Jabiru cooling

[coinz]

This has worked for me.  Move the oil cooler to the rear of the engine and duct air to it via a side naca duct (like carby inlet), reduce the size of the lower air intake that was previously there for the engine mounted oil cooler, built a close fitting duct from this reduced inlet to the sump. Max CHT less than 140 on the ground which quickly reduces to 110 for climb at 80 knots (700-1000 fpm), cruise CHT at 100 knots 105 degrees C.  I had a similar setup on my Corby Starlet and replicated it on the Jabiru. No need for cowl skirt or big mods to inlets.  I did add a bit to the cooling ducts to prevent air from going under the front cylinders.

 

105C at cruise is about what i see after a straight in approach and rolling out,at those temps i would imagine most all problems with Jab valves and

 

heads would never have occurred,and they may have gone on to rule the Recreational engine market.

 

Too high temps was the dirth of British motorbikes,i'll always remember back in the 80's while working in the Pilbara being told that "british bikes can't handle the heat up here and just burn up",seems Jabiru are the same and it's pretty easy to overcome.

 

Keenaviator,do you have individual CHT probes fitted?

 

colin

 

 

[facthunter]

105 degees C is even colder than a liquid cooled engine operates at and well below what would achieve best efficiency. I think the motorcycle thing is slightly BS as the engine only gets hotter by the same amount the ambient changes by, as the rate of heat flow is proportional to the temp diff between the engine and what temp it's operating in. A British bike might  suffer if it already had high operating oil temps but one particular Yamaha suffered from high oil temps and wasn't even sold here. I'm only talking of aircooled motors. If it's liquid cooled it may need bigger radiators as does a liquid cooled aero motor. Merlins had only a short time to overheat in the tropics. You had to get them into the air pretty fast.   Nev

 

 

[Keenaviator]

105C at cruise is about what i see after a straight in approach and rolling out,at those temps i would imagine most all problems with Jab valves and

 

heads would never have occurred,and they may have gone on to rule the Recreational engine market.

 

Too high temps was the dirth of British motorbikes,i'll always remember back in the 80's while working in the Pilbara being told that "british bikes can't handle the heat up here and just burn up",seems Jabiru are the same and it's pretty easy to overcome.

 

Keenaviator,do you have individual CHT probes fitted?

 

colin

 

CHT probe on no. 4.  I'd prefer the temperatures to be regarded as too low and inefficient than risk dropping a valve seat.  BTW I have been running a mixture control for almost 200 hours and monitor EGT and plug colour.

 

 

[onetrack]

Most air-cooled motorbikes will overheat rapidly if they're not moving, as in sitting still, waiting for lights to change, or if you leave them idling whilst talking to someone. They rely on movement to keep the air flowing over the fins.

 

Most British equipment does poorly in high ambient temperatures, such as the tropics and Northern Australia. In fact, quite a bit of American-designed equipment also performs badly in those same conditions.

 

 

[facthunter]

I don't know  what you mean by performing BADLY.  They will all cook your legs but a big Harley Lead sled will only run  20 degrees hotter on a 40 degree day than a 20degree day.  Half of them pull a little caravan /tent/trailer.. Plenty on the Nullarbour, as well as north of Adelaide.  Nev

 

 

[Thruster88]

CHT probe on no. 4.  I'd prefer the temperatures to be regarded as too low and inefficient than risk dropping a valve seat.  BTW I have been running a mixture control for almost 200 hours and monitor EGT and plug colour.

 

I have often thought Jabirus would be better off with mixture control. Be interested how you did it and general operating procedures, rich or lean of peak at cruise etc.  

 

 

[facthunter]

Running Jabs lean was where the problem started. Lean  mixtures behave as if they are lower octane and have less cooling due to reduced evaporation of fuel and an "oxidising" combustion situation will remove more of the oil from the cylinder walls and be more likely to backfire into the inlet manifold. Last thing it would try with a Jab. They actually lowered the compression ratio in them and retarded them as well  IF they need that they are a BIT critical.  Nev

 

 

[coinz]

Most air-cooled motorbikes will overheat rapidly if they're not moving, as in sitting still, waiting for lights to change, or if you leave them idling whilst talking to someone. They rely on movement to keep the air flowing over the fins.

