Guest davidh10 Posted January 25, 2011 Posted January 25, 2011 ...Just a thought .... but this is not the only Rotax with the oil tank below the engine is it? If others are not having the problem, surely this is either a faulty indication or something in the engine is worn or damaged? .. There's at least eight 912 trikes at Yarrawonga and I've flown three of them (including mine). None have the length of delay in achieving oil pressure after start that is the subject of this thread. Pressure is usually up in 2-3 seconds. Nev; My CFI demonstrated pre-filling the new oil filter before fitting it, at my first oil change. It is certainly a good idea.
Guest davidh10 Posted January 25, 2011 Posted January 25, 2011 Can get back through any bearing in the motor They all have running clearances and some have squirt holes. When the engine is shut down hot the oil internally is pretty thin. Oil doesn't stay in the galleries. Mostly it drains. Some filters feature anti-drain-back valving to stop some of it draining back through the oil pump. Nev I have noted that with mine, in winter, it takes more than one idle day for all the oil to drain back. Makes a difference on the dipstick of perhaps a third of the difference between the min and max marks if dipped one and then several days after flying.
Bluey Posted January 25, 2011 Author Posted January 25, 2011 After a quick connection of the analogue unit in place of the lead to the skydat, I can confirm that oil pressure on the analogue unit rose as soon as the engine fired up without delay. This after more than three days of sitting idle. Normally after this length of time a delay of around 10 seconds would have been seen on the skydat. So what have I learnt from this is that the issue lies somewhere between the vdo sender unit and the skydat. most likely it is an issue with the skydat itself. We tested it a number of times with the engine warm and the same occurred, no delay. With the skydat connected, a small delay was noted but this is not unusual with a warmed engine. Bottom line, I don't trust the skydat.
Bluey Posted January 25, 2011 Author Posted January 25, 2011 The oil pressure gauge installed is the one recomended by Bert floods for the vdo unit installed on the 912. The pressures it indicated on warm up were very steady and in the ball park of the skydat system.
Bluey Posted January 25, 2011 Author Posted January 25, 2011 Thanks everyone, I tried having both units plugged into the same sender unit and the result was higher than normal pressures on the analogue gauge and an open circuit on the skydat. This makes sense as the reduced current going to each unit would result in a larger than normal indicated pressure. The analogue unit coped much better than the skydat as it seemed to take most of the load and so the indicated pressure was around 1 bar higher than expected. The skydat just didn't get enough current and so went open circuit. It would be great to be able to have both working normally as I think a backup analogue pressure gauge is required especially after the issues I and others have had. This whole exercise has cost me more than $300 that could have been better spent had an analogue unit been fitted in the first place. My advice to anyone with oil pressure issues is: Before you do anything, bypass the skydat with either a multimeter as stated by davidh or obtain a cheap analogue unit as I have done. The only problem with the analogue unit is you need to either hook it up to the trike power supply in order to get an effective earth or earth the sender unit to an external 12v supply (something I haven't yet tried but should work provided you can secure the earth to the outside of the sender unit using a clamp). Speaking to a repco dealer today, it turns out that a vdo sender unit is available with two indipendent outputs but it may be too large to fit in the space for the sender unit on the 912. Also quite expensive from what I was told (> $400).
fly_tornado Posted January 25, 2011 Posted January 25, 2011 you could contact skydat and see if the oil pressure guage can be calibrated.
Bluey Posted January 25, 2011 Author Posted January 25, 2011 That's a good idea. Will have to look into that.
Guest Crezzi Posted January 26, 2011 Posted January 26, 2011 AFAIK the skydat display panel just receives digital information so its a bit hard to see what could go wrong with that which would just affect the oil pressure display in the manner described. I suppose rapidly changing values could be damped by the firmware (though why just the OP ?). The latest 912 have a different (better) solid state oil pressure sender but it doesn't work with the same analogue gauges as the old one so would probably require a different revision of the skydat capture unit. Something else worth checking is your oil pressure relief valve as these are a known cause of problem oil pressure indications. There is a newer version of this available which damps out fluctuations better and should give longer life of the OP sender. Cheers John
Guest davidh10 Posted January 26, 2011 Posted January 26, 2011 AFAIK the skydat display panel just receives digital information so its a bit hard to see what could go wrong with that which would just affect the oil pressure display in the manner described. I suppose rapidly changing values could be damped by the firmware (though why just the OP ?). The latest 912 have a different (better) solid state oil pressure sender but it doesn't work with the same analogue gauges as the old one so would probably require a different revision of the skydat capture unit.... Interesting. Yes, the SkyDat receives a one way serial data link from the Engine Data Capture Module (Wires: Data, Battery, Ground). In the back of my mind there's a thought that it is asynchronous RS-232 (V.24), But I cannot find why I have that thought. Perhaps it was something I saw when I had it opened up to replace the cold cathode lamp. Usually, and to properly conform to that standard, there should be both positive and negative power supplies, but I've seen implementations, elsewhere, where this was not the case. It could also be a current loop method, although that is a much older standard, dating from mechanical teletypes. You can see the four conductor ribbon cable connecting to the circuit board, which is the connection of the Engine Data Capture unit and battery supply. All the analogue to digital conversion is done in the Engine Data Capture Module. I haven't given any thought to solid sate pressure transducers, but a little Googling indicates that they can have several different outputs including an analogue one that emulates the analogue transducer. Obviously, solid state transducers require at least three connections (Voltage regulated power, Data, Ground). If a solid state pressure sender that emulated an analogue unit was used, then the only change would be a regulated voltage supply, which could be provided separately and the SkyDat module would not have to change. * Attached Photo is Copyright 2010 David Hunt.
