Nigel my comments are in quotation marks as replies on this website are
difficult
to use insertions.
Your Comment:
You have discussed the aerodynamic pros and cons, but of equal importance is the
mechanical consequence of an offset engine.
The apparent pitch difference of blade rotating around an offset engine will be
double the engine offset. A blade will experience a change from -1.5 to +1.5
so a delta of 3 degrees. Now if a customer of yours came to you with a fixed
pitch Warpdrive, and you discovered he had set one blade 3 degrees coarser than
the rest Im pretty sure you would send him away with a flee in his ear and
tell him to correct it. But we seem quite happy to accept the same degree of
blade variance if we offset our engine without question.
"The change in pitch of an airplane from takeoff, climb, cruise at differing
speeds
and descent speeds is more effective change of the pitch than torque offset.
We know that propellers are designed to take these dynamic loads. That is
why I am not a fan of propeller blades with limited lifetimes of only a few
years now being sold. I was able to actually break one of these blades by lying
flat on the table and pulling up on the tip and breaking it with my scrawny
hands. Good props have very long life, shrug off the elements, bugs, rocks,
and are not subject to any concern about the variances in angle of attack, yaw
or normal dynamic loads. As an example, think about the downward moving blade
and the upward moving blade at a small angle of attack say during climb out.
The effective difference between the upward and downward blade is about 5
degrees
and the prop just shrugs off this minor gnat of a force. Props are designed
for this loading."
The constantly fluctuating angle of attack introduces cyclic loading and
unloading
of the blades which can produce torsional vibration.
This is then transmitted to the swash plate and drive pins of the constant speed
unit which is not a good thing.
A good buddy of mine (and one of your fellow countrymen) has a successful
business
designing and building custom propellers and wings for the Formula 1 Reno
boys. He showed me a picture of one of his custom two-blade fixed pitch props
that had failed catastrophically during a race. It was unusual in that it had
split from tip to root.
All calculations indicated that it should have been more than strong enough to
absorb the power; however the prop had failed due to extreme torsional
oscillation
along the blade length. By working closely with the owner, he was able to
establish that the plane builder had offset the engine. A new (identical) prop
was made, the engine offset zeroed out and the racer went on to win gold
with no further problems. It was during one of our sitting by the pool drinking
beer and talking planes sessions that he first asked what I was going to do
regarding the offset of my then new Europa. it got me thinking.
"A bit of apples and oranges here: Identical prop with only a change in offset
on a racing plane is not a good example. One off custom means just that, custom
and one must look at the variances in build tolerance. A good manufacturer
will have very few defects, but there are still defects so most blades are
overbuilt
except for extreme needs. Too many ifs and questions on that example
as he changed more than one thing, blade and engine angle, which means mounts
and cowl and many other little things we dont know about. Blades on an O-200
turning some 3500+ RPM and pulling 4-5 Gs goes through much more than offsetting
a prop a degree or so on a small engine. The gyroscopic, pitch change on
a racing prop limits their life. More than likely, the culprit may have been
bad trim from the start and a worn out prop. Who knows for sure."
Now with regard to the suggestion of fitting a rudder trimmer (purely
hypothetical
as I have no plans to take a saw to my fin), I was a little surprised by the
strength of reaction to this suggestion on the grounds of increased drag. I
am also curious as to why our attitude to controlling yaw trim is so different
to the way we control pitch trim.
"I think rudder trim is a glorious idea and feel it is worth the weight and drag
---From a pure convenience point. Go for it. I too dont want to spend the
time.
Ive got everything for it for 12AY but I just dont have the time. I even
like using springs rather than tabs to just tug a bit one way or the other using
a trim motor setup. "
The pitch control system uses an all flying tailplane with a (very
good) trim system. According to Don Dykins book, during the cruise, the
tailplane
is constantly flying the rear of the aircraft downwards to maintain level
flight.
This will be generating drag too but we accept this without question!
"Again, the lifting stabilator on the Europa has a drag bucket associated with
the small angle of attack near neutral on the series six type laminar airfoil
used. The increase of drag for a tail force down is exceedingly small on a
Europa.
However the change in main wing angle to offset this due to an excessively
forward CG will slow the plane down considerable. The aircraft longitudinal
stability is more important than the drag as is a more aft CG for speed as
it decreases tail down force a bit."
When considered against the cumulative drag created by the nose wheel , main
gear,
outriggers tailwheel, flap hinges, GPS antenna fuel vents, strobes and door
handles, surely, the extra drag of a rudder trimmer would pail into
insignificance
but surely make life so much easier in the climb out or cruise.
