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 .

Hot Wings

Grumpy Cynic
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Putting this in the Supplier/Manufacturer section because it is kind of an informal market analysis. Been thinking about this for quite a while and it's looking like I may need a project to occupy my time when it's too cold to venture outside.

What I'd kind of like to find out is just how much of a demand there would be for a clean sheet designed air-cooled VW head for aircraft use. These would incorporate dual plugs, ports designed for direct drive RPMs, better cooling of the exhaust valve and overall and a few other features to make them better for aircraft use. These would be A and B heads, or front and rear thus requiring 1 head per cylinder, similar to the SCAT split port head concept.

Any ideas or thoughts, positive, negative, or even extremely outlandish are welcome. No hardware is promised. For now this is just a Vaporware thought project.
 
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dougwanderson

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Is dual ignition really needed? Bigger cooling fins, both cylinders one piece, bronze valve seats.
Or revive the water cooled heads. And a gearbox redrive on the flywheel side!!!
 

Hot Wings

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Is dual ignition really needed?
Needed as in to be functional? No. For aircraft redundancy and better combustion efficiency? Very likely.

A and B heads reduce the cost if only one head is damaged and needs to be replaced - and they can be used on 1/2 VWs. It does double the amount of tooling needed for the castings.
 

FritzW

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About a month ago I picked up a low time HAPI conversion with Mosler heads. The heads are pretty neat but I wonder what the advantage is (I don't know much about them) better cooling? more HP from better airflow? The spark plug holes are pretty close together, is cracking between the holes an issue? I also wonder if dual ignition prevents more problems than it causes.

I voted for "close to the same cost but better" ...not knowing what "better" means. But if there was a newfangled set of VW heads on the market and they seemed realistic and affordable I'd buy a set in a heartbeat.
 

blane.c

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I like the idea of independent heads so they can be used on 2 cylinder conversions. From recent reading about VW, the valve seats and the pencil thin valve stems are as much in need of improvement as the need for improved cooling.
 

Vigilant1

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Yes!
Thoughts:
1) Why separate heads? The unitary front/rear shared head adds a lot of rigidity which reduces strain on the through-bolts (and where they are tapped into the case), reduces strain on the spigot/case joint, and helps keep the cylinders in alignment which reduces strain on the connecting rods and even the crank. I don't see an advantage to anyone building a 4 cyl engine, and I would need to see them be successful in a lot of 4-cyl VW airplane engines before making the leap. Our magnesium case is a known "limitation," and reducing vibration overall and stress on the crank bearing saddles and cylinder joints in particular helps it live a longer life. It would seem that the unitary fore/aft head contributes to these goals.
2) A "for airplanes" head should have smaller valves than the big-bore racing heads do. This allows more "meat" between the valve seats and also between the valves and the spark plugs, less cracking. At 3400 RPM, we just don't need the larger valves.
3) Pre-inserted steel liners for the plugs to reduce hole stripping at plug changes.
4) Yes, dual plugs.
5) Minor nit: Maybe a convenient, good pre-tapped spot for a CHT sender.
6) Obviously, fatter fins esp near the exhaust valves. Just as important: better cooling airflow through the fins in that area. No flashing, no "dead end" channels, airflow designed to run smoothly from top to bottom.
7) Single vs dual port (assuming a unitary head)-- I think (IIRC) we determined the crossover point was approx 1900 CC: below this, a single port offered better torque at "airplane RPMs", above this RPM a dual port was needed to provide adequate flow. There was nothing scientific about the rationale (except it matched the flow rate at which VW changed from single to dual ports, and it appeared to match the experience of those who fly these engines).
8) For consideration: Deliberately keeping the aluminum extra thick around the exhaust valves will allow more heat to migrate to the cooler parts of the head and help even out the temperatures across the head (reducing cracking). You asked for outlandish ideas: keeping the aluminum very beefy around the exhaust valve might also make it possible for owners (on their own) to bore a hole straight through this area (on each side of the exhaust runner) and insert a straight liquid cooling line (for oil) through each of them. This could take a >lot< of heat away. Just a thought.

We've hashed this "for airplanes VW head" idea over before, I think Pops threw in some good suggestions I probably missed. Thanks for bringing it up.

Go! Go! :) (easy for me to say, from the sidelines!)
 
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BBerson

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Dual ignition is useful for combustion on large bore cylinders.
The Limbach is single ignition. The valve seats should be less corrosive prone metal.
 

