to plenum or not

[HSANTIBANEZ]

Dear Cummunity, Happy new Year all,

Im near the first flight and some things are in mi mind so I will apreciate your help.

I have a Brand new TMXIO-360, is there a reason to not put a plenum before the breake in finish?

If we dont want a lot of heat in this process, may be the plenum temperatures will add some glassing posibilities in our cylinders?

[fstringham7a]

Hi

I did the plenum over my cylinders based on advice from Robbie Attaway and have found some interesting things.

Robbie Attaway (he is the best and really helped) info here:

http://www.attawayair.com/New%20RV6%20QB.htm

Robbies Plenum:



My Plenum



First depending on how you build it ... (fiberglass or metal and shape)
Second the air flow under the lid
Third the ease of engine inspections.........

I built mine in metal and I believe (????) with out alot of pressure testing a solid fit to keep the air from leaking.
I am not sure about the airflow. I do know that if you have a baffle mounted oil cooler you will want a smooth flow of air to that location at least some folks smarter than me here at VAF have stated such..
Finally, it is a bit of a pain to install/uninstall/install/uninstall......during times when testing the engine.

So with all this said would I do it again. I just don't know for sure but I am a real believer now of thinking long and hard before you leave the path established by Van's. Build it like he and the company suggests and you just won't go wrong.

I hope others with more experience and info will weigh in and help you out in your quest to build the best airplane possibe.

Originally Posted by HSANTIBANEZ

Dear Cummunity, Happy new Year all,

Im near the first flight and some things are in mi mind so I will apreciate your help.

I have a Brand new TMXIO-360, is there a reason to not put a plenum before the breake in finish?

If we don't want a lot of heat in this process, may be the plenum temperatures will add some glassing posibilities in our cylinders?

[pierre smith]

Baffles really make servicing so much easier and there hasn't been a real conclusive speed benefit to a plenum if your baffles are done correctly. It's one area that should be carefully done, all openings sealed with no air loss anywhere. Pay close attention to the crosswise baffle behind the spinner, that it seals well and prevents air from coming out of the cowl/spinner gap. creating drag.

I had baffles on both my -6A and now my -10 and both airplanes exceed Van's cruise and top speed numbers by a few MPH.

Best,

[billnaz]

Why would you build a top of a cooling air flow area just under a top of the already there cooling air flow area (the cowl top)? seems redundant.

[jrs14855]

If you want to race you need a plenum. If you don't care about speed might as well build a Pietenpol and enjoy the scenery. The performance improvement from a plenum has been well documented by San James, Dave Anders, Chris Zavatson and others.

[pierre smith]

A friend of mine has a -10 with 40 more horsepower than I do and a Sam James cowl and plenum and is 6 knots slower.

Too many other factors come into play.

Best,

[Cfrisella]

I put one in for engine breakin. No problems and temps are all under 400.

[John Clark]

Originally Posted by billnaz

Why would you build a top of a cooling air flow area just under a top of the already there cooling air flow area (the cowl top)? seems redundant.

I agree, building a box within a box doesn't make sense to me. Never mind the additional weight, complexity, and time spent taking the plenum on and off for inspections and service. A well thought out set of baffles for me thanks.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

[FloridaJohn]

I think the basic idea behind a plenum is to make the airflow more efficient so that you can reduce the size of the air inlets. This reduction in air inlet size will improve the aerodynamics of the plane and that is what results in an increase in speed.

Just adding a plenum does not make your plane faster, but it allows you to do things to your plane that will.

[jrs14855]

The typical homebuilt airplane sacrifices 5 to 30 m/h from the firewall foreward. There is no way that a conventional baffle system can be made as efficient as a plenum. The round inlet really serves just one prupose-the junction between nose cowl and plenum can easily be sealed for zero leakage. This can be done with the rectangular inlet with rounded ends, but it iks very difficult. One example of perfection with the rectangle inlet is Cory Birds Symmetry. If you take two absolutely identical non plenum airplanes and put a plenum on one and optimize the inlet/outlet, the plenum airplane will be faster. Or more fuel efficient. The access issue is hogwash. Allen head capscrews and a power driver make this a non issue. If access is such a big deal then all homebuilt airplanes should have an ugly set of cowl doors that can be opened without tools.