Replies to This Discussion

Permalink Reply by Dr. Edward L. Olds III on June 15, 2013 at 11:41pm

Tom,

Looks like your project is a great one.  Have you flown yet?

Ed

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Permalink Reply by RANDY L HALLOCK on June 14, 2013 at 11:00pm

just in time for the warm summer.

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Permalink Reply by Dr. Edward L. Olds III on June 15, 2013 at 11:41pm

Randy,

Took a look at your panel pics.  Great job.

Ed

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Permalink Reply by Clint L Gosch on June 15, 2013 at 9:34am

Glad to hear persistance paid off for you!  Next time I fly over the Savanna area I'll keep an eye out for you.

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Permalink Reply by Dr. Edward L. Olds III on June 15, 2013 at 11:42pm

Clint,

You can find us at LL07, about 6 east of KSFY.  Stop in.

Ed

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Permalink Reply by Dr. Edward L. Olds III on June 16, 2013 at 12:30am

I'm not sure if I'm writing this on the proper spot on the Discussions, but here goes.  Forgive me if this isn't correct.

As I said earlier, I finally finished my 40 hour phase one on June 2nd.  The airplane is now in Wisconsin, being painted.

I had a difficult time with the Phase one because I could never get the CHT temp on #5 to stay cool enough.  I first flew in Oct. and had problems with the CHT's right off the bat.  They seemed to get better as the fall got cooler and I thought I had made a turn around.  Unfortunately, that did not last and my temps went way up as soon as the spring turned warmer.

I tweaked the ram air dams by shaving a bit off of the ones above #1 and #3 and added a plate in front of #1, using aluminum tape and nothing got better.  I started keeping a spreadsheet of the CHT's and EGT's in an effort to isolate the issue.  No matter what I did, in terms of moving the aluminum plate up or down or shaving off air dams, nothing made the temp on #5 go down.  I was consistently over the 356 degree max for continuous operation and could never get more than 5 or 10 minutes in the air.

I got a lot of great advice from many of you, especially the ones mentioned in my original post, but I continued to have high CHT's and oil temps.  At one point, I was really frustrated because I started to have EGT problems, or so I thought.  That turned out to be a function of the fact that I could never get the plane to altitude for long and could not get any time on the engine.  Finally Pete, at Jabiru, looked at my numbers and thought I was OK for EGT's, so I just quit worrying about them.

At John's suggestion, I added his version of the oil sump cooler and my oil temps went down!  I still had high CHT's, but at least I had some progress.  At this point, I was off to Ireland for 2 weeks and testing stopped.  When I got back, I really began to get frustrated because it seemed that nothing would get #5 below 356.  I moved the aluminum plate around, took it out, put it back, removed the cowl extension I had made, put that back, and was getting no where.

Dave Prizio suggested that I might not be getting enough air flow through the ram air because of the high drag airframe and that jived with the theory one of my friends came up with during his A&P classes.  We thought about taking the Jabiru ram air ducts out and installing a typical plenum used in a Lycoming or Continental, but that thought was too daunting.  Instead, I took Dave's suggestion to use some chaffing material to add a flap above #5 to force the airflow to stay closer to the cylinder.  At the same time, Roger, at Zenith, suggested I reshape my aluminum plate in front of #5 and curve it around the barrel a bit.  I did as he suggested and also took the time to again use some chaffing material to extend the ram air ducts forward until I had a very tight seal against the cowl around the prop.  And finally, I rebuilt the lower cowl lip extension suggested by John Austin and made it stick down about 3 to 4 inches below the fiberglass lip.

And, with that, things seemed to change immediately!  My CHT on #5 dropped to the 330's and every other one was @ 290 to 310.  I was able to fly for several hours at a time and my temps never varied.  I still don't like the big spread between #5 and the others, but I am hoping that getting more hours on the engine will stabilize things.

