Soaring to Spec: Designing a Concept Aircraftfor Cargo Deployment

Yunseok Choi Robert Cohenyunseokc97@gmail.com roboco555@gmail.com

Trisha Datta Sumita Rajpurohittdatta@htps.us sumitar56@gmail.com

Navin Raonr@pds.org

ABSTRACTAerial firefighting has proven itself to be

a valuable procedure in containing thewildfires that consume millions of acres ofland every year. Unfortunately, aircrafts mustdescend drastically to deliver the water andfire retardant they carry, thus exposingthemselves to dangerous thermal winds,smoke, and debris.

In order to make aerial firefighting safer,a prototype cargo plane was developed to testthe feasibility of using water bombs for spottreatment. Using such bombs would allowaircrafts to fly at higher altitudes and avoidthe dangers associated with proximity to fire.The prototype was designed with an originalairfoil with a high coefficient of lift. Thefuselage of the plane was based off of aninverted Kline Fogelman design for extra liftand easy cargo storage. The water bombsused were 3D printed cylinders that werereleased by a mechanical arm.

The model was made of extrudedpolystyrene. All cylinders burst upon contactwith the ground, showing that such bombscan be used to fight actual wildfires.

1. INTRODUCTIONForest fires are an old and ongoing issue.

In 2012, there were 67,774 fires thatconsumed 9,326,238 acres of land in the US

alone.1 The most damaging fire that year cost$353 million, as estimated by the RockyMountain Insurance InformationAssociation.2 Despite the benefits of naturalwildfires, most fires are still destructive innature. The issue at hand is the containmentof wildfires to prevent extensive damage ofproperty, resources, businesses, and life.

Wildfires are battled by conventionalground techniques and aerial firefightingtechniques. For containment purposes, aerialfirefighting is the superior method. Aerialfirefighting consists of dumping water, gel,foam, or specially treated fire retardant ontothe flames below. Planes need to flydangerously close to the fire to ensure even aloosely accurate delivery of payload,3 and thethermal winds and other dangers associatedwith proximity to forest fires can easilyinfluence moments on aircrafts and endangercrew members.

The goal of this project was to improvethe safety of aerial firefighting, thus reducingrisk for the pilots and aircraft involved. Thispaper specifically addresses the feasibility ofusing water bombs in fighting wildfires. Toexplore this, a small scale aircraft wasdesigned that could deploy cylindrical waterbombs one by one. Calculations relating tobalancing flight forces and moments were

performed, and a system was designed topartially deploy cargo, which would allow apilot to target the wildfires in crucial areas.

2. AERIAL FIREFIGHTING ANDAERODYNAMIC CONCEPTS

2.1. Aerial FirefightingAerial firefighting vehicles come in three

types: land-based airtankers, helitacks, andscoopers.4 These three models differ by theirmethod of loading retardant or water. Whileairtankers fill up at airport tanker bases,helitacks use buckets or tanks to carry water.Scoopers, on the other hand, gather theirwater supply from natural water sources.

A common misconception about aerialfirefighting is that it is the sole method offighting wildfires.4 In fact, conventionalfirefighting squads put out most of the fire.Airplanes, in addition to attempting tocontain the fires, use spot treatment to cooldown the area for the safety of the groundsquads.

The three main types of attack employedby aerial firefighting are indirect attack,parallel attack, and direct attack.4 Indirectattacks target wildfires by deployingretardant away from the actual fire, which isextinguished before it reaches the point ofdeployment.4 For this type of fighting,airtankers are the most ideal. Similar to anindirect attack, parallel attacks do not deployretardant directly onto the fire.4 However,they do deploy the retardant at a smallerdistance from the fire’s edge. This acts as a“control line”, meaning it makes the path ofthe fire smoother and sets a boundary forwhere the fire will die out. In a direct attack,aircrafts deploy retardant directly onto “hotspots” or larger fires.4 For this type offighting, scoopers are the best type of aircraft.

These techniques, while effective to anextent, are by no means ideal. For example,to deliver the retardant, planes must divetowards the fire, risking damage from heat,debris, smoke, and thermal winds.3,5

Maneuvering in these conditions is time-consuming and inefficient, and in situationswhere time is of the essence, these issues areeven more pressing. Low altitudes forcefirefighting aircraft to only fly during the daybecause flying low over populated areas istoo dangerous at night.6 If planes try to fly athigh altitudes, the water diffuses by the timeit reaches the ground, thus becomingnullified.

