IBob
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Everything posted by IBob
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Facthunter, I don't disagree with your theory, in any respect. But I do read much of what is written here, and what I don't see is any undue pattern of weakness or failure for the 912. It is what it is: not the 'perfect' engine, not ideal for everything and everyone. But for the slot it does fill it seems to me to function remarkably well, and especially so since the designers grasped the nettle of liquid cooled heads and high engine speed, securing many benefits, but also complicating the design.
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I'm sure you're right Nev. But I'm left with the thought that, for an engine with so many design shortcomings.....it works remarkably well....)
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Earlier in this thread, I made a reference to troubleshooting Rotax problems by finding what had changed since the factory, then putting things back as per the factory build. I need to qualify that: It has been pointed out to me that variations in third party exhaust systems etc on the Rotax engine may affect carburettor performance, and that adjustments to the jetting, properly carried out, may offer a workable solution to that.
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Glen, I've just come to accept that my plugs look awful after a home taxi (and to that I should add most of the finals of the landing, since the Sav uses very little power if you're wanting it to land). But must be working fine at other power settings, since it runs so smoothly and never misses a beat (well, okay, one cough once, travelling just under cloud base without carb heat on). Add to that I ran the first set of plugs for almost 200hrs (as per the LM Manual, though some change them every 100). If it works, don't fix it??? With the Jab, I can see where LCHs could result in a number of changes...as you point out. Is there history from other users you can draw on? My 912 has no EGTs. It has the standard coolant temperatures on 2 and 3 (LHfront and RHrear), Rotax used to do CHT but moved to the coolant. I would think temperatures are very location specific, so would expect comparisons between different engine types to be worthless.
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Glen, I know nothing about Jabiru engines, and just a bit about the Rotax 912 since I own and maintain one, so have a particular interest there. I do understand the importance of the float bowl vent, as providing appropriate float bowl pressure (in the Sav the vent/s are plumbed into the airbox downstream of the filter, which makes sense). I am fortunate that my enrichment (aka choke) has a free action, and shuts positively as soon as released. I hadn't thought about carb heat, but try not to make that a set and forget thing: I can set various degrees of that, so tend to return and adjust it when in use. Having said all that, it is perhaps 800m of taxiing from touchdown to my hangar and any time I have pulled the plugs they look very rich. However, my fuel consumption is certainly not excessive and the thing has run like a dream from new, so I have just assumed that the Bing setup runs rich near idle. You say the Jabiru was about right, now rich after LCH? I'm not quite sure what you mean there???
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All the best with that Kgwilson. And I wasn't referring to any post you may have made.
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Before moving onto Holden........I would like to say how much I like the Rainbow Aviation approach to troubleshooting Rotax engines, as set out in their excellent carburettor functional descriptions in the links posted above. They take a 2 step approach: 1. Find out what has changed since the engine came from the factory. 2. Put it back to how it was when it left the factory. Which might sound glib or simplistic, but not so long ago we had someone in another thread here experiencing erratic or rough running problems. And when last reported, they were off to alter the carb needle settings...........(
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That article referencing the Australian dark sky takeoff accidents study makes for sobering reading: "Interestingly enough, investigators found that in every case the doomed aircraft struck the ground within 3 nm of the airport, and within one minute of becoming airborne. In 87 percent of the crashes, the aircraft impacted to one side of the extended centerline with wings showing little or no bank at the time of impact. In every crash, the wreckage indicated that the aircraft was under control at the time of impact. Specifically, the investigators noted that the aircraft damage was consistent with the pilot being unaware of any unusual attitude." -
RFGuy them's the numbers........however with that fat wing and various other gear hanging out in the breeze, the reality is you'd need to be doing something well past radical to reach 124kts. As most owners will agree, the Sav is happy at about 85kts. Anything much above that and there is very much the sense that you are pushing it..........)
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Skippy, I think part of the problem is that we label this particular control as a choke, because that's the sort of function it performs, and that's how we are used to thinking of it. And I am no different: mine is labelled 'choke'. But as others have stated here: 1. It is actually a starting carburettor. 2. The throttle also needs to be fully closed for it to function (because it is this full closing of the throttle that provides the necessary 'choking'.) Here is mine.....labelled choke:
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Skippy, here are two excellent detailed writeups, with illustrations, on the Bing64. The first covers the operation of the main carburettor. The second covers the operation of the starting carburettor. https://electricmotorglider.com/2017/02/01/bing-64-cv-carburetor-part-1/ https://electricmotorglider.com/2017/03/01/bing-64-cv-carburetor-starting-carb-part-2/
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Go for it, Gary......and don't forget to post pics of air under the wheels.......)
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The story does just seems to get worse. As for nobody speaking out: I have wondered if it might in part be a reluctance to be the first to speak out. I was thinking of the famous B52 crash, where the pilot had been variously bending and breaking the rules for years, but nobody (apart from one man who died with him) was prepared to do anything about it. Ridiculous as it seems, maybe it's a sort of male gungho chicken thing, where speaking up is chickening out.......(
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It certainly works very well for me, RFguy: in 230+hrs the only time I have not had near instantaneous and smooth starts, was due to stale fuel after lengthy Covid lockdown. So much so that if I ever start to get less clean starts, I will be looking for the problem. Further to all this: a while back, someone posted a link to a very good video on this carburettor. I did watch it, but cannot now recall where it was. Anyone???
