Paul davenport

I hope I got this right and the photos re attached of the oil stains on cowling of air flow ,interesting to see where the oil -air flows around this area

Admin This is thin ice here

Yes Paul I have been very arsy for sure. Usually I couldnt win a naughty in a brothel with a fist full of dollars but its been pretty good for a change. The reason I got the aircraft from a whole heap of people who wanted it, was according to The owner I was the only one who wanted the aircraft and the engine to rebuild it. Everyone else who contacted him wanted just the engine and would scrap or part the aircraft out. He loved the aircraft and would have preferred to see it reborn in some way so thats why i got it especially for the price. This parts engine was a score....and its a not what you know but a who you know thing. I have gone halves with Danny in this engine so it was extremely cheap when you keep it for spares this way. Mind you I dont think we will be robbing too many bits as the rotax's are pretty good the only real thing that could be a issue is the sprag clutch so there is a spare there and also the coils . Just good to have spares really...I like to have spare parts..probably why I am a bit of a hoarder :)

You seem to be in the right place at the right time ,first a savanah then a rotax . Where do I sign up for this program

Back from an early fly around the traps on Saturday cht at 300 on climb and 270 in cruise at 2900 rpm, back off to 2600 rpm and temp drops to 250 ,I am using around 21 lph at cruise,a quick call to Jabiru and a new main jet is on its way ,stay tuned

Guys, I've been following this thread as I've just installed a Jab2200 rollercam in my Cygnet which previously had an 1835VW, and I've had the usual issues sorting out cooling. I've now got about 23 hours with the Jab motor.My CHT temps at cruise with 25C OAT and at 90kts are 140, 122, 135, 120 & EGTs at around 15.5lph are 695, 650, 690, 645 at between 4000asl and 5000asl. Rpm 2900. They max if I throttle back to 14lph and 80kt and 2750rpm at 720, 660, 720, 645. No matter what I do I can't get the stb cylinders cooler. No 1 & 2 were my hottest cht wise, but baffles in the pressure ducts were adjusted to get rear cylinders chts as close as possible to the front.

 

I originally had over 120C egt spread and that was mostly fixed by putting a fence of about 2cm high in front of the air inlet (which is simply a hole in the side of the cowl). This makes sure there is no ram air. Drawing cowl air made no difference. I also have flow straighteners in the airbox outlet and carb inlet. I do not have a simple cross because, if placed in the nsew orientation, the bottom interferes with the emulsion tube air inlet on the Bing and minute changes produce crazy results. When I installed the fence on my air intake my egt spread dropped and the average egts dropped so I've gone one size smaller on main and needle jets (230 & 2.8 if my memory is ok).

 

I was getting over 140C CHT on no.1 in cruise and oil temps over 90C so I ditched the 50mm lip on the cowl outlet and replaced it with a ramp for more suction. Result was a 5-10C drop on all CHTs and oil temps now mid 70s...so my next step is to put in a plate to exhaust the oil cooler air separately from the cylinders and adjust for mid 80C OT.....I'm worried about winter. Downside is higher Chts on 3&4 when taxiing (+135C).

 

My problem is on climb. When I go WOT, no.4 goes lean and the egt will, if allowed, runaway over 720C. So I throttle back to 3050 rpm where my egts are 650, 670, 645, 690 (Fuel flow somewhere around 25lph). CHTs on climb at 70-75kts don't go above 150C so far. If I rotate the carb to even mixture on cruise, it makes it much worse on WOT. And yes, the butterfly throttle is limited to 80 degrees open. By throttling back I lose about 50 to 100 revs on climb.

 

So now I'm reasonably happy and thinking there is just some tweaking on the cowl outlet with perhaps a bit of exhaust augmentation. I'm thinking my right bank is running hotter because that side is leaner and that may be because the inlet plenum diffuser is not exactly centre, or because of the orientation of the 4 horizontal holes in the emulsion tube/ atomizer which the needle jet sits in, or how the needle lays in the needle jet, eg it might lie against the stb side causing the fuel spray/plume to favour the port side?

 

I get a small drop of oil at the front crankshaft oil seal. Is this normal? Motor runs very smooth.

Down this way we call those bits Jobber bits. Good to see you back in harness ,you are doing something most of us would like to try ,keep going you have our complete attention

I try to do a BFR in something other than my a/c just to try them out and sharpen my skills, and as stated it's lots of fun

I will follow with interest, to see how you repair it . Compared to a new build what would be the time and monetary input . Please lots of pictures to show build and repair

Gliding comps at Benalla ,so the Benalla gliding club is opperating out of Wang for a few weeks, give Geoff a ring on 0413152288 for the details and restrictions (if any)

There is a picture of an oil cooler some where on this thread that has been encased in a chamber that allows it to discharge its heated air to a low pressure area not into the engine cooling lower cowl area,that has merit and I may next oil change try some thing similar. Give the dirty oil dot on the cowl trick and let us know what your results are

This is interesting stuff Paul, as I am currently investigating what seem to be high oil temps on my Jab courtesy of the oil cooler inlet being a cross between the old and new.Those I have seen with great cooling seemed to have more of a 'scoop' thing going on. I can only hypothesise that this stops the airflow simply running down the face of the cowling below the prop, with only the occasional lucky bit heading into the cooler?? Mine is the first photo and the later version is the second. You can see how the indentation on the second type would at least cause the air hit the lip and go in. Also no rounded lower edge. Ahh, more glassing I suppose....