Hot Wings

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Clarification:
My definition of better is a set of heads that produce at least as much Hp as the originals, with at least the same BSFC, don't weigh too much more (extra fins do add weight), and most importantly last a lot longer with a better MTBF.

Other thoughts:
1) Separate heads can actually reduce the stresses on the block. The stock heads don't expand when hot in a universally linear fashion. If purely separate heads do turn out to have stability problems they can be modified with a one piece Rocker box to tie the 2 heads together, much like a 911. Getting rid of the different length head studs helps a lot too.

2) Yes, the ports and valve sizes need to be made for direct drive aircraft rpm's. They can be moved a bit too to make tighter cowling possible.

3) Maybe. Use of a torque wrench is good practice. TimeSerts can always be installed in the field if needed.

5) Good thought! The location would have to be determined from test heads. Having a standard location makes it a better diagnostic tool when comparing one plane to another.

6) A primary goal.

7) Dual ports - with either dual or A/B heads - of the appropriate dimensions. Can't ram tune the single port as well/easy as the dual. It does complicate the induction system a little bit.

8) "insert a straight liquid cooling line (for oil) through each of them. This could take a >lot< of heat away. Just a thought"
Possible, but may be counter productive and add heat to the system. Keeping the exhaust port short in the aluminum head and transitioning as quickly as possible to steel exhaust moves the heat away from the head quicker. Some auto heads actually cast in steel liners to keep the heat from transferring.
 

Tiger Tim

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I like the idea of independent heads so they can be used on 2 cylinder conversions.
And radials! Also, if the heads are developed from a clean sheet perhaps they can be arranged for top intake and bottom exhaust. That may allow all four heads to be the same while also allowing them to be used in VW-derived inline engines. Or maybe I’m just getting too wishful over the whole thing.
 

Hot Wings

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And radials!
Another option I hadn't considered! The way I've got things laid out the intake port is easy to move to the side, as for a 1/2 VW. For a radial all that would be needed is a set of A or a set of B heads.

radial.jpg

Edit: That is a 33" diameter overall.

Edit #2:
After thinking about this far too much last night this may not be the way to go for a radial. A flat or "L" head like the old VW radial kit or similar to the D engine would make a more compact radial.
 
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Toobuilder

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With the understanding that I've yet to be interested in the low end of the HP scale for aircraft engines, hasn't the "heyday" of VW conversions passed us by? Seems to me if there was a real need we would have seen it developed by now.

As a tangent- I always wondered why people didn't focus on the Type 4 engines... Much larger and certainly plentiful.
 

Hot Wings

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Much larger and certainly plentiful.
Plentiful may be a geographic thing? Even when I was in the VW biz IVs (1.7 to 2.0) were rare around here. There are probably more Corvairs available now.

They were a more robust engine than the Tp1 but with only 500,000 TP IVs produced and then the engine being used in the later buses and 914 there never were too many in circulation.
 

Topaz

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... They were a more robust engine than the Tp1 but with only 500,000 TP IVs produced and then the engine being used in the later buses and 914 there never were too many in circulation.
Plus, in the 914 installation, they're fuel-injected. Which, until relatively recently, meant it was a lot harder to convert one for airplane use, since that process also involved a change of the entire induction system. The D-Jetronic and L-Jetronic injection systems aren't as flexible as modern ones, and aren't really suitable for airplane use.
 

Vigilant1

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As a tangent- I always wondered why people didn't focus on the Type 4 engines... Much larger and certainly plentiful.
AFAIK, there are no new Type 4 cases. A major attraction for the VW Type 1 is that they can be built entirely of new parts. Cases ares still being made, as well as plentiful aftermarket versions of everything else. This is a major advantage to a business wanting to sell kits or completed engines to homebuilders--the process of finding, transporting, evaluating, and reconditioning used cases adds a lot of manhours, cost, and hassle to the business of selling engines or engine kits. Some individuals with the requisite engine skills have done Type 4 conversions for airplane use, but it is a lonely road.
Plus, almost every new aftermarket part that is specific to a Type 4 is significantly more expensive than its Type 1 counterpart.


. . . hasn't the "heyday" of VW conversions passed us by? Seems to me if there was a real need we would have seen it developed by now.
I know that a VW conversion a homebuilder can build right now is as good/better than they ever were. There's still not another auto engine out there that is flying in direct-drive mode in significant numbers. I don't know about the "heyday" and sheer numbers in the past. But modern manufacturing methods may make it possible for HotWings to produce a custom, small production-run head more economically than could have been done before, and that's why it may be practical today when it wasn't practical in 1980.
 

