docjell Posted November 16, 2008 Share Posted November 16, 2008 Hi all My 28 hour 6 cylinder engine has been running very sweetly but decided to have a rest as my wheels touched the ground this morning. Pleasantly peaceful but a bit alarming if I'd needed a go-round. Idling was between 850-900, long powered approach, closed throttle over the threshold and kept it closed through the roundout,flare and touchdown. Restarted first push and I attempted to reproduce the problem but no luck. Still idling at 850-900. Any thoughts - I'd really be pleased if it didn't occur again! Cheers Chris Link to comment Share on other sites More sharing options...
motzartmerv Posted November 16, 2008 Share Posted November 16, 2008 G'day...have had this a couple times...is it the jab engine?? firewall mounted throttles by any chance? Link to comment Share on other sites More sharing options...
Steve L Posted November 16, 2008 Share Posted November 16, 2008 hi, the near new 160 i'm training in done exactly that a few weeks ago - no problem just a quick hit and away it went. steve Link to comment Share on other sites More sharing options...
Guest Pioneer200 Posted November 16, 2008 Share Posted November 16, 2008 Same happened to me in our clubs J160 the other day as the wheels touched the ground. Was a bit concerned ( what if it happened on finals) but was rightly informed that if you are to throttle back to idle you are to high on approach and if it was to stop you should clear the fence, On restarting when it happened I pulled throttle back to idle and it was fine It is a concern though if you did need to go around( enough to think about without trying to get the prop turning again! Link to comment Share on other sites More sharing options...
jetboy Posted November 16, 2008 Share Posted November 16, 2008 Its very common with the Jabiru setup for this to happen. Usually worse when you "need" to stop short? Mine doesnt falter or stop anymore since I put a sleeve around my throttle linkage that prevents pulling the idle setting back past the idle adjust position. This probably was not an issue with the original lawnmower throttles, but a proper aircraft one can easily bend the idle tab back further than it was set for. My sleeve is in fact the primary idle set adjusment, which stays on the high side - 950 rpm. Ralph Link to comment Share on other sites More sharing options...
docjell Posted November 17, 2008 Author Share Posted November 17, 2008 Thanks everyone - seems to be a common problem which I think is unsatisfactory - might give Jabiru a call. Yes - 120 HP 6 Cyl jab engine with the old style 'grovel between your legs' throttle. Is there much of a difference between that and the firewall mounted throttles- and if so why? Chris Link to comment Share on other sites More sharing options...
Jabiru Phil Posted November 17, 2008 Share Posted November 17, 2008 Happened to me a couple of times in the 230 until I adjusted the float level, no problem since. Link to comment Share on other sites More sharing options...
Guest brentc Posted November 17, 2008 Share Posted November 17, 2008 There should be no difference between the firewall versus under-leg design. Both have stoppers that stop you from pulling too far. There is also a stop on the engine that can be adjusted easily with a screw driver. If this is set correctly then in theory it should be impossible to stop the engine via the throttle lever. Link to comment Share on other sites More sharing options...
Yenn Posted November 17, 2008 Share Posted November 17, 2008 Iv'e had this happen a couple of times when reducing to idle at base turn, I set the idle speed up a touch and it hasn't happened again. It shows that it is best to keep the field well within reach. Link to comment Share on other sites More sharing options...
docjell Posted November 17, 2008 Author Share Posted November 17, 2008 More useful thoughts guys - thanks. I think this is a fundamentally important issue If the engine dies unexpectedly at any stage of the approach/landing the safety of the aircraft and crew is seriously compromised with potentially fatal consequences - especially at a challenging strip such as ours which is rough, surrounded by trees, with take off and landing distances reduced by the significant foliage at either end. I contacted Jabiru today and spoke with one of their engineers who volunteered the following wise council Idling between 850-900 is best set at idle taxi and not stationary with brakes on consider changing the idle jet from 35 to 45 adjust the idle screw (this had been done) look at the float level (??? will consult a LAME! what do I look at?) Always use a powered approach, only closing the throttle at flair He recommended 1600rpm for base and 1100rpm for finals He seemed to know what he was talking about- thoughts on an email/posting! Chris Link to comment Share on other sites More sharing options...
Jabiru Phil Posted November 17, 2008 Share Posted November 17, 2008 Happened to me a couple of times in the 230 until I adjusted the float level, no problem since. I should have explained further. Cut out on landing was put down to the rough strip and carbie flooding. Engine stopping before touchdown is another matter. Link to comment Share on other sites More sharing options...
