Cooling Plenum

[racaldwell]

Has anybody tried a one piece plenum? I am more familiar with them than a separate plenum for each side. (I made one for the RV-6 in '99) It seems to me that the increased volume inside the plenum would slow the air more than individual plenums and the slower air would increase the pressure. As seems that the uneven airflow into the intakes caused by prop swirl would even out for a better average airflow down thru the cylinders. The two piece plenum seems to be all I see on Jabs whereas one piece plenums are very common on lycomings. Just curious if anybody knows why that is.

Rick Caldwell
Xenos 0057
Cammit 3300
RV-6 985 hrs & climbing

[Kai]

Rick,

A traditional cooling plenum on the Jab like the ones we see on LyCons is not that uncommon. As you say the genaral consensus is that it slightly improves cooling and evens out cht's. However, it is a lot to work to properly fence in and seal off everything, and- as Jab supply the cooling ducts as standard, and Sonex has developed their own ducts, many elect to go down that way.

Thanks
Kai

[peter anson]

I made a traditional plenum chamber for my 3300.

I think it works well and was no more difficult to make than many of the other fiddly changes that you'll make as you build your aircraft. I was hoping for more even temperatures but still found that #3 and #5 cylinders ran hotter than the others so ended up with a dam behind #3 while #5 gets most of its cooling air from the LH intake. The engine runs cool, almost too cool at times and I have recently started using a hotter grade spark plug - D8EA, which seem to be working well. Temperatures are pretty even on cruise.

Peter
Sonex 894, 362 hours

[Kai]

Peter,

What kind of prop are you using? Exact make, type etc.

And what kind of performance does it give the Sonex with the 33A?

Thanks
Kai

[peter anson]

Hi Kai - hmmm, is that a form of poetry? That photo is from about 4 or 5 years ago and the prop was an expensive failure called the Bolly Duralite. They were trying to make a ground-adjustable carbon fibre prop that had the gentle damping characteristics of a wooden prop. It worked OK but unfortunately the hub had the structural integrity of warm butter and I replaced it with a Prince. I have threatened to resurrect the Bolly with an aluminium hub and even bought some 7075-T6 plate to make the parts but unfortunately it's a bit beyond the capabilities of my small lathe, small milling machine and small machining skills. It performed about the same as a Sensenich.

Peter

[racaldwell]

Thanks for the response, guys. Something else to think about. Anybody else out there with a singular plenum on your Jab?

Rick Caldwell
Xenos/CAMIt 3300 underway

[fastj22]

I’ve gone with a plenum and have found much lower temps and balanced CHTs on my Jabiru.

[racaldwell]

Hi John,

Could you post a picture of your plenum? Did you have to make some asymmetrical parts to even out the cooling like Peter did?

Rick C.
Xenos/CAMit underway

[Kai]

Hi Kai - hmmm, is that a form of poetry? That photo is from about 4 or 5 years ago and the prop was an expensive failure called the Bolly Duralite. They were trying to make a ground-adjustable carbon fibre prop that had the gentle damping characteristics of a wooden prop. It worked OK but unfortunately the hub had the structural integrity of warm butter and I replaced it with a Prince. I have threatened to resurrect the Bolly with an aluminium hub and even bought some 7075-T6 plate to make the parts but unfortunately it's a bit beyond the capabilities of my small lathe, small milling machine and small machining skills. It performed about the same as a Sensenich.

Peter

Peter,

As long as we can leave out the 'Hai Kai', I'll live with the poetry :-) And judging by the products on your website, I must take exception to your 'small machining skills'......

I have recently heen informed that Sensenich has come out with a GA composite prop especially tailored for the 120HP UL-P/Sonex combo: I thought maybe you had got your hands on one of these.

Just out of curiosity- is there anything going on Down Under concerning the Jab oil pressure relief valve? Up here, on the other side of the globe, many of us are living in constant fear of a split oil filter and/or oil cooler; the reason being the pressure spikes generated in the system by the lunatic behaviour of said relief. Not to mention the replacement program some have to run for the VDO oil pressure sender, which packs in proper function with depressing regularity :-(

Thanks
Kai

[peter anson]

A problem with the pressure relief valve is news to me. Looks like I have to do some reading. There was a problem found about 8 years ago with pressure pulses from the oil pump thought to be causing oil cooler failures. The Jabiru solution was to change the oil pump porting but I would assume that newer engines than mine would be supplied with the modified porting. I have never seen the pressure go above 85 psi. I have had to replace the oil pressure sender once. Well, twice really, because it didn't work from new, but my engine had been in storage for about 10 years.

Peter