Recently, to combat the problem of flyingtoo close to fire, Boeing has tested theeffectiveness of biodegradable water bombs.3

After being deployed from the plane, eachbomb holds its shape during its drop andbursts upon contact with the fire. Just oneaircraft full of these bombs would performwork equal to that of 100 helicopterdeployments. Furthermore, the bombs can bedropped from 1,000 to 2,000 ft. above theground, high enough to avoid thermal winds.

Another effort on Boeing’s part to makeaerial firefighting safer is its PrecisionContainer Aerial Delivery System(PCADS).7 This system deploys retardant incontainers and allows pilots to fly at a high,level attitude, thereby eliminating thedangerous dive-bombing efforts of currentplanes.

2.2. Design Principles andAerodynamics

In order to build a plane, the basicprinciples of aerodynamics and how theyaffect aircraft design need to be understood.

2.2.1. ForcesFour forces govern flight: weight, thrust,

lift, and drag (Figure 1).

Figure 1. Four Governing Forces8

Weight is the force caused by Earth’sgravitational field on the plane and its cargo.Thrust is typically generated by a rotatingpropeller, which is powered by either anengine or a motor.

Drag and lift are the two components ofaerodynamic force.9 When an object movesthrough a fluid like air, the pressure of thefluid creates a force on the object that acts onthe plane at its center of pressure. This iscalled the aerodynamic force.

Lift is defined as the component of thisforce perpendicular to the object’s motion,while drag is defined as the component of thisforce parallel to the object’s motion.9 Bothlift and drag are determined by the shape andspeed of the aircraft and the density,temperature, and composition of thefluid.10,11

Drag can be thought of as air resistanceand is calculated by Equation 1. Cd is aconstant called the coefficient of drag that isdetermined by the shape of the object inflight, ρ is density, A is planform area or thearea of the top view of the wing, and v isvelocity.

D = Cd ρAv2/2 Equation 110

Lift is the force that makes flightpossible. The wings of an aircraft contributethe most lift, while additional and lesssubstantial lift is generated by the rest of theplane.12 A solid object generates lift when itturns the moving flow of a gas. In doing so,the object diverts the flow in one directionand, according to Newton’s law of equal andopposite reactions, generates lift in theopposite direction.13

Lift is generated because the air around aplane can have different velocities andtherefore, according to Bernoulli’s Principle,different pressures.14 The total lift can beobtained by integrating the pressuredifference multiplied by the fuselage area.

Because the airflow must be turned,motion is essential for lift to exist. In addition

to turning the air flow, the solid body must bein contact with the fluid for lift to occur. Liftis calculated by Equation 2. CL is a constantcalled the coefficient of lift that is determinedby the shape of the object in flight, ρ isdensity, A is planform area, and v is velocity.

L = CLρAv2/2 Equation 211

Weight is the fixed variable of flightdynamics. In designing an airplane, one mustconsider how all the other forces interact withweight. Lift opposes weight and allows theaircraft to become airborne. Lift isexponentially related to thrust, but higherthrust also creates higher drag, which reducesthe effective lift. The lift limits how muchweight the aircraft can carry. Thus, it is clearthat weight, lift, thrust, and drag are affectedby each other and numerous other variablesthat need to be considered in design. A stableaircraft requires balance of all these forces.

2.2.2. Reynolds NumberAnother factor that affects the

aerodynamic force acting on an object is theReynolds Number of the air. The ReynoldsNumber is a measure of the viscosity of theair and is calculated by taking a ratio of theair’s inertial forces and viscous forces. Theequation for calculating a Reynolds numberis given by Equation 3; v is the velocity of theobject, L is a length scale, and ѵ is thekinematic viscosity coefficient. The higherthe Reynolds Number, the smaller theimportance of the fluid’s viscous forces. Thelower the Reynolds Number, the bigger theimportance of the fluid’s viscous forces. Inaddition, lift and drag vary by operatingReynolds Number. It is imperative toconsider this when designing the wings.

Re = vL/ ѵ Equation 315

2.2.3. WingsFigure 2 shows a diagram of a standard

wing.

