Yet another VW power argument. Again.

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

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  1. Nov 22, 2015 #61

    mcrae0104

    mcrae0104

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    I thought that looked familiar... http://www.homebuiltairplanes.com/forums/volkswagen/14648-new-brazilian-vw-3-1l-new-head-castings.html?highlight=Motorav
     
  2. Nov 22, 2015 #62

    TFF

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    Perspective is non of these engines are VW. They are VW platform. Unless you are going to build a true '60s VP or Tennie Two engine, you are building a catalog engine. Flip through the internet and pick the parts you need. Horsepower is easy; someone is making 700hp for a Rail Job and its aircooled. 400hp Drag Bugs are common, and 200hp street is a daily driver. All if using their max hp is for 20 seconds or less and then they park and let cool. If you need 85hp you better have the best cooling head on the market. If you want 100hp and not have a 10X6 model airplane prop on the front, you will have a gearbox. If you notice the Revmaster specs,it took 400 more RPM to get 3 horsepower over the old. The engine is overextended to make 85 and it is probably not a useful 85; Detroit advertised horsepower for sales. None of these engines are VW engines.
     
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  3. Nov 22, 2015 #63

    BJC

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    From their web site:
    "The first model should be on the market in the upcoming future."

    Do you consider it to be a VW?


    BJC
     
  4. Nov 22, 2015 #64

    Klrskies

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    It's based on the vw engine, yes. I use it as an example as to how extensively modified a stock vw has to be to reach the sought after hp and sustainability that we would like to obtain with lesser modified engines. There is no free lunch. The range of power on the vw based engine is quite extensive, and if one does not ask more of the power plant than it's capable of delivering without damaging itself, then alls well. Can it be re-engineered to be much, much more than it is capable of being in it's stock form? Of course. It's range is quite broad, yes? Look at the CAD drawings of yhe case and cylinder head they have designed to handle the heat and loads. Impressive. Will anyone buy one? I wouldn't. Im sure it will be extremely expensive. I can appreciate the engineering in all ranges of the vw engine as a power plant for many applications.

    The engineering that the homebuilders have accomplished has improved the capability substantially, but without radical redesigns, it seems that the engine is limited to around 13 to 18 hp per cylinder in a sustained load. The addition of purpose built engine componets changes that capacity.
    Ken
     
  5. Nov 22, 2015 #65

    Jake Levi

    Jake Levi

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    Great discussion. I will have excellent help on the installation, actually on the whole project, my flight instructor besides being a commercial pilot, and flight instructor is also a certified A&P, and both of his assistant instructors are A&Ps, so I will have capable guidance , and probably just doing some work, with me helping/learning. They are almost a 3 hr drive but well worth it. I do the instruction multiple hours in a day with study breaks in between. It makes a full, and good day. They like Continentals but are flying 3. Tom also buys and sells some, but bigger then I want or need.
     
  6. Nov 23, 2015 #66

    BJC

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    I did look at the drawings; that is why I asked if you considered it (still) to be a VW. Looks like a mew design to me, based on the VW concept.


    BJC
     
  7. Nov 23, 2015 #67

    Vigilant1

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    The CX5 seems like a very good choice for those wanting VW-based power and enough room/payload for two large people. 479# of payload with full fuel (about 3 hours worth), and 28" of cabin width in tandem seating--that's pretty roomy (wider than an RV-8). It's not a STOL ship, aerobatic, or built for high-speed long distance trips, but it appears to fill the bill for the type of fun flying 90% of us do 90% of the time. Looks and flies good-- and cheap.

    The "secret" in this case is having a fairly clean, light design and generous wing (126 sq ft area, 28' span). That's more wing than a Zenith 701, and about the same as an RV-9.

    I do have some "suspicion" about the claimed 1000 fpm ROC for the CX5, that seems very high for a 1320 lb airplane with 80-85 HP on the nose. When more of them are built and flying we'll have more data points. I certainly never saw a ROC that high in a C-152 at MTOW, and it is a plane with similar span loading, wing loading, and power loading to a CX5 at MTOW. That same comparison supports the idea that the CX5 can fly safely at that weight and power, but it will be a lot more "sprightly" if flown at lower weights. It's a good tradeoff for the majority of folks who fly alone most of the time, but would like to take a friend along occasionally.
     
    Last edited: Nov 23, 2015
  8. Nov 23, 2015 #68

    cheapracer

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    I wouldn't have gone with the seperate heads, it weakens the casings which is already the VW casing based problem, and makes cooling harder. This is part of the Jabiru's problems in my mind.

    Also the heads are loose copies of 1950 aviation heads, another downside.
     
  9. Nov 23, 2015 #69

    Topaz

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    If the CX5 really requires 80-85hp, then with the possible exception of the new Revmaster (an as-yet unknown quantity to me), there isn't a VW-derived engine out there that's a suitable powerplant for that airplane. The AeroVee is claiming 80hp continuous but, even then, the CX5 would be demanding top performance out of the engine at all times. That seems inadvisable to me. If the airplane really needs 85hp for an extended climb, then even the AeroVee is not a good choice.

