Използване на бушони при теглене с лебедка

Безопасни практики. Инциденти и авиационни събития!
Site Admin
Мнения: 6
Регистриран: нед яну 20, 2019 1:29 pm

Използване на бушони при теглене с лебедка

Мнение от viper_weasel » пет май 01, 2020 11:51 pm

Повечето самолети имат точно определена здравина на бушона който се използва при теглене.
Забелязва се обаче че Британската Асоциация по Безмоторно Летене използва завишени стойности на бушоните за някой самолети.
Ето и обяснението на това от съветника на Британската Асоциация по работа с лебедки:

For a number of gliders, we established many years ago that the manufacturer certified weak links were not strong enough for the glider. This was probably because gliders were quickly getting heavier, winches were getting more powerful and some manufacturers at the time did not realise how much load the glider would be subjected to on the launch. We found that some gliders had a significantly increased number of launch failures when using the manufacturer certified link. This in turn significantly increased the risk of an accident particularly when the weak link failed at low level or an awkward height. The BGA countered this by using the next colour up on a few gliders. They never go any further than the next colour up so as not to risk damage to the glider. Fortunately, we no longer need to make concessions for new gliders as manufacturers are now certifying them with more appropriate weak link strengths.

A good example of the issue would be the Twin Astir which is a big heavy two seat glider. In 1980 this glider was certified to use a blue weak link. The manufacturer quickly realised that it was impossible to launch the glider with a blue link so in 1982 the certification was amended to allow the use of a red weak link. The BGA found that the Twin Astir would still break the red link frequently, causing a high risk of accidents so a concession was applied to allow it to use a brown link. This just shows how little the manufacturers knew about winch launching at the time! It is unbelievable that anyone could think the appropriate link for a heavy two seater would be blue! This is the problem we faced with a lot of gliders from this time that necessitated the use of BGA concessions.

All BGA clubs to my knowledge are using the BGA concessions where they exist. I know from experience that with a powerful enough winch and a Single Astir in a good 45° climb, even the blue weak can break easily on windy days, so I would definitely avoid using white for this glider.

Regarding the reserve system, it uses two links of the same colour. When a large load is applied, the main weak link breaks. If the load is greater than the strength of the reserve weak link, this will also break and protect the glider. If however the load is actually less (because the main weak link was old / hole stretched), then the reserve weak link will take the load and allow the glider to continue to launch.

I would advise against using the reserve system as intended with two links of the same colour. This is because on many occasions two links of main type or two or reserve type have been used by mistake. This has the effect of doubling the overall breaking load as each link takes only half the load.

I would also advise against using the two weak links of different colours because the strongest weak link will always determine the strength of the system and you may as well just use the one link.

My recommendation for determining which link to use would be to use the BGA concessions where they exist. I would also recommend using just the one weak link in the weak link assembly and then discarding when the hole appears stretched.