Jabiru cooling

[Paul davenport]

I have just looked at my knife sharpener with a high speed steel blade looks like it might do the trick 

 

 

[jetjr]

Thanks jetjr, yes I did that sb years ago. They supplied a moulding which replaced part of the front lower cowl leaving more room for the oil cooler and actually lowering the drag.

 

Yes, not that one, theres one regarding rear exit of cowl. they have system for estimating how bad overheating is and then 2 or three different cowel exit mouldings

 

https://jabiru.net.au/wp-content/uploads/2018/05/Engine-Cooling-JSB016-1.pdf

 

Theres a similar one for J230 that discussed Gull wing baffles removal and theres pics of std ram ducts going deep into cylinders like pictured before

 

The plates joining heads on the outside - preventing air leaks, were also tried by CAE and crack after a short time. Cylinders must move independently it seems

 

 

[facthunter]

 Nearly all  cowl/engine seals rely on a rubber seal strip bent to the pressure side to form about the last 20 MM or so. Between the heads you might be alarmed how much the cylinders move if you want to connect them with thin sheet.  Nev

 

 

[Yenn]

That doesn’t apply to Jabiru, which have two separate plenum. Nor would it apply to any other plenum equipped engine. Plenum can be sealed to the cylinders with RTV silicon.

 

 

[facthunter]

Don't count on it, if you don't allow for some flexing and movement. Separate cylinders are always a source of concern where they are linked . Twin siamesed heads and triples like a Corvair are NOT the  answer. It's just easier to produce and service. You get a way with it at low(er) outputs, but when you push things you need it "more Better" to coin a phrase .. Nev

 

 

[Paul davenport]

I just mounted my plates with silicone , it allows for flexing without cracking and the silicone rubs off when you want to remove it ,use as much or as little as you want. To date they have not ever come off . The inner cylinder baffles just drop in allowing for easy removal and refitting of plenums . Also for those ac fitted with heaters look at blocking off the heater air inlet in the summer as it dumps air in the low pressure area of the cowling, I made a simple nylon plug fitted with an O ring and inserted it into the hole in the cowling . I have also blocked off the two holes allowing air to bleed into crank case past the barrels at the front of plenum chambers. Like I said still the same axe

 

 

[mikeavison]

Sorry I haven't read all six pages of replies so perhaps someone has already said this.

 

One bank of cylenders is set back by one cylender width compared withe the other (since the pistons are all in a line).

 

On our plane the ducts are not different to take account of this, neither is the shape of the the cowling. So when we got it there was a gap between the cowling and the duct which was much bigger on one side than the other. CH cooling was not great. We fabricated a short extension to the ducts so that the cowling meets the duct on both sides now. This improved CH cooling greatly.

 

I hope this helps

 

Mike

 

 

[Bruce Tuncks]

Mikeavison, I reckon they made a mistake with your ducts.  In all the ducts I have seen, the LHS ones have been longer to allow for that cylinder set-back. You sure did the right thing fixing this on your plane.

 

 

[Bruce Tuncks]

 

 

[Bruce Tuncks]

Yesterday ( ambient 27 degrees ) the temperatures were more equal than ever before, much to my surprise. All I did was to remove the tape which had been sealing off the inch-sized hole in the LHS duct ( the higher-pressure one ) and the subsequent flight showed temperatures amazingly even.

 

T1=143, T2=141, T3=143, T4=140.

 

This reinforced the idea that air-cooling is indeed a black art.  I have no good ideas as to why this happened or if it will repeat itself, but of course I hope it will stay like this. I was, as usual, climbing carefully at 80 knots and could have got higher temperatures by trying.

 

Looking into the intake of the LHS, you can see the vacuum cleaner hose which goes to the RHS, and adjacent to the vacuum cleaner hose is the hole which is now uncovered. You can also see the small deflector which partially shields no 1 cylinder from cooling air.

 

[Old Koreelah]

An intriguing story, Bruce. I'm a little confused about your LHS- as seen by pilot from behind, or as seen from in front, as the pic suggests?

 

 

[Bruce Tuncks]

Good point Old K. Yep, I have used LHS as if looking from the front. I should have used port and starboard. What I have called the LHS is actually the starboard side. Sorry if I confused anybody.

 

Actually, this cooling business is confusing enough without any help from me.

 

 

[Old Koreelah]

Bruce you seem to have had success at the"black art". Well done.

 

That's a blurry big hole in your cooling duct- even bigger than the standard one. It always amazed me that Jabiru would divert any of that precious cooling air. 

 

I closed mine off to ensure all the air coming in went past the fins and ran separate scat hoses to cool the coils.

 

I've noticed on the Jab/CAMit forum that some people run separate air ducts to cool their fuel pumps,

 

 

[facthunter]

 In normal set ups those things are known as blast tubes  With a uniformly pressured area (large volume) you can peel off a bit of air anywhere for a good cause Nev

 

 

[jetjr]

Yes, CAE recommended blast tubes to coils and fuel pump

 

I recall they had problems getting fuel pressure correct to limits and once springs correct there was some incidents of pump plunger binding - probably linked to heat

 

Efforts spent on ensuring max gravity flow , see 60lpm ?? required without any pumps (std Jabiru gets around 30lpm) and they had special jigs to realign fuel pump on assembly.

 

The extra blast tube does make getting duct on and off tricky

 

 

[Bruce Tuncks]

what diameter of blast tube jetjr? and rigid or flexible? Coming from the existing duct or from another opening?

 

I don't have any blast tubes at all, but I have put in shields  to intercept radiant heat from getting to the coils.  

 

 

[jetjr]

Reckon they are 1/2 ali tube ,bent into a right angle (slow radius)

 

Come out the back of the duct and end sits just above coils and pump, just flocked in.

 

 

[Old Koreelah]

what diameter of blast tube jetjr? and rigid or flexible? Coming from the existing duct or from another opening?

 

 

 

 

 

I don't have any blast tubes at all, but I have put in shields  to intercept radiant heat from getting to the coils.  

 

I hadn't thought of that; might check if mine are copping radiant heat.

 

[facthunter]

 They make a bit of heat on their own especially when they are old. Nev

 

 

[Bruce Tuncks]

 

 

[Thruster88]

All good, time to move onto the alternator? ?

 

 

[Bruce Tuncks]

The temperatures are T1=145, T2=144,T3=140,T4=139 

 

Yes, T4 is the coolest but they sure are even huh. They are doing this for several flights now. I wish I understood why things have come so good quite suddenly.

 

 

[Bruce Tuncks]

Funny you should say that Thruster, I just had a parcel delivered with some electronic stuff in it, including a 2 pole heavy-duty master switch.

 

My plan is to make an alarm buzzer sound when the battery goes over 14.4 volts. At which point the master is turned off, isolating the battery from the rest of the plane. ( the rest of the plane still has the alternator and a few capacitors which the alternator thinks is the battery )  My problem was how to make the alarm stop without leaving some electronics still connected to the battery. Remember the aim is to use a LiFePO4 battery with the Jabiru alternator and to switch off the charging as soon as the start-draw has been replaced.

 

The answer turned out to be simple: when the master switch is turned off, then so is the buzzer, but the buzzer switch is electrically ( but not mechanically ) separate from the master switch. The rest of the voltage-sensing circuit could still be on, connected to the alternator system, or it might be possible to also turn it off with the buzzer using that second switch.