BULLETIN DE LIAISON 12
Flying CRICRI’s we start loosing the count on the exact numbers. Around fifty CRICRI's are listed, but from time to time a new one pops up: the builder probably did not inform us. So, numbers are estimated to be around fifty.
CRICRI’s at BRIENNE
Few aircraft flew over due to the (bad) meteo. In addition, the limited participation was caused by a general feeling of frustration amongst the owners, as a result of the latest discrimination. Five aircraft builders were present: Mr BOUILLOT, Mr CAMUS, Mr GUIDON, Mr HUBER and Mr MAHE flew over, regardless of the rather poor meteo conditions. We thank them all and hope for better conditions in 1988. Regarding the 1988 meeting, it will probably not take place at BRIENNE-LE-CHATEAU. Reason is the worsened “diplomatic” relationship between the owner/manager of the field and our Foundation President Mr CARIOU. We ‘ll keep You updated.
CRICRI’s at MERIBEL
Five aircraft were present: Mr GUIDON and Mr GUILLAUMAUD on an individual basis, and Mr CONSTANT, Mr DUVAL and Mr LAURENT represented BRITTANY FERRIES during their aerobatic display. Again, the meteo was not favourable. We note that Mr GUIDON took advantage of his stay at this High-Altitude airfield in order to obtain his local site qualification (in less time than a TPL (A) Pilot with X thousands of flying hours), after which he was able to conduct some magnificent mountain flying.
The BRITTANY FERRIES CRICRI’s
The CRICRI engines have caused a lot of worries with most of the builders. However, nearly all of the original problems have been solved, and although their reliability is not optimal (yet), there has been a considerable step forward. In order to illustrate this, I intend to make a case study of the Brittany Ferries CRICRI’s, Using some of the 1987 figures: 3 aircraft were equipped with JPX PUL 212 engines 19 meetings with 2 displays per meeting a complete follow-up of the Airborne Tour de France (yes, with an aircraft, and not by bike), including an up-and-down between STRASBOURG and LILLE (900 km) in one day, including a display at LILLE. This gave a total of 50 Hours x 3 aircraft x 2 engines = 300 Hours of engine time. During these 300 hours, the technical problems (during the Tour de France) were: One case of faulty Contact Breakers: Insufficient gap between the patina’s and non-regular RPM One tube got partially broken (not a big problem) One case of dirty Spark Plugs, caused by a too rich mixture These technical problems did not cause a complete engine failure. This is a rather encouraging fact, if we compare this with the earlier situations. I have to admit nevertheless, that the maintenance times are still much longer than for a “Flat Four”, but it demonstrates that engines, which are correctly fine-tuned and looked-after, can be reliable indeed. In order to enhance this, we need necessary precautions, preparations and modifications. In our next bulletin, we will publish a list provided by Mr LAURENT.
Accident reports Indeed, there have been no fatal accidents since one year from now. But, without being pessimist, I think this consists of a “calm” period and that the driving factor is pure luck, rather than the attitude of certain pilots who continue to “show-off”. Only 2 CRICRI’s have been destroyed by accident. First aircraft: Take-Off followed by a steep turn at about 180 ft AGL! One of the engines runs irregularly and the pilot decides to cut both engines in order to avoid (the possibility) to operate on one engine. The aircraft touches down in a field and turns over.
Second aircraft: Training flight with practice double-engine shut down: Landing too short, leaving the runway into the crops and turning over.
That ‘s all about the damages. The pilots got out unhurt, luckily.
