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Deutscher Hängegleiterverband e.V.

DHV

Safety checks on LTF-A and B paragliders: second test series

The resonance we received for our first safety check article published in DHV-Info 174 was overwhelming. Feedback was almost unanimous with comments such as “Please continue this work on all current gliders” being most often received. This article extends the initial safety check article in DHV-Info 174. Details on how we rated manoeuvres, their relevance to accident statistics, LTF test criteria and other details can be found in the original article.
The DHV safety and technical department chose a smaller set of gliders to perform tests on for the second series, in order that results could be published with a minimum time lag.
The following gliders were tested:

Launch preparations

Glider user-friendliness was tested for launch preparations. Novas Ion 2 was the clear winner in this discipline; only a few easily sortable main lines, a well arranged set of risers and soft hanging gallery lines. No other glider was as easy or quick to get ready to launch. The Alpha 5 from Advance and Bodyguard 3 and Emotion 2 from U-Turn were also easy to prepare, but more attention was required in sorting the gallery lines. Emotion 2 pilots need to familiarize themselves with the risers on this glider, the Big-ears help system and long B-risers make handling a little more complicated. The Emotion 2 does not have a middle point marking on the glider canopy. UPs Makalu 3 has lots of gallery lines which are also on the stiffer side and tend to build loops; careful sorting is required. Releasing the brake handles from the press stud fastener on the risers needs a good pull! Gin Gliders Evo Sprint needed the most attention: thin risers and unsheathed gallery lines must be carefully checked for knots, twists and tangles.

Launch characteristics

All tested models had no real launching problems, none of the gliders showed marked tendencies to hang behind or overshoot the pilot during launching. All 3 LTF-A gliders behaved excellently, smooth inflation and good feedback via the pressure on the A-risers as the canopy climbed to the zenith. Aside from the Alpha 5 which needed a little more brake, all canopies could then be easily stabilized over the pilot with normal brake appliance. The Ion 2 starts well too, but requires a clear brake input to stabilize at the zenith. The Sprint Evo begins climbing somewhat slowly and then requires a marked brake input to prevent it overshooting at the zenith. UPs Makalu3 is unproblematic, the canopy climbs moderately to the zenith and stabilizes over the pilot with no marked brake input required.

All test flight manoeuvres were documented with data-loggers, ground- and GoPro cameras.


Info: data logger technology

The pilot data logger is firmly attached to a main suspension strap on the pilots harness.
A second smaller glider logger is attached to a cell wall inside the glider using two strong magnetic plates. The best position for data collection has been determined to be where the C-gallery lines are attached to the canopy at the 70% collapse marker points. Logger data is collected continually from the beginning to the end of the test flight and the two instruments are synchronized  with each other via a low-range radio signal. Data sets are transferred from standard micro-SD memory cards to a PC after landing.
The loggers collect the following information:
   - Pitch, roll and yaw angle,
   - Pitch roll and yaw acceleration,
   - Vertical velocity calculated over a 0.5 second window from the barometric altitude sensor,
   - Velocity: the pilot data logger contains a 5 Hz GPS, from which the velocity over ground is calculated,
   - G-Force: from the accelerometers contained in the pilot data logger the G-force acting on the pilot is calculated,
   - Altitude: both the barometric height (recorded at 100Hz) and the GPS height (5Hz) are recorded.

Data processing: the processing software is written to automatically recognize the beginning and end of a test manoeuver. Pilot and glider movements are simulated from the recorded data, and this simulation is synchronized with the video material of the test flight. Test pilots check the synchronized results for plausibility. Data loggers are instruments to assist test pilots and provide additional objective information on parameters which are difficult to judge in the air such as roll and pitch angles, height loss,  course changes and durations.
 
Flight stability

Through induced pitch testing a measurement of a gliders pitch stability can be made. The angle to which a canopy dives forward during pitch testing is a good indicator of the potential dynamics which may develop during such circumstances. Pitch angels were measured after the third pitch cycle during testing.

 

Asymmetric Collapses

Asymmetric collapse testing produced a surprising result: the winner in this discipline was the LTF-B glider Makalu3 from UP. This glider collapses softly with no serious dynamic reactions which makes it easy to manage. More demanding were the Emotion 2M and Bodyguard 3M from U-Turn. Both these gliders collapse abruptly with a lot of wing area and large folding angles when compared with other gliders in their respective LTF classes. Due to the large resistance of the collapsed part of the wing, large pitch- and yaw-values result. In practice, such massive collapses only occur under severe turbulence, and we have no evidence in our accident statistics that these gliders are particularly dangerous. The Alpha 5/26 and Ion 2M demonstrated typical behavior for their respective LTF classes. The Sprint Evo M clearly indicated its positioning in the high-end LTF-B class, with reactions to asymmetric collapses which were more demanding and dynamic that the other (low-end) LTF-B gliders.
None of the tested gliders indicated a tendency to cravat after an asymmetric collapse.

