Nigel, following on from this, I am most reluctant to believe that Ivan
Shaw and Don Dykins (one of the outstanding aerodynamicists of our
time!) got it wrong, or for that matter generations of designers of
Spitfire/Hurricane era aircraft - which I believe al had engine offset
and fin offset incorporated, but even so were close to unmanageable if
full power was used on take off. Performance then was very much a matter
of life and death and an immense amount of research went into optimising
performance - I certainly don't buy the notion that folk have always
done it because someone did it back in the dark ages and no-one has
thought rationally about it since!
Offsetting the engine 1.5 degrees makes negligible difference to
forward thrust - actually reduces it by just 0.03%, but using permanent
right rudder induces extra drag which must be an appreciably greater
amount.
Regards, David Joyce, GXSDJ
On 2017-01-16 09:58, JonSmith wrote:
>
> Hi Graham, I found your posting most interesting and thought provoking. You go
beyond my old "pilot book"! We are all familiar to a certain extent with the
old classic theories of propeller effects; torque, asymmetric blade, gyroscopic
etc but I'd never considered detrimental effects caused by an engine offset.
>
> I remember quite well the famous diagram of the propeller slipstream helix
> spiralling
around the fuselage and whacking the fin on one side or the other depending
on direction of engine rotation - in our Rotax-Europa case the left side
of the fin causing the nose to yaw more and more to the left with increasing
power. Certainly in my aircraft on the rare perfectly calm and smooth day with
no other influencing factors I notice on take off that at the point of lift
off a considerable amount of right rudder input is required at that point,
nearly
half I'd say.
>
> I suppose that aircraft design is always a compromise and there are various
> solutions
to counter this problem, engine offsets, rudder trims (fixed and inflight
adjustable), offset fins etc, all designed to help make life easier for the
poor pilot who has to cope with the cacophony of forces his machine is
constantly
bombarded with! Our Europa is as basic as you can get in it's standard
form with the options of an offset engine mounting and/ or fixed rudder trim tab
or nothing!
>
> I note and accept what you say about an engine offset causing inefficiencies
and undesirable handling tendencies and that from a perfect performance point
of view it would be absolutely the best for the engine to be mounted square on
to the airflow but wouldn't the overall effect of the thrust vector being offset
completely outweigh these minor undesirable tendencies and make life easier
for the pilot? My instinct tells me that the unwanted effects would be
relatively
insignificant but I genuinely don't know....!
>
> I've always considered that aircraft compromised by simplicity would in the
> ideal
world be set up to fly perfectly straight and balanced with hands and feet
off in the cruise as that's what we spend most of the time doing. Thus in a
perfect aircraft with the engine correctly offset this should be achieved
without
any extra trim tabs, assuming the designer got his sums correct with the offset!
(I'm lucky I think because my aircraft seems to achieve this quite nicely!).
I also note that you believe a rudder trim tab to be a better solution than
an engine offset. Do you consider that having the rudder permanently offset
into the airflow to keep the aircraft balanced to be more efficient than the
minor unwanted propeller blade effects caused by having an engine offset? Again
I'm only asking the question because I genuinely don't know..!
>
> I believe that a correctly offset engine will assist the pilot during take off
by reducing the amount of right rudder deflection required throughout. Without
any offset to help, surely more right rudder deflection would be needed to
keep straight thus effectively reducing the maximum crosswind component from the
left that the aircraft itself could cope with? A rudder trim would not help
this situation of course - it might make reduce the load on the pilot's leg but
the actual rudder deflection is still required.
>
> As I say, an interesting post, I'm very open minded but am yet to be convinced
that I have made a mistake by following the manual and building mine WITH the
quoted 1.5 degree offset....!
>
> --------
> G-TERN
> Classic Mono
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=465129#465129 [1]
>
Links:
------
[1] http://forums.matronics.com/viewtopic.php?p=465129#465129
[2] http://www.matronics.com/Navigator?Europa-List
[3] http://forums.matronics.com
[4] http://wiki.matronics.com
[5] http://www.matronics.com/contribution
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