NACA inlet geometry

[jdubner]

Below is an image of my Long-EZ's NACA inlet.  Note the two annotated areas near the firewall end.

Can anyone tell me: what is their intended purpose?  Are there any other Long-EZs with them?

Some background: O-360 with cylinder cooling issues.  Measured not enough air into the lower cowl.  I'm tempted to cut off the "wings" and see if things improve.

Thanks.

[Kent Ashton]

2 hours ago, jdubner said:

Below is an image of my Long-EZ's NACA inlet.  Note the two annotated areas near the firewall end.

Can anyone tell me: what is their intended purpose?  Are there any other Long-EZs with them?

Some background: O-360 with cylinder cooling issues.  Measured not enough air into the lower cowl.  I'm tempted to cut off the "wings" and see if things improve.

They are to minimize "spillout" at the corners of the duct which can be seen here

https://www.canardzone.com/forums/topic/18661-kents-long-ez-project/?do=findComment&comment=67608

Various folks have used them.  They seem to help a bit but a bigger effect is mounting a few vortex generators ahead of the scoop.   Surface flow that far aft has a thicker stagnant layer and does not like to turn to go into the NACA.  The vortex generators stir up the stagnant layer and mix in some energised air.  They can also create a swirl that swirls air into the scoop.  Also make sure your landing brake is flush so it does not create any turbulence.

If you're having cooling problems, I suggest a check of pressure differential above and below the cylinders with a manometer and piccolo tubes.  Lycoming says you need 5 1/2" of water differential for adequate flow through the cylinders.  If you don't see that, you start trying to figure out why not.  You might post some pics of your baffles.  Sometimes there is some obvious problem that can be diagnosed.

[jdubner]

Thanks for your reply, Kent.  I had not seen that thread you pointed me to -- thank you very much.

I tried to keep my original post brief but I've already accomplished a differential pressure check (it's low) and temporarily installed vortex generators (in accordance with this KitPlanes article).  VGs designed according to this article are not a good fit on my Long-EZ; they need to mount on the speed brake and they're eff'ing BIG -- nothing like those tiny ones some use on their canards.  But they did increase pressure (not enough) and improved cooling somewhat.  It's just that I can't live with them 😞

I "tufted" the inlet with dishwasher soap (rather than dirty oil) and it shows good airflow back to the area of the "wings".  Then it spills out over them as if they're breaking up the vorticies that attach to the inlet sides.  Hence my desire to try doing without them but first I'd like to hear from those with experience.

I'm also looking at some sort of diffuser at the NACA inlet interface with the firewall.

[Kent Ashton]

I’ve found (in a downdraft installation) that getting the air out is as important as getting it in.  I see lots of updraft cowl exits that look small and force the air towards the prop hub which I think is an obstruction.    Vents on top of the top cowl seem to work for some but not for others but aft facing vents on the bottom of my downdraft cowls really made a big difference

https://www.canardzone.com/forums/topic/18661-kents-long-ez-project/?do=findComment&comment=74509

I tend to think that for an updraft installation, a couple of 9 sq inch (~18” total) aft facing vents on the top cowl positioned to grab the air coming out of the cylinder fins would be pretty effective.    I’m guessing that the smaller flush top-cowl vents do not help much because the outflow from the engine is very turbulent and can’t get through narrow vent openings.    I tried them on my Cozy and could not detect much improvement.

oh yeah, one other thought: with an O360 you gotta move more air in and out than an O-235 or 320 engine.    I imagine the cowl inlets and outlets need to be similar sq inches to a Cozy or Velocity.

Edited July 27, 2021 by Kent Ashton

[Kent Ashton]

Here is are some oil flow pics using VGs on my cozy with O-360.  It appears my intakes are a fair amount bigger than yours.  Could be part of your cooling problem.  I eventually went to four small VGs along the scoop.

https://www.canardzone.com/forums/topic/18661-kents-long-ez-project/?do=findComment&comment=53400

 

[MikeD]

Long-Eze (New build and testing for first flight)
Lycoming O-320 B3B
Cooling configuration: Downdraft with exhaust augmentation.
Instrumentation: MGL Xtreme EFIS with four (4) "K-type" thermocouples  on bottom plugs

Done some engine testing today in calm conditions and 21 deg C, I had been told of someone testing their downdraft cooling by placing some wool strands in from of the inlet to check if the exhaust augmentation was effective so I thought I'd do the same. (See attached photos: The photos show that the pieces of cloth hang down when engine stopped. With engine at circa 900 rpm the cloth is being sucked into the inlet with some force.)

