Who Wants Zero Cooling Drag?

[rv6ejguy]

Originally Posted by BillL

This is why my good friend Bill Brogdon designed the Continental 4 cylinder diesel as a 2 stroke. Also, it is not just the prop, the reaction to compression torque at idle is a huge oscillating moment on the airframe. Smaller displacement engines (diesel) with high boost yield the highest hp/lb. Until direct injected gasoline is used as a stratified charge combustion to mitigate detonation, 100LL severely limits high BMEP with low BSFC.

A new product, gasoline or diesel, is limited by ROI not technology.

I do a detailed comparison on various aero engines, including the new Adept 320T SI engine here: https://www.youtube.com/watch?v=GJy93vrbvw0&t=4s

From dyno data, it competes favorably on BMEP and BSFC fronts with the new Conti CD-300 diesel, using "old school" port injection.

On the cooling drag question some of you may have missed my 2015 Kitplanes article here: https://www.kitplanes.com/the-meredi...ct-or-fiction/

I am currently working on another video on liquid cooling, looking at other successful flying examples from some of my customers and friends flying auto conversions.

[Cumulo]

Originally Posted by scsmith

I know that adding heat to the boundary layer will cause transition if it is laminar (in a gas. In a liquid, it has the opposite effect.) Once you have a turbulent boundary layer, IIRC heating lowers the skin friction coefficient. We did a flight test on a Lear Jet years ago where we heated the fuselage to lower the cruise drag. It was a modest benefit, not huge. The test results agreed with the pre-test predictions. There may be a trend with Mach no. where the opposite result might be true at very low Mach no., I don't remember. Certainly in supersonic boundary layers, the skin friction reduction from heating is very significant.

I think it is correct that the speed record runs with the ME 209 were indeed done without radiators, but I don't have a reference to verify that right now.

Steve, you are correct. My first thought in reading the thread regarding putting the heat on the leading edge surface was that it would trip the boundary layer to turbulent. Maybe a skin radiator should be aft somewhat to preserve whatever laminar flow that might be possible.

I dug down and found my Hoerners. You are right. Adding heat to a turbulent BL will reduce the turb BL fiction somewhat. However, he goes on to say that the heated wing, being mostly in accelerated flow may produce a negative thrust component due to the added heat. Somewhat like a negative ramjet. Effects could be neutral.

OK, how about this:
We use ebullient cooling but dump the wet steam between the spars of somewhat conventional wings and recover the condensed coolant. Presto. The wings are radiators.

Ron

[rv6ejguy]

The folks who know most about this topic retained a traditional rad in a very modified ventral scoop sans scupper, to set the piston world speed record a few years back. Freeze frame at 1:00 to have a look at that: https://www.youtube.com/watch?v=jha18gdhI6Y

They are also spraying water through the HX of course. Best pass, 545 mph. Unfortunately the engine went south before 4 good passes could be completed.

Bottom line is nobody would consider surface conduction cooling on a GA aircraft. Completely impractical for numerous reasons.

Few liquid cooled GA aircraft apparently care much about low cooling drag as they continue to use dreadful radiator layouts. The new Diamond DA50RG, despite turbocharging and retractable gear, is no faster than a good 300hp RV-10. They must have massive cooling drag given the poor duct layout for the rads and intercoolers.

[jrs14855]

Super Unlimited's , a sight unlikely to ever be seen again.