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Hot Wings

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So I am looking at cooling options to get longer engine life and better all round efficiency and performance .
As Topas mentioned pay attention to the design and detail of the overall cooling system.

For points specific to the VW engine: Make sure it has a good valve job with minimum slop on the valve guides and adequate seat/valve contact area. While this isn't technically a cooling issue it does make sure that all of the heat from the exhaust valve (the critical part) has at least a fighting chance to get passed to the head.

Take a look at the cooling shrouding on a '71 or newer bug engine and try to emulate the air flow around and through the head. Make sure all of the casting flash is filed or cut away at the center line of the head where the mold parting line is. Some castings are actually completely closed in some areas.

Next find Veeduber's HVX mods and make sure that all are included, especially a full flow oil filter/cooler and the valve lifter modification. These make such a big difference in cooling and longevity that I quit offering a warranty on my ground bound engines unless they were included. VW makes a fine aircraft engine, but to fracture a quote 'A man's got to know his engines limitations'.
 

Kmccune

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Of course the VW can output more then 36hp, but when maintained at higher outputs it creates a lot of heat. If you are flying a slippery fast airplane, you may well get away with this. But if it a draggy airframe flying relatively slow you will not. The fat fin mod mentioned was used on a CH701 using a redrive and a long 3 blade prop. He is maintaining 3600 to 3800rpm ( I forget the exact numbers at the moment) on a 2276cc engine going all of 80-85mph. This was suppose to be a positive message boys ...didn't mean to upset the applecart.
 

Topaz

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Of course the VW can output more then 36hp, but when maintained at higher outputs it creates a lot of heat. If you are flying a slippery fast airplane, you may well get away with this. But if it a draggy airframe flying relatively slow you will not...
Depends entirely upon the competency of the cooling setup, and of the cowling first and foremost. The speed of the aircraft has nothing to do with it. Any engine will toast if it's not properly cooled. The VW is no exception, but it's also not more susceptible.

Sorry, but this myth needs to be quashed for good. The VW is one of the few four-stroke engines in the 50-65hp (rated) range that's got a proven track record for airplane conversion, is affordable, and can be easily adapted. These poorly-reasoned rumors are starting to have an entirely undeserved effect on their consideration by current homebuilders. VW conversions have been in use for decades, mostly in low-and-slow designs, with a very good service record. These new "experts" tend to forget or overlook that plain and simple fact.
 

Hot Wings

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I'm not interested in inflaming this "debate" but I just happened to run across this web site:

Heat Transfer Resulting from Laminar Flow Over an Isothermal Plate

I grabbed a VW head and did some VERY quick measurements of the cooling fins (there are 8 and look to account for about 50% of the total cooling area)

Plugging in some numbers that I kind of picked out of the air (SWAG) for a slow VW powered plane at cruise on a standard day the site says a VW head should be able to dissipate around 16 KW of energy.

There are lots of assumptions involved but if you figure a 50% efficiency of the surface area that pretty much offsets an assumed 50% efficiency of the VW in turning fuel into thrust. (if the engine is making 8 KW of thrust it's making 8 KW of waste heat)

8 KW times 2 heads = 22 Hp.

Upping the allowable head temp 50 deg F added almost 50% to the heat transfer to around 38 Hp.

Just thought some formulas and numbers would be interesting :gig:
 

Autodidact

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FWIW, an 1835 cc engine producing 65 hp @ 3400 rpm has a BMEP of 135.3 psi. At 70% power this would be roughly 115 psi BMEP. This is about .58 hp/ci (at 100% power). All of these figures sound reasonable to me. The Aeroconversions 80 hp engine is operating at a higher stress than this. The problems with excessive heat in the cylinder heads would manifest as burnt valves, valve seats that have popped out, etc. These problems can be compensated for with valves made from much better materials (maybe sodium filled) and better valve seat materials and carefull installation of the valves and seats with an interference angle on the valves and seats (supposedly transfers less heat to the seats because of less contact surface). There is a limit to what can be got out of any engine without redesigning the entire engine. An engine with valves designed for high heat operation will do better than a stock engine. And, of course, high performance valves in a head with more fin area will do even better, but how much would have to be determined by a program of experimentation. Detonation may become a problem, and the combustion chamber may need to be redesigned or special fuel used. Blanket statements, while based on some truth, tend to leave the gamut of possibilities unexamined. In my mind, it would seem easier to design a head that had cooling characteristics that would allow good power to be produced with less exotic valve and seat material, but either path will cost some extra money.
 

