diff --git a/.gitignore b/.gitignore
index ab983c66..34976985 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,9 @@
+# documentation temp files
+*.md.py
+*.aux
+*.generated.tex
+*.md.tex.md
+
 # iPython checkpoint folders
 .ipynb_checkpoints/
 
diff --git a/1682/build.sh b/1682/build.sh
new file mode 100755
index 00000000..80124871
--- /dev/null
+++ b/1682/build.sh
@@ -0,0 +1,4 @@
+python -c 'import gpkit; exec gpkit.mdmake("gas_hale.md")'
+pandoc --template default.latex gas_hale.md.tex.md -o gas_hale.pdf
+
+
diff --git a/1682/default.latex b/1682/default.latex
new file mode 100644
index 00000000..bef63549
--- /dev/null
+++ b/1682/default.latex
@@ -0,0 +1,263 @@
+\documentclass[$if(fontsize)$$fontsize$,$endif$$if(lang)$$babel-lang$,$endif$$if(papersize)$$papersize$paper,$endif$$for(classoption)$$classoption$$sep$,$endfor$]{$documentclass$}
+$if(fontfamily)$
+\usepackage[$for(fontfamilyoptions)$$fontfamilyoptions$$sep$,$endfor$]{$fontfamily$}
+$else$
+\usepackage{lmodern}
+$endif$
+$if(linestretch)$
+\usepackage{setspace}
+\setstretch{$linestretch$}
+$endif$
+\usepackage{amssymb,amsmath}
+\usepackage{ifxetex,ifluatex}
+\usepackage{fixltx2e} % provides \textsubscript
+\ifnum 0\ifxetex 1\fi\ifluatex 1\fi=0 % if pdftex
+  \usepackage[$if(fontenc)$$fontenc$$else$T1$endif$]{fontenc}
+  \usepackage[utf8]{inputenc}
+$if(euro)$
+  \usepackage{eurosym}
+$endif$
+\else % if luatex or xelatex
+  \ifxetex
+    \usepackage{mathspec}
+  \else
+    \usepackage{fontspec}
+  \fi
+  \defaultfontfeatures{Ligatures=TeX,Scale=MatchLowercase}
+$if(euro)$
+  \newcommand{\euro}{€}
+$endif$
+$if(mainfont)$
+    \setmainfont[$for(mainfontoptions)$$mainfontoptions$$sep$,$endfor$]{$mainfont$}
+$endif$
+$if(sansfont)$
+    \setsansfont[$for(sansfontoptions)$$sansfontoptions$$sep$,$endfor$]{$sansfont$}
+$endif$
+$if(monofont)$
+    \setmonofont[Mapping=tex-ansi$if(monofontoptions)$,$for(monofontoptions)$$monofontoptions$$sep$,$endfor$$endif$]{$monofont$}
+$endif$
+$if(mathfont)$
+    \setmathfont(Digits,Latin,Greek)[$for(mathfontoptions)$$mathfontoptions$$sep$,$endfor$]{$mathfont$}
+$endif$
+$if(CJKmainfont)$
+    \usepackage{xeCJK}
+    \setCJKmainfont[$for(CJKoptions)$$CJKoptions$$sep$,$endfor$]{$CJKmainfont$}
+$endif$
+\fi
+% use upquote if available, for straight quotes in verbatim environments
+\IfFileExists{upquote.sty}{\usepackage{upquote}}{}
+% use microtype if available
+\IfFileExists{microtype.sty}{%
+\usepackage{microtype}
+\UseMicrotypeSet[protrusion]{basicmath} % disable protrusion for tt fonts
+}{}
+$if(geometry)$
+\usepackage[$for(geometry)$$geometry$$sep$,$endfor$]{geometry}
+$endif$
+\usepackage{hyperref}
+$if(colorlinks)$
+\PassOptionsToPackage{usenames,dvipsnames}{color} % color is loaded by hyperref
+$endif$
+\hypersetup{unicode=true,
+$if(title-meta)$
+            pdftitle={$title-meta$},
+$endif$
+$if(author-meta)$
+            pdfauthor={$author-meta$},
+$endif$
+$if(keywords)$
+            pdfkeywords={$for(keywords)$$keywords$$sep$; $endfor$},
+$endif$
+$if(colorlinks)$
+            colorlinks=true,
+            linkcolor=$if(linkcolor)$$linkcolor$$else$Maroon$endif$,
+            citecolor=$if(citecolor)$$citecolor$$else$Blue$endif$,
+            urlcolor=$if(urlcolor)$$urlcolor$$else$Blue$endif$,
