Summer is upon us and it is a good time to review how our balloon system performance changes with higher temperatures (hot days) and especially at higher altitudes. On hot days our system will perform as if it is at a higher altitude reducing the amount of useful load we can carry and increasing the amount of fuel burn. So, it is especially important to know the ambient temperature and check your Flight Manual’s performance charts as part of your pre-flight planning.
As the ambient temperature increases the air expands, therefore the air is less dense, which mimics the density of the air at a higher altitude. This means that your balloon system will perform as if it is at a higher altitude than it actually is. This higher altitude is referred to as density altitude and effectively reduces the amount of lift your system will generate.
For example, if you usually launch at 5000’MSL, on a standard temperature day (42F) you might be able to lift a maximum gross weight of 1500 lbs, but if the temperature is 20F hotter you may only be able to lift 1300 lbs. This would be a 200 lb reduction in your useful load that day or said another way, you can’t carry that extra passenger!
So, throughout these hotter days, please make sure you:
- Check your Flight Manual’s performance tables for the reduction in the maximum allowable gross weight for the day’s temperature
- Calculate the useful load you can carry that day – people, cargo and fuel – your AAAA Performance Calculator is useful for this
- Expect slower system response times and higher fuel burn (i.e. shorter flights)
Have fun and fly safe!