| With the donation of a Volkswagen
engine our existing Rotax mount became a concern. It was canted 3°
to starboard to compensate for the rotation of a 912. The VW rotates
in the opposite direction. Even if it could be made to fit, the
thrust would be 6° off.
We decided to weld up a new mount. Here
Mr. Smith has created a jig with the engine's bolt pattern so that we can weld
without igniting the engine.
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Mr. Smith created a disk of MDF (medium density fiberboard)
that replicated the bolt pattern on the rear of the VW engine case.
This way we could fabricate the mount without having to keep the heavy
engine in place. |
The concern, of course, is that the
mount will only be as accurate as the bolt pattern template. If it
doesn't fit, what is lost? The material cost is low. The wood
was available in the shop and cost less than $5. The tubing is about
$1.50 per foot. A mount like this will consume 10 or 12 feet.
There are small pieces of plate that the tubing connects two.
Most of the cost would be in time. It took
several hours to create and place the disk in the correct location.
It took the better part of a Saturday to cut, fit, and weld all of the
tubing. |
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Mr. Smith created a template that recreated the angled cuts on
the tubing. He took a 3/4" dowel and put two moveable sleeves
in it, one at each end. He then cut, angled, and lengthened or
shortened the paper sleeves until the template fit both the airframe and
the disk representing the engine bolt pattern. It was then a
'simple' matter of cutting a piece of tubing to duplicate the
template. |
| Most of the fitting was
straightforward. Only one tube was fit to another tube which
required a 'fishmouth' or compound cut to fit without gaps. |
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The welding was done with a TIG
(Tungsten Inert Gas) torch. Sometimes called GTAW (Gas Tungsten Arc
Welding) or Heliarc™ welding, it is done using an electric torch which
has a tungsten electrode. The electrode is constantly bathed in a
wash of argon, an inert gas. The gas protects makes the arc uniform
and keeps the weld material from forming oxides and
contaminates. |
| The long, thin stick in Mr. Steed's
hand is a piece of filler metal. When two pieces of metal are
welded, a third is added to complete the joint.
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The arc from the torch is extremely
bright and produces strong ultraviolet rays. If skin is unprotected,
it will develop 'sunburns' ranging from embarrassing, to irritating, to
painful, to dangerous. Most welders don't make this mistake more
than once. |
| Here the mount has its initial fitting. It is
attached to four points at the rear of the engine. This is a pattern
that has been used successfully in many VW conversions for years, but we
worry about the ability of the flange to bear the weight and thrust of the
engine indefinitely. We are looking at adding a front support which
would 'cradle' the engine and provide more support. The trade-off,
as always, is added weight. In this case the weight is far forward
where it affects the flying balance of the aircraft disproportionately.
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