Gliders towing is a technical means to give speed and height necessary to the autonomy of the glider by the use of a tow plane .
At the same time there are other means to take off gliders like Winch or autonomous systems (motor gliders).
Towing implementation is via a tow plane , a tow rope (inelastic) of about 60 meters provided at its ends standardized rings and the glider towed.
Ideally for glider towing must allow height gain about 500 meters during minimum time to minimize the time cycle (takeoff, climb, dive and landing) thus allowing minimize the cost of the operation and to take off a maximum of gliders in the shortest time.
Cost towing is indexed to Time use engine (often counted 100th hour) from the attachment of cable towed glider to stop the aircraft engine or hooking the next glider.
The project has resulted in:
- coupling the glider to the tow plane
- take off the hitch as promptly as possible (passage of 15 m)
- climb as soon as possible to 500 meters / ground (maximum Vz = maximum vertical speed uphill) at the speed of 120 km / h (adapted to each glider or glider generation).
- Dive as fast as possible
- release the tow cable on the runway
- incorporate a runway circuit and landing
- Drive to the next glider to take off
average performance of current (certified or microlight) tow planes are about:
- + 2.5 m / s for a single-seat glider towed
- + 1.5 m / s for a two-seat glider towed.
The tow plane itself is, in most cases, a plane derived from a tourist plane (microlight or certified) or aerial work aircraft as training or agricultural labor (see section on the history of the French tow planes).
Towing gliders is obviously not the first intended of these planes and if they are provided to carry 2 or 4 people at over 200 km/h over long distances , they can excel in the art of efficiently climb to 120 km / h ?
There is little chance, so
Why, from the beginnings of gliding, are there no specific aircraft design ?
This is actually a niche market and, industrially speaking, it is obvious that reuse existing tools to achieve tow plane from a tourist plane has technical and financial benefits.
There has in France one hundred tow planes in operation and more in Europe, including Germany ambassador of gliding.
Microlight world , well aware of the impasse is gliding, tries to seize the market by making slight changes on their existing planes (up to 100 hp, hook, mirror …) bringing no additional performance (climb or take-off). These aircraft used for Aerial Work fly without certification .
Today we see carbon fibre microlight planes fully adapted to the speed and perfect runways.
Are they at this point maids of all work at the point of asking them to fly slowly for 15 minutes, full gas, high angle of incidence, and land on a full of holes grass runway even on a gravel field ?
In other words, wouldn’t be more appropriate than a 5 set road sedan to tow (alone) a plow?
It is important to insist on this fact. Tourist aircraft , whether certified airplanes (DR400, Rallye) or microlight today are absolutely not suited to tow gliders in spite of the adjustments made for three main reasons:
- Their design is initially too shifted in relation to towing. They are made to carry a load, to fly fast and to consume few at this speed (200 km/h).
- They have a small propeller and a engine who is running too fast . Propulsive efficiency if it is okay to over 200km/h (high speeds and the small diameters) can not be at 120km/h and will be even less if we increase the power (which also increase the mass).
- Their morphology does not allow an increasing of propeller diameter and their airframe consumes too much power at 120km/h (high incidence angle).
Given that the glider towing mission is special (low airspeed and vertical speed maximization), it is impossible to obtain a good tow plane starting from an existing tourist plane or microlight plane.
It is therefore necessary to start with a blank sheet and create a specific tow plane to this unique mission.
PSX Aviation designs “Nout” a tow plane dedicated for towing gliders mission.
Designed by glider pilots for glider pilots, “Nout” is a powerful tool but especially efficient for gliding.