Yet another VW power argument. Again.

Discussion in 'Volkswagen' started by BoKu, Nov 18, 2015.

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  1. Nov 19, 2015 #21

    Turd Ferguson

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    Re: New Aircraft design tube fuselage with foam core wing

    That's not really how cooling air works. It's not about how much you get, it's about how the air is used. For max cooling you need the differential pressure, or delta P across the cylinders to be as high as possible. I've seen an engine in a fast plane toasted because a piece of baffling was either left out or fell off. Plenty of airflow, however, the air was just sailing through the cowl unrestricted. And lycoming used that little factoid, delta P <x.x to deny the warranty claim.
     
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  2. Nov 19, 2015 #22

    don january

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    I know Dan. this is top secret if ya showed me then you would have too eliminate me:gig: Your pictures are always a joy to see.;)
     
  3. Nov 19, 2015 #23

    mcrae0104

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    Re: New Aircraft design tube fuselage with foam core wing

    Yes, it is how cooling works.

    Higher q is exactly what makes higher delta P possible in a faster plane. In order to assume Vigilant1 is incorrect, as you do, one would have to assume "air is sailing through the cowl unrestricted," as you say. Of course you need baffling to separate the high pressure from the low pressure and direct the airflow. Vigilant1 knows this; give him a little credit, will ya, Turd?
     
    Last edited: Nov 19, 2015
  4. Nov 19, 2015 #24

    Vigilant1

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    Re: New Aircraft design tube fuselage with foam core wing

    Delta P produces what? Airflow. That airflow (mass of air) is what cools the cylinders. And airflow is what counts: if we had a 1 sq inch cowl opening in front with high dynamic pressure and very effective cowl flaps we'd have high delta P but insufficient cooling because it's airflow we need. The same thing pertains across the fins--we need good delta P and therefore good airflow across them. Now, if all things are equal a plane moving through the air at 120 knots has a lot more potential to generate delta P (and airflow) than one moving at 60 knots. That's obviously true at the intake (due to dynamic pressure) but also at the "exhaust" (because the faster plane can generate more "negative pressure" (compared to ambient) than the slower plane--a given cowl flap or other device will be more effective at higher speeds).

    Now, that's just potential. All bets are off if the delta P/airflow over the cylinders is crummy due to poor baffling, sending airflow to where it isn't needed, etc. But that's not a lick on the VW, or a case that they can't be made to cool well.

    More fundamentally: Hundreds and hundreds of planes are getting more than the posited max 30-50 reliable HP from their VW based engines, and doing it for many hundreds of hours of flight time. Anyone making the assertion that it can't routinely be done should explain that before the case can be taken seriously, right? I mean, it's happening all the time, so it's a bit of a stretch to say it can't be done.
     
    Last edited: Nov 19, 2015
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  5. Nov 19, 2015 #25

    Turd Ferguson

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    Re: New Aircraft design tube fuselage with foam core wing

    I'm not aware of any data collection going on for VW aero engines. No idea how many are in service, what kind of hrs they are compiling, rate of failure, TBO, actual power output, etc. If you have something like that I'd be interested in seeing it.
     
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  6. Nov 20, 2015 #26

    Pops

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    First-- I don't turn the 60" prop at 3600 rpm. You must be thinking of a short prop on a VW in a clean fast airplane.

    Pictures of engine installation and airplane. Its really a Fisher Super Koala construction but built to the dimensions of the Koala 202 for the Cub look.

    On the engine, the SS for the intake and exhaust are bathroom handrail material from Lowes box store.
     

    Attached Files:

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  7. Nov 20, 2015 #27

    Aesquire

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    Re: New Aircraft design tube fuselage with foam core wing


    I don't think that "posited 30-50 reliable HP" is anyone's argument.

    The argument is more "100 HP out of a VW air cooled Beetle based engine is likely to be short lived".

    Just from the claims by people actually selling VW based engines, 70-80 HP with a lot of modification seems state of the art.

    30% more is likely to lead to early fail. Cooling, as said, is the primary limit. Push the revs too high, and you find another limit, loudly.