    I think it's a far better practice to choose a VW-based powerplant based on its continuous power rating, not on its takeoff power rating. Doing that, the Great Plains 2276cc engine would be an appropriate choice for an airplane that needs 72hp (the engine's continuous rating) under all flight conditions except the takeoff run. That it produces 102hp for up to five minutes or so should be considered "extra power on-tap" for things like takeoff or a quick emergency climb, not "normal" operations.

    In other words, the "102 hp" GP 2276cc engine is not a suitable replacement for an O-200. It's a suitable replacement for, say, an A-65. I think many of the "problems" that have been seen with VW's in terms of "inadequate power" and low TBO in-practice are a result of selecting the engine based on the takeoff power rating, rather than the "real" continuous power rating. All the manufacturers except Hummel provide continuous power ratings on their websites, and Hummel is very quick and forthcoming to state realistic continuous power ratings when asked, as I've learned first-hand.

    A two-seat "VW-powered" airplane, carrying two "modern" US adults (200+ lbs. each), plus baggage, plus fuel for some decent range, is going to be a very light aircraft, and be very likely to have more span (and aspect ratio) than the typical sportplane case. This is all to keep the power required for climb down into the range that the engine can produce continuously. Back in the 1960's and 1970's, when the average US adult really was closer to 170 lbs., a two-seater with small wings like the KR-2 really could be VW powered if you kept the airplane light like the orginal. Today, the airplane would be carrying an extra 60 lbs or more just in people, plus everyone these days seems to have the "need" to pack even a little KR-2 with a full IFR panel and all the amenities, adding even more weight to the airplane. Power requirements have thus climbed out of what the VW can reasonably produce, and up into the Corvair range.
     
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  10. Nov 23, 2015 #70

    Vigilant1

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    Yes, I should have been more clear: The engine Dave Thatcher recommends for the CX5 is the Revmaster R2300.

    Hopefully when more are flying we'll get an idea of how it performs over a wide range of conditions. If the Revmaster 2300 gives good climb performance and stays adequately cool during climb, future builders may be satisfied with a slightly lower MTOW in exchange for being able to use another VW-based engine rated at 75-80HP. But for most builders, the Revmaster is a proven name and available at an attractive price, so it would be a natural choice unless special circumstances were in play (e.g. the desire to learn how to build an engine, having an existing engine on hand, living somewhere where it was expensive to ship a Revmaster, etc).

    And it's worth saying that the Great Plains 2276cc engine that makes 105 HP for takeoff uses a geared reduction drive (so the engine can rev higher with reasonable prop speeds). That reduction drive increases weight and cost.
     
    Last edited: Nov 23, 2015
  11. Nov 23, 2015 #71

    Topaz

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    Ah. Okay. As I said, I know very little about the "new" Revmaster and their engines. The "old" Revmaster built very nice "65hp" VW conversions, but their attempt at the time for a 100hp turbocharged engine ended up killing the company, IIRC. Apparently the new company has worked past those issues.
     
  12. Nov 23, 2015 #72

    cheapracer

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    Case well stated, you get 32 internet points.
     
  13. Nov 23, 2015 #73

    Topaz

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    Woohoo!!!! I'm off to buy a cup of coffee!!! :gig:
     
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  14. Nov 23, 2015 #74

    Turd Ferguson

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    I've been following development of the CX5 but the end result is yet to be proven. I also don't think it will prove practical with a backyard assembled VW conversion. Everything Pops says about Revmaster engines here is absolutely true. Revmaster has a long and documented history of what their engines can do; the backyard VW conversion seems to be assemble an engine, paint some HP numbers on the rocker covers and take the leap of faith that the engine matches expectations. While a CX5 may be "flyable" at gross wt. with the Revmaster engine, flyable doesn't always equal "enjoyable." I have flown some airplanes that were downright scary because of deficient performance.

    I do think the CX5 should be scaled just enough to accept an 0-200. That along with conventional landing gear would make it a winner!
     
  15. Nov 23, 2015 #75

    Pops

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    With the CX5 power loading of 15.52 lbs per HP, using the Revmaster 85 HP engine and using a 56"x48" prop, claiming a ROC of 1000 fpm , using 126 sq ft of wing area, color me skeptical.

    If the engine was 100 hp, with the correct prop, I would start to believe it.


    On the JMR Special, with a C-85 engine with a Power to weight ratio of 11.17 , with a 68" x 48" prop , I am expecting a 1000 fpm , using 112 sq ft of wing area.
    They are expecting a cruise at 75% of 120 mph, I am expecting a cruise at 75% of 115 mph.


