PHAB-17 Flight Planning Part 2
Tony Campbell W5ADC
Calculating the Flight Performance
This will be covered in the next installment of the instructions in a few days. For now, start construction of your payloads. If you have any questions, feel free to post them to the groups and we will get you answers.
As the payload string develops, we will publish a flight “Fast Facts”. This will give a listing of the payloads, weights, frequencies and other important information. As this develops, we will begin to run the flight predictions. There are a number of applications to do this, but we generally use an online tool from a http://habhub.org/. We use the http://predict.habhub.org/ application. Now this is a UK based application, it defaults to UK locations. It is easy to move around the map to locations closer to where we live.
Let’s start with the following initial conditions:
· 1200 gram Kaymont Balloon
o That is the type of balloon we have now
· Desired burst altitude 100,000 ft or about 31,000 meters
o It is always cool to go over 100,000 ft
· 10 lbs of total payload or 4.5 kg
o Just a guess at this point
· 1,000 ft/min ascent rate or about 5 meters per second
o No magic here is a good rule of thumb. This just provides for a reasonable balance of flight time versus altitude
· Hydrogen as the lift gas
o Just a cost issue. $85 for hydrogen / $300 for helium
So, lets do some calculations. I will start by assuming a launch from Princeton High School. Why? We have to start from somewhere and that is a familiar location for us. Going to the Hab Hub Prediction Website, https://predict.habhub.org/.
If you go to that website you should see the following, or you can input the data as shown.
This shows our location, launch time, ascent rate and desired burst altitude and descent rate. These are nice initial conditions, but we need to determine if the Burst Altitude is achievable. Clink on the Use Burst Calculator tab.
Entering in the assumed data of 1200 gram Kaymont balloon, 4500 grams for the payload, hydrogen for the gas, and a Target Ascent Rate of 5 m/s. Clink on the Use Values button,
And you get the following:
With these parameters we have a predicted Burst Altitude of about 93,000 ft. Not bad. If we want to go higher, we can slow down the ascent rate, but that will make the flight longer, or we can reduce the weight of the payload string. Going from 4.5 kg to 3.5 kg get us another 3,000 ft.
So, let’s do our first flight prediction. You can see that this did not result in a good landing location.
The landing is right in the middle of Lake Ray Roberts. If we want to stick with Princeton for the launch site we could increase the Ascent Rate. If we went to 6 m/s that would reduce the burst altitude to about 90,000 ft. It would land way short of the lake.
Selecting the Launch Site
The most important key to selecting the launch site is predicting where the balloon will land. Since these predictions are not perfect, we need to consider the following:
· Should not land in a city.
· Should not land in a lake.
· Should not land where there are a bunch of trees.
· Cannot land anywhere near an airport or military installation.
So, we are generally looking for a landing spot with large open fields. Now that we know what we are looking for, lets start the flight planning.
We really need a final payload weight estimate to start doing serious flight predictions and picking a launch location. I will be running the calculations daily; we will have changes in the winds aloft as the week progresses. Right now, the weather looks OK, but the winds are marginal and there is a slight chance of rain. This far out, it is just a good guess.