PARAGLIDER DESIGN HANDBOOK
CHAPTER 9. RISERS
9.2. Analysis on 4 riser speed system

9.3 Trimers

9.4 Vario seat

9.1. Introduction

The risers are linking the main carabiners with the lines and grouped into classic areas named "A ", "B", "C" and "D", on each side of the wing and symmetrically.

The simplest paragliders of beginnings only had 2 risers per side, then were added, 3, 4,... and even more, for a better control of the pilot on the wing. With the progressive reduction in the number of lines in the directions along and across the wing, gliders go back with three or two risers per side.

Normally, the lengths of the risers are all equal to each other, except in the prototypes, which may be necessary to make special risers each of a different length, to adjust the wing.

To adjust the flight speed, risers can be shortened or lengthened using different devices:

- speed bar (operated dynamically with your feet)
- trimers (manual setting)
- vario seat (weight shift back and forth on special harness "sellette de pilotage")
- rods or plates...

9.2. Analysis on 4 riser speed system

9.2.1
Statement of the problem and analytical solution

Below is a classic speed system of 4 risers, and the analitical calculations of the effective lengths of each riser LA, LB, LB, LC in applying displacement in the cord (a).

Figure 9.1 Risers length variation by applying a real speed system

Figure 9.2.
System of equations for solving the problem of calculating the variations in calage and ideals lengths of each riser, by applying the displacement (a) in the cord of the speed system.

Figure 9.3. Resolution using only distances.

Figure 9.4. Resolution using cosine law and angles.

Distances PA, PB, PC, PD are considered the necessary to rotate the airfoil around point D without deformation. Note that in the real speed system (described above), distances LA, LB ,LC , LD approximate those ideals and the profile is deformed slightly above the ideal

9.2.2 Numerical examples

Geometric parameters:
 OA' 24,34 A'B' 54,41 B'C' 73,03 C'D' 68,73 D'F 65,87 OF 286,38 A'A 15,91 B'B 20,03 C'C 14,2 D'D 6,07 AD 195,81 A'D' 196,17 PD 706,2

 Riser lengths real speed system Riser lengths ideal speed system a LAR LBR LCR LDR LAT LBT LCT LDT Calage % 0,0 47,0 47,0 47,0 47,0 47,0 47,0 47,0 47,0 40,0 2,5 46,2 47,0 47,0 47,0 46,2 46,4 46,7 47,0 39,0 5,0 45,3 47,0 47,0 47,0 45,3 45,8 46,4 47,0 37,9 7,5 44,5 47,0 47,0 47,0 44,5 45,2 46,1 47,0 36,9 10,0 43,7 46,2 46,6 47,0 43,7 44,6 45,8 47,0 35,9 12,5 42,8 45,3 46,2 47,0 42,8 44,0 45,6 47,0 34,8 15,0 42,0 44,5 45,8 47,0 42,0 43,4 45,3 47,0 33,8 17,5 41,2 43,7 45,3 47,0 41,2 42,8 45,0 47,0 32,8 20,0 40,3 42,8 44,9 47,0 40,3 42,2 44,7 47,0 31,7 22,5 39,5 42,0 44,5 47,0 39,5 41,6 44,4 47,0 30,7 25,0 38,7 41,2 44,1 47,0 38,7 41,0 44,1 47,0 29,7 27,5 37,8 40,3 43,7 47,0 37,8 40,4 43,8 47,0 28,6 30,0 37,0 39,5 43,3 47,0 37,0 39,8 43,5 47,0 27,6 32,5 36,2 38,7 42,8 47,0 36,2 39,2 43,3 47,0 26,6 35,0 35,3 37,8 42,4 47,0 35,3 38,6 43,0 47,0 25,6 37,5 34,5 37,0 42,0 47,0 34,5 38,0 42,7 47,0 24,6 40,0 33,7 36,2 41,6 47,0 33,7 37,4 42,4 47,0 23,5 42,5 32,8 35,3 41,2 47,0 32,8 36,8 42,1 47,0 22,5
LAR LBR LCR LDR (Real riser lengths)         LAT LBT LCT LDT Theoretical or ideal riser lenghts
a= applied cord (cm)
Real riser length using figure 9.1 formulation. L=47 cm, x1=2,5 cm, b=15 cm (amax=45 cm, using 2 pulleys ).
Theretical (ideal) riser length using figure 9.2 and figure 9.3 formulations.

Figure 9.5. Risers lenth and calage variations with speed system.
RED ----> "A" riser
GREEN ----> "B" riser
BLUE ----> "C" riser
MAGENTA ----> "D" riser (47 cm)
GREY ----> calage %
The solid line shows the ideal lengths to avoid deforming the airfoil. The dotted line shows the real risers lengths with an speed system as shown in Figure 9.1 and an spacer between the elevators A and B of 2.5 cm

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