Gerolf Heinrichs <gerolfontour> writes (but not to me):

I am well aware that we are already in week thirteen since the annual CIVL meeting. I know - formally speaking - the mandate from the plenum has long expired, but despite us running out of time, handing it back to the CIVL bureau seems a no go, since the bureau got no mandate at all. And the prospect of Max Bishop and the EHPU coming up with the fix for safer competition flying seems a really scary thought, isn't it? ;-)

I think we heard enough good arguments from each side now and despite my original fears of this ending in a dead lock, I now feel we can form this into something where all involved parties - pilots, CIVL officials, delegates and manufacturers - in the end can conclude: yes, this could actually work!

I suppose, I will speak for all here when I say, we don’t have to convince each other anymore on whether or not we are going to measure sprogs in Laragne: Pilots already have agreed on doing so in the last CAT-1 event, the Europeans in Greifenburg.

Now, instead of confronting you with yet another proposal to choose from, I decided to go with Dennis’ latest approach (I basically agree with it in all points), and just add a few aspects that have been addressed since.

I also agree with Klaus Tanzler (now that must be a first, huh?), that we need to get this first round of measurements out of the way before the competition actually starts. I doubt one afternoon will do to measure 120-130 pilots, so I would suggest that the CIVL officials to be available during the two to three days before registration to measure glider throughout this period. This will allow pilots who have to do substantial sprog adjustments to fly their gliders once more before the meet starts - a safety aspect that has not yet been addressed.

A sticker of approval for pilot and glider is also a good idea, to distinguish who’s been measured and who is yet to come. If we don’t want to have pilots compete with unchecked gliders, we may as well do it properly. I would hope during the competition the focus should shift towards flying again and sprog measuring would become a side show only. After all this is a World Championship, not a sprog measuring contest.

To remind you all what we are talking about, I include Dennis’ proposal below and add my suggestions:

1. All sprogs will be measured at the World Meet in Laragne. This measurement will normally take place in the landing areas, but may be taken on launch in special situations. Selected gliders will be measured multiple times in order to gather data as to the repeatability of measurements.

2. I add: "All gliders have to be available for inspection and measuring during the practice days before the meet." All measurements will be published with the pilots' name and glider particulars as well as their certified setting and I add: "and their minimal permitted sprog limits."*

3. Gliders will be measured randomly during the competition in a non-obtrusive manner. All subsequent measurements will be published.

4. Any glider that is deemed exceedingly low will have to be raised before the pilot can continue to compete. I suggest to replace this with: "Any glider that is found to be more than the measuring accuracy (0.2degs) below the minimum permitted sprog limits (MPSL) will have to be raised before the pilot can continue to compete."

5. A glider with a tail will have to have the certified tail dimensions and angle setting published. It is the responsibility of the pilot to supply these values to the CIVL officials.

6. Prototypes will be allowed in the competition as long as the pilot supplies a letter of approval from the manufacturer and documentation that the glider has passed a certification pitch test along with the settings of the pitch devices (sprogs, tail, etc.).

7. All pilots must attend a safety discussion relating to pitch stability.

8. These rules are understood to be subject to change after this competition or during this competition if clear safety issues arise. **

* * Any proposed rule change during a CAT-1 competition needs the majority approval of the team leaders. This CIVL sprog working group has no say in the matter during the Worlds.

*  As you see, I have introduced the term “minimum permitted sprog limits” (MPSL) here: It will simply not go anymore to tell pilots we are measuring against certification limits and the measuring tolerance is 2 degrees! This is hypocritical.

We all know meanwhile the measurement accuracy for sprog measuring with angular gauges is about 0.2 degs, not 2 degrees (regardless how hot or humid it may be). If we want the pilots to be honest with us, we got to be honest with them. The MPSL is the compromise between what pilots/manufacturers think is still flyable and testing bodies think is still tolerable - it is the current outcome of a bargain, so to speak. Lets not beat around the bush here.

The DHV formula "Certification-limit minus 2 degrees" (CLM2D) was not such a bad guess for this compromise. But, we need to remember, it is still only a guess, after all. A guess that has not yet been backed with sufficient testing data for the various models in use. This is where manufacturer’s input is required. Manufacturers can certainly provide safer, more reasonable MPSL, based on past experience with their various models.

An example and short technical excursion can illustrate best what I mean:

The Litespeed RS-4 is currently certified (DHV Gütesiegel) with 4.55/7.7 degrees (see Christof’s Excel sheet).

According to CLM2D this would entitle a pilot to set such glider to 2.55/5.7 degrees for the MPSL and compete with it. From my four year experience with this model I know such set-up would be rather unsafe to fly, since the load balance between inboard and outboard sprog is seriously distorted – CLM2D practically disables the inboard sprog and puts most all the pitch load on the outboard sprog.

Technical note:

(i) the outboard sprog, due to its more backward position, has better leverage and therefore gives about 12-15% more pitch gain per washout degree as compared to the inboard. The inboard sprog on modern topless gliders in turn is about 2.5-3 times stiffer than the outboard! While raising the outboard sprogs will provide quicker results on the test car where sprog loads hardly exceed 10kp, upon a hard hit in real in-flight situations the inboard sprog will determine whether the whole sprog system will sustain the imposed pitch load or not. Studying the pitch figures from Christof’s Excel-file one can find that most gliders have similar outboard to inboard sprog ratios. This ratio is not god given, but. 5.5/7.0 or even 6/6.2 may provide just as much pitch as 4.55/7.7. From most recent experience I would conclude: The more balanced your sprogs are set, the more even the pitch load will be absorbed. And the more even that absorption, the higher the maximum load can be before your recovery system gives in.

