Steps to scratch build a VW

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

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  1. Aug 21, 2019 #241

    Vigilant1

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    Important to stay apples to apples. The 1835 will make 60 reliable continuous HP at 3400 to 3600 rpm. The 1600 will make 50 HP. Now, burning the fuel to make the 10 additional HP in the 1835 will require more heat to be shed.
    - If you have good baffling, both engines can do fine at these HP levels.
    -. If you restrict your throttle hand to 50 HP, both engines require the same baffling (and the 1835 will make it at lower RPM)
    - if you want 60 HP from the 1835, then the baffling will need to be good. Not "great":. There are fast little planes that can use 2180cc engines to make 75 HP, they have the same fin area as the 1835, and the don't exceed 375f CHT in cruise. So, keeping an 1835 within limits is not a big challenge.
    The 10 extra HP in a plane like a V-Witt, iMO, would provide not just more performance but more safety.
     
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  2. Aug 21, 2019 #242

    Little Scrapper

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    Thanks. Appreciate the explanation.
     
  3. Aug 21, 2019 #243

    Pops

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    I think the 1835 cc engine is as large you can go for a HP increase and still get the reliability of the 1600 cc engine ( and the most HP for the money) with just having the case bored for the 92 mm cylinders and pistons. You get a good honest 60 hp at 3400 rpm with a prop. Noticeable increase in power from a 1600 cc engine with the same reliability.

    I would build the 1835 cc engine and used the Force One prop hub ( requires machining of the front of the case) . New late model dual oil regulated case , stock,VW balance rods of equal length, Good quality 92 cylinders and balance pistons ( case will need bored). 7.5 CR on EACH cylinder. Good German forged stock STD 69 mm crank checked at a good VW machine shop even if new. Stock new German cam with double thrust bearing. Bob Hoovers HVX mods to the oil system. New Single port heads with SS valves, custom made 1 1/4" dia intake tubes with a Zenith carb with the custom made hot oil box and full flow oil system to the oil cooler and filter on the firewall with 2 -- 2" dia scat tubing air to the VW doghouse type oil cooler. Zenith wood prop. Single new 4316 Slick mag mounted with GP's simple flywheel engine mag mount. Slick shielded wiring harness with 14mm ( Franklin engine aircraft spark plugs) for top plugs. Non electric, but a electronic ignition distributor in the stock location and the single port heads drilled for bottom spark plugs (10MM) in the heads for dual ignition when wanted ( take-off, etc) powered from a small 7-9 amp, 5 lbs sealed battery that also powers the handheld radio and GPS on a 7 or 8" tablet .

    Then get busy building the electronics for monitoring the mag and turning the electronic ignition on after .5 sec of the mag failure.
     
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  4. Aug 21, 2019 #244

    Pops

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    Like, Like and Like.
     
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  5. Aug 22, 2019 #245

    Little Scrapper

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    I'm sold. Thanks again.

    This thread is gonna result in a running engine eventually. I just need to do a little more studying. I do appreciate everyone's patience.

    I would really like to scratch build this as the thread implies instead of buying everything done and assembled. I'm off to do more reading.
     
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  6. Aug 22, 2019 #246

    blane.c

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    One of the things to my understanding about the 1835 is it is about as big as you can build and work well with the single port heads which are to my understanding the most reliable (least crack prone) heads.
     
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  7. Aug 22, 2019 #247

    Little Scrapper

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    And if I'm clear the largest size for a shrink fit hub.
     
  8. Aug 22, 2019 #248

    Vigilant1

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    Most recommend a Force One for any stroke above 69mm. So, a 1915cc would still be okay (but the 1915 has other issues).
    I'd choose to use a Force One for an 1835.
     
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  9. Aug 22, 2019 #249

    Little Scrapper

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    I'd like to avoid sending a case to GPAS if I don't need to. MOFOCO is close to me. It also ropes me in to the GPAS ecosystem of parts etc. If it's not necessary I'd just assume avoid that whole thing. I'm not against it by any means, just seems unnecessary.

