ISSUE DESCRIPTION
Description of the issue:
Simulation of superheat is missing.
Expected behavior (real aircraft):
Superheat is a very important part of airship physics and Zeppelin NT operations.
Superheat is the difference between the helium temperature and the outside air temperature (OAT).
Example:
- OAT: 10°C
- Helium temperature: 15°C
- Superheat: +5°C
The amount of superheat directly affects the airship’s static lift. Physically, this happens because warmer helium has a lower density than the surrounding air, increasing the difference between the weight of displaced air and the weight of the helium gas. This density difference creates additional buoyancy.
For the Zeppelin NT, approximately 1°C of superheat corresponds to about 30 kg of additional lift.
The Zeppelin NT is typically operated at a weight of around 200-350 kg heavier than air. This provides stable handling characteristics and prevents the airship from becoming difficult to control on the ground.
- Below approximately 200 kg heavier than air, ground handling becomes more difficult. The airship can have a tendency to lift by itself, especially in gusty conditions.
- At approximately 350-400 kg heavier than air, the airship approaches its performance limitations.
For transfer flights or training flights, the Zeppelin NT can also be operated up to approximately 200 kg lighter than air. In this condition, landing requires a different technique, including the use of reverse thrust.
Therefore, even small changes in superheat can have a major operational impact. A change of only 3°C of superheat corresponds to approximately 90 kg of lift difference, which can easily move the airship outside its intended weight envelope if not accounted for.
Superheat behavior in real operations
Superheat changes continuously during flight and depends on environmental conditions:
- When the airship remains on the ground for an extended period with sunlight exposure, the envelope absorbs heat and the helium temperature rises. Depending on envelope color and solar radiation, superheat values of up to +12°C can occur.
- Darker envelope colors absorb more solar energy and therefore create higher superheat.
- After takeoff, the moving airflow cools the envelope. A superheat value of +12°C can reduce to approximately +3°C to +5°C within 30-40 minutes, corresponding to a loss of roughly 210-270 kg of lift.
This means an airship that departs at a weight condition of, for example, 200 kg heavier than air could arrive after a short flight at a condition close to 400 kg heavier than air, potentially exceeding performance limitations.
Other conditions can have the opposite effect:
- Rain and evaporation from water on the envelope can significantly reduce helium temperature, resulting in very low or even negative superheat.
- During nighttime operations, superheat can decrease to approximately -4°C while the airship is on the ground.
A particularly interesting and operationally important situation occurs during nighttime operations with a low-level temperature inversion. In this case, the temperature relationship between the air near the ground and the air at altitude can change significantly, affecting superheat, buoyancy, and flight performance in ways that are unique to airship operations.
Current behavior in the simulator:
The simulator currently does not model superheat. It seems to be a fixed value of +5°.
As a result:
- Helium temperature does not appear to affect lift.
- Changes caused by sunlight, airflow, rain, evaporation, and nighttime conditions cannot be reproduced.
- Important operational considerations such as weight planning, trim management, and performance limitations are missing.
Without a superheat model, one of the defining physical characteristics of airship operation is not represented.
FREQUENCY OF ISSUE
Every time on sim load
REPRODUCTION STEPS
Please list clear steps you took in order to help our test team reproduce the same issue:
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Load Zeppelin NT
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Set different environmental conditions (sunny, cloudy, rainy)
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Observe no change in Superheat