Dafydd Llewellyn

OK, I'm a glider pilot, so I'm not bound by (or even aware of) RAAs Ops rules. I'm approaching a non-towered field, and it's not been made a temporary CZ under a NOTAM. No special procedures are given in ERSA. I call inbound on the area frequency (and if it's a known gliding field, on the gliding assigned frequency). I may or may not get a response. The response may or may not be useful. I take it into account in joining the circuit, along with any other circumstances that affect that. If the strip is a private one, I need to have the owner's permission before I can land there, other than in an emergency. If the owner happens to be an RAA entity, that's how I find out about it. If the owner has made a stipulation in response to my request for permission to land there, I must observe that stipulation. However, the responsibility is still mine, as PIC. Nobody on the ground, or in another aircraft, can direct me as to what I may or may not do. They can advise me of what's going on (kangaroos on strip, etc). That's my understanding; what have I missed?

Is the CHT instrument included in the engine parts catalog? I didn't think it was . . . That being said, I agree you cannot expect the engines to tolerate 180C on the CHT gauge continuously - especially if the cold junction of the CHT system happens to be exposed to heat. Putting a multi-probe EMS into one of these aircraft is, I suspect, cheap insurance. There has been a big change in thermocouple instrument designs in recent years; 20 years ago, the typical aircraft CHT instrument used a massive-wire thermocouple, and it came with a set of calibrated leads, made from the thermocouple alloys, not copper wire, that must not be cut to length. That was because its meter was a simple milliamp meter that measured the current in the circuit that resulted from the voltage generated by the temperature difference. For that style of instrument, the cold junction was at the instrument itself. Those instruments are invariably self-powering, that is, they need no external power, unless it's for the instrument's internal lighting - they will give a reading even if the master switch is off. More recently, the instruments use fine-wire thermocouples, and they have an amplifier chip in them, so they measure the circuit voltage directly. By doing so, they have a very high impedance - which means they draw almost no current from the thermocouple circuit - so variations in the electrical resistance of that circuit have vastly less effect on their accuracy. This style of instrument won't give a reading with the master switch off. Ideally, the leads are still made from the thermocouple wire, all the way to the instrument, which puts the cold junction at the instrument. However, thermocouple alloys are expensive - especially the K-type (Chromel/Alumel), which is almost universally used in modern instruments, because it behaves linearly over a very large temperature range, so some manufacturers use copper wire to carry the circuit back to the instrument. In such a situation, the cold junction is where the wires change from the thermocouple alloys to copper. That's the type that can easily give grossly wrong readings. The instrument manufacturers do not point out this subtlety. In the last year or two, EMS systems have started to appear that have an intermediate module, that can be located in the engine bay. The thermocouple wires run to it, and it contains the cold junction and the amplifier module, and it sends the data on to a display in the cockpit. It needs to include cold junction compensation; in effect, the cold junction compensation is a separate sensor that tells the intermediate module how hot it is; the thermocouple tells it how much hotter the cylinder head is, and it adds the two together and sends that on to the display. Provided all that works correctly, the result can be very accurate. All this post-dates the original certification of the Jabiru. I'm not an instrument expert - but I have had to learn this stuff in the process of doing certification flight testing, because I have always found that the most difficult aspect of that work is getting instruments that do not tell lies.

I'll offer a crumb: The instruments used for measuring CHT are thermocouples. How many of you really understand how thermocouple instruments work? What a thermocouple does, is measure the difference in temperature between its hot end ("hot junction") and its cold end ("cold junction"). If the cold junction is NOT at the temperature the instrument manufacturer designed it for, and if it is a simple instrument lacking "cold junction compensation", it will have an error; if the cold junction is located in a hotter place than the instrument manufacturer expected, the thermocouple instrument will read low. I suggest you look at your CHT instrument and find where its cold junction is located. Then look it up in the instrument maker's specifications, and find out what the assumed cold junction temperature is, that the instrument was designed for. This is not likely to be an issue for the more sophisticated EMS-type instruments, because they usually have cold junction compensation (but read the fine print!). It's most likely to be an issue with a single-purpose instrument. VDO commonly assumes, as far as I can discover, that the cold junction will be at 30C. It will read wrongly by the amount the actual cold junction temperature differs from this. I suspect some of the Jabiru problems may arise because their CHTs are reading low, from this cause. It would certainly account for the variability we hear so much about. People need to be careful about where the cold junction is located. Keep it cool.

OK, Shell has withdrawn its "Aeroshell Sport Plus 2" oil, which was "specially formulated for Rotax 2-stroke engines" . That leaves the other oils that are listed in Rotax SI 2ST-008; or any super 2-stroke oil meeting ASTM standard API-ST. Amsoil Saber is one that meets this standard. You don't HAVE to use it at 100:1 So, the experts on this thread have never tried it, and therefore do not know anything about it. How helpful.

It seems some people in RAA have not heard of Service Bulletins. Or Airworthiness Directives. The waffle on this site about the RAA "advising CASA that there are too many failures of Jabiru engines" - or whatever actually happened - is fatuous. Do you imagine that CASA does not already know? How naive of you! There are mandatory requirements to report aircraft accidents, and also to report defects. If CASA considers there is an identified problem, it will use CASR Part 39 to issue an Airworthiness Directive. If it has not done so as yet, what do you imaging that indicates?

