COMMENT ON DHV-2 RATED GLIDERS
Two articles which appeared in DHV-Info No. 92, September 1997. Translated from German by Ulf Arndt and Laura Nelson
NEW PARAGLIDER GENERATION
by Karl Slezak
The article stemmed from experiences with newly rated Class 2 gliders during safety course training exercises.
The first incident occurred during assymmetric exercises over the Aachen Lake, when a DHV 2 glider went into a spiral dive, which could only be ended by massive pilot input.
A few days later on a similar glider during an exercise without countersteering to get to know the characteristics of the glider, the tuck did not open, the glider spiralled down with great sink rate, and only with greatest effort could the pilot stabilise the glider. A week later during soaring at 200m above take off, a pilot experienced a tuck, did not react immediately, the tuck stayed in and the glider went into a spiral. Only after instruction over the radio did the pilot react, and manage to stabilise the glider. Similar gliders, similar problems.
It may not sound so spectacular, but for the pilots it was a real negative sensation. That a high performance glider during sideward/forwards movement from lost airflow caused by serious situations such as full stall, spins, etc, can cravat, is logical, explainable and can often be observed. That a Class 2 glider can repeatedly cravat from a simple tuck, and with the wing in, start falling, is new, shocking and frightening.
One thing is clear: with a side tuck the glider must immediately be stabilised through countersteering. When the tuck turns into a cravat through lack of countersteering, the glider often progresses into a breathtaking spiral dive. In addition, the forces become so strong that it is sometimes completely impossible to control. Added to this is the pilot who had been surprised by the suddenness, and who freezes and reacts far too late, or reacts completely wrong, or not at all.
Another example: a new Class 2 glider with an extended full stall gets a massive tuck, which does not cravat but after a very fast 360o turn opens explosively by itself. The suddenness of the opening leads to a strong pendulum to the opposite side which tucks in, this cravats, and the glider spirals in. The lady pilot reacts slightly late by pulling both brakes hard in an effort to full stall to clear the cravat. Because of the extreme brake pressure she could not manage, but at least dampened the spiral so that the water landing was not too hard.
Basically this reconfirms: when the glider cravats, fast reactions are required. As with "normal" tucks, one tries to stop the turn by countersteering. In managing this, the cravat must be loosened. This can be achieved by deep pumps on the tucked side. Should the tip be tucked between the A or B lines, the best possibility is to pull down the whole A-riser on that side. The general advice to loosen the cravat by pulling on the stabiliser line puts the pilot of most gliders to a difficult task. To try and find the stabiliser line amongst the mess of lines hanging down is very difficult, while still countersteering. Lucky the pilot whose stabiliser lines are a different colour! Often the turn tendency of the cravated glider is so strong that the stabilising effort with the other brake is unsuccessful. In spite of strong countersteering the glider keeps turning towards the tucked side. Or the open side is stalled when more brake is applied to stop the turn. Before the glider can get into a heavy rotation
which can deteriorate fast, the decision must be made. With at least 300 - 400 m height above ground a full stall is recommended. Both brakes are pulled down all the way. This can be very difficult if the glider is already in a spiral. The violently thrashing wings in a full stall free the cravat in most cases. A full stall is however an extreme manoeuvre and can only be half controlled by someone who has practiced it once before.
The same situation in less height clearance requires the immediate throwing of the reserve parachute. In safety training it is repeatedly noted that the decision to throw the reserve parachute is usually taken too late. At least on course there is luckily the radio to give the instruction with, but the accidents over the last months prove that this is a general problem.
Many modern gliders have a fast impetuous tendency to open side tucks. Typically a Class 2 glider reacts after a strong side tuck without pilot input: fast 270 - 360 degree turn (sometimes more) and sudden unexpected re-opening.
As described above, this explosive re-opening often leads to a strong pendulum to the opposite side, which can cause a counter-tuck through the load being taken off the lines.
As the glider in this instance does not tuck dynamically from the front but from the side towards the middle of the glider, this type of tuck has more potential to cravat. Even if a cravat does not occur, the side tuck leads to another turn movement.
As the weight of the pilot still moves in the direction caused by the original tuck when the counter tuck throws the glider in the other direction, there is also a twist danger which should not be underestimated. The whole thing can cost 30 - 50 m height loss and is extremely dangerous in the vicinity of the ground.
A counter tuck can only occur when the original tuck puts the glider in a dynamic turn movement. In this case too, the immediate stabilising of the glider is the only correct reaction.
