REFLECTOR: CHT's

Scott Derrick scott at tnstaafl.net
Tue Oct 20 08:35:22 CDT 2009


I think because of the way the ducts enter my plenum the air has to make
a 70 degree turn to go through 1&2.  Its much easier for it to travel
straight back and go through 3-6. 

I'm probably going to try some kind of turning vane in the plenum to see
if that will cool the first two cylinders better.

To bad about sending your first plenum through the Lycoming Cuisinart! 
Must have made a really loud racket!  I've sent two small bathroom mats
through mine.  I place them on the strake next to the engine to provide
a workplace and protect the paint.  The rubber bottom of the mat grips
the paint really nice so they don't slide around.  It's amazing how easy
you can forget about the one on the co-pilots side!

thanks,

Scott

Rene Dugas wrote:
> Scott
> The only big difference I have is mine enlarges to capture the entire width
> of the plenum and extends over half way back over the engine.  Mine also
> wraps around the engine support so air is blowing directly on the upper half
> of both front cylinder fins and heads except for valve covers.  I have a
> very tight fit to all the cylinders.  I can send better pic off line if
> desired.  IF it will help in any way.
> Rene'
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Scott Derrick
> Sent: Monday, October 19, 2009 2:25 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: CHT's
>
> Rene, what engine are you running? 
>
> here's an early picture of my plenum.
>
> http://tnstaafl.net/canards/img134.jpg
>
> it was from the factory for a 550, close enough for a 520.  The attachment
> has changed but the overall shape is identical.
>
> Scott
>
> Rene Dugas wrote:
>   
>> I don't know what your naca to plenum looks like but mine is attached 
>> and no diverter was needed.  All my CHT's are within 20 degrees.
>> Hope it helps somehow.
>> Rene'
>>
>> -----Original Message-----
>> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
>> On Behalf Of Scott Derrick
>> Sent: Sunday, October 18, 2009 3:10 PM
>> To: Velocity Aircraft Owners and Builders list
>> Subject: REFLECTOR: CHT's
>>
>> Flew this morning after plugging holes in the TCM/Cessna supplied 
>> "between cylinder baffles".  I should have made my own, because the 
>> stock baffles have huge holes in them.  They also don't wrap up around 
>> the sides of the cylinders for optimal cooling flow. I may try to 
>> tighten things up a bit more but it will require me to remove all the 
>> injection plumbing, spark plug wiring and some other stuff..
>>
>> Also adjusted the fuel map and smoothed out a few bumps in the oil 
>> cooler exit duct.
>>
>> The CHT's are really coming into a comfortable range.  Cruising at 165 
>> KTAS(low power setting) they all stay below 360, but increasing power 
>> to above 200 KTAS and  #2  climbed to 395, #1was about 365, the rest 
>> were all below 330.  I'm mostly concerned with #2 but would like to 
>> see
>> #1 more inline with the other 4 as well.
>>
>> I'm debating installing some kind of diverter(s) inside the plenum to 
>> direct more air onto #1 & #2.  Anybody do that to lower CHT's with 
>> success?  How did you do it?  Got pictures? Controlling air movement 
>> is such a funny thing, sometimes what seems logical or intuitive is 
>> exactly the wrong thing to do!
>>
>> The fuel map is as good as I will be able to get it, until I get the 
>> new prop.  At least I am not running at peak EGT in RPMs above 2200 now.
>> That helped the temps a whole lot.
>>
>> Now to getting the oil temp down some more. Right now I am not running 
>> the fan on the secondary cooler as I see it as a summer time auxiliary
>>     
> cooler.
>   
>> With OAT in the 60's I shouldn't need it.  The oil temps were OK, but 
>> a bit on the high side at a low power cruise speed of 165KTAS.
>> about 210F, but as soon as I fire-walled the throttle it started to 
>> come up and seemed to stabilize at around 230, though I didn't stay at 
>> that power setting more than a couple of minutes.  With the IO360 my 
>> current oil cooler was good enough but marginal.  On hot days I had to 
>> step climb.  I don't have an exit scoop or air dam on the exit duct.
>> The duct opening is flush with the fuselage. I'm really intrigued with 
>> Don's idea of an Oil cooler flap that can be adjusted from the 
>> cockpit. When flying with the IO360 I had too much cooling in the 
>> winter and marginal in the summer. I would tape some of the cooler 
>> face in the winter so my temps were hot enough to get a bit of warm 
>> air in the cabin.  With a hinged controllable flap I could set it for 
>> whatever the conditions were.  It would probably work out to 3 or 4
>>     
> settings that covered all scenarios.
>   
>> Scott
>>
>>
>>
>>
>>
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