    But I'm still learning so I don't know what I'll do yet
     
  10. Aug 22, 2019 #250

    Vigilant1

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    Just for info, not to push anything:. IIRC, GPAS provides the instructions for machining the case for the Force One, so it could be done by a local shop (mine was). And there wouldn't be an ongoing need for parts from them (aside from maybe a rubber seal well down the road). I don't know what your plans are for the engine/prop extension/cowl, but the Force One does put he prop hub 2-3 inches farther away from the case, which might be handy if you are trying to avoid a long extension.
     
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  11. Aug 22, 2019 #251

    lakeracer69

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    Scrapper, Check out the Mofoco heads if you haven't already. they also have dual plug options. https://www.mofoco.com/item/Mofoco_...ead_12mm_spark_plug_holes_92mm_bore_/3520/c52

    Above, if you decide to go with the 1835 and 92mm jugs.

    Also check out member 103 on the HBA site. he has a Cygnet with a VW and had some good real world experience with Fomoco heads, spark plug info, and using a Mag and an electronic ignition on his engine.

    I looked at the Fomoco heads quite a while back and liked them. It was nice to see 103 had used them and they are working well for him.
     
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  12. Aug 22, 2019 #252

    dmar836

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    Please take this in the spirit it is intended. Not gonna poopoo the suggestions above as they are great and I'm a little hypocritical with what I had started with mine. Just reflecting, I had a J-3 Kitten ultralight with a 340 Kawasaki. Great fun! Others had 430s and even bigger. We all went pretty much the same speed as that's just the 103 design(intentionally draggy and lightly built). The engines didn't make as much difference as one would think. A buddy just put a 1/2 VW on his Kitfox light and that does make a difference. He says he looks down and sees almost 80mph and climbing! What do we think would give if flown that way for long or even when subjected to the torque of throwing such a fun little plane around with the new gyroscopic forces? Could you resist? I couldn't! I've read all these threads about fairings and streamline tubing covers to make a 103 faster. Also about adding batteries and lots of unintentional weight. That's not the limiting factor to part 103 - they just are not designed for more weight and more speed. I have mentioned the guy at OSH at the SV forum asking, "Why not have an O-200 class?" Not designed for it! Clearly. There is a difference in a Cassutt and a V-Witt/Sonerai - not just engine size. They look to be the same size and similar and they are but there are half the fasteners on V-Witt aileron hinges, thinner materials, and no house beam-style spar carry through. I'm not criticizing, honestly, but we can see the slippery slope growing. Pop's is primarily his own design and these other designs might handle the increases well but I would be the guy who overstresses the plane when it's safety margin is already used up with extra weight and engine torque. God forbid but the compromise and/or downside might have nothing to do with the engine reliability at all! I don't oppose more power but my hesitation for my V-Witt is that Steve didn't design it for a C-65, a Corvair, a Buick V6, a 912, or a 2L VW. I have to ask, would it be built exactly the same if he did? Who could say yes? I'm sure it is quite capable with a 1600 and I fear for my motor mount just with what I have done. Adding weight here and there, which appears inevitable today, exacerbates the problem.
    One must stop and ask, just because there are more powerful options out there does it need more power?
    Please continue as I don't mean to stop the conversation. This has talked me into detuning mine even more or maybe even turning some spacers to fit smaller cylinders and go 1600 myself!
    No judgement to those contributing here as it's awesome but I just had to vent even though it applies even more to other threads and other people I know.
    Dave
     
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  13. Aug 22, 2019 #253

    Pops

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    The good thing about just going to the 1835 cc engine over the 1600 cc engine is NO weight increase for 10 more HP. The long block of each weighs 116 lbs. Everything you add for the running of each engine has the same weigh because you are using all the same parts. I also used the GP's carb #1617 that is for 1600-1700 cc engines on the 1835cc engine with great results, ( I happen to have it ). GP's list the #1819 carb for the 1835-1915cc engines.
    On the SSSC the firewall forward weight is 141 lbs. That is engine mount and a running and flying engine with prop. Going to be hard to get a flying 4 cylinder 1600cc VW under that weight. My intakes were .049 thick instead of .032 that I would liked to used but I made them from SS bathroom handrails from the aviation section of Lowes box store.
     
