VW Heads Designed for Aircraft- Poll

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Value of purpose built VW aircraft heads

  • Why bother. Who would try to use '30's auto technology to fly.

    Votes: 1 4.2%
  • It's an interesting idea but what we have now is good enough.

    Votes: 2 8.3%
  • If they were close in cost AND better I'd probably use them

    Votes: 11 45.8%
  • It's been needed for a long time. They will make the VW a far better option.

    Votes: 10 41.7%
  • It would be the best thing to happen to EABs in the last 2 decades

    Votes: 0 0.0%
  • Why bother. Who would try to use '30's auto technology to fly.

    Votes: 1 4.2%
  • It's an interesting idea but what we have now is good enough.

    Votes: 2 8.3%
  • If they were close in cost AND better I'd probably use them

    Votes: 11 45.8%
  • It's been needed for a long time. They will make the VW a far better option.

    Votes: 10 41.7%
  • It would be the best thing to happen to EABs in the last 2 decades

    Votes: 0 0.0%

  • Total voters
    24
  • Poll closed .

Vigilant1

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Sorry, but just to re-mention an idea previously brought up by BBerson many posts ago: maybe the head casting and machining ($$, time) could be simplified a lot through the use of add-on extruded AL fins. That just requires flat spaces on the head, a few tapped spots to affix the fin blocks, and the right heat transfer paste. It's easy and cheap to extrude very fine fins (compared to casting them, cleaning out flash, etc), and stock heat sink extrusions are widely available (experimentation will resolve suitable mix of fin thickness, spacing, length, etc). It also allows easy customization for different possible airflow directions. Want bigger fins near the exhaust port? Bolt 'em on.
There might even be folks that would use the flat pads as a basis for oil or glycol cooling of the heads. I think air and AL heat sinks make more sense but it is another option, and it would open up other packaging possibilities.
Again, sorry to step back, but as you are now deep into the details of prototyping I didn't want a possibly good idea to be overlooked.
 
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dwalker

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So here is a 911 head and cam tower. Without the cam, the "tower can be machined as a simple rocker box. The head is finned, but a very simple and nothing terrible to machine. Also pictured are CMW Billet 911 heads. I see a design such as this as a legitimate improvement to the VW cylinder head.
 

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Always good to go back to make sure we are actually going down the correct path. Not so sure I'm doing that but I'm so far down the road I'd kind of like to see the if the gate is open or closed at the end.

My personal preference would be water cooled heads. But that requires a whole different set of modifications - and some new airframes designed around a radiator.
Water cooled heads have been made in the past by simply TIGing on some metal around the existing top and bottom fins with some tubes to seal off around the head studs. There are such things as bolt on water pumps.

H2O head.jpg Not a stock head, but the same idea.

I too would like to see a modular approach like the 911. There just isn't enough room on the 1/2 VW head unless you basically copy the Mosler's in post #158. For a 4 cylinder it looks like it might be possible.
For now the 1/2 VW head set looks like a simpler path. Pic of the stock VW pushrod angles (sketch) and what could be done with individual stud mounted rockers:
V3 angles.JPG If the rocker studs were screwed into a rocker carrier similar to the 911 then there would only need to be A and B heads. With a siamesed head, like the stock VW, we would still need right and left castings to fix the pushrod angles. Or just accept the lousy pushrod angles and just move the exhaust port for better exhaust valve stem cooling.

If only someone would put the 356/912 crankcase back into production............
 

Vigilant1

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My personal preference would be water cooled heads. But that requires a whole different set of modifications - and some new airframes designed around a radiator.
With more fins, good baffling plus a head designed to reduce heat uptake by the exhaust valve stem, it seems 75 reliable continuous HP should be available from an air cooled Type 1 without a problem. That's great, and it starts bumping against other limits (esp of the Mg case and bearing saddles). Water cooling might still be attractive to some folks, given the more uniform head temps possible and the packaging options. I'd think planes designed for an 80 HP Rotax 912 might be adapted readily (especially faster ones where a smaller prop wouldn't be a big problem). A Sonex with an underbelly rad scoop would look fine, and shaving some cooling drag while allowing more continuous HP (say an honest 75 HP with moderate CHTs) would be welcome.
 
