Okay, I gotta ask--how did you get/find that? And if we need to move 800 CFM against that pressure, can we figure out the approx wattage/HP needed by the fan?An 8" diameter wheel at 3600 rpm would produce roughly 3.6" water column or .13 psi.
Okay, I gotta ask--how did you get/find that? And if we need to move 800 CFM against that pressure, can we figure out the approx wattage/HP needed by the fan?An 8" diameter wheel at 3600 rpm would produce roughly 3.6" water column or .13 psi.
Right, my fan book shows an 8" diameter wheel at 3735 rpm would produce 4" static pressure at 349 Cfm and .41 hp.An 8" diameter wheel at 3600 rpm would produce roughly 3.6" water column or .13 psi.
Coud produce. Actual pressure will be a bit lower to get a decent flow. The Briggs fans are annular, so it's lower again, but they gain a bit by being forward curved.An 8" diameter wheel at 3600 rpm would produce roughly 3.6" water column or .13 psi.
8"π*3600÷60÷12)^2*.5*.00237÷144=.129 psiOkay, I gotta ask--how did you get/find that? And if we need to move 800 CFM against that pressure, can we figure out the approx wattage/HP needed by the fan?
Well at some point oil or liquid/water cooling methods are cooled by air. Just moving the heat to a place it can be removed more easily or faster.Heat exchange due to forced convection will be a lot more effective in this case than radiation. If we just consider the fins, they contribute virtually zero to radiative heat exchange (since what little they radiate goes into another fin). And the oil cooler won't shed significant heat via radiation.
I think you'll find forced air is what you'll need: plenty of it, and kept close to the hot bits.
FWIW, 4.0"wc (0.145 psi) dynamic pressure would be at about 91 MPH. The expected dynamic pressure (standard day, SL) at 100 MPH would be 4.9"wc.My Limbach is rated at 4" static pressure. (thought that was around 100 mph)
TiPi, If you have accurate RPM measurement, measure the pressure drop at max revs and about 2k, from that I could make a table of pressure and flow at any reasonable rpm.I'll try to measure that on my mower (18hp 40-series) this weekend
I am poking my calculator...the numbers that I have for cooling airflow (at 3,690rpm, no external load)):
total flow into the engine (fan intake): 920cfm
airflow through the oil cooler: 72cfm
airflow for intake air and air filter flushing: ~20% (180cfm)
cooling air flow through cylinder heads: ~670cfm
Temp drop at oil cooler: 10deg C (80 to 70)
Cooling power: 3.3kW
Oil pump volume: 12 lpm (the 2lt oil content circulates completely every 10s), I wouldn't worry about filtered or not
Cooling air intake area SE-33: 73cm2 per cylinder head
I know you are planning for a low speed project, but going with the breeze does give you the "free" flow from the airspeed dynamic pressure. Also the cooling air that gets dumped out the back helps reduce the magnitude of the low pressure zone that would otherwise exist behind the blunt engine. If you are planning for a flywheel drive prop, the hot side of the jugs will be forward, of course.I am thinking about blowing the air forward. It doesn't matter to the fan which way it blows and I need some heat source in the cockpit most of the year anyway. The fan intake would be the center of the pusher prop which is a dead zone anyway. Might even reduce drag.
With a proper inlet, you'll get a little help from the airflow, right? Similarly, on the back end you can arrange things (that exhaust/ejector . . . ) so that the pressure is slightly below ambient. Every little bit . . .I am poking my calculator...
920cfm at 1kPa, ~.147psi or 4" water, is 434W of work. If the fan is 60% efficient, thats 720W, or about 1hp.
I don't think scooping up dynamic pressure is really "free," compared with a streamlined nacelle and a buried fan. Especially when gliding.I know you are planning for a low speed project, but going with the breeze does give you the "free" flow from the airspeed dynamic pressure. Also the cooling air that gets dumped out the back helps reduce the magnitude of the low pressure zone that would otherwise exist behind the blunt engine. If you are planning for a flywheel drive prop, the hot side of the jugs will be forward, of course.
That's possible, I did that some time ago and it was a rough measurement of air velocity out of the cooler (and no load on the engine). Will redo this when I have the engine running under load and properly instrumented.There is something wrong with your oil cooling numbers, TiPi.
3.3kW into 72cfm would raise the air temp 80C. That'll be tricky with 80C oil and non Siberian temperatures.
12lpm and 10C drop I get around 3kW, so that is in the ball park.
you might need to add quite some prop extension to get the cylinders back far enough to clear the belly slope. Might be best to hang the Briggs upside-down, add the prop extension to the flywheel and leave the fan on there. Just reduce the weight and size of the fan shroud and use any opening in the fuselage to expel the hot air. This is going to be a beast to cool with airfow only.Inlet will be annular behind the spinner. I might have the exit under the mufflers, stealthy, but not the best place aerodynamically. Alterntivley, a nice rearward exit thanks to a 'badly fitting cowl'! Mufflers will be external and disguised as ejector pipes. That ticks the 'some external components' box for 103 power calculation.An ejector system would be nice, but a major PITA to build with my twin mufflers.
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The thing that looks a bit like an air scoop beind the spinner is an oil deflector for the reliably leaky Rotol prop. Walk back a few more paces.
I cut the former that is about at the end of the first ejector stub last weekend. It's the approximate firewall. My 'lil Briggs looks small sat on it.
Very true. And if you'll be gliding with the engine shut down or at low throttle, relying on the fan for airflow will also reduce the chances of shock cooling the engine.I don't think scooping up dynamic pressure is really "free," compared with a streamlined nacelle and a buried fan. Especially when gliding.
I'll be using a redrive. My engine bay looks like it will have an echo. Lots of space. I need to know the pressure drop before I can determine what airflow aids are needed.you might need to add quite some prop extension to get the cylinders back far enough to clear the belly slope. Might be best to hang the Briggs upside-down, add the prop extension to the flywheel and leave the fan on there. Just reduce the weight and size of the fan shroud and use any opening in the fuselage to expel the hot air. This is going to be a beast to cool with airfow only.
Keeping the flywheel will allow you to mount a light-weight 3-blade prop for authenticity.
"Tiny engine package!" was what I thought when I saw the drawing Hot Wings posted (below):I cut the former that is about at the end of the first ejector stub last weekend. It's the approximate firewall. My 'lil Briggs looks small sat on it.