Yet another VW power argument. Again.

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

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  1. Nov 18, 2015 #1

    BoKu

    BoKu

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    Moderator Note: This thread was forked off from another, so as not to disrupt the topic of the first.

    ---------------

    This is the article I was looking for yesterday. It is the best summation of VW vs. horsepower I've ever met:

    Bob Hoover's Blog: AV - The Christmas Engine

    There's a handy search tool on Blogspot that lets you search an author's posts. I recommend it; Bob Hoover did an amazing amount of research and testing.

    Thanks, Bob K.
     
    Last edited by a moderator: Nov 18, 2015
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  2. Nov 18, 2015 #2

    Topaz

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    Re: New Aircraft design tube fuselage with foam core wing

    Without intending to derail this thread, that particular post by the late Mr. Hoover is one of the most-quoted, most-misunderstood pieces ever written on the subject of VW conversions. It mostly describes a conversation regarding one of the smaller 1600cc variants, which Mr. Hoover is quite correct in stating cannot sustain 60hp continuous. It's just too small. An O-200 can't put out 150hp sustained, either, for the same reason. However, most people reading the article stop there. Lower in the same article, Mr. Hoover goes on to describe a 2180cc VW conversion with which he's reliably gotten 55hp continuous. "At prop speeds", which means 2700 rpm or so. Which means, as anyone who has read his blog knows, Mr. Hoover is extremely conservative in his VW setups. IMHO, too conservative.

    Unfortunately, Mr. Hoover isn't around anymore to qualify his statements. Unfortunate, because this one blog post has done more to set back the use of VW engines in aircraft than anything else, ever. Mr. Hoover chose to limit his engines to lower speeds. Other reputable manufacturers - Great Plains, Hummel, AeroVee, Revmaster - have been running VW's reliably at higher speeds for decades. Great Plains offers engines turning out 60-65hp continuous (large displacement, custom heads, oil coolers) and has been for many, many years. Back in the 60's and '70's, you couldn't attend an airshow without seeing at least three VW powered homebuilts, and nobody was complaining about some mysterious underperformance of the engine compared to the stated specs. If Great Plains has been ripping off customers to that tune for decades and nobody has figured it out, I'll eat this monitor. Does anyone have any evidence of this gigantic horsepower conspiracy of lies?*

    No.

    For one, there isn't just one "VW engine". There are quite a few different displacements. And yet, magically, they all can only produce <insert 30hp or 50hp here, depending on how badly you've misread Mr. Hoover's post>. That's pretty remarkable. Other engines produce more power with more displacement. VW's don't? How strange!

    I wish Mr. Hoover were still alive. I wish he could clarify the misinformation he's put out there. He's not, and he can't, and we're all the poorer in engine choices because of it. The VW was the auto conversion engine of choice for many, many, many years. But, today, "everyone knows" they're "only good for about 50hp", because "Bob Hoover said so in his blog!". It's bunk. It's always been bunk, and it will always be bunk.

    ---------------

    *As always, someone is going to try and say, "But what about all those KR-2's that had to mount O-200's to make the original design specs!!! See, that's proof that the VW under-performs!!!" Breathless gloating ensues. Except... Show me a single one of those KR-2's and other such airplanes, originally designed for the VW, that actually had to trade up to an O-200 because they were 100lbs or more overweight empty, and then being flown by a "modern-style" American citizen. The original KR-2 design has an empty weight of 480lbs. There have been maybe three customer examples that came in that light. And occupants? Ken Rand was about 120-130lbs. Not a 200+lb. "average" American. So you've got an airplane that's flying 200-300 lbs (and often more) over its design MTOW of 900 lbs, and the fact that it underperforms and needs more power is somehow the engine's fault? Come on.

    Customary VW rant by Topaz over, we now return you to your regularly scheduled thread. If you want to learn more, there have been one or two threads dedicated to this subject here on HBA. Look it up there.
     
    Last edited: Nov 18, 2015
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  3. Nov 18, 2015 #3

    BoKu

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    Re: New Aircraft design tube fuselage with foam core wing

    I think that the article is perfectly clear. Bob was consistently adamant, and had the chops to back it up, that:
    * The VW could indeed support 200 HP for short periods.
    * The max continuous horsepower limitation is related to rates of heat rejection and maximum allowable materials temperatures.
    * The rate of heat rejection is limited by architectural constraints inherent in an inexpensive lightweight motor for an inexpensive lightweight car.

    Blogspot's search widget makes it pretty easy to search up everything Bob wrote on the topic:

    Bob Hoover's Blog: Search results for horsepower

    And yeah, if you wanted you could make sooper dooper VW heads that addressed some or all of those constraints. But few if any car guys would buy them; almost nobody hotrods air-cooled VWs these days, and them that do don't really need a lot of continuous power. And without the car market, economies of scale push the prices up to where few airplane folks would buy them either.