Figure 2. Standard Wing16

The cross-section of a wing is called theairfoil, while the chord is the tip to tipdistance. Airfoil selection is a crucial processthat has more of an impact than any otherfactor on a plane’s ability to fly. Because asignificant majority of an airplane's lift isgenerated by the wing’s airfoil, the liftgenerated by the wing must be large enoughto lift the entire body of the plane. However,changing the shape of the airfoil to increaselift can also increase drag, and if the airfoilproduces too much drag, it will negate theplane’s thrust. Another consideration whenchoosing an airfoil is the operating ReynoldsNumber because some airfoils are notdesigned to fly at certain Reynolds Numbers.

2.2.4. Control SurfacesMost aircrafts have control surfaces,

which are adjustable surfaces that allow thepilot to rotate the plane around its axes. Thethree most common types of control surfacesare ailerons, elevators, and rudders (Figure3).

Figure 3. Control Surfaces17

Ailerons work in pairs and are located onthe back of the wings.18 Moving the aileronscreates a change in shape of the wing, whichwill cause the aircraft to roll either right or

left, allowing the plane to turn.19 When theleft aileron is up and the right one down, thelift generated by the left wing decreases,while the lift generated by the left wingincreases, causing the plane to roll left.18

When the right aileron is up and the left onedown, right wing lift decreases and left winglift increases, causing the plane to roll right.The challenge in designing ailerons is beingable to control the sensitivity of the roll.

The elevators are attached to the back ofthe horizontal stabilizer, one of two parts ofthe plane’s tail, and work together to pitch theplane up or down.20 When the elevators arepointed down, more lift is generated in theback of the plane, causing the back of theplane to rise and the nose to drop.Conversely, when the elevators are pointedup, less lift is generated in the back of theplane, causing the back of the plane to dropand the nose to climb. Similar to designingailerons, designing elevators requiresbalancing pitch moments for a stablecontrolled flight.

The rudder is attached to the verticalstabilizer, the second part of the plane’s tail,and can change whether the nose is pointedleft or right.21 When the rudder points left,more lift is created on the tail in the rightdirection, causing the nose to bank left. Whenthe rudder points right, more lift is created onthe tail in the left direction, causing the noseto bank right. Many forces, such as propellerwash, wing tip vortices, and engine exhaust,induce moments on the aircraft, causing it toroll or yaw. The rudder ensures that the noseof the airplane is pointed in the rightdirection. These parameters must beconsidered in rudder design.

3. DESIGN OF SCALED MODELThe plane described in this paper was

designed to be able to lift its own weight incargo, specifically plastic water bombs thatcould hold fire retardant or water.

3.1. Airfoil Design

The first step in picking an airfoil wasfinding a minimum required coefficient oflift. Since the function of the plane is todeploy retardant and water, its wings need tobe able to carry a significant weight. To findthe minimum coefficient of lift, Equation 4, amodified version of the standard lift equation,was used.

CL=2L/(ρv2A)) Equation 4

CL is the coefficient of lift, L is the liftgenerated by the wing, ρ is the density of theair, and A is the planform area.22 Since thepredicted weight of the plane was 7 lbs., thecargo would also weigh 7 lbs., and so thegenerated lift would need to equal 14 lbs. Tofind the speed of the plane, the online serviceeCalc was used. eCalc uses details aboutcertain plane components to calculate usefulflight information.

Some of the necessary details were asfollows. The motor is a Cheetah A4120-7, thebattery cell is a five cell LiPo battery, and thepropeller is a two blade 16” x 8” APCElectric E propeller with a gear ratio of 1:1.The local elevation used was 52 ft., the airtemperature was 85 °F, and the air pressurewas 29.91 in. Hg. The temperature and airpressure were those recorded on the day ofcalculation. eCalc predicted a top speed of 55mph, and assuming the speed drops almost inhalf for the sake of simplicity, the coastingspeed of the aircraft was predicted to be 30mph (44 ft./s).

According to the DeNysschen air densitycalculator, the density of the air inPiscataway is 0.0727 lbm/ft3.23 The humidityand temperature used were those of a typicalday during this project. The lift coefficientequation requires units of slugs, so thedensity of air used was 0.00226 slugs/ft3. Theplanform area of the wings was originally660 in2 or 4.583 ft.2, obtained by a 66”wingspan and 10” chord. However, thecoefficient of lift required by thesedimensions was 1.40, and taking into account

a partial efficiency of 0.8, the required CL

would be 1.75.When looking at CL, one must also look

at Reynolds Number. Kinematic viscosity isnecessary to calculate the Reynolds Number,and using a table from Engineering Toolbox,the kinematic viscosity for these purposes is2.234 x 10-4 ft.2/s.24 Using a ReynoldsNumber calculator with a velocity of 30 mph,a chord width of 10”, and a kinematicviscosity of 2.234 x 10-4 ft.2/s, the ReynoldsNumber is 164,087.25 More generally, theReynolds Number is on the order of 100,000.