As far as the CRICRI community is concerned, it seems, based on the different inputs, that there exists some confusion between the cautious way of flying and the ability to fly. We hear more and more critiques on the actual training methods, which produce so-called “aircraft-drivers”, rather than skilful pilots. But if we analyse the different accidents involving CRICRI-aircraft (please let us not pretend that they do not exist), it seems that nearly all of them are not related to the ability to fly the aircraft, but rather to a lack of discipline and carelessness. In the last bulletin, I already pointed out a number of dangerous types of behaviour amongst some CRICRI drivers. Sadly enough, the list keeps on growing: When Mr W enjoys flying INTO the firebreaks of the Landes Woods: Is this related to flying incompetence? When Mr X makes a high-speed fly-by at 3 feet above the runway, in someone else’s aeroplane: Did he think about the unforeseeable, which could lead him making a wrong manoeuvre and subsequently crash into the ground? Is this related to flying incompetence? When Mr Y starts an aerobatics manoeuvre at low altitude, but recovers at a (near) stalling speed, did he realise that he narrowly missed the fatal frontier? Is this related to flying incompetence? When Mr Z is buzzing above a lake, with his wheels nearly touching the surface, does he realise that, if he would have been less lucky, he would have been unable to talk about his “performance” later at the bar ? Is this related to flying incompetence?
The answer to this long list of events, which unfortunately did not grow out of my imagination, is simple: Performing such manoeuvres requires a certain degree of flying skills, but moreover a high degree of stupidity. Of course, you must have heard these pilots say: “There is no risk”, “Do not worry, I am familiar with this aircraft”, “I know what I am doing” or even worse: “Mister, I have X thousands of flying hours”. And in most cases, the pilots didn’t want to fool you and were convinced of what they were saying.
Sadly, such an attitude reveals a certain lack of imagination into the (un) foreseeable. In order to understand this, it is helpful to reverse the problem: Do not estimate the level of risk, based upon the perception, but rather consider the lack of perception when analysing accidents. Each of us knows some examples. It is always a circumstance, which a pilot did not foresee, that has lead him/her towards an accident. Even if the pilot was not less intelligent than other fellows; He THOUGHT he had foreseen all eventualities, he THOUGHT he was able to cope with anything. So what now?
The conclusion is self-explanatory: Let ‘s face once and for ever the reality: Our lack of ability to cover ALL eventualities and the fact that, whatever the level of proficiency, everyone of us can make mistakes. As a result, we must consider SAFETY MARGINS. Let us not come too close to the limits of the aircraft flight envelope, or structural limitations, or to the limits of our own flying skills. And above all, let us include ALTITUDE MARGINS. Let us keep in mind following hard facts: Out of 7 CRICRI fatal accidents, 5 were caused during the performance of risky manoeuvres, at low level and executed voluntarily.
If we analyse the accidents one by one, we realise that if these evolutions were carried out at 60 or 150 feet higher altitude, there would not have been 5 mourning families.
Another type of behaviour seems important for me to analyse: The behaviour of the environment. Recently, a conscious aircraft builder made a complaint to one of the responsible organisers of a meeting, about a CRICRI-driver who happened to execute some aerobatics, which were noticeably risky and could have ended in disaster. The answer sounded like: “ Well I have no comments, I don’t want to make a fuzz about this”. Well, I remain convinced, even when taking the risk to upset some people, that this poor attitude contains some complicity towards suicidal behaviour. It opens the way towards new dramas and could be considered (for example in the case of a drunken pilot boarding his aircraft) as a lack of assistance to endangered persons. If someone has a responsible duty and wants to carry this out with dignity, then this must be done completely: Including the less popular aspects of it. The same remark is valid for the environment of the pilot, which often responds to these “show-off behaviour” with smiles and jokes, with compliments and even cheering. This type of reaction appears to the pilot as an approval, a support and an encouragement to repeat his suicidal manoeuvres.
Those would-be acrobats cannot support the good reputation of General Aviation and more specifically our community.
As a result, I am asking to anyone who is confronted with these phenomena, not to react to these irresponsible pilot behaviour with a smile, but rather with a clear attitude of disapproval and to do every effort to bring them back to a prudent way of aircraft operation. Most pilots remain (very) sensitive to the reaction of their environment and only a few remain “incurable”. It is beyond doubt that the relationship spectator-pilot has an influence on the behaviour of the latter.