    Most of the VW engine builders either use "hotrod" improved parts, extensively, or make those parts for sale to gearheads, air & ground. With modern parts, it's still 80 hp. ( which is actually very impressive. )

    Does anyone sell a 1600 cc. engine using all stock parts? If so, why? ;)

    Another thing to consider is, I believe the UK only allows 3000 RPM on VW based engines. Please correct me if I'm wrong on that.
     
  8. Nov 20, 2015 #28

    Topaz

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    Re: New Aircraft design tube fuselage with foam core wing

    Seriously? Show me a database of those same real-world data points for the entire fleet of any GA piston engine, certified or not, let alone an auto-conversion. Let's not be absurd, okay?

    EDIT: What I can give you is this: In the 1983 edition of Firewall Forward, Tony Bingelis listed VW installations (of all displacements) at 1075 aircraft using data from the FAA. This made it the #5 most-used engine in homebuilts at the time. The top-used engine, the 160hp Lycoming, had 1284 installations from the same data.
     
    Last edited: Nov 20, 2015
  9. Nov 20, 2015 #29

    Topaz

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    Re: New Aircraft design tube fuselage with foam core wing

    No, that's exactly what some people try to say, especially after mis-interpreting Bob Hoover's blog. Check the list of threads given above. You'll find plenty of 30-50hp "limits" thrown about, with nothing at all to back them up except, "I read it on Bob Hoover's blog, and Bob knows a lot about VW engines!" Yes, he did, but he never said anything of the kind for all VW engines. In the page Boku pointed to at the top of this thread, which is the usual one trotted out in these arguments, Mr. Hoover was talking about 1600cc engines. Great Plains makes a 2276cc version, with special heads and other mods. And yet we're to believe that they have exactly the same maximum continuous horsepower? See the point I'm making? Also, Mr. Hoover pretty much staked out the more-conservative end of the VW aeroconversion industry. Kept his lower-performing to satisfy his own feelings about what should be done. I'd say the first incarnation of Revmaster was probably the opposite pole, with their attempt at a 100hp continuous-power turbocharged VW in the mid 1980's. Which, reading the trade magazines at the time, wasn't very successful, and had the expected large amount of problems resulting from pushing the VW that far.

    And, with the provision that we're talking about continuous horsepower ratings, nobody is arguing against that. Certainly not me. The 2276cc Great Plains engine can put out 102hp for takeoff, and do it for about five minutes consecutively, then it has to be throttled back to about 72hp. That's just an operating limitation of the engine, just like the "forbidden" RPM bands in some Lycomings.

    70-72 hp continuous is about the maximum in the market from the larger, reputable vendors. I think there may be a few higher claimed outputs, but I don't know much about them, including the level of modification. I tend to "buy" maximum continuous horsepower ratings for aero-conversion VW engines topping out in the 70-72hp range. Above that... I start to squint a little bit and wonder what they've done.

    I doubt a "stock" (i.e., directly out of a car) VW engine has swung a prop since the very early 1970's. Even then, they weren't being pushed very hard. The plug-in Vertex magneto mod became the first, most common, aeroconversion item, along with thrust bearings and oil slingers. As power levels climbed, more extensive mods became the norm, and eventually oil coolers became common. Custom heads are common now.

    It's a conversion of an auto-engine for airplane use. Such conversions involve some conversion regardless of the engine involved. The Corvair sees its share of mods, too. I'm sure the Sube's get modded a bit as well. Part and parcel of the entire concept.

    I have no idea. There is no such restriction in the USA, and 3400-3600 are normal maximum RPMs for these engines, at least from the reputable vendors.
     
    Last edited: Nov 20, 2015
  10. Nov 20, 2015 #30

    gearhead

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    I've posted this shot before from the Jan. 1977 edition of Implement and Tractor Red Book which is presumably based on VW factory literature:

    VWaircooledInd.jpg

    From this I conclude that VW was not comfortable with providing warranty on the Type 1 industrial engine at more than 46 continuous horsepower, while they felt that the Type 4 was reliable at ~50% more thermal load. These ratings are with forced air fan cooling and all of the factory proven baffling.