"I completely agree with that, plus a good pilot is a lazy pilot and a well
trimmed
airplane, flown smoothly is more efficient in its operation and a delight
to fly in."
I have re-read my original response to Jonathan and I stand by everything I
said.
I think the explanation of the aerodynamics is accurate (certainly nobody has
challenged it) and my advice that if it ain broke, dont fix it also stands.
For every pilot happily flying a Classic with no engine offset and reporting no
problems, there seems to be another flying an XS with offset experiencing
problems.
I suspect that the real explanation is muscle memory. Experienced feet
will move by themselves without the owner even being aware. Those with slower
feet will find themselves behind the curve.
"I am working with Creighton Smith on 96EG, a classic with 80 HP and only inch
of offset. It flies fine at 5000/24 inches. Anywhere else on the power curve
and he must add rudder. If he had a 914 he would be seeing a different story
on the takeoff rudder needed to keep straight and would tire without rudder
trim. By the way, he too wishes he had rudder trim. Just not enough hours to
allocate to justify modification. So like most of us he just leans on the right
rudder if flying at 5500, and left on a 4600RPM saunter. Every experimental
is slightly different so one knows apples and oranges are different but are
still fruit and a Europa built and equipped by one builder will be slightly
different
than another. There is little homogeneity in home-made airplanes.
Trim it up and enjoy the flying.
Bud"
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of
nigel_graham@m-tecque.co.uk
Sent: Tuesday, January 17, 2017 9:03 AM
Subject: Re: Europa-List: Re: 1.5 degrees right?
Hi Bud,
Another gem of a post that will be copied into my burgeoning "Bud's Tips"
folder.
I agree with nearly all of what you say but as is always the case; a good
explanation
prompts another question.
You have discussed the aerodynamic pros and cons, but of equal importance is the
mechanical consequence of an offset engine.
The apparent pitch difference of blade rotating around an offset engine will be
double the engine offset. A blade will experience a change from -1.5 to +1.5
so a delta of 3 degrees. Now if a customer of yours came to you with a fixed
pitch Warpdrive, and you discovered he had set one blade 3 degrees coarser than
the rest Im pretty sure you would send him away with a flee in his ear and
tell him to correct it. But we seem quite happy to accept the same degree of
blade variance if we offset our engine without question.
The constantly fluctuating angle of attack introduces cyclic loading and
unloading
of the blades which can produce torsional vibration.
This is then transmitted to the swash plate and drive pins of the constant speed
unit which is not a good thing.
A good buddy of mine (and one of your fellow countrymen) has a successful
business
designing and building custom propellers and wings for the Formula 1 Reno
boys. He showed me a picture of one of his custom two-blade fixed pitch props
that had failed catastrophically during a race. It was unusual in that it had
split from tip to root.
All calculations indicated that it should have been more than strong enough to
absorb the power; however the prop had failed due to extreme torsional
oscillation
along the blade length. By working closely with the owner, he was able to
establish that the plane builder had offset the engine. A new (identical) prop
was made, the engine offset zeroed out and the racer went on to win gold
with no further problems. It was during one of our sitting by the pool drinking
beer and talking planes sessions that he first asked what I was going to do
regarding the offset of my then new Europa. it got me thinking.
Now with regard to the suggestion of fitting a rudder trimmer (purely
hypothetical
as I have no plans to take a saw to my fin), I was a little surprised by the
strength of reaction to this suggestion on the grounds of increased drag. I
am also curious as to why our attitude to controlling yaw trim is so different
to the way we control pitch trim.
The pitch control system uses an all flying tailplane with a (very
good) trim system. According to Don Dykins book, during the cruise, the
tailplane
is constantly flying the rear of the aircraft downwards to maintain level
flight.
This will be generating drag too but we accept this without question!
When considered against the cumulative drag created by the nose wheel , main
gear,
outriggers tailwheel, flap hinges, GPS antenna fuel vents, strobes and door
handles, surely, the extra drag of a rudder trimmer would pail into
insignificance
but surely make life so much easier in the climb out or cruise.
I have re-read my original response to Jonathan and I stand by everything I
said.
I think the explanation of the aerodynamics is accurate (certainly nobody has
challenged it) and my advice that if it ain broke, dont fix it also stands.
For every pilot happily flying a Classic with no engine offset and reporting no
problems, there seems to be another flying an XS with offset experiencing
problems.
I suspect that the real explanation is muscle memory. Experienced feet
will move by themselves without the owner even being aware. Those with slower
feet will find themselves behind the curve.
Keep the thoughts coming.
