Aerodynamic Armlinge

August 30, 2020

In high-speed flight, the arms of a pilot become an aerodynamic flow disaster. The Vietnamese PWC driver Bach Le Hoang is taking action against this with profiled arm warmers. The Xuctu arm warmers are automatically pulled into a clean profile in high-speed flight. // Source: Bach Le Hoang competition pilots also have black humor. If some of you want to get the last bit of power out of the final approach at full speed, then let go of the brakes or B-handles (for two-line vehicles) and cross your arms in front of your chest, close to your body to reduce air resistance. They call this technique the coffin style. And that is quite ambiguous. On the one hand, it actually looks as if the pilots are lying in their harnesses like in a coffin. On the other hand, this maneuver naturally also entails an increased risk that a possible full-speed collapse will get out of control and the pilots could end up in the wooden deck chair without seatbelts. Whatever. The coffin style is not for everyone, and so it is only understandable that pilots wonder how they could achieve better aerodynamics with extended, controllable arms. The latest idea in this direction comes from Vietnam and comes from PWC pilot Bach Le Hoang. He had already started some time ago to pimp the aerodynamics of reclining harnesses and to carry out complex flow calculations (see Lu-Glidz: Pimp the spoiler). In the beginning, for the sake of simplicity, he left the pilot arms out of his calculation models. But then he found ways to simulate them and was shocked to see how much the arms disturb the orderly flow around the pilot. Arm warmers called Xuctu Bach Le therefore set out to find a solution. He developed special arm warmers, which he named Xuctu and even had copyright protection. The Xuctu are made of a windproof, elastic fabric and are cut so that they reach from the hands (there they are held by a thumb loop) to over the elbows. In normal flight they hang relatively loosely and do not interfere with the control movements. But as soon as the pilot steps into the accelerator, the Xuctu are tensioned to the rear using a pull line that is also connected to the accelerator. They then form a teardrop-like aerodynamic profile on the arm, around which the air flows much less turbulence. It remains to be seen whether this technology is actually so effective in practice that pilots will be willing to accept the additional expense. After all, the harness has to be changed a bit in order to integrate the routing of the Xuctu lines. In addition, the pilot has to slip into the Xuctu gauntlets when putting on the harness. However, many competition pilots are also real performance fetishists. And if you carry kilos of ballast up mountains in order to achieve a speed advantage of perhaps 1 km / h, you may also be enthusiastic about leashed aero arm warmers. By the way, the idea with the arm profiles is not entirely new. At the PWC Superfinale 2018, Maxime Pinot was tested with permanently profiled forearm cuffs (see Lu-Glidz: The new slipperiness at PWC). However, at least this variant has not prevailed in the field of competition pilots. The Xuctu offer at least the advantage that they can only be opened up in high-speed flight and that they do not represent a major visual obstacle during thermal flight. In addition, their profile looks much cleaner, at least visually. Bach Le Hoang has published a video on Youtube in which he demonstrates the Xuctu in flight. You can see how the gauntlets are opened when accelerating and how they hang loosely on the arm when in trim flight.

Deutsch
This article has been translated for your convenience and was originally written in Deutsch.

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Lu-Glidz
A popular German Paragliding Blog written by Lucian Haas

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