IBob

Drifting threadwise here (as we do) I recently had a lengthy but fruitless exchange with FR over their use of the term 'Calibrated Height' which is what they claim to display. The only references I have been able to find online to 'calibrated height' imply that it is a corrected value: the actual height. But what FR displays appears to be raw transponder data, not corrected for barometric pressure. Anyone got anything to add to that?

True enough. But very few warnings systems are entirely foolproof. So I believe the emphasis needs to be on understanding the system. And the number of forced landings due to poor pilot fuel management would seem to bear that out. I think most here would agree that tanks should always be physically dipped before flight. After that, in the case of the Savannah, there are sight glasses for the inboard wing tanks, which inevitably slosh around some, but still provide the pilot with a reasonable indication of tank contents. I would go so far as to say that I think the Savannah has a very well thought out fuel system.

Hi Ivark, the newer Savannahs have a vent pipe, from the top of the receiver tank up to the top of the LH wing tank. This allows any air in the receiver tank to vent. The older Savannahs do not have this vent pipe, so if you get some air in the receiver tank (perhaps from momentary unporting of the wing tanks), it can become trapped there, and you may get false low fuel indications. Typically this happens as you gain altitude, because the trapped air bubble increases in size as the air pressure is reduced. I have flown in a VG that did this. This may be the reason for your warning light coming on. If there is an air bubble in your receiver tank, you may be able to see it with a bright light. ................................................................................................................................................................................... The low level switch is a simple reed switch, operated by a floating magnet in the tank: when the level falls, the magnet closes the switch. It is possible for this switch to fail. I do not know if this would cause the intermittent fault that you describe.

kgwilson I picked up that habit from my Savannah instructor. I am not sure how much it proves, as it is my understanding that the ignition modules tend to fail by degrees, the first indication being failure when cold. But I do it anyway, at 3000RPM, where I see a drop of maybe 200RPM. ---------------------------------------------------------------------------------------------------------------- As an aside to that: I used to see a quite uneven drop when doing this, with distinctly rough running on one ignition module. However, this cleared up while I was chasing a minor radio issue, as follows: I had started at the plugs and leads, could tell nothing much from the plugs: we have a reasonably long taxi in from the strip, and my plugs have always looked kinda terrible after this, but the engine is new, starts and runs like clockwork etc, so I've come to accept that's how the plugs look after a long taxi. I took them out, looked at them, put them back, checking the leads and caps in the process. What I did notice while doing this was a certain amount of rubbing where the leads for the lower plugs pass down between the cylinders. These leads sit inside a heatproof sleeve, but there is nothing to prevent this sitting against the heads, so I cut a couple of square rubber guides from large grommets, centered the leads through these. I also cut the cable ties off these leads, then fitted new ones with the leads centered in this manner. None of this improved my radio issue, but since then I get equally smooth running on each mag during my pre-shutdown 3000RPM mag check.

Or register your ownership with Rotax, and get regular news, updates, and notifications etc from them.

Lots of folk here do the same, Skippy, so you're in good company! It'd be interesting to run a survey. And we could print 50 and 100hr t-shirts and stand at opposite ends of the bar.........)

Lovely to see the punters wandering all over the paddock, and not a single individual minced up! That must have been when they were still delivering Common Sense with the milk every morning............)

It's surprising (to me) how many elect to change the 912 oil at 50hrs. I assume that Rotax built in some margin when nominating the 100hr change. This isn't intended as a criticism.......clearly it is for every operator to decide what suits them....but I am just curious.

However, as recent events around the Covid vaccination have shown, there are entire segments of humanity living in alternative worlds where the logic of this world does not apply.............

I have also read that manufacturers may change their oil formulations without notice, but that Shell have agreed to consult with Rotax before doing that with Aeroshell Sport Plus 4. It seems to me that cost of oil is a very small part of the cost of operating a 912. Given that we depend on the engine to keep us in the air, I don't know why anyone would consider moving away from the Rotax recommended oils, unless for some reason they are unobtainable.

