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Plenum

 
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DCS317(at)aol.com
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PostPosted: Wed Jan 18, 2006 3:35 pm    Post subject: Plenum Reply with quote

I'd like to change to a plenum and make it myself rather than use the
available "off the shelf" types. Aluminum vs. fiberglass? Anyone made one similar
to Diamond Aircraft's two-part plenum? Reason for change--running ok except
hot weather CHTs go to 425+ on a couple cylinders despite injector sizing
changes on my IO-540 with Lasar and proper baffling. Please no comments on the
IO-540--I just like excess power!

Don Schmiesing
Seattle
110 hours on 417DS


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Terry Watson



Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

PostPosted: Fri Jan 20, 2006 2:06 pm    Post subject: Plenum Reply with quote

Don,

I was hoping someone with more experience would have responded to your
question by now, but since I haven't seen anything, let me mention my
experiences to date:

I bought an expensive carbon-fiber plenum for my 0-360 and have spent months
trying to make it work. Most of the blame belongs with me; I seem to need to
build something two or three times before it starts to be acceptable.
Everything worked reasonably well until I got to the front inlets and
connecting the plenum up to the cowl. I totally rebuilt the front of the
carbon fiber plenum twice to get it to line up with the cowl inlets, then
ordered a new baffle kit from Van's and set the plenum aside as a maybe
winter project once I get this thing flying.

I have seen three general approaches to plenums in RV's. The first is the
Sam James composite plenum and cowl combination where the cowl inlets are
round and connect up with a flexible sleeve to the round inlets on the
plenum.

The next approach is essentially to do the baffles but instead of doing the
flexible rubber seal from the baffles to the top cowl, cut down the baffles
and use either aluminum or composite to make a plenum out of the baffles.

The third approach I have seen is best shown my Mark Philips on his RV-6
website, which I can't find at the moment. I have also seen similar plenums
that come with a new Jaibaru engine from the factory. These are somewhat
distorted composite or aluminum tubes that run from the cowl air inlet over
the cylinders, one on each side. The bottom of the tube is open of course to
force the air down through the cooling fins on the cylinders.

If I do another plenum, I will probably do the baffles, cut them down, and
then lay up a composite top that would fasten to the baffles on the sides
and back with piano hinges. I still haven't figured out how I would connect
it to the air inlets at the front.

Terry
RV-8A #80729, finishing (Whirl Wind 200RV prop came yesterday!)
Seattle


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Nuisance



Joined: 10 Jan 2006
Posts: 9

PostPosted: Thu Jan 26, 2006 8:55 am    Post subject: Re: Plenum Reply with quote

Don, the easiest way for you to solve your CHT problems is to dump that LASAR system (excessive timing advance) and get Lightspeed or just plain magnetos. You can test this by removing power from the LASAR system when the engine is running too hot...you will reduce CHTs by 30 degrees as the timing reverts to baseline.

A plenum will help reduce cooling drag, but probably not make the engine run cooler unless you didn't fit your baffles well.

fun fun, John
[/quote]


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walter(at)tondu.com
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PostPosted: Thu Jan 26, 2006 9:27 am    Post subject: Plenum Reply with quote

On 01/26 8:55, aflyer wrote:

>
>
> Don, the easiest way for you to solve your CHT problems is to dump that LASAR system (excessive timing advance) and get Lightspeed or just plain magnetos. You can test this by removing power from the LASAR system when the engine is running too hot...you will reduce CHTs by 30 degrees as the timing reverts to baseline.

The LASAR system will generally only increase CHT's by 15-20 degrees.

http://www.unisonindustries.com/products/lasar_installation/lasar_inst_seven.html
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Walter Tondu
http://www.rv7-a.com
Flying!


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Nuisance



Joined: 10 Jan 2006
Posts: 9

PostPosted: Fri Jan 27, 2006 6:54 am    Post subject: Re: Plenum Reply with quote

Walter, you can believe my testing, or their marketing fluff.

I would often switch the LASAR off in a climb on a warm day, and even in cruise if it was warm at altitude, and if anything, 30 degrees is conservative. I am speaking from 150 hours experience with that system. During the second summer, I replaced it with dual Lightspeeds...problem solved. I have not seen 400 degrees since.

John


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PostPosted: Fri Jan 27, 2006 9:03 am    Post subject: Plenum Reply with quote

On 01/27 6:54, aflyer wrote:

>
>
> Walter, you can believe my testing, or their marketing fluff.
>
> I would often switch the LASAR off in a climb on a warm day, and even in cruise if it was warm at altitude, and if anything, 30 degrees is conservative. I am speaking from 150 hours experience with that system. During the second summer, I replaced it with dual Lightspeeds...problem solved. I have not seen 400 degrees since.

Precisely why my P-Mags should be arriving in a few weeks!
I have examined everything I could related to the high CHT issue
and replaceing the LASAR system is next on the agenda. I
certainly hope I see the same numbers you have seen. Thanks
for the info.
--
Walter Tondu
http://www.rv7-a.com
Flying!


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