So, in the end, I think it was a combination of finding the lucky perfect placement for the aluminum plate, the flap over #5, the use of the chaffing material to tighten the ram air intakes, the oil sump cooler, and the extension of the lower cowl lip that finally combined to make things work.  I had previously tried the cowl lip and the plate, but they apparently needed the other things to work?

So, I'm flying, the aircraft is being painted as I type this, and I'm really happy with how it flies!  It was a long journey, but a satisfying one at this point.  I can't thank all those mentioned, enough for listening and offering moral support and ideas for a solution.  This website, and the people who contribute to it, have meant the difference between losing my sanity and finally finding some success.

I salute you all.

Ed

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Permalink Reply by John Austin on June 16, 2013 at 6:09am

Great report, Ed! I think the bottom line is that with a 6 cylinder, air-cooled engine in a high drag/low speed airframe, all the cooling tweaks have to work in concert like a symphony ... and you finally found the right "key!"

I'm confident you'll see the temps settle a bit more over the next 40 hrs - mine did. For the long haul, are you going to run 15-50 mulitweight or straight 50 weight? Jabiru just came out with a service recommendation to use Aeroshell 100W if you're running Avgas and change the oil at 25 hrs - if you're running 93 unleaded, multiweight is OK and Pete said they generally change at about 30-40 hrs when it starts to look dirty. (I'm running 93 unleaded/no ethanol and Aeroshell 15w-50.)

Have fun!

John

N750A

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Permalink Reply by Dr. Edward L. Olds III on June 17, 2013 at 2:01pm

John,

I have been using Avgas, but am interested in going to 93 unleaded/no alcohol.  I've just had the Aeroshell 100 mineral so far.  I'll be talking to you via phone.

Ed

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Permalink Reply by Tim Treat on June 16, 2013 at 8:47am

Congrats. I have a few hours left to finish my 40 hours. I am hauling bags of rocks and dog food to bring up my weight.

As far as cooling goes, I'm glad that you nailed it. IMHO, the secret is in the ducts. Where I live we have temp swings from 20F at takeoff on a cool morning to 70F when I return to land at Noon. I run a Rotec carb that allows me to lean my mixture so temp swings are controllable. I suffer from 5 and 6 being the coldest on takeoff and the warmest on cruise.

Things I learned:

1. Chasing the 5/6 temp issue on a hot day will create the opposite problem on a cold day. Visa verse for 1 and 2.

2. Having mixture control allows you to determine if the temps pull together as you lean.

3. I always tuck the spark plug wires carefully in the ducts with flow in mind.

4. I nailed the duct design fairly quick by focusing on adjusting the air "leaking" down the front edge of 1 and 2. My front vertical baffles are angled back to nearly touch the front edge of the fins of 1 and 2.

5. My air boxes only have a very small gap from the cowl AND I have a rubber boot between them.

I followed the Jab air duct instructions to the tee. I did consider drilling holes in the center diverter instead of trimming it but paying close attention to sealing off the front of 1 and 2 and sending as much air back as possible made it simple.

The bottom line is: On cold mornings 5 and 6 are the coldest and on a hot day they are the hottest. I consider that balanced. For those of you at the ram duct stage I would suggest starting your tuning on a cold morning vs a hot day.

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Permalink Reply by Dr. Edward L. Olds III on June 17, 2013 at 2:04pm

Tim,

I agree that the ambient temps are a big factor.  I am pretty well pleased at the moment, but still haven't had any 100 plus days, so we'll see?

Did you talk to Jabiru before installing the Rotec carb?  Any problems doing so?

Ed

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Permalink Reply by David Gallagher on June 17, 2013 at 1:33pm

For those who will be at Oshkosh, I see there is a forum titled "Cooling the Jabiru 3300" on Wednesday, July 31 at 0830 in the forum building #1  I no longer have any cooling problems myself, but will be there to pick up any other tips for improvement.

 

Dave

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Permalink Reply by Dr. Edward L. Olds III on June 17, 2013 at 2:04pm

Dave,

Thanks, I'll be there, I hope!

Ed

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