So it is up to ourselves to have respect for and to impose a certain discipline. The flying pleasure will not diminish, as long as future dramas are avoided.
Engines: The Pistons
After a number of early problems were solved, one important source for many engine failures remained: Broken pistons and blocking of piston rings into their ring gaps. Several analyses of the metals used in the pistons were carried out on the initiative of builders, such as Mr CAMUS and Mr NUVILLE. They revealed the same results: Insufficient and inconsistent quality of the metals used. As a result, some trials (very humble at the start) were made to replace the original JPX (BRETILLE) piston by other types. After some research was carried out, it became apparent that 2 types of pistons were eligible: A 175cc Motorcycle piston from YAMAHA and a similar one from KAWASAKI. The KAWASAKI option seemed to be the best choice and up now several aircraft have flown successfully with it since more than a year. We can now start with preliminary conclusions, based upon some revealing cases.
Mr Gerard CONSTANT Configuration: 1986 JPX - original Chromed cylinders JPX-1986 with 3 transfers Pistons: 6 mm with original JPX rings Oil: MOTUL 300, initially 3% and gradually 3 and 2.5 % Ignition timing: 2.8 mm ahead of DHP RPM: 5300 - 5500 Results: After 10 hours of operation: The bottom of the piston is completely darkened (black like charcoal) and the rings get blocked. After 80 hours of operation: The bottom of the pistons gets less darkened (only at the reinforcements parts) and the rings are free: This reveals a long run-in period: More than 50 hours for the piston and about 80 hours for the rings. The latter appear to be very hard and leave a clear mark at the DHP of the cylinders. The pistons themselves did not get broken. However, engine failures during approach and taxi (hence at low RPM) were frequently observed. But the number of failures gradually diminished, as the engine was getting ran-in: After 50 hours of operation, this type of failure had disappeared. This phenomenon reminds us what happened with the ROWENA engines which powered the prototype: The (failure) was said to be caused by excessive cooling of the cylinders (during the approach), which caused the pistons (having less “free-movement” space between them and the cylinder) to get blocked. This phenomenon disappeared completely and forever, after one hour of “artificial” run-in using special oil containing an abrasive substance. Both these observations provide the evidence about the necessity to have a well defined “Free-movement” distance between piston and cylinder and, most probably, about the need for well sealed rings.
Mr Yves GUIDON Configuration Chromed cylinders JPX with 3 transfers Pistons: 6 mm with original JPX rings Oil: CASTROL TTS, 2% with SUPER auto and normal mixture Ignition timing: 2.5 mm ahead of DHP RPM: 5500 Results: After 20 hours of operation: The peripheral area of the piston gets stained yellow and black underneath the rings. The piston rings get blocked in their ring gaps due to burned oil particles. The bottom of the piston is entirely black. The engine does not perform optimally and the aircraft barely reaches 190 km/hour. Modifications After 30 hours of operation in NIKAZIL cylinders, metal rings from a STIHL chainsaw replace the original JPX rings.
No other modification was introduced. The “Free movement” distance between piston and cylinder was 0.38 mm. Results with the modification After 5 hours, the engine was back at normal operational level (200 RPM extra) as well as the aircraft (Max speed 215 km/hour). After 50 hours of flawless operation, the bottom of the pistons still shows a black deposit, but its shape is reduced to that of a 10 FF coin. The rings maintain free movement into their gaps. The black and yellow colouring underneath the rings is reduced by 80% (as stated in the de Detailed report from Y. GUIDON). The overall functioning of the engine seems to be more consistent and confidence is regained. Instead of the former circuit flying, small trips of 200-300 km and mountain flying are being carried out. A certain influence by the chrome/metal association has been noted: The friction chrome/chrome or metal/chrome has the advantage to create a very slow rate of deterioration of the rings. But on the other hand, the initial sealing is poor (hence a long period for run-in) which leads to the explosion flames getting through, overheating the rings, burning the oil, which deposits in the gaps and in turn blocks the rings: a vicious circle. It is possible to lower the friction-coefficient by using less hard metals (Elasticity module E = 10.000 for standard metal, versus 17.000 for GS metal and 21.000 for steel), which could reduce the heating by friction. Sadly, I could not find documents on the subject. Mr CAMUS and GUIDON observed (after using metal rings in stead of chrome) that the propeller moved more smoothly, when hand-driven. This could apparently confirm the theory of the diminished friction. But no precise measurements were carried out, so these conclusions are subject to some reservations.
