Jabiru cooling

[Old Koreelah]

Where is old K involved in this conversation?

 

Left Right Out!

 

I did a little bit of experimenting on my own installation a few years back, partly inspired by Dafydd Llewlelyn's work testing the CAMit engine. Like much in life, I learned just enough to be dangerous. Based on my experiences, I suggested that in-flight cameras should record all the data, so the pilot can concentrate on what he should be doing.

 

 

[Yenn]

Why I asked that question is because I suggested something and others said it came from you Old Koreelah.

 

If my ideas don't work you will get the blame!

 

 

[Old Koreelah]

No worries,Yenn. I'm used to getting the blame; I'm married.

 

 

[Keenaviator]

I made quite a few changes to my cowls and oil cooler position which have resulted in cool CHTs.  CHT on number 4 (generally the hottest) gets to about 130C on taxi  then drops to about 105 or less in the air.  I climb out at 80-85 knots @ 700fpm or better. Laurie

 

 

[dlegg]

I just taped some cardboard on the bottom of my cowl when testing the lip, easy to do....

 

 

[Bruce Tuncks]

Keenaviator, thanks for your reply... please tell us more about what you have done. 

 

Just today, I have put a 32mm ribbed hose between the 2 ducts, as suggested by oldK  who was right about how the difference between the RHS and LHS ducts should be measured. The measurement showed 45mm of water head difference.

 

Tomorrow I will fly with a connecting duct in place. My hope is that it will equalize things .

 

 

[Keenaviator]

Keenaviator, thanks for your reply... please tell us more about what you have done. 

 

Just today, I have put a 32mm ribbed hose between the 2 ducts, as suggested by oldK  who was right about how the difference between the RHS and LHS ducts should be measured. The measurement showed 45mm of water head difference.

 

Tomorrow I will fly with a connecting duct in place. My hope is that it will equalize things .

 

Next time I'm at the hangar with the cowls off will take photos outlining what I've done.  The balance scat hose between the cooling ducts sounds like a good idea too. The main thing I did was reduce the pressurising of the lower cowl be moving the oil cooler to the rear of the engine, ducting air to it from another vaca duct on the right hand side of cowl. I can control this air to the oil cooler from the cockpit - monitoring oil temperature. 

 

 

[Old Koreelah]

Keenaviator, thanks for your reply... please tell us more about what you have done. 

 

Just today, I have put a 32mm ribbed hose between the 2 ducts, as suggested by oldK  who was right about how the difference between the RHS and LHS ducts should be measured. The measurement showed 45mm of water head difference.

 

Tomorrow I will fly with a connecting duct in place. My hope is that it will equalize things .

 

Bruce I'm blushing get the credit for such a good idea, but it wasn't me who suggested this.

 

 

[Thruster88]

Keenaviator, thanks for your reply... please tell us more about what you have done. 

 

Just today, I have put a 32mm ribbed hose between the 2 ducts, as suggested by oldK  who was right about how the difference between the RHS and LHS ducts should be measured. The measurement showed 45mm of water head difference.

 

Tomorrow I will fly with a connecting duct in place. My hope is that it will equalize things .

 

Bruce I hope this works for you but the turbulence, drag caused by the 32mm holes in the duct might reduce total airflow. Just a thought. 

 

 

[Yenn]

The turbulence caused by the holes would be minimal as there is flow through them from low to high, but should be little flow across them.

 

I wait to hear what happened.

 

 

[Bruce Tuncks]

Today I tried the ribbed hose connecting the 2 ducts. I took a picture of how it looks.

 

I reckon it worked well! The manometer ( measuring between the ducts ) showed about 12mm difference, well down from the 45mm difference before the connecting hose.

 

The day was cool, ambient=18 degrees and overcast.

 

On climb, T1=128 T3=139 ( the cooler RHS)

 

T2=153 and T4=151 ( the warmer LHS )

 

There are a few other things to do...

 

1. do the test again on a hotter day... adding 17 degrees for a 35 degree day puts that T2 at 170 degrees.

 

2. putting a deflector in front of no1 cylinder to stop it being so cool

 

 

[Bruce Tuncks]

Sorry Yenn, I must have had a senior's moment when I attributed your good idea to Old K. But your and old K's  planes look very similar on your icons, maybe this is why I mix you up sometimes. Anyway, thanks for the good suggestions. And  old K is no slouch either. I'm in my 70's here and guess you guys are close behind, age-wise that is.

 

I know I am being real fussy trying to get the temperatures all exactly equal, but it is fun and I reckon interesting too. I love it when a bit of real progress happens.

 

 

[Yenn]

Bruce you are just a young bloke. I hope you get it all where you want it.

 

It appears that the left bank always runs hotter than the right with Jabs, probably something to do with the rearward position of the inlet.

 

Good cooling depends upon the air flow being close to the fins. Anywhere air can flow without going between the fins reduced the efficiency. Lycomings usually have ducting close to the fins beneath the cylinders to stop air exiting directly downwards and force it around the lower part of the cylinder.

 

 

[Bruce Tuncks]

Darn, its a lot easier to make a cylinder run hotter than cooler.

