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# 'Everplane' Concept Vehicle Definition (Autonomous High Altitude 1-Month Endurance Solar-Powered Airplane) - Technical Report

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## Abstract

This paper forms part of the 'Everplane' Group Design Project and aims to present the Vehicle Definition of an autonomous high-altitude long-endurance concept aircraft, designed for flying continuously over one month in an environmentally sustainable manner. The platform has the capability of acting as an aerosattelite, providing affordable internet to remote areas. Note that this report is part of a group of 20 approaching this design challenge from different perspectives. The focus points of this particular report are: initial and final aircraft configuration design; accurate mass and centre of gravity determination; computer-aided design for technical (CFD, FEA, Drawings) and media (rendering) purposes. The results, consistent with previous studies, indicate that an optimum configuration is a conventional one, featuring a high aspect ratio wing, a cruciform tail, 4 electric engines powered by H2 fuel cells, recharged by a large solar panel array. Furthermore, the total mass for the most recent aircraft iteration was determined as 539.65kg, within the flight allowance of 559kg. Finally, the concept was determined to be technically feasible from the perspective of all teams involved.
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function [Rho,P,T] = Atmosphere(Alt)
% This function takes input 'altitude' [km] and interpolates using
% tables of atmospheric data to find parameters
% Find value from tables
j=1;
while Alt > density(j,1)
j=j+1;
end
Rho = ((Alt-density(j,1))/(density(j+1,1)-density(j,1)))*(density(j+1,2)-
density(j,2)) + density(j,2);
P = ((Alt-density(j,1))/(density(j+1,1)-density(j,1)))*(density(j+1,3)-
density(j,3)) + density(j,3);
T = ((Alt-density(j,1))/(density(j+1,1)-density(j,1)))*(density(j+1,4)-
density(j,4)) + density(j,4);
%Name: Balloon size & Cost
%Goal: Determine a first approximation of the balloon size and associated cost to
launch at a given altitude. Plot variation of cost and balloon size w.r.t desired
altitude.
%Created by: SERGIU PETRE ILIEV. Date: 10.06.2015
%Imperial College London | Aeronautical Engineering | GDP | Coursework
close all; %clean workspace
clc;
clear all;
%% Assumptions
% consider just the limiting case, when the balloon reaches desired altitude and
has to sustain all mass; neglect ascent time, drag on envelope and A/C
%% Initialize parameters
fprintf('Inputs \n');
h=[20,0:0.1:30]; %first value is the input height,
following values are from 0 to 30km in steps of 100m
h(1,1)=input('Desired altitude to be reached by the balloon (km): ');
m=input('Aircraft total mass (kg): ');
k=2.77; %\$/kg of liquid H2 (cost)
%% Researched Data, source: www.redbullstratos.com/technology/high-altitude-
balloon/
t=2.03200*10^-5; %m thickness of balloon envelope skin
(based on Red Bull Stratos)
%Polyester-fiber reinforced load tapes are incorporated for weight bearing
%Balloon mass = of skin + estimated mass of reinforcements wires, parachute,
balloon avionics, release valve nylon "destruct line" will release the helium so
that the balloon returns to Earth. Then, the team will gather the envelope into a
large truck, to be inspected at the base and reused.
q_material=889.6; %kg/m3 smeared density of balloon
V_stratos=849505.398; %m3
R_stratos=(849505.398*3/4)^(1/3); %m
m_balloon_stratos=q_material*t*4*pi*R_stratos^2; %kg mass of the entire balloon
%knowing the actual mass of the Red Bull Stratos as 1680kg, a loop was done to
find the smeared density above that would give m_balloon_stratos=1680kg
%% Initialize
% find the AIR atmospheric parameters for all heights using a function that
interpolates experimental data NB: better results can be obtained is the
interpolation is not done between 1km height values
for i=2:302 %from 2 (to skip the input value) to 302 (size of h)
[Rho(i),P(i),T(i)] = Atmosphere(h(i)); % air density, pressure and temperature
end
%% Loop to stabilize mass of the system for all possible altitudes
%acceptable error of 100 grams
% find the H2 atmospheric parameters as a function of AIR atmospheric parameters
(assume H2 and AIR behave the same (same Cp)
% using H2 because it has a lower density, is cheaper, but has the
disadvantage of escaping the envelope over a long time
m_total(1)=m + 15+50+54.57+2+50; %15kg wires and quick release system, 50kg
vaporiser, 54.57±0.1kg of H2, 10kg recovery parachute and 2kg control unit
m_balloon(1)=0; %assume massless balloon initially
eps(1)=20;
for j=2:302
c=2;
while eps(c-1)>0.01 && c<100 %within 10 g not more than 100 iterations
rho_h2(j)=0.0899*( (P(j)/P(2))*(T(2)/T(j)) );%kg/m3 hydrogen density at sea
level * from perfect gas law ratios = hydrogen density at various heights;
assuming it adapts perfectly to temperature and pressure of the exterior
R(j)=((3*m_total(c-1) )/( 4*pi*(Rho(j)-rho_h2(j)) ))^(1/3); %m balloon
V(j)=(4*pi/3)*R(j)^3; %m3 volume of balloon at altitude
m_balloon(c)=1.5*q_material*t*4*pi*R(j)^2;%50% safety margin
m_total(c)=m_total(1)+m_balloon(c);
eps(c)=m_total(c)-m_total(c-1);
m_balloon_save(j)=m_balloon(c); %remember balloon mass
c=c+1;
Cost(j)=k*V(j)*rho_h2(j)*50; %\$ H2 cost associated with 50 Everplanes
end
m_total(j)=m_total(c-1);
end
%% Plot
figure
subplot(1,2,1)
plot(m_balloon_save(2:end), h(2:end), 'b') %plot the experimental response
xlabel('Baloon Mass (kg)'); %label the vertical axis
ylabel('Desired insertion (i.e. neutral buoyancy) altitude (km)'); %label the
horizontal axis
% plot(R(2:end), h(2:end), 'b') %plot the experimental response
% xlabel('Balloon Radius (m)'); %label the vertical axis
% ylabel('Desired insertion (i.e. neutral buoyancy) altitude (km)'); %label the
horizontal axis
subplot(1,2,2)
plot(Cost(2:end), h(2:end), '--r') %plot the reference signal
xlabel('Fleet launch cost (\$)'); %label the vertical axis
ylabel('Desired insertion (i.e. neutral buoyancy) altitude (km)'); %label the
horizontal axis