IBob

Yep, as I found trying to measure my jet size. We had suggestions like 'stick a pin in it' (the hole is too small and the taper on a pin and even a small needle is far too abrupt to get any accurate reading) and 'file a taper' (anyone here ever tried filing a round taper on a 0.4mm needle?).......

Nice to see someone come up with figures from practical testing. The figure of 2L/hr gets bandied around a lot, but I have never been able to find where it comes from. And I have suspected my own return flow is higher than that while observing it raising the level in a valved off near-full tank while in flight.

Skippy, I used a very fine sewing needle, then tapered it by hand, then inserted it in the (slightly recessed) aluminium 'jet', marking the place with my thumbnail, then extracted it and used vernier callipers. Easy to write, but in practise not so easy to be confident of an exact measurement. Which is why I wrote 0.38 - 0.4mm I have remeasured a number of times now, I would say it is around the lower figure. ( But I do know it is bigger than 0.35mm, as I have a wire of that size, and it fits with some additional wiggle room.) If so, then your current jet at 0.5mm is 42% larger in cross section than mine. And if the recommended jet size is 0.35mm, your current jet is over twice that size. So, yes, I agree that the next step is to source and fit a 0.35mm jet. To answer your question: mine is not a jet, as such. It comes as part of the ICP Savannah kit and is a fuel coupling or spigot, with the end blanked (probably not fully drilled out) and the hole drilled in the end. Possibly manufactured in house. If you get really stuck, I can send you one, though you would need to figure out thread size and how to mount it. However, it would probably be easier and also better to source a genuine 0.35mm jet, if you can. As you say, reducing the jet size may well sort your problem. If not THEN might be a time to check whether it is poor pressure or a poor reading.

Skippy, I have misinformed you: I just remeasured the return jet/s on my (spare) fuel splitter, using a fine needle cut to a long taper with emery paper and vernier callipers: I am seeing a measure of approx 0.38 - 0.4mm, certainly not the 0.5mm I previously estimated.

There was a reference earlier to other owners having similar problems and just 'learning to live with it.' It did not say if these were other owners with glass cockpits, but if so I would begin to suspect either the equipment or the way it is being installed. And while I can see the logic in keeping the fuel lines out of the cockpit, where possible, I am not sure about siting the fuel pressure transducer/sender in the engine bay. Quiet simply, if there is any pressure (over static pressure) in the engine bay in flight, that additional pressure will be subtracted from the fuel pressure reading.

Skippy, Alan recently posted to his thread 'CHT sensor Temperature versus original below sparkplug thermocouple' regarding the amount of trouble and expense he went to, only to discover that his instrumentation was not reading correctly: he was chasing false hi temperature indications. It seems to me you may be in a similar position, in that we are still not sure whether you have poor fuel pressure, or just poor fuel pressure readings. You stated early on that the aircraft has never shown any signs of fuel starvation. You may install a smaller return line jet, but I doubt this is your problem. If at all possible, I would beg/borrow/steal a steam gauge, hook it up temporarily, and establish which it is. Because if it is something wrong with the readings, you could be mucking around forever with fuel system components without seeing any improvement.

Skippy, I am confused by (part of) this: EG: the drill size chart I am looking at has a 56 drill as .046" or 1.18mm So clearly we are looking at different standards/charts. BUT The main thing here is that you have been able to find something that fits in the jet, and that you can then measure with your micrometer. I can only add that, if your jet is 0.5mm, then it is approximately the same size as the one I have fitted (may be exactly the same size, but I have no exact fit to measure). I hope that is of help.

Sounds like you need to get the V callipers/micrometer out and measure...um....what you are poking in there? Based on your reported flow (which must be a constant if the pressure is) I would guess your jet is just under 1mm.

