Chin scoop and rad vs ventral

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raymondbird

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Could any of you great fellas please comment/critique the cooling system of Ray Watson's Bull Moose here in the video? Seems to be cooling great for him but would it be just a little, or a lot more drag than a good ventral installation like rv6ejguy's fantastic example of.

Installing an LS2 engine into my project and just thinking, why go to all the extra bother of a ventral rad if this will work with a fan and shark gills or like the P85 with a chin scoop setup as well.

Thanks!
 

wsimpso1

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Two reasons for a belly scoop:
  • Significantly lower drag - a decently well done belly arrangement will be better than the best possible chin arrangement because inlet to rad area ratio and duct lengths are important to drag, and both are tough to get in a chin arrangement;
  • W&B management - if your water cooled engine is a tad heavy and/or long, you can get too much nose down moment. Shift the radiator and/or oil cooler aft and help your CG. The more efficient radiator might make for lower weight too.
One reason to skip the belly scoop:
  • You might not be able to find a combo that gives enough radiator with enough ground clearance and leaves enough baggage space. Back country haulers like their belly pod baggage.
Billski
 

llemon

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NACA scoops are TLAR rather than following the guidelines. Might not matter all that much given their location.

Not sure about his radiator, its hard to make out the duct work and especially the outlet. However extremely slanted radiators with short ducts was the direction quite a few aircraft manufacturers were headed in at the end of WW2. This style of rad/duct is also very common in motorsports.
 

rv7charlie

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Airframe structure can influence choice, too. Typically easy to submerge the rad into the fuselage of a tube/fabric design, but trying it on an RV-x is far trickier for a homebuilder to mod safely (P-51 was designed for it from the start). Plumbing an aft installation can be an issue, as well, especially in an airframe not designed for it.

Some of the old docs indicate that placing the inlet as far back as possible improves heat exchanger performance by minimizing the pressure pulses from the prop. But given our limited optimization resources as homebuilders, the difference between the inlet at the prop vs aft fuselage might not be detectable.
 

llemon

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Plumbing an aft installation can be an issue, as well, especially in an airframe not designed for it.
This is a very important issue. Some T-51 had a radiator in the belly. The fittings came lose in flight and the pilot was severely burned.
 

Voidhawk9

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As noted, either setup can work and cool adequately, it's more a question of whether the extra effort to produce a more efficient and lower drag installation is worth it in your case.
In my case, it certainly is, as cooling drag will be a major portion of total drag due to a very clean airframe.
 

rv7charlie

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Kinda like the updraft/downdraft argument among the EZ guys? ;-) The one done best, works best....
 

wsimpso1

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NACA scoops are TLAR rather than following the guidelines. Might not matter all that much given their location.

Not sure about his radiator, its hard to make out the duct work and especially the outlet. However extremely slanted radiators with short ducts was the direction quite a few aircraft manufacturers were headed in at the end of WW2. This style of rad/duct is also very common in motorsports.
Who said anything about NACA scoops? Don't even think they are a good idea for feeding HX's.

Oblique radiators and short ducts make for lousy efficiency, but that is all they have room for in most racecars. A little efficiency loss in race cars is not a big deal because they usually do not get to max steady state speed anyway, constantly accel then decel, corner, accel ...

Airplanes on the other hand climb in one steady state and cruise in another, so the efficiency loss means reduced climb rate and reduced cruise speed. Cooling efficiency matters.

Billski
 
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