Just back from a flyin to Mt Beauty and before I left I put some small dobs of oil on the cowling to check air flow and was surprised to see that the air flow was great around the front to sides of the cowling BUT it did not flow down and passed the cooling lip on the bottom cowl, there was a stagnant patch of air above the oil cooler inlet and interestingly air was actually spill out of the cowling at the inner cowling surfaces. Air flow down the cowling seems to split well before the nose wheel. My cht gauge indicates 250/275 on cruise 290to 300 on climb and the oil temps range from 70 to 100 depending on situation so any improvement will be great. Looking at the profile of the cowl it always looked like the oil cooler was shielding a large portion of the cowl lip and I was right. Now what ,any

Just back from a flyin to Mt Beauty and before I left I put some small dobs of oil on the cowling to check air flow and was surprised to see that the air flow was great around the front to sides of the cowling BUT it did not flow down and passed the cooling lip on the bottom cowl, there was a stagnant patch of air above the oil cooler inlet and interestingly air was actually spill out of the cowling at the inner cowling surfaces. Air flow down the cowling seems to split well before the nose wheel. My cht gauge indicates 250/275 on cruise 290to 300 on climb and the oil temps range from 70 to 100 depending on situation so any improvement will be great. Looking at the profile of the cowl it always looked like the oil cooler was shielding a large portion of the cowl lip and I was right. Now what ,any

jj_ a HUGE apology!. I am starting to build a brand new airbox, and looked at the ( absolutely AWFUL) cobbled-up abortion on my aircraft, that was obviously done when changing from the 1600 engine to the 2200. Id I posted a picture ( that facility seems to have disappeared from the site), I probably wouldn't, to save people from throwing up their Weeties all over their keyboard.I had removed it and thrown it away in disgust, to the back of the workshop - but I dragged it out to look at what I might - possibly - use in the new set-up.

 

You are absolutely correct: the majority of the hot-air passes through the airfilter, though there is a small by-pass in the hot air intake (about 1 inch square in area that exits after the filter.). That has the carby balance tube installed in it.

 

That arrangement is just not kosher: the hot-air intake is supposed to also provide an alternate inlet in the case of filter blockage. Further, it means that a % of hot and unfiltered air was ALWAYS being fed into the engine: power reduction issues and excessive wear issues...

 

If hot air is selected, it certainly DOES bypass the main inlet SCAT hose connecting the cold air intake on the side of the cowl to the airbox - it's a 100% bypass. You get full HOT air - but when cold air is selected, you don't get 100% cold air. In ambients of maybe 20C or lower, that's probably not an issue - but it could be an issue if trying to claw out of a short-ish hot-and high airfield at MTOW.

The more we learn the more we don't know? !

Just saw your post JJ seems to me that there doesn't seem to be two jabs the same,what works for you may not work for me or others cooling science seems to be a black art indeed

From my investigation to date (and I cannot remember where I found it ) the top and bottom of the Cowl inlet are of equal importance ,something to do with a pressure wave and pressure recovery ,where the cowl inlets accept far more air than the engine and low pressure area can get rid of causing drag and a spilling out of air from the cowl (correct me if I am wrong but that's the best way I can describe it) . I have some expanding foam and at the earliest chance I intend to try it out. Getting it to stay put with out moving and blocking off the cooling system is a concern

Just a thought has any one experimented with the inlet ramps on the cooling system, on looking at Lo Presti and the like they all seem to have smoothed out the flow in . Jabs blunts and crude looking head and cylinder covers seem to be counterintuitive to smooth airflow in ?

