Getting simplicity back into the Jabiru engine

[Jabiru7252]

Nature is pretty smart. The image shows the lining in our intestines. The 'villi' greatly increases the surface area allowing more nutrients to be absorbed. Using Nano technology we do similar stuff with electronics so we can store huge amounts of energy in batteries and capacitors. It does seem reasonable that having the inside of the sump lined in a similar fashion, one would be able to draw more heat from the oil therein. However, not being a scientist's arse there could be something I'm not seeing. 

[facthunter]

Oil will carry heat away if it touches the material and there's flow to somewhere cooler. If you have fins too long and too finely spaced they get less efficient unless there's a close fitting cowl and the fluid is forced past it.. To cool pistons in supercharged aircraft  engines there's often a copious JET of oil squirting on them. A flowing fluid takes the path of least pressure drop.  Oil is not being agitated much in a sump . That's why it gets sludge on the bottom, and that doesn't help heat transfer.  Same with a dry sump set up. It's mainly a reserve of oil to make sure there's always enough.  IF your remote tank only gets warm  and not stinking hot there's no need for more oil or a cooler.    Some radials have large oil tanks (and a facility to transfer oil during flight ) as they consume a lot (sometimes)..  It's nothing to do with keeping the oil cool.  Once it's hot the ability, for the heat energy to escape from the hot parts is what matters . You must have an equilibrium state or the power setting will be for a limited time..  The engine itself is the main heat sink. Some car engines did have too little oil  but they also had no real effort applied to deal with long trips at highspeed on hot days and many had mud and grunge all over the engine and oil sump, and a marginal sized Radiator..Nev 

[Kenlsa]

My Colt has a 6lt capacity but has a running minimum of 2lts.

at a cruise rpm of 2300, mass of 110kg, sump of 6/2lts, compression in the 6’s,  no cooler (or filter) Lycoming has got the parameters right for this aircraft, speed and longevity.

 

But it takes many $ and time to get it right. Change just one thing, be that speed/cruise/ climb, weight, prop etc, it all starts again.

 

 I think Jab has it right for a 2200 @100kts in a slippery airframe and a 3300 @120kts.  All this with only a relatively few engines built compared to others.

 

Ken

[onetrack]

Jabiru7252 - I personally believe you're comparing oranges to apples by trying to introduce intestines operations into a discussion about engine oil cooling. For a start, the intestines are made of organic, living materials, and engines are built from inorganic, non-living materials.

 

The former are constantly growing and changing and interact internally with possibly up to 200 other organic chemicals to carry out their mission.

The latter do not grow, and interact only on a limited basis, externally, with other inorganic chemicals. The chemistry and physics applicable to each, are very different.

[RFguy]

intestine image looks like a pin-fin heatsink.

 

same principle. maybe.

[RFguy]

pin-fin heatsinks work by being relatively insensitive to orientation, airflow, generate their own turbulence with forced flow.... useful for consumer electronics stuff. and there is lots of surface area, 

 

the pins are long, so the top half of the (aluminium sink) pins doesnt do very much, but if you are not limited on height or space, why not....

the pure copper ones are the best- better conduction up to the top of the pin , so more of the pin does work (higher thermal conductivity) 
 

fairly interesting : https://www.diva-portal.org/smash/get/diva2:24268/fulltext01

page 12 onwards. or start at page 34

or, for something lighter, you might prefer 

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiuwtTPkIbuAhWjwTgGHRqwCF4QFjAJegQIEBAC&url=http%3A%2F%2Fwww.iieta.org%2Fdownload%2Ffile%2Ffid%2F4193&usg=AOvVaw2SUrAlh8Qkk7s-WYWMainw

 

 

 

Edited January 6, 2021 by RFguy

[Yenn]

What you are doing if the engine is built like the stomach is transferring oil heat to the engine sump. You then have to transfer it to the surrounding air from the aluminium sump. Hence fins, which some sumps have. An oil cooler is far more efficient.

[RFguy]

yes. an oil cooler has the advantage of flow.  sump is just a random sloshing place. 

 

[facthunter]

Rubber pipes, pump&drive and a weak (structurally) easily damaged, heat exchanger. Who likes that IF you can do without? Anyhow it's all eventually in need of speed through the air to dissipate the heat . The trouble with aero engines is they need the most power when they have the least speed. Take-off and climb. IF the engine can handle that well the rest should be easy, but it's a wide range of conditions..Some cockpit controlled adjustment would seem to be required. Nev

[onetrack]

All cooling systems that encounter a wide range of temperatures need some form of airflow control or oil flow control. A simple oil thermostat is a wise investment.

[Yenn]

The big advantage of oil cooling is that when you take off your oil is usually at a low temperature at the start of the roll and there is a fair amount of oil to heat up. Of course if you fly a Rotax and spend the usual 20 minutes pre take off warming the oil, you are negating that advantage.

My Jab is usually airborne in about 4 minutes from start up and no problems. Over 1000 take offs like that.

[kgwilson]

I take a little longer to warm my 3300A & don't start to move till the CHT temperature is at the start of the green zone but before the oil temperature gets to 50 deg. After taxi the oil will normally be at 40 deg or more before I do the runup. I always wait till the temperature reaches 50 deg before applying full power for takeoff and by the time I get to 500 feet the temperature is about 70 deg eventually settling around 90 deg. Original Jabiru operating instructions were 50 degrees before applying full takeoff power but in the latest update this has been reduced to 40 degrees.

