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  • #16
    Exhaust Gas Temps

    Thermocouple sensor lead lengths don't matter.
    Dave

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    • #17
      Exhaust Gas Temps

      Paul PM'd me with this:
      "Dave,
      Appreciate your comment re length of egt sensor cables.
      However from Westach installation instructions "patch leads may be extended up to 22 feet but sensor cables should not be shortened"!
      Paul"

      But my comment above was public, so should the answer - but it is my theory, not proof...

      I suspect that Westach's comment about not shortening the sensor leads is to be sure they are far enough away from the hot junction to be truly at ambient temperature.
      In the complete thermocouple circuit, EVERY junction of different metals is another thermocouple junction, generating an associated voltage.
      This includes thermocouple leads to (probably copper) patch leads to instrument terminal posts and internal instrument wiring.
      So long as all of these junctions are at similar temperatures, the parasitic thermocouple voltages will all cancel out, just leaving the much hotter actual thermocouple head voltage to be read.

      So, in summary, I think Westach wants you to keep the sensor leads as long as possible to keep the external connections well away from the heat source.

      Dave

      Comment


      • #18
        Exhaust Gas Temps

        Progress report:

        I had limited time with the 'plane at the last visit but it was long enough to confirm that the main jets were a standard 165 size and the needle clips were in the standard 3rd groove. I had time to put the clip of one of them into the 2nd groove and start the engine, with an immediate improvement (in my case a rise) of EGT reading on that cylinder even at a lowly 3000rpm. Obviously I shan't fly the aircraft until I've adjusted the other needle clip also. A bonus of the brief twiddling was that for some unknown reason (perhaps the needle fitting more snugly in the needle jet?) the idle was as smooth as silk at 2000rpm instead of the usual shaking that encourages one to throttle up a bit!

        Also, I've realised that I was talking twaddle (not unusual!) in a previous post about a cold day producing low EGTs....in fact, of course, with colder, denser air producing a leaner mixture, the EGTs should be higher (duh!). Encouraging to think, though, that the EGTs will be lower in the heat of Summer - if we get one this year.

        Can't wait to reset the clip on the other carb then fly her!! I'm hoping for EGT readings of 550 on each cylinder but I won't be moving the needle clips further if I don't get them.....enough is probably enough and it'll be interesting to check plug colour afterwards....I shall report back!

        I also checked the length of the sensor cables and they seem to be about a metre in length - certainly not shorter.

        Phil.

        Comment


        • #19
          Exhaust Gas Temps

          Hi again all,

          Well, today I dropped the needle on the second carb by one notch (as per the first carb) and test flew her....disappointingly, the EGTs are both still well under 500 degrees.....about 480 in fact. Sadly I was distracted by an unassociated electrical problem and I forgot to check the plug colour before putting her away.

          Does anyone think it's worth reducing the main jet from 165 to 162?

          I'm beginning to think that the gauges are under-reading!

          Phil.

          Comment


          • #20
            Exhaust Gas Temps

            Dont forget Phil...the type of thermocouple we use is only accurate at 24c oat...below that the ind temp reads higher......above lower...prob has more of a bearing on variations on the gauge reading than the cold dense air.
            "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

            https://www.youtube.com/user/nickjaxe/videos.

            Comment


            • #21
              Exhaust Gas Temps

              Thanks Nick.....what you say is even more depressing though, since the gauges should've been reading higher than the ACTUAL temps, being as it was so chilly yesterday; furthermore these gauges will continue to over-read until we get a Summer heat wave!

              I just can't understand why so many pilots are struggling to keep their EGTs within upper limits whilst I apparently can't get mine high enough to be anywhere near efficient....

              As an aside, I remember reading as a lad when I was interested in getting the best out of my two-stroke motorcycle that 'reading' your plug colour is only useful after doing an engine 'chop' during a full throttle run (ie. a sustained period on main jet).....removing the plugs after the engine's been idling for a couple of minutes would not be representative.

              Oh well, maybe next time at the strip!

              Cheers,

              Phil.

