Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

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  1. Aug 16, 2019 #81

    TFF

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    A 1835 turning a regular prop would be a much nicer and less high strung. Like they say, no substitute for cubic centimeters. Performance would be about equal.

    Like a Chevy 305 against a 350. A 305 has to be racy to match a lazy 350, and they fit in the same space. Same performance but one is touchy and one your mom could drive.

    If goal is 100% copy, do it 100%. Workable easy to use makes the 1835 a better pick for the regular man.
     
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  2. Aug 16, 2019 #82

    Little Scrapper

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    Excellent. Thanks guys. 1835 is what I'll shoot for.
     
  3. Aug 16, 2019 #83

    karmarepair

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    I haven't updated this in a LONG time, and many of the links are now broken, but this is a compilation of my research. http://users.lmi.net/~ryoung/Sonerai/Engines.html

    My engine, never flown, ended up as a 2180, with a very conservative cam (designed for agricultural wind machine work), ratio rockers, most of the Hoover mods, stock heads, a new case, flywheel drive. I forget where I sourced the end piece for the ChinCom counterweighted forged stroker crank, maybe from Steve Bennet of GPASC. I have a spool type prop extension I bought from the guy who builds them for RVs. Electronic ignition driven from the distributor hole, no starter. Tillotson X carb. Sterba Prop. No pictures, because my engine builder hasn't been heard from in years, and i haven't gone out there to try and recover my parts.

    Early Jodels and Druine Turbulents flew with 1192cc engines. Teenie Two was designed for 1300cc. By the time the Volksplane came along, I think 1500cc was the norm. For a narrow (low frontal area) single place airplane, 1600 cc is plenty.

    I have all the references already mentioned, plus the Falconair Avia book on conversion from VERY early experiments in Canada, which has things like drawings for mechanical tach drives, dual carb intake manifolds (downdraft), dual ignition heads, homebuilt accessory cases, etc.

    Wittman used a flywheel drive with an extension and I think a Cadillac front wheel bearing as an outboard bearing to isolate the prop loads from the crank and case. I think I have plans for his Oldsmobile aluminum V8 conversion around somewhere. The earliest Monnett conversions ("SuperVee") followed in suit with a cast housing, but then went to the "EconoVee" pulley end drive with their "X-Casting" to drive the magneto.

    Veduber's web site has drawings of the bits needed to make a flywheel drive engine, both the crank end piece (cut down flywheel) and the spool extension, as well as motor mounts and mounts for a Harley alternator. No starters.
     
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  4. Aug 16, 2019 #84

    dmar836

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    That front carrier bearing in the cone of the VWitt was I think a Ford part. Can’t remember off hand but I found it new easily and it dropped right in. Have the part number somewhere.
    The one thing I chose not to do on my engine was use ratio rockers. Additional lift isn’t what one is after IMO. An understressed valvetrain is. I bought a cheater cam and that would have been great but was constrained to use big bore cylinders by the existing case which had the cyl spigots already machined. Ended up with a 2110. Frankly the cam was just too small. I started picking parts based on a torque curve I wanted and then dynamic compression, etc. They finally came out with some heads that cool better and have redesigned runners that flow well without the typical huge runner area and huge valves.
    You are really detuning anything larger than the 1600 as aftermarket parts have a “bigger is better” automotive view in mind. Its more difficult to do than one would think. If I had my choice I would have gone with the 1600. To me the Aerovee and other conversions are just automotive engine designs that stop just before the returns start diminishing.
    One must also consider the motor mounts, etc. just weren’t designed for anything but the 1500/1600 named in the formula. An early Cassutt looks quite similar but I would guarantee the plans spec out different tubing sizes. This is often overlooked IMO when modifying things right next to beefing everything up until it’s a turd.
    Dave
     
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  5. Aug 16, 2019 #85

    lakeracer69

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    On the subject of cams, what sort of rpm range are we looking for as a compromise between performance and engine longevity?

    I know this will also directly effect the above, what about the max prop diameter for direct drive( I know to only use a wood prop ), and subsequently the maximum RPM needed at full power and cruise?

    Are those rpm ranges something that will vary much with displacement, or is it somewhat constant between motors of varying displacement? Take a 2180cc for instance, built for longevity with a CR of 8:1 or less.
     