 

My engine has got better with age. I used to top up the oil a couple of times during run in on mineral oil for the first 25 hours and also for the next 50 hours with W100 plus. Also when pulling the prop through compressions were a little uneven. Since then everything has smoothed out & I do not top up at all between 25 hourly changes and the oil remains relatively clean, the only disadvantage of which is, it is hard to see the level on the dipstick. I am just doing another 50 hourly and annual at present & got the least amount of condensate out of the oil catch bottle (about 15 ml) ever.

 

As I see it the moral of my example is ensure adequate cooling, operate and maintain your engine as per the manufacturers recommendations and you will be rewarded in spades.

[facthunter]

The jab 4 and the Corby seem like a good match. Your speed helps the cooling and your engine is not over propped.  Aircooled engines have larg(er) piston clearances and it's better to get near to normal running clearances  to stop "barrell facing" rings which leads to more blow by. Engine all over temps are more stabilised also (less stresses) if you don't roar away  too cold .Nev

[Yenn]

The Jab 2200 pre 4 is perfectly good for the Corby. The 1600 was just OK, but a bit short on power on hot days.

[BrendAn]

Old thread but interesting.

I am thinking I might tape over the cooler on my j2200, the temp needle barely makes the bottom of the green ever.  The cooler is also mounted flat across the front of the sump so I wouldn't think there is much airflow through it. On the xair the engine is fully exposed to the air.

If I can remove the cooler after testing it would get rid of potential oil leaks.

[kgwilson]

Have you had the gauge tested for accuracy? The first thing a Lame will do when looking at cooling issues is check the gauge.

[BrendAn]

50 minutes ago, kgwilson said:

Have you had the gauge tested for accuracy? The first thing a Lame will do when looking at cooling issues is check the gauge.

We did a 50 km flight this morning and oil temp went to 90 and stayed there so I will leave it as is. It is  a hot day , I have never seen it come up to 90 before . Cooler did its job.

[BrendAn]

1 hour ago, kgwilson said:

Have you had the gauge tested for accuracy? The first thing a Lame will do when looking at cooling issues is check the gauge.

No ,I haven't checked the gauge. I am sure it works fine. I don't have any issues , its just low oil temp on cold days. I usually only run it early in the day.

[tillmanr]

Have you tried using hard sponge like industrial flooring with holes punched into it. A friend has a number of them with different sized holes punched into them. Different air temps he changes the blocking screen. The airflow holds the screen against the oil cooler. Simples. 

[skippydiesel]

Everyone seems to go for the air inlets (when reducing flow) - On my last aircraft, I found it easier and very effective, to have Winter & Summer fixed cowl flaps. The Winter flap, went on when day temperatures consistently remained below 25C and off when temperatures consistently went above 25C. As I had an overcooling situation, in the warmer months, I replaced the large Winter flap with a very much smaller Summer version.

 

The flaps were just shaped Aluminium sheets, held in place using small screws/washers/lock nuts. The larger flap, had two small  aluminium angle stiffeners/ribs pop riveted to the inside, to reduce the chances of flutter.

 

I probably went through three test versions of each to get the right size/air flow restriction.

[tillmanr]

Entirely up to you skippy. The nature of our sport. 

[BrendAn]

25 minutes ago, skippydiesel said:

Everyone seems to go for the air inlets (when reducing flow) - On my last aircraft, I found it easier and very effective, to have Winter & Summer fixed cowl flaps. The Winter flap, went on when day temperatures consistently remained below 25C and off when temperatures consistently went above 25C. As I had an overcooling situation, in the warmer months, I replaced the large Winter flap with a very much smaller Summer version.

 

The flaps were just shaped Aluminium sheets, held in place using small screws/washers/lock nuts. The larger flap, had two small  aluminium angle stiffeners/ribs pop riveted to the inside, to reduce the chances of flutter.

 

I probably went through three test versions of each to get the right size/air flow restriction.

Good Idea but my ultralight has the engine fully exposed not In a cowl.

 

[skippydiesel]

2 hours ago, BrendAn said:

Good Idea but my ultralight has the engine fully exposed not In a cowl.

 

Well there you go - I apologise for my assumption  that your aircraft has a cowl - I see so few aircraft with open to air engines, in fact I can't remember when I last saw one, must have been many years ago. I guess you have little choice, other than to restrict airflow for each heat exchanger, if you want to raise temperatures.

[BrendAn]

10 minutes ago, skippydiesel said:

Well there you go - I apologise for my assumption  that your aircraft has a cowl - I see so few aircraft with open to air engines, in fact I can't remember when I last saw one, must have been many years ago. I guess you have little choice, other than to restrict airflow for each heat exchanger, if you want to raise temperatures.

[BrendAn]

15 minutes ago, skippydiesel said:

Well there you go - I apologise for my assumption  that your aircraft has a cowl - I see so few aircraft with open to air engines, in fact I can't remember when I last saw one, must have been many years ago. I guess you have little choice, other than to restrict airflow for each heat exchanger, if you want to raise temperatures.

There are plenty of ultralights still around . Mine is a 2004 model but it is still available new.