Improving the effectiveness of NACA scoops

[John Slade]

I came across the following link which shows the results of oil flow tests on a NACA inlet with and without "corner baffles". The baffles provided a 30 degree CHT reduction.

 

http://4dw.net/marcborom/LongEZ/NACA_AirFlow.htm

 

Also, there was a study in Central States a while back on belly vortilons. I think Eric Westland did the experiments. He was able to reduce operating CHT considerably also. There's a web site on this somewhere.

[macleodm3]

Wow... thats some serious extra cooling! Cheap Too!! Just cardboard and duct tape. It seems to be turning the NACA into a "scoop" but without all the extra drag. Why don't we already do this on the NACA ducts? Thank heaven for the "experimental" in this hobby.

[John Slade]

Just cardboard and duct tape.

Ok, I suppose. I was thinking of using something a bit more substancial - like fiberglass:D

 

Why don't we already do this...

Cause it's just been discovered, by me at least.

[CBarber]

Don't let Paul L. know.....actually, I think he has already disregarded the website and once again referred to the original research circa 1950.

 

All the best,

 

Chris

[marbleturtle]

Without the baffles he has air spilling out of the NACA duct... I couldn't see any pictures of the rear of his plane. Does he have a large enough exit area? Its the old suck air out the back to get more air in, or ram air in the front and force it through the system scenario.

 

Still looks like a good idea regardless!

[John Slade]

Yep. Paul said these tests don't mean "beans" and that the bottom line is further pressure measurements.

 

I sent a post to the list:

Hmmm. Isn't the CHT a valid measurement? I'd have thought that the "bottom line" was the net RESULT of the experiment - i.e. "cylinder head temperatures are lowered by about 30 degrees for each cylinder", or did that not come through in the PDF/RTF/LINUX translation?

Paul responded privately accusing me of trying to make trouble.

 

I replied

NACA says the scoop does not "give desirable charateristics at ALL flight conditions" (which perhaps means that it does at SOME) and they go on to say "The design of such inlets is more critical than of other types...", so perhaps these modifications can make it work better. In addition to this, NACA have been wrong before.

 

Here's a guy who's demonstrated significant improvements in cooling after modifying his NACA slightly. Another guy (Eric Westland I think) also showed big cooling improvement with belly vortilons. If (large if) a rotary pusher CAN be cooled with a NACA we'll see much improved efficiency. Why is it that you won't even discuss it?

 

You say the bottom line is pressure measurement.

I say the bottom line [of a cooling system] is temperature reduction.

,but he won't publish that either.

Pity. There are a lot of experts on that list who would LOVE to discuss such issues as water pumps and NACA scoops openly and without censorship. I wish they'd come over here.

[John Slade]

Oops. I tell a lie. Paul did publish my comments. Things are improving in the ACRE list.

[Jim Sower]

Originally posted by John Slade

Oops. I tell a lie. Paul did publish my comments. Things are improving in the ACRE list.

He probably accidently pushed the wrong button. Actually, I'm encouraged. It is intuitive (and that counts most of the time) and I can't see any way AT ALL that it can make anything worse. I'm going to incorporate it on my EZ soon and Cozy later.

 

BTW, it's [V]ortex [G]enerators upstream of the NACA, not Vortilons.

[CBarber]

I agree that I wish we could have a more open discussion on the ACRE site as I know some topics are very taboo but I still want to learn more....of course I am one of these freaks who like all comments, even SAR's, makeing them a virtual hanger and a great tool for education.....even wrong opinions can add value. We should all take everything we learn (esp from the net) with a grain of salt. IMHO.

 

However, Paul seems to be listening....I really thought the tread on computer OS's the other day would errupt into a flame war, which to the best of my knowledge it did not. Also, I questioned his opinion on hiring others to build a plane and he was very respectful of aanohter opinion. As a rule, I try to never "challenge", just question. Guess it can be tough to be the 800lb Gorilla.

 

All the best,

 

Chris

[Hookr55]

I initiated the thread on ACRE when I saw the recent oil flow study but now kind of regret ever doing it.

 

I feel the NACA scoop application on the belly of the Long EZ is pretty unique. Therefore I don't think we can appply conventional wisdom (Paul L.) to our application. I'm surely open to trying it when I get that far.