Why not just use Aeroshell Sport Plus 4 as Rotax recommends? Here is a list of recommended oils: https://legacy.rotaxowner.com/si_tb_info/serviceinfo/si-912-016.pdf

Hi JG. I converted my Savannah underwing breathers to forward facing ones, much like the one in your pic, but using a very small 90deg bend from a garden irrigation system. On the first outing, with just the inner tanks valved on, I experienced a huge amount of crossfeed, one tank level going down at a rate, the other tank level going up, so turned back after only a few minutes. On landing I found fuel stains on the wing top from the tank that was going up: the tank caps were screwed tight as usual, but the additional pressure in the system had caused that tank to bleed pressure at a minor imperfection (a slight dip) in the lip of that tank. As a result of that experience, and after some thought, I reverted to the standard underwing setup for three reasons: 1. I had no wish to experience that degree of crossfeed again. 2. I was concerned that the additional tank pressure could 'bug out' the tanks, with the possibility of damage to the wing structure. (Note that the pressure has nothing to do with the size of the aperture. Note also that very small pressures can generate huge forces over large areas, so for instance a controlled atmosphere coolstore for apples, which seals hermetically and is tested with a domestic vacuum cleaner, can be imploded if the vacuum cleaner is left on for too long. And a pressure of 1PSI in a Sav tank may generate something like 500lb of 'bug' between it's top and bottom surface.) 3. Cessna, who have been messing with this much longer than most of us, position their forward facing breather behind the strut attachment, not directly in the airflow. The main problem with the basic Savannah setup is that the plastic underwing pipes do not sit straight, and can also rotate. My intention now is to mount solid aluminium pipes down through through the wing,, with flexible pipes from the top of these to the caps. At the underwing I will cut these pipes at an angle into wind, which should give a small positive pressure. And the pipes will be held in some way to prevent rotation.

Hi Marty. 1. ICP advocate the use of Loctite 577 at the fuel tank fittings. I used this also on my manifold fittings etc. 2. ICP provide nicely made worm drive hose clamps. I needed some extras but was unable to source anything of the same quality locally.. If there is a better option, as outline by Skippy above, I would definitely go for that. 3. The fuel manifold and fuel taps we are sourcing from China (it may be possible to get them locally, but you pay a premium). They are one size down from the domestic ball valves used for isolating taps and WC cisterns etc. I use Ali Express, first search for 'air manifold' and locate the required manifold block: they come with various numbers of ports, are normally used as workshop air line splitters. This allows you to check the thread size, you can now go hunting for ball valves of that thread size. The down side is that delivery will be slow and sometimes they stuff up the orders. 4. ICP supply the 5 way fuel splitter for the Savannah. It is very simple, a block of aluminium with 5 threaded ports. 3 of the ports take standard barbed hose fittings: these are the fuel coming in, and the fuel going out to the two carbs. The other two ports have a very small orifice, they go to the fuel pressure gauge and the fuel return (this latter is crucial to avoid vapour lock, especially if taking off with the engine still warm after a recent shutdown). I don't know if anyone supplies this part. It would not be hard to make if you can ascertain the orifice size: suggest you ask Mark.

Kurt, you're not talking gibberish at all. I believe Mark has his fuel return plumbed back into his fuel selector valve block. Seems to me it would work fine, let's see if Mark has anything to add to that> Eightynots, the air bubble in the receiver tank problems dates back to the older Savannahs, which had no vent pipe from the receiver. The problem was that once you got air in there, it had nowhere to go. The manual now calls for a breather pipe from the top of the receiver tank to a point high in the L inboard tank. This effectively addresses the problem.

Hi Kurt, really interesting to read of your control mods and see your progress! I'm most interested in your Arduino work: I do a bit myself. Credit where it's due: my fuel valve setup is a direct copy of Mark Kyle's setup on his original XL, and I referenced his build thread here a great deal during my own build. Also, and as Mark mentions, I fitted a flashing LED instead of the bulb supplied for the low fuel indication. I then fitted a second one in parallel on the pilot's side (the standard indicator goes on the RH side of the panel). The flashing LEDs were sourced from RS, the fuel manifold and valves we source from China, though you may have more economical sources where you are. Keep the pics coming: it's great to see another aircraft coming together.

Yep, a couple of things struck me. The first was that, while Juan Browne is an excellent and knowledgeable commentator, in this case he was commenting on something that he clearly has little practical experience of. The second was the amount of time they spent stacking that aircraft: a full 30seconds and it may have gone on longer without the stall, the way they were mucking around. During which time the aircraft is burning off height and flying on beyond the spot. Given that the thing has handles and steps, it should be easily possible to stack and leave in half that time.

It does sound like the Camloc would be your better option. That's what I have on my oil inspection hatch, which is opened every preflight. I think they are better suited to that sort of constant use.

