I was thinking of chem-milling some VW heads to get more air flow and make them lighter for low rpm aircraft use.
VW Heads Designed for Aircraft- Poll
- Thread starter Hot Wings
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TFF
Well-Known Member
Heads are only part. If you are going to push one of these things, cylinders with bigger fin area is right there with the heads. Single cylinders are easier to make, but siamese would be stiffer which means it can handle more power. As for the dreams of the 1/2 VW owners, with CNC its just a button away from making singles. One piece heads with small valves lots of fin area. If you were to fix everything, you would close up the open chamber some and add a pocket to the piston, for equal compression, matching the head for better detonation control on low octane fuel.
A pocket in the piston would help with regard to the location of the squish band but that means another custom part. I'm thinking that with a good chamber designed for fast burn, even with a flat piston, 10/1 may be realistic for a VW aircraft engine. We know a LOT more about this than when the VW chamber was designed.
Siamesed heads are bad enough. Doing that with the iron cylinders would introduce all kinds of unwanted thermal stress. It seems intuitive that the paired components would be better due to increased rigidity but there is around a 200F difference in case and head temp. This tends to push the top of the cylinders out more than the base on the VW. The air-cooled 911 gets by because the main heads are separate and joined by cam carrier that is closer to the block in temperature.
I wonder if a combination of casting and efficient "MCM" (manual controlled machining"
) is the right mix for this type of relatively small batch production. Cast the basic shape of the head with all rough ports and the rough combustion chamber, use carbide saw kerfs to make a large number of generous fins, and drill as required to finish air passages "under" ports and other places where they can't be sawn. With some smart jigs it could probably be fast work not requiring expensive machines or highly-skilled labor. Machining is required in many other parts of the head anyway, this would be an extension of that.
I like that term
Even with lost wax casting this may be of some advantage. Thin fins are good for heat transfer but would probably end up looking like Lasagna after a heat, quench and age to T6. Thick cast fins could be mechanically thinned after heat treat.
pictsidhe
Well-Known Member
T6? I think you are looking at the wrong alloy...
The only heat treated alloy heads I know of are water cooled. They are scrap if they oveheat. Likely to around A/C running temps.
The only heat treated alloy heads I know of are water cooled. They are scrap if they oveheat. Likely to around A/C running temps.
All I promised was Vaporware. Delivered! See post #65. and 4 cyl version below:We've been yammering on about this for two weeks already. Where are these long-promised new heads? What is the hold up?
:gig::ban:
"T6? I think you are looking at the wrong alloy..."
As cast or T5 A356 just isn't up to the job - IMHO. T6 is probably as good or better than any aftermarket VW head. 242 should be better, but I've had spotty results casting with it.
Well, I can't argue with that.
Pretty neat. Is your cylinder head wider (from edge of top fins to edge of bottom fins) than we see on most aftermarket heads? You've got lots more fins, and they look deeper than usual. Regarding the rocker arm shaft--one per cylinder or one per side (exiting between the two valve covers)? More seals = more leaks. I do think that a unitary cover (front and back cylinder) will probably be more popular.
Yes, just Napkin Grade at this point. Don't let the pretty? pictures fool you.Well, I can't argue with that.
The fins look deeper because they are. The also can't be made with a clam shell style permanent mold like the originals. They will require something like 3D printed sand or lost wax to cast.
The bored rocker method does make for more leak paths, but is super simple to fabricate and assemble. This feature is still under review along with the separate rocker boxes. Siamesed rocker boxes would require the same number of casting molds and might actually require less machining time. They might weigh a bit more than the individual units. If it weren't for the #@$* shared cam lobes (by now it's pretty obvious I REALLY don't like that feature :gig
An OTS stud mounted roller rocker from a V8 would be cheap, easy and leak free.I'm also trying to consider if there is a need for 1/2 and 4 cylinder versions. If this ever got to the real hardware stage I think there might be more of a market for 1/2 VW heads? There would be a better profit margin/cylinder.
The heads as shown are almost identical to the stock VW with regard to overall outside dimensions. It is about 10mm wider due to combustion chamber shape. Right now they weigh too much by at least a pound/cylinder. Some of the fins are not where they add much to the cooling, but the CAD cut for the shape was easy.
The valve center to center shown is larger than the stock VW to allow more metal between the valve seats. The cylinder in the pics is a 94mm bore so if used with a stock 85.5mm bore the valves would be pretty shrouded.
Edit:
Why isn't my banana dancing in post #89 :dis:
There'd be a greater market for the 1/2 VW if . . .
wait for it . . .
