Just talking about VWs

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Vigilant1

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"Fat Fin" modification

I think it is important to say, from the start, that from what I've read, most folks who have used VW-based engines in airplanes have had no problems with cooling of the heads >if< they have appropriate baffling >and< they aren't trying to get more than about 70-75 HP from the engine.
So, what follows is for applications where a VW-based engine is gong to be asked to supply more than that, at least occasionally, or where outside temperatures are very high, etc.
I have read about the "fat fin" modification of VW heads that is intended to provide additional cooling capacity to those heads, especially the area around the rear exhaust valves/ports. Bob Hoover had some entries in his blog about this, and he was a believer.

Here's a short quote from a Kitplanes article by Wayne Clagg, who added fat fins to the VW engine (with redrive, etc) in his Zenith 701:
He had been talking to Bob Hoover of fat-fin fame, and then he found Durafix, a new material that would allow him to attach the cooling fin extensions to the repaired original heads without a TIG welder. “I couldn’t believe the difference,” Clagg said. It lowered the CHT 100° in climb and 80° in cruise. Fat-fin testing went well until the 11.5-hour mark, logged last May, the airplane’s last flight as of summer 2010.
The article also has a picture of the fat fins he added.
Pops, I recall that you know Mr Clagg and the story of this airplane. If I remember right, the VW engine proved not to be a good choice for that plane: just too much "grunt" required, and with the redrive the weight was high enough that other engines would have been a better choice.

The drawing below is from Bob Hoover's blog, the "fat fin" extensions are depicted in blue. They are bigger than I would have guessed.



The temptation is there. The 2180cc to "2400cc" engines can make 75-85 HP, the problem (especially on hot days) tends to be overheating of the heads. And it's not just a case of wanting more HP--keeping the heads cooler helps reduce exhaust valve/exhaust seat erosion and head cracks. There are a lot of folks who are operating their VW's "responsibly" who would nonetheless like to get the 100 deg F CHT reductions that Wayne Clagg talked about.

So--any thoughts on "fat fins"? Good, cheap "insurance"? Unnecessary craziness?
 

Pops

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You have it all correct on the fat fins. Wayne Clagg is a local pilot and a good friend of mine that fly's to my field often. His grass field at his home is called "Crazy Horse" ( 12 WV). He had about 80 hrs on the VW engine and on the way to Oshkosh, the case cracked and loosing oil and he had to land at an airport and trailer the Zenith 701 back home. Wish someone would have new VW heads made with the large fat fins for the aviation world, but I guess the market isn't large enough to make it profitable. The large fins would be to large to go under the cylinder tin of the VW for car use. IF there were a fat fin VW head on the market at a not insane price there would be very few aero-VW engines using the stock heads. That would solve the problem for the large stroker VW engines and make the VW are far more desirable engine for aircraft use.


Might want to watch Wayne go in and out his field a couple of times. This is flying in WV.
https://www.youtube.com/watch?v=2533V-TIwKg
 

Vigilant1

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You have it all correct on the fat fins. Wayne Clagg is a local pilot and a good friend of mine that fly's to my field often.
I just came across his very good blog that provides a lot of info on his VW engine modifications. It will be important reading for anyone considering fat fins, it is at: https://waynesexperiments.blogspot.com/2011/01/?zx=82ba1853619aeb8f
He made a lot of observations as he worked on this engine, and provides them in his blog. It is important to remember that he was burning up to 9 GPM in climb, so producing approx 100HP. In cruise he was burning 7.2 GPH, so probably making about 86 HP. His compression ratio was about 8.3 in the last version of his engine. I couldn't find what size engine it was.

Interesting points:
Effectiveness of the fat fins: He made several changes to his engine/prop (added fat fins, camshaft, later a prop with more pitch, etc), and it is worth reading his write-ups of them. But the bottom line is that his CHTs in climb dropped about 90 deg F (from 410 F to 320 F, measured at the head stud over the exhaust port). He also included a letter he received from Tom Huebbe, a Sonex builder with a 2276cc engine. He saw CHTs (measured under the spark plug, after climbing to pattern altitude), go from 450 deg F to 376. Cruise CHTs (at 22-23"MP) went from 360-370F to 290-300F. (Tom was well known and liked in the Sonex community. Sadly, he passed away several years ago in an aircraft accident. His son, who was flying with him at the time, fortunately was not seriously injured).
Attaching the fat fins: It looks like he was able to attach them with an oxyacetylene torch and Durafix. It also looks like he was able to do it with TIGG. His blog has several good pictures.
Weight: He weighed the engine, redrive, oil cooler, brackets, exhaust and intakes, magnetos, dual ignition, starter: everything except the prop. His total was 223 lbs. The only thing unusual about his engine was the redrive. The weight of all the "non-engine" stuff adds up.

