The Murphy Builders Site

Several Moose builders have installed fin fairings. Presumably for the same
reason Cessna chose to add these to the C-180/C-185 airframes; enhanced
fuselage stability for float plane landings. However, merely from the
perspective of looking at some of these fairings that have been installed to
the Moose aircraft whose photographs are commonly displayed on the internet it
seems feasible that some of these fairings are larger than they need to be to
get the job done. If this is true, then they also add a complicating factor
during cross wind flight conditions.

Who or what is the "technical direction" regarding the size & shape of these
fairings? MAM? Knowledgable aftermarket aircraft service organizations? All
of these are possible. I'm just curious to know how technically rigorous these
designs are (i.e., like the use of Finite Element Analysis). In view of the
differences among these I would conclude there is more subjectivity in some of
these designs than should be present, but all might increase the airframe
stability during float plane landings.

Obviously, I'm also asking if these fairings are required. Meaning, can the
vertical fin be left as designed by MAM and some owners have merely decided to
increase the airframe stability, whether it is required or not. This is also
completely acceptable...particularly since it only takes one bad landing to do
a lot of damage...and dare I say worse!

Another question is why SR2500 owners do not seem to have these installed as
much as the SR3500 aircraft... Hhhmmmm...puzzling!

Thanks everyone,

Rick





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I assume your talking about the fairing on the leading edge of the vertical
stab... not sure if you can find a picture of the original SR2500, but it
had a fairly good sized aluminum fairing here... the small fiberglass curve
that is the standard in pictures on Murphy's site now was an option.

Ah... found a picture of the original fairing...
http://www.murphyair.com/complete/VincentSR.htm

I plan to build my Moose like this, I like the aluminum fairing instead of
the fiberglass one... I also like the looks better.

Mike
195SR

----- Original Message -----
From: <ravc1@dcsol.com>
To: <rebel-builders-d@dcsol.com>
Sent: Wednesday, November 16, 2005 5:05 PM
Subject: Moose Fin Fairings

Several Moose builders have installed fin fairings. Presumably for the
same
reason Cessna chose to add these to the C-180/C-185 airframes; enhanced
fuselage stability for float plane landings. However, merely from the
perspective of looking at some of these fairings that have been installed
to
the Moose aircraft whose photographs are commonly displayed on the
internet it
seems feasible that some of these fairings are larger than they need to be
to
get the job done. If this is true, then they also add a complicating
factor
during cross wind flight conditions.

Who or what is the "technical direction" regarding the size & shape of
these
fairings? MAM? Knowledgable aftermarket aircraft service organizations?
All
of these are possible. I'm just curious to know how technically rigorous
these
designs are (i.e., like the use of Finite Element Analysis). In view of
the
differences among these I would conclude there is more subjectivity in
some of
these designs than should be present, but all might increase the airframe
stability during float plane landings.

Obviously, I'm also asking if these fairings are required. Meaning, can
the
vertical fin be left as designed by MAM and some owners have merely
decided to
increase the airframe stability, whether it is required or not. This is
also
completely acceptable...particularly since it only takes one bad landing
to do
a lot of damage...and dare I say worse!

Another question is why SR2500 owners do not seem to have these installed
as
much as the SR3500 aircraft... Hhhmmmm...puzzling!

Thanks everyone,

Rick





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Rick, like you said the only reason is for float operations, it doesn't need
a thing on wheels.

That is why I like the C-185 style coupled with the removable sea fins on
the horizontal stabilizer and the removable ventral fin. If you really
wanted to you could make the top fuselage to fin fairing removable too and
put on a smaller one for wheels.

As far as size the only testing that I know of is trial and error. The
larger top fairing, in either style out there is not enough on floats that
is why you see the sea fins and the dorsal fin. Of course some of it is
personal preference on how much you like to struggle with the rudder pedals.
In my opinion the Moose was awful to fly on floats without the extra
vertical tail area. We flew it with just the larger top fairing and it was
still marginal, added the ventral and the stab tip fins and it was much
better. The sea fins on the stab tips don't really added any more exposed
side area as far as cross winds and of course x-wind not usually a factor on
floats anyway.