Guest Crezzi Posted January 26, 2011 Posted January 26, 2011 I'm pretty sure that the new Rotax pressure sender outputs voltage (or maybe current) rather then varying the resistance. Maybe they could have used/designed one which provided a compatible output but, on a factory built aircraft, its not an option for us to fit a non-manufacturer part. It could also be a current loop method An unwelcome blast from my past if they have but I suspect a b*st*rdised simplex form of RS232 is most likely Cheers John
Bluey Posted January 27, 2011 Author Posted January 27, 2011 I am going to continue testing with the analogue gauge to see if the initial results are repeated under different conditions (ie longer periods between flights). I especially want to know how the pressure at start up behaves when the engine has sat idle for around a week. So far my initial tests were after 2.5 days resting and those results clearly indincated no problem with oil pressure. I will report back if future results indicate a problem.
Admin Posted January 27, 2011 Posted January 27, 2011 Bluey Have a read of this thread from a couple of years back: http://www.recreationalflying.com/showthread.php/96-Good-On-Ya-Rotax?highlight=flydat
Bluey Posted February 20, 2011 Author Posted February 20, 2011 My Oil pressure issues seem to come and go. I now go through quite a lengthy process to hand turn the prop before starting the engine. I even turn it over with the ignition switches off for about 5 sec as well before lighting it up. I have had mixxed success doing this. After sitting idle for nearly 3 weeks due to the horrible run of weather lately. It fired up with no delay what so ever to the oil pressure rising to 5+ on the skydat. I have checked it with the manual gauge since reporting the all clear and on one occasion there was a noticealble delay of around 6 seconds. Yesterday after sitting idle for a week, I measured a 10 second delay between zero oil pressure and a quick jump to 5.5 on the skydat. Anyway, after a good flight without issues we opened up the old oil filter and analysed it. It had been in the engine for 90hrs and it was as clean as a whistle. I detected 2 very small specs at one point on separate folds of the paper but I can't be sure if they came from the engine as the bench space we were working on was not clean of metal particles. Anyway bottom line is if the oil filter is in such good nick after all the supposed oil pressure issues at start up I've been having, isn't it now probable that A) the oil pressures issues may not have been real or B) If they are real, then they are not having a detrimental effect on wear and tear in the engine. Either way, I will be cutting the oil filter apart after every oil change from now to have a look at it. On a side note, does the oil flow to the magnetic plug before it reaches the filter as the material build up on the plug seems to suggest it flows through quite a few galleries before it gets to it. If it flowed the other way, wouldn't it have a much lower chance of being covered in feromagnetic material given that it is placed right next to the filter? Bluey
Guest Maj Millard Posted February 20, 2011 Posted February 20, 2011 Bluey, You are worrying way too much about your oil pressure problem. 912s are very reliable in terms of oil pressure. Skydats are not reliable, and my guess is that is where you drama is. The magnetic plug should also be checked at each oil change for metal. The oil passes over the magnet after leaving the gear box. There is more chance of getting metal from the gear-box, than from the engine. I've yet to see a skydat that is 100% trouble -free..................................................................................Maj...
Bluey Posted February 20, 2011 Author Posted February 20, 2011 Yeah, Thanks Maj... Your not the first person to say that. At least now I know the problem is not likely the engine.
Mc Guyver Posted February 20, 2011 Posted February 20, 2011 Bluey, not sure how you checked your filter, but you need to wash the element in petrol in a plastic container and then strain the petrol through a very fine white cloth. That way you can then examine the clean element for metalics and see any metalics that have been washed off the element. You need very little space to do it!
Bluey Posted February 20, 2011 Author Posted February 20, 2011 Mcguyver we cut it open and slowly pulled out the filter element. As each pleat was pulled out I ran a finger along it and closely examined it that way. A couple other guys with experience cutting open filters had a look at it too and thought it looked very clean as well.
Mc Guyver Posted February 20, 2011 Posted February 20, 2011 I did a 2 day course presented by Rainbow Aviation Services of America at Maitland a few years ago. The HGFA brought them over. The presenters were highly qualified and were certified in GA as well as Recreational Aviation, This is the way they recomended we did it
Dieselten Posted February 21, 2011 Posted February 21, 2011 If I recall that course was run by Brian Churchill and his wife, they own Rainbow Aviation. I was on the first course and Brian demonstrated the technique of washing the filter and straining the residue, which I have also done on occasions when doing an oil-change on a Jabiru. Our local LAMEs use the visual inspection of the pleats without washing - unless there is significant metal. Then they wash, strain and examine the metal with a lens to determine if it is bearing-metal or aluminium, or chips scraped from cylinder-walls at startup etc. Seen plenty of metal from Lycomings and Contis (usually scrapings from cylinder-walls) but nothing yet from Jabiru or Rotax 912 filters. Either technique works, provided you know exactly what you are looking for and exactly what you are actually seeing...and how to interpret it.
Guest rocketdriver Posted February 21, 2011 Posted February 21, 2011 Our local LAMEs use the visual inspection of the pleats without washing - . What is the best way of opening the filter so the act of cutting the can does not itself contaminate the pleats? REgards RD
facthunter Posted February 21, 2011 Posted February 21, 2011 There are specific cutters available that do this. You are correct to be concerned. Nev
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