    The issue with the Type 1 cylinder head is its architecture; running the exhaust ports out the ends of the head leaves very little room for cooling air to pass around the critical exhaust valve guide area, so the guide runs hot and wears rapidly at higher power levels. Engine designs that run the exhaust port down, such as VW Type 4, Corvair and most aircraft engines are not immune to this problem if not properly cooled, but their design inherently allows more cooling air around the exhaust guide and resultant higher heat rejection than VW Type 1. The exhaust valve stem "wiggle test" has been prescribed for both Type 1 and Lycoming, for example.

    CHT thermocouple location on the head can make a big difference in accuracy of information delivered by the gauge. In the case of VW engines, placing the thermocouple under an inboard upper cylinder stud is almost useless because that location is cooled externally by air over the substantial cooling fins in the area and internally by intake charge through the port as well as being far from the exhaust. This image taken from the 1967 edition of Hot Rod Complete Book of Engines (which probably lifted it from a GM service manual) shows the wide variation of temperature at various points on a _Corvair_ cylinder head under load:

    Corvair head temps.jpg

    550°F is, IMO, hot enough to allow cast aluminum to warp enough to unseat valves, crack and generally weaken the cylinder head structure.
     
  11. Nov 20, 2015 #31

    Topaz

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    And this argument again. You detractors are hitting all the usual canards. You can conclude anything you like from that chart, but you're looking at installations for cars, not for airplanes. As I just finished saying, a pure-stock VW very likely hasn't swung a prop since the very early 1970's. All VW aeroconversions involve some conversion, to make them work better for aircraft use, just like every other kind of auto engine converted for airplane use. Show me a chart like that for aeroconversion VW's and then we'll have something that actually applies to this discussion.

    And, as has already been pointed out by more than one person in this thread, if you're going to use car-manufacturer data, thermal analysis, or a divining rod to say that no VW aeroconversions can run at 55-70 hp continuously, in a properly designed cowling, you're going to have to explain all the KR-2's, Sonarai's, Sonexes, ad nauseum that actually use or have used those engines and performed as-expected for the power rating. If you can't also show that it never happened, your argument is what's flawed, not history. If you want to say it never happened, good luck. It'll have to be one heck of an argument, since you'll have to prove that all those articles in Sport Aviation from the time, all the flight reviews, all the pireps, and all the guys who built VW-powered airplanes were all part of this vast conspiracy of lies to falsely pump up the ratings of these engines. I'm sure the guys flying Sonexes behind AeroVee's are going to be fascinated to hear how they really can't be getting the performance they're getting from that engine. I guess someone from Sonex must've snuck into all their garages and messed with their ASI's and VSI's when they weren't looking. I'll alert the media.

    Can I ask a question of you doubters? That question is "why?" There's a solid history of VW's pulling aircraft just fine, at performance levels commensurate with the claimed power outputs. Decades of history. So why the strident need, in the last ten years or so, to say that it never happened? Why? I guess there's nothing the Internet loves more than a potential conspiracy, but this one? It's ludicrous. We hit this every couple of years or so, and it's always, "because I read on Bob Hoover's blog...". Is that really where all this is coming from? One blog???
     
    Last edited: Nov 20, 2015
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  12. Nov 20, 2015 #32

    Lucrum

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    No hijacking intended

    When I was maybe 10ish (around 1971) one of my first day dream home built 'designs' was a scaled down P-38 powered by a pair of VW engines
     
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  13. Nov 20, 2015 #33

    mcrae0104

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    You forgot to mention that they're screwing with GPS satellites too.
     
  14. Nov 20, 2015 #34

    Topaz

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    Yep, and they do chemtrails in their spare time.
     
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  15. Nov 20, 2015 #35

    Vigilant1

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    Re: New Aircraft design tube fuselage with foam core wing

    If so, they need to quickly pull over all the old VW Beetles turning about 4000 RPM to try to keep up with traffic on the M1. ;)

    Maybe someone here knows if the UK authorities are prohibiting the many VW-based airplane engines there from operating above 3K RPM. If so, it certainly seems arbitrary. I'm fairly sure that the certified VW-based rated for 3400 RPM for takeoff. There's a long history of good service at 3200 RPM and more in aircraft use, they routinely operate at 4000 to 4500 RPM in automobiles around the world (racers operate them higher, obviously with careful attention to engine balance and to CHTs).
     