Jacques & Robert LAURENT Configuration: Chromed cylinders JPX-1986 with 3 transfers Pistons: 6 mm with original JPX rings Oil: SHELL 2.5% 100LL and normal mixture Ignition timing: 2.6 mm ahead of DHP RPM: 5300 Results: Bottom of the pistons black Pistons broken Rings blocked in their gaps Circumference of the pistons black underneath the rings. Modifications The original pistons were replaced by 175cc KAWASAKI ones, with metal rings and assembled into new NIKAZIL JPX Cylinders. Results after 45 flying hours (mainly aerobatics) Bottom of the pistons shows no black deposits, even no yellow ones. Rings are free, the circumference of the piston is slightly darkened underneath the rings. No operating problems. No engine failures after the pistons were replaced. Similar results were obtained by other builders, when using KAWASAKI pistons.
Mr Bernard CAMUS Modification The original piston was replaced by a 175cc KAWASAKI one, into NIKAZI JPX cylinders. The oil = BOL D’OR with 3% and 100LL AVGAS. Results After 01;30 hours of operation, the piston gets stuck and blocks into the cylinder, without getting broken. The upper ring gets blocked by the metal particles, but not by the deposit of burned oil in the gaps.
After checkout, it was revealed that the free-movement distance between piston and cylinder was only 0.13 mm. This insufficient free movement distance (JPX advises 0.30 mm) had obviously caused the blocking. But it is important to note that the pistons were not destroyed.
Conclusions I will limit myself to these 4 case studies. But the acquired experience by these builders and some other ones makes it possible to formulate the following recommendations: Pistons The 175cc KAWASAKI Motorcycle pistons (KDX-reference 13001-1048) seem to be better designed and more resistant than the original pistons. Furthermore, the total weight piston/axis is 35 gr less than the original materials. This can only have a beneficial effect regarding the vibrations. There also exists another version of the KAWASAKI pistons, produced by WISECO. This one is molded, but (unfortunately) is 50 gr heavier. Free Movement The free movement distance on the upper part of the pistons, at the DHP, is of great importance. We have observed that a distance of 0.13 mm can lead to blocking, while a distance of 0.30 mm gives full satisfaction. So, when you acquire a KAWASAKI piston, make sure that the diameter of the piston is 0.33 mm smaller than the internal circumference of the cylinder. The internal circumference can be given by JPX, if you can provide them with the serial number of your engine. Rings We used metal rings, which were originally provided with the KAWASAKI pistons. References = KAWASAKI KDX 175cc 13008-5034.
Spark Plugs During operations, we noticed that the (average) lifetime of a spark plug, mounted on a MC15, rarely got beyond 20 hours. Once passed 20 hours, small symptoms start to appear: such as irregular engine functioning and irregular spark plug ignitions at full RPM. According to R LAURENT, the lifetime is about the same, whether using a CHAMPION N2C with copper electrodes or a N2G fitted with platinum electrodes. When taking into account their operating conditions and specific limitations on this type of engine, it seems that the main cause for the problems with the spark plugs is to be found in lead deposits and progressive deterioration of the isolating capacities of the porcelain. Sadly, platinum electrodes are not used with the main purpose to resolve this problem. Taking into account their acquisition prices (between 10 and 12 FF for a “copper one” and 54 FF for a “platinum”), the solution proposed by R. LAURENT seems to be logical: Use a new set of spark plugs, at 10 FF a piece, every 20 hours.