Hot Wings

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small production-run head more economically than could have been done before,
That would be nice but in the numbers likely to be saleable, and the methods needed, I really doubt if it could be done much cheaper than in the past - adjusted for inflation. There is really no practical way to get the kind of fin spacing needed with CNC.* That leaves casting. And that leads to lost wax**, lost foam, or printed sand. I have no experience with printed sand so it might be the best choice? Final machining can be done with nothing more than a lathe, a drill press, and some jigs if designed for that.

This all excludes exhaust and induction systems which will have to all be created from scratch. The exhaust is no big deal but the intake will need to be built or provided. OTS VW gaskets could be used.

Casler sells 1/2 VW heads for $425 each. Great Plains sells heads for $299ea + $40 for cylinder cut + $125 ea for dual plugs ($232/cylinder). Based on my previous experience a best guess at price is that there would be no way to match Great Plains price and a slim to fair chance of matching Casler's price per cylinder.


*The Jabiru is a much simpler head.

** 3D printed wax is expensive. It's an option for prototypes only unless the price comes way down.
 

Vigilant1

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BTW, I think the market for an aviation-specific Type 1 head is generally at the higher end (2180cc and up) or among those wanting to do something unusual (1/2 VW, etc). At more modest displacements the presently available aftermarket heads seem adequate (to me)--we aren't asking very much of the heads, they don't get as hot, valve seats last many hundreds of hours, cracks are less of a problem, etc.
 

Vigilant1

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There is really no practical way to get the kind of fin spacing needed with CNC.*

*The Jabiru is a much simpler head.
I'm sure you've thought this through, but for my understanding can you flesh this put a bit? Why does the VW head have to be more complex than the CNC'able Jabiru head? It would seem there's be a lot of flexibility on intake and exhaust runner geometry, some flexibility on valve train geometry, etc.

Oh, just to throw this out there, it is totally unsuitable for the simple approach you want to take here: A heat pipe can move a LOT of heat with a small diameter unit--hundreds of times more heat than a similar size copper rod, etc. The heat can be taken some distance away to a regular finned air heat sink. A couple of suitable "pads" on the head for mounting a heat pipe near the exhaust seats could, in theory, get rid of a lot of heat from this critical area for very little weight. Technically, I suppose it would be "liquid cooling," but with no pumps, hoses, clamps, valves, and probably about 16 ounces of coolant for the entire engine. A very elegant technology. Heat pipes: Wikipedia
 

BBerson

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I would make a simple head casting, then bolt on big heat sink finned parts.
A little bit of assembly is no problem for Homebuilding. The car was designed for mass manufacturing not light weight. No need to duplicate the vehicle.

I remember my brother bolted some aluminum plates to the head of our Cat 30 pony motor that was overheating. It worked perfectly.
 

Vigilant1

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I would make a simple head casting, then bolt on big heat sink finned parts.
A little bit of assembly is no problem for Homebuilding. The car was designed for mass manufacturing not light weight. No need to duplicate the vehicle.

I remember my brother bolted some aluminum plates to the head of our Cat 30 pony motor that was overheating. It worked perfectly.
Is there some kind of goop/material that could assure good heat transfer between the head and new, larger fins that are bolted on?

There is a type of brazing/welding rod that reportedly works well for attaching new fins to the existing ones, for people that want to go that route. Bob Hoover liked that approach.
 
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Hot Wings

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Why does the VW head have to be more complex than the CNC'able Jabiru head?
I'm familiar with heat pipes. Kind of like the idea. Requires some more thought. :ponder:

The complexity comes from the @#$%@$% location and it's lobe spacing VW chose for the camshaft. It works well to cut down on the number of lobes, give increased ground clearance and allows symmetrical L/R heads.

This has cascade effects that limit where the ports can go. The Tp IV and Corvair heads have the advantage here. Building, or finding, some asymmetrical rocker arms, like the Tp IV or 356/912 would be another way around the problem but so far i haven't run across any existing rocker arms that would work. Custom CNC ones are still an option.

It also limits where the second spark plug can be located. FritzW's Mosler heads, if he has the ones I think from his description, simply put 2 plugs next to each other in the stock location. It gives dual ignition but does little to improve burn efficiency.

Of course, I've been quite guilty more than once of not seeing the obvious.
 
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