    As to all those bygone VW-powered airplanes of yesteryear, when by one means or another they reached the ends of their service lives, folks just moved on to things that offered better return on investments both personal and financial. No conspiracies or proving-of-negatives required.

    Thanks, Bob K.
     
  4. Nov 18, 2015 #4

    Topaz

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    Re: New Aircraft design tube fuselage with foam core wing

    So I guess Great Plains, Hummel, AeroVee, and Revmaster have been lying all these decades? Ripping off everyone with inflated power numbers they can't really achieve? That's a pretty serious claim to make, based off of nothing more than one blog.

    Either Bob Hoover is right, or they are. If Bob is, they've been successfully ripping off the entire homebuilding industry for over 30 years. Or maybe Bob was just more conservative than most, and he understates what can reliably be achieved. You know, achieved like Great Plains, Hummel, AeroVee, and Revmaster have been doing for many, many years.
     
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  5. Nov 18, 2015 #5

    Hot Wings

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    Re: New Aircraft design tube fuselage with foam core wing

    It should also be noted that he wasn't satisfied with these limitations and was working on ways to increase them. His experiments with thermal coatings were showing promise. He was also talking to Steve Bennett about collaborating on a "clean sheet" VW conversion that would still be affordable. It's too bad this project never went any further.

    Even F. Weick noted that his work matching props to engine/airframe combinations would have been easier and more efficient if he could just get accurate hp numbers from the engine manufacturers. "Optimistic" hp figures, it seems, are part of aviation tradition. ;)
     
  6. Nov 18, 2015 #6

    Topaz

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    Re: New Aircraft design tube fuselage with foam core wing

    And the myth continues. Are you seriously saying that, for example, Great Plains has successfully ripped off the entire VW-powered aircraft community for 40+ years, and nobody has ever caught on? And AeroVee, and Hummel, and Revmaster? Seriously? :speechles

    So, are the Corvair vendors "optimistic" with their power numbers now too? How about Lycoming? Continental? Rotax? Limbach? Maybe even Pratt & Whitney?

    Or is it just all the VW vendors?

    The Internet is truly a amazing place.
     
    Last edited: Nov 18, 2015
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  7. Nov 18, 2015 #7

    Himat

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    VW engine for aircraft use, a much discussed theme on this site.:)

    I tried VW POWER as the search term on the site search and these where some of what turned up:
    https://www.homebuiltairplanes.com/forums/volkswagen/4158-how-much-hp-can-vw-engine-produce.html
    https://www.homebuiltairplanes.com/forums/volkswagen/14409-100hp-vw-reliable-practical.html
    https://www.homebuiltairplanes.com/forums/volkswagen/20150-cost-comparison-vw-options.html
    https://www.homebuiltairplanes.com/...-aerovee-vw-producing-100-hp-sonex-tests.html
    https://www.homebuiltairplanes.com/forums/volkswagen/4929-flywheel-drive-vw.html
    https://www.homebuiltairplanes.com/forums/volkswagen/16205-looking-volkswagen-engine.html

    All about the old flat four air cooled engine.
    To add it here too, today a VW engine to many is typified by the inline four turbo diesel engine of 1,9l capacity.
    Mounted in an airplane it can look like this:
    [​IMG]
     
    Last edited: Nov 18, 2015
  8. Nov 18, 2015 #8

    BoKu

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    Re: New Aircraft design tube fuselage with foam core wing

    Actually, no. This is that proving-a-negative thing I mentioned earlier. Nobody has proven that those guys couldn't do thus and such a thing. But Bob Hoover proved to his own satisfaction and mine that he couldn't do it. And when one of the best, who has no skin in the game, can't do a thing that folks with a lot on the line say they can do, I know which way I'm going to place my bet.

    Two points:

    * That's kind of a false dichotomy. Bob knew that those big horsepower numbers could be met, and said so. He just said that they couldn't be met for long; that the temperature/time/cycle counts would cause the heads to distort and fret and weaken at an accelerated rate.

    * I think accusations of scams and ripoffs are against HBA's terms of service... ;)

    Thanks, Bob K.
     
  9. Nov 18, 2015 #9

    Topaz

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    My ultimate point is this: The VW can be a fine little powerplant for smaller airplanes, and the mythos that has grown up around the late Mr. Hoover's blog is really hurting the homebuilding community by steering people away from what has, over the decades, been a very good choice when (like any engine) used within its capacity.

    A large-displacement VW can be set up without drastic modifications to put out up to about 70hp continuous. But not all VW engines can do this, especially anything under 2100cc. Even the Great Plains model in this power range is punched out to 2276cc, and you need to have a care with the oil cooler and your cowling setup.