A CL of 1.75 is a fairly high value for aReynolds Number on the order of 100,000.To remedy this, the wingspan was increasedto 72”, and the chord was increased to 11”,giving a new planform area of 792 in2 or 5.5ft.2 and a required CL of 1.16. Taking intoaccount partial efficiency, the chosen airfoilwas picked to have a CL = 1.16696/0.8 = 1.45,a much more feasible CL.

The step after calculating the minimumcoefficient of lift was to search for anappropriate airfoil. It needed to generate asmuch lift as possible without creating toomuch drag in order to carry the relativelymassive weight of the cargo. Furthermore, itneeded to be feasible to create in a workshopsetting.

The UIUC database was the primarysource of airfoil information for thisproject.26 Airfoil Tools was used to analyzeCL v. Cd plots of ten airfoils at ReynoldsNumbers on the order of 100,000. Of thoseten, three were eliminated (CH10-Smoothed,GOE 523, and FX 76-MP-160) because theirCL v. Cd plots in the specific ReynoldsNumber range was jagged. See Figure 4 fordetails.

Figure 4. Example of Jagged Graph27

CL v. Cd graphs are often used todetermine the predicted performance ofairfoils at different Reynolds Numbers.Cusps in such graphs indicate an unsteadyand volatile pitch level throughout the flight,which is dangerous for a small aircraft.

Another six airfoils (Clark YM-15, ClarkZ, FX 63-137 13%, MH 113 14.62%, Eppler395, Wortman FX 60-126) were eliminatedbecause their CL was either too low or tooclose to the minimum required value. The lastairfoil, the S1223, was eliminated because ithas a characteristically sharp and suddentrailing edge that makes the manufacturingprocess difficult and its durabilityquestionable. Finally, finding no success inthe databases, the Java applet JavaFoil™ wasused to experiment with different designs.After experimenting with iterations of theNACA 4-digit style airfoil, Joukowskyairfoils, and Horten Brothers airfoils, the bestairfoil turned out to be a modified NACA 4-digit style airfoil with 18% thickness and10% camber (Figure 5).

Figure 5. Final Airfoil Design

JavaFoil™ and XFLR 5 both returnedresults of a CL > 1.64 at an attacking angle of3º (±.003), in addition to promising CL/Cd

ratios and smooth CL v. Cd plots. This highcoefficient of lift would allow the plane to flyhigher, avoiding dangerous thermal winds,and carry the cargo more easily.

3.2. Fuselage DesignObtaining extra lift is specifically useful

for cargo planes, and one way to do this is touse a fuselage that generates lift. An airfoil-shaped fuselage, while certainly capable ofproducing extra lift, compromises the spaceavailable for cargo storage. An inverted KlineFogelman-like design (Figure 6), on the otherhand, also provides more lift than a typicalcylindrical fuselage and is advantageous inseveral ways for cargo deployment. Its flatbottom lends itself to simple cargo storage,and its stepped underside allows for an openback from which cargo can be dropped.

Figure 6. Inverted Kline Fogelman Design28

The design for the fuselage was heavilyinfluenced, though not dictated, by aninverted Kline Fogelman model. In addition,the fuselage was designed with flat sides for

proper aerodynamic flow as well as ease ofconstruction.

Based on general rules of thumb from theguidance of an experienced mentor, thefuselage length was determined to be around48” or 70% of the wingspan.

3.3. Tail DimensionsThe tail consists of the horizontal

stabilizer, the vertical stabilizer, the elevator,and the rudder. The final dimensions forthese pieces came from generally acceptedconventions.29

The horizontal stabilizer’s area is usually20 to 25% of wing area. In this case, since thewing area is 792 in2, the horizontalstabilizer’s area should be 158.4 to 198 in2.The area was chosen to be around 158 in2.Additionally, the traditional aspect ratio for ahorizontal stabilizer is from 4.5 to 5. Lettingx be the chord, the leading to trailing edgedistance, of the horizontal stabilizer and y bethe span, a system of equations can be set up.This system is given by Equations 5 and 6.Solving this system gives approximate valuesof x = 6” and y = 26”, giving an area of 156in2. The horizontal stabilizer span should alsobe about 33% of the wingspan, and 26” isclose to 24”, which is 33% of 72”. Theelevator area should be 20 to 25% of thehorizontal stabilizer’s area, meaning 31.2 to39 in2. Because the span of the horizontalstabilizer is 26”, the chord of the elevator is1.5”.