+$else$
+            pdfborder={0 0 0},
+$endif$
+            breaklinks=true}
+\urlstyle{same}  % don't use monospace font for urls
+$if(lang)$
+\ifnum 0\ifxetex 1\fi\ifluatex 1\fi=0 % if pdftex
+  \usepackage[shorthands=off,$for(babel-otherlangs)$$babel-otherlangs$,$endfor$main=$babel-lang$]{babel}
+$if(babel-newcommands)$
+  $babel-newcommands$
+$endif$
+\else
+  \usepackage{polyglossia}
+  \setmainlanguage[$polyglossia-lang.options$]{$polyglossia-lang.name$}
+$for(polyglossia-otherlangs)$
+  \setotherlanguage[$polyglossia-otherlangs.options$]{$polyglossia-otherlangs.name$}
+$endfor$
+\fi
+$endif$
+$if(natbib)$
+\usepackage{natbib}
+\bibliographystyle{$if(biblio-style)$$biblio-style$$else$plainnat$endif$}
+$endif$
+$if(biblatex)$
+\usepackage$if(biblio-style)$[style=$biblio-style$]$endif${biblatex}
+$if(biblatexoptions)$\ExecuteBibliographyOptions{$for(biblatexoptions)$$biblatexoptions$$sep$,$endfor$}$endif$
+$for(bibliography)$
+\addbibresource{$bibliography$}
+$endfor$
+$endif$
+$if(listings)$
+\usepackage{listings}
+$endif$
+$if(lhs)$
+\lstnewenvironment{code}{\lstset{language=Haskell,basicstyle=\small\ttfamily}}{}
+$endif$
+$if(highlighting-macros)$
+$highlighting-macros$
+$endif$
+$if(verbatim-in-note)$
+\usepackage{fancyvrb}
+\VerbatimFootnotes % allows verbatim text in footnotes
+$endif$
+$if(tables)$
+\usepackage{longtable,booktabs}
+$endif$
+$if(graphics)$
+\usepackage{graphicx,grffile}
+\makeatletter
+\def\maxwidth{\ifdim\Gin@nat@width>\linewidth\linewidth\else\Gin@nat@width\fi}
+\def\maxheight{\ifdim\Gin@nat@height>\textheight\textheight\else\Gin@nat@height\fi}
+\makeatother
+% Scale images if necessary, so that they will not overflow the page
+% margins by default, and it is still possible to overwrite the defaults
+% using explicit options in \includegraphics[width, height, ...]{}
+\setkeys{Gin}{width=\maxwidth,height=\maxheight,keepaspectratio}
+$endif$
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% ADD YOUR \usepackage{...} COMMANDS HERE
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\usepackage{longtable}
+\usepackage{booktabs}
+
+$if(links-as-notes)$
+% Make links footnotes instead of hotlinks:
+\renewcommand{\href}[2]{#2\footnote{\url{#1}}}
+$endif$
+$if(strikeout)$
+\usepackage[normalem]{ulem}
+% avoid problems with \sout in headers with hyperref:
+\pdfstringdefDisableCommands{\renewcommand{\sout}{}}
+$endif$
+$if(indent)$
+$else$
+\IfFileExists{parskip.sty}{%
+\usepackage{parskip}
+}{% else
+\setlength{\parindent}{0pt}
+\setlength{\parskip}{6pt plus 2pt minus 1pt}
+}
+$endif$
+\setlength{\emergencystretch}{3em}  % prevent overfull lines
+\providecommand{\tightlist}{%
+  \setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}
+$if(numbersections)$
+\setcounter{secnumdepth}{5}
+$else$
+\setcounter{secnumdepth}{0}
+$endif$
+$if(subparagraph)$
+$else$
+% Redefines (sub)paragraphs to behave more like sections
+\ifx\paragraph\undefined\else
+\let\oldparagraph\paragraph
+\renewcommand{\paragraph}[1]{\oldparagraph{#1}\mbox{}}
+\fi
+\ifx\subparagraph\undefined\else
+\let\oldsubparagraph\subparagraph
+\renewcommand{\subparagraph}[1]{\oldsubparagraph{#1}\mbox{}}
+\fi
+$endif$
+$if(dir)$
+\ifxetex
+  % load bidi as late as possible as it modifies e.g. graphicx