Hot Wings

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One thing to plug in, Hot Wings. Those formulas are for laminar flow. Heat transfer is significantly higher from a flat plate to a turbulent flow, and the flow over the cooling fins on an air-cooled engine is most definitely turbulent. So the results you got are low.
That would be my assessment as well. Even the SWAG numbers I picked could be off 30% on top of that.

One thing I found interesting after messing around with that site is that it indicated that in the speed ranges we are interested that faster the air moved the better the cooling. This is contrary to a lot of claims on these forums that we need to slow the air down and let it "linger" to pick up as much heat as possible. That may be true with water in a radiator but my experience with the VW is that the more mass that flows over the fins the better.
 

Kmccune

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You guys are being influenced by emotion and misinterpretation. We are talking about sustained power here, for more then an hour. The engine has to run 60-75 % for hours and hours during its life time. The VW head was not designed for this, if you start getting up in the redrive rpm range its even worse.(this is my target rpm BTW) No one is saying that the VW is a bad engine at all, only that it can be made much better, to serve a broader type of airframes. Why do you think VW owners commonly have spare heads sitting back at the hanger? Ever heard of a Jabiru owner with a set on the shelf? And if the VW can be made better, why would any of you argue about semantics, its just good progress. And inexpensive by the way. Or would you rather that things stay the way they are forever?

If you read Bobs blog at all, you would have picked up on the fact that he flew VW powered airplanes for a long time. Do I belive everything in that blog...nope. But there is a lot of good info there from a life time of real experience with the topic at hand. Only an arrogant person would so easily dismiss an opportunity like this so quickly. Give it an honest read. The Revmaster guys, obviously have. Not taking away from them in any way, but that new 2332 is strangely close to Bobs O-142 VW, it even has improved head cooling.... go figure! Although Bob would have slung it around backwards;)

Kevin
 

BBerson

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Kevin's comment in post 22 was a VW with a redrive at 3800.
Most direct drive will not have much problem at around 3000 continuous.

It's true, the VW heads don't last as long as other engines. The valves tend to rust from lack of use as much as anything from heat. But the heads are cheap ($100-200 on sale). Change the heads every 5 years or so, is what I do.
 

Topaz

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You guys are being influenced by emotion and misinterpretation.
No, we're being influenced by proven in-service history. Which you conveniently keep ignoring.

We are talking about sustained power here, for more then an hour. The engine has to run 60-75 % for hours and hours during its life time. The VW head was not designed for this, if you start getting up in the redrive rpm range its even worse.(this is my target rpm BTW)
And again, thousands of airplanes have been flying this way with takeoff-rated 65hp VWs for nearly fifty years, meaning they're cruising at 75% power at close to 50hp. You still haven't addressed that simple fact. If the VW engine can't do this, how is it all these people with VW engines in their airplanes are doing it? Your argument stands on the notion that the entire line of VW engines can't be run continuously at more than about 36hp. And yet that's in exact contradiction to real-world service history. Would you care to explain that little discrepancy?

Why do you think VW owners commonly have spare heads sitting back at the hanger?
They do? This is the first I've heard of it. In fact, I don't know of a single VW-powered airplane owner that's doing that, and I know a few. The Ogar motorglider at my home airport with a Limbach in it certainly doesn't have spare heads lying around. And he flies slow at full continous power for quite a while getting that heavy airplane up to altitude.