Pops, when you see Wayne Clagg, thank him for sharing all his experiences, it is very interesting reading.

Might want to watch Wayne go in and out his field a couple of times. This is flying in WV.
https://www.youtube.com/watch?v=2533V-TIwKg
Pretty country. But way too many trees covering the needed landing spots.:)
 
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dino

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Is the magnesium case up to the 80hp+ output of some type II VWs?
 

Pops

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I just came across his very good blog that provides a lot of info on his VW engine modifications. It will be important reading for anyone considering fat fins, it is at: https://waynesexperiments.blogspot.com/2011/01/?zx=82ba1853619aeb8f
He made a lot of observations as he worked on this engine, and provides them in his blog. It is important to remember that he was burning up to 9 GPM in climb, so producing approx 100HP. In cruise he was burning 7.2 GPH, so probably making about 86 HP. His compression ratio was about 8.3 in the last version of his engine. I couldn't find what size engine it was.

Interesting points:
Effectiveness of the fat fins: He made several changes to his engine/prop (added fat fins, camshaft, later a prop with more pitch, etc), and it is worth reading his write-ups of them. But the bottom line is that his CHTs in climb dropped about 90 deg F (from 410 F to 320 F, measured at the head stud over the exhaust port). He also included a letter he received from Tom Huebbe, a Sonex builder with a 2276cc engine. He saw CHTs (measured under the spark plug, after climbing to pattern altitude), go from 450 deg F to 376. Cruise CHTs (at 22-23"MP) went from 360-370F to 290-300F. (Tom was well known and liked in the Sonex community. Sadly, he passed away several years ago in an aircraft accident. His son, who was flying with him at the time, fortunately was not seriously injured).
Attaching the fat fins: It looks like he was able to attach them with an oxyacetylene torch and Durafix. It also looks like he was able to do it with TIGG. His blog has several good pictures.
Weight: He weighed the engine, redrive, oil cooler, brackets, exhaust and intakes, magnetos, dual ignition, starter: everything except the prop. His total was 223 lbs. The only thing unusual about his engine was the redrive. The weight of all the "non-engine" stuff adds up.

Pops, when you see Wayne Clagg, thank him for sharing all his experiences, it is very interesting reading.


Pretty country. But way too many trees covering the needed landing spots.:)
Wayne's blog is good reading learning about the VW engines. In the blog he mentioned Vic Dawson as being his machinist, also mine. Vic's father Kieth ran Kieth auto parts and machining ( VW only). Kieth was my age but passed a few years ago. When I started overhauling VW engines in 1970, Kieth did all of my machine work and Vic was about 10 years old. Vic grew up in the business. These are not shade tree VW machinist , at one time they had the top VW dragster in the nation. When I have a VW question, I go to Vic.
 

Pops

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Is the magnesium case up to the 80hp+ output of some type II VWs?
That is a good question. IF the engine is balanced as good as possible to keep the soft crankshaft center main saddle from pounding out and the temps are good. That is where the stronger aluminum case would help, IF you can stand the extra 17 pounds. SO the correct answer is-- I don't know.
 

Vigilant1

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Is the magnesium case up to the 80hp+ output of some type II VWs?
Sorry, I don't know. But IIRC, the largest stock Type II engines ('75 and later, 1800cc and 2000cc) were rated at about 70HP, so the stock Type II engines in vehicles (geared transmissions, so higher RPMs even at low road speeds/high loads) might not tell us a lot about the Type I engines installed in airplanes turning lower. Folks have hopped them up, I'm sure many Type 2 engines can make 80+ HP, but I don't know what % of their typical duty cycle would be at these high outputs.
A cracked case was the final nail in the coffin of Wayne Clagg's reduction-drive Type I, but it sounds like he ran it at 100 HP for climbs (what, maybe 30 % of the time?) and 80+ HP for another 50%+ of the time, pulling that draggy 701 around the sky. I would think the fatigue/cracking stresses on the case of a direct drive VW putting out, say, 80HP for climb and 65-70HP the rest of the time would be a lot less.
 

blane.c

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On the intake manifold heater, the oil comes out of the engine thru the manifold heater and then to the oil cooler?

How do you set up to drill for 10mm spark-plugs, location and angle?

Same bushing for 14mm plugs and 10mm plugs, just tapped different or smaller diam. bushing for 10mm plugs? Time serts?

What heat range for the two sizes of plugs? Resistor plugs? what kind of spark plug wires?

Flywheel drive?

No fly wheel use prop?

