# VW Heads for Aircraft - Billet

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#### Vigilant1

##### Well-Known Member
It would be important to find a fin configuration (and overall head configuration) that is practical to fabricate (so, able to be manufactured and profitably sold to the prospective buyers) and "good enough". In general, the aero VW market is famously "price sensitive".

#### Hot Wings

##### Grumpy Cynic
Log Member
the aero VW market is famously "price sensitive".
Is that just a polite way to say some of us are parsimonious?

Cheap.

#### Aviacs

##### Well-Known Member
{re: Phlatties):
Simplicity would be the goal.
Besides intrinsically reducing the thermodynamic efficiencies/(HP) at a given displacement, I'm pretty sure a re-design to flat head/sidevalve design would be far more complex than a pushrod overhead valve replacement head for an existing motor. You've simply moved the thermal issues down to the cylinder, to an area which is much more sensitive to distortion due to asymmetry & often a generally more restricted/limited area for heat rejection

Especially if there is a preference to use aluminum for the cylinder. (has it even been tried successfully?) With CI cylinders, there is still the matter of a cast design, in which the bores stay suitably round & straight, at both ends of the scale from cold to running temperature.

I'm starting to wonder if going the opposite direction would not be simpler & more productive overall, if the merits of re-locating the intake and exhaust ports are strong enough. For an opposed twin, there seems little merit to other than *perhaps* better finning, considering a VW based design. Just add some better finning and leave it alone.

For the 4, all things considered and re-locating the ports, an OHC design starts to look like the easy solution.
Weight would increase by aprox one extra camshaft & a gear (or belt) train. A belt design might almost be offset by the reduced casting material for bosses and the parts including rubber & metal, of the pushrod system.

smt

#### blane.c

##### Well-Known Member
Started looking at inline flathead engine. If able to source block like @ link below could be not a lot heavier than VW and 1/2 again the power?

#### Hot Wings

##### Grumpy Cynic
Log Member
Don't want to derail the OPs thread but:

OHC IS a simple solution to the head problem but leads to other problems for a retrofit.
Gears and belts are relatively trivial.
It increases the width of the engine by more than an insignificant amount.
2 new cams need to be produced.
How to plug up the oil system from the now missing original cam?
How to drive the oil pump if the original cam is removed?
There is also what to do with the original engine block that now doesn't need all 8 pushrod tubes for oil return.

This path kind of leads to both new heads and a new block. This makes Subarus look more attractive............

#### Aviacs

##### Well-Known Member
Re: Donvan Model D block:

Intriguing idea.
Certainly looks good in the pix.

200.5 ci/3285cc
single plug

Roughly $12,000 in kit form, plus a few necessaries like pistons, rings, carburator? Stock crank included above @$2950.00
How much for a crank that would support a direct drive propellor?

Assuming constant loss electronic ignition, what does it weigh all up with a cooling system, & extended crank?
How about with an alternator, or magneto, or both?

Will it run for hours at a time at 75%+ without distortion, or is it optimized for sub 9 second runs?

Note that for increased HP they essentially suggest the OHV conversion.
I'm not conversant with drag machines, not sure what (stock/OEM?) heads they are designed to use?

So many things are simple.
Then they have to work in systems to better than prior standards & costs.

Seriously, with a well designed extended crank propshaft, for the right airplane, that could be ideal after a total weight, total cost, total durability comparision with existing designs such as an O200 or 0235 is considered.

smt

#### rmeyers

##### Well-Known Member
Machining Thoughts

As Aviacs said, finding the correct fin pitch and thickness takes some thought. Early on in the original thread there were several references to engineering reports concerning air cooling. One that I like and didn't see mentioned is this; NASA TP-1054 'Effect of Cylinder Head Fin Passage Length On Optimization Of Cylinder Head Cooling Fins'. The graphs are easy to read and compare.

Also as Aviacs said, a contoured cutter would be desirable. The reason that I did not at first advocate using one is the cost and time/cost involved. Besides the cost of having a cutter custom made the contoured cutter would be much slower in machining. A saw only cuts on its edge, the contoured cutter by definition cuts on all sides. This means shallow cuts and many passes for each groove. Is it worth it? Don't know, possibly. We should keep it in mind. I was thinking the same as the comment above, that 'the aero VW market is famously "price sensitive" '. Along those same lines, I have had slitting saws modified to radius the cutting edge so that the groove they create has a radiused bottom instead of sharp corners.

#### blane.c

##### Well-Known Member
Re: Donvan Model D block:

Intriguing idea.
Certainly looks good in the pix.

200.5 ci/3285cc
single plug

Roughly $12,000 in kit form, plus a few necessaries like pistons, rings, carburator? Stock crank included above @$2950.00
How much for a crank that would support a direct drive propellor?

Assuming constant loss electronic ignition, what does it weigh all up with a cooling system, & extended crank?
How about with an alternator, or magneto, or both?

Will it run for hours at a time at 75%+ without distortion, or is it optimized for sub 9 second runs?

Note that for increased HP they essentially suggest the OHV conversion.
I'm not conversant with drag machines, not sure what (stock/OEM?) heads they are designed to use?

So many things are simple.
Then they have to work in systems to better than prior standards & costs.