If you read Bobs blog at all, you would have picked up on the fact that he flew VW powered airplanes for a long time. Do I belive everything in that blog...nope. But there is a lot of good info there from a life time of real experience with the topic at hand.
I've read some of his stuff. I agree, RS Hoover does seem to know quite a bit about the VW engine in aircraft use. Unfortunately, a lot of his followers don't, and take what he says and misquote it to be something totally wrong.

Let's take, for example, the excerpt linked over at rec.aviation.homebuilt. It's a prime example of what I'm talking about, and seems to be the single most-quoted post from him by people spouting the "36hp limit" nonsense. It even showed up here, in the VW conversion part of our forum.

Bob says in that post that, while other manufacturers claim to get more power from the it, he doesn't know how to get 60hp continuous from the VW engine in question, without running the engine so hard (higher RPM) that the heads would burn up. And you know what? He's right. Absolutely right. I agree with him completely.

Because he's talking about a 1600cc Type 1, the very smallest of the four-cylinder VW aero-conversion line. The prospective "customer" in question brought him a 1600cc engine and wanted to get 60hp continuous out of it - and with the standard crank, no less. That's insane, and Bob, in his gentle way, said so. But the 1600cc Type 1 isn't the only engine in the VW line. You people took what he's saying about the smallest VW engine and painted the entire family with the same power limitation. What you're doing is the equivalent of saying a 65hp O-145 is the same as a 180hp O-360:
"DANGER!!! DANGER!!! If you run an O-145 at enough RPM to put out 180hp, the heads will burn up!!! Lycomings are only good for 65hp!!!"
The first part is true - the O-145 was never meant to put out that much power. But this says nothing about the ability of the larger-displacement O-360 to do it. The final conclusion that "Lycomings are only good for 65hp" is patently absurd. Just because they both say Lycoming on the data plate does not mean that they're the same engine with the same power output.

Carrying it over, the 1600cc Type 1 VW was never meant to put out 65hp continuous. But that says nothing about the ability of the 1915cc, 2180cc, or 2276cc engines to do it. And they're "VW engines", too.

Bob then goes on to talk about larger-displacement VW engines, saying his produce less power than other manufacturers at the same displacement. What gets missed is that he chose to redline them at 2400 RPM for the sake of efficiency of a larger propeller, when the VW is clearly good for 3000 RPM or so with plenty of reliability. He says himself that he had a 2100cc VW with 1500h on it, beat to death in course of his experiments, and it runs just fine. He de-tuned it to about 50hp by running it at 2400 RPM, and that's his choice. The rest of the world runs 'em at 2800 or 3000 and 65hp (takeoff) with a smaller-diamter prop (or a redrive) and gets 1200 TBO. But all of this gets overlooked by eager readers who draw the conclusion that "the 2100cc VW is only good for 50hp because Bob says so", and the myth gets perpetuated.

Can the VW line be improved? Sure! Do I have any objection to improving them? Not at all, so long as the low-cost of parts and original engines, ease of maintenance, and simple systems are maintained. It's much too easy to turn this into yet another über-expensive airplane motor with some of these "improvements". But you don't have to throw the old motor under the bus to make your case for improvements. The currently-available, been-in-use-for-decades VW line of engines is perfectly suitable for a lot of applications, just as they are. You don't need to spread misinformation and unfounded rumor about power and reliability limitations when trying to build a "better" engine. You're hurting a lot of potential aircraft builders when you do.
 
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Topaz

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Kevin's comment in post 22 was a VW with a redrive at 3800. Most direct drive will not have much problem at around 3000 continuous.
Exactly, and yet his comments are generalized to all VW engines. Which is precisely my point. You can't do that. A 2100cc Type IV is a very different beast than a 1600cc Type 1, even if they're both "VW engines".

