diff --git a/notebooks/hotair-box.ipynb b/notebooks/hotair-box.ipynb
index 1184600..efafcdb 100644
--- a/notebooks/hotair-box.ipynb
+++ b/notebooks/hotair-box.ipynb
@@ -30,7 +30,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 36,
    "id": "6ea87a15-f571-4611-8487-5b7556e2ef45",
    "metadata": {
     "extensions": {
@@ -63,12 +63,15 @@
     "from termcolor import colored\n",
     "\n",
     "#from scipy.interpolate import interp1d\n",
-    "#import numpy as np"
+    "#import numpy as np\n",
+    "\n",
+    "#math\n",
+    "from math import sin, tan, sqrt"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 37,
    "id": "d075a994-76bb-46f7-bdfb-cc6ef449dc43",
    "metadata": {
     "extensions": {
@@ -107,7 +110,28 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": 40,
+   "id": "0e94979b-5973-4607-9d5f-e7b597a8374f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Ascent rate at ground level\n",
+    "# https://northstar-www.dartmouth.edu/~klynch/pmwiki-gc/uploads/BalloonCalulations.pdf\n",
+    "\n",
+    "# Coefficient of Drag assumed to 0.3 (flat top)\n",
+    "Cd = 0.3\n",
+    "g = 9.81 # [m/s2]\n",
+    "\n",
+    "def ascentRate(volume=1.0, airDens=1.0, liftForce=1.0, topArea=1.0): \n",
+    "    val = ( 2 * liftForce * g  ) / ( Cd * airDens * topArea )\n",
+    "    if val < 0.0:\n",
+    "        val = 0.0\n",
+    "    return sqrt( val )\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 41,
    "id": "2f3b63fd-d5ea-40b6-a2f9-b31c84cfef36",
    "metadata": {
     "extensions": {
@@ -129,7 +153,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "d8b847f39e5f4582b7392e58279f0843",
+       "model_id": "7cd59b71891c4d47b1ab8c9e559e5cfd",
        "version_major": 2,
        "version_minor": 0
       },
@@ -137,7 +161,7 @@
        "VBox(children=(FloatSlider(value=2.0, description='Width [m]:', layout=Layout(width='500px'), max=5.0, min=0.1…"
       ]
      },
-     "execution_count": 25,
+     "execution_count": 41,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -180,8 +204,11 @@
     "            color = 'red'\n",
     "        else:\n",
     "            color = None\n",
-    "        print( colored(\"{:<20}{:>6.1f} [g]\".format(\"Free lift force:\",freeLiftForce),color))  \n",
-    "\n",
+    "        print( colored(\"{:<20}{:>6.1f} [g]\".format(\"Free lift force:\",freeLiftForce),color)) \n",
+    "    # Ascent rate        \n",
+    "        topArea = width * depth\n",
+    "        ascRate = ascentRate(volume, airDens/1000.0, freeLiftForce/1000.0, topArea)\n",
+    "        print( \"{:<20}{:>6.1f} [m/s]\".format(\"Ascent rate:\",ascRate))  \n",
     "\n",
     "    geometry=BoxBufferGeometry(\n",
     "                                width=width, \n",
diff --git a/notebooks/hotair-pyramid.ipynb b/notebooks/hotair-pyramid.ipynb
index 0450715..1605726 100644
--- a/notebooks/hotair-pyramid.ipynb
+++ b/notebooks/hotair-pyramid.ipynb
@@ -30,7 +30,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 19,
    "id": "6ea87a15-f571-4611-8487-5b7556e2ef45",
    "metadata": {
     "extensions": {
@@ -71,7 +71,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 20,
    "id": "d075a994-76bb-46f7-bdfb-cc6ef449dc43",
    "metadata": {
     "extensions": {
@@ -110,7 +110,28 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 21,
+   "id": "612a3232-e9cb-4405-86dd-bd60ac09cd2f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Ascent rate at ground level\n",
+    "# https://northstar-www.dartmouth.edu/~klynch/pmwiki-gc/uploads/BalloonCalulations.pdf\n",
+    "\n",
+    "# Coefficient of Drag assumed to 0.285 (spherical top)  \n",
+    "Cd = 0.285\n",
+    "g = 9.81 # [m/s2]\n",
+    "\n",
+    "def ascentRate(volume=1.0, airDens=1.0, liftForce=1.0, topArea=1.0): \n",
+    "    val = ( 2 * liftForce * g  ) / ( Cd * airDens * topArea )\n",
+    "    if val < 0.0:\n",
+    "        val = 0.0\n",
+    "    return sqrt( val )\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 22,
    "id": "229c0a36-bf1f-4c07-884c-f3522d5eaae5",
    "metadata": {},
    "outputs": [],
@@ -143,7 +164,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 23,
    "id": "2f3b63fd-d5ea-40b6-a2f9-b31c84cfef36",
    "metadata": {
     "extensions": {
@@ -179,7 +200,7 @@
     {
      "data": {
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "0fb51f22550140339b0a47adcd7d8f9f",
+       "model_id": "3db54b9e2ef24677a45a78c94e21ed79",
        "version_major": 2,
        "version_minor": 0
       },
@@ -187,7 +208,7 @@
        "VBox(children=(IntSlider(value=3, description='Segment num:', layout=Layout(width='500px'), max=12, min=3, sty…"
       ]
      },
-     "execution_count": 7,
+     "execution_count": 23,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -230,7 +251,10 @@
     "        else:\n",
     "            color = None\n",
     "        print( colored(\"{:<20}{:>6.1f} [g]\".format(\"Free lift force:\",freeLiftForce),color))  \n",
-    "\n",
+    "    # Ascent rate        \n",
+    "        topArea = base_area(width,num)\n",
+    "        ascRate = ascentRate(volume, airDens/1000.0, freeLiftForce/1000.0, topArea)\n",
+    "        print( \"{:<20}{:>6.1f} [m/s]\".format(\"Ascent rate:\",ascRate))  \n",
     "    \n",
     "# coating geometry    \n",
     "    bottomGeometry = CylinderBufferGeometry(\n",