Seriously, with a well designed extended crank propshaft, for the right airplane, that could be ideal after a total weight, total cost, total durability comparision with existing designs such as an O200 or 0235 is considered.

smt

#### Vigilant1

##### Well-Known Member
Also as Aviacs said, a contoured cutter would be desirable. The reason that I did not at first advocate using one is the cost and time/cost involved. Besides the cost of having a cutter custom made the contoured cutter would be much slower in machining. A saw only cuts on its edge, the contoured cutter by definition cuts on all sides. This means shallow cuts and many passes for each groove. Is it worth it? Don't know, possibly.
I do have doubts that the difficulty of cutting tapered fins will be worth the trouble (just make them sub-optimum straight sided and a few percent longer. Cheaper, just as much cooling, and a couple more ounces). But, if this is to be a CNC operation and tapered fins are desired, they could be made with a regular saw by slightly tilting the arbor (or the piece) and making two passes on each slot. A saw with a rounded radiused edge would make a nicer filleted bottom for the fins, increasing heat transfer a little and reducing stresses/ potential cracking. If the blade with a rounded edge is more expensive or less effective at cutting, it really only needs to be used for the final cut of each slot.

#### rmeyers

##### Well-Known Member
I do have doubts that the difficulty of cutting tapered fins will be worth the trouble (just make them sub-optimum straight sided and a few percent longer. Cheaper, just as much cooling, and a couple more ounces).
My thoughts exactly.

But, if this is to be a CNC operation and tapered fins are desired, they could be made with a regular saw by slightly tilting the arbor (or the piece) and making two passes on each slot.
That might work but there is a high probability that it won't. The first cut would be fine but the saws are not rigid enough to make a cut half in and half out of the metal. The saw will most likely bend away from the cut. It probably would be worth an experiment to see.

A saw with a rounded radiused edge would make a nicer filleted bottom for the fins, increasing heat transfer a little and reducing stresses/ potential cracking. If the blade with a rounded edge is more expensive or less effective at cutting, it really only needs to be used for the final cut of each slot.

#### Hot Wings

##### Grumpy Cynic
Log Member
The saw will most likely bend away from the cut.
So will the fin on the back side cut. To bad EDM is so slow.

#### rmeyers

##### Well-Known Member
So will the fin on the back side cut. To bad EDM is so slow.
I don't know exactly what you mean. Could you explain further?

#### rmeyers

##### Well-Known Member
So will the fin on the back side cut.
Sorry, I meant the part about the back side cut.

#### Hot Wings

##### Grumpy Cynic
Log Member
Actually - I was mis-imagining this.
Only the top and bottom fins would have any real tendency to deflect. The inner fins would still have a good solid mass on the 'backside'.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
My immediate thoughts on reading the OP:

Fin shape for maximum heat transfer is not straight, but is tapered, thicker at the base, thinner as they get towards the free end. This means your saws would be tapered and cut on the flanks, or you would make two passes with angled saws or have a gang of progressively smaller saws on a shaft and pass the shaft at an angle to the bore;

How do you cut fins around the exhaust port with slitting saws? Nominal aircooled head design has air and fins around the exhaust port, and (IIRC) the exhaust valve guide too. Is that not one of the big limitations for sustained power in Bug engines? This part of the head may require some significant 5 axis time with little cutters;

Stresses in heads are not huge, so I suspect that raw strength is not so important. Head temps on certified airplanes set max continuous power. Go above creep temperature, and the engine life will be short. My bet is you want to select head alloy based upon creep characteristics, and that may not even resemble the casting alloys currently used.

Good luck with this...

#### Hot Wings

##### Grumpy Cynic
Log Member
This video, starting at 4:40, shows what kind of work is needed to cast well optimized fins.....................lots of work.

#### rmeyers

##### Well-Known Member
How do you cut fins around the exhaust port with slitting saws?
Funny you should say that, my next post (now this one) was going to address that very issue.

I'm going to digress here and give a little background that lays the basis for what I am going to describe.

What is our immediate goal? To get rid of waste heat. More specifically, to get rid of waste heat from areas where it can cause malfunction. For example, we really don't care, within reason, how hot our exhaust pipes get. They're usually steel or stainless and can stand the heat without losing their functionality. We are concerned about how hot the cylinder head, and more specifically some areas of the cylinder head, get. The areas of greatest concern are the EX valve, cracking between adjacent parts, for example valve seats that have different thermal profiles, EX valve seat and the EX valve guide. Taking these in order.

EX valves are not much of an issue in themselves anymore. A normally aspirated, gasoline burning engine is hard put to do any damage to a stainless steel or Inconel valve. You can hurt one over time but you almost have to try. Not to say that valve selection isn't important, it's just that if everything else is good, valves are the least areas of concern.

Cracking between valve seats or valve seats and spark plug holes is best taken care of by careful design and ensuring that the heat gradient between hotter and relatively cooler parts (EX seats and IN seats) is kept as low as possible.

EX valve seat and the EX valve guide; keeping these cool is the prerequisite for having a successful engine.

There are two ways of keeping the EX cool. The first, and the way most everyone focuses on, is to extract heat from these areas and discharge it to the air, either aluminum --> air with fins or aluminum --> water --> air with a radiator. The second way is to keep the heat away from those areas to start with. This is a design philosophy that the Japanese have used with great success.

After all that build up it's actually simple. Make the EX port as short as humanly possible. And then make it shorter. Get the hot gases into the exhaust system pipes as soon as possible. The longer the hot gases are in contact with the aluminum cylinder head the more they heat it up. Less contact, less heat build up , less heat to remove with our fins. This post is getting long and I still have more to cover but I can give examples of successful use of this design philosophy if anyone is interested.

Attached is a kind of low res (didn't know what the rules were about pics) section view of an actual cylinder head designed and built for a customer. This engine is successfully meeting all of its' specs and is used in a research environment. The EX port is in red. The reason it looks bigger than the IN port is that this is really a 3 valve engine and only one IN valve is shown. To put the size in perspective, the cam bearing bore at the top is approx 1.0 inch (25mm). The recessed area at the right hand end of the EX port is the area where the exhaust spigot is threaded.

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