Hi all,
Just for the record. In the early pre history build of the classic
Europa the instructions said that the correct setup for the engine
would be achieved if the 'washers' were adjusted such that the spinner
lined up with the cowling. That supposedly gave us the 1.5 degree right
offset. Nothing further was said on this issue. My only comment is that
it was a bit crude but seemed to work.
A word of advice for Bob is that if you change your current setup for
the engine mount then your spinner will not line up with your cowling.
It is possible to address this misalignment but not simple.
Pete J
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Robert
Borger
Sent: 15 January 2017 23:07
Subject: Re: Europa-List: 1.5 degrees right?
Nigel,
Thanks for the detailed description. I have often wondered about the
effectiveness of the offset. It just didn=99t seem right to me.
At some point in the future I=99ll have to unbolt the engine for
something. When I do, I=99ll remove the offset and see what
difference it makes.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (75 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger@mac.com
On Jan 15, 2017, at 4:08 PM, nigel_graham@m-tecque.co.uk wrote:
Jonathan,
I think you have provided the answer to your own question.
The fact that you have run your Classic with no engine offset and
noticed no asymmetric flying characteristics speaks volumes.
The whole idea of canting an engine sideways and forcing the propeller
disc through the air at anything other than normal to the oncoming
airstream is daft.
The theory that canting the engine sideways will counter the yaw effect
of the prop wash seems to be based on a misunderstanding of what is
really happening and it=99s done because =9Cthat=99s
how it=99s always been done=9D!
On your Classic, you sensibly mounted your engine head on to the wind
and you set you propeller blades pitch to the recommended angle. Each
time the blades rotate their angles of attack remain equal to each other
and constant to the oncoming wind and each blade generates the same
thrust throughout each revolution of the prop.
Now consider what happens when you follow the XS build instructions and
cant the engine 1.5 degrees to the right.
If you=99re flying straight-and-level behind a right-hand tractor
(Rotax 912, 914), each time a blade passes over the top of the ark, its
pitch is effectively reduced by 1.5 degrees and as it swings through the
bottom of the ark, its effective pitch is increased by 1.5 degrees.
This means that your propeller is producing significantly more thrust
---From the bottom half of the propeller disc than the top half =93
and that produces a pitch up change in attitude =93 and not the
sideways thrust you had hoped to achieve by mounting the engine
sideways.
=9CSo if that=99s true, why has nobody noticed this pitch up
attitude?=9D =93 a good question (even though I asked it
myself).
All Europa=99s are fitted with a pitch trimmer =93 so these
effects are unconsciously trimmed out by the pilot during different
phases of flight.
=9CAh, but what about the propensity to swing to the left on
take-off?=9D - Same thing, different plane.
The Monowheel sits on the ground at a deck angle of (is it about 12
degrees? I forget) so the engine is now canted up at the front by this
amount. At the beginning of the take-off run, the upcoming blade on the
left hand side has 12 degrees wound off its effective pitch, while the
down going blade on the right has 12 degrees added to its pitch. This
produces significantly more thrust on the right hand side of the disc
than the left, resulting in a turning moment to the left. It's a
potential problem with all tail-draggers
The Tri-Gear variant of course sits horizontally on the ground, so has
none of this asymmetric thrust =93 so is less prone to dive off to
the left on take off; another reason why the Tri-Gear is perceived to be
more benign than the Mono.
Canting an engine is a very crude way of addressing a relatively
transient problem =93 Fitting a rudder trimmer would be a far more
elegant solution =93 should it be necessary.
Hope that wasn=99t too long winded!
Nigel
PS the roll issue has nothing to do with engine position.
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01/15/17
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