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Induction cold air plenum

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Dec 15, 2021 6:18 am Post subject: Induction cold air plenum

Dear Europa fans,



I am in the process of removing the two K&N cone style air filters that have served me well for the first 100 hrs of my new Europa flying career and replacing them with the induction cold air plenum (per strong recommendation from Bud!).



I have installed the plenum and I am in the process of making the NACA scoop. However, I have found that the plenum is so high that it sits very close to the cowling to the point that clearance at each of the plenum's forward corners is minimal. The biggest issue I see is that the NACA scoop bottom sits bellow the top surface of the plenum, very different from what the manual shows and certainly doesn't look very efficient from an air flow perspective.



Just to check, are there two different plenums for the Classic and XS? Mine was not in the kit and was donated by a nice person in the UK so not sure if I have the right one. If the same them I guess it is what it is.



Thanks for the feedback,

Chris

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SteveIvell(at)pestproof.c
Guest

Posted: Wed Dec 15, 2021 6:56 am Post subject: Induction cold air plenum

Hi Chris



Our Europa is an XS and there is a reasonable clearance such that the bottom of the NACA scoopsits just above the filter. The gaps around the edges of the planum are made up with rubber strip. Seems to work great. Our cowling came from the factory with lines set into the gelcoat showing the position to cut out the hole for the scoop......made life easy.



I guess your plenum could be fairly easily cut down to give you the required position. So my idea would be to cut out a strip and glass the two halves back together. I hope that make sense......and good luck.



Kind Regards



Steve Ivell

G-STES

XS 912s Hightop with a wobbly prop. ðŸ˜Š

Mob: 07971 128842

E-mail: steveivell(at)pestproof.co.uk



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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Dec 15, 2021 7:01 am Post subject: Re: Induction cold air plenum

In my quest to seek the answer to my question I found a 2018 parts catalog from Europa and they do list a plenum for the XS and the Classic. 



Now the job is to determine which one do I have. Anyone out there with some basic dimensions such as height of the plenum top from the carburetor bore centerline?



Thanks,

Chris

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Dec 15, 2021 7:08 am Post subject: Re: Induction cold air plenum

Thanks for the reply Steve. 



I have though of modifying the plenum but before I jump the gun I will see if I can get any feedback on whether there are two different plenums and determine if I have the wrong one. Some basic dimensions when possible would help (in case there are indeed two different ones). 



I can then entertain the idea of buying a new plenum or modifying this one (it's composite and we have the knowledge of how to fix almost anything, right?). 



I have invested quite a bit of time on this one (reinforcements, aluminum tubes on the carb tubes) but I'll see when time comes to make a final decision.



For now I guess I will keep flying with my K&N cones.



Best Regards,

Chris

SteveIvell(at)pestproof.c
Guest

Posted: Wed Dec 15, 2021 7:37 am Post subject: Induction cold air plenum

I'm no expert but I'd say you could probably build a whole Europa quicker than you can get a new plenum from the Europa Factory. Lol.........I'd be fixing the one you have if I was you. 



Kind Regards



Steve Ivell

Mob: 07971 128842

E-mail: steveivell(at)pestproof.co.uk



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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Dec 15, 2021 8:07 am Post subject: Re: Induction cold air plenum

Probably true Steve. I am going to have it quoted though but I was looking at the plenum and modifying it may not be too bad. At least I can try and I am in no rush since my airplane, after all, is flying.



I was curious to see how much better the engine would run with this plenum.



Chris

SPURPURA

Joined: 04 Apr 2015
Posts: 68
Location: KAPV

Posted: Wed Dec 15, 2021 12:56 pm Post subject: Re: Induction cold air plenum

Thatâ€™s the same as my XS plenum and fits pretty tight, just like everything else.

_________________
N951EU - Tri-gear & 912ULS, N77EU- Mono & 914
I'D RATHER HAVE A BOTTLE IN FRONT OF ME THAN A FRONTAL LABOTAMY.