It's true, the VW heads don't last as long as other engines. The valves tend to rust from lack of use as much as anything from heat. But the heads are cheap ($100-200 on sale). Change the heads every 5 years or so, is what I do.
IIRC, most of the VW conversion manfacturers are saying 1200h TBO, which certainly is less than a 2000h TBO certified O-200. But 2000h isn't a magic number down from on-high. 1200h is just the TBO for these engines. And it doesn't cost $10,000 to do it, either. ;)
 

Topaz

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...One thing I found interesting after messing around with that site is that it indicated that in the speed ranges we are interested that faster the air moved the better the cooling. This is contrary to a lot of claims on these forums that we need to slow the air down and let it "linger" to pick up as much heat as possible. That may be true with water in a radiator but my experience with the VW is that the more mass that flows over the fins the better.
Interesting. That's odd. I wonder if that's yet another consequence of the stipulation of laminar flow in that research. Turbulent flow carries away more heat because the turbulent boundary layer brings a larger amount of cool air into contact with the plate, by virtue of the tumbling and mixing action present. A laminar boundary layer would have a thin "skin" of air flowing past the plate, with air farther out largely insulated by the boundary layer itself.

Under those conditions, the only way I can think to improve the total flow of cool air over the plate would be to increase the velocity of the flow, just as you're saying.

In a turbulent flow, I would think you'd want to slow the air down a bit, to let the turbulent mixing bring the maximum amount of cool air into contact with the hot plate (cooling fins, in our case) before being flushed from the cowling.

It would be interesting to see that comparison.
 
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Kmccune

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Topaz,
I belive I clearly stated the RPM at some point earlier. If I did not I am sorry. But I have been speaking of these RPMs. In addition, even at the lower 3000ish RPM that you speak of, the manifold pressure CAN be too high...more of that pesky heat that you have to get rid of. Why do ou think that the Jabiru has such big fins?. How big are the A-65 fins compared to the VW?
My point once again, is why not build a better animal?

Kevin
 

Mac790

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Flaglor Scooter, Pober Pixie, Aerosport Scamp, Hovey Beta Bird, Evans VP-1, various Jodel single-seaters, Pazmany PL-4, Stewart Headwind, Watson Windwagon...
To that list you could also add Tipsy Nipper, was also powered by VW engine, I loved that airplane when I was a kid, it's a pity that you can't buy plans for it, it's really piece of art compared to those mentioned by you. The plane looks very simple to build, many people would probably like to build it if the plans were available.
Here is some restoration gallery. Tipsy Nipper • View topic - Restoration of ZS-UAD, Tipsy Nipper T66 mk 1
one more Picasa Web Albums - bamf.bamrs - Tipsy Nipper

Seb
 

Topaz

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To that list you could also add Tipsy Nipper, was also powered by VW engine, I loved that airplane when I was a kid, it's a pity that you can't buy plans for it, it's really piece of art compared to those mentioned by you. The plane looks very simple to build, many people would probably like to build it if the plans were available.
Here is some restoration gallery. Tipsy Nipper • View topic - Restoration of ZS-UAD, Tipsy Nipper T66 mk 1
one more Picasa Web Albums - bamf.bamrs - Tipsy Nipper

Seb
Ah, yes. Thanks, Seb. I'm sure there's a lot of examples that I missed.
 

gschuld

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For what it's worth(not much I'm afraid), I believe that Topaz has a very good grasp on what a converted VW is capable of regarding aircraft use. It seems to me that a great part of the problems resulting from the use of the vw engine were as a result of several factors. A poorly converted engine(inferior parts/engine conversion layout), a poorly installed and maintained engine, and of course the desire to simply push the engine to do more work than is comfortable handling. I have met several people who decided on installing a vw knowing that it would be "on the underpowered side" for the plane they were building but did it anyway for economic reasons. Unfortunately, in an under or marginally powered airplane, it is FAR more likely to be over worked and abused than a larger engine. If you push ANY engine too hard, it will fail. If you need a 100hp+ engine with lots of torque to haul a heavy/draggy a 1300lb gross STOL aircraft into the sky, a direct drive N/A VW conversion is NOT for you. Sure, perhaps something like Aerovee's new turbo charged version that's under developement may perform well, but there are realistic limits.

VWs seem to do rather well in lightweight aircraft. As Topaz mentioned, thousands of airplanes have successfully flown behind VWs. Many dozens were designed specifically for their use. I would think long and hard about using the engine option that is the lowest HP available for the application for financial reasons, regardless of the engine type.

