{"id":13512,"date":"2016-12-08T19:09:08","date_gmt":"2016-12-08T18:09:08","guid":{"rendered":"https:\/\/www.dg-flugzeugbau.de\/en\/?page_id=13512"},"modified":"2017-01-05T11:45:00","modified_gmt":"2017-01-05T10:45:00","slug":"side-string","status":"publish","type":"page","link":"https:\/\/www.dg-aviation.de\/en\/library\/side-string","title":{"rendered":"Everything Depends On the Side String"},"content":{"rendered":"

By SIEGFRIED PIONTKOWSKI from Magazin Segelfliegen<\/a><\/span> 2\/2009<\/p>\n

Gliders generally don’t have stall warning systems, even though they could do with one as soaring is done frequently close to stall speed. Because airspeed is only one condition indicating stall (vertical acceleration plays a role too), it makes sense to measure the angle of attack. It is amazing, how little a ‘stall’ string features in most text books, let alone mention or description.<\/p>\n

\"\"<\/a>\u00a0<\/span>The angle of attack is quite easily done with a string. It should be approximately 30 cm long and is taped to the left side of the canopy, about 5 cm above the canopy rail. If the position of the string is marked at best L\/D speed, it provides a clear indication of the angle of attack during thermalling, winch launch and positioning of flaps. The advantage:<\/p>\n

The string always shows the current angle of attack, under the inclusion of all parameters like air speed, all up weight, acceleration due to turning or stick movements and gusts. If the entire range of airflow separation is marked additionally the pilot has an excellent stall warning device at his disposal, the function of which is described below in detail.<\/p>\n

What is the Side String?<\/h4>\n

\"\"<\/span>The side string, attached to the side of the canopy, shows the current angle the airflow assumes at the profile nose radius in relation to the airfoil chord. It is indeed a universal angle of attack indicator. The angle of attack can change continuously due to internal factors (pilot input) or external factors, i.e. vertical and horizontal air movements. Piloting an aircraft is a constant control loop between internal and external effects to achieve stationary flight. This goes for all flying conditions, be it straight and level flight or turning, winch launch, during landing, at all wing loadings and altitudes as well.<\/p>\n

It is just the same valid for borderline cases like too slow or fast.<\/p>\n

Fly too slow and the glider falls from the sky and crashes, too fast and the aircraft disintegrates in mid air.<\/p>\n

The normal range for most airfoils is from +15 degree to -5 degree, measured between the airfoil chord and airflow direction. During inverted flight it can reach -10 degree (see also Liienthal polar diagram)<\/p>\n

What can the side string do?<\/h4>\n

It delivers information about the current situation of the aircraft. If I remain always in the functional range of the angle of attack, the aircraft will not crash. It supplies good information, which the pilot needs to interpret. The side string can do a lot, the pilot however must come to the correct conclusions and act accordingly.<\/p>\n

What is the side string good for?<\/h4>\n