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Wed Dec 15, 2021 1:53 pm Post subject: Re: Induction cold air plenum

Thanks "Spurpura",



It's good to hear that mine is like other XSs. I am probably going to do some surgery to this plenum anyway as I want to ensure enough clearance, smooth flow from the scoop into the plenum and some protection against water ingress. 



As a good airplane homebuilder friend of mine says: "There you go, adding another two month of work to the project"   



Chris

budyerly@msn.com

Joined: 05 Oct 2019
Posts: 285
Location: Florida USA

Posted: Wed Dec 15, 2021 3:52 pm Post subject: Induction cold air plenum

For those on the matronics list: 

A good dimensional analysis of the “NACA” duct for proper operation is in the attached NACA document. 

A ratio of 4 to one width to depth and a shape as shown in the NACA  Ames Research Center document 5121 attached gives the optimum shape of the inlet. 

The NACA document has a lip that was changed over the series of tests but in reality just a flat thin inlet  (thickness of the skin) works very well giving a good pressure flow rate. 

I did a paper on plenum inlet design some time ago due to poor fit and questions on how large to make the  plenum flange on the cowl and also some shapes but the Europa install manual is good enough for most.  I would recommend some changes as in my pdf attached on preventing water intrusion. 

   As a technique, try to have the NACA inlet into the cowl capture the pressure  by being semi sealed to the plenum and as we have found out, in rain, the water tends to “stick” to the boundary layer or skin of the aircraft and will flow into the inlet filling the filter.  Of course,  when parked rain will catch in the NACA duct and funnel into your inlet unless you prevent that.  One can make a slight deflector on the inlet lip that funnels the water from inflight and ground use out of the engine inlet.  See Airbox water intrusion in the carb box pdf attached.
For those with home made plenums, be sure to install 1/8 inch drain holes  in the plenum at a point lower than the air inlet to the carb (some sort of dip prior to the carb inlet would be nice) to prevent water from pooling in the plenum.
Every oil change, pull the filter and look into your plenum as in damp  environments, water, will pool in the plenum, and from the drain holes, some pollen or dust will form around the drain hole water drip hole and may in fact plug the drain causing water to get into the carb/engine.  Nasty.
For the 912/912S owners, in cold and rainy environments, you may be well  served to install a carb heat system and consider a water deflector or siphon on the inlet to divert water from directly entering the air filter/plenum hole.  On home made plenums I have seen the owner elevate the filter to prevent water intrusion also. 

I toyed with the idea of a Rotax 912S plenum in the Europa.  It would work with possibly less work when changing from two cone type air filter to a carb heat and inlet setup. 

See drawing: 

                     <![endif]--><![if !vml]>[img]cid:image003.png(at)01D7F1E4.94C31790[/img]<![endif]><![endif]-->  

Best Regards, 

Bud Yerly 

  

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budyerly@msn.com

Joined: 05 Oct 2019
Posts: 285
Location: Florida USA

Posted: Wed Dec 15, 2021 5:24 pm Post subject: Re: Induction cold air plenum

One more thing.

How to you place the NACA duct for your plenum is an issue many have fought.



I simply put on the top cowl and screw it down.  I then set the front elevation properly to the spinner.  Using a marker to trace the outline of the plenum on the cowl inside allows me to precisely plan my cowl seal flange.  Once the flange is set, the cowl seal or foam or whatever you wish to get a nice airflow semi seal will work well.  That sets the position fore and aft/ left and right for the NACA inlet much easier.  From that many plans and measurements can be made and finally whack the curvy lines and set the slope of the inlet ramp.  (Technically it is a 7 degree slope for isentropic flow.)  Make the sides sharp.  It enhances the vortex from the side. 



If you just follow the manual, it can be a bit misleading, but the NACA placement can be fined tune once the engine is installed by doing the above.



Best Regards,

Bud Yerly

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Thu Dec 16, 2021 6:45 am Post subject: Re: Induction cold air plenum

Thank you bud. Very insightful as always.



I already chopped the plenum and I'm starting to bond it back together.



Will report with pictures when I get it done.



Chris

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