    Last edited: Nov 20, 2015
  16. Nov 20, 2015 #36

    Vigilant1

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    Every engine has limitations. No one is claiming that the VW head, as available from aftermarket sellers, is perfect for aircraft use. But the thermal limitations of the design are very well known and understood and are "baked in" to the continuous HP numbers that we're talking about.

    Yes, true. Some builders use the CHT thermocouple under the plug seat, some use a cylinder stud. Sonex recommends drilling and tapping a hole near the spark plug to use for the screw holding the CHT probe--this gives readings very close to an under-plug probe, with less CHT probe breakage that can accompany that location.
     
  17. Nov 20, 2015 #37

    Pops

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    Revmaster's R- 2300 cc engine is rated 85 hp and 80 continuous HP. They don't use a VW or another aftermarket heads, they make their own head for more efficient cooling. IMO they make the best VW style engine on the market. Also NOT a kit of parts that you have to assemble.

    http://revmasteraviation.com/

    Dan
     
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  18. Nov 20, 2015 #38

    Tiger Tim

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    Perhaps the distinction that needs to be made is that once you start modifying, it's no longer really a VW...

    I mean, that's what everyone around here says about airframe design changes, right?
     
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  19. Nov 20, 2015 #39

    Topaz

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    Okay, so let's go with that. It's got VW cylinders, a VW case (with some re-machining done), VW valve train, a forged VW crank, some have modified VW heads, etc. But while the vast majority of parts are originally VW, it definitely has some modifications.

    What should we call it, then?

    Is a Corvair engine converted for aircraft use no longer a Corvair?

    Is an LS-1 modified for aircraft use no longer an LS-1?

    rv6eguy certainly still calls his modified Subaru engine a "Subaru". What, instead, should we call that?

    This topic - and this proposed solution - only seems to crop up with regard to VW's. Why not for anything else? Corvairs certainly have as many mods - fifth bearings, etc. Why is the VW aero-conversion so hard for the modern mind to believe - despite the history - that we have to call it something else, and we don't have to do that for anything else?

    How about we call it a "VW aero-conversion" and have done? You know, like everyone else has been doing for 40+ years.
     
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  20. Nov 20, 2015 #40

    AdrianS

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    Disclaimer : I don't know a lot about aircraft, but I do know engines.

    As far as I can see, the continuous power limit on VW engines is heat dissipation from the cylinder head.

    At a very rough estimate, 1/3 of the fuel turns the prop, 1/3 goes into heating the engine, and 1/3 goes out the exhaust as waste heat, so for every prop hp, you are dumping about the same into the oil / air cooling.

    It appears that a well-built VW can deliver 70 hp continuously, with good heads, oil cooling, etc. This means the cooling system is dissipating 70-odd hp.
    You can bore it, stroke it, turbo it, and get a lot more hp from a VW, but if you can't get the heat out, it won't last at that power output. You may well be able to get 100+ hp from a VW engine, but getting rid of another 30hp (nearly 30% more) of engine heat is the issue.
    That doesn't matter as much for automotive use, because even on a race track you are not at full throttle the whole time.

    I don't pretend to know the actual numbers for reliable continuous VW power rating, and a lot depends on installation, but some people seem to make the mistake of thinking that if you can get X hp from Y cc, increasing the capacity automatically increases the continuous power rating.

    As an extreme example, we dynoed a (non-VW) drag car the other day : 1100 hp from 3 and a bit liters, with lots of boost. It can deliver this repeatedly, for 10 seconds at a time. How long would it last at peak power? My estimate is one minute (tops), before it overheats catastrophically.



    ps I am currently trying to persuade a formula-v team that they are losing more power due to heat issues on track than they gain from cutting down of cooling fan drag : they got better dyno numbers by slowing down the fan, but the driver has to watch CHT's like a hawk, and back off the throttle on occasion to preserve the engine.
    I reckon he would lap quicker with 1 or 2 less crank hp if he could just drive the thing flat out and concentrate on racing.
     
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