 

I don't think that we can assume success here without SOME drag penalty though. Any thoughts?

 

Bob Geis

Long EZ planning

"Livin the Dream" in Iraq

[John Slade]

but now kind of regret ever doing it.

Hi Bob,

PL can ignore it, but that doesn't really matter because he's building a backwards plane anyway. At least I THINK he's building something. It's not worth arguing with the guy once he's made his mind up, which he did many years ago on issues like NACA scoops and electric water pumps.

 

I take the ACRE list for what I can get from it, which isnt very much. Paul doesnt seem to want input unless it agrees with what he's already said.

 

I'm glad you posted that link. I plan to try the corner things and the belly vortex generators after I've tried without. I'll report the differences. As you said privately, the effect may well be different on a Cozy with a wider belly, and there may be a drag penalty. But - maybe there's a free lunch waiting here....

 

Thanks for what you're doing out there.

[Neverquit]

On chapter 7 I believe is when the NACA gets put on the bottom of the fuse. If anyone's there or remembers, can you tell me if the bottom of the NACA has a curve in it front to back or is it flat all the way to the firewall?

[ZUCZZ]

On chapter 7- bottom of the NACA has a curve in it front to back or is it flat all the way to the firewall?

Flat all the way, the "scoop" part is about 4" forward of the firewall.

 

Mine works just fine as per plans, I did drop the lip an extra inch.

 

Cozy Mk IV, IO-360 angle valve, 70 x 80" prop, blue print, blah, blah.

[Phil Kriley]

I get an error 404 when I try the link...

[Jon Matcho]

It's at this site now... click the "Oil Flow Tests on NACA Inlet" on the left side: http://marc-borom.com/

[Neverquit]

I re-watched the intake cooling forum download from the EZ org (CSA) website. I looked yesterday at my NACA scoop and realized how wrong it is. Not by the plans but by the builder and a little by the plans. After making my beautiful landing gear cover I realized now the ramp angle is 3 deg. then 7 deg. then 15 deg. Yuck! Three flat surfaces!

 

Here's a good cheat sheet I found on the web from an old article. TO NEW BUILDERS...It's okay if the ramp is a bit curved but as Gary Hertzler says, "NO BUMPS".

 

Gary shows a good example of bumps on the ramp by showing a belly NACA with a landing gear cover and flush screws. Go figure.

 

 

Cozy builders note to that website: the Cozy has a flat belly which won't show the same results with the oil test.

[jpolenek]

Here's a good cheat sheet I found on the web from an old article.

There's something I've been wondering about for years, with regard to these NACA inlet coordinates:

What's going on with the y value of 0.307 at x=0.4? When I plot it, it looks too high to produce the smooth curve given in the pictorial. It looks like a value of around y=0.290 would produce a smoother curve. Has anybody else noticed this or have I somehow been plotting it wrong all this time?

 

Joe Polenek

[Neverquit]

Your numbers are good. I got the same thing. I think if you used besiea (bes-ee-ay) curve software it would smooth it out. Have you tried the M drawing curve to see how it matches up?

[dpaton]

Besiea = Bezier for us engineering types.

[jpolenek]

I think if you used besiea (bes-ee-ay) curve software it would smooth it out.

I thought the coordinates are supposed to represent the actual points along the duct. If so, then connecting the dots, and interpolating between them, should give the correct shape.

 

Joe Polenek

[Neverquit]

Besiea = Bezier for us engineering types.

 

Thanks! Haven't used that word in 10 years since I got away from the tube (thank God). Surfaces, layers, point clouds...ahhhh:O

 

I thought the coordinates are supposed to represent the actual points along the duct. If so, then connecting the dots, and interpolating between them, should give the correct shape.

 

Here's some more NACA data to play with to hurt your brain.

NACA-RM-A9L29.pdf

[dpaton]

One thing...the document is for transonic small NACA inlets. If anyone on this board is planning on putting their plane into a situation where there will be air above 0.7 mach (~460kts) at an inlet...well....

 

I think these might be more applicable to the thread:

Link deleted,

see post below...

 

Please be nice and mirror them, they're served from my DSL line at home, so be patient. For some reason, the forum uploader kicked out the smaller of the two, which is under the size limit.

[dpaton]

Files are rehosted at the links below.

 

Mods: Please delete links in above post!

 

A7130

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