 

Most British equipment does poorly in high ambient temperatures, such as the tropics and Northern Australia. In fact, quite a bit of American-designed equipment also performs badly in those same conditions.

 

Yes i agree with the American HD's being affected too,i bought a new '86 evolution new,cruising back from Fitzroy crossing at 140k's arrived at Karratha

 

with a ticking noise from the rear cylinder,which it had from then on.This is probably what Bruce is experiencing,radiated hot air flow heating rear cylinder,i suggested he try increasing air flow that side but he was more into equalizing Ram air pressures,ie increasing pressure LHS to experience a cooling effect.

 

 

[coinz]

I have often thought Jabirus would be better off with mixture control. Be interested how you did it and general operating procedures, rich or lean of peak at cruise etc.  

 

Probably no doubt mixture control would be an improvement but as Nev alluded too,who would know what's best for a Jab.The bottom of my 230's Fuse quickly browns after cleaning,i don't know if it's oil or rich mixture but it would be good to know it's not running too rich.The auto mixture is good,and easy to see why it was fitted for Recreational flyers but surely manual mixture control by somebody competent is superior.

 

cheers

 

colin

 

 

[coinz]

CHT probe on no. 4.  I'd prefer the temperatures to be regarded as too low and inefficient than risk dropping a valve seat.  BTW I have been running a mixture control for almost 200 hours and monitor EGT and plug colour.

 

I'm with you 100%,a dropped valve is my biggest concern,and i'm only new to Jabirus and that has been brought on only through reading about that issue,and through personal experience with overly hot engines testing design limits.

 

Anyone know what uncowled radials run CHT wise,must have been pretty cool at high altitude,in minus temps.

 

cheers

 

colin   

 

 

[facthunter]

 The dropped valve is a genuine concern. There is away to check valve guide wear with just the covers off but if the valve is overheated fine cracks appear in the stem and you only confirm that by stripping them out and inspecting them. If you suspect that has happened replace them They are not expensive. The earlier non hydraulic lifters( solid lifters/ Manual adjustment,) you get an indication of stretch or valve recessing (they are not thes ame) that a hydraulic lifter masks as it self adjusts until it can't anymore. Nev

 

 

[jetjr]

Yeah 100 deg cht is a low number, you need higher than this to get oil temps up Id have thought

 

But number isn't that critical so long as they are even and you have some idea what variation from actual cht

 

Two now talked about good results but none saying what was done?

 

 

[Bruce Tuncks]

some confusing results today..

 

Firstly, the deflector on the front RHS made things worse! This was put there to deflect upgoing air into the duct and thereby increase the duct pressure.  The manometer showed that with this in place, there was 50mm of LESS  pressure  compared to the LHS duct. When it was removed, the differential dropped back to about 12mm. So the deflector made the RHS duct pressure less not more.

 

I thought the deflector was quite good. It extended out about 20mm and curved gently to suit the contours of the upper cowl . I'll post a pic tomorrow when I retrieve the camera.

 

BUT the temperatures didn't follow the duct pressures as they should have, with the higher duct pressure after removing the deflector giving more cooling.

 

On the first flight, with the deflector in place, the coolest no1 was 136 and the hottest no4 was 156C, that is a difference of 20 degrees.

 

On the second flight, with the deflector removed, the coolest was 142 and the hottest was 164, a difference of 22 degrees.

 

Ambient was 25C , and this probably increased 2 degrees between the first and second flights.

 

I'm stumped. Maybe Ken is right and I'm chasing a small signal in a noisy situation.

 

 

[Yenn]

I would try putting an aluminium deflector under cylinders 2 and 4. Shaped to follow the contours of the fins and ending just ahead of No2 lowest point and just astern of No4 lowest point. The shape would be like W with the two outer legs cut short and the central apex up between the two cylinders at their closest point. A piece of wire would hold it in place easily. That is going to get air round the lower part of each cylinder. Don't let air go down between the cylinders without it being inside the duct. You could also do a similar thing above the cylinders, but only cover 15 degrees of the curve, so that air can get between the deflector and the barrel, via the fins.