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  6. Aug 16, 2019 #86

    Mcmark

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    I've done a ton of research on camshafts and their tech trying to figure out the best options for an aircraft engine. The reading I've done on projects that have worked indicate the stock camshaft in a VW is about as good as you'll get for this application. How you install it can have a noticeable effect on performance.
    I have some time behind a Lyc 360 with the camshaft advanced 1 tooth (13*) on install and that airplane made more torque than any other I've flown. Mark Langford did some dyno testing on this process using a Corvair with very positive results. It takes time and understanding to make sure there are no conflicts as the valves gets a lot closer to the piston. Look in his blog for the info.
    As to the VW, I recently left the bottom end stock but got a set of heads from Pops guy in WV with just slightly larger valves, left the compression at just over 7:1 added 1.4:1 ratio rockers and a set of Webber 40 knock off carbs. The engine came to life. It would struggle to get to 60mph prior to the changes. After, the car would accelerate strongly thru 80mph and still be pulling. I could run all day at 70mph and get 24mpg. Strongest 1600 I'd ever driven.
    Any performance camshaft will likely degrade performance because most aftermarket cams are designed to operate above where we operate in rpm range.
     
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  7. Aug 16, 2019 #87

    dmar836

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    Im certainly not the pro but it’s a good idea to look at the plane one is building or buying and determine the ground to prop clearance available. You generally want to use the longest prop possible but this measurement will tell how big you can go. It’s not big math but Culver has a calculator you can use to determine tip speed per prop length,rpm, and resultant airspeed. With that you will now know what rpm you will be cruising at. A cam with peak torque in that range without being too peaky is a good place to start.
    JMO
    Dave
     
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  8. Aug 16, 2019 #88

    Mcmark

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    A VW will likely not ever have a prop clearance issue. 62" is about as long as you can get and have it work. Mid to high 50's is where most end up. Prince VW props are 52" in length.
     
  9. Aug 16, 2019 #89

    TFF

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    Displacement, compression, RPM, intake manifold and carb or fuel injection, types of exhaust, prop, drag, weight of airplane are going to play a role in picking the cam. A full racy cam for a 1200 is going to be a yawn in a 2180. The big problem is cams on the market are for cars and generally too racy for an airplane engine. Stock cams tend to be the ones. They could be better suited but no one would want one for a car. 3000 RPM seems to be the sweet spot for power so a 7000 rpm cam is worthless. More power only if you can spin 7000, which you can’t with a prop. Degreeing the cam and being able to bias the shaft is always worth a try. One way tends to be torqueier and the other edges RPM. Middle is middle. All the parts being used are repurposed. They are not being used as intended, so all the adjustments and choices are the builders. And like belly buttons there are than many choices. Some are just better.

    You have to decide if you are going to cap the RPM with the prop where it can’t spin faster than your picked RPM or be willing to spin it faster and manage the engine. As much as you want it to be perfect out if the box, it’s an experiment. And tweaking it will be different for every plane.
     
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  10. Aug 16, 2019 #90

    dmar836

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    I guess I don’t understand. Two issues I’ve encountered are ground clearance when the tail is raised and tip speed vs the sound barrier and inefficiency.
    As already mentioned there are many variables.
    Dave
     
  11. Aug 16, 2019 #91

    Pops

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    Hard to beat a stock cam. The VW engine has a sweet spot at 3000 RPM . That is where it all comes together at that rpm as designed for highway cruising speed.
    The prop has to match the airframe drag and speed as well as the HP. We all know that a longer prop is more efficient but you also have tip speed to think about.

    Listen to the prop in this video. Its a Culver 60" X 26" turning at 3200 rpm and is starting to get a little noisy.
    Wouldn't want to go to a flatter pitch or increase the diameter of the prop. This is the best prop for the HP, airframe and cruise speed. Cruise at 80 mph at 2650/2700 rpm at 3 gph. At that power its developing about 32/33 HP and running cool and happy. WOT is about 95 mph but way overspeed for the trim of the airplane. The airframe likes between 75 to 85 mph cruise and so does the engine. IF I run below 2500 rpm cruise all the temps go to far down.

     
    Last edited: Aug 16, 2019
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  12. Aug 16, 2019 #92

    Pops

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    If you build then right, it will make the boys with the factory street cars shake their heads. Have out run Porsches from stop light to stop light.
    Don't tell anyone, but also a blue light auto on long straight roads and mountain roads with no straights. Chassis set up for high speed but still handled like a go-cart in the curves. I was young then. My mother had a name for it :)
     
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  13. Aug 16, 2019 #93

    dmar836

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    “Tractor motor” is something the car guys just can’t get their heads around.
     