No, they'd simply turn and look at him. Ever used an air horn to shift a flock of Galahs off the road? Galahs are smart compared to most humans . . .

It might be that, if you mean the total head from the fuel at the outboard end of the wing, to the drain valve location at the inboard end - provided the aircraft is laterally level. However the actual tank depth is around four inches as I recall, so the "slosh" program won't work properly if the thing is hitting the lower limit of the pressure transducer.

It depends upon the nature of the hypothetical system. A flowmeter depends upon a simple mechanical calibration, and it just counts pulses, so electronically it's stone-axe simple, and not particularly susceptible to interference. The main potential for inaccuracy is the miniaturisation of the impellers that is necessary to measure the small flows involved. The big jets use pressure refuelling from an underground hydrant system; the fuel truck for that system carries a reel of large-size hose and a large and very accurate flowmeter; it hooks into the nearest hydrant and the aircraft, and the operator zeros the meter and turns the tap on - just like any service station, but about five times the size. He gives the meter reading to the pilot, who enters it into his fuel log, and the aircraft uses its own flowmeters from then on. This is the reason the domestic airlines run a "hub-and spoke" pattern of operations. They can of course, use overwing refuelling if the airport is not equipped for pressure refuelling; but not if they can avoid it. The fuel quantities are normally figured in weight units, but I'll let one of our ex-airline pilots speak on how that is figured from the volume - there are "standard" fuel densities that are required to be used for weight & balance calculations. Some military types may have load cells built into their undercarriages, but I'm not aware of this system being generally used for fuel management. For certification flight testing, it is not uncommon to weigh the aircraft, with the test crew aboard, before and after each flight.

No, it's simpler to install a flowmeter.

Ideal job for an undergraduate thesis. I wonder whether the thing will resonate, given that it has to have vents.

A hot pipe will ignite fuel at a little over 300C. If it will melt electrical solder, ignition is likely. Oil ignites at a considerably lower temperature.

Where does Amsoil fit in all this? The AMS bit, I understand, stands for "Alkyl Modified Silicone" - of which an example is Methyl Silicone - and this has considerably better high-temperature properties than straight mineral oil. The Rotax 505 that Bill Riley fitted to a Blanik in the 1980s ran 1:100 Amsoil - and the exhaust port was always wet with oil after a run. Bill switched to Amsoil in an attempt to reduce plug oiling in his inverted motor installation. It did some 250 hours without problem (apart from persistent plug oiling - but fine-wire platinum-point plugs are now readily available, and the CDI ignition systems have more power), as I recall, before being put back onto the PIK 20E from which it had been borrowed. Amsoil produce a grade for outboard motors, so the stuff cannot be deficient in corrosion protection. That grade would seem appropriate for a liquid-cooled engine.

Flying is an unsafe practice - as the old lady said: "If God had meant us to fly, He'd never have given us the railways!"

Drip trays with drains are quite common on aircraft, if the exhaust is lower than the fuel system. They are one of the means of compliance for FAR 23.863 (and there are similar words in most aircraft design standards): § 23.863 Flammable fluid fire protection. (a) In each area where flammable fluids or vapors might escape by leakage of a fluid system, there must be means to minimize the probability of ignition of the fluids and vapors, and the resultant hazard if ignition does occur. (b) Compliance with paragraph (a) of this section must be shown by analysis or tests, and the following factors must be considered: (1) Possible sources and paths of fluid leakage, and means of detecting leakage. (2) Flammability characteristics of fluids, including effects of any combustible or absorbing materials. (3) Possible ignition sources, including electrical faults, overheating of equipment, and malfunctioning of protective devices. (4) Means available for controlling or extinguishing a fire, such as stopping flow of fluids, shutting down equipment, fireproof containment, or use of extinguishing agents. (5) Ability of airplane components that are critical to safety of flight to withstand fire and heat. © If action by the flight crew is required to prevent or counteract a fluid fire (e.g. equipment shutdown or actuation of a fire extinguisher), quick acting means must be provided to alert the crew. (d) Each area where flammable fluids or vapors might escape by leakage of a fluid system must be identified and defined. [Amdt. 23–23, 43 FR 50593, Oct. 30, 1978]

I can only agree with you. And do you know how this could be achieved? By sensible application of the RPL. We HAVE to get rid of the "separate turf" situation that divides recreational aviation up into uneconomic specialised sectors. Think about it.