 

 

[Paul davenport]

In order to get my cht temps down on the 230 I discovered that closing up the air gaps only raised temps and in my case allowing the air to pass through the plenums by opening up the rear cylinders plenum ,allowed air to flow to the rear and by default cool the other cylinders. Also closing the large gap between the rocker covers with a plate making the travel down through the fins rather than sideways helped. I made plates that drop down between the cylinders on the crankcase side again making air drop through fins again carrying away heat and making the fins work to max efficiency, filling in the under barrel with butterfly deflectors reduces the volume of air that can carry away heat, it will however even out your temps raising cool ones . The exit ramp and opening size on my 230 were too small,  modifying the ramp and increasing the opening size helped. It is indeed a black art

 

 

[jetjr]

Jabiru and CAE worked with "gull wing deflectors", they sat in valley between cylinders, Jabiru placed on top to shift more air to rear cylinders on 6 cyl, they were later deleted (actually was a direction to remove)

 

I fitted these under cylinders and it stabilised temps but no reduction

 

CAE supplied larger versions under cylinders std.

 

They also fitted shields to CHT temp probes to preventing air blast cooling and some high quality probes to try to sort out erroneous readings. CAE reads hotter (125 -137 in cruise, 150 on take off) but I think its just closer to reality, Previous Jab setup read probably 10-15 deg cooler and moved around much more in phases of flight.

 

Which is a worry when you consider some 150+ temps being seen with std Jab supplied probes

 

 

[Yenn]

Pauls remark about air getting past the rocker covers is a good point, it could be an idea to try to restrict any air going down the face of the rocker covers, but that would depend upon what type of plenum you have. My J220 doesn't pass air down there, it is all via the cylinder head fins.

 

 

[Keenaviator]

Here are a few photos of my under cowls set up. I'll get photos of the sump cooling duct later...

 

 

[Paul davenport]

I suspect but I can only find limited information on the subject, that the shape of the head cooling fins tapering from the base to the outer edge has a real effect on CHT. A mates 230 has rounded ends on his cylinder head fins and his motor cooled better than mine with out some of my mods ,and better after I made some mods to his. There is a real difference when comparing his heads to mine. When I get the chance I will modify the hottest head on mine and see if it has any effect.  All aircooled motors that I have looked at (funny how you notice these things when you really look) have rounded ends to the fins. I have questioned Jab about this bit cannot get any definitive answers

 

 

[Paul davenport]

Spotted this unusual cooling mod done to a (I think) Extra aerobatic aircraft, at Oshkosh  had something todo with cooling but couldn’t find someone to explain it 

 

[onetrack]

Interestingly, there's a Wartime report on the 'net, whereby the Aircraft Engine Research Laboratory, a division of NACA, carried out engine testing during July 1942, with regards to improving aircraft engine cooling, using copper.

 

One of the thing they found was an 0.008" thickness of copper plating on cylinder fins increased the cooling ability by 11%. That's quite a substantial increase, and one that could be done to any engine fins.

 

Copper-plating aluminium is quite feasible, it just requires a several-stage process to ensure adequate adhesion of the copper.

 

The lab also tested pure copper fins on a steel barrel of a Wright C9GC (R-1820) and got an 84% improvement in cooling capacity.

 

 

[Jabiru7252]

I'm no expert but aluminium and copper are 'dissimilar metals' and don't like contact with each other, leads to corrosion. I discovered this when building antennas as a kid. So, I wonder how they did it.

 

 

[skippydiesel]

I'm no expert but aluminium and copper are 'dissimilar metals' and don't like contact with each other, leads to corrosion. I discovered this when building antennas as a kid. So, I wonder how they did it.

 

The exclusion of air and electrical current will allow most metals to coexist.  Bonding (chemical)/plating (electro)/painting (adhesive) may achieve this end.

 

 

[onetrack]

Aluminium needs to have its normal aluminium oxide coating removed, and a surface amenable to copper deposition prepared.

 

This is quite a complex process, and usually, some other coating such as nickel is used as the initial coating, and copper is then deposited onto the nickel coating. 

 

 

[facthunter]

 It's usually the other way around. Copper is done first  On the heads they would be relying on the conductivity and an .008" thick layer is not a lot  of area, if you consider the cross section. BRONZE (copper-tin) heads were often used ( but are incredibly heavy) where heat must be removed quickly, like between the exhaust valves of 4 valve heads. Bronze heads don't like leaded fuel and the seats last no time at all. The DeHavilland Gypsy 1C motors had these with no inserts for the valves. Nev