Mrs Hélène MALITCHENKO noted the same phenomena after similar operating times (20 to 25 hours). But she recommends to clean the spark plugs and to reset their initial electrode gaps. After that, they should “operate fine again” for “some time”. The same was observed by Mr Y. GUIDON and Mr J. DAVID.
Ignition Timing Several builders reported the same thing to me: The ignition timing became irregular, either by the blocking of the cam on the camshaft, or simply as usage time elapses. I remind everybody that when assembling the cam, the thrust bearings need to be cleaned using trichlore, in order to prevent this phenomenon. In addition, this checkout is required after a blocking occurred and afterwards on a regular basis.
Breaking of Exhaust Pipes Certain exhaust pipes get cracked or even break apart at the joining with the exhaust manifold. Taking into account the amount of vibrations, caused by the alternated coupling forces exercised by a single-cylinder, it is logical that the “most painful” place is situated there.
In order to “relieve the pain”, it is necessary to minimise the labour exercised on this exhaust as much as possible: 1. Using a connection between exhaust pipe and tube, which is as light as possible. 2. Verifying the good flexibility of the tube. A lot of tubes were observed to be too rigid and their mass is added to the mass of the exhaust pipe. This leads to additional exhaust pipe fatigue. If the tubes are too rigid, they need to be bent until the pot is hanging almost loose by itself. In addition, this added flexibility is beneficial regarding the engine vibrations, which are being “transmitted” onto the fuselage.
Engine Fittings In order to increase the rigidity of the engine fittings, some tests have been carried out by several builders. Two out of four “piano cords”, having a 3 mm diameter, were replaced with 4 mm cords (either the two top ones, or the two lower) It seems that the vibrations filtering is not affected (too much): Only the resonance level (normally attained at 3500 RPM) is slightly displaced (by an additional 100 to 200 RPM). The main advantage taken from this added rigidity lays in the fact that the engine will “hit” the shock absorbers less easy and less frequently. This gives an added comfort during taxi and during turbulent flying conditions. Some American builders even went straight for 4 times 4 mm cords as a standard set-up and pretend to be happy with this: So let’s keep this approach ready for use. There is one disadvantage: At the farthest point (limited by the shock absorbers), the strain level exercised on the cords is multiplied by a factor of 4/3. Therefore, it is strongly recommended to use piano cords of exceptional good quality and, whenever possible, with fatigue treatment.
Weight and Balance Warning: More and more CRICRI’s are being used for overland flying and small trips. People start thinking about installing additional fuel tanks, situated probably between the pilot’s seat and frame Nr7: This will alter the position of the CG dramatically. You can also see from time to time some real nasty payloads crammed into the rear pilot’s cockpit.
Regarding this matter, I need to warn anybody that, although this place seems to be quite suitable for loading some additional stuff, it cannot be considered as an approved storage compartment. Loading this part of the aeroplane and taking off without making a proper W&B check, reveals - at least - a certain degree of carelessness, and there is no reason for applauding.
What happens when the CG moves aft? The movement and degree of effort to be exercised on the stick, in order to obtain a given change in the aircraft’s angle of attack, becomes gradually smaller. The G forces diminish accordingly. In other words, the aircraft becomes more and more sensitive along its pitch-axis.
When the position of the CG is moved towards its limit, the required movement and effort on the stick become nullified: The static stability disappears and the aircraft looses its ability to be flown in a controllable manner. Once this limit is passed, the aircraft becomes unstable: This means that as soon as the nose wheel leaves the ground, you could loose control instantly as the aircraft moves into auto-rotation. If you try to counter-react, your corrective action will be followed by rapid and uncontrollable up and down movements. The rest can be imagined easily.
As a conclusion, we can state that, if you want - as a minimum - to avoid damaging your aircraft, You need to perform a W&B check. For this purpose, you are being provided with the necessary graphs in Your Aircraft Operating Manual.
This bulletin has been translated to the best of my knowledge. If there is any doubt, there is no doubt and you should refer to the original document.