 

My latest try at 29 ambient showed T1=145 (still coolest ) and T4=167. Delta T = 22C

 

Comparing this with the first test with the extended "eyebrow" on the front cowl RHS entry, with 4 degrees added to adjust for the extra 4 degrees of ambient:

 

T1=140 (coolest ) and T4=165.  Delta T=25C

 

Not much difference huh.  I have put a spoiler-deflector in front of no4 ( just a small bit of backwards-sloping sheet metal in front of the cylinder ) and there is that pipe joining the LHS and RHS ducts.

 

The discouraging thing is that the hottest no4 has not got cooler.

 

If that LHS could be made to run as cool as the RHS, then there would be no problems on climbout unless the day was really hot.

 

So there is the skirt to consider, but first I'm going have another go with that eyebrow entry extension. Maybe that was discarded too quickly. And there is also the notion of another scoop to force air into the LHS duct from the top. This scoop would be glassed to the LHS duct and poke up through a matching hole in the top cowl.

 

 

[jetjr]

be aware of air blast onto sensors

 

Fitting CAE wind shields around probes raised temps a bit

 

A slight block to cool side will help more get sucked into warm side,

 

Id prefer slightly high temps and even under limits of course

 

 

[Old Koreelah]

You lucky buggers, being able to actually fly and do some testing.

 

We've had months of crap weather. Dust, smoke, near-constant wind. 

 

On Saturday morning for the first time in months, I got to taxi my baby around for half an hour, but you couldn't see the other end of the strip thru the smoke haze.

 

 

[facthunter]

Use less upper cylinder lubricant. Nev

 

 

[Bruce Tuncks]

No upper cylinder lube in there for these tests Nev. But I have started using some Moreys, it goes in when I remember. How could doing that  raise the CHT's ?

 

Here's another idea I have wondered about: Spraying a very small and fine water spray into the  inlet on a hot day. It would be a bit like flying through a small rain shower.

 

I looked this up on account of it seeming to be a crazy idea, but apparently a Reno winner has been doing this for years.

 

Now the water can be injected into the inlet manifold, sprayed onto the oil cooler, or sprayed onto the cooling fins of the cylinders.

 

The latent heat of evaporation would sure cool things down, you would want a very fine spray I guess and work up from a tiny flow rate at the start.   

 

 

[facthunter]

That was a bit TIC to OK Bruce re the runway visibility. Water plus some methanol works well . Been used on many motors including turbine.. I'm not suggesting you do that  to your plane for obvious reasons.  It's injected separately after the power is  set at full throttle and will cool the manifold as well the more methanol used. Nev

 

 

[onetrack]

I'm old enough to remember from many decades ago (the 50's), when water injection units for cars were advertised in the Modern Motor magazine to fit to cars and trucks. 

 

There were imported water injection units and locally-made units. Most used a mixture of methylated spirits with water to give the required alcohol content.

 

They were popular due to the inadequate octane rating of the petrol of the day, causing detonation or combustion knock ("pinging" or "pinking") due to engine compression ratios rising faster than the oil companies could raise the octane rating of petrol. That problem brought about the division of petrol into "standard" grade and "super" grade, which many of us older blokes can probably still recall.

 

The water/alcohol injection systems worked well enough to a certain degree, but the problems were corrosion of the components, corrosion of bores because the water was still being sucked in on engine shutdown, and trying to get an even flow rate, according to throttle opening.

 

I have little doubt if someone wanted to revive the idea, with brass, stainless, or plastic components, electronic control of injection rate, and shutdown of the water flow as the ignition was cut, it would probably be a winner today.

 

https://trove.nla.gov.au/newspaper/article/206087995

 

 

[facthunter]

Don't forget over a litre of water is produced by burning a litre of petrol, so water is there anyhow. That's taken care of by running the engine at the right (not too cold) a temperature. One other benefit is the engines stay almost free of carbon deposits with water injection. Nev

 

 

[Yenn]

To get the best from the airflow you need to make sure it is going between the fins, if some can get from the upper high pressure area to the low pressure underneath, without being close to the fins, it will not be an efficient coolant. It should be possible to bend some aluminium around to closely follow the tops of the fins and keep the air closer. rather like a curved V shape, both above and beneath the cylinders.

 

It seems to be a fact that No 4 is always the hottest cylinder on a 2200 Jab.

 

 

[jetjr]

Might be wrong but reckon Bruce is talking about water mist on outside of cylinders, not water /meth injection

 

Gets used in some road vehicles but dust turns to mud, bakes on and clogs things up. Aircraft dont really have water proof electricals etc

 

 

[Bruce Tuncks]

Yep, I am talking about water mist on the outside of the cylinders. I wouldn't think you would use so much that there was any liquid got past the cylinders, you would only use the minimum amount on account of the weight and, as you say, the mess.

 

At one atmosphere pressure, any surface over 100 C would immediately turn any liquid to steam.

 

Well the idea is so obvious that it must have been tried, so I looked it up and found that it was used at Reno, but the Reno guy used it on his oil cooler and not on the cylinders, at least that is what I think. There was no mess as it all evaporated to dryness, nor was there a need to use only distilled water.

 

I can imagine a trigger-spray type nozzle fed by an electric pressure-pump. But if the idea is sound, why is it not routinely used? 

 

Air-cooled motor-bikes for example.

 

On the Jabiru, the water spray would only be needed on the climb.

 

 

[turboplanner]

Because it's easier to use the fuel jets.