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I suppose we are all talking about the same carburettor here: the Bing 32???
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Bleuadventures Blueadventures, I don't think that's quite right either: pulling the choke rotates a disk that exposes one of two different sized ports. A full pull is a big port, a partial pull is a smaller port. So a partial pull is still giving some enrichment, I would think (always assuming the main throttle is fully closed).
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Skippy, you may well be right. No doubt ambient temperatures have a bearing, and they are normally not low here. All I know is that I have evolved a routine that sees near instantaneous clean starts with a fairly prompt transition to an initial idle of 2200RPM, choke off, during which the engine neither labours nor overspeeds. I say fairly prompt as it is several seconds before the timed ignition goes to fully advanced (at which point the RPM rises). As a side issue, it is worth checking the idle speed (throttle stop) and the idle mixture screw settings, as set out in the line maintenance manual under basic throttle adjustment. These are very quick simple adjustments. My new engine had the throttle stops set correctly, but the idle mixture screw settings were only approximate, and not identical. I have also seen a new 912UL with various idle and running problems, where the problem was incorrect setting of one carb needle. Which is to say that whoever does the Rotax carb settings is not bullet proof.
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Skippy, that's odd: when I pull the choke button on the panel, it turns a little disk in the internals, exposing one of two enrichment ports. I'm pretty sure it does nothing whatsoever to the main butterfly.
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Skippy, congratulations! As for the choke.......whether it is lockable or springs back, I am ambivalent. Since I only use it at starting the 912 and almost immediately let it go, and since it does not work once you begin to open the throttle, I cannot see a reason to have it lock on. But quite probably others have different needs.
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Blueadventures, I believe the throttle bar stop may go some way towards maintaining carb synchronisation. I have the standard setup, with two cables coming from the quadrant bar to the two carbs. Initially, as this bedded in, and as expected, the carb sync required periodic minor adjustments. But since approx the 45hr mark, no further adjustment has been required: I still check it periodically, but it will be almost 200hrs since I last adjusted it. I put that down to careful routing and securing of the cables and the throttle bar stop, which prevents the carb arms being pulled beyond the carb arm stops. And I would count it as one of a very small handful of worthwhile improvements to the Savannah build. The Savannah throttle bar has a centrally placed quadrant, presumably for those wishing to put in a centre knob throttle, but otherwise unused. This comes back and strikes a block of MDP, cut to thickness once I had everything else in, and riveted to the firewall. In the pic you can see the MDP block, it is white and just to the right of the voltage regulator, with the unused quadrant resting againts it.
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CScott and Skippy....no disagreement with any of that! And no reason for a newer 912, properly installed and wired, to be hard starting. However, the older ones without the timed spark retard could be nasty: supposedly the spark advanced once the engine reached 650RPM, but the crude circuitry of the ignition module measures that in an odd way, and having seen them 'spit back' on many occasions, I'm not convinced it does it well or accurately. The newer modules have been a huge improvement. At the other end of the process, I get clean shutdowns too. I fitted a stop at my throttle quadrant bar, so that the throttle can be pulled back quite firmly without risk of bending the carb throttle arms, which are light in construction. At shutdown I first go to 3000 and run a mag check (not a very demanding test with warm modules, just a habit I picked up from another flier), then back to about 2000RPM. Then two fingers on two ignition switches, pull back firmly on throttle and switch off ignitions promptly, 1 then 2 as soon as RPM falls. This almost always gives me a clunk-free stop. A lighter prop also helps in this, though mine is a 70" Bolly, so not particularly light.
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Hi Supacat, and congrats on your purchase. It's a great machine! FWIW: The S comes with multiple mounting holes for the rudder pedals, suggesting they can be moved forward. Note however that the S has a redesigned fuselage, so it does not necessarily follow that the rudder pedals can be moved in the VG. You would need to look at available space etc. Moving the pedals would require replacing or reworking the nosewheel linkages. You would also need to look at whether the rudder cables would adjust, or need modifying or replacing.
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I have a separate choke that springs back: it's the silver knob at the lower left in the pic. The starter switch is just under the throttle, and it works fine for me: throttle closed, fully pull choke, hit the switch, and as soon as she fires my hand goes from switch to throttle. Pause a moment, then feed in some throttle while letting the choke off. My engine does have the timed spark retard, and that makes for much better starting than the earlier arrangement where the spark was advanced as soon as the engine hit a certain RPM. I also have a heavy negative cable from engine back to battery: some years ago i read something from an Australian Rotax guru, who reckoned he had noticed a strong correlation between aircraft with starting/sprag clutch damage problems, and aircraft that relied on the hull for the negative return. A combination of the above has always given me very good starting.
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Tried to PM you, CScott, but you don't accept msgs?
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Hi NathanS, and welcome to the site. Suggest you contact Mark Kyle, he posts as Kyle Communications on this site. He is the resident expert, and may well be able to help you. You can Personal Message him by going to the little envelope logo on the left (assuming you are on a computer). Select Compose New, type in Kyle as the recipient and it will bring up the Kyles. From there select Kyle Communications and drop him a message.