...you just went ahead and casted/fabricated an optimized 1/2 VW >case< while you are going down this road. Cutting a full case down takes a lot of time and using the full case without cutting it costs weight. I mean, as long as you're making the heads, it seems just a tiny step farther to make a case. Better yet, a 2-banger, stackable >modular< case. Front plate, back plate, and as many opposed 2-cylinder units as folks want to add (better plan ahead: for stackability the heads should have the intake on top and exhaust through the bottom). It eliminates the cost of clearancing stock cases, allows you to build in a robust prop bearing (axial and thrust loads) right from the start. A 6 cylinder at a conservative 19 HP each = 114 HP. 8 cyl = 152
Heck, by eliminating stuff we don't need in the present case, I'll bet you could save enough weight to allow your case to be made from Al rather than Mg--fewer cracks later AND easily recyclable (for environmental brownie points). We've found our VP-21 engine!No one can say what makes another person's banana dance--a mystery.
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This for me that would be going backwards down the road. I started out with that idea - a new version of the Mosler - and it kind of mushroomed into a full re-think of the 2 cylinder VW based engine. But I decided there wasn't enough of a market. Then about a year later along came the O-100 project. There is too much overlap on that project for me to reconsider my old project.
Weight was going to be in the 65-70 pound range, with Hummel style heads. I bought Harley top end parts with the thought of using those as well. The case would have been modular enough to bolt on either - VW or Harley. The Harley stuff weighs a LOT more, but is bolt on and can be had in really large bore compared to VW TP1. (106mm bore x 82mm stroke = 1447cc/88cu in)
I may still build one just for myself.........
one of my 1/2 VW heads on top of a Harley cylinder for reference.
rmeyers
Active Member
Been thinking a good bit about this. As to whether single or dual cylinder heads are preferable, I don't have much of an opinion. Either can be made to work well. Someone suggested a dual cylinder head that could be cut in half for a single cylinder.
Novel thought, possibly could be made to work.
Before I make any suggestions or comments I guess I should ask, do you or will you have access to a moderate size VMC with at least a CAT40 spindle? Something like a Haas VF2- VF4?
I ask because the experience I have in this type of manufacturing is a mix of casting and CNC work. The correct mix is always changing and is highly dependent on the part being produced.
Novel thought, possibly could be made to work.
Before I make any suggestions or comments I guess I should ask, do you or will you have access to a moderate size VMC with at least a CAT40 spindle? Something like a Haas VF2- VF4?
I ask because the experience I have in this type of manufacturing is a mix of casting and CNC work. The correct mix is always changing and is highly dependent on the part being produced.
Do have access? - no. Will have? - probably not unless I farmed this part of the work out.
While lost wax is rather time consuming, for the low production numbers these things warrant, it should be cost effective. Most of the post casting machining needed is actually pretty simple and can be done using a lathe and a drill press with some jigs. A few details, like o-ring groves for sealing can be cut with something as basic as a 2 1/2D router. Good QC for the shrink fit valve seats makes me a bit nervous. Might have to rig up some kind of air gauging....
I'm pretty old school. It's not that I don't/can't use CAD/CAM but I also was around when we didn't have these things, and could still build fairly complex parts efficiently in low volumes.
For now the how of making these is not, to me, really important as one would have to answer the question of "is there is any possibility of breaking even on the project". To me it's an interesting problem to 'solve' with only a small probability that it will ever go beyond the VaporWare stage.
FW - You have enough evidence now.....
The other day, I was thinking about your proposed VW heads and how you might make them. I remember having some nice aluminum parts made by a prototype place called Protolabs. I'd send them a CAD file and get an automated (I think) quote back in hours. Parts in a week or two, as I recall, though that might be different now. Might be something to check into. I'm sure there are other companies that do this as well. Not sure if their materials are just right. They have 6061-T651 for machining and AlSi10Mg for laser metal sintering (3D printed, I think).
No need to invent something that's been successfully done by others. Copy the Rotax 912 head design and attach a small water pump on the pulley or flywheel end and go flying. A combined oil/water cooling is a proven method. Thousands of rotax engines plus hundreds of thousands of BMW heads. They never need adjusted, no dicking with valves or re-torquing them. Original VW was designed to produce 32 hp. When you start talking about 80-120 hp the heat will need to be ported away with liquid coolant and oil. You can leave the rest of the motor as it is.
?? Why would water/glycol be needed? Oil alone will do the job in this case, just pump a lot of it through the heads using a high volume/ low pressure stage added to the existing pump. A second system, separate radiator, etc is a lot of weight.
The heat rejection ability of the present heads is the thing that limits the HP of theType 1 VW. But push it above 80 hp and other things start to break/wear out fast (case cracks, bearing saddles, etc). IMO, the goal should be even better reliability/longevity at 75 to 80 hp max (through lower head temps, among other things), not moving the goalposts (again) to more HP. It has been tried a lot.
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I did not read through the entire thread, but I though that there were all ready some water cooled VW heads out there, at least for a while.