+  $if(latex-dir-rtl)$
+  \usepackage[RTLdocument]{bidi}
+  $else$
+  \usepackage{bidi}
+  $endif$
+\fi
+\ifnum 0\ifxetex 1\fi\ifluatex 1\fi=0 % if pdftex
+  \TeXXeTstate=1
+  \newcommand{\RL}[1]{\beginR #1\endR}
+  \newcommand{\LR}[1]{\beginL #1\endL}
+  \newenvironment{RTL}{\beginR}{\endR}
+  \newenvironment{LTR}{\beginL}{\endL}
+\fi
+$endif$
+$for(header-includes)$
+$header-includes$
+$endfor$
+
+$if(title)$
+\title{$title$$if(thanks)$\thanks{$thanks$}$endif$}
+$endif$
+$if(subtitle)$
+\providecommand{\subtitle}[1]{}
+\subtitle{$subtitle$}
+$endif$
+$if(author)$
+\author{$for(author)$$author$$sep$ \and $endfor$}
+$endif$
+\date{$date$}
+
+\begin{document}
+$if(title)$
+\maketitle
+$endif$
+$if(abstract)$
+\begin{abstract}
+$abstract$
+\end{abstract}
+$endif$
+
+$for(include-before)$
+$include-before$
+
+$endfor$
+$if(toc)$
+{
+$if(colorlinks)$
+\hypersetup{linkcolor=$if(toccolor)$$toccolor$$else$black$endif$}
+$endif$
+\setcounter{tocdepth}{$toc-depth$}
+\tableofcontents
+}
+$endif$
+$if(lot)$
+\listoftables
+$endif$
+$if(lof)$
+\listoffigures
+$endif$
+$body$
+
+$if(natbib)$
+$if(bibliography)$
+$if(biblio-title)$
+$if(book-class)$
+\renewcommand\bibname{$biblio-title$}
+$else$
+\renewcommand\refname{$biblio-title$}
+$endif$
+$endif$
+\bibliography{$for(bibliography)$$bibliography$$sep$,$endfor$}
+
+$endif$
+$endif$
+$if(biblatex)$
+\printbibliography$if(biblio-title)$[title=$biblio-title$]$endif$
+
+$endif$
+$for(include-after)$
+$include-after$
+
+$endfor$
+\end{document}
diff --git a/1682/gas_hale.md b/1682/gas_hale.md
new file mode 100644
index 00000000..69d0ddb0
--- /dev/null
+++ b/1682/gas_hale.md
@@ -0,0 +1,238 @@
+# Gas HALE model
+```python
+#inPDF: skip
+
+from numpy import pi
+from gpkit import VectorVariable, Variable, Model, units
+from gpkit.tools import te_exp_minus1
+import gpkit
+import numpy as np
+gpkit.settings['latex_modelname'] = False
+
+class GasPoweredHALE(Model):
+    def setup(self):
+        constraints = []
+```
+
+
+## Flight segment definitions
+```python
+
+        # define number of segments
+        NSeg = 3
+        #Note: NSeg has to be an odd number
+        # defining indices of different flight segments
+        NLoiter = (NSeg-1)/2
+        if NSeg == 3:
+            NCruise = [0,2]
+        elif NSeg == 7:
+            Nclimb = [0,2,4,6]
+            NCruise = [1,5]
+```
+
+
+# Fuel weight model
+```python
+
+        MTOW = Variable('MTOW', 'lbf', 'max take off weight')
+        W_end = VectorVariable(NSeg, 'W_{end}', 'lbf', 'segment-end weight')
+        W_fuel = VectorVariable(NSeg, 'W_{fuel}', 'lbf', 'segment-fuel weight')
+        W_zfw = Variable('W_{zfw}', 'lbf', 'Zero fuel weight')
+        W_pay = Variable('W_{pay}',10,'lbf', 'Payload weight')
+        W_avionics = Variable('W_{avionics}', 2, 'lbf', 'Avionics weight')
+        f_airframe = Variable('f_{airframe}', 0.25, '-', 'airframe weight fraction')
+        W_airframe = Variable('W_{airframe}', 'lbf', 'airframe weight')
+        W_begin = W_end.left # define beginning of segment weight
+        W_begin[0] = MTOW
+```
+
+## Assumptions
+
+*  Mass take off weight is greater than the end of the first segment weight plus that segment fuel weight.