FWIW
Scott
Moose 174




-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
ravc1@dcsol.com
Sent: Wednesday, November 16, 2005 7:06 PM
To: rebel-builders-d@dcsol.com
Subject: Moose Fin Fairings

Several Moose builders have installed fin fairings. Presumably for the same

reason Cessna chose to add these to the C-180/C-185 airframes; enhanced
fuselage stability for float plane landings. However, merely from the
perspective of looking at some of these fairings that have been installed to

the Moose aircraft whose photographs are commonly displayed on the internet
it
seems feasible that some of these fairings are larger than they need to be
to
get the job done. If this is true, then they also add a complicating factor

during cross wind flight conditions.

Who or what is the "technical direction" regarding the size & shape of these

fairings? MAM? Knowledgable aftermarket aircraft service organizations?
All
of these are possible. I'm just curious to know how technically rigorous
these
designs are (i.e., like the use of Finite Element Analysis). In view of the

differences among these I would conclude there is more subjectivity in some
of
these designs than should be present, but all might increase the airframe
stability during float plane landings.

Obviously, I'm also asking if these fairings are required. Meaning, can the

vertical fin be left as designed by MAM and some owners have merely decided
to
increase the airframe stability, whether it is required or not. This is
also
completely acceptable...particularly since it only takes one bad landing to
do
a lot of damage...and dare I say worse!

Another question is why SR2500 owners do not seem to have these installed as

much as the SR3500 aircraft... Hhhmmmm...puzzling!

Thanks everyone,

Rick





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Hi Rick !

The reason for the larger fin fairings is to increase the
area of the tail section - nothing to do with crosswinds, since
float pilots usually land straight into wind on the water.
This increase is needed to improve longitudinal stability. Think
of the tail like the feathers on an arrow - the area back there
keeps the pointy end going forward !

Without increased fin area , the SR, Moose, and Elite all
tend to "fishtail" slightly in cruise. This is greatly aggravated
by adding floats. The reason is the floats add considerable SIDE area
to the FRONT of the aircraft, and need more area at the rear to
balance this. Possibly the big round engine cowling adds extra
area up front, too...

If you sideslip a normal aircraft, when you release the rudder
pressure, it will nose down - that is - turn toward the lowered wing.
Now, if you add floats, (= more forward side area), when you start to
sideslip, the aircraft will tend to yaw towards the HIGH wing,
because of the extra area up front !! This is obviously NOT
desireable !! :-) And makes it VERY difficult to recover from
a spin !! ;-)

As for size and shape, most folks follow examples from the past -
this problem has been around since the beginning of flight ! The
huge ventral fin is an effective solution, if there's an easy way
to mount it. Dorsal fin additions are popular because they are
relatively easy to do, and many believe they improve the appearance
of the airplane. The worst that could happen, if you made a fin
that was too large, is that you would increase longitudinal
stability so much that it would be difficult to get the aircraft
to turn ...... pretty unlikely ! :-) Lots of rudder would
overcome that, in any case ....

Some manufacturers have opted to increase the height of
the fin, to gain effective area. The area at the base of
the vertical fin is not too effective in adding to longitudinal
stability because often there is less airflow there - it's
partly blanketed by the fuselage, so you need a much larger
area. Of course, to increase the height of the fin requires
some serious re-engineering, as the loads at the base can get
quite high !! Soooooo - most people just add bigger fin fairings. :-)

The only condition that might cause landing problems is
a GUSTY crosswind, and they can be exciting even if everything
IS alright with the side area !! :-)

.....bobp

-------------------------------orig.-------------------------
On Wednesday 16 November 2005 09:05 pm, ravc1@dcsol.com wrote:

Several Moose builders have installed fin fairings. Presumably for the

same

reason Cessna chose to add these to the C-180/C-185 airframes; enhanced
fuselage stability for float plane landings. However, merely from the
perspective of looking at some of these fairings that have been installed

to

the Moose aircraft whose photographs are commonly displayed on the

internet it

seems feasible that some of these fairings are larger than they need to be

to

get the job done. If this is true, then they also add a complicating

factor

during cross wind flight conditions.

Who or what is the "technical direction" regarding the size & shape of

these

fairings? MAM? Knowledgable aftermarket aircraft service organizations?

All

of these are possible. I'm just curious to know how technically rigorous

these

designs are (i.e., like the use of Finite Element Analysis). In view of

the

differences among these I would conclude there is more subjectivity in

some of

these designs than should be present, but all might increase the airframe
stability during float plane landings.

