VW Heads Designed for Aircraft- Poll

[Aviacs]

for whatever reason, the "fineness" of the fins on these cast heads appears to be limited (e.g instead of 8 fins, could they cast 10 fins in the same distance?). Now, they need to be thick enough to survive and to carry heat their full length, and sufficient air must move through the slot between them. But, given that, more fins per inch = more surface area for heat exchange = cooler heads. Can we get better fins if we extrude or cut them? Cost?

Re: finning, the common aero comparison is between traditional Lycoming cylinders (larger, fewer fins ) being designed to "withstand" heat, vs Continental being designed to "shed" heat. Also, based on fin theory, there are a range of options and a specific cross section. "more/thinner" is not necessarily better, at some point.

The Porshe heads machined from solid aluminum block ("Billet" is a sales word that annoys most machinists - a billet is the rolled blank you sometimes see on a flat bed, headed somewhere to be divided down and rolled or cut to small blanks) seem to work? So one avenue for design exploration. Nonetheless, casting is more likely to approach optimum fin shape (cross section).

I'm going to beat on is some more:
Casting, per se, is not the inhibiting cost factor in most cases. If it is, with complete designs and a stated volume (# of parts), it is easy to compare with a "cnc"'d analogue. A foundry will quote per part, based on volume, that appoaches the retail raw metal cost. They of course have to remove the mould & cores from the casting, cut off the sprues and risers, and lightly de-flash/deburr. ("snag" the castings). For a complex item, about 1/2 the metal poured becomes your casting, the rest (risers, pouring basins, sprues, runners) goes back in the pot. A foundry does need enough volume to amortize the rigging they design, develop, and apply to your pattern to make it pourable; + perhaps a few test pours to prove it. This is what makes only one, or only a"few" castings so expensive.

The real, big, costs of getting a part out of the wishing stage is 1.) thorough design and engineering. 2. tooling.

smt

 

[sotaro]

Re: finning, the common aero comparison is between traditional Lycoming cylinders (larger, fewer fins ) being designed to "withstand" heat, vs Continental being designed to "shed" heat. Also, based on fin theory, there are a range of options and a specific cross section. "more/thinner" is not necessarily better, at some point.

The Porshe heads machined from solid aluminum block ("Billet" is a sales word that annoys most machinists - a billet is the rolled blank you sometimes see on a flat bed, headed somewhere to be divided down and rolled or cut to small blanks) seem to work? So one avenue for design exploration. Nonetheless, casting is more likely to approach optimum fin shape (cross section).

I'm going to beat on is some more:
Casting, per se, is not the inhibiting cost factor in most cases. If it is, with complete designs and a stated volume (# of parts), it is easy to compare with a "cnc"'d analogue. A foundry will quote per part, based on volume, that appoaches the retail raw metal cost. They of course have to remove the mould & cores from the casting, cut off the sprues and risers, and lightly de-flash/deburr. ("snag" the castings). For a complex item, about 1/2 the metal poured becomes your casting, the rest (risers, pouring basins, sprues, runners) goes back in the pot. A foundry does need enough volume to amortize the rigging they design, develop, and apply to your pattern to make it pourable; + perhaps a few test pours to prove it. This is what makes only one, or only a"few" castings so expensive.

The real, big, costs of getting a part out of the wishing stage is 1.) thorough design and engineering. 2. tooling.

smt

Got me! I had looked at that motorcycle design in the last 6 months. Moto Morini... It is true that I don't think of Heron heads as being high performance, and the Morini was thought of as being so... Memories, so fleeting.

 

[sotaro]

What about additive printing longer fins, or extra fins on production heads, or on a new head that would be too expensive for the low volume, to make as good at heat rejection as we need?

 

[sotaro]

View attachment 120437 View attachment 120441
Seems about the same, heart chamber piston looks sleeker.
WaterBoxers were also Heron Heads. No to air cooled pairs.

You got me! I looked at the Moto Morini in the past 6 months. It is a conundrum that the Heron head is not considered high performance, and yet in it's day the Morini was high performance. Cost control was central to Morini's success, and the Heron head was part of that.

 

[TFF]

This guy makes home casting look easy. Some of his stuff is quite complicated. At minimum making patterns for someone else to cast could be done

 

[Hot Wings]

Yes, he has done some pretty intricate castings using his lost foam method. But he still has the problem of the time needed to make the foam patterns - and they are all single use items. For the very low number, and high value, castings he does the time is acceptable. Making tooling for efficient production of the foam patterns for lost foam for low to mid range production numbers is a nut that hasn't yet been cracked.

I personally think that given the constant upgrading of hobby level tooling it wouldn't be long before we can fabricate the tooling to make foam patterns for 100s/year number of castings. In another thread Addictedtoclimbing posted a link to a DIY plastic injection molding unit. If you follow the YouTube down that rabbit hole far enough you can find examples of people making the aluminum molds on 3018 desktop CNC machines (with some upgraded parts) that look to be doing a good enough job to make molds for EPS foam. The process just needs to be scaled up a little bit and polystyrene bead processing added.*
From there the actual aluminum casting process has already been demonstrated, developed and proven by AL203 above.

*Finding a source of less than pallet quantities of expandable Polystyrene beads is another "small" problem to be solved. Shipping for foam beads is just as expensive as it is for aircraft grade spruce or micro, by volume. Andi it degrades over time..............into bean bag filler.