+* The end of each flight segment weight must be greater than the next end of flight segment weight plus the fuel weight of the next flight segment.
+* The end of the last flight segment weight must be greater than the zero fuel weight
+
+```python
+
+        constraints.extend([MTOW >= W_end[0] + W_fuel[0],
+                            W_end[:-1] >= W_end[1:] + W_fuel[1:],
+                            W_end[-1] >= W_zfw,
+                            W_airframe >= f_airframe*MTOW])
+```
+
+
+# Steady level flight model
+## Assumptions
+* Steady state flight
+* Angle of attack zero
+* Thrust equals drag
+* Lift equals weight
+* The weight is approximated by the average weight of the flight segment.
+* The average weight can be approximated by: $W_{avg} = \sqrt{W_{begin} W_{end}}$.  Where $W_{begin}$ is the beginning of the flight segment and $W_{end}$ is the end of the flight segment.
+
+```python
+
+        CD = VectorVariable(NSeg, 'C_D', '-', 'Drag coefficient')
+    	CL = VectorVariable(NSeg, 'C_L', '-', 'Lift coefficient')
+        V = VectorVariable(NSeg, 'V', 'm/s','cruise speed')
+        rho = VectorVariable(NSeg, r'\rho', 'kg/m^3', 'air density')
+        S = Variable('S', 16, 'ft^2', 'wing area')
+        eta_prop = VectorVariable(NSeg, r'\eta_{prop}', [0.8,0.6,0.8], '-',
+                                  'propulsive efficiency')
+        P_shaft = VectorVariable(NSeg, 'P_{shaft}', 'hp', 'Shaft power')
+```
+
+# Climb model
+```python
+
+        h_dot = Variable(NSeg, 'h_{dot}', [200,0,0], 'ft/min', 'Climb rate')
+        constraints.extend([P_shaft >= V*(W_end+W_begin)/2*CD/CL/eta_prop + W_begin*h_dot/eta_prop,
+                            0.5*rho*CL*S*V**2 >= (W_end+W_begin)/2])
+```
+
+# Engine Model
+```python
+
+        W_eng = Variable('W_{eng}', 'lbf', 'Engine weight')
+        W_engtot = Variable('W_{eng-tot}', 'lbf', 'Installed engine weight')
+        W_engref = Variable('W_{eng-ref}', 4.4107, 'lbf', 'Reference engine weight')
+        P_shaftref = Variable('P_{shaft-ref}', 2.295, 'hp', 'reference shaft power')
+```
+
+## Engine Weight constraints
+```python
+
+        constraints.extend([W_eng/W_engref >= 0.5538*(P_shaft/P_shaftref)**1.075,
+                            W_engtot >= 2.572*W_eng**0.922*units('lbf')**0.078])
+```
+
+# Weight breakdown
+```python
+
+        constraints.extend([W_airframe >= f_airframe*MTOW,
+                            W_zfw >= W_pay + W_avionics + W_airframe + W_engtot])
+```
+
+# Breguet Range
+## Assumptions
+* Constant speed during each flight section
+* Constant BSFC
+* The $\ln$ can be approximated using a Taylor-series expansion
+
+```python
+
+        z_bre = VectorVariable(NSeg, 'z_{bre}', '-', 'breguet coefficient')
+        BSFC = VectorVariable(NSeg,'BSFC', [0.5,.55,0.6], 'lbf/hr/hp', 'brake specific fuel consumption')
+        t = VectorVariable(NSeg, 't', 'days', 'time on station')
+        R = Variable('R', 200, 'nautical_miles', 'range to station')
+        g = Variable('g', 9.81, 'm/s^2', 'Gravitational acceleration')
+
+        constraints.extend([z_bre >= V*t*BSFC*CD/CL/eta_prop,
+                            R == V[NCruise]*t[NCruise],
+                            t[NLoiter] == 5*units('days'),
+                            W_fuel/W_end >= te_exp_minus1(z_bre, 3)])
+```
+
+
+# Aerodynamics model
+## Assumptions
+* The wing is a box shape.
+* The non-wing drag is a constant
+* The stall factor is based off standard airfoil polar.
+* Reference length for Reynolds number is teh chord.