xy = 158 Equation 5y/x = 4.5 Equation 6

The vertical stabilizer’s area is usually 7to 12% of wing area. In this case, since thewing area is 792 in2, the vertical stabilizer’sarea should be 55.44 to 95.04 in2. The areawas chosen to be around 71.28 in2, which isapproximately 9% of the wing area. Thetraditional shape of a vertical stabilizer isroughly a trapezoid with two right angles, ashape that can be made by making a cut from

the midpoint of the top side to the midpointof the left side of a rectangle and attaching theresulting triangle to the bottom left corner ofthe rectangle (Figure 7).

Figure 7. Vertical Stabilizer

Thus, the dimensions of the verticalstabilizer can be treated as the dimensions ofa rectangle. The accepted aspect ratio for ahorizontal stabilizer is from 1 to 1.25. Lettingx be the horizontal distance and y be thevertical distance, a system of equations canbe set up, given by Equations 7 and 8.Solving this system gives approximate valuesof x = 7.6” and y = 9.5”, giving a total area of72.2 in2. This means that the verticalstabilizer is a right angled trapezoid with atop side of 3.8”, a bottom length of 11.4”, anda height of 9.5”. The rudder’s horizontallength should be 30 to 50% of the verticalstabilizer’s horizontal length; this length waschosen to be 2.75”, which is around 36% ofthe vertical stabilizer’s horizontal length.

xy = 71.28 Equation 7y/x = 1.25 Equation 8

Tail volume coefficient calculations wereused to check the general reliability of thesedimensions. The horizontal stabilizer volumecoefficient is calculated by Equation 9. Shs isthe area of the horizontal stabilizer; TMA isthe tail moment arm, meaning the distancefrom the center of gravity to the tail’saerodynamic center; Sw is the area of thewing; and Cw is the chord of the wing. Theareas and chord length are inherent parts ofthe plane’s design. By convention, the TMA

is 2 to 3 times the length of the wing’s chord,so for these calculations, it was assumed to be2.5 times the chord length, which is 27.5”.For the purposes of this plane, the Vhs shouldbe in the 0.35 to 0.5 range, and [(156in2)(27.5 in)]/[(792 in2)(11 in)] = 0.492,which is right in the target range.

Vhs = Shs*TMA/(Sw*Cw) Equation 9The vertical stabilizer volume coefficient

is calculated by Equation 10. Svs is the area ofthe vertical stabilizer; TMA is the tailmoment arm; Sw is the area of the wing; andbw is the wingspan. For the purposes of thisplane, the Vvs should be in the 0.02 to 0.035range, and [(72.2 in2)(27.5 in)]/[(792 in2)(72in)] = 0.0348, which is right in the targetrange.

Vvs = Svs*TMA/(Sw*bw) Equation 10

3.4. Propeller and Motor SpecsThe propeller used for this plane is a 16”

x 8”APC Electric E propeller with two bladesand a 1:1 gear ratio. The motor is a CheetahA4120-7 with a 530 KV. The battery cell is aLiPo battery with a cell capacity of 3700mAh and a weight of 3.6 oz.

The motor was chosen because it fits thisproject’s budget. Its maximum current is55A, and accordingly, the Electronic SpeedController was chosen to be a Phoenix EdgeLite 100 that has a maximum amperage of100A.

Six servos were needed for this project:two for the aileron, one for the rudder, one forthe elevator, one for the cargo, and one for thefront wheel. Each needs approximately 0.5amps. The Battery Eliminator Circuit, whichensures that the battery doesn’t overload theengine thus needed at least 3 amperes.Fortunately, the Phoenix Edge Lite 100 has abuilt in BEC that can take up to 5 amps.

Thrust testing was done with the samebattery but a slightly different sized propeller,and 10.8 lbs. of thrust were generated, whichis enough to lift the plane off the ground. A16” x 8” propeller was chosen because itwould have a necessary 1” ground clearance.