(ii) If you look across tumbles in most recent time for which we have detailed technical information, you find one baffling fact that all those tumbles have in common: all gliders show very low inboard sprogs! With very low I mean 2.5 degrees or less. Richi Meier’s glider was no exception to this, his glider was set to 2/4 degrees, if I recall right. The inboard sprog is our best friend against nasty air, we got to make use of it.

Given those arguments, I would always want to correct the above given figures 2.55/5.7 degs into something like 4/5 degs. Note, that the overall sprog count (the sum of the two sprogs that is) after correcting is even higher now. Interestingly, this corrected setup will not only make the glider safer than before, it will also lead to better handling (remember: a glider’s roll rate at +50% VG is compromised by the outboard sprog much stronger than by inboards), and likely also lead to a more responsive VG system – the pilots acceptance for this setup will be higher – everyone wins.

I understand that there might be concerns this could be misused for an “anything goes” rule. I don’t share this fear, because manufacturers themselves have a very strong interest in having their gliders NOT tumble. However, a side condition as given below which will help to prevent this.

Thus, I come to the following addendum to rule 2 in Dennis’ proposal:

add 2) Manufacturers shall suggest minimum permitted sprog limits for each glider model. Condition: The overall sprog count shall not be reduced by more than 4 degrees against certification, the outboard sprog shall not be reduced by more than 3 degrees, the inboard sprog shall not be reduced by more than 2 degrees. In case a manufacturer cannot or will not provide such limits on their part, the minimum permitted sprog limit for each sprog will be set to 2 degrees below certification.

Having the manufacturers set the limits for their gliders also will help solve the problem of the smaller sizes. Since the DHV test ignores smaller gliders/lighter pilots which logically require less pitch moment to be at the same safety level, manufacturers could in this way take the bite out of the plain CLM2D rule.

In his last posting, Klaus is the first to make a more detailed proposal on how to actually measure, so I use this as a starting point.

I think specifying your measuring method is crucial to escape endless arguing with pilots if their sprogs don’t cooperate. Since the Spi-Tronic Pro is a fine but rather costly gauge, I doubt CIVL will have several of those organized for Laragne. Therefore I suggest not to prescribe the exact make of the angular gauge in the rules, and just establish a certain required accuracy, say +/- 0.1degs per measurement. The quality of the angular measurement of course depends on a minimum length of said device, 150 mm seems a good compromise between it being too short and too clumsy, inside the sail. All used devices shall be of same make. Since each sprog angle reading is actually the difference between a keel measurement and a sprog measurement the realistic overall sprog-accuracy then is only +/-0.2degs. I guess we’re all in agreement here.

The keel measurement is easier to get right, while measuring the sprog angle requires a skilled hand, as the gauge needs to be held to the sprog without either pushing it up or pulling it down – an error of 0.5 degrees easily occurs this way.

While measuring gliders for DHV certification the leading edges are supported to make sure the side cables are firm tight. During in field tests this support is sometimes neglected. This will lead to differences exceeding the measuring accuracy of 0.2 degs and will show the tested glider lower than the certified model.

I know everyone of you has already fallen in love with angular devices, but trust me the string method is just as practical and has several advantages over the gauge: (i) the string averages out left and right, (ii) needs no perfectly level glider, (iii) needs no skilled hands, (iv) measures the trailing edge, (v) costs next to nothing, (vi) measuring precision is higher: 1mm = 0.05degs, (vii) string data are available for all models already.

As for the where on the sprog to measure, I see no other way, but to measure exactly the way the glider was measured upon certification. All certification numbers we may refer to are based on the assumption of this being the case. And the method that Christof and Co came up with back then, is: as close as possible to the back end of the sprog (the sprog wire fixing point that is), to permit a relevant and reproducible measurement.

Now, in this context also the concern of pre-bent/pre-loaded keels has to be addressed, also the practice of over-cambering outward batten shapes that don’t comply with the model in use. The issue of carbon vs aluminum tubing/battens, or altered wing tip/ glass tip angles. Altering any of these elements can easily change pitch figures in the equivalent of at least 1-1.5 degree washout.

I frankly admit I have no solution to this problem yet, but to let it slide this time (since tackling those issues will get us in way over our heads and the Worlds could then really turn into a sprog measuring meet)

Any solutions for such “infringements”, Klaus - except spanking or electro-shocks? ;-)

Last, but least, what is 100% VG? I suppose Klaus means 100% VG of what the pilot shows up with. That is not necessarily what the glider was really tested with. I am cool with this, I just want to clarify it here. (and remind you all that deliberately backing off on full VG setting and adjusting sprogs to this new level – light pilot will likely resort to this as they may fear their gliders locking up on them otherwise - will lead to a less stiff “battle” between sprogs and sail push, and thus result in less “washout stiffness”. A lot less, a little less? Hard to tell, without going on the test vehicle.

You see, the devil is always in the detail. Anyone already getting cold feet about sprog measuring, haha? ;-)

For the actual measurement procedure I suggest a walk-through tent, where pilots show up one after the other, rather than the officials going around from glider to glider like we had in Greifenburg. This allows a more consistent measuring setup, and guarantees more acceptance for the produced figures. There is also more privacy if required, protection from weather and wind not to mention.

I think I’m getting a little long here. I might save my last two subjects for a second post: (i) prototypes and (ii) education/penalties.