    A 100hp continuous "VW" is going to need so many mods that it practically won't be a VW anymore.

    But those who say, "A VW can't put out more than 50hp continuous", based solely on reading Bob Hoover's blog, are doing a huge disservice to the homebuilt community. Great Plains, AeroVee, Hummel, and Revmaster went beyond that years ago, and in any case, it begs the question about what kind/displacement VW you're talking about in the first place. Bob Hoover said a 1600cc VW is good for about 40hp continuous. I think that's a little conservative, as was Bob, but it's not really far off. 45-47 is probably more in the ballpark. But not all "VW's" are 1600cc, nor are other manufacturers sacrificing reliability to get higher numbers out of different models.

    I wish people would read Mr. Hoover's otherwise excellent blog in that light. We need all the engines in this power range we can get. It's a shame to throw away a good one just based on "what everyone knows" on the Internet.
     
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  10. Nov 18, 2015 #10

    slevair

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    I probably read everything Mr. Hoover ever wrote. I would agree that he is very mis-quoted. He was very conservative by his own admission and very specific about his expectations; simple, low rpm, low maintenance, low temperatures, smaller displacement, continuous power on drag laden airframes, and testing that could be verified. Many people read only the parts they wanted to see and compared it to other peoples' ideals. Comparing his engines and standards to Sonex is fish to apples. Sonex and the rest supply great products, but to a different standard than the one Mr. Hoover was searching for.
     
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  11. Nov 18, 2015 #11

    Pops

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    OK, I'll put my .02 cents in. In the 1970's, I had a side business building VW engines and a VW only car sales. Have built a hundred or so VW auto engines and owned and sold many, many VW's. Also built hot, street VW engines. I have had VW's that would beat about anything on the street. With that being said, an aero VW engine is a completely different built engine. For a straight drive engine you build for torque, not rpm.
    The best VW aero engine is the Revmaster, because that don't use VW heads off the shelf. They make their own heads with larger fins for more efficient cooling. No one else,s heads cool as good as the Revmaster heads and that is why they can claim more continuous HP.

    Bob Hoover had it correct. I have built several Aero VW engines with no problems. In my 1835 cc, 60 HP engine the CR is 7.55 to 1. 141 lbs firewall forward weight. I have the Bob Hoover's oil mods and it almost runs to cool. I can climb at WOT all day at 95 degs OAT's with no problem with high oil or CHT temps.

    Friend of mine built a 2300 VW engine on a Zenith 701 with belt drive with starter and alt and had a firewall forward weight of 235 lbs and the engine lasted a little over 75 hrs. Cruise was 3900 rpm. Ran hot all the time and he tried welding larger fins on the heads that helped somewhat but about that time the case cracked and he gave up on the VW engine. Very common occurrence for someone that don't understand the limitations of the VW engine.
    A VW off the shelf head that everyone is using except for Revmaster will limit your continuous HP in any stroked VW engine of any size.


    Dan
     
    Last edited: Nov 18, 2015
  12. Nov 18, 2015 #12

    Topaz

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    I have never disputed that Bob Hoover knew what he was talking about. What I dispute is the people who read his words and then trumpet all over the Internet that all VW aeroconversions are "only good for about 50hp."

    That never was true and, if he were around today, I think even Bob Hoover would say that they've got it wrong.
     
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  13. Nov 18, 2015 #13

    Pops

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    I believe you are 100% correct. I have never heard anyone say such a flat statement. Certainly not true on my VW engine.

    Dan
     
  14. Nov 18, 2015 #14

    saini flyer

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    Pops are you suggesting that your 60HP VW can do WOT all day long :para::ponder: or that it can do WOT for climb and then need to be cooled and must go to lower power?
     
  15. Nov 18, 2015 #15

    Hot Wings

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    I don't see it as hurting the homebuilt community at all. In fact I see it as exactly the opposite. You're the one that seem to be the one missing the point he was trying to make ... and just restated by you.

    Like Pops I've built several hundred VW engines and lived with many (my own and my customers) on a daily basis. My experience with converted aircraft VW's, none of my own, can be counted on my fingers, so I'm not at the same level of experience there. But the point is I've got enough real world experience to know that Hoover's words regarding durability should be taken as close to the truth as anyone's.

    There is a thermal limit imposed by the stock heads. That's just basic physics. If you read what Hoover wrote you will not that his self imposed limit was for low and slow type aircraft. The Taylor Bird being specifically mentioned. Put the same engine in a faster plane with maybe more mass flow over the heads and you can probably up the continuous hp a bit. Add on some oil cooling and some thermal coatings and you can get even more.