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dwalker

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Always good to go back to make sure we are actually going down the correct path. Not so sure I'm doing that but I'm so far down the road I'd kind of like to see the if the gate is open or closed at the end.

My personal preference would be water cooled heads. But that requires a whole different set of modifications - and some new airframes designed around a radiator.
Water cooled heads have been made in the past by simply TIGing on some metal around the existing top and bottom fins with some tubes to seal off around the head studs. There are such things as bolt on water pumps.

View attachment 119041 Not a stock head, but the same idea.

I too would like to see a modular approach like the 911. There just isn't enough room on the 1/2 VW head unless you basically copy the Mosler's in post #158. For a 4 cylinder it looks like it might be possible.
For now the 1/2 VW head set looks like a simpler path. Pic of the stock VW pushrod angles (sketch) and what could be done with individual stud mounted rockers:
View attachment 119042 If the rocker studs were screwed into a rocker carrier similar to the 911 then there would only need to be A and B heads. With a siamesed head, like the stock VW, we would still need right and left castings to fix the pushrod angles. Or just accept the lousy pushrod angles and just move the exhaust port for better exhaust valve stem cooling.

If only someone would put the 356/912 crankcase back into production............


The 996/997 Cup cars used water cooled heads with an air-cooled (930 part number) engine case. The 962 water cars used a similar setup. The amount of power that could be made and maintained for endurance racing was quite impressive.

The advantage Porsche heads have always had is they could be used from 4cyl all the way to 12cyl with very little modifications. I am unsure about the 1/2VW, but I had at one point helped with a 4cyl 911 engine based on a VW crank, custom engine case, and stock 911 cylinders. It did not survive testing (ran out of money and talent started leaving) but showed promise as a potential "big bore" road race engine. It was also shopped around to offroad racers but the price and complexity was just too discouraging.

Not sure you could use a 911 head per se, but the idea of a modular head system would work, and be cost effective. While VW cyl heads are cheap, the issue is they WILL crack and they need service at short intervals, and often need to be replaced rather than renewed. The value in a modular billet or cast head system is that the front end cost is a little higher, but the long term cost of ownership and increased reliability outweighs those initial costs. Being able to replace a single head or a single rocker box is a good thing to have as well.
 

Vigilant1

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While VW cyl heads are cheap, the issue is they WILL crack and they need service at short intervals, and often need to be replaced rather than renewed. The value in a modular billet or cast head system is that the front end cost is a little higher, but the long term cost of ownership and increased reliability outweighs those initial costs. Being able to replace a single head or a single rocker box is a good thing to have as well.
The available VW aircraft heads are so inexpensive and so readily available that doing much work on them is cost prohibitive.
Here's the head Sonex sells, already drilled for a second plug. $325 per side, with new valves, springs, guides, bored for 92mm cylinders, etc, ready to run. Now, I suspect aftermarket heads with better cooling are available (thinking hard about the CB Panchito heads....), but they are all relatively inexpensive, and that can make things tough for someone trying to make a better mousetrap, to be handcrafted in small numbers.
I suspect Hot Wings is right to concentrate on heads that can appeal to the 1/2VW market. Some full VW builders will be interested too, but many of those guys are price sensitive.
 
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ToddK

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The available VW aircraft heads are so inexpensive and so readily available that doing much work on them is cost prohibitive.
Here's the head Sonex sells, already drilled for a second plug. $325 per side, with new valves, springs, guides, bored for 92mm cylinders, etc, ready to run. Now, I suspect aftermarket heads with better cooling are available (thinking hard about the CB Panchito heads....), but they are all relatively inexpensive, and that can make things tough for someone trying to make a better mousetrap, to be handcrafted in small numbers.

Heard very good things about those Panchito Heads
 
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It was also shopped around to offroad racers but the price and complexity was just too discouraging.
Same problem for aircraft conversions. :(
We are thinking along the same lines as to what is desirable but having to work around existing architecture can be extremely limiting. I've been thinking about this since well before Hoover died and I just haven't come up a simple/cheap solution. A modular head that could be used in the future with a purpose built crankcase - and - existing hardware would eliminate one part of the development process.

I suspect Hot wings is right to concentrate on heads that can appeal to the 1/2VW market.

