................... 10
Pre-flight checks:.......................................................................................................................................... 10
Test Videos: ...................................................................................................................................................... 10
Exercises: .......................................................................................................................................................... 11
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2
Acknowledgements: ........................................................................................................................................ 11
Centre For Innovation – cfi-iitm.org
Indian Institute of Technology Madras
Introduction:
About foam plane:
Foam plane is a basic model of a plane made entirely out of foam. Like every other RC Plane, it is
manually controlled by a pilot on the ground with a transmitter. Such a plane is very light in weight as
foam is the major building material.
Materials and Avionics
The major constraint in the making of such planes is the weight of the material and avionics used.
So every material used must have a high performance to weight ratio. For details of these refer to
Module 1 & 3: Introduction to flight and Electronics in Avionics.

High Density Foam: Stronger than a normal thermocol, it is
used to design most of the parts of the foam plane.

Coroplast: It is sturdy, light, resilient, and inexpensive, making
it ideal for making control surfaces such as ailerons, elevators,
rudder, etc.
Propeller
Landing Gears
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Brushless Motor
 Servo Motor: It is used to control the control-surfaces of the plane i.e. the ailerons,
elevator and the rudder.
 Control Rods: Which connect the servo motors and the control surfaces
 Foam Glue: General super glue such as feviquick, araldite, fevitite etc, cannot be used to
stick foam, as they eat up on it. Foam glue is used instead.
 Hot Wire Foam Cutter/ Knife Cutter:

Other hand tools and power tools.
Designing – plane parameters
This is the first and most important step in making a plane. All the calculations are done and then
the material and avionics specifications are decided.
Weight Estimation
The calculations for the plane start by approximating the max takeoff weight of the plane. The
materials used in the foam plane are well known. So the approx. weight of every part is taken to
calculate the entire weight. Mostly, a foam plane won’t exceed 1.0-1.5 kgs. Tabulate all the data.
Let this total weight be W.
Estimated Weight = W
Wing parameters
Now that the total estimate weight of the plane is known, the wing shape and other parameters
can be decided.For an efficient design the lift needed should be taken to be 1.5 – 2 times the
weight. Let this Lift force be L.
Lift = 1.5 * Weight
The amount of lift generated by a wing depends on:




