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Cylinder cooling issues - Guidance from Jabiru

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Andy Silvester

Joined: 10 Jan 2006
Posts: 18
Location: Marica, Rio de Janeiro, Brazil

Posted: Tue Sep 11, 2007 6:01 am Post subject: Cylinder cooling issues - Guidance from Jabiru

The following information was received by Dealers from Jabiru, and is posted in advance of being incorporated into manuals and warranty policy:



To avoid overheating problems of the Jabiru engines in non Jabiru installations, it is vitally important that all installations provide a greater that 6 inch of water, air pressure differential to provide enough cooling for the Jabiru engine. Attached is a diagram of the tube placements to measure this and photos. We are in the process of having this included in the engine manual as a condition of warranty.

Attached is a diagram and photos that demonstrate how to perform this test.



Andy Silvester

Suncoast Sportplanes Inc.

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Gilles.Thesee(at)ac-greno
Guest

Posted: Tue Sep 11, 2007 1:04 pm Post subject: Cylinder cooling issues - Guidance from Jabiru

Andy Silvester a écrit :

 	  Quote: 	
		   1. The latest test has different reference points than before, when the pressure was compared with ambient and at an airspeed of only 1.3 Vs.

 2. The higher pressure differential reflects both pressure and suction, i.e. inside the cooling duct is compared to a point adjacent to the cowling outlet.

 3. The 6" differential will be obtained at normal cruise speeds, which is easier to monitor in the air rather than (in my view) trying to maintain a speed of 1.3Vs and looking at the manometer.

   


	


Andy, Jerome and all,



Thanks for this interesting data from Jabiru, and rather consistent with 

other sources.

On a different type of engine, I'm achieving 140-150 mm H20 (5.5"- 6") 

mean cylinder differential pressure (between upper and lower cowling) on 

a 125-135 kt airplane.

Didn't retrieve direct Lycoming numbers, but a quick search yielded  :

 	  Quote: 	
		   Lycoming Engine Installation Manual does specify that the O-320 engine 

 requires 5 - 1/2 inches of water while the O-360 engine should have 6 

 - 1/2 inches pressure drop for good cooling.

(quoting from http://www.rv7-a.com/phase_1_page2.htm)
	


Of course, actual numbers will depend on the pressure measuring setup, 

but those values are in the same ballpark.

FWIW,



Best regards,

-- 

Gilles

http://contrails.free.fr

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue Sep 11, 2007 1:28 pm Post subject: Cylinder cooling issues - Guidance from Jabiru

Andy,

Is this a requirement for cooling of the engine or for cooling the coils?

I think it would be very difficult to find a pressure differential of 6"

water at anything less than 140KTS. Can you confirm how this can be done. I

have taken measurements using a water manometer and found 4" static pressure

from a point near the cowl inlet at 120KTS.



 Peter



--

Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Tue Sep 11, 2007 1:38 pm Post subject: Cylinder cooling issues - Guidance from Jabiru

Andy,

Now that I understand we are talking about differential pressure inlet vs

outlet pls disregard my last post.

But is it not sufficient to run within the required CHT ?

Peter



--

Gilles.Thesee(at)ac-greno
Guest

Posted: Tue Sep 11, 2007 9:27 pm Post subject: Cylinder cooling issues - Guidance from Jabiru

Peter Harris a écrit :

 	  Quote: 	
		   But is it not sufficient to run within the required CHT ?

   


	


Peter,



Of course it is.

Adequate cooling is certainly achievable with less than 5" in the case 

of the Jabiru. I've seen adequately cooled Jabirus with less than 

optimal intake diffusers and exits.

The mass flow through the fins is proportional to the square root of the 

pressure differential. 4" would provide about 90 % of the flow at 5", so 

things are not so critical.

By asking for optimal pressure drops, Jabiru is protecting itself 

against warranty claims related to overheating.



Best regards,

-- 

Gilles

http://contrails.free.fr

pj.ladd(at)btinternet.com
Guest

Posted: Wed Sep 12, 2007 1:35 am Post subject: Cylinder cooling issues - Guidance from Jabiru

By asking for optimal pressure drops, Jabiru is protecting itself against 

warranty claims related to overheating.>>



Hi All,

this is my first posting to this list and it is obvious from lurking that 

you guys are much more technically knowledgeable than I. On a scale of 1 to 

10 put me in as zero.

I fly a Kolb Extra with a Jabiru pusher, in the UK.  I have had little 

experience as I managed to  start the engine with the throttle wide open 

after only a few hours flying . I hit a barn, and a parked car. The rebuild 

has just been completed and I am waiting for Permission to Test Fly at the 

moment.



I queried the rumours of Jabi`s overheating with the dealer when I ordered 

the plane and he assured me that it was a thing of the past and more up to 

date engines were OK.  My engine must now be around 2 years old.  Any 

comments?



Cheers



Pat

matronics(at)rtist.nl
Guest

Posted: Wed Sep 12, 2007 1:53 am Post subject: Cylinder cooling issues - Guidance from Jabiru

Pat,



Jabiru has made several changes to the engine to improve cooling (more and 

finer fins, new airducts), but a bad installation 8 years ago will continue 

to be a bad installation today if nothing is done about it. As more Jabiru's 

find their way to the skies, more experience will be built up and many 

common mistakes early on will be known and corrected today.



Rob



---

japhillipsga(at)aol.com
Guest

Posted: Thu Sep 13, 2007 8:51 am Post subject: Cylinder cooling issues - Guidance from Jabiru

Pat, how big was the barn ?

 

 

 --

pj.ladd(at)btinternet.com
Guest

Posted: Thu Sep 13, 2007 9:44 am Post subject: Cylinder cooling issues - Guidance from Jabiru

Pat, how big was the barn ?>>

  

 Big enough to see but too big to  avoid.

 I fell victim to the Jabi policy of the throttle  going to full throttle in case of failure.  I had been flying a Challenger  with Rotax 503 for many years with no need to adjust the throttle  friction.

 In the Kolb there is a friction adjustment under  the pilots seat and I obviously had not tightened it quite enough. The choke is  high behind my right shoulder. In my left hip trouser pocket I had my credit  card case. In starting I needed to set or reset the choke several times and each  time I twisted in my seat the wallet nudged the throttle open. The Jabi  propensity to go to open throttle did the rest.

 The engine fired and she went like a bat out of  hell across the farm yard. My wife who had helped me rig, and thank heaven was  standing behind the wing swears that I took off , in 30 yards, before impacting  an RSJ (I beam) supporting the corner of the barn about halfway along the port  wing.

 I had intended only to taxi onto the field to fuel  up, a matter of a hundred yards, and had strapped in  only as a reflex  action. Very lucky as otherwise I would have gone from being pushed back in the  seat by the acceleration to a 150 degree swing and sudden deceleration as I hit  the parked car, which would certainly have thrown me around the cockpit, (its a  side by side 2 seater) with resulting injury.

 Thank goodness the engine was high and behind the  wing and the prop hit nothing. If it had been a tractor set up it would have  meant new prop and probable shock loading of the engine to deal  with.

  

 Cheers

  

 Pat

   [quote][b]

japhillipsga(at)aol.com
Guest

Posted: Fri Sep 14, 2007 9:15 am Post subject: Cylinder cooling issues - Guidance from Jabiru

Pat, we only asked about the barn in an attempt at humor, but I now see it was inappropiate. I am happy you were not injured and your plane is repairable. I recommend you make and use a better starting/taxi checklist and hope you accept my apology at my failed dark humor, Best regards, Bill 

 

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