 

Frontal collapses

Again, the Makalu 3M from UP demonstrated excellent characteristics after front collapse tests. Recovery after massive front collapses is similar to the U-Turn Bodyguard 3M, with no delay and little height loss. The Alpha 5 and Emotion 2 need a few seconds more to return to normal flight. The Ion 2 reacts well to smaller frontal collapses up to about 40% of the span, but does demonstrate a tendency to  fold at the middle of the canopy. This tendency becomes marked after a complete front collapse across the entire span, the canopy horseshoes, may rotate and requires significantly longer to recover. The wing ends may tangle and cravat in the lines during this. The Sprint Evo demonstrated this behavior more severely, after a front collapse the glider tends to horseshoe, then begins to rotate and finally recover asymmetrically. In some cases recovery was only possible through pilot action.

 

LTF B

UP Makalu 3 M

40% Collapse

20-29 m

30-45°

30-45°

no

10-14 m/s

Moderate pitch back and forward. Delay free recovery, no course change low height loss.

Max. possible collapse

30-39 m

45-55°

30-45°

no

10-14 m/s

Marked pitch backwards, moderate pitch forward. Delay free recovery, rapid return to normal flight. Occasional horseshoe tendency, but with out impact on recovery times, no course change low height loss.

Nova Ion 2 M

40% Collapse

20-29 m

-30°

-30°

no

10-14 m/s

Low pitch back and forward, slight delayed opening, no course change.

Max. possible collapse

40-49 m

30-45°

30-45°

Occasional

10-14 m/s

The greater the collapse, the larger the horseshoe tendency. Occasional large horseshoe with course change and severely delayed recovery.

Gin Sprint Evo M

40% Collapse

40-49 m

30-45°

-30°

no

10-14 m/s

Moderate pitch back and low pitch forward. Delayed recovery, no course change.

Max. possible collapse

60-100 m

55-65°

55-65°

Marked course change tendency.

>2G

15-19 m/s

Severe pitch back and forwards. Large deformation tendency, largely delayed recovery, occasional pilot action required. Asymmetric recovery possible, large height loss, course change possible.

 

Spiral dives

With the exception of the Gin Sprint Evo, all gliders behaved well during this manoeuvre. Generally, on exiting gliders accelerate slightly after the brakes are released and this is immediately followed by the canopy pitching up and exiting with no further action required by the pilot. The Emotion 2 has a relatively short brake travel length, and quickly enters into a high sink spiral – something newcomers to the manoeuvre should observe. Both the Alpha 5 and Makalu 3 demonstrated well balanced behavior while spiralling. These gliders accelerate and increase sink rates moderately. The Bodyguard 3 enters a dive more abruptly, steep pitch angles and relatively high G-forces build up quickly. The Ion 2 behaves very similarly. Gin Gliders Sprint Evo requires the most care when performing spiral dives, as to be expected for a high-end LTF-B glider. After the second 360°, sink velocities of up to -20m/s are reached. On release of the inner brake to exit the manoeuvre the glider can remain in a stable spiral for longer periods but further acceleration was not measured. Sprint Evo pilots must be able to control a spiral via the outer brake and must know how to exit correctly from a stable spiral dive.
Spiral dive testing was performed with test pilots sitting in a neutral position. Should weight shifting to the inner side of the spiral be additionally applied, more severe acceleration and exiting reactions are to be expected.

Spiral dives

 

Vsink after

360°,

720°,

max.

 

G-Force after

360°,

720°,

max.

Height loss

after

360°,

720°,

max.

Height loss from brake release to regaining normal flight

Time to

360°

720°

Total

Action after brake release

Notes

LTF A

U-Turn

Bodyguard 3 M

7 m/s

14 m/s

17 m/s

2,7 G

3,8 G

4,1 G

30 m

80 m

130 m

50 m

0-8 s

8-12 s

12-18 s

Acceleration from 14-17m/s within first 90°, then pitch up recovery to normal flight within next 180°

Generally not problematic, high G-force.

U-Turn Emotion 2 M

9 m/s

15 m/s

17 m/s

2,4 G

3,7 G

3,7 G

40 m

80 m

120 m

40 m

0-7 s

7-11 s

11-17 s

Acceleration from 15-17m/s within first 90°, then pitch up recovery to normal flight within next 180°

Glider has relatively short brake travel lengths and enters spiral quickly. Exiting behavior not problematic.

