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  #11  
Old 01-26-2012, 05:39 PM
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LifeofReiley LifeofReiley is offline
 
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Default

Quote:
Originally Posted by RV6_flyer View Post
But there is no flight data listed to know how well it worked.
That is correct. I actually have the template drawings for the final design from Mark. I think there is actually "cooling drag" issues with this type of design with standard size of the inlets as you have a lot of cooling air with a limited area to flow.
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  #12  
Old 01-26-2012, 06:37 PM
Bob Axsom Bob Axsom is offline
 
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Default I did a reasonable amount of work on cooling drag

I did a reasonable amount of work on cooling drag and published the results in this forum. After I had achieved a 4 KTAS increase in speed at 6,000 ft density altitude with a lot of lower cowl experimentation I started working with stock Van's inlet size for more speed. I reduced the size in 1/4" segments from the center outboard and the only significant change I saw was a direct increase in CHT with each inlet size reduction. There was no increase in speed. However, I did observe that the shape of the "plug" between the spinner and the inlet opening could reduce the speed.

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  #13  
Old 01-26-2012, 07:18 PM
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Default plenums

Seems like the cyl. plenums would be less than optimal. The set I saw on a 0-233 LSA were very sweet looking. Per Dans statement they may have only been the tops. Just tops would be easier to build but much less effective. The smaller engine and less horsepower would require less mass. This would mean a larger engine like the IO-320 would be more difficult to do. If it could be worked out it looks like a market for someone to start selling prefab.
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  #14  
Old 01-27-2012, 09:22 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by LifeofReiley View Post
I think there is actually "cooling drag" issues with this type of design with standard size of the inlets as you have a lot of cooling air with a limited area to flow.
In our conventional cooling scheme, a plenum is a sealing device, nothing more. In the context of cooling drag (not necessarily cooling capacity), a full plenum or two partial plenums would be no different if they seal equally well.

A "limited area to flow" decreases cooling mass flow. If the system throttle is at the inlet (per Bob's experiment above) the decrease in drag due to reduced mass flow is offset by an increase due to momentum loss, i.e. low exit velocity. If the throttle is at the exit, the decrease in mass flow is accompanied by higher exit velocity, the result being reduced cooling drag.

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Last edited by DanH : 01-27-2012 at 09:25 AM.
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  #15  
Old 01-27-2012, 11:16 AM
gereed75 gereed75 is offline
 
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Default I believe

what Dan and Bob are saying (and both please correct me if I am mistaken, I'm continually trying to learn here) is that poorly managed airflow through the inlet/plenum/exit system is more detrimental than mis matched inlet size.

"Poorly managed" would include leaky seals between inlet and plenum, leaky plenum, leaky cylinder baffles, slow/turbulent exit flow, etc etc.

These will all have a greater detrimental effect on cooling efficiency and cooling drag than mismatched inlets because the drag created by inlet spillage is relatively small.

This of course assumes that you have a spill tolerant inlet shape, such as Dan's or Van's stock inlet.

The best gains are from getting the air that comes in to do the most amount of work (heat transfer) and get it out efficiently. If it is too much air (more than is necessary) you'll have a bit more drag than you need and lower temps than you need. By restricting that air mass flow (by restricting exit size), you will reduce the mass air flow to what is necessary, and have a net reduction in drag. That is because the air that is forced to spill at the inlets causes very little drag. Less than the gain you will see from having lesser, well managed, air flow through the system.

That's my theory, and after reading a lot of threads and references, talking with some fast and cool guys, and building a couple inlet plenums and exit fairings, I'm stickin to it.
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  #16  
Old 01-27-2012, 01:18 PM
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Default Experimental=Education=enjoyment

OK so -
I need to change some names around to fit my brain. I hope they are the same.
Mass = volume
Momentum = velocity
Keep the volume of cooling air to a minimum by increasing efficiency of cooling air by having a well sealed, smooth path. If you are able to reduce volume, do it by reducing exit at the bottom of the cowl. This increases the velocity of the exit cooling air.
One of my main questions is, If you design and tweek a cooling system to work properly at top end, is that worse case? Or would there be concerns at idle on the ramp? I do understand heat=HP so I tend to believe that top end would be worse case but I also worry about inlet air volume being very low at idle.
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  #17  
Old 01-27-2012, 01:48 PM
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Mark, better to stick with "mass"...volume varies with density.
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  #18  
Old 01-27-2012, 02:09 PM
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Default Cylinder Head Plenums...

...and to follow up with Dan, also with temperature. If it's doing its job properly, the air will be hotter (and take up more volume) on its way out than it did on its way in. So, technically, to prevent an adverse pressure gradient the hot side of the plenum should be larger than the cold side.

This is probably the neatest area with which to experiment. But since I did CFD for food years ago, I'm going to experiment with something else.
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  #19  
Old 01-27-2012, 03:40 PM
gereed75 gereed75 is offline
 
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Default Mark

mass is essentially equivalent to the total flow rate of the air - pounds per hour - how much air is going through the system.

Volume of that air will vary some with temperature. Don't confuse it with volume of the plenum.

I can live with velocity=momentum. They are not technically the same but using that equivalency won't get you into trouble.

You are right, with a non-variable system (no adjustable cowl flap) you are going to have to accept some compromises. In my experience, taxi is not a problem, it does not last long enough to be a concern and heat generated (HP) is small.

The biggest problem (worst case) is climbs for CHT and oil temp - high horspower with low mass flow. This can be a problem but your climb times are generally short in these airplanes. I try to optimze for fast crusie. That is where I spend the most time. I have lower cruise temps than I need but never had a problem with high temps in the climbs. That might be different if I squeak down the flow rate (exit throttling) to increase cruise temps and further reduce mass flow (and drag). It's all a compromise.

Build on now and deal with the tweaks latter.
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Last edited by gereed75 : 01-27-2012 at 03:44 PM.
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  #20  
Old 02-09-2017, 07:05 AM
madhun madhun is offline
 
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Sorry to drag up a very old thread here, but my Dad built an aluminium plenum over the io-320 in his Mustang II, which i have recently purchased and note that we are experiencing a situation where we struggle to get the engine warm, even on a hot day. In winter we have to restrict the airflow through the oil cooler just to get it to normal operating temperature!
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