Talk:NACA cowling

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added Reference on the "Anello Magni" as stated in the Italian wikipedia —Preceding unsigned comment added by Robyvecchio (talk • contribs) 14:57, 2 November 2009 (UTC)[reply]

Increased thrust

All my readings indicate that the NACA cowling was to decrease drag while still permitting cooling. None of them indicate anything about increased thrust through an unspecified effect. I suspect the unsourced statement in this article is due to conflation of a NACA cowling with the discovery of the Meredith effect as observed in liquid filled radiators and NACA's subsequent research into ramjets prompted by being told about the Meredith effect. That this article does not specify that the Meredith effect is only observed in liquid filled radiators is also a deficiency. Waerloeg (talk) 14:31, 6 August 2014 (UTC)[reply]

NACA cowling

(relocated from my talk, re [1])

Sorry Andy - I see so many "dubious" tags without comment in the talk page that I didn't check the comment there before "fixing" the tag. Give me an hour or two and I'll do it properly... Shem (talk) 10:14, 10 August 2015 (UTC)[reply]

Take a look at Meredith effect.

The problem is that it's implausible that a Townend ring gives any measurable boost in thrust and it's barely credible that a NACA cowling would either. We should certainly trail Meredith effect and the idea that heating the cooling air in an enclosed duct can generate thrust, but we (in general) need to source such claims, and where it's really rather unlikely, then we would definitely have to source it. I doubt that there are such sources. It would be a small effect, it would be an effect dwarfed by the simple reduction in drag, it would be an effect no-one went looking for. I'd be surprised if anyone had done the awkward large wind tunnel experiment necessary to measure it, let alone that they've written it up in a traceable publication (although the NACA published papers are the place to look). Andy Dingley (talk) 10:19, 10 August 2015 (UTC)[reply]

Your change now is just plain wrong and an abuse of that source.

Meredith was British and, because of local politics, was only looking at R-R engines rather than Bristols - i.e. liquid-cooled inlines. So Meredith was looking at a liquid cooling radiator, which dumps a great deal of heat into a small duct. Optimum conditions for this effect.

In a large air-cooled radial, the energy density is far lower. It is impractically hard to achieve a useful effect.

If this ever happened, it's going to be the later-war US engines with the close shrouds, the Bristol Centaurus in the Sea Fury (the most likely combination of all) or the German radials and circular-shrouded inlines. It's really most unlikely in the pre-war US radials. For two reasons, firstly their power / duct size is too low and secondly the aircraft airspeed is too low. The great advantage of Meredith is that it's a jet: its efficiency increases with vehicle speed (comparable to jet velocity), unlike the propellers that were becoming speed limited in the mid-war period. Pre-war this second effect just wasn't an issue, by mid-war it was.

The content that's there now has to go. It's just plain wrong. Andy Dingley (talk) 10:25, 10 August 2015 (UTC)[reply]

Fine. Give me an hour or two to put it right and reference it right. If you don't like it when I've finished, feel free to revert (again). Shem (talk) 10:35, 10 August 2015 (UTC)[reply]

There's another linked bit of text that needs correcting - at radial engine it says "The thrust generated by both the Townend ring and the NACA cowling was due to the Meredith Effect (discovered by British researchers), whereby the heat added to the air being forced through the ducts between the cylinders expanded the exhausting cooling air, producing thrust when forced through a nozzle." Whether the Meredith effect is zero in the NACA cowling, or merely insignificant, that text at radial engine is just plain wrong. I'll try to fix them all ... Shem (talk) 10:42, 10 August 2015 (UTC)[reply]

Thanks. It'll probably get shot down again though with the "There's no such thing" / "Dude, of course it's American, so of course its radial engines" argument that bedevilled Meredith effect a while back. Andy Dingley (talk) 10:45, 10 August 2015 (UTC)[reply]

Andy, have a look at the text now I've re-worked it. I'm going to have a look at radial engine and Townend ring, and I would appreciate any feedback, if that's convenient. And - thank you for your patience. Shem (talk) 11:03, 10 August 2015 (UTC)[reply]

NACA cowl generated forward lift?

