NACA Air Inlet

[jrevens]

Does anyone have any real world experience or data to show that the NACA scoop for radiator air on the 7 SS is more effective by bringing the sides at the inlet cutout straight up (forming a sharp-cornered vertical wall), or basically finishing them with the curved edges, as molded by Kitfox? I'm wondering how many people have done it either way.

[Esser]

Hi John,

I went with the Kitfox moulded way because I view that scoop as more of a ram air than a true NACA vent due to the size and the position on the cowl.

[jrevens]

Thanks Josh. I think you're probably right. I couldn't find many pictures of the inlets... am just curious how most do it.

[Dave S]

John,

Is this what you mean?

[jiott]

I went with fairly sharp vertical sides. I doubt there is any measurable performance difference, but I liked the sharp-cornered look better.

[jrevens]

John,

Is this what you mean?

Yes, exactly. I see you went with the curved, Dave. That's what I'm doing too. I think that theoretically the NACA scoop is more efficient with the vertical walls & sharp corners (I could be wrong), but I think that Josh is right, in that the opening is at more of an angle to air flow than optimum for a NACA scoop. It might even be a little better at higher angles of attack when climbing with the curves... maybe not. Anyway, I made my cutout a little bigger than I wanted too, and decided to go with the curves.

[jtpitkin06]

At the speeds we fly it probably makes no difference between curved edges and straight edges. There's a ton of info on line, both theory and application. I've never studied NACA inlets before so I got a real education when I did a search. The inlet appears to work because of the local turbulent flow. I suppose the sharp edges contribute to that turbulence. But, again, we are puttering about at 90 knots, not 250.

Given that the local flow is already turbulent, your slightly curved edges should work just fine. If technical perfection is your goal, along with a small amount of coolness factor, then creating the sharp edges shouldn't take but a few globs of filler and some sanding.

For what it's worth, I looked around at the airport and all the certified airplanes that have NACA inlets have sharp edges and straight sides.
John Pitkin

[Dave S]

For what it's worth, I looked around at the airport and all the certified airplanes that have NACA inlets have sharp edges and straight sides.
John Pitkin

John,

I think there is much wisdom in your comment:) Certificated aircraft, although they certainly can be saddled with excess tradition and economic strictures, have a lot stuff figured out which makes for a good starting point for us experimental folks so we pretty much can figure out what works, what does not; and, what doesn't matter.:cool:

Anyone who is ever grounded by bad weather or bored by some other means could find spending time with the engineering achievements and design contributions associated with Kelly Johnson in his book titled "More than my Share" inspiring.....a lot of folks have gone before us and given us a good place to start from.