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  #11  
Old 12-01-2016, 08:13 AM
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Quote:
Originally Posted by Tiger 74 View Post
Thanks for the friendly words guys! Sorry if I have offended the purists!
CHT temps were up around 410-415 F oil up to 210 in climb.
Have Showplanes cowl, 10:1 Pistons on a Superior IO360, James plenum chamber (modified to fit and seal properly), standard Vans oil cooler.
OAT was around 70F at the time of testing.
P-Mags were set to 25c.
Everything looked to be set up right, but the temps were too high.
I added the louvres to get the problem solved during flight testing to get the permit to fly.
It worked. CHTs now steady and balanced at 370-380 in climb, oil no higher than 180.
I saw no noticeable reduction in speeds, so drag penalty seems low. Why not keep these on permenantly? They don't look too bad (pretty good actually).
Thank you David.

You're a serial builder with past RV-8 experience. A parallel valve with p-mags and 10:1 pistons is a difficult case, but it's not greatly unlike your previous RV-8.

Did the previous -8 present a cooling problem? If not, what individual factors do you feel made this one different?

BTW, you said "to get the permit to fly". Is there a temperature limit of some kind in the UK?
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  #12  
Old 12-01-2016, 11:28 AM
g zero g zero is offline
 
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Default High CHT

I apologize if my post offended anyone , but 3 times a week someone has this same problem . As far as purist goes ,I'm pretty far from it , Sam James Cowl , Plenum ,10-1 pistons , 17 row oil cooler ,4:1 exhaust ,Bendix Mags 25*

Now some more info on yours , how did you match your plenum to the cowl (photos) . I had an issue with mine . Exhaust ? How many pipes out the cowl ? Prop to cowl seal ?
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  #13  
Old 12-01-2016, 11:31 AM
jrs14855 jrs14855 is offline
 
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Default Temps

22 or even 20 degrees timing can help during break in. Some of the angle valve 360's in certificated aircraft REQUIRE 20 degree timing.
I personally hate the look of the louvers. A cowl flap is a much more elegant solution.
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  #14  
Old 12-01-2016, 11:31 AM
sblack sblack is online now
 
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Quote:
Originally Posted by Toobuilder View Post

Do you have the bypass ducts on #3 and #1 to address the well known "zero fin depth issue"? Also, did you tune up your intercylinder baffles to seal ALL air leaks, or are they just installed staight out of the box?
sorry for the thread drift, but where could I learn more about zero fin depth and bypass ducts. First I have heard of it.

Agree that there is nothing magic about louvers. Opening the outlet a bit more, or fairing it a bit better (bottom of the firewall) could do the same thing. I have the vetterman straight pipe RV4 system and it calls for a 1/8" by 3/4" aluminum brace bar going right across the air outlet. I will find a different way to stabilize the exhaust as that seems like it will act like a big dam.
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  #15  
Old 12-01-2016, 12:05 PM
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Toobuilder Toobuilder is offline
 
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Dan has eloquently illustrated the issue in several threads and building off that, several of us have documented our successes in our own threads.

A search for "Hot #3" or similar will turn up multiple results. You can search for my or Dan's screen names as authors to narrow the search.

Here is one of mine to get you started down the wormhole of info.
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Last edited by Toobuilder : 12-01-2016 at 12:07 PM.
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  #16  
Old 12-01-2016, 03:58 PM
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Tiger 74 Tiger 74 is offline
 
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Dan,
Our Permit to Fly is granted after satisfactory flight test schedule and sign off. It's the Certificate of Airworthiness, essentially.
The differences to my last 8 (which had no cooling issues at all) are:
High compression pistons
Showplanes cowl
James plenum
That's about it. On my last 8 I never once opened the oil cooler grills. The oil struggled to get up to temp with them closed. The new one has to have the oil cooler grills open constantly. Same cooler and installation on both.

When I first experienced this overheating on the first test flight, I was really shocked. The flight had to be cut short to avoid overheating the engine. I had the standard vans plenum arrangement at that point. I then fitted he James cowl, modified it and made sure no leaks. I wasn't pretty, but it was sealed. I put spacers at the back of 3 & 4 cyls. Still not enough cooling. I was running out of time to get the testing done in my allotted schedule, so I added the louvres to solve the immediate problem, with the view to re-addressing the issue once testing done and Permit issued.
Hence my original post. I am now thinking "it works well as is, good temps, not great drag penalty, and I think they look ok". Why change it?
I have read all the historical posts on this subject, and see no single magic cure to the cooling/drag issue.

Last edited by Tiger 74 : 12-01-2016 at 04:02 PM.
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  #17  
Old 12-01-2016, 06:41 PM
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Toobuilder Toobuilder is offline
 
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There is no single path for efficient cooling of a Lycoming. It is a game of inches. EVERY SINGLE area for air to get through without a cooling fin in the way needs to be sealed. Those intercylinder baffles are a major job to seal all by themselves.
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  #18  
Old 12-01-2016, 06:57 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Tiger 74 View Post
The differences to my last 8 (which had no cooling issues at all) are:
High compression pistons
Showplanes cowl
James plenum
Interesting. Upper and lower pressures, as well as exit temperature, would tell a lot.

Quote:
I am now thinking "it works well as is, good temps, not great drag penalty, and I think they look ok". Why change it?
Then don't change it. A few knots won't make much difference, given English distances

I'm kidding.

Seriously, not knowing the root problem(s) would bother me. And there is a drag penalty. I'd guess two, maybe three knots. Sound about right?
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Last edited by DanH : 12-01-2016 at 06:59 PM.
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  #19  
Old 12-02-2016, 11:24 AM
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Tiger 74 Tiger 74 is offline
 
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Probably about right.
As you say, 2-3 knots over a 2-3 hour trip no great penalty for healthy temps.
So without measuring top/bottom pressures, outlet temps and tinkering with a myriad of other factors (I've read all the threads on this topic), I think I'll take the easy option and go flying with what I've got! I was seeing 173 knots IAS (178 TAS from Skyview) flat out at 1,000ft at close to ISA, so that'll do me!
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  #20  
Old 12-02-2016, 11:35 AM
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I solved a cooling issue on my high compression Pmag'd lyc by cleaning out the flashing between the fins that are located near the spark plug. You can buy needle files for a few bucks at harbor freight. I polished each fin until there was absolutely no evidence of flashing casting flaws. The results were a 20F drop in CHT during extended climb. Plan on spending 3-4 hours on this job.
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