Nigel
-----------------------------------------------------------
Quoting Bud Yerly <budyerly@msn.com>:
> To All,
> An airplane is 20,000 compromises flying in close formation. Each
> change we make affects others, and some are necessary to fine tune the
> aircraft for normal operations.
>
> Off the very empty top of my head:
> From an aero standpoint, fuselage squareness, tail squareness, wing
> incidence differences in construction, etc. cause most of our trim
> problems at cruise in the Europa.
> As for rudder/fin offset vs. engine offset to correct for P factor,
> drag due to tail area for an offset to counteract the slipstream and P
> factor affect is small at cruise for each. However, in a full power
> 914 with Airmaster on takeoff and climb out, the rudder required to
> hold yaw in check is reduced with offset. Interesting to note is in
> propeller testing, if you trim a plane for perfect ball with a fixed
> pitch, then put on a constant speed, a touch more right rudder is
> required to hold the wings level and the ball solidly in the center.
> Reduce power on the Constant Speed prop and suddenly left rudder is
> needed. I prefer engine offset myself as the offset is really small
> (a degree or so) to accommodate P factor and slipstream yaw.
> Offsetting the rudder/fin on a short fuselage and induced drag becomes
> a factor. A one degree offset of the rudder is .01 Cd which is not
> much drag or about 5 pounds per degree on a 15 sq ft fin/rudder, but
> it is drag, whereas prop offset drag is nill and the loss of thrust is
> nill also at such low angles. I agree with the Europa designers, as
> does David and others, drag is drag. On Classics in my shop, the
> offset on an 80HP fat nosed Classic was very little. Lets face it,
> the instructions said align the engine with the cowl. If you cut the
> cowl, who knows what you have without measuring. But on the Classic,
> that was not mentioned.
> Oh well, progress was made with the XS.
>
> The light propeller aircraft is trimmed for one airspeed and power
> setting. Change speed, weight (angle of attack), propeller length or
> pitch, or power setting and the trim in pitch and roll due to yaw
> changes. Since the fuselage longitudinal axis and engine are at the
> same pitch setting, the small yaw offset of the engine is not going to
> be much, nor is a yaw due to fin trim. Normally, the 1 and 1/16 inch
> offset is fine and if not, I decrease the length of the right/left
> rudder cable about inch to spring the rudder over a bit on some
> aircraft to trim the ball. However, for any roll and yaw combined
> problem, I would look at a droopy flap. Somehow flaps sometimes get
> leaned on and just a 1/16 of an inch flap droop is quite a bit of roll
> and yaw. Whereas changing the engine offset will be very little yaw
> (and small roll).
>
> Fly the plane and center the ball. If it is still rolling it is most
> likely your wing trim. Either a flap is drooping, or somehow spring
> has been built into your ailerons. (Spring in the ailerons is seen
> when the stick does not stay exactly where it is put on the ground.
> Some builders build in problems that cause the aileron to spring one
> direction or the other.) Also look at your wing drag covers, and
> pants on a Trigear for alignment. A droopy wheel pant due to rough
> field operations is quite a bit of drag as are the wing flap bracket
> covers if misaligned.
>
> When the ball can be centered and all roll stops (pat yourself on the
> back for well trimmed wings) your problem is most likely P factor.
> Shorten the cable on the side of the rudder is depressed will normally
> fix it. If that is not enough, then a tab (or stronger spring) is
> necessary on that side. Keeping a plane well trimmed out is a
> constant problem. Every 5 years, look hard at the plane as due to
> wear and tear, things get out of alignment. Any change from your
> original fly off trim settings must be investigated, as something has
> changed.
>
> Just my thoughts.
>
> Bud Yerly
> Im pulling in 12AY soon for Sun n Fun prep. Join us this year in
> Lakeland and meet up with Club members and Europafiles alike at site
> N-55 again this year and get away from the winter doldrums. Our
> display emphasis this year will be on the Airmaster propeller which
> was a game changer for transforming the Europa and many other aircraft
> into efficient cruising airplanes.
>
> From: owner-europa-list-server@matronics.com
> [mailto:owner-europa-list-server@matronics.com] On Behalf Of
> davidjoyce@doctors.org.uk
> Sent: Monday, January 16, 2017 5:42 AM
> To: europa-list@matronics.com
> Subject: Re: Europa-List: Re: 1.5 degrees right?
>
>
> 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:
>
> <jonsmitheuropa@tiscali.co.uk<mailto:jonsmitheuropa@tiscali.co.uk>>
>
>
> 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
>
>
> ttp://www.matronics.com/Navigator?Europa-List
>
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