3.5. Water Bomb DesignIn place of simply dumping water and

retardant on fires, this plane was designed touse cylindrical water bombs to target “hotspots” in direct attacks. This allows the planeto fly at higher altitudes because thepackaging ensures that the retardant will notdiffuse in the air. Moreover, this higheraltitude would allow firefighting to occur atnight, and planes could fly level whiledeploying cargo rather than dive.

The water bombs for this plane werecylinders made of polylactic acid (PLA) by aMakerbot Replicator 2 in the Mabel SmithDouglas Library. The cylinders have 4”diameters, 6” heights, and caps that fit snugly(Figure 8, Figure 9). These dimensions arejust smaller than the plane’s exit port. PLAwas chosen because it is biodegradable.

Figure 8. Water Bomb Design

Figure 9. Water Bombs

3.6. Cargo Deployment System

The cargo deployment system for thisplane is a ramp coupled with a mechanicalarm (Figure 10).

Figure 10. Mechanical Arm

The release process is demonstrated byFigure 11. In the first stage, all threecylindrical bombs rest on the ramp duringflight. While in this position, the lower partof the arm prevents the bomb closest to doorfrom rolling out. In the second stage, thelower part of the arm moves up, the bombclosest to the door rolls out, and the other partof the arm prevents the second bomb fromfalling out. In the third stage, the arm thenshifts back to its original position, and thebombs roll down the ramp to fill the gap. Inthe fourth stage, the cylinders have rolleddown the ramp, and the second and thirdbomb can be deployed the same way as thefirst.

Figure 11. Deployment System

3.7. Landing GearFor the front wheel of the landing gear, a

fixture was constructed out of plywood andspruce (Figure 12).

Figure 12. Landing Gear

It consists of a backing that is mounted ona rectangular support that separates the noseand cargo bay. Two square pieces areperpendicular to the top and bottom of therectangular support, and the rod to which thewheel is attached runs through the center of

the squares. A 1” spring with collars at bothends rests between the two square pieceswithout touching the rod. The purpose of thespring is to absorb shock when the plane hitsthe ground. This spring, which has a 0.6”travel, can absorb 48 lbs., which is threetimes the weight of the plane and cargo.

The back landing gear is shown by Figure13. The legs are made of aluminum.

Figure 13. Back Landing Gear

4. CONSTRUCTION OF PROTOTYPEAll foam used in the plane construction

was extruded polystyrene. Both sides of theplane consist of one uninterrupted piece of3/4” foam. Both pieces of foam were madeusing the same paper template and hot wirecutter and then sanded down to equal size.The bottom and top of the back of the planewere similarly created and attached to thesides with an epoxy. The top and bottom ofthe front of the plane were made withseparate 2” pieces of foam, attached with theepoxy, and then sanded down to match theprofile created by the sides. All edges werebeveled slightly. For support, a beam wasadded between the tops of the sides, and arectangle was placed between the walls. Thissecond structure additionally separates thecargo bay from the nose, where theelectronics are stored. The wing and top ofthe front of the plane were attached last inorder to place the electronics in more easily.

Figure 14 shows the fuselage resting upsidedown.

Figure 14. Fuselage

To create the wing, six 11” x 24” x 2”pieces were cut by a hot wire cutter, and threefinal pieces were created by using spray glueto attach two pieces together. These threepieces had total dimensions of 11” x 24” x 4”.Then, with two laser cut wood templates(Figure 15), the hot wire cutter was used tocut the final airfoil design.

Figure 15. Airfoil Template

To create a polyhedral shape for thewings, the edges of the three pieces weresanded at an angle of 4 degrees to create atotal angle of 8 degrees. Carbon fiber rodswere placed inside the wings to preventbending and buckling. To prevent vortices,wing tips were fashioned out of balsa wood.For extra strength, fiberglass cloth was gluedonto the foam and painted with polycrylic,which is a liquid plastic that cures and makes

the cloth stronger. The ailerons were cut outof the same foam as the wing. The saddle forthe wing was also created with foam pieces.The final wing is shown in Figure 16.

Figure 16. Wing

The vertical and horizontal stabilizerswere cut with a razor blade from 3/4” foamand sanded and beveled down to the designdimensions. They were also coated withfiberglass cloth and polycrylic. The rudderand elevators were made out of the samefoam as the tail. All of the parts were attachedwith an epoxy, and the final product can beseen in Figure 17 and Figure 18.

