seb7701

H.F. - I KNEW I should have checked what plane, before making assumptions about the streak!!!!! :) Ok, well I am intrigued, as I have often wondered about some of the setups I have seen with ducted oil coolers. I am curious to know how that works, but am guessing it just send the hot air nicely 'south' towards the outlet? I too would like to see some shots if that's OK... So the 160 will have bigger cowl inlets than me and presumable hydraulic lifter donk, so the jetting is going to be different anyway i guess, otherwise I'd be asking a needle jet size to try out. (I am having interesting results with jetting trials...) In any case, they are very enviable temps at 20 degrees OAT! I have just removed both baffles from my muffler, so will be interesting to see if there is a difference.

Horsefeathers - for starters, great temperatures, which I could only dream of!! Oil temp is great also. have been very interested to know what sort of difference I would see between the speak plug probe vs screw type, so that's interesting to hear that you tried it and that they are in fact similar. I am gathering that you don't have EGT's which are a good indicator of mixtures, but nonetheless, I would be thinking that no. 4 is running a little leaner. Not sure how it works if you have a pusher installation, as per your avatar, but the change in intake for me clearly richened up no.4 specifically, so who knows... If you don't mind me asking, how many hours on the engine? What sort of jetting and what sort of ambient temps are you operating in?

Thanks guys - yep, very pleased! Geoffrey - the Jab factory is currently playing with the NACA duct (which is where I got the idea), although the are covering it and replacing with a 2.25 inch (I think?) hole. I just covered the lot... :) As such, I dare say you will hear more. Thanks Bruce - No.2 CHT at a more regular 3500 ft was around 152, but would probably have stabilised out a bit more if I wasn't busy step climbing to 5500 as it was easily doing 1000ft increments while reaching max CHT of 165 on the hottest. Therefore hopefully sub 150 will be fine. Just sucks mind you that no.1 was like...99 degrees!! Anyhow, will wind back the thirst via the jetting, hopefully at the detriment of the EGT's rather than the CHT's... Also going to check the inlet static pressure now that I have the trusty manometer. Might give some more clues.

Well, a few further figures since the deletion of the naca duct and the move to simply sucking air from inside the cowl. Today at a previously iffy ambient temp of 26 degrees, I saw EGT's more even than ever before!! Admittedly, these end figures were at 5100ft, but still- CHT/EGT's as follows: 99/619 140/626 120/606 120/564 The comparison is a previous flight at 24 degrees ambient where EGT's were more like 106/632 155/686 116/580 145/679 Biggest gap in EGT's went from 106 to just 62!!! Would love to know what jetting you guys are running, but the 2.82 needle jet is going to be swapped for maybe a 2.80 for a try, as I am (unfortunately) averaging 19LPH with a few good climbs thrown in. Anyway, some of you guys may perhaps wish to check out the air box biz as I have!!

O.K - turbulence yes, but from prop wash, well, not really convinced. Well, I'll get a photo for you, but as I say, that duct is essentially right on a curve in the fuse, meaning the NACA intention of being a non-force-fed intake is somewhat lost. I had a very interesting conversation with a very trusted source the other day who stressed that all issues come from 'upstream' of the carb, starting from the fact that air is shoved into the airbag from outside and would start by being thrown against the airbox's far wall and the turbulence and pressure starting from there and only getting worse as it trips over the less that preferable surface of the scat hose and into the carb. Planesmaker - the force fed air (I think) increases pressure, which in turn slows the velocity, which can't be good for feeding a carb, so you are kinda right. I do have one underlying query of my own and that is why this engine is so sensitive to an issue which doesn't present itself elsewhere. That being said, most people probably don't have individual monitors on their 912, but I hear that they are actually quite uneven. In any case, their issues are solved by a carb for each pair of cylinders. We have a Tecnam here which is simply fed by pod filtered carbs inside the cowling, so there really isn't anything diabolical about what I have tried. I am interested though, in the difference between current test and removing internal flat filter and simply putting a pod on the old NACA intake. Just comes down to which filter offers the most air, which will then require some re-jetting. I did chew 19LPH on my test, but I am still climbing the bejeezus out of it at regular intervals (temp permitting) given the fact that I still only have 13 hours on the clock. That could easily add 3 litres to the predicted hourly rate I would think! During my discussions the other day, this example came up - the intake for a Robbo helicopter. Simple and works!

Consider just leaving the hose off - I have a temp probe in the engine bay as we had a spare left over. Originally had it in top of the airbox, but was floating around the engine bay lately adjacent to the firewall - only read 17 degrees, so I think you'll find that there is plenty of airflow to supply cool-ish air and nothing as warm as carb heat. Would love to hear what happens if you tried the same thing!