What is the problem with the new Class 2 gliders?
When one compares the classical DHV 2 gliders (Vision, Compact) with the current Two's, there is a noticeble essential difference: the unequalled greater responsiveness of the new gliders in all flight characteristics.
Less dampening on the roll and pitch axles provides impressive reactions with little steering action, or from light turbulence. With test flights in smooth conditions this is great fun. In strong thermic conditions or turbulence one quickly experiences the flip side.
The glider is only subdued through very active flying, every movement of the air the glider interprets stronger, the long line length makes the glider seem as if it has its own life separate from the pilot. Beware that one can get a killer front tuck when the canopy shoots fo
rward, when falling out of a thermal.
A loss of quality of the testing for Gute Siegel could not be observed. It is clear that there can be glider behaviour found in demanding flight conditions which cannot be covered by test methods.
The older 2-rated designs were within limits which an average pilot could handle. Nowadays the gliders however, obviously due to the bigger possibility for own reactivity, have a bandwith of critical glider reaction which is bigger and the tolerance for pilot error less.
In spite of this, these canopies are not basically dangerous or bad. For pilots who fly often and have solid thermal experience and know their glider reactions from a safety course, the new more powerful Class 2 paragliders are a real enrichment.
It is sad that a lot of occasional pilots are over estimating their skills. Certainly status plays a roll in the choice of equipment.
During every safety training course there are always pilots who are not comfortable with ordinary flight requirements of take off, turns and landing. And someone like this is expected to react correctly to a 2/3-tuck at 20m height with his brandnew 2-rated glider! This won't work. We have made it a habit to point out the dangers to such pilots, and to advise them to change over to a better handling glider. Usually one gets a defiant reaction which would be regarded in other situations as rather strange behaviour. One gets the impression sometimes, as if reason has been switched off. So as if man in his all-round secure life
wants to keep some risk.
If I had a say in which pilot should be allowed to fly what canopy, I would make the following conclusion: Pilots who have less than 10 flight hours, i.e. 10 thermal flights of 1 hour each, per year (which I believe the majority of the occasional pilots cannot do) should not fly anything more than a Class 1 glider. The Funiac or Philou is so sensationally well-behaved compared to the Two, that it cannot be described in words. And the things fly so well that one is not at all disadvantaged in thermals.
The classical fun flyer with 30 - 50 flights in a year, the definite and false target group for the new Class 2 gliders, gets from me a maximum 1-2 rated glider.
Who has once flown an Airwave Harmony, UP Vision Classic, Paratech P23, etc in stronger thermals, will be impressed by the performance, stability and flying behaviour these items provide.
Only those who really fly regularly, have shown ability to control every day flight situations, and in safety training showed solid skills, are ready for DHV 2 paragliders. All high performance canopies, no matter whether it is 2-3 or 3 rated, are not recommended, except to a handful of above average talented and constantly flying pilots.
To paraglider sellers: Often when one has pointed out the problems of the pilot's choice, one hears: my instructor has recommended that I buy this one. This should not be. He who sells to a beginner or one who does not fly so often a performance canopy, abuses the often endless trust of his unspoiled customer. And he sins against our sport. There is no such reason as: he wants it - if I don't sell it to him, he will buy it from someone else. It is defenceless reasoning, shortsighted and jeopardises the existence of us all, who lives from the sport.
This season, which started with so many accidents, should make us think. The Association, the manufacturers, the schools, and above all, the pilots. Only the pilot can decide when he flies, where he flies, what he flies, and how he builds up in the sport.
The problem begins and ends where all problems begins and ends: between both ears.
ANSWERS FROM HANNES WEINIGER REGARDING MODERN GLIDERS
Hannes Weiniger is responsible for glider certification within the DHV-Technical Committee. He is Chief Test pilot with many years of experience.
At present the DHV has feedback of incidents with current tested gliders showing that some pilots cannot handle the behaviour of the gliders.
The reports come from schools, safety courses and pilots.
Problems arise in all classes from the fast turns after a side tuck. Particularly noticeable are those in Classes 2 and 2-3. The gliders turn with fast speed and show distinct tilting along the roll axle with simultaneous forward dive on the pitch axle. The pilots are surprised about the dive and often react wrong. They don't control, or do it too late, or so hard that loss of airflow is experienced.
A further problem is the stable steep spiral in discussion. But this problem is not new.
Many gliders long regarded as successful and in accident statistics not noticeable have under predetermined conditions gone into a stable spiral.
