Fig. 1.
![NASA Helios [11] and Arbus Zephyr Solar High Altitude Platform System [5].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0008_fig_001.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251205%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251205T175705Z&X-Amz-Expires=3600&X-Amz-Signature=269cbf63dd7e040033cb5cdc0cb88bc0f67021d5c5a6e477bf9c66f1fe2a2c6c&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 2.
![Diagram of two-way fluid-structure interaction implemented in XAVEL (from [28]).](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0008_fig_002.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251205%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251205T175705Z&X-Amz-Expires=3600&X-Amz-Signature=43403d4d11477090106735eae15e836e65a93e315f3d1b55fd01ac9e6387cb2b&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 3.

Fig. 4.

Fig. 5.
![The shape of the MOD-42 airfoil with a flat-upper surface, adopted from [40].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0008_fig_005.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251205%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251205T175705Z&X-Amz-Expires=3600&X-Amz-Signature=2e346f2bd05536ff5dbdc109da0e7c814ef40e97ca971cb4adcfa7140aafd89c&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 6.

Fig. 7.

Fig. 8.
![Average wind speeds in m/s vs. altitude in km (figure adapted from [41]).](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0008_fig_008.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251205%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251205T175705Z&X-Amz-Expires=3600&X-Amz-Signature=5fa09ca171ff9473f758ee82a19868076573a6500fdd75dab598e257718ec742&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 9.
![Lift coefficient vs angle of attack: comparison XAVEL and wind tunnel test (WTT) (from [27]).](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0008_fig_009.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIA6AP2G7AKOUXAVR44%2F20251205%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20251205T175705Z&X-Amz-Expires=3600&X-Amz-Signature=34924a51f42719297c114dd54fe0fc933908b89a460cc596d8b81317c163ab8b&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 10.

Fig. 11.

Gross specifications of current F1A FAI flyers [38,39]_
| Code Class | General Type | Brief Description |
|---|---|---|
| F1A | Gliders (A2 ‘Nordic’) |
|
Wing geometry parameters_
| Parameter | Value |
|---|---|
| Span [m] | 3 |
| Reference area [m2] | 0.51 |
| Aspect ratio | 17.65 |
| Mean aerodynamic chord [m] | 0.17 |
Flight conditions under analysis and required lift coefficient_
| Altitude [km] | Air Density [kg/m3] | Speed [m/s] | Design total lift [N] | Angle of attack [deg] | Coefficient of Lift |
|---|---|---|---|---|---|
| 20 | 0.089 | 18 | 4,9 | 4 | 0.67 |