Skippy, so #54- #55 is 54 -55 thou. (or 1.3 - 1.4mm) Which is huge. My jet (see above), is approx 20 thou. (or 0.5mm)

Hi Skippy, following this with interest. Here is a pic of the (spare) return jet setup from my aircraft. (It as 2 identical jets, the second one goes to the fuel pressure gauge). My measure of the hole is a best guess: I can get a .35mm strand of wire into the hole, but certainly not 2 strands. I would guess the hole is 0.5mm I should add that this is mounted where the fuel line splits to the two carbs, and works fine for me: I have had vapour lock after short shutdowns: I always use the booster pump pre-start, and with vapour it runs fast for 5 to 15secs before settling down once the vapour is gone, at which point I get a fuel pressure reading. (Obviously, vapour will pass through the jet much faster than liquid.)

rgmwa it's not something I would fit, but then we do not have the distances that you have in Australia: it may be a different matter if I was over there. As for making some use of your red cube: with many instruments, I think it is change that you are interested in. So even where there is an offset, as with the Rotax fuel return, you will still have a reading that it normally sits at in, say cruise, or climb. With that in mind (or marked) you can then be looking for change. Aside from that, if you are able to access the return line easily (it is accessible in the Savannah) you could establish the return rate at a set pressure, so arriving at an actual fuel burn rate.

They need to sweep the sand off that aircraft carrier..........)

Hi Ian, yes all of that makes good sense. And while I had good hearing for most of my younger life (as a young 'un in the UK I could tell you when there were bats around at night) I have always struggled to make out what people are saying in noisy pub type environments. I don't know why, and I find it very tiring trying to maintain contact in such environments. Since taking up flying much later in life, and while my hearing for normal conversation remains fine, I have found I need all the help I can get in the cockpit. I am very happy with my Lightspeed Zulus, and even without the ANR switched on, they really do a great job of reducing the ambient noise.

I grew up near High Wycombe, in Buckinghamshire. Ansons were a common sight overhead in the '50s, I believe they operated out of Booker airfield and were used for navigation training.

I think APenNameAndThat's original proposition is quite cunning, and certainly worth considering: 1. 'Turn down' hearing by inserting earplugs (hopefully without sacrificing clarity). 2. Compensate by turning up headset volume. 3. Ratio of headset sound (radio and comms talk) to external sound is now improved.

Skippy, the Sav (amongst other aircraft) has a 6L 'receiver' tank behind the passenger seat with a drain cock underneath (this being the low point in the system) and a float switch in the top which activates an indicator on the panel unless it is full. This arrangement gives approx 20mins of warning of fuel exhaustion. It also compensates for unporting of tanks, as may happen in long descents or momentary unbalanced flying. And some folk run their fuel return back to that tank, so avoiding the problem of overfilling a wing tank with returned fuel. All in all, I see the receiver tank as a very worthwhile innovation. Might it be possible to fit something similar, albeit smaller, in the Sonex?

PS here's a further minor complication for you: the air behaviour under your cowl quite probably alters not only with speed, but also with angle of attack. For instance I found the Naca scoop on my cowl top doesn't work well at high angles of attack, so I was drawing air from under the cowl instead of outside air. I was able to correct that by greatly reducing the gap between Naca scoop and airbox inlet. How much such things may affect your fuel pressure sensor mounted in the engine bay.......if at all.......we'll never know, without something else to check it against. But I'm not surprised to hear that some pilots get odd results, if that's where they are putting them.

Skippy, I confess I have not spent time studying my fuel pressure in flight. I do know that sometimes it is at or just above 2PSI in a climb, other times (and more usually) it is at or above 4PSI. And I have seen it shift quite quickly from one to the other, but I don't know why it should do that. I shall watch it more carefully when next out, and see if I can add to that. I am on steam gauge. I don't know why your sensor would be slow to catch up with air pressure. Having said that, these sensors (once you get away from the VDO stuff) are standard industrial equipment, and I suppose it is possible they could have a very tiny or filtered internal atmospheric aperture....since they are normally deployed in static applications, not required to respond to rapid or large atmospheric changes, and the manufacturers quite probably have internal filtering etc to protect the works from the ingress of moisture and dirt. It's certainly interesting. If problems persist, one option would be to borrow a steam gauge and plumb it in, You would then be able to clearly establish if you have a fuel pressure problem, or a fuel pressure sensing problem.

