VW conversion economics

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cluttonfred

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I pulled some numbers from Scott Casler's Hummel Engines site and thought others would be interested as well. Note that the half VW options are substantially more expensive per horsepower than full VW conversions. The best bang for the buck appears to be the 1915cc 65 hp full VW with the lowest price per horspower of any of them and right in the middle of the pack in terms of weight per horsepower. Maybe the "21st century Volksplane" ought to be a basic two-seat motorglider along the lines of the Scheibe SF-25A Motor Falke but simplified even further?

1663495178726.png

CYLINDERSHORSEPOWERWEIGHT (LB)LB/HPPRICE (US$)$/HP
232852.663700115.63
237852.304200113.51
242842.005100121.43
245841.875200115.56
4501402.80440088.00
4601452.42460076.67
4651452.23462571.15
4761471.93620081.58
4851471.73660077.65
 
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$/hp makes sense. Many costs are there regardless, one cylinder or 4...

That is a sweet looking airplane! And I just love the high wing motorglider.
Wikipedia says that the later versions were "improved" with lowering wing. Any idea what this means, or if it's even real?

I would love a small, low-cost motorglider like this with VW power.
 

Pops

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Extra machining with the 1/2 VW is a large increase in cost. The most bang for the buck is the 1835/1914 cc 4 cylinder engine. Also the engine components are not stressed as much as in the larger cc engines.
 

cluttonfred

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$/hp makes sense. Many costs are there regardless, one cylinder or 4...

That is a sweet looking airplane! And I just love the high wing motorglider.
Wikipedia says that the later versions were "improved" with lowering wing. Any idea what this means, or if it's even real?

I would love a small, low-cost motorglider like this with VW power.

Yup, it’s real, over 1200 built of many different variants but the first 56 had the high wing and monowheel landing gear, with optional outrigger wheels for easier solo operation. That one in the pic I posted had a curvy canopy and conventional gear, the originals had a flat-sided canopy.

1663519728012.png
1663520105776.jpeg
 

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Regdor

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I pulled some numbers from Scott Casler's Hummel Engines site and thought others would be interested as well. Note that the half VW options are substantially more expensive per horsepower than full VW conversions. The best bang for the buck appears to be the 1915cc 65 hp full VW with the lowest price per horspower of any of them and right in the middle of the pack in terms of weight per horsepower. Maybe the "21st century Volksplane" ought to be a basic two-seat motorglider along the lines of the Scheibe SF-25A Motor Falke but simplified even further?

View attachment 129946

CYLINDERSHORSEPOWERWEIGHT (LB)LB/HPPRICE (US$)$/HP
232852.663700115.63
237852.304200113.51
242842.005100121.43
245841.875200115.56
4501402.80440088.00
4601452.42460076.67
4651452.23462571.15
4761471.93620081.58
4851471.73660077.65
The French have produced just what was needed, look at this VW powered aeroplane:
 

Vigilant1

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Some of those older motor gliders (Grob 109, Dimona, etc) with VW engines are beasts (up to 1900 lb MTOW). A VW can lift 'em, but it requires a clean plane with a healthy wingspan.
 

TiPi

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My first few training flights were in the Schleicher ASK-16 (Schleicher ASK 16 - Wikipedia). The flight school used them to reduce the number of aero-tows at the start of the glider training. I still remember the instructor dealing with the 3-position prop and gear up/down, all I had to do was trying to fly the plane.

1,700cc Limbach engine, but they claimed 72hp.
 
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I pulled some numbers from Scott Casler's Hummel Engines site and thought others would be interested as well. Note that the half VW options are substantially more expensive per horsepower than full VW conversions. The best bang for the buck appears to be the 1915cc 65 hp full VW with the lowest price per horspower of any of them and right in the middle of the pack in terms of weight per horsepower.
The 1915 has the thickest cylinder walls, too, so plenty of steel is there for many honings.
 

Vigilant1

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The 1915 has the thickest cylinder walls, too, so plenty of steel is there for many honings.
I vaguely remember that there is a minor downside to going from the 1835 (92mm bore) to the 1915 (94mm bore). Maybe it was the strength of the remaining case after boring for the 94mm thick wall cylinders? Something with the piston skirt clearance? Am I misremembering something? I'm sure it wasn't a dealbreaker, but something to watch for.
 
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Yes that was a concern, and IIRC, there was some debate about putting helicoils in the stud holes, or if it was really an issue. I don't recall ever hearing/reading about anyone experiencing cracks between the studs and cylinder openings, nor pulled studs (unless over-torqued). There was some discussion about filing the skirts to clear the journal cheeks, but I don't know if it ever was needed or if it was just a case of some armchair VW mechanics who read Muir's book, pondering out loud.
 

Pops

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I vaguely remember that there is a minor downside to going from the 1835 (92mm bore) to the 1915 (94mm bore). Maybe it was the strength of the remaining case after boring for the 94mm thick wall cylinders? Something with the piston skirt clearance? Am I misremembering something? I'm sure it wasn't a dealbreaker, but something to watch for.
When boring the case for 94's the area behind #3 cylinder, the flywheel side of the case is paper thin, that was the reason for welding that area up. My case that is cleared for a 82 mm crankshaft and bored for 92 mm cylinders is welded behind #3 and I did all the Bob Hoover modes. Flywheel drive engine.
 