    Last edited: Aug 22, 2019
  14. Aug 22, 2019 #254

    Little Scrapper

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    I believe I'm friends with him on Facebook. He lives pretty close to me. I'll reach out to him. Thanks
     
  15. Aug 22, 2019 #255

    Little Scrapper

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    You bring great content to the table here, keep it up.
     
  16. Aug 22, 2019 #256

    Little Scrapper

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  17. Aug 22, 2019 #257

    Vigilant1

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    Dave, you're smarter than I am on this (and much more personally involved), but for what it is worth:
    Regarding power/torque: Does anyone know how Steve Wittman's 1600cc racing engine was set up, and how he ran it (RPM)? It's quite possible that his 1600cc engine, set up for racing, put out more than the 60 HP of a mild, suitable-for-daily-use 1835cc VW engine.
    Regarding stress on the motor mounts: If Steve Wittman pylon raced that plane (4000+ RPM?) with an approx 12" prop extension and a metal prop, I would think the mounts would be likely be fine for a same-weight 1835cc engine turning a wood prop with a shorter extension at 3600 RPM. But, I am not an engineer.

    Wittman's flywheel drive 1600 would be the same weight as a flywheel drive 1835, but a little lighter than a pulley-side 1600 or 1835. But that prop extension setup would likely weigh more than the difference between a flywheel drive and pulley-drive engine.
     
    Last edited: Aug 22, 2019
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  18. Aug 22, 2019 #258

    TFF

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    Bonzo, the second small one, sure is close. Can’t tell if it has two wing panels or not. Chief Oshkosh/ Buster(1) looks close too. Not that I would slap a Continental on one, but I bet there is not much difference between Bonzo and the V-Witt in many ways.
     
  19. Aug 22, 2019 #259

    dmar836

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    Not sure how Steve’s engine was set up. There are tricks the FV guys still won’t reveal. It obviously wasn’t hopped up to the point of destruction.
    I’ve never seen plans drawn for Bonzo so I’m of the conservative type that would assume the similarities might be cosmetic. Not that it’s a bridge-like structure vs. the V-Witt but I wouldn’t want to be quoted saying they are identical in structure, which is tempting based on pics, and that the engine is the biggest difference. Many of SJ’s ideas were reused to great effect in later designs but I think the V-Witt was a new deal. It took a while to design and build the V-Witt and quite a bit longer for Steve to feel comfortable releasing the plans. That would be strange with all the experience he had with Chief Osh/Bonzo if all it took was just measuring and drawing up his own plane (of over 30yrs of development) and downsizing the engine for a new class.
    Y’all might be right about his engine layout vs. a pulley drive. We still aren’t sure - I’m not convinced anyway - that shifting a pulley drive VW forward enough to fit the V-Witt profile and CG would be sound. Who wants to draw up that extended motor mount? If I may channel my inner Steve, “...that might be a waste of a lot of airframe space and necessitated ballast.”
    I like the idea of getting rid of that troublesome extension as much as anyone but not sure how, in reality, one could do it. Shifting 140lbs forward 12” all ahead of the CG won’t be offset with the weight saving of 20lbs of extension. That design was not an afterthought. Steve was quoted as saying that he moved the gear forward to prevent a “nose over” in lieu of easing ground handling as he was okay with the latter. The tiny size of the rudder reiterates that he was Steve Wittman!
    Dave
     
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  20. Aug 22, 2019 #260

    TFF

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    https://www.eaa.org/eaa-museum/muse...-folder/1948-wittman-dfa-little-bonzo---n1292 there is not much room in there. Fuselage is longer for sure.

    I imagine minor things to him would actually be the root socket spar connection. Not without thought, but with consistencies as they are, I think the older planes were done with bolt through straps. I think he sold a couple of tailwind plans with that plane like that. Being really a hinge point the root joint you don’t want it to move, pretty much any hinge point is ok. Solved the trailer and assembly issue. Clearly it’s not the same airplane. I would imagine his VW made 80 hp in race trim; at least all the no no’s about high rpm engines don’t apply in this case. I would imagine the early Goodyear engines made 100-120 hp for a C85 in race trim. Not a lot has to be paired down; you can only make a useable small race plane so small anyway. A little less weight, a little less g load, a little less speed. Tweaked application. Not bad for really a design thought that starts about 1934.
     
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