Metal vs Wood or T2 vs VP (Part II)

On Mar 29, 2:44*am, Bob Hoover wrote:
On Mar 28, 9:20*pm, Copperhead wrote:

... I looked at the VP
and used the plans as a means of determining if I could build the ribs
and bulkheads with store front or scrap lumber. I could and did, but
my height and weight pretty much ruled out the VP for me.

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Dear Joe,

Agreed, sadly. *The design is such a tumbleweed it limits its market.
Unfortunately, in most cases it doesn't do that until time for that
all-important first flight rolls around. *Based on the Volksplane
Group, the exact same features that limit the plane's practicality for
one group of pilots turns out to be one of the most critical factors
for another, in that smaller/lighter pilots often acquire their bird
as a bargain, already built. (But I gotta tell you pard, There is some
BIG people flying Volksplanes. [See their Photos archive. *They've got
some wizard videos].)

Since the short-coming (ie, excessive drag) is largely a function of
its design I suspect there are a few examples of cleaned-up copies.
On the other hand, I weighed about 190 when I had my first flight in a
VP1 and found it an enjoyable experience. *I was especially impressed
by the coordination of the tail. *But the take-off was best described
as leisurely. (I was six feet tall back then. *Now, I'm exactly one
vertebrae shorter :-)

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Your information about the rear shaft VW engine was much appreciated
as I've purchased the Great Planes Type 1 Engine Assy Manual and found
it to be every bit as good as you'd told me it was. W/O a doubt any VW
engine I build will be a rear drive, if for nothing else due to the
weight savings and lesser amount of money involved.

I'd intended to send you an e-mail asking about the "mission"
differences of the front vs rear drive VW engines but was unable to do
so.

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Yeah, Steve's manual is pretty good. *I think he's also got a video
now. *As for tracking me down...

*Try:

I've a hunch Steve spends a good part of his life on the
telephone :-) *(Steve produces a really beautiful flywheel-mount.
There are some pictures of it in my blog.)

As for the 'mission' business it might help if you couch the question
differently. *For example, name all the automobile engine conversions
in which the propeller was attached to the pulley-hub of the
crankshaft?

Then ask yourself 'why?' *Because the truth is, putting the prop as
close to the thrust-bearing as possible makes the best kind of sense.
In effect, the typical VW with its prop on the pulley-hub is an
EXCEPTION to the standard practice of auto engine conversions.

As for any reference to the clutch-end of the crankshaft as being the
REAR, it is actually located on the FRONT of the VW engine. *At least
it is to those with any experience with Volkswagen vehicles. ( ALL
references for Volkswagen are relative to the driver or the front
bumper.)

I've explained how the first flying VW's used the pulley hub and how
those advantages were lost by the time the engine's displacement
surpassed 1200cc. *The sad part of the tale is that everyone continued
to try and emulate the success of the 1000cc engine with its 'built-
in' engine mount.

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Regardless the 1835 cc and 1915cc R/D VW engines are remarkably
affordable looking to me, with the difference between them and the
2180cc cost wise being considerable. HP does indeed cost money as
you've written quite often.

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The reason for the big difference is that you don't need the special
crankshaft nor the 'Force 1' prop-hub. *But depending on which
airframe you're interested in, there may be even LESS COSTLY
alternatives.

In the above you've mentioned 'horsepower.' *I understand what you
meant but it would be far more accurate to refer to TORQUE and more
specifically to THRUST. *In fact, when it comes to homebuilts, we'd
probably all be better off if we referred to our engines in UNITS OF
FLYABILITY or UF's. *It certainly wouldn't be any crazier than the
situation we have now, where some fellow tells you his engine produces
80 horsepower then in the next breath sez it burns only three gallons
per hour. *The tricky bit here is that both statements may be
correct.. but it would be impossible for them to be correct AT THE
SAME TIME.