Not the market so much as it is a cheaper place to make mistakes. Half of the parts, aluminum that needs to be melted and almost half of the machining steps/jigs.
 

reo12

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Sorry, but just to re-mention an idea previously brought up by BBerson many posts ago: maybe the head casting and machining ($$, time) could be simplified a lot through the use of add-on extruded AL fins. That just requires flat spaces on the head, a few tapped spots to affix the fin blocks, and the right heat transfer paste. It's easy and cheap to extrude very fine fins (compared to casting them, cleaning out flash, etc), and stock heat sink extrusions are widely available (experimentation will resolve suitable mix of fin thickness, spacing, length, etc). It also allows easy customization for different possible airflow directions. Want bigger fins near the exhaust port? Bolt 'em on.
There might even be folks that would use the flat pads as a basis for oil or glycol cooling of the heads. I think air and AL heat sinks make more sense but it is another option, and it would open up other packaging possibilities.
Again, sorry to step back, but as you are now deep into the details of prototyping I didn't want a possibly good idea to be overlooked.
Fins need to have a rather critical thickness to length ratio and spacing distance. The requirements change for type of airflow(pressurized and if high pressure or low pressure or free air). A good example of high pressure air cooling was used on the Corvair engine. Low pressure air cooling was used on VW's. I used to have the formulas for aiding in determining fin requirements. They were on the net some 20 years ago. Possibly someone can still find them.
Just adding length to fins may not accomplish much.
Increasing number of fins by reducing space between the fins can compromise the air flow between the fins needed to remove the heat from the fins.
A fin that is too thin for length will get cold easily but will not have sufficient thickness to conduct much heat to the edge of the fin. A good demonstration of this is to remove a 2 inch wide strip from a roll of kitchen aluminum foil. Crease it lightly lengthwise so it can be held by hand from one end and remain rigid. The opposite end can be heated with a torch or stove burner to the point of melting yet the hand held end remain cool enough to hold onto with bare fingers.
 
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Vigilant1

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Fins need to have a rather critical thickness to length ratio and spacing distance. The requirements change for type of airflow(pressurized and if high pressure or low pressure or free air). A good example of high pressure air cooling was used on the Corvair engine. Low pressure air cooling was used on VW's. I used to have the formulas for aiding in determining fin requirements. They were on the net some 20 years ago. Possibly someone can still find them.
Just adding length to fins may not accomplish much.
Increasing number of fins by reducing space between the fins can compromise the air flow between the fins needed to remove the heat from the fins.
A fin that is too thin for length will get cold easily but will not have sufficient thickness to conduct much heat to the edge of the fin. A good demonstration of this is to remove a 2 inch wide strip from a roll of kitchen aluminum foil. Crease it lightly lengthwise so it can be held by hand from one end and remain rigid. The opposite end can be heated with a torch or stove burner to the point of melting yet the hand held end remain cool enough to hold onto with bare fingers.
Right. The fins have to be right dimensions, at the right spacing, to optimize heat transfer to the passing air. There are a lot of variables, but we know a couple of things:
Here are some purpose-built aircraft heads designed by folks who presumably knew what they were doing. They produce acceptable cooling of 4 cylinder aircraft engines of about 70-80 HP at typical climb speeds:
Jabiru 2200:
1639440504268.png
Continental C-75
1639440682725.png

Aero VW:
1639442192917.png

Comparing the fins on the VW to the Jabiru and the C-75:
1) The fin spacing and the fin thickness doesn't seem to be very different.
2) The fins on the C-75 and Jabiru seems to be a LOT deeper, especially on the head
3) The fins on the C-75 and the Jabiru continue well past the top of the combustion chamber. On the VW, the tiny bit of fin area above the combustion chamber and on the exhaust port appears to be little more than an afterthought.

The VW fin depth is constrained by the need to fit inside the stock cooling enclosure used on VW cars. There's no reason a cylinder head designed specifically for VW aero engines would need to be constrained in this way.

FWIW, from a couple of online sources it appears the stock Type 1 blower moves about 1500 CFM of air and generates about 5 PSI of pressure inside the cooling shroud. That's not a lot of pressure, we have about the same amount of dynamic pressure available at 50 MPH airspeed. So, even a slow plane in climb, with well done and sealed baffling, should be able to match the airflow through the fins of a VW bug. But the 1600CC VW bug put out a max of approx 58HP, and typically didn't do that for very long. If we want to make a reliable 75 HP or so for a long time in an airplane, especially at climb speeds (where we'll be limited in the amount of dynamic pressure available), it's not surprising that we might need more fin area.
 