Advance Alpha 5/26

6 m/s
12 m/s
16 m/s

2,1 G
3,2 G
3,8 G

30 m
80 m
110 m

30 m

0-10 s

10-15 s

15-19 s

Acceleration from 12-16m/s within first 90°, then pitch up recovery to normal flight within next 90°

Generally not problematic

LTF B

UP Makalu 2 M

5 m/s

13 m/s

17 m/s

2,1 G

3,2 G
3,7 G

20 m

60 m
100 m

40 m

0-10 s

10-14 s

14-18 s

Acceleration from 13-17m/s within first 90°, then pitch up recovery to normal flight within next 90°

Generally not problematic

Nova Ion 2 M

7 m/s

14 m/s

18 m/s

2 G

2,5 G

4,1 G

30 m
80 m
130 m

50 m

0-8 s
8-13 s
13-19 s

Acceleration from 14-18m/s within first 90°, then pitch up recovery to normal flight within next 180°

Generally not problematic, high G-force.

Gin Gliders Sprint Evo M

8 m/s

19 m/s

22 m/s

 

 

2,6 G

4,0 G

4,6 G

30 m

80 m

170 m

90 m

0-8 s

8-12 s

12-20 s

Acceleration from 19-22m/s within first 90° then continued rotation at 20m/s for 360° before pitch up recovery to normal flight within next 180°

Dynamic entry to spiral with rapidly increasing Vsink and G-forces. Demanding recovery. Tendency to enter stable spiral dive with high Vsink rates on brake release.

 

B-Line stalls

Both the Emotion 2 M and Bodyguard 3 M have a special construction on the extra long B-risers to help perform this manoeuvre: a handle with line / pulley attachment. The system works well: with little force (and long travel lengths) gliders enter a minimal B-stall with sink velocities of about -5m/s. The canopies sink at a steep angle rather than the classic vertical sink behavior of most other gliders. Entering and exiting the manoeuvre is accompanied by only little pitch movement. A conventional B-stall can also be performed on both gliders but to do so a long reach is required to grab the B-risers at their tops. Sink velocities increase by 2m/s for the Bodyguard and 3m/s for the Emotion. As with all the Alpha 5s predecessors, a good pull is required to initiate a B-stall. The sink and canopy deformation are both very stable, and very similar to the Makalu 3 from UP. Deformations can occur on Novas Ion 2 after longer B-stalls, but are not as severe as with the Mentor 2 and are clearly announced by the canopy becoming restless. A short B-stall is all that is required to demonstrate that this is not the best rapid descent method for this glider. The wingtips begin to fold back, and an immediate exit is required.
 

B-Stall

Glider

B-riser construction and ergonomics

Sinkrate in stable B-stall

Tendency to deform,

Rotation

Pitch back / entry

Pitch forward / exit

Height loss on exiting

Notes

LTF-A

Advance Alpha 5.26

 

8 m/s

no

no

30°-45°
15°-30°

-20 m

High entry force, very stable sink phase

U-Turn Bodyguard 2 M

Special handle on B-risers

5 m/s

no
no

15°-30°

15°-30°

-20 m

Simple entry with special handles, moderate Vsink, very stable sink phase

U-Turn Emotion 2 M

Special handle on B-risers

6 m/s

no

no

15°-30°

15°-30°

- 20 m

Simple entry with special handles, moderate Vsink, very stable sink phase

LTF-B

UP Makalu 2 M

 

8 m/s

no

no

15°-30°

15°-30°

-20 m

very stable sink phase

Nova Ion 2 M

 

9 m/s
Slight horseshoe tendency after long B-stalls

no

 

30°-45°
15°-30°

20-30 m

 

Gin Gliders Sprint Evo M

 

8 m/s
Wingtips bend back after short B-stalls

no

15°-30°

30°-45°

- 20 m

B-Stall difficult, marked deformation tendencies

 

Big-ears

All tested gliders mastered this manoeuvre without any problems. The highest sink velocities (3.5-4.5 m/s) were measured on Novas Ion 2 due to its 2 A-line construction, followed by the Bodyguard M (3-4 m/s) which looses substantial surface area when its wingtips are collapsed. All other gliders lay between 3.5 m/s (trim speed) and 4.5 m/s (accelerated). No glider showed a tendency to oscillate during the manoeuvre, and brake appliance to exit from the manoeuvre was not required. All gliders exited without pilot input, the Makalu 3 and Sprint Evo demonstrated slightly delayed exiting. No glider indicated deep or parachutal stall tendencies, even after longer periods of big-ears flying at trim speed. When flown accelerated, all gliders reached at least their normal trim speeds whereas most of them flew slightly faster.

Further tests will follow.