Aircraft DesignMEC 4200

Assignment 1

Due Date : 3/4/14

Using the details on aircraft in Lab Sheet #1, do the trade studies as below.

1. Range Trade

A range trade can be calculated to determine the increase or decrease in design takeoff weight if required range is changed. Calculate take off weight for required range 1000nmi and 2000nmi. Draw a plot of range versus takeoff weight.

1

2. Payload Trade

A payload trade can be made in similar fashion with range trade, only the varying weight fraction is now different. The given payload requirement in above example is 10,000 lb of avionics. Draw a plot of payload versus take off weight for assumed payload weights of 5,000 lb, 15,000 lb and 20,000 lb.

2

3. Material Trade

The bomber aircraft, which used here for sizing was based upon existing military bomber, which are all of aluminum construction. Determine the effect of building

3

aircraft out of composite materials. It is noted that the use of the composite materials reduces the empty weight by 5%.

4. Computer Programming (OPTIONAL QUESTION)

a- Sketch the program flow chart of a computer programming to calculate the takeoff weight.

b- Write a computer program (using Fotran or C or Mathlab) to calculate the takeoff weight of an aircraft using the procedure of the takeoff weight build-up method.

c- Using the program written in (b), calculate the range trade and payload trade for the aircraft in question 1, 2 and 3.

MEC 4200 : aircraft DesignAssignment 1 (Programming)

Sample solution using C++ program

1. Ask the user the nature of the set of data available on hand (units).

2. Define the aircraft criteria : crew and payload weight,maximum lift-to-drag ratio, operating speed, the engine type.

3. Based on the engine type, calculate the required SFC.

4. Define the mission profile : numbers of climb, cruise and loiter segments.

4

5. Based on the mission profile, calculate the fuel weight fraction for the climb, cruise and loiter segments.

6. Calculate the fuel weight fraction with the intended reserved fuel portion.

7. Define the empty weight fraction variables.

8. Do the iteration and comes up with the estimated takeoff weight.

The sample program (using C++).

#include <iostream.h>#include <math.h>#include <stdlib.h>

int main ( ){char unit, engine; // variables for engine type and the unit system used for the dataint climb, cruise, loiter;double A, C, Kvs; // variables for the empty weight fraction equationdouble percentage, Wempty, Wnew;double Wcrew,Wpayload,LDmax,LD1,velocity,range,efficiency,endurance,Wloiter;double Wtotalcruise,Wcruise,SFCloiter,SFCcruise,efficiency1,Wtotalloiter;cout<<"PROGRAM TO CALCULATE THE INITIAL ESTIMATE OF THE TAKEOFF WEIGHT"<<endl;cout<<"Data in (S)I Unit or(B)ritish Unit? ";cin>>unit;cout<<"Input the required aircraft criteria :-"<<endl;cout<<"Crew Weight (kg/lbm):";cin>>Wcrew; // variable for the crew weightcout<<"Payload Weight (kg/lbm):";cin>>Wpayload; // variable for the payload weight// conversion of crew abnd payload weights to British Unit for data input in SI Unitsif (unit=='S'){Wcrew = Wcrew*2.204622622;Wpayload = Wpayload*2.204622622;}if (unit=='s'){Wcrew = Wcrew*2.204622622;Wpayload = Wpayload*2.204622622;}cout<<"The Max. Lift-to-Drag Ratio :";cin>>LDmax; // variable for maximum lift-to-drag ratiocout<<"Operating Speed (m/s or ft/s):";

5

cin>>velocity; // variable for velocity// conversion of velocity to British Unit for data in SI Unitsif (unit=='S')velocity = velocity*3.280839895;if (unit=='s')velocity = velocity*3.280839895;cout<<"Engine type [(J)et or (P)ropeller] :";cin>>engine; // variable for engine type// calculate the SFC for propeller aircraftif (engine=='P'){cout<<"Enter the propeller SFC (lb/hp.hr) :"<<endl;cout<<"Cruise :";cin>>SFCcruise; //variable for SFC in cruisecout<<"Loiter :";cin>>SFCloiter; // variable for SFC in loitercout<<"Enter propeller efficiency :"<<endl;cout<<"Cruise :"; cin>>efficiency; // variable for propeller efficiency during cruisecout<<"Loiter :";cin>>efficiency1; // variable for propeller efficiency during loiter// conversion of SFC (lb/hp.hr) into SFC in (1/hr)SFCcruise= (SFCcruise*velocity)/(550*efficiency);SFCloiter= (SFCloiter*velocity)/(550*efficiency1);}else{cout<<"Enter the jet SFC (1/hr) :"<<endl;cout<<"Cruise :";cin>>SFCcruise; // variable for SFC during cruisecout<<"Loiter :";cin>>SFCloiter; // variable for SFC during loiter}cout<<"Define the nature of the mission profile for the aircraft."<<endl;cout<<"No. of Climb Segment :";cin>>climb; // variable for numbers of climb segmentscout<<"No. of Cruise Segment :";cin>>cruise; // variable for numbers of cruise segmentscout<<"No. of Loiter Segment :";cin>>loiter; // variable for numbers of loiter segments// assigning the fixed values for takeoff, climb and landing fuel weight fractionsdouble WTO = 0.97; double Wclimb=0.985; double Wlanding=0.995;int n=1; double dummy = 1;double Wtotalclimb = Wclimb;// loop to find the product of all climb fuel weight segment fractionswhile (n<=climb)