    The German engineers that developed the later VW engines went to great length to make sure the cooling was as good as it could be. They had the economy of scale working for them and their testing was far more rigorous than any of the aviation conversions. If you have ever looked inside the VW cooling shrouds you will see little vanes that have been designed to move the cooling air around where it is really needed to eliminate hot spots.* The later model oil coolers were moved out of the internal airflow and the capacity of the fan was increased to handle the added heat of the 1600cc engines. The FI engines had their compression ratio reduced partially for emission reasons but also to help keep the cylinder head temperatures under control. If the engineers thought this level of development, and expense, was needed when moving up from a 44hp 1500 to a 50hp 1600 it makes one wonder where the added capacity to dissipate an additional 30 hp worth of waste heat is being found on the various 80hp aircraft conversions?


    *Other than using the later model under cylinder air deflectors none of the aircraft conversions employ any of this more sophisticated cooling architecture. A simple head temp sensor isn't going to tell you much other then the temperature at that one location.
     
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  16. Nov 18, 2015 #16

    Pops

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    In a climb or level flight ,WOT all day long on a 95 OAT day, with the oil temps not going over 195 degs and CHT not over 295 degs. At cruise of 2700 rpm the oil temp is about 185 degs and the CHT at 270 degs. Using a Culver 60" dia x 26" pitch prop. No need to step climb because of temps.

    Dan
     
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  17. Nov 19, 2015 #17

    Vigilant1

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    Re: New Aircraft design tube fuselage with foam core wing

    Okay, so Pops is getting 60 honest, all-day HP from an 1835cc engine at a modest compression ratio and RPM. Given that, it seems very reasonable that the 2180CC engines with 8.0 CRs and at 3200 RPM are producing 75-80 HP--just like the dynomometers say.

    So the only question is longevity and reliability. Pops has successfully flown a draggy plane for hundreds of hours with good results. The mass airflow through a clean, fast airplane is going to allow better cooling--is it really unrealistic to expect that it might be about 25% better? Just maybe those 2180cc engines are cooling okay and getting good reliability and longevity--just like hundreds of Sonex, Onex, Sonerei, KR2, etc, etc pilots are saying. And they'll all say close attention to the cowling and carefully using every bit of air that comes in is important to making the engine last.

    75-80 HP at 60 MPH? Expect it to get hot, and don't expect to go 500 hours before taking those heads off and doing some work.
     
    Last edited: Nov 19, 2015
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  18. Nov 19, 2015 #18

    Topaz

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    Yep, that's a decent assessment. Nobody is arguing that VW's don't need care when pushed to higher power outputs. And even as big a fan as I am, I get skeptical when I see claimed continuous power ratings pushing much over 70hp. Even Great Plains doesn't claim over 72hp continuous, IIRC.

    Engine life (TBO) for most of the VW's out there is about 1200h. No, that's not 2000h. But there's no magic about that latter number, and what's a Rotax? 500h for their inline models, I believe? 1200h is more time than many homebuilts will ever accumulate, and it's maybe two or three overhauls in the life of many others? We're talking 10-12 years between events for most.

    I think the observation about airframes is astute as well. Most older designs running VW's have the cylinder heads hanging out in the wind. It wasn't until the 70's and 80's that people really started tucking them into modern-style cowlings. Optimize the cooling intakes and exhaust for cruise, with no cowl flaps or suchlike, and at low speeds the engine will run hot, and probably more readily than a certified engine.

    A 1200h TBO and paying more attention to a decent cooling setup are what you trade for an engine that costs a fraction of an equivalent certified engine, and pennies on the dollar for overhauls. Like everything else in aviation, it's a compromise.
     
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  19. Nov 19, 2015 #19

    Pops

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    I did put some effort in my cooling. First the air holes down between the fins has to be cleaned out of casting flashing. A assortment of round files and some hand labor will do wonders. You will notice the air scoops on my engine are on the large side. The air has to go down through the opening of the head, not over the heads. Just like VW designed with the fan housing in the auto. I tried different air scoops until I had the cooling that I wanted and did hi-powered run-ups and used a point to shoot temp gauge to make sure that all parts of the heads were cooled with no hot spots. I used Bob Hoover's oil mods to get equal oil flow to each side of the engine for equal cooling. I use a full flow oil system. Oil from the oil pump- to the hot oil box at the base of the carb ( cools the oil 20 degs) then to the full time oil cooler, then to the filter and then back to the engine. I use 2-- 2" scat air ducts to the air box above the oil cooler.

    Added -- I also used the VW ground power unit lower cylinder baffling that is sold by GP's.

    Dan
     
    Last edited: Nov 19, 2015
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  20. Nov 19, 2015 #20

    saini flyer

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    Dan,

    I remember now that you have posted this information elsewhere on HBA too.
    Care to share some pics and details of your aircraft+installation+ cooling work on VW. Also, how is a 60" prop working at 3600RPM.... Genuinely curious!
     

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