Wing span
Chord length Area of wing = Wing span * Chord length
Coefficient of lift
Aspect Ratio = (Wing span)2 / Wing Area
Air velocity Density of air
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The relation is: 𝐿 = 1 2 𝜌𝑣 2 𝐴𝐶 L
The velocity for RC Plane is taken to be approximately 10 m/s and the density of air is 1.225 kg/m3.
Thus, the value coefficient of lift (CL) is calculated in terms of Area.
The Aspect Ratio for glider like planes is kept around 5 – 6.
Optimization: Create an excel sheet and list down columns with all the parameters like in shown
Table 1.
Weight
(Kg)
Velocity
(m/s)
Density
(Kg/m3)
Wing span
(m)
Aspect
Ratio
Chord
length
Area
Coefficient
of lift
Table 1
Now take a Wing span (of 1 m or close) according to the size of plane you want to make. Get the
Chord length from the Aspect ratio, i.e.
Chord =
Wing span
Aspect ratio
…. For rectangular wing
Get the area of the wing by multiplying Chord and Span. Using the lift equation get the value of
Coefficient of lift (preferably <1).
You should have tabulated all the data by now as in Table 1.
Note: For swept wings the Area of wing is the product of wing span and average chord length,
where Average chord = 0.5 * (Tip chord + Root Chord).
Airfoil Selection
The airfoil of a wing decides how much lift it can generate at a given velocity of flight. Along with
that it decides also, the amount of drag it would induce on the wing. The parameters C L , CD decide
the lift and drag for a particular airfoil.
The most effective design would have max CL and minimumCDat minimum angle of attack, α.So
their ratio is used to decide the best airfoil for a given airplane. Now it’s time to select your airfoil.
Go to an airfoil plotting website: for example: http://airfoiltools.com/compare/index
Select some airfoils (preferably having close to flat bottom shape) and add them to the plot. Go
down the page and tabulate the Cl vs Cd ratio for a given Reynold’s number.
Alpha
The best airfoil would be the one having max ratio of the two coefficients while having the least
angle of attack for the same. Now, your complete wing parameters are ready.
5
Cl/Cd
Page
Airfoil
Horizontal and Vertical Stabilizer
The horizontal and vertical stabilizers are used to control the lateral movements of the plane. For
more detailed info, see Module 1 Introduction to Flight.
The area of horizontal and vertical stabilizer is taken to be around 1/5th and 1/10th that of the wing
respectively. The chord length of both is taken to be around 1/3 rd that of the wing. The width of
the elevator and rudder would then be taken as approx. 1/3 rd or some value that would look
suitable by visual inspection.
Fuselage and other parameters
The fuselage would hold everything together. So it must have enough room for attaching the
wings, control surfaces and the avionics i.e. there should be enough width to prevent toppling of
wing and there should be space to keep the battery and other stuff. The front of the fuselage
should have enough space to easily attach a motor mount (if it is a nose motor plane).
Thumb Rule: Fuselage length is generally taken as 0.7 times the wing span.
Next the fuselage should be efficient by creating the least possible drag and, if possible, providing
some lift. So the fuselage can be designed in an airfoil contour. Try reducing the number of sharp
edges and blunt faces, as they induce a lot of drag and therefore aren’t aerodynamically efficient.
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Now that we are ready with all our design parameters, let’s start building our plane.
Building Steps:
Since most of the framework has to be made out of foam, we use a hot wire foam cutter to shape out the
foam. Hot wire cutter is a simple tool, having a high resistance wire stretched tightly, through which passes
a current to heat the wire enough to cut foam.
Shaping the wing
First of all, draw a sketch of the wing on the foam, with proper dimensions. Repeat this on all three faces
so that you get a rough idea of how much foam you’ll have to cut.
Check out youtube videos for an idea on how to cut foam using hot wire cutter.
https://www.youtube.com/watch?v=R0ZCnR_g6ZU
For rectangular wing with constant area of cross section, the complete wing can be cut at once. But for
sweep wing the wing will have to be cut in two halves which shall be joined later while fixing.
Take print out of the airfoils you have decided and shape out wooden pieces in that shape. Now paste the
shapes on the sides of the foam and cut out the wing along the edges of the wood. Mark 1/4th chord length
from the leading edge of the wing. This is the point where resultant lift force acts on the wing.
¼th chord
Do the same for horizontallength
and vertical stabilizers. Then using sand paper smoothen the rough and
irregular edges.
Making the fuselage
Take thicker foam enough to accommodate the desired shape of fuselage and draw its shape on the foam.
Remove extra foam using wire cutter and sand paper.
Mark ¼th length of the fuselage from the nose end. This would the point where the wing’s ¼ point would
be merged.
¼th length from tip
Fixing control surfaces
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The control surfaces would be made out of Coroplast. Cut Coroplast of the dimensions selected earlier
along the flutes and cut an edge to make a hinge as shown in the figure. Cut the wing of the right shape as
of the control surface and fix the control surface below wing, horizontal & vertical stabilizer using foam
glue.
Hinge
Reinforcements
Though we are using the strongest foam, we can’t just rely on it to lift the weight of the whole
plane. So we need to strengthen the wings using carbon fiber rods to avoid foam breakage due to bending
because of excessive load.
Attaching everything together
After the wings and stabilizers are ready, stick them to the fuselage. The wing’s 1/4 th point would
merge with 1/4th point of fuselage. The horizontal
stabilizer would come at the extreme end of the
fuselage with the vertical stabilizer on top of it.
Turn the elevator and rudder to see if they are
free to turn. Cut out extra surface if any blockage
occurs.
Attach the landing gear on the fuselage below the wing
according to the C.G. Fix a wheel at the rear end.
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The plane structure is ready…
Avionics setup
A motor on the fuselage’s nose and servos for control surfaces are the electronics involved. Fix the
motor on the nose using motor mounts and connect the ESC. Make grooves and put servos on the wing
and connect its head to the control surfaces using control horns. Similarly connect servo for elevator and
rudder.
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Connect the ends of the two aileron servos using a ‘y’ channel to the receiver channel 1. Connect the
elevator and rudder servo on channel 2 and 4 respectively. ESC should be connected on channel 3 for the
throttle.
Finishing it up
Turn on the transmitter and connect the liPo. Place the liPo such that the C.G of the plane comes
nearly at the ¼ fuselage length or so. Check all the channels and their directions. Reverse if needed.
Cover the wings and stabilizers using monokote. Monokote won’t stick directly on foam, so try using
double-sided tape or some glue to stick it. Using Monokote reduces the drag experienced by the plane. An
alternative to monokote could be any smooth sheet/paper etc. Fabricate the parts and decorate as
required.
Fly through the sky
Go to an open area for flight.
Pre-flight checks:







All connections are tight and working.
Direction of turning of control surfaces.
Calibration of ESC.
The motor is turning in the right direction i.e., the propeller is blowing air towards the tail of the
plane (backwards).
Hold the plane and check motor at different levels of throttle.
Gently chuck the plane in air, it should glide smoothly. If not, adjust the CG of the plane by varying
the position of Li-Po.
Wheels turn freely, without any wobbling – to prevent any sideslip.
Go, fly….. Let your plane soar high… in the sky.
Test Videos:
Flight 1
Flight 2
Control Surface Test
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Ground Run Test
Exercises:
1. What are advantages of using a swept wing than a rectangular wing?
2. Why is 1/4th chord length of wing so significant?
3. What value of chord length will you use for a swept wing?
4. Why do we use monokote?
5. Where should you position the liPo for a steady flight?
6. Why should all the electronics be placed below the wing?
7. What’s the range and frequency of the radio transmitter you are using?
8. Why should the motor be connected to channel 3?
9. What is elevon configuration?
10. Should the control horns be placed close or far away from the hinge?
11. Why is a ‘y’ channel used for the servo motors connecting the ailerons?
We hope you have enjoyed your experience in designing and making your own foam plane.
Once you are done with making the foam plane, you can send the images of the plane and answers to the
above exercises to any one of the following mail id’s – [email protected] ,
[email protected] . We would be very happy to look at the results of the hard work you have put
in.
For any queries/feedback on the procedure of making the glider, materials procurement you can write an
email to any one of the above mentioned addresses.
To join aero club, go to the Clubs tab -> Aero Club on the CFI website, and click on Join Aero Club.
Acknowledgements:
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This course on Intro to RC Modeling was formulated, prepared and compiled by the following members of
Aero Club:
(In the order of the module of the courses)
1. Anil Kumar
2. Hanut Vemulapalli
3. Dheepak N Khatri
4. Sanjesh Hoskopple
5. Nikhil Gupta
6. GuruPrasad Kallanje

Aero Club Make a Foam Plane - Centre For Innovation

Transcription

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