I started of with an engine run without top cowling to check for leaking etc. Run the engine for 4-5 minutes at circa 900 rpm, the CHT reached about 160 deg C (320 F). 

Second run was 5 minutes later (engine had cooled down a little bit) for 10 minutes at circa 1100 rpm, CHT reached 216 deg C (420 F) and Oil temp at 90 deg C (194 F).  I stopped at that point.

Question: How does this compare to other LE's with the conventional (updraft) cooling set-up? Bearing in mind that I was stationary and there wasn't any wind.  I have been told that the conventional cooling requires you to start moving the aircraft quite quickly. 

[Kent Ashton]

It is hard to tell anything about the cooling without flying.  Looks like the exhaust augmentation is working though.  Intake size seems adequate but you might post more pics of your setup.  Here is a popular ground run procedure that many Vans owners use.

Break-in Schedule.rtf

[MikeD]

Thanks very much for the info, it looks like a sensible way to go.  I'm trying to evaluate or get a rough idea of how the downdraft setup is compared to the updraft layout on the Long-Ez.

I've attached some more photos that show the downdraft with exhaust augmentation setup, it's basically sealed between the top cowl inlets and cylinder plenums. The inlet and outlet area was calculated or rather taken from numerous technical articles on the subject.  As you can see from the previous post, the augmentation is working.

Mike

[Kent Ashton]

Interesting.   I have used a downdraft installation before.  Initially it did not cool but the problem was that my exit area was not adequate to let the cooling air out (pic 2, before).  I added some more exit area below the cylinders and that fixed it [or did it?, Marc Z  😉 ].  Pic 3, after.    Anyway, my setup was fairly different so you will have to see how yours behaves.   The  problem became obvious with some piccolo tube testing.  I was not getting 5.5" of water differential pressure drop through the fins; only about 3.5".   Your intakes appear to be a bit smaller than mine but higher in the airflow and you have the usual EZ-style exit so maybe you'll be fine.

[MikeD]

Once again thanks, that's the kind of information I'm looking for.  Now it has to be tested in flight.

Mike

[MikeD]

Thinking about it logically, I need a suitable method of ground testing before first flight. 

Did you do any ground testing, if so what method/equipment did you use?

[Kent Ashton]

1 hour ago, MikeD said:

I need a suitable method of ground testing before first flight.

There's no practical way I can think of to test cooling on the ground.  Your setup looks like it will work well enough for flight.   Just make sure your plenum is nice and tight and you didn't leave obvious air-holes like the large hole between the lower halves of the cylinders or at the sides at the lower halves.  All cracks sealed with silicone sealant.  All the air must go through the fins.  Usually, the cooling is adequate to prevent frying the engine and you can see how it goes.  You might check if your upper cowl is stiff enough that plenum pressure and lift over the cowl doesn't force the cowl off your rubber seal and allow plenum air to escape.

And a new engine will run hotter for a while anyway.

Edited September 18, 2021 by Kent Ashton

[MikeD]

Thanks, I will take note of all those facts.

[A Bruce Hughes]

It is very important to have temp. info on ALL FOUR cylinders.  

Also you did not say if you are using a "wafer" type sensor under the sparkplug or a "bayonet" type on the side of the cylinder; there is a BIG difference.

[MikeD]

I have temperature 'wafer' (ring type) under all four (4) BOTTOM sparkplugs. I figured this would be the hottest place so the safest place to get the temperatures.

[A Bruce Hughes]

We need to see what Marc Z or some other expert says on that.   I don't know; but I do use 4 bayonet types.

[jdubner]

On 7/26/2021 at 2:23 PM, jdubner said:

...  I'm tempted to cut off the "wings" and see if things improve ...

Don't know if anyone is still following in spite of the thread drift or even cares but thought I'd close the loop for future reference.

Yesterday I cut off the "wings" and flew.   No discernible improvement in CHT.