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Vigilant1

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When boring the case for 94's the area behind #3, the flywheel side of the case is paper thin, that was the reason for welding that area up. My case that is cleared for a 82 mm crankshaft and bored for 92 mm cylinders is welded behind #3 and I did all the Bob Hoover modes. Flywheel drive engine.
Pops,
Thanks, I couldn't remember the potential "gocha". Still, if it's a good idea to beef up the case for the 92mm cylinders anyway, it seems worthwhile to go up to the thick 94s and get the 5 additional HP at no additional weight, cost, or trouble.

For stroker engines in airplanes (82mm stroke), I'm under the impression that the 92mm bore (for 2180cc) is more popular than the 94mm bore (for 2276cc). Maybe at that point folks don't see much point in the additional displacement and power if it is already a struggle to keep the CHTs in the green with the 2180cc engine at full output. The advantage of a 2276, if any, is that the CHT-limited 75 HP might come at a lower RPM (more torque), allowing use of a longer and slightly more efficient prop. In practice and at 130mph, the efficiency difference of a 2' longer prop won't be noticeable.

Boy, a "for airplanes" VW head would be great...
 
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Bill-Higdon

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When boring the case for 94's the area behind #3 cylinder, the flywheel side of the case is paper thin, that was the reason for welding that area up. My case that is cleared for a 82 mm crankshaft and bored for 92 mm cylinders is welded behind #3 and I did all the Bob Hoover modes. Flywheel drive engine.
Dan,

On the Flywheel drive do the shims go inside the case between the crank & the bearing or do the go in the stock location?
 

Pops

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Dan,

On the Flywheel drive do the shims go inside the case between the crank & the bearing or do the go in the stock location?
Now that is a good question.
I talked to Scott Casler at Hummel engine about that question. The way I understood it Scott says he builds the flywheel drive engine with the 3 shims in the stock location and let the inside shoulder of the #1 bearing turn against the machined surface on the crankshaft. Also made oil 3 grooves on the inside flange of main bearing shoulder the same as the other side. Said he has never had any problems doing it that way.
Using an open engine case, I put 3 of the thinnest shims between the flange and crankshaft on the opposite side of the #1 bearing and then saw how the other main bearing are off center on the crankshaft journals and the rods are also off to one side on the piston pins more than stock. Definitely not going to work.
What I did-- I turned the inside shoulder of the #1 bearing down .009" and made the 3 oil grooves as Scott, and install one .009 shim on that side between the machined surface of the crank and the inside shoulder of the #1 bearing. That does not move the crankshaft forward on the main bearings and gets one shim at that location for the thrust load.
Added-- also use the stock location of the 3 flywheel shims. On the flywheel drive engine I cut out the center of a stock steel flywheel and bolted the prop extension to it. Just as in Bob Hoovers instructions.
So in short-- Did what Scott did except added one thin .009 shim between the inside flange of the #1 bearing and machine surface of the crankshaft and turned down the shoulder of the bearing flange to make room for it.

Not a very good job of explaining it.

Dan
 
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Bill-Higdon

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Now that is a good question.
I talked to Scott Casler at Hummel engine about that question. The way I understood it Scott says he builds the flywheel drive engine with the 3 shims in the stock location and let the inside shoulder of the #1 bearing turn against the machined surface on the crankshaft. Also made oil 3 grooves on the inside flange of main bearing shoulder the same as the other side. Said he has never had any problems doing it that way.
Using an open engine case, I put 3 of the thinnest shims between the flange and crankshaft on the opposite side of the #1 bearing and then saw how the other main bearing are off center on the crankshaft journals and the rods are also off to one side on the piston pins more than stock. Definitely not going to work.
What I did-- I turned the inside shoulder of the #1 bearing down .009" and made the 3 oil grooves as Scott, and install one .009 shim on that side between the machined surface of the crank and the inside shoulder of the #1 bearing. That does not move the crankshaft forward on the main bearings and gets one shim at that location for the thrust load.
Added-- also use the stock location of the 3 flywheel shims. On the flywheel drive engine I cut out the center of a stock steel flywheel and bolted the prop extension to it. Just as in Bob Hoovers instructions.
So in short-- Did what Scott did except added one thin .009 shim between the inside flange of the #1 bearing and machine surface of the crankshaft and turned down the shoulder of the bearing flange to make room for it.

Not a very good job of explaining it.

Dan
You did a good job of explaing both what Scott said & what you did. The only thing I could find was Bob Hoover saying to machine 3 groves on the iside of the bear that match the other side of the bearing.
 

Vigilant1

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Dan,

On the Flywheel drive do the shims go inside the case between the crank & the bearing or do the go in the stock location?
What I did-- I turned the inside shoulder of the #1 bearing down .009" and made the 3 oil grooves as Scott, and install one .009 shim on that side between the machined surface of the crank and the inside shoulder of the #1 bearing.
We have some really good books and even DVDs on aero VW engines, but discussions like this indicate we still don't have everything tied up in a bundle anyplace. The Hoover mods, tricks to get the pushrod tubes to seal, inspection and maintenance ("how much should my crankshaft move when I pull on the prop hub?), etc.
 
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