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Old Oct 21, 2004, 10:11 AM
Neil Stainton
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Aerodynamics Question - pylon mounted wing

This message from "Neil Stainton" <neil@itpartnership.com> brought to you by EFLIGHT!

I am hoping that Don will bless us with his expertise, but am asking this
here as I would love to hear other people's ideas too.

I am gong to build an ultra light room flyer type electric model. AUW approx
1/2oz (14g) and a wing loading of around 0.4oz/sq ft. I am basing the design
on the Stubenfliege, AKA Kolibri (see
http://www.rcgroups.com/links/index.php?id=3505) and I was wondering what
the benefit of the high mounted wing was?

For a glider I think there may be a small drag benefit for mounting the wing
on a short pylon, buy I don't think this is important for a slow flyer. A
also don't think that there is "pendulum stability" effect. In fact I seem
to remember that mounting the wing far above the centre of gravity actually
decreases dynamic stability, but I could well be wrong.

The extra weight is undesirable, and if there isn't an aerodynamic or
stability benefit I will mount my wing so the TE is flush with the fuse
stick.
What do people think?

Neil Stainton.
Leamington Spa, UK.


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Old Oct 21, 2004, 10:11 PM
Steve Corbin
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Re: Aerodynamics Question - pylon mounted wing

This message from "Steve Corbin" <crash_corbin@earthlink.net> brought to you by EFLIGHT!

I'm not an engineer, just an experienced model flyer. I have noticed what I
believe to be improved pitch and roll stability with the wing elevated above
the center of mass of the airplane. I conducted some experiments with a 16"
span free flight rubber model about 15 yrs ago. This model had 2 plastic
tubes rubber banded to the fuselage, I could easily slide them fore&aft to
adjust the cg. Balsa sticks attached to the wing were a snug fit in the
tubes, so I was able to try a variety of elevations. I made alot of flights
with this model, all indoors, and eventually came to the conclusion that the
best stability was achieved when the wing was from 1/2 to 1 1/2 chord
lengths above the fuselage. It's been a long time but as I recall, the
higher the wing the more down-thrust I needed. If you make this adjustable
you can fine tune your airplane to have the stability and handling qualities
you like best. Good luck!
----- Original Message -----
From: "Neil Stainton" <neil@itpartnership.com>
To: <eflight@ezonemag.com>
Sent: Thursday, October 21, 2004 7:53 AM
Subject: [EFLT] Aerodynamics Question - pylon mounted wing


> This message from "Neil Stainton" <neil@itpartnership.com> brought to you
> by EFLIGHT!
>
> I am hoping that Don will bless us with his expertise, but am asking this
> here as I would love to hear other people's ideas too.
>
> I am gong to build an ultra light room flyer type electric model. AUW
> approx
> 1/2oz (14g) and a wing loading of around 0.4oz/sq ft. I am basing the
> design
> on the Stubenfliege, AKA Kolibri (see
> http://www.rcgroups.com/links/index.php?id=3505) and I was wondering what
> the benefit of the high mounted wing was?
>
> For a glider I think there may be a small drag benefit for mounting the
> wing
> on a short pylon, buy I don't think this is important for a slow flyer. A
> also don't think that there is "pendulum stability" effect. In fact I
> seem
> to remember that mounting the wing far above the centre of gravity
> actually
> decreases dynamic stability, but I could well be wrong.
>
> The extra weight is undesirable, and if there isn't an aerodynamic or
> stability benefit I will mount my wing so the TE is flush with the fuse
> stick.
> What do people think?
>
> Neil Stainton.
> Leamington Spa, UK.
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.779 / Virus Database: 526 - Release Date: 19/10/2004
>
>
>
> *** Any complaints or problems? Send an email to monitor@ezonemag.com
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>




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Old Oct 23, 2004, 02:11 PM
Rick Page
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n/a Posts
RE: Aerodynamics Question - pylon mounted wing

This message from Rick Page <rick-page@shaw.ca> brought to you by EFLIGHT!

At those speeds, the drag of a CF tube is negligible. The advantage of the
mounting arrangement is easy modification of the wing angle of attack and
replacement with a smaller wing for speed. I suspect there is a pendulum
effect -- I'm sure the design won't sustain inverted flight

Rick.


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Old Oct 23, 2004, 02:11 PM
Dave VanHorn
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n/a Posts
RE: Aerodynamics Question - pylon mounted wing

This message from Dave VanHorn <dvanhorn@dvanhorn.org> brought to you by EFLIGHT!

At 12:16 PM 10/23/2004, Rick Page wrote:

>This message from Rick Page <rick-page@shaw.ca> brought to you by EFLIGHT!
>
> At those speeds, the drag of a CF tube is negligible. The advantage of the
>mounting arrangement is easy modification of the wing angle of attack and
>replacement with a smaller wing for speed. I suspect there is a pendulum
>effect -- I'm sure the design won't sustain inverted flight


Helicopters do, and their CG is way below the wing.


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Old Oct 30, 2004, 02:11 PM
Don Stackhouse @ DJ Aerotech
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n/a Posts
Re: Aerodynamics Question - pylon mounted wing

This message from "Don Stackhouse @ DJ Aerotech" <djaerotech@erinet.com> brought to you by EFLIGHT!

Neil Stainton asks:

>I am going to build an ultra light room flyer type electric model. AUW approx
>1/2oz (14g) and a wing loading of around 0.4oz/sq ft.... and I was
>wondering what
>the benefit of the high mounted wing was?...


The commonality of a high-mounted wing in an application like yours is in
part a "tradition" item borrowed from indoor free-flight technology.

As others have mentioned, it does allow for easy adjustment of incidence on
free-flight models, but at the weights typical of indoor R/C I suspect that
the typical methods (which usually rely on friction fits to hold incidence
settings) must be getting a little risky. Also, for an R/C model where we
generally have elevator and/