Three gallons of fuel is about 18 pounds *One of the most critical
specifications for an engine is its Specific Fuel Consumption, which
is how many POUNDS of fuel it burns PER HOUR to produce ONE
horsepower. *Normally aspirated air-cooled engines are clustered near
the .500 mark, meaning they burn about half a pound of fuel per hour
for each horsepower. *Economy of scale applies so you'll find a big
radial down near the bottom of the curve and your lawn-mower up near
the top, but your flying Volkswagen will be found clustered with the
small (ie less than 500cid) Lycomings and Continentals.

The best SFC EVER for a spark-ignited, gasoline-fueled aircraft engine
was for those humongous *turbo-compound radials like the ones used in
the B-36. *Their SFC was under four-tenths of a pound of fuel per
hour. *(!!)

Then comes this expert with his converted VW that has an SFC of .225!
By every engineering measure in the world the man should be given the
Nobel prize... right after they give him the Harmon Trophy. *I mean,
an SFC of .225! *The guy has got to be the best engineering GENIUS of
all time!

(What's that? *You're saying he FIBBED a little? *Well... okay. *But
did he cross his fingers at the same time? Because if he DIDN'T it
means we get to call him 'Liar Liar pants on fi..' What? *Ah! *He DID
cross his fingers. *Ah! *You're saying he DID cross his fingers. *I
see. *Thanks for clearing that up for us.)

Well shucks. *I was really looking forward to the Awards Ceremony.

So maybe we should lay horsepower aside for the moment and stick with
just the engine and the prop. *Including the prop is the honest way to
do it because you need to figure-in your prop's efficiency. *If you're
lucky your prop's efficiency will be between 60% and 70%. *That's
because we're using a fixed-pitch prop, which has to be a compromise
between take-off and cruise. *If you carve your prop for its optimum
climb (or take-off) performance you're going to have to give away a
lot of fuel during cruise. *But if you carve a prop for maximum cruise
performance you're liable to need a mile of concrete to get that puppy
into the air.

Of course, what you'll do is try to find a good compromise between the
two.

But having said all that, you're probably still wondering about this
less expensive option I mentioned, which is to leave your heads and
the crankcase alone -- don't machine them for bigger jugs. *Then
install a crankshaft having a longer throw... and a set of longer
connecting rods.

Odds are, you'll stick with a stroke of about 78mm the longest set of
rods you can afford. *The savings comes in because you don't have to
do any machining on the crankcase or heads; you use the stock items.
You WILL have to clearance the case because the longer throw is now
going to hit the webs inside the crankcase -- exactly as they would if
you opted for a 2180 -- but clearancing is a minor chore and something
you can do for yourself. *So you end up buying a new crank, new rods
and a set of SPACERS that allows all this stuff to bolt together.

What you GET is an engine that develops its torque 'way down near the
bottom of the rpm curve. *That means you can carve a more efficient
PROP because it will be spinning a lot SLOWER. *Slow means low rpm's
and low rpm's means low wear.

Bottom line is that you get an engine that provides all the TORQUE you
can use. *How big is it? Umm lesssee... 78mm crank and stock jugs is
1791cc. You can call it 1800 if you wish.

How many 'horsepower?' *Well.... spin *it up to about 5000 rpm on the
dyno, you'll probably see about 100hp. *For mebbe a minute :-)

-Bob

"Bottom line is that you get an engine that provides all the TORQUE
you
can use. How big is it? Umm lesssee... 78mm crank and stock jugs is
1791cc. You can call it 1800 if you wish." BH

Now that's just the information I was wanting Bob as I'm looking at
the M-19 Flying Squirrel or the Rag a Bond. It would sure be nice if
the BK 1.3 plans were out, but the Beta testing he's having done is a
positive indication of his intent to do right by others.

Oddly enough I've had more fun researching and experimenting with
plans and parts building then I'd ever have thought possible and have
spent very little money so far. Mostly this has been due to the fact I
already have most of my woodworking power tools as well as a lot of
metal cutting and bending tools.

Regards

Joe S.