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  #1  
Old 02-02-2006, 10:12 AM
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Default Cooling vrs engine intake manifold

i may just give up the idea of the central plenum intake manifold with equal length cool formed runners and go with a central plenum with two sets of runners along the top of the cylinders.

Ima tinkin.

the box plenum around the cylinders with a straight tube in and a straight tube out just bugs me.

The airflow just has to be wayyyyy turbulent with all of those sharp 90 degree bends that have to occur in the box

i'm thinkin top of the cowl scoops that gradually get bigger internally as they bend the air down to be pushed through the cylinders and then the opposite on the outflow to the big hole in the back.

The problem is, the cooling air needs to be where the central plenum runners need to be. I think cooling efficiency is more important than engine efficiency

Aviation = trade offs

in my wood working dust collector i made a central distribution box for the 6 - 6" x 6 foot tubes that collect the dust.

When i blow it and don't empty the dust and shavings bin under the cyclone - three of the tubes fill up first - that is what has to happen with the box plenum 90 degree method of cooling. I'm thinkin three runners per side, so the air goes where i tell it and not where it feels like goin. the tubes would basically fill the cowling but go from a small opening on top to a big wide opening as gradual as i can make it, top dead center of each cylinder.

why is the p51 scoop so efficient? the air goes near straight, near as 2/3 of the radiators are above the fuse. the air is brought in, expanded pushed and pulled through the radiators and guided back out. near straight
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  #2  
Old 02-02-2006, 12:09 PM
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Okay, here's 4 photos with different inlet scenarios. Including one like John was mentioning at the wing root. You can see in the photo where it looks like a 3rd cowl-mounted scoop was needed as well. Jack mentioned that the NACA scoop setup on his Eracer worked well. Although you mentioned he changed the exhaust config?
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  #3  
Old 02-02-2006, 01:02 PM
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Dust, been working on my P51 type scoop. You'd be proud. (maybe)I used balsa and 3 oz cloth to build the transitions. Very light. Note diffuser shape to rad and convergent shape after rad. The exit shape is hard to see in the photo. The scoop lower floor profile sweeps upwards. A cockpit controlled exit door hinged to the belly skin inside the sccop controls rad airflow and should trim cruise drag considerably. I'm going to instrument the duct with pressure taps and fore/ aft pitot tubes plus temp sensors to gather some cooling data in flight.

For your air cooled Conti maybe a variation of this plenum which covers the entire intake fed by your choice of scoops. Our testing has shown that even the best NACA duct with the best orientation and location only recovers about 60-65% of the total dynamic pressure available compared to forward facing ones. The rake angle is very critical. Is the drag increase from the frontal area increase from a conventional scoop offset by the better pressure recovery and smaller inlet compared to a NACA duct? Hard to say. Both have been made to work.
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Old 02-02-2006, 01:34 PM
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I love it - what is the outside shape? looks like 20% outside and 80% inside, if I'm seeing right.

Balsa - rots with moisture - would have used (of course) foam. heh heh heh

i'm proud of you - this glass thing rubs off a little, but you probably been makin scoops outa it for years
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Old 02-02-2006, 01:37 PM
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Rake angle? more words
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Old 02-02-2006, 02:31 PM
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Outside shape is like a Pro Stock scoop 'cause that's what it is. Fairly pleasing to the eye. Looks like P51 inlet and Hawker Hurricane exit. Hey, composites not my bag so I save time wherever I can. The balsa is well preserved with epoxy and glass. Got some cool urethane foam to reshape the inlet and boundary layer bleed on the nose of the duct. Subie twin turbo power. Where no RV10 has gone before!

Rake angle on NACA ducts is the effective angle of attack. Run these at zero and they are pitiful. 10 degrees rake doubled the average pressure recovery on the flow bench. I evaluated a complicated rear fuselage rad placement fed by twin huge NACA ducts exiting through twin exit ramps and adjustable doors like a P47 intercooler setup. Complicated, heavy and when I found out how the NACAs would perform here, that was the end of that exercise.
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Old 02-02-2006, 02:53 PM
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Gotcha - didn't realize you were still on the naca - 7 to 10 degrees is supposed to be optimum.

I've been ponderin the whole use of NACA and I've come to the conclusion that it may not be the best, but it is a Low Drag configuration that works and is easy to build.

Since the conti is intake on top and exhaust on bottom, lycoming is both on bottom. top down cooling just makes sense.

but i think by goin top of the cowling down i can reduce drag, more gentle curves and gradual opening. buy making the tubes separate - the air goes where i tell it instead of turbulently into a box

the balsa is fine - just had to say its ONE drawback, i think GM found out about that draw back some years ago in the corvette floor pans
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