              Comment


              • #22
                Exhaust Gas Temps

                Check your idle jet size as well. Are you fitted with an intake silencer?

                Comment


                • #23
                  Exhaust Gas Temps

                  Hi Dominic, thanks for your input.

                  I think you probably mean my needle jet size - I don't think my idle jet will have much influence on my EGTs in the cruise - and yes, I will check it just as soon as I can dismantle the carb properly without my fingers turning to icicles. It may have to wait a few weeks.

                  I don't have an intake silencer fitted but I do have an after-muffler which, according to the Rotax documentation, shouldn't affect the carburation but I suspect that it must do, a little. Common sense tells me that strangling the flow of gasses would require less gasoline
                  (ie. smaller jets) to match the diminished air throughput.

                  Comment


                  • #24
                    Exhaust Gas Temps

                    Is the engine making its full static RPM...low RPM = rick mix cooler EGT.
                    "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                    https://www.youtube.com/user/nickjaxe/videos.

                    Comment


                    • #25
                      Exhaust Gas Temps

                      Thanks Nick, Yep she's making the required 6000rpm (plus!) static revs - in fact the motor is really sweet if a little noisy compared with other 582s at my strip - maybe I need a new silencer although there's no external evidence of that other than a fine coating of rust; no leaks as far as I can see......Perhaps the internals are shot. But then why would it make as much power as it does!

                      I can't complain about the power, I'm just looking for a little better fuel economy and less carbon build up between services.

                      Oh well - I'll continue tinkering!

                      :-)

                      Comment


                      • #26
                        Exhaust Gas Temps

                        Mmmmm less carbon between services...that could be a clue...with modern oil you should get very little...that maybe a sign of a quite rich mixture.

                        Is it oil injected??
                        "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                        https://www.youtube.com/user/nickjaxe/videos.

                        Comment


                        • #27
                          Exhaust Gas Temps

                          No, it's pre-mix at 50:1.

                          As I said at the start of this thread, my problem stems from an over-rich fuel/air mixture, as evidenced by ridiculously low EGTs and high carbon deposits. I'm working towards leaning everything off.....

                          I only hope that my EGT instrument is accurate cos that's what I'm relying on to tell me when I've hit the ideal mixture (that and the smooth running of course).

                          Comment


                          • #28
                            Exhaust Gas Temps

                            Sorry I forgot.
                            "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                            https://www.youtube.com/user/nickjaxe/videos.

                            Comment


                            • #29
                              Exhaust Gas Temps

                              Best to check your CHT system by another means before going too far on the mixture...
                              You could use a IR non contact thermometer.. around 10 on flea bay, but I have found it difficult to get accurate readings on the cylinder head...... and my arms are not long enough for use in the air:-)

                              In the past I have used

                              http://www.ebay.co.uk/itm/Black-Type-K-Digital-Thermometer-TM-902C-Thermocouple-Probe-50-to-1300-/281901918185?hash=item41a2a9e7e9:g:qFUAAOSwX~dWjB9 u

                              3.56 inc postage
                              plus a 14mm under plug K type thermocouple

                              http://www.ebay.co.uk/itm/CHT-K-type-Thermocouple-Temperature-Sensors-for-Cylinder-Head-Temperature-14mm-/380900301451?hash=item58af6d5a8b:m:mSbuOF0PZZZmNoK JR6BUNPg

                              May be worth also getting an EGT probe (needs minor mod to fit the rotax fitment)

                              http://www.ebay.co.uk/itm/EGT-K-Type-Thermocouple-Temperature-Sensors-with-Clamp-Bendable-Probe-Special-/381561443278?hash=item58d6d593ce:g:yhwAAOSwmmxW2gV k
                              6.77

                              Hope it helps

                              Comment


                              • #30
                                Exhaust Gas Temps

                                Wally what handy gadgets...just ordered the egt probe and meter...I am just about to set up an old British 2 stroke motor bike and I have been wondering how I can look at how its running...should be just the job...I suppose I should also get an under plug sensor as well.

                                Nick.
                                "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                                https://www.youtube.com/user/nickjaxe/videos.

                                Comment

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