Obviously, I'm also asking if these fairings are required. Meaning, can

the

vertical fin be left as designed by MAM and some owners have merely

decided to

increase the airframe stability, whether it is required or not. This is

also

completely acceptable...particularly since it only takes one bad landing

to do

a lot of damage...and dare I say worse!

Another question is why SR2500 owners do not seem to have these installed

as

much as the SR3500 aircraft... Hhhmmmm...puzzling!

Thanks everyone,

Rick

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This brings up a question that I have wanted to ask for a while. Have any of
the Murphy aircraft been spin tested on floats?
Jesse

From: Bob Patterson <beep@sympatico.ca>
Reply-To: <rebel-builders@dcsol.com>
To: rebel-builders@dcsol.com
Subject: Re: Moose Fin Fairings
Date: Thu, 17 Nov 2005 14:12:40 -0500

Hi Rick !

The reason for the larger fin fairings is to increase the
area of the tail section - nothing to do with crosswinds, since
float pilots usually land straight into wind on the water.
This increase is needed to improve longitudinal stability. Think
of the tail like the feathers on an arrow - the area back there
keeps the pointy end going forward !

Without increased fin area , the SR, Moose, and Elite all
tend to "fishtail" slightly in cruise. This is greatly aggravated
by adding floats. The reason is the floats add considerable SIDE area
to the FRONT of the aircraft, and need more area at the rear to
balance this. Possibly the big round engine cowling adds extra
area up front, too...

If you sideslip a normal aircraft, when you release the rudder
pressure, it will nose down - that is - turn toward the lowered wing.
Now, if you add floats, (= more forward side area), when you start to
sideslip, the aircraft will tend to yaw towards the HIGH wing,
because of the extra area up front !! This is obviously NOT
desireable !! :-) And makes it VERY difficult to recover from
a spin !! ;-)

As for size and shape, most folks follow examples from the past -
this problem has been around since the beginning of flight ! The
huge ventral fin is an effective solution, if there's an easy way
to mount it. Dorsal fin additions are popular because they are
relatively easy to do, and many believe they improve the appearance
of the airplane. The worst that could happen, if you made a fin
that was too large, is that you would increase longitudinal
stability so much that it would be difficult to get the aircraft
to turn ...... pretty unlikely ! :-) Lots of rudder would
overcome that, in any case ....

Some manufacturers have opted to increase the height of
the fin, to gain effective area. The area at the base of
the vertical fin is not too effective in adding to longitudinal
stability because often there is less airflow there - it's
partly blanketed by the fuselage, so you need a much larger
area. Of course, to increase the height of the fin requires
some serious re-engineering, as the loads at the base can get
quite high !! Soooooo - most people just add bigger fin fairings. :-)

The only condition that might cause landing problems is
a GUSTY crosswind, and they can be exciting even if everything
IS alright with the side area !! :-)

.....bobp

-------------------------------orig.-------------------------
On Wednesday 16 November 2005 09:05 pm, ravc1@dcsol.com wrote:

Several Moose builders have installed fin fairings. Presumably for the

same

reason Cessna chose to add these to the C-180/C-185 airframes; enhanced
fuselage stability for float plane landings. However, merely from the
perspective of looking at some of these fairings that have been

installed
to

the Moose aircraft whose photographs are commonly displayed on the

internet it

seems feasible that some of these fairings are larger than they need to

be
to

get the job done. If this is true, then they also add a complicating

factor

during cross wind flight conditions.

Who or what is the "technical direction" regarding the size & shape of

these

fairings? MAM? Knowledgable aftermarket aircraft service

organizations?
All

of these are possible. I'm just curious to know how technically

rigorous
these

designs are (i.e., like the use of Finite Element Analysis). In view of

the

differences among these I would conclude there is more subjectivity in

some of

these designs than should be present, but all might increase the

airframe

stability during float plane landings.

Obviously, I'm also asking if these fairings are required. Meaning, can

the

vertical fin be left as designed by MAM and some owners have merely

decided to

increase the airframe stability, whether it is required or not. This is

also

completely acceptable...particularly since it only takes one bad landing

to do

a lot of damage...and dare I say worse!

Another question is why SR2500 owners do not seem to have these

installed
as

much as the SR3500 aircraft... Hhhmmmm...puzzling!

Thanks everyone,

Rick

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