    Dan
     
  16. Nov 23, 2015 #76

    Daleandee

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    Great post! We're not far apart on our numbers but IMHO, having owned an Aerovee Sonex and now a Corvair powered Cleanex I'm not convinced on the claim that is seen on this chart:

    HP-Torque_graph.jpg

    During take-off and climb (where excess power is needed most) the RPM is never gonna be into the range to give you this kind of power unless you are under propped. Most likely you'll see 70-72 HP (if the chart is accurate) and during a warm summer day you will be getting out of it at 1000' or so as the CHTs will be heading to the limit pretty quickly. The good news is that once you get the throttle back and lower the nose to gain some speed the head temps drop rather quickly. From my experience I could ask the engine for 60-65 HP continuous and expect it to keep itself cool. I used to have my CHT sensors under the rear plugs. Some builders put them under head bolts or drill them into a spot close to the plugs to get a lower reading. Some guys must put them under the valve cover bolts as their CHTs are far better than what the manufacturer shows. Don't believe everything you read on the internet.

    By contrast the Corvair will climb at 3100 RPM and during break-in the CHTs never exceeded 350 or so. Now it cruises in the 225-250ºF range. Climb isn't much higher. Yes the CHT sensors are under the plugs.

    I'm not saying the VW is a bad engine ... quite the contrary! Pops has shown that they are excellent engines when used in a wise manner. My Sonex flown solo on a not so hot day was an adequate performer (I didn't care for the Aerocarb at all). However I could never fill it with fuel, people, and bags and go anywhere. In reality it wasn't designed for that and as an economical bird to blast around the sky in and take a small passenger for a ride now and again it was a success.

    With the VW so many have looked and thought, "if they can get 80 HP I can do a few tricks and get 90." Trust me ... the tricks have all been done and unless you are going to turn it into something else (think Revmaster) then it's never gonna so the work of an O-200.

    IMHO (worth absolutely nothing) asking a VW to power a two place aircraft is a bit optimistic. It works on the Sonex but it cruises fast enough to help keep it cool. Still the caveats are that the gross is 1100 lbs, the take-off run and climb at gross is not impressive and less so on a hot day, and the engine works very hard requiring frequent head and valve work. Most Aerovee owners I know have had to do head work inside of 200 hours because of leaky valves. Maybe that's par for the course on VWs but I think Pops is getting much better service that that ... because he's not working the engine to death on every flight.

    Dunno if this helps ...

    Dale Williams
    N319WF @ 6J2
    Myunn - "daughter of Cleanex"
    120 HP - 3.0 Corvair
    Tail Wheel - Center Stick
    Signature Finish 2200 Paint Job
    110.3 hours / Status - Flying
    (Myunn is in the "Completions" section of Kitplanes for November 2015)
    https://www.youtube.com/channel/UC49h6Qijc17_Ebfz0CbRFtg/videos
     
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  17. Nov 23, 2015 #77

    Pops

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    Well said.

    Dan
     
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  18. Nov 23, 2015 #78

    Topaz

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    Indeed. And I think this goes to the point that you can't discuss the "worthiness" of the engine without also discussing the airplane in which it's installed. Just like putting twin O-360's in a King Air and watching the result fail, putting a VW into an airplane too large and/or heavy for it isn't an indictment against the engine, either.

    Exactly. The "problem" with the VW is mostly wishful thinking on the part of a lot of people installing them on too-large/too-heavy airplanes. The engine just isn't designed for that kind of load. The fact that most people simply ignore or refuse to recognize the difference between "continuous power" and "takeoff power" simply makes the whole thing worse.

    Part of the problem is that Sonex (and KR-2, etc.) has relatively stubby wings, meaning the airplane needs greater installed power to develop a decent climb rate. For speed at the top end, the wings are a plus, but in climb the airplane needs longer wings if a smaller engine is going to be used. Something more like a Aeronca C-3 or a motorglider would climb like the proverbial homesick angel on 65+hp, but would be slower on the top end.

    As for "valve work", hopefully they're just having to adjust the valves - an idiosyncrasy of the VW that is just as present in automotive usage. It's a matter of popping the valve covers and relatively quick work, but it needs to be done. That's "regular maintenance" on a VW, just like changing the oil. Just part of the package.
     
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  19. Nov 23, 2015 #79

    bmcj

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    JL, since we are making some comparisons to other engines, you might add the D-Motor to those side-by-side comparisons.

    Home - D-motor

    92 hp (89 hp continuous)
    125 lbs
    162 ft-lbs torque (can swing a big prop)
    direct drive
    liquid cooled
    very small (easy to fit in cowl)
    currently around $13-14K in price, if I am correct.

    (Yes, I know I mentioned this in another thread, but it looked like it would fit in good here too.)
     
  20. Nov 23, 2015 #80

    Daleandee

    Daleandee

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    Not quite what I was referring to. I used to check/set the .006 valve lash at every oil change. The concerns that many are having with the Aerovee are valve warping/leaking and thus the need to pull the head and lap them back in if caught early enough. A few that didn't turn the prop over by hand now and again to check the health of the engine (mags and fuel OFF!) sometimes were surprised at annual at some really poor numbers.

    The other concern is that using the big valve heads (I'm not certain that at prop RPMs these are needed) leaves little room between the valves and cracks appear pretty early in the life of the heads. Here's my thoughts on another site:

    SonexBuilders.net View topic - End Play when hand turning prop

    New Aerovee's are using Mofoco heads instead of the CB044 heads. Perhaps they are having better results with the different heads.

    Dale
    N319WF
     

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