Now THAT one is worth some serious research! In regard to losing fuel out the vents due to crossfeed, there's a way to prevent that, but . . . The way is to run the vent line for the stbd wing tank across the aircraft so its outlet is further outboard than the outer end of the port wing tank, and vice-versa. The lines need to be as high as possible within the wing before they turn downwards to exit below the wing. The "but . . ." to that is that there will be a low point - or possibly a pair of low points - in each vent line where it crosses the fuselage; and every such low point must have a drain line and drain valve, otherwise the low point can collect water and freeze. (and you can't combine them to a single drain valve, or it crossfeeds again). Also, if the system is to be "all on", it needs a larger-bore intercommecting vent between the upper outboard corners of the wing tanks, to equalise the pressure in the airspaces - and that needs its low-points drained, too. You can end up with a dozen or so drain points - look at the most recent Cessna 172. The fuel system design in recreational aeroplanes does not, in general, inspire admiration, so far as I am concerned. The very simple fuselage tank setup in the early Jabirus was actually very good, and although the prospect of 60 litres in the cockpit looked alarming, it didn't happen in practice.

You can put the filler at the inboard end of the tank - on a glider, which can have its wing tip on the ground when you're filling the tank. Bit of a problem for an aircraft that can't do this.

Let's see you do that on a Bonanza - unless it's almost full. The dihedral takes the fuel completely out of sight until the tank is almost full. Same with many low-wing types.

Depends on the details of the fuel system. In many aircraft, it results in fuel crossfeed from one tank to the other, with fuel leaking out the tank vent, so you leave the aircraft with the tanks full, and come back to find it half empty (or worse) and a big patch of dead grass. Also, if the tanks have a positive gravity head to the engine, you're relying on the carbie float needle to prevent fuel loss. If the float needle doesn't seal perfectly, you're likely to have fuel dripping inside the engine cowl - which is an invitation to a fire if some idiot walks past with a cigarette.

Thanks, FT; looks very interesting. I'd be most interested to hear of people's results with it. There are a variety of industrial devices, for tank contents gauging, some of them ultrasonic, and various other principles, but this is the first one that I've seen that looks potentially suitable for "difficult" aircraft tank shapes; most of them are obviously for industrial plant applications.

That's a bit off-topic for fuel contents gauging - but it's a constantly-recurring cause of accidents; possibly the greatest single cause of EFATO, in fact; especially with the carburettors used on Lycomings etc, which have carburettor bowls the size of soup bowls, and let the aircraft get to a couple of hundred feet before the engine stops. The best answer I've seen for that, is to mount the starter button behind the "apron" of the fuel selector, so you can't access the starter unless the fuel is on. (There's at least one recreational type that does that). The downside of that is that if you get an engine fire due to a backfire on startup, you can't shut off the fuel and then crank the engine with the starter, which is the standard drill; you have to start the engine and then turn off the fuel. (No matter what the designer does, somebody is going to argue that it caused a problem; he can't win.) However, on the balance of benefit, I'll take an engine fire on start-up in preference to an EFATO, any day.

I wouldn't put it past a ramp check to drain the fuel and measure it. However, your defence would be that there is no means to accurately verify the fuel gauge readings other than to start with full tanks. In theory, one of the jobs to do on a periodic inspection is to re-calibrate the fuel gauges and replace the fuel gauge calibration card. How one can in reality do that for an aircraft with long, thin fuel tanks and not have it a polite fiction, eludes me. I agree the situation as it stands is unsatisfactory, and not only for the Jabirus that have wing tanks. This is an area in which the design standards have not caught up with reality.

The patter "I always dip the tanks" is the no-brains response usually applied whenever a potential fuel-starvation accident is reported. It's a sensible response - up to a point - for a Victa Airtourer*, A PA-28, an Auster, and a few other aircraft whose manufacturers provided a calibrated dipstick. *Provided the rubber bag has not come loose from the buttons that retain the top of the bag. However, let's see you get a sensible result trying to dip the tanks on a Bonanza, or almost any aircraft with long, shallow tanks in the wings. Or anything that uses a rubber bag, actually; if the bag collapses, it can give a "full" reading with almost nothing in the tank. So "dip the tanks" is not really a valid answer, except in those cases where the designer catered for that method. It has been used for decades in transport-category aircraft, where one can walk around under the wings, in the form of "drip-sticks", and in that form there can be a number of them in each tank, and the combined reading is very accurate in most cases. I've never seen a drip-stick on a GA aircraft. Fuel contents gauges conventionally come in a variety of types; the "old faithful" float - arm - rheostat (which puts electrical power into the fuel tank vapour space, but let's not worry about that) ; the capacitance type - which also puts electrical power into the vapour space - and gives wildly incorrect readings if it gets some water in the sensor; Sight-tube types - which work very well on tall, compact fuselage tanks, but vary wildly according to roll and pitch attitude, on wing tanks; Mechanical float gauges that can be read from the cockpit - these come in float/arm and twisted-strip types; they can be quite accurate if located at the geometric centre of the liquid surface area of the tank, but in a dihedral wing, that changes as the fuel is used. The simple fact is, fuel contents gauging is not simple. There is hardly a single aircraft type with wing tanks that extend over more than a short length of the wing, that has a satisfactory form of fuel gauge, because no such thing exists. One can improve on it by using a number of senders, distributed along the length of the tank, but adding their outputs correctly is by no means simple - and not fail-safe. So in practice, about the only practical approach for aircraft with long flat wing tanks, is to use a calibrated fuel flow meter, and start with full tanks.

See new thread - "Fuel contents gauging"

So? That just says to me, there are more Jabirus around than any other type.