Figure 17. Completed Plane Front View

Figure 18. Completed Plane Side View

The battery was placed in the nose of theplane, with the rectangular support separatingit from the cargo area. This was done toprotect the battery if the water bombs leaked.

Six servos were used; two were attachedto the bottom of the wings, one to the rudder,one to the elevator, one to the mechanicalarm, and one to steer the landing gear. Theseservos were connected to an RC receiver andcontrolled by a remote (Figure 19).

Figure 19. Electronics

5. RESULTSGround deployment testing was

successful. The mechanical arm was able torelease one bomb at a time.

Then, taxiing was attempted, and thoughthe plane could travel in a straight line for afew seconds, it eventually tipped forwardonto its nose. This was because the frontlanding gear was too short and not centered.As a result, the nose was angled downwards,and a moment was created that caused theplane to turn more in one direction than theother. This made takeoff impossible. Toaddress this issue, the single front wheel wasreplaced by a setup similar to that of the backwheels, shown by Figure 13.

The first test flight lasted 11 seconds andtook off in 15 ft. During takeoff, the planeveered slightly to the left, flew at around 30ft. above the ground, and flipped over uponlanding. The flight itself was fairly steady.However, there was a roll imbalance, whichcaused the plane to bank in one directionmore than the other. This was likely because

of a weight difference between the right andleft sides of the wings. Roll sensitivity wasalso not calibrated properly, making mid-flight corrections difficult.

The second test flight lastedapproximately 30 seconds. Again, straightflight was relatively stable, but turning wasdifficult.

Due to limited time and flight issues,midair deployment tests were not conducted.Two water bombs were thrown into the airand burst upon contact with the ground.Based on observations from the first twoflights, the plane would have been able totake off with the intended cargo.

The biggest limitations of this prototypeis its scale. Making this plane life-sized couldadd complexity, making more advanced andprecise moment calculations necessary.

6. CONCLUSIONS AND FUTUREWORKThe prototype plane was successful in

midair flight. Limitations in time preventedmidair cargo deployment testing. However,ground testing of the deployment system wassuccessful, and the bombs did burst uponcontact with the ground, proving thefeasibility of the design.

The implementation of water bombs inaerial firefighting would make the entireprocess safer by allowing planes to fly athigher altitudes, which has a number ofbenefits. The most important of these benefitsis avoiding dangerous thermal winds, smoke,and debris that are present at low altitudes;flying level rather than diving towards thefire; and being able to fight fires at night.

Because the test flights indicated that theairplane would have been able to carry 100%of its weight, adopting this new style ofwildfire fighting would not compromisecurrent industry standards. Thus, this planeshows promise for being used in real lifesituations.

Immediate future work includes midairdeployment testing and corrections for the

roll imbalance. Other future work includesscaling up and making sure that the planefunctions similarly on a larger scale. In doingthis, the biggest challenge would bedetermining the moments, which wouldbecome more significant with increasing sizeand weight. Another aspect would be creatingenvironmentally friendly bombs. AlthoughPLA is technically biodegradable, it iscertainly not the best option for thecontainers. Research could therefore beconducted to synthesize water bombs thatcreate almost zero impact on the environmentand ecosystems. Another area of study wouldbe to test GPS target systems to deploy thewater bombs and using efficiency testing tofind the optimal plane design.

7. ACKNOWLEDGMENTSThis research could not have been

accomplished without Jonathan Holzsager,Jeet Panchal, Jim Vigani, Maya Saltzmann,Harrison Killen, Assistant Dean Jean PatrickAntoine, Dean Ilene Rosen, RutgersUniversity, The State of New Jersey, MorganStanley, Lockheed Martin, SilverlineWindows, South Jersey Industries, Inc., theProvident Bank Foundation, and NovoNordisk.