I thought the entire point of the NACA duct being "shaped as an airfoil" is that the air flowing across it actually generates LIFT, in an outwards and slightly forward direction, thus "pulling" the plane along behind it, which basically acts the same as adding a small amount of thrust. I've even seen diagrams showing how this works, somewhere. If the entire point is merely to modify airflow and decrease drag, like a Townend ring, why is it shaped like an airfoil? Isn't the entire point of an airfoil to generate lift? The only other possibility I can think of is that it's shaped as such to accelerate the air flowing past the cylinder heads, to compensate for the fact that the opening allowed a smaller volume of air to enter than an uncowled engine, and perhaps also to cause the airflow to "stick" to the inside of the cowling, rather than separating and blowing around the crankcase, leaving little flow around the cylinder heads. If that is the case, it could be stated more clearly in the article?

I also wonder if the idea that the cowling used the Meredith effect comes from statements like this:

  "They also had to design an exit slot that released the air at a slightly higher velocity and lower pressure than it entered the cowling with"

(from http://history.nasa.gov/SP-4219/Chapter1.html) Which might suggest at least slight Meredith effect to some people.

.45Colt 20:07, 8 October 2015 (UTC)[reply]

A Vlaicu III engine cowling

I would like to bring up for discussion and early case of what appears to be NACA cowling i.e. that of airplane A Vlaicu III. Thank you. Simiprof (talk) 03:03, 26 September 2017 (UTC)[reply]

It's a cowling, but obviously it's not a NACA cowling, whatever it looks like. The plane first flew in 1914, while the NACA cowling was developed in 1927. Whether or not the A Vlaicu III's cowling has the same aerodynamic characteristics as the NACA's can't be determined from photos, which are not reliable sources anyway. - BilCat (talk) 03:48, 26 September 2017 (UTC)[reply]

Not only that, but it wouldn't have made any sense for it to have the form of a NACA cowling even if the A Vlaicu III's designer could have somehow known the appropriate shape, by whatever means. The NACA cowling was designed for cooling stationary radials with minimal drag from the air flowing into the cowling, past the cylinders, and out through the annular duct at the rear of the cowling. But the A Vlaicu III's engine was a rotary radial; the engine cooled itself by spinning rapidly, pushing its cylinders sideways through the air. Such engines, by mechanical necessity, always used a total-loss lubrication system and sprayed used oil out of the cylinder heads. The purpose of the cowling was to catch this oil and prevent it from being blown into the pilot's face. If the cowling had a NACA-style annular duct, that oil would simply have been blown to the rear and out the duct, which would negate the cowling's purpose. --Colin Douglas Howell (talk) 04:47, 26 September 2017 (UTC)[reply]

"what appears to be" is not enough. By a long way.

First, what is a NACA cowling? This is a specific design of cowling where the aerodynamics of its inside shape were carefully designed for low drag: it was not just a cowling, it was a duct. Not every tin can wrapped round an engine is a NACA cowling.

Secondly, it's not a NACA cowling, as it pre-dates NACA. Maybe this whole article needs to be renamed to "Vlaicu cowling", because Vlaicu was there first. But you are going to have an uphill struggle to source that claim.

Thirdly, it's not a cowling, it's a shroud. Vlaicu didn't make any attempt to route air through it. At most, this is an oil scoop. It doesn't even have the prop wash going through it.

Finally, WP:RS and WP:V still apply. "what appears to be" is not enough. By a long way. Andy Dingley (talk) 11:51, 26 September 2017 (UTC)[reply]

Can we then include a section on precursors of NACA cowling? Simiprof (talk) 16:56, 28 September 2017 (UTC)[reply]

See Townend ring

This isn't one. It is no more a precursor to the NACA cowling than a bucket is. Andy Dingley (talk) 17:13, 28 September 2017 (UTC)[reply]

So Andy is of the opinion that buckets are the only precursors to NACA cowling. What about the other editors? Can we vote on this Simiprof (talk) 23:39, 29 September 2017 (UTC)[reply]