+* The skin friction is based off of Blasius flat plate.
+* The form factor for the wing is constant.
+
+```python
+
+
+        Cd0 = Variable('C_{d0}', 0.02, '-', 'Non-wing drag coefficient')
+        CLmax = Variable('C_{L-max}', 1.5, '-', 'Maximum lift coefficient')
+        e = Variable('e', 0.9, '-', 'Spanwise efficiency')
+        AR = Variable('AR', '-', 'Aspect ratio')
+        b = Variable('b', 'ft', 'Span')
+        mu = Variable(r'\mu', 1.5e-5, 'N*s/m^2', 'Dynamic viscosity')
+        Re = VectorVariable(NSeg, 'Re', '-', 'Reynolds number')
+        Cf = VectorVariable(NSeg, 'C_f', '-', 'wing skin friction coefficient')
+        Kwing = Variable('K_{wing}', 1.3, '-', 'wing form factor')
+        cl_16 = Variable('cl_{16}', 0.0001, '-', 'profile stall coefficient')
+
+        constraints.extend([CD >= Cd0 + 2*Cf*Kwing + CL**2/(pi*e*AR) + cl_16*CL**16,
+                            b**2 == S*AR,
+```
+
+In place of an actual structural model, we impose $AR \leq 20$.
+```python
+
+                            AR <= 20,
+                            CL <= CLmax,
+                            Re == rho*V/mu*(S/AR)**0.5,
+                            Cf >= 0.074/Re**0.2])
+```
+
+# Atmosphere model
+## Assumptions
+* Valid only to the top of the troposphere.
+
+## References
+* [wp:Density of Air](http://en.wikipedia.org/wiki/Density_of_air#Altitude)
+
+```python
+
+
+        h = VectorVariable(NSeg, 'h', 'ft', 'Altitude')
+        gamma = Variable(r'\gamma',1.4,'-', 'Heat capacity ratio of air')
+        p_sl = Variable('p_{sl}', 101325, 'Pa', 'Pressure at sea level')
+        T_sl = VectorVariable(NSeg, 'T_{sl}', [288.15,288.15,288.15], 'K',
+                              'Temperature at sea level')
+        L_atm = Variable('L_{atm}', 0.0065, 'K/m', 'Temperature lapse rate')
+        T_atm = VectorVariable(NSeg, 'T_{atm}', 'K', 'Air temperature')
+        a_atm = VectorVariable(NSeg, 'a_{atm}','m/s', 'Speed of sound at altitude')
+        R_spec = Variable('R_{spec}', 287.058,'J/kg/K', 'Specific gas constant of air')
+        TH = (g/R_spec/L_atm).value.magnitude  # dimensionless
+
+        constraints.extend([#h <= [20000, 20000, 20000]*units.m,
+                            T_sl >= T_atm + L_atm*h,  # Temp decreases w/ altitude
+                            rho == p_sl*T_atm**(TH-1)/R_spec/(T_sl**TH),
+                            h[NLoiter] >= 15000*units('ft'), # makes sure that the loiter occurs above minimum h
+                            ])
+```
+
+
+# Wind speed model
+```python
+
+        V_wind = VectorVariable(NSeg, 'V_{wind}', 'm/s', 'wind speed')
+        wd_cnst = Variable('wd_{cnst}', 0.0015, 'm/s/ft',
+                           'wind speed constant predicted by model')
+                            #0.002 is worst case, 0.0015 is mean at 45d
+        wd_ln = Variable('wd_{ln}', 8.845, 'm/s',
+                         'linear wind speed variable')
+                        #13.009 is worst case, 8.845 is mean at 45deg
+        h_min = Variable('h_{min}', 11800, 'ft', 'minimum height')
+        h_max = Variable('h_{max}', 20866, 'ft', 'maximum height')
+
+        constraints.extend([V_wind >= wd_cnst*h + wd_ln,
+                            V >= V_wind,
+                            h[NCruise] >= h_min])
+```
+
+
+# Conclusion
+```python
+
+        objective = MTOW
+        return objective, constraints
+
+if __name__ == "__main__":
+    M = GasPoweredHALE()
+    M.solve()
+```
+
+
+# Solution
+```python
+#inPDF: replace with sol.generated.tex
+    with open("sol.generated.tex", "w") as f:
+        f.write(M.solution.table(latex=True))
+```