8. REFERENCES1 “Total Wildland Fires and Acres,”

US Fire Administration, 2 Apr 2013,http://www.usfa.fema.gov/statistics/estimates/wildfire.shtm (17 July 2014)

2 Bill Gabbert, “The Cost of SavingMoney on Wildfire Suppression,”Wildfire Today, 2 Mar 2013,http://wildfiretoday.com/2013/03/02/the-cost-of-saving-money-on-wildfire-suppression-2 (17 July2014)

3 Rick Sanford, “Water Bombs,”Boeing Frontiers, 2003,http://www.boeing.com/news/frontiers/archive/2003/august/i_ids4.html(17 July 2014)

4 “The ‘Scoop’ on Water Bombers,”Associated Aerial Firefighters, 27Feb 2011, http://airtanker.org/wp-content/uploads/2012/11/Scoopers-Fireboss-NW-Aviation-Conference.pdf (17 July 2014)

5 Kenneth J. Solosky, “AerialFirefighting,” Officer.com, 20 Nov2007,http://www.officer.com/article/10249287/aerial-firefighting (17 July 2014)

6 Kohyu Satoh, Iwao Maeda, KunioKuwahara, and K. T. Yang, ANumerical Study Of Water Dump InAerial Fire Fighting. Fire SafetyScience 8: 777-787 (2005).

7 “Precision Container Aerial DeliverySystem (PCADS),” FlexibleAlternatives Inc, July 2012,http://flexalt.com/wordpress01/wp-content/uploads/2013/02/PCADS_Global_July2012.pdf (17 July 2014)

8 Tom Benson, “Simplified AircraftMotion,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/smotion.html (17 July2014)

9 Tom Benson, “AerodynamicForces,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html (17 July2014)

10 Tom Benson, “The Drag Equation,”National Aeronautics and SpaceAdministration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html (17 July2014)

11 Tom Benson, “The Lift Equation,”National Aeronautics and SpaceAdministration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/k-12/airplane/lifteq.html (17 July2014)

12 Tom Benson, “Lift from FlowTurning,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html (17 July2014)

13 Tom Benson, “What is Lift?”National Aeronautics and SpaceAdministration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/k-12/airplane/lift1.html (17 July 2014)

14 Tom Benson, “Bernoulli andNewton,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html (17 July2014)

15 Tom Benson, “Reynolds Number,”National Aeronautics and SpaceAdministration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/reynolds.html (17 July2014)

16 Paul Cantrell, “Airfoils,” All StarHelicopters, n.d.,http://www.copters.com/aero/airfoils.html (17 July 2014)

17 “Atmospheric Flight,” NASA Quest,n.d.,http://quest.nasa.gov/aero/planetary/atmospheric/s+c1.html (17 July 2014)

18 Tom Benson, “Ailerons,” NationalAeronautics and SpaceAdministration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/alr.html (17 July 2014)

19 Tom Benson, “Shape Effects onLift,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/shape.html (17 July2014)

20 Tom Benson, “Horizontal Stabilizer– Elevator,” National Aeronauticsand Space Administration, 12 Jun2014,

http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html (17 July 2014)

21 Tom Benson, “Vertical Stabilizer –Rudder,” National Aeronautics andSpace Administration, 12 Jun 2014,http://www.grc.nasa.gov/WWW/K-12/airplane/rud.html (17 July 2014)

22 Tom Benson, “Wing GeometryDefinitions,” National Aeronauticsand Space Administration, 12 Jun2014,http://www.grc.nasa.gov/WWW/k-12/airplane/geom.html (17 July2014)

23 “Air Density Calculator,”DeNysschen, llc, n.d.,http://www.denysschen.com/catalogue/density.aspx (17 July 2014)

24 “Absolute and Kinematic Viscosityof Air at Standard AtmosphericPressure – Imperial (BG) Units,” TheEngineering ToolBox, n.d.,http://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.html (17 July 2014)

25 “Reynolds Number Calculator,”Airfoil Tools, 2014,http://airfoiltools.com/calculator/reynoldsnumber?MReNumForm%5Bvel%5D=13.4112&MReNumForm%5Bchord%5D=0.2794&MReNumForm%5Bkvisc%5D=20.76E-6&yt0=Calculate (17 July 2014)

26 “UIUC Airfoil CoordinatesDatabase,” UIUC AppliedAerodynamics Group, 2014,http://aerospace.illinois.edu/m-selig/ads/coord_database.html (17July 2014)

27 “GOE 523 Airfoil,” Airfoil Tools,2014,http://airfoiltools.com/airfoil/details?airfoil=goe523-il#polars (17 July2014)

28 “48" Divinity II Build***Now withProof of flight video***,”

RCGroups.com, 4 Sep 2012,http://www.rcgroups.com/forums/showthread.php?t=1048425&page=39(17 July 2014)

29 “Rules for Determining PlaneDimensions,” RCGroups.com, 19 Sep2009,http://www.rcgroups.com/forums/showthread.php?t=1114115 (17 July2014)