One cannot say that modern paragliders are less safe. On the contrary, through the last updating of the manufacturer's regulations a number of steps for improvement of handling have been made. These allow for safety in the every day flying environment.
The gliders are less inclined towards flat spins, narrower turns are possible and the flight enjoyment is improved. The higher speed is also a safety improvement. One thinks about strong valley winds on landing or similar. The performance of the Two, One-to-Two and even the One's has clearly improved. These can now even be used in competitions.
In 1993 and 1994 the DHV test criteria were nationally and internationally criticised, as keeping glider development back to slow, spin prone and sluggish-handling gliders.
It was said that some tests were unrealistic. Amongst these were the flat spin, the hard turn or wingover, and small allowance for dive from full stall.
A seminar/workshop with experts such as test pilots, manufacturers, as well as representatives of the Technical Committee were held. The task was to make recommendations for the improvement of the test criteria and assessment. The young sport of paragliding is still developing and is influenced by test procedures. It was important to keep the safety standards although new developments must be fitted in.
All test procedures were revised according to practical experience and tried to be made objective, reproducable, and practical. These recommendations were accepted by the DHV. Since mid-1995 the new guidelines were applied for testing.
The flight test for hard turns was struck, and the one-sided tuck with countersteer brought in. The flat spin is no longer between 0 and 360 degrees stopped, but after 360 degrees by introducing trim speed, and after 180 degrees by introduction of a slow turn.
Today it is tested whether the glider spins stable. A stable spin fails the glider. Added is a test on canopy behaviour if the canopy is accidentally stalled on one side. For the full stall there is a more exact description for the dive. It is now more relevent whether a tuck results, or the glider dives forwards so much that the lines go slack and the pilot is flung towards the canopy, and the danger exists that the pilot can fall in the glider. Further a more detailed description for one-sided tucks are used.
The test criteria for side tucks have not been made less stringent. For clarification the changes to the criteria is available in German. One can see from that that the requirements have been increased.
A discussion is currently being held with all relevent groups to change the test criteria. In Class 2 a fast turn after a side tuck will not be accepted anymore, not even a small degree.
In how far the dive along the roll and pitch axles in the rating can be part of the test criteria, is being probed and discussed. The steep spiral is also under reconsideration. All pilots will be made aware of the behaviour of the gliders in the steep spiral and how to recover.
During the testflights in the framework of a certification predetermined possible objective and
reproducable test procedures are followed by the test pilot and rated according to redetermined criteria. The manoeuvres are chosen in such a way that they highlight strong evidence in the spectrum of flight behaviour of the canopy.
The rating chart should show the trends in the flying behaviour and allow a comparison between different canopies. The test procedures cannot deliver a complete and absolute representation of the reaction of a paraglider in all flying conditions.
This is the only neutral reassurance of the manufacturer's experience during the development period.
Therefore it is quite possible that a paraglider in flight under certain meteorological conditions and due to certain pilot reaction shows a different behaviour as under the strict defined and objective test environment. A test flight cannot simulate every wrong pilot reaction or type of turbulence, as these parameters are not definable.
The choices of the paraglider: the experience of the schools and safety training show that a frightening high number of pilots cannot cope with the chosen equipment. If you address the pilot on their own over-assessment of their abilities, they will mention the improved performance of the canopy in comparison to the more safe glider. But only a pilot who can master his equipment will perform and fly safe.
The silly prestige thinking towards other pilot friends who are already flying a 2 or 2-3, should nowadays be a thing of the past. A leading example should be someone who flies with a safe 1-2 and delivers the performance with it.
The modern paraglider class 1-2 shows a combination of good performance and very good behaviour and are therefore for the majority of the pilots the only right choice.
DHV-Info is the official magazine of the German Hang Gliding Association.
Funwings Footnote 1:
In 1998 the DHV changed their test requirements for DHV 2 gliders. It must be remembered that there have been 3 different test criteria for DHV 2 ratings - 1996 and before, 1997, and from 1998 onwards (unfortunately the exact dates of change-overs are not known). The current test criteria are aiming once more for more stable gliders.
Funwings Footnote 2:
It is now August 2005. Having just re-read this article, it struck me that very little has changed over the years. Pilots still choose to buy higher rated gliders for perceived performance gains, sometimes gliders that they cannot handle, even though there has been amazing performance increases in low intermediate rated gliders. But also, it has become clear that a pilot's risk management approach is still one of the top reasons for accidents.