Give us a clearer idea of what you are trying to do Spacesailor. My aircraftt has Dzus for the fg cowlings (higher load, greater weight) and camlocs for oil inspection and belly hatches. Different fasteners will be more appropriate in different applications. In all cases there will be lookup tables identifying the sizes and how they are measured. It's just you sometimes have to do your own homework finding the appropriate table. And you have to know how they are measured, or you're just guessing. I would guess Aircraft Spruce only take orders for part numbers to avoid arguments with folk who guessed, then didn't get what they wanted. Camloc info is here: scroll to the bottom and it says how to measure for them: https://www.aircraftspruce.com/catalog/hapages/camloc4002.php It doesn't look as if they carry the shortest size. If it helps, the shortest (slotted head, undercut) Dzus is the AJ3-25 for 3/16" diameter or AJ4-25 for 1/4" diamrter. (So the first part of the number is diameter in 16ths and the last part is the length in decimal....gotta love this stuff!) They have a length of .25 or 1/4". If they are still too long (or if you have to buy the next size up which is AJ3-30 or AJ4-30) all you do is pack and/or rework the spring they get hold of.

Blueadventures, my cowl is inside and I would do the same again. The purists would say it is less streamlined, but this is not a streamlined aircraft and I can't see the overlap making any difference. I also like the idea that my cowling is more likely to stay with the aircraft, tucked in as it is......) My understanding is that it used to be a struggle to fit some cowls this way, but for me it went very easily. Maybe this is a feature of the XL and S, probably also it is due to the corrugated steel hoses that allow very tight smooth bends without flattening.

PS for anyone building: due to variations in cowl thickness, some adjustment of the individual fasteners will probably be required. I did this by reworking (okay, bending) the springs, and in some cases by packing under the spring where it is attached to the inner cowl. As with all cowl fitting, this really needs to be done before the paint.

It's also challenging for those of us with more than the usual pair of thumbs, Nev.....)

Here is the Aircraft Spruce page that spells out the dimensions: https://www.aircraftspruce.com/catalog/hapages/dzus.php Note they are measured from the head to the spring bar they attach to. That's the -40 and -45 of the number, which are 400 and 450thou respectively.

Savannah supply homegrown aluminium fasteners that can bind and spread. I replaced all mine with steel Dzus from Aircraft Spruce: Model Cat # Quantity 121J-540-Z3C AJ5-40 13 121J-545-Z3C AJ5-45 3 That includes a couple of spares, though I have learnt to be really careful taking them out when on grass.

Plus one for the Lightspeed Zulus here. I've always struggled to hear over noise, I find them very good. And surprisingly good even if you don't turn on the ANR (don't ask.........).

You're welcome, Kurt. During my build, I benefited hugely from the posts of others on this site. My aim was to add to that by posting some of my own. Further fuel system comments after 2 years of flying. In no particular order: I have had no fuel leaks. I am very happy with the fuel valve arrangement (copied from Mark Kyle's first build) which I firmly believe is the best option when using 4 tanks. This allows flexible management of all 4 tanks (typically I would take off and climb, descend and land on inboard tanks, switching to outboard for cruising). It allows simple periodic testing of the low fuel switch in the collector tank, which cannot otherwise be tested without draining all tanks. (There is a test button on the panel, but this tests only the indicator, not the switch, and the switch can fail.) And it allows the outboard tanks, which are less often used, to be flown to exhaustion in cruise. If building again, I would pass the various tubes to the face of the inboards tanks through larger grommets and holes in the ribs, since the tanks may shift and swell some with use: that is, I would allow more clearance round tubes where they pass through the rib. The newer kits now have inspection hatches allowing access to the tank fittings. I think this is an excellent idea. I fastened my under-tank panels with rivnuts, but fitting inspection hatches is a far more workable solution. I had uneven feed from L and R tanks. Apparently most aircraft have this, and it is very difficult to eliminate completely. In my case, more fuel was invariably taken from the RH. I was able to greatly improve this by removing all undulations from the LH lines where they passed across the rear of the cockpit. The lines were hose at this point, and I now have them held straight by tying them to a length of aluminium L section with cable ties. (This is all tucked away inside the simple shelf I made to carry the lines across.) This has effectively removed high spots where air can sit, impeding fuel flow. A final improvement I may make, though not essential, is underwing breathers of solid pipe, rather than the plastic lines I currently have. These work well enough, but do not sit straight, so despite trying to trim them evenly they will tend to give slightly different tank pressures. My thought is to have aluminium tube down through the wing, with the plastic pipe on top allowing removal of the fuel caps. I would have the underwing part trimmed at approx 45degrees to the airflow, like the plastic ones. At one stage I did experiment with forward facing breathers, but abandoned that very quickly as it resulted in excessive tank pressures and a huge amount of crossfeeding. All the best with the build, Kurt. Do post some pics as you go, we all enjoy seeing an aircraft coming together.