6

{Wtotalclimb = Wtotalclimb*dummy;dummy = Wclimb;n = n+1;}n=1; dummy=1;LD1=LDmax;// loop to find the product of all cruise fuel weight segment fractionswhile (n<=cruise){cout<<"Input cruise segment "<<n<<" range (m or ft):";cin>>range; // variable for the respective segment’s range// conversion of range to British units for data in SI Unitsif (unit=='S')range = range*3.280839895;else if (unit=='s')range = range*3.280839895;// assigning lift to drag ratio values with respect to engine typeelse if (engine=='J')LDmax=LDmax*0.866;else if (engine=='j')LDmax=LDmax*0.866;// calculating the particular cruise fuel weight segment fractiondouble x = (-1*range*SFCcruise)/(velocity*LDmax*3600);Wcruise =exp(x);Wtotalcruise = Wcruise*dummy;dummy=Wcruise;LDmax=LD1;n=n+1;}n=1; dummy=1;// loop to find the product of all loiter fuel weight segment fractionswhile (n<=loiter){cout<<"Input loiter segment "<<n<<" endurance (seconds):";cin>>endurance; // variable for the particular segment’s endurance// assigning lift-to-drag ratio values with respect to engine typeif (engine=='P')LDmax=LDmax*0.866;else if (engine=='p')LDmax=LDmax*0.866;// calculating the particular loiter fuel weight segment fractiondouble x = (-1*endurance*SFCloiter)/(LDmax*3600);Wloiter =exp(x);Wtotalloiter = Wloiter*dummy;dummy=Wloiter;

7

LDmax=LD1;n=n+1;}// calculate the fuel weight fractiondouble Wproduct=WTO*Wlanding*Wtotalclimb*Wtotalcruise*Wtotalloiter;cout<<"Enter the percentage of intended reserved fuel (%):";cin>>percentage; // variable for the reserved fuel percentagedouble dummy1=percentage/100;double Wfuel= (1+dummy1)*(1-Wproduct);cout<<"Enter the empty weight fraction variables :"<<endl;cout<<"A :";cin>>A;cout<<"C :";cin>>C;cout<<"Kvs :";cin>>Kvs;double error=1;double Wguess=10000;

// iteration to find the estimated takeoff weightwhile (error>=0.00001){Wempty=A*pow(Wguess,C)*Kvs;Wnew = (Wcrew+Wpayload)/(1-Wfuel-Wempty);error = abs((100*(Wnew-Wguess))/(Wguess));Wguess=Wnew;}// conversion of the answer back to SI Unit for data in SI Unitsif (unit=='S'){Wnew = Wnew*0.45359237;cout<<"The initial estimate of takeoff weight is : "<<Wnew<<" kg.";}else if (unit=='s'){Wnew = Wnew*0.45359237;cout<<"The initial estimate of takeoff weight is : "<<Wnew<<" kg. ";}elsecout<<"The initial estimate of takeoff weight is : "<<Wnew<<" lb. ";return 0;}

8

PROGRAM TO CALCULATE THE INITIAL ESTIMATE OF THE TAKEOFF WEIGHT

Data in (S)I Unit or(B)ritish Unit? S

Input the required aircraft criteria :-

Crew Weight (kg/lbm):326.59Payload Weight (kg/lbm):73.41The Max. Lift-to-Drag Ratio :13Operating Speed (m/s or ft/s):100Engine type [(J)et or (P)ropeller] :PEnter the propeller SFC (lb/hp.hr) :Cruise :0.4Loiter :0.5

Enter propeller efficiency :Cruise :0.8Loiter :0.7

Define the nature of the mission profile for the aircraft.

No. of Climb Segment :1No. of Cruise Segment :1No. of Loiter Segment :1

Input cruise segment 1 range (m or ft):1000000Input loiter segment 1 endurance (seconds):600

Enter the percentage of intended reserved fuel (%):6

Enter the empty weight fraction variables :A :2.36C :-.18Kvs :1The initial estimate of takeoff weight is : 1274.27 kg.

*The answer in comparable as in lab assignment #1 solution.

Question 3.

Using the program, the resultant data with changing variables of range and payload weight are tabulated below.

For range trade;

9

Range (km) Takeoff Weight (kg)500 1186.501000 1274.271500 1371.232000 1478.70

The corresponding graph;

Conclusion : As can be seen from the graph, the increase in range will correspond to an increase in the takeoff weight. This might be due to the extra fuel needs to be carried to cope with the additional range. The relationship is a straight line meaning that the increase in takeoff weight is related to the increase in range by a product of a constant.

For payload trade;

Payload (kg) Takeoff Weight (kg)50.00 1266.0973.41 1274.27100.00 1337.69150.00 1455.46

The corresponding graph;

10

* As can be seen from the graph, an increase in payload weight will increase the takeoff weight. This is a logical relationship since the extra payload weight will certainly increase the overall takeoff weight. Since the graph is not a straight line, the relationship between payload and takeoff weight and the takeoff weight is not proportional by a constant.

11