Guest check-in Posted December 4, 2008 Share Posted December 4, 2008 My Jabiru 2200 powered aircraft has a Cessna plunger-type throttle. With the idle set to 950-1000 rpm I can still cause it to cut out if I pull the throttle back too much against the idle-stop. Pulling it all the way back is the instinctive thing to do on landing. I don't think it's just the rough airstrip, because I can get it to do this when parked. I assume that the idle-stop at the carby end must have some flex in it. The alternative may be to set the idle up another 100 rpm, but then we get into the area where it's likely to cause the aircraft to 'float' on landing just when I don't need that to happen. Link to comment Share on other sites More sharing options...
Guest brentc Posted December 4, 2008 Share Posted December 4, 2008 As I said in my post earlier, you need to adjust the stopper on the carby to stop this from happening. If it's adjusted correctly, the engine will not stop. Link to comment Share on other sites More sharing options...
Ross Posted December 8, 2008 Share Posted December 8, 2008 There does not seem to be any mention of "carburettor heat" in this discussion especially with long approaches under minimal power! Link to comment Share on other sites More sharing options...
docjell Posted December 8, 2008 Author Share Posted December 8, 2008 Thanks Ross - I can hardly believe you wrote that.Not mentioned because it absolutely goes without saying for any pilot with more than two brain cells to rub together Link to comment Share on other sites More sharing options...
BigPete Posted December 8, 2008 Share Posted December 8, 2008 Fair suck of the sav Chris. :ah_oh: Ross has made an observation which could have been a factor in the problem. :thumb_up: Giving him a serve for contributing what you may feel is a "no brainer" :yuk: will only serve to inhibit people from sharing on these forums. kindest regards :big_grin::big_grin: Link to comment Share on other sites More sharing options...
Deskpilot Posted December 8, 2008 Share Posted December 8, 2008 Well said Peter. I've had an engine out due to icing up on the decent. Easy to forget, or to misjudge the atmospheric conditions. Link to comment Share on other sites More sharing options...
Guest check-in Posted December 8, 2008 Share Posted December 8, 2008 Well, I cured it, by INCREASING the idle stop to 1020 RPM, so that when I pull the throttle back hard against the stop it can't go below about 950 RPM. Therefore there must be some flex in the stop mechanism. Of course it's also possible that the tacho is not dead accurate and what I thought was 950 RPM was sufficiently less to have been causing it to cut out out. A 100 RPM error across a 3300 RPM possible range is not all that much, I suppose. Better for it to over-read slightly. Re carb heat; although I have it and do use it by applying full carb heat on base leg, then removing all carb heat for final approach, so far my Jabiru installation has never showed any signs of carb icing, and apparently the previous owner never found any need to use it. Anyway, I thought that there were some home-builts out there running Jabiru engines without carb heat? I am flying a Sonex, not a Jabiru, so maybe there is enough warm air circulating near the air intake for carb heat not to be required. But I will go on using it, just in case. Especially with 98 octane Mogas. Link to comment Share on other sites More sharing options...
turboplanner Posted December 8, 2008 Share Posted December 8, 2008 Check-in, I didn't experience carb icing in 10 years of flying all conditions, then a couple of weeks ago it was there in a Jab, needs a few circumstances to combine so its a bit like a lottery ticket. Link to comment Share on other sites More sharing options...
docjell Posted December 9, 2008 Author Share Posted December 9, 2008 Ross - my apologies - hasty and unnecessary- sorry to have been so rude. I learnt to fly in the UK ,where virtually any lowering of power setting mandated carby heat - I don't think I can bring myself to throttle back without reaching for the carb heat control without a tremendous effort! I routinely apply carby heat as soon as I slow in the circuit and remove it about a minute from touchdown - something I was chastised for doing in Townsville when I revalidated my PPL in '99. Link to comment Share on other sites More sharing options...
Guest check-in Posted December 9, 2008 Share Posted December 9, 2008 Docjell, why were you chastised? Unless you need high power, as in takeoff and initial climb, applying carb heat can't hurt. And you do need to get rid of it before landing, in case of a go-around, so it seems to me you were doing the right thing. Especially anywhere near the east coast, which is usually humid at any time of the year. I don't use carb heat continuously on descent, but if it's humid I pull it on for 30 seconds or so about every 3 minutes. Having said that, I don't throttle back much on descent anyway, as the aim is to keep the cylinder temps in the cruise range. The Sonex has a high Vne - 170 knots - and a cruise descent stays a good 30 knots under this, so I would probably still be running at 2650 rpm minimum unless it was turbulent. But any type where you do have to throttle back to descend, surely continuous carb heat is good insurance. Link to comment Share on other sites More sharing options...