George
 

Topaz

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...It seems to me that a great part of the problems resulting from the use of the vw engine were as a result of several factors ... and of course the desire to simply push the engine to do more work than is comfortable handling. I have met several people who decided on installing a vw knowing that it would be "on the underpowered side" for the plane they were building but did it anyway for economic reasons. Unfortunately, in an under or marginally powered airplane, it is FAR more likely to be over worked and abused than a larger engine. If you push ANY engine too hard, it will fail. If you need a 100hp+ engine with lots of torque to haul a heavy/draggy a 1300lb gross STOL aircraft into the sky, a direct drive N/A VW conversion is NOT for you. Sure, perhaps something like Aerovee's new turbo charged version that's under developement may perform well, but there are realistic limits.
Amen. That's always been the biggest issue with auto conversions - the guy with the wrench. Most pilots think that just because they know how to fly airplanes, they know about airplanes. As in design. The two disciplines are almost completely unrelated.

Just out of curiosity (and unreliable memory), I just went back and checked the specs on the Ch701 example that Kmccune is using to "demonstrate" that the VW is inadequate without special cooling.

He specifically mentioned that the installations involved (that needed special cooling) were Type 1 VW conversions. As I said, most Type 1 conversions are rated at 50-65hp takeoff power. Anything over 65hp continuous pretty much demands a Type 4 conversion for all practical real-world purposes, from just about everything I've seen and read.

The kicker:

The Ch701 website shows that aircraft as being designed for 80hp Rotax 912 or 100hp Rotax 912S.* Putting a poor little Type 1 VW in that and expecting it to pull all the way through a reasonable climb at the same rate as a 80hp engine is foolhardy, to say the least. Using it for STOL work as is usually expected of a Ch701 is beyond foolhardy. Blaming the engine for it is like saying all pickup trucks are bad because you tried to pull an 80,000lb big-rig trailer with a four-cylinder Tacoma and doing so damaged the truck.

*The site mentions that the aircraft is capable of taking engines down to 50-65hp, and engines up to 185lbs, but that "Alternative engines will affect performance, specifications and flight characteristics of the aircraft." In fact, these "minimum power" specifications for kitplanes are a lot like the "minimum system requirements" for software. Sure, you can get World of Warcraft running on that fifteen-year-old Pentium III computer, but it sure isn't going to be very usable on that machine! An airplane designed for 80-100hp might well get off the ground with a lightweight 50-65hp motor (Rotax 582, etc.), but climb and other performance is going to be spectacular in completely the wrong manner. Since a small VW is both low-powered and heavy, it's a really poor choice for the Ch701.
 
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Andy

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I hope this thread isn't too old to revisit but I'm interested in vw cooling. Has anyone experimented with water/alcohol injection? Pretty simple to rig, not much weight. Just wondering...
 

bmcj

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I hope this thread isn't too old to revisit but I'm interested in vw cooling. Has anyone experimented with water/alcohol injection? Pretty simple to rig, not much weight. Just wondering...
I had a friend that rigged up a water injection systyem on hi VW Bug. He said it worked well, but he said that even when the cylinders were driven to detonation, the water masked the telltale signs. His concern is that, if adjusted improperly, the engine could be run in a detonation mode without the operator knowing it.

I don't know how he came to his conclusion about the symptom masking, but I do know that he is a very sharp, methodical person who is not prone to make random statements without some basis or backup.
 

Andy

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Are you still in touch with this guy? It would be interesting to know how he came to this conclusion. The turbo vw guys commonly use water/alcohol (windshield wiper fluid for example) delivered thru an injector nozzle at the intake manifold to control detonation and cool the combustion camber by evaporative cooling. Some claim the expansion of the steam gives a small bump in HP. I never had one on a dyno so I couldn't say. I'm putting one together that I'm going to run in a bug just to experiment with it. The injector will run off of boost pressure so no additional pump will be needed. I'm limiting boost to 6 pounds. It will be interesting to see how well it works.
 

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