What kind of adapter do you use to attach the prop?

Do you have the prop balanced with the engine running?

When you balance piston and rings, and rods, do you use that information to have the crankshaft balanced?

Do you balance any other parts, like camshaft, accessory gears or other?

Pulley for alternator drive, dia. and a sketch? (The John Deere 20 amp)

What fuel do you use?

What oil do you use?

Do you use unwaxed floss between case halves?

Exhaust tube lengths?

There is a flexible connector on the fuel line to the carb., can you adlib about that?

Do you use book torque values or do you have "notes" for special items?

What oil and CHT temps are you considering normal? and what do you consider maximum?

What oil pressure @start, @idle, @normal power, @max power and in climb?

What valves do you use? what guides? any special rocker bushings?

Any special bearings, rods, or other items?

Any more information you can think of.

Thank you.
 

blane.c

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What gross weight aircraft are these engines good for? (the one person plane analogy is ambiguous)

How many hours can you get out of the cylinders and case?

What is the "all up weight" when it is attached to the firewall with all the accoutrements and propeller?
 

pictsidhe

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White paint won't do much good at reflecting heat from cylinders. With the wavelength of heat radiated from cylinders, you want to look for a surface that has low emmisivity. As Vigilant suggested, chrome them instead. Polished stainless is pretty good too, in case you have stainless things you don't want absorbing engine heat.
 

mcrae0104

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So some people say you want high emissivity, others say white is not low enough. I give. Does anyone have any science to offer?
 

pictsidhe

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Emissivity and absorbtivity actually are the same thing, but measured at different temperatures. Absorbtivity is a measure of heat absorbtion from something hot, like the Sun. Think 5000K. Emissivity is for radiation from warm things, under red hot. Thermal radiation is reversible. That means that for a given radiation wavelength, emissivity=absorbtivity. The wavelengths given off by a body vary with temperature.

Now, who's going to talk about hot black bodies?
 

blane.c

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The hot spots are around the chamber and exhaust ports, only so much you can do there due to space considerations between adjacent parts. Very long fins start to have diminishing returns with regard to heat dissipation rates. Look at some of the radial engines with sawed finning for guidance here.

Around 60% of the cooling on the P&W R2800 is from oil, the other 40% from air.
 

blane.c

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I am wondering if it wouldn't be a good idea to run a 2180cc with stock cam and 6 1/2 to 1 compression? You could pull maybe 65hp at a lower RPM than the 1815cc pulls 60hp? Maybe a prop a few inches longer dia. because of the lower RPM? Lower CR, lower RPM's, maybe lower CHT?

Just wondering.
 

blane.c

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What I am finding for information so far is saying the VW heads are good for around 200 flight hrs, does this sound about right?

So if you invest in an extra set of heads when you build the engine, to insure they are all matched, it will likely be many years before you actually need them (25hrs to 50hrs a year is typically a lot). It will be an effort to keep them from corroding in that amount of time. What do you do, keep them submerged in a container of oil?

So only wooden props? Has anyone had any success with other kinds of props, or it is just the way it is?
 

BBerson

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No need to run the compression lower than modern available fuel 87 octane. 8-1 should be fine. My Limbach VW is 8.7-1 and needs 91 auto fuel. The larger prop will hold the rpm down.
 

Pops

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I am wondering if it wouldn't be a good idea to run a 2180cc with stock cam and 6 1/2 to 1 compression? You could pull maybe 65hp at a lower RPM than the 1815cc pulls 60hp? Maybe a prop a few inches longer dia. because of the lower RPM? Lower CR, lower RPM's, maybe lower CHT?

Just wondering.
You mean sort of like my 1835 cc with single port heads, 1 1/4" dia intakes, 7.55 to 1 CR, Zenith carb, Slick mag, Culver 60" dia X 26" pitch prop. I use local 91 non-ethanol auto fuel ( $4.00 a gal) or 100 av fuel. Wouldn't want any higher CR than 7.55 for the 91 octane auto fuel. It might turn 25 more rpm at WOT on 100 octane. Cruise at 2.9/3.0 gph at 2650/2700 rpm and flying cross country with my neighbors Cont - A-65 Pete, I have to go back to 2450 rpm to stay in formation. It runs to cold at that rpm, so I have to run 2500 and up to keep the temps up and every few miles make a circle to stay back with the Pete.

Local friend of mine put a thousand hours on his 35 hp, 1/2 VW without any work on the engine in a Mini-Max. One winter he torn the engine down just to check it, nothing wrong , but he overhauled it anyway. He was a past motorcycle mechanic and cut the crank and welded on the counter weights and balanced and did all the machine work ,assembled the engine himself.
 
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