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  14. Aug 16, 2019 #94

    Mcmark

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    I would bet you will have almost a foot clearance on most airplanes using a VW engine. The Formula V airplanes might be closer but probably more than 6" in most of those.

    I kept this from the Samba forum;
    !st off I meant the change from 108 to 100 is a lobe center change. Engle is not correct when they told you that going from 108 to 106 lobe centers whould move hp from 6500 to 6000 rpm. They told me the same thing and my dyno proved it took an 8 degree change to move it that much. I'll bet none of you have ever seen a motor of 2300 or bigger pull a full load at 1000 rpm on a dyno with a cam like fk-43, well you can do it if the lobe center is 100. They are all done by 6000 but the torque curve is almost flat.
     
  15. Aug 16, 2019 #95

    dmar836

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    A flat torque curve is certainly desirable for a car and especially an aircraft engine but, again, it's all different when you have gears and these guys are still thinking this way. You can pull hard at low rpms with some combos but they still have a lot more in them after that. There is a constant poor of fuel in those dyno runs that is pulling it through the rpm range we will stay at all day. If they let off enough to sustain a modest rpm they wouldn't see those numbers. It would be interesting to see one of these street torque motors in a plane but why dabble in that end of the pool? The required rpm range and torque curve sacrifice won't help us. Cams can have overlap that makes them anemic or that requires them to spin and require much more CR than we want. Personally I will have intake runners from a Posa style carb that are quite long by necessity, as do many, and that alone throws a lot of the car advice off the table(for me). I've had to consciously detune this build and push for efficient flow over max flow. I just don't want any more performance. I'm not to the point of saying use only single port heads to get this but that's likely better advice than most of the car guys would give. I have to think about it like this - it isn't hard at all anymore to build a 160hp stroked VW with off the shelf performance parts(and cheaply to boot). Yet nobody is building 160hp or even 125 hp aircraft VWs.
    Before this becomes a p*ssing contest I think we are all trying to say the same thing. I just wish I had a 1600 to massage rather than a 2110.
    Dave
     
  16. Aug 16, 2019 #96

    Mcmark

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    Take a look at the data on Mark Langford’s KR 2 site. It has the Dyno sheets showing a flat, but maxed out torque value that starts to decay about 27-2800 rpm but still producing hp above that rpm with an off the shelf camshaft install 10* advanced.
    I think that 2110 would be a monster with the right cam combo in it as an aircraft motor.
     
  17. Aug 16, 2019 #97

    Vigilant1

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    There were some back-of-the-envelope rough estimates in this post about where a single-port head might work best and where the 2 port head would be needed. I know Pops has experience with the smaller engines and has found the single ports to work well, and this advantage might extend higher than what I calculated in the post above (I estimated a single-port would work fine in a 1915cc engine up to 3445 RPM, but might be insufficient for a 2180cc engine starting at about 3000 RPM).
     
    Last edited: Aug 16, 2019
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  18. Aug 16, 2019 #98

    Pops

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    I have be preaching for a long time about using single port heads for under a 2180 cc engine and 1 1/4" dia intakes tubes instead of the 1 1/2" tubes for a higher velocity intake charge for more low rpm torque for a straight drive engine. Yes, efficient flow over max flow for prop RPM's. Side benefit of no head cracks between the spark plug threads and valve seats.
    "But the hotroders do this " is in peoples thinking.
    Also the hot oil box was a big improvement in power and smoothness plus lowered the oil temp 20 degrees.
    My 1835 cc engine is a torque engine and when at the end of the runway and start adding power, you feel it.
     
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  19. Aug 16, 2019 #99

    Pops

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    I agree on the engine size and rpm 100%.
     
  20. Aug 17, 2019 #100

    dmar836

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    Since I am building a Super Vee racer I picked the speed I wanted, the planned cruise rpm, and the prop pitch. Knowing the engine size I was forced to use(well, what I had to start with) I sort of backed into an engine recipe. I wanted to allow some extra rpm for “war power” and a broad enough torque curve to hopefully cover whatever I miss.
    I also like the idea of smaller intake runners.
    Dave
     

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