Ross Posted December 9, 2008 Share Posted December 9, 2008 Hi Chris (no offense taken or offered) and others I am a relatively low time powered pilot and will stay that way until I can get my kit J160 into the air. I thought over that observation a number of times before posting it. My primary reason for finally deciding to do so was not to castigate you but I was aware that there was another audience out there not posting but reading the posts and many of those are new and would be pilots with little experience who are reading these posts avidly and looking at all the details and assuming that they are reading the whole story. Hence the brevity of my observation which was not advice one way or the other. They may also be flying in a variety of aeroplanes/weather that may behave quite differently from ones being discussed in the particular posting and so the actions required may be quite different for their scenario. I try in my posts to tell all that I know on the subject which may not be much but which can make them quite tedious to the experienced and also say that I am not an authority on the subject. I still remember a trip back in the 60's as a first time passenger in a small Cessna on a trip to Trangie from Narrandera in the Bishops plane. I still don't know what model it was. We had just climbed a few thousand feet some where near Parkes to clear some thermals I suppose when the pilot noticed the engine was starting to run slightly roughly. I am not sure that I had noticed ( a certificate mechanical engineer no less!). I always thought that the engine and airframe of light planes that I had been anywhere near were all out of balance and made odd noises and vibrated excessively. The pilot soon applied carbie heat for a few minutes and the vibration was cured and did not return after turning off the carbie heat. Now I think I have a better understanding of the process but you could elaborate. I admit that I forget to apply carbie heat periodically when in the circuit and can see a need to have a comprehensive check list that can be readily and easily accessed when flying. It will be high up on my priority list when I start flying my J160. It is also quite difficult to write these posts without offending anybody with no intention of doing so. I just checked to see that so far there have been 596 observations of this subject and very few of those have made any response all though that number would probably include the people who posted as well as each of their editing sessions. Regards Link to comment Share on other sites More sharing options...
Guest check-in Posted December 9, 2008 Share Posted December 9, 2008 Seeing as this thread has drifted towards carb ice, I just pulled my old DC3 notes from way back when men were men and barmaids ate their young. I will quote from these, as readers may find them interesting. And if they don't, tell me to p.ss off and I will take my footy and go home. "Carburettor icing is likely to take two forms when operating in tropical conditions - either throttle ice when at high altitudes and low throttle openings, or evaporation ice. Throttle ice can occur in moist air temperatures up to 3 deg C. Evaporation ice can occur in moist air with carburettor air temperatures as high as 30 deg C, especially in rich mixture. Indications of carburettor icing are: a) decrease in manifold pressure due to restriction of induction b) rough running caused by change of fuel/air ratio c) sticking of throttle butterfly" Then it goes on to describe how to apply and remove carb heat, but this is not relevant to an engine without a carb temp gauge and fitted with a pressure carburettor. Basically it says, richen mixture, pull heat on to get at least 32 deg C in the carb, then lean mixture (if in cruise or descent), but don't exceed carb temp of 38 deg C in lean. Richen mixture again before removing carb heat. Of course with the Bing carby, we have no direct control over mixture, but my understanding is that it is always running rich below about 5000 ft. Someone correct me if I am wrong. We also may not have manifold pressure, but a reduction of RPM with a fixed pitch propeller in steady flight is another way of recognising possible carb ice. Link to comment Share on other sites More sharing options...
Guest Macnoz Posted December 9, 2008 Share Posted December 9, 2008 As a Jab owner / driver I identify with your concerns about stopping on close throttle after flare. Note you pre take off checks include a “check idle” after the 2k mag test for good reason. Of course you are likely to be more gentle in closing the throttle on check than you are after flare on your rush to get in pinned to the ground. BrentC rightly referred to the carbie detent adjustment. Another one to watch for is the collar with grub screw on the throttle rod at the back of the panel. This is accessible through a hole in the side panel with the driver’s door open. This has been known to work its way loose resulting in too much reliance / force on the carbie stop. If you pull back hard you can flex the panel toward you resulting in cut of if the carbie stop is not correctly set Link to comment Share on other sites More sharing options...
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