Gentle men with the greatest respect to you and the experience you have in aviation could I ask that we keep the discussion to relevant modern ideas and actual confirmable, quantifiable and documented evidence ,reference to second or third hand ,"I know some who saw or experienced etc etc " does not do this discussion justice. I am asking question because I don't know the answers ,if you don't know either ,but have a verifiable reference please please refer me to your information source . In MY experience EFI systems in autos WHEN correctly serviced are reliable and trouble free ( and I must say some owners don't do any maintainence and the systems certainly are not maintained like aero systems are ) and when combined with electronic ignition and a knock sensor result in outcomes which simply cannot be replicated by ancient magnetos and carburettors . Im sure aviation fuel quality in some countries leaves a lot to be desired even if it is still available and as you said it is being phased out. The system I am envisioning will stand alone without an alternator functioning for at least 30 minute ( depending on battery size) while you decide what you are going to do or go . Systems like this eliminate the need for such stringent controls on fuel quality ( no I am not advocating using any old fuel but there maybe circumstances where you may have to use a lower octane fuel to top up to get home, GA pilots have done this before ) as ignition timing is adjusted to suit fuel quality while still keeping the maximum power available for the fuel used . A pilot simply cannot monitor the fuel and ignition system in the same way. I would agree that aero engines have been optimised for 3 basic operating conditiions start, full power and cruise that leaves a lot of areas in between which could be optimised (cruise for endurance ,loiter etc )In the cruise mode even this could be improved as injection and timing would be in a constant state of flux with the system always looking for the peak operating conditions adjusting for temperature ,air density cylinder head temp egt . The current series of auto engines run just such a system ( without CHT) AND a compression ratio of 13 to 1 plus and all on 91 Ron and mogas which lack quality assurance so what I am asking for on our modest compression ratio,s is not really going to be an issue

I can only base my comments on personal observations . Cherry pick and leave out the stuff that we don't want NO EGR As I see it experimental will have to do the bulk of R&D so we can move forward . Some might say that's just what Jab have been doing all along

Now this is more like it a real conversation. My working life has been generally speaking spent working on Japanese and european cars MAZDA (our dealership is Mazda and was the other two) PEUGEOT RENAULT with a fair amount of every thing else in the middle. I still spin nuts and I must say on the vast majority of the cars now worked on I just don't see the problems you have been talking about.it may have been so back in the 80 s and I can only report on what I saw but even then we had relatively little failure of emission equipment BUT it is not and has never been my intention to introduce emission equipment to aero engines (other than the infamous crank case vent system )

Nev I have heard about the infamous under the power pole stopping and stopping at other rf signal points but until someone gives me proof you know ,who what where and it can be replicated I will have to put it in the myth buster files to be conclusively confirmed or busted

Jet I don't think in my shop we ever tampered with a pcv system as we never saw problems with them that a wash and clean would not repair at the time of servicing and if some one presented a car for a road worthy with such a blatant modification it would not have passed ,EGR on the other hand was not so easy to check BUT in the cars we sold the failure was in the closed position no gasses passed to the combustion chamber. These failures are really red herrings as I am not suggesting we use them ( except for that pesky pcv)

The type of technology I really want used is the fuel injected ignition integrated systems where advance and mixture is tightly controlled and cruising at lower than 75 % would be more economical . CHT and EGT would be more even ac cros the engine operation range

Nev I know you and jet you think this is out of our reach but I have a little more confidence in the designers and technology

Found the reference to potential blockage it was by another contributor to this thread

Nev either some one has removed some of your earlier post or I read it incorrectly saying potentially blocking inlets if you did not say this pleas accept my apologies

Great discussion and I detect perhaps a slight change in ALL our posts .i have started some few weeks ago to separate oil from the bypass gasses keeping the original catch can at the end of the vent line, at the moment I have not had to add any oil to the engine and no oil is accumulating in the catch can so after some more flying I will move to the next phase of creating a drafting tube on the inlet system up stream of the carburettor (the reason for the first post).I will keep you posted. Nev A VALIANT how old did you say you were! They were discontinued in the 70s no wonder it was blocked (sounds like we are the same age) . EGR now there's a nice subject remember we are talking advancements here , that was introduced in petrol and Diesel engines to lower combustion temps and lessen nox gasses and apart from making jobs for my trade was NEVER considered an improvement . I have Never in this thread suggested we adopt some of the crazy ADVANCED ? ideas from the auto industry , but I think the word used was cherry pick to our advantage, and although I have used the auto industry as a stepping stone (and I fly behind a subaru ea81 with an Amax redrive in the avid) I am not suggesting we use auto engines as best practice ,aero engines are as you quite rightly put it the athletes of the engine world and opperate under special conditions. Having said that there are some mighty fine alloy engines coming out from auto manufactures the quality of the castings and engineering is mind blowing (makes aero engines seem crude in comparison) These engines have some demanding testing conditions placed on them,runing them fully loaded for 24 plus hrs on an engine dyno is something not done to my knowledge on aero engines. When you pull down an engine these days (and that's not as often as it used to be) they are relatively un worn and you would be hard pressed to measure the wear. Temperature control seems to be the answer here and you just cannot beat liquid cooling for that. Trotting out AUTO yes I would agree it just not realistic to grab an auto engine and lace it up to an aircraft without a properly designed redrive unit but I was never suggesting that in the first place .it takes MONEY to R&D a redrive unit and quite honestly I don't see anyone with deep enough pockets to volunteer for the job ,so we are stuck with a couple of engines to choose from, old design aero engines, new (and improved although some woud disagree with improved) jabiru engines (I like mine ) rotax who to there credit are putting some effort into some of those modern ideas I keep talking about and a smattering of other manufacturers who are at least trying . Great discussion let's keep it up