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Pops

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Maybe generate more sales of heads by designing a new cooling enclosure to fit the VW fan housing so they could be used on VW engines in autos
Added-- Need to measure how much the bottom of the fan housing can be trimmed for clearance for larger and taller cylinder tins.
 
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I thought about the idea of different housings for ground bound. The more I thought about it the less appealing the idea became. Most (all?) of the non-stock VW heads have been aimed at high flow race use.
Valves and ports for 100 efficient Hp @ 3600 rpm (very optimistic) probably don't work so well at 6000+.

What is the best engineering tool available? Lots of people would say Excel.
For me it is a shower. I seem to get an inspiration to solve a nasty problem after only a couple of minutes in the shower. The whole idea of utilizing the 911 style modular heads was about getting to the point yesterday that I was considering giving up on the idea. I just couldn't find enough area for the bolts needed to keep everything together. I think I may have figured out how to bolt a rocker carrier to a single head, or a pair, during my last shower.

New problem - My CAD computer has taken to just simply shunting down at random. Nothing hot, but I suspect a power supply.

Fin thickness and spacing? I'm using monkey see, monkey do. Limit is probably going to be what I can mold/cast.
 

Vigilant1

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Fin thickness and spacing? I'm using monkey see, monkey do. Limit is probably going to be what I can mold/cast.
Look at that Jab head for inspiration?. Just machine flat pads on the outside of your head wherever it is convenient, screw on a block of extruded fins as thick and tall as you want, and bore down into it to make clearance needed for any bolts, spark plugs, exhaust flanges, etc you need. No flash to clear out, no fragile fins on your casting, etc.
 

Pops

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I thought about the idea of different housings for ground bound. The more I thought about it the less appealing the idea became. Most (all?) of the non-stock VW heads have been aimed at high flow race use.
Valves and ports for 100 efficient Hp @ 3600 rpm (very optimistic) probably don't work so well at 6000+.

What is the best engineering tool available? Lots of people would say Excel.
For me it is a shower. I seem to get an inspiration to solve a nasty problem after only a couple of minutes in the shower. The whole idea of utilizing the 911 style modular heads was about getting to the point yesterday that I was considering giving up on the idea. I just couldn't find enough area for the bolts needed to keep everything together. I think I may have figured out how to bolt a rocker carrier to a single head, or a pair, during my last shower.

New problem - My CAD computer has taken to just simply shunting down at random. Nothing hot, but I suspect a power supply.

Fin thickness and spacing? I'm using monkey see, monkey do. Limit is probably going to be what I can mold/cast.
I usually get the answers to questions that is troubling me doing the middle of the night when I wake up with the answer. I'll try that shower thing :)
Usually its trying to find something I put up in a place where I will not forget where I put it.
 

stanislavz

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Just use one valve per cylinder (opened full for exhaust/intake stroke) and direct petrol injection... Event at bdc, just after exhaust stops. So not so high pressure needed. And much cooler head - valve and air duct is being cooled not only by external fins, but buy internal too.

Or even like this one :
1639502482831.png

1639502500027.png
 
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dave wolfe

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Ive been looking at some details for my Sonex project and came upon an interesting issue. With 55cc combustion chambers, 2180s and 2276's need way too much cylinder shims to get the CR set, resulting in like .250" squish. I havent seen any dished pistons for sale that would help get squish back into the .040" range. The biggest CC heads Ive seen for sale are Panchtos that can be ordered with 68cc chambers when cut for 94mm cylinders.

It seems the 2180s are often poor running and maybe this is part of the problem? I had always assumed it was poor carburation but maybe not?
 

dave wolfe

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More what Im getting at is engines run better when the squish (piston top at TDC to bottom of cyl head perimeter) is near .040". To do that on a big VW, you need a combustion chamber volume around 68cc's to get 8.5 CR. The common VW heads are 55cc.

Dishing the pistons by 13 cc would also do it. Im not sure if there is enough meat there.
 
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