Nev, this is bizzare. As a person living on a pair of islands with about 25minutes water between, I take a real and ongoing interest in this stuff. And I fly a Savannah , so I am doubly interested in how that might behave in a ditching. What I am not so much interested in is Walruses or airliners in Tanzania. I certainly made no claim that my own position was 'representative'. As for facts, I'm not sure what your problem is with the statistics that Bertorelli dug up, but I personally am far happier going with those than some notion of 'physics. And that's it from me on this.

Nev, nobody here at any point has suggested that ditching is a piece of cake. However, stirring a big pot full of stale theories, adding a few airliners and dishing up the results in a doom-laden fashion does nothing to help- anyone. Did you miss the recently posted Savannah accidental ditching? High wing, fixed undercarriage, didn't flip. Could have but didn't. However the doors (which cannot be opened safely inflight) were held shut by water pressure until the fuselage filled. They then opened. I found that description of actual events useful.

I see that, Bluedaventures and it does need investigating. But we need more info: Is this a bottle just for the fuel pump vent, or is it also for oil reservoir vent. If so, which is the oil coming from? Also, is oil still coming? I was taught to troubleshoot by formulating a theory, based on my understanding of the machine, that matched the symptoms...then formulating tests to test the theory. And doing all that before actually picking up any tools. In Skippy's case here, I am very interested to know more precisely when the problem appears and also to what degree. Does it appear immediately on takeoff, or does it increase with altitude? I have also learnt to simplify wherever possible: remove extraneous stuff rather than adding to it, in order to focus on one specific thing.

To explain the gauge/sender/transducer thing further: All of these devices have some sort of diaphragm (or similar setup) normally open to atmosphere on one side and connected to fuel/oil/whatever on the other. They work by measuring how much the diaphragm is flexed or deflected. So, on the ground, engine off, there is equal atmospheric pressure on either side of the diaphragm, pressure reading zero. Start the engine and there is atmospheric pressure on one side and atmospheric pressure plus fuel pump pressure on the other side. The atmospheric pressures cancel out, so you get fuel pressure. Climb to altitude and the atmospheric pressure is reduced, but equally on both sides, so it still cancels out. But if the atmosphere side of the diaphragm is not open to atmosphere (the shipping bung is left in the gauge) the atmospheric pressure reduces on one side of the diaphragm as the aircraft climbs, but not the other. And the result is what looks like a loss of fuel pressure. I have seen this twice with steam gauges, and the fix is simply to pop out the rubber shipping bung on the top of the gauge body. If this is the problem, then the setup will read okay on the ground, but the the fuel pressure reading will appear less the higher you go. (This probably needs to be checked with the aircraft level in cruise, as a hard climb may show a reduction in fuel pressure, confusing the picture some.) In a perfect world, the atmosphere side of the transducer would be hooked to the static port setup. But a gauge mounted in the cockpit (and so accessing cockpit atmospheric pressure) is accurate enough for practical purposes. A sender or transducer mounted on the front of the firewall is accessing atmospheric pressure there: if mounted in a high or low pressure part of the airflow, this would also affect the reading. In this case I would expect to see the effect immediately after takeoff, rather than progressively as altitude increased.

Skippy, reading back over this, you stated that fuel pressure meets the Rotax spec on the ground. That is quite a wide range, I believe. FYI I normally see approx 4.5PSI at fast idle (booster pump off).

The boost pump raises the pressure further, so certainly will improve the reading. I'm not saying the gauge is the problem, I'm saying it's the way it is hooked up: it's a differential gauge, close off the atmosphere side, and this is what you get. And nobody so far mentioned altitudes or circuits. I just worked an example.