Well, today's discovery was nothing short of a revelation!! Following the discussions about blocking off NACA ducts etc, I did just that, but instead then just pulled the hose off the air box which fed from the NACA duct. The air into the air box was then just drawn from inside the cowl but was still filtered. Well, all I can say is holy crap! My little 4 bar graph of EGT's went from having 2&4 clearly elevated to having 1,2 & 3 level pegged with no.4 only being different because it was 25 degrees lower than normal!!!! So, even out the EGT's? Yes, it does. Dropped about 7-9 degrees off no. 2 and a clear 25 degrees off number 4, which was totally unexpected. Forgive the fuzzy photo, but it was from the other day, while the second clear shot is from this morning. Kinda illustrates the point... Next step, gonna try silicone hose instead of the cobra head....just in case! Incidentally, had a little look at the NACA duct. The funny thing is that looking along the side of the fuse (in the vicinity of the firewall) the fuselage 'swells' outwards, right where the NACA duct is. That means that the air runs along the side of the fuse and actually gets forced straight into the NACA duct as it is positioned right on the outward curve, which I think defeats the whole purpose of a NACA duct!! We're making headway...

That's a darn good idea - the dark room/torch bit! The jetting is providing AT LEAST enough fuel at this stage, so back to the airflow and what you've said!

Would be very interesting stuff Oscar - near Toowoomba isn't it? Given the issues seem to occur 'upstream' of the carby, I was curious today as to whether anyone has stuck a pod filter on the car for kicks. I am awfully curious about that - works fine for Rotax! That Jet - sealing is the least of my worries unfortunately, as oil cooler is sealed to perfection and ducts no dramas. You are right with regard to the deflectors though - few little bits to be done there!!

Oscar - now that is cooling! Was it fed with the standard carby setup? The ramp effect you mention is interesting - we only noticed this morning that the front of the left hand side intake is actually set back around 30mm further than the right side from the closest part of the propellor to pass by it, namely the trailing edge. Makes you wonder what air is being forced from the prop straight over the top of the cowl. O.K. - Not quite even I'm afraid - what I didn't mention is that no. 1 was running at 103 degrees C and no.3 was 110C!! Imagine if I could get 2/4 doing that??

Thanks Oscar - yep, assuming everything was accurate, ducts seemed nicely symmetrical! Good point re the plugs for sure. Now just considering at present what to mess with in terms of intake to correct mixture issues or to put it bluntly, stuff more air in the L/H intake and do some creative ducting to get the CHT's down some more, as the initial opening of intake and deflectors etc have been the only successful measure to date. That said, the fact the no.2 is hotter than no.4 does scream out mixture issues... (At 21 degrees C ambient, no.2 was cruising at 150-151 C, with no.4 at 144 C.)

Just finished a flight with digital manometer fitted to each duct and a probe a couple of inches 'North' of the cowl outlet, to get differential pressure readings. Well, after hours of staring at what looked like identical ducts, in turns out that they basically are!! At least I can cross diff. press. off the list... Left side - 162mm H2O cruise (100kts) and 125mm climb (80kt) (2.7 x higher than outlet pressure) Right side- 158mm H2O cruise (100kts) and 111mm climb (80kt) (2.0 x higher than outlet pressure) Also upped the needle jet to 2.82 from 2.76. Hottest CHT (no.2) down by around 6-8 degrees with a EGT now of 670. Still looks like mixture issue! AArrgghhh!!! Somebody please knock up a fuel injection setup for each cylinder!!!

Can anyone advise as to whether there has ever been changes to the 2200 plenum chamber (after the carb). Turns out that my engine has previously done a valve on no.2 cylinder, so given that it is all new top end and still hot on no. 2, I'm wondering if there were any changes to the way that the mixture was distributed. Looks like jetting may have been a little too frugal, but about to try different jets...

Well that sounds like some success! Will be interested in how the covered NACA duct goes, but the carb tilt is a curious one. I tried it to no effect, but was told that it is moreso successful with the 3300, which seems to be the case alright. In any case, that's a good drop in temp!

Men - out of interest, what jetting is everyone using? I will be checking tomorrow (after I decide whether I have to pull the darn carb off or not??), but seems I have the odd combo of 255 main and 276 needle jet? Stuck a finger or two into the exhaust pipes this arvo. While I know the pipes have a common muffler, the 'cool' side's pipe had only the slightest bit of black soot while the 'hot' side had nothing at all!! I think we need more juice...

Will be trying the taped of NACA intake at some stage for sure. I re-read the article Europa/Jabiru article from 'Custom Flight Creations' and saw that bit. Am also going to have another look at things in terms of sealing gaps inside the ducts themselves. Interesting that they claimed to have re-fitted one of the ducts incorrectly and were 'off by one fin' which resulted in temps up by 30 degrees F. Anyhow, still annoyed that I have one side which struggles to get warm enough for take-off when the other may potentially have all means of crap inside the duct to try and get things manageable...

O.K. - You mean gull wing baffles? Just had another look and seem to have missed a whole important aspect - the air needs to go through the head fins and not the giant gap between the barrels!! Thanks Oscar - I haven't in honesty looked yet, but the small lengths that came with it are pretty tiny! I also happen to have a nice hole in the firewall which (is due to be covered...) will work a treat. Once I figure out how to drive it, the pressure investigation will be an interesting one!

Yep, frustrating alright!! I should say a thanks in the mean time to you guys for your thoughts on this one a - much appreciated and thanks for hanging in there with this discussion! Yep, it's a funny deal. For eg. after the success had by adding the tin 'fence' to no. 2, I tried adding a bigger one which covers the whole triangular outline of no.2 head. It ended up raising it's temp by 11 degrees, but dropped no. 4 by another 10 degrees! The aeronautical engineers out there will laugh perhaps, but I wonder that there isn't too much air pressure/velocity in the left duct, which is causing the flow to head straight for the back end. Doesn't explain why it isn't heading down between the barrels, which should be lower pressure.

Yeah, might try an direct the air from running along the roof of the duct from the up swirl just for curiosity sake. Can't remember if I mentioned already, but just for kicks a few weeks back, I taped off both intakes completely and made a smal slit in each and poked the compressor nozzle in there to see where the air was exiting. On the cool side, air was exiting noticeably from down between there cylinders (perfect right?) while on the other side, it was shooting straight to the rear and out the back between duct/fins. Even after I taped off the gap (there is about 3mm more gap on hot side between duct/fins at the rear..) it was finding it's way straight out between the fins on no.4. I know this doesn't take into account the drawing effect from the lower cowl, but we'd see what happens with the manometer. It seems the laws of physics operate differently between each of my bloody ducts!!!

O.K. - you've lost me Lol! You might have to explain a little as I'm not sure how taping off the cooler side intake will help? Main issue that has me stumped is that the front cylinder on the left is warmer than the rear. Small fence but might try fence above to direct air through fins more, as seems air is shooting straight down the back and out the rear , possibly something to do with it's whack of prop air coming from the upwards blast from the prop, whereas the right side is being forced 'down and in' over the heads a little more directly? Oh, and uniform egt's usually only seen straight after takeoff. From there, 2 and 4 are elevated above the other two, just like the CHT's...

Thanks Oscar - yep, I guess in hindsight it would be unusual for anything to be run in much by 8hrs!! O.K. - todays little session seemed to be in the vicinity of 15LPH, give or take, but have been living on 2900rpm (aside from descending and climbing out to vary things). Looking at old records from this plane, even with the old heads etc, she was always very frugal. I am going to take a look at the jetting next - the carb is engraved with 255main/276 needle, which is interesting as the needle should be 278 according to Jab. Anyhow, will have a look - I know the main IS 255, but thought I might richen things a touch and see if it helps the hot side. (Just wonder what might happen to the cold side...) Anyhow, the show will go on...not out of strategies yet thankfully!

Oscar, yep, that's the one. Just have to find a longer length of the correct hose diameter and will find out how she goes. I did see a youtube video of someone verifying the calibration of this model, so I thought I would give it a run. Will be interesting alright. I would love the CHT probes to be reading out of whack but did verify them with an infrared thermometer a while back and was within 1 degree. Worse still, the readings all seem really quite viable. Noted today that EGT's on initial climb out are all neck and neck, but CHT's are as described. From then on, the EGT's on 2&4 are correspondingly high. Had a peep in the plug holes today and seems that rings on 1,2 & 3 are not bedded in just yet, as the pistons looked a little oily looking as opposed to no. 4 which looks just right. Despite having followed all instructions to a tee, I am guessing I might need to put some more load on it in climb to try and get thing sorted. Climbs have been 80kt in general with plenty of climbing/level/throttle variations, yet here we are, but anyhow. 8hrs on the clock so far, so not sure where ring seal etc should be at this stage, but hopefully not too late?

All I can say is 'Wow' Oscar - unbelievable attention to detail there! I would love to know exactly how the oil cooler exhaust affects the low pressure area. I have just picked up a digital manometer, so will be interesting collecting some data from the 'downstairs' section of my cowls. My biggest mystery is still why I have 2 ice cold cylinders on one side and two hot ones on the other. Given what has been achieved with cyl 1&3, I can only think the lower cowl/ low pressure area in my setup is just fine at removing hot air, (unless there is something strange going on directly under one bank of cylinders, but I doubt it...) When both ducts are near identical, it's got me buggered. I have EGT's all fairly similar, with maximums of 650-690ish seen on the last flight, while the max on my problem child, no.2, was 713 degrees on the last flight. I am going to try dropping the clip on the needle down one notch to richen things up a little, as I am currently looking at around only 13LPH, but it may prove to stuff the other cylinders up. We'll see....

Out of all my readings, this site in the U.S. fascinated me the most - looks like cluey people. They did the ducted oil cooler bit too. (Pics included in the PDF) http://www.customflightcreations.com/sitebuildercontent/sitebuilderfiles/cooling102.pdf

Hate to break it to you O.K., but in my case, I was given the newer style 4cyl oil cooler and a new nose bowl and simply made it work!Lol. The inlet fits the oil cooler very well as they are made for each other. I got a glass duct from Jab which slips over the opening from the inside of the cowl to bridge things a little across to the cooler and simply glassed here and there to make it the best fit for the cooler's area. There is currently only about a 10mm gap from the cooler to the inlet which I just haven't sealed around with rubber yet, but will for sure. I ran compressed air from the outside just to see and yep, it found the largest gap and leaked around the cooler wherever it could. That said, 95% would be going through the cooler and the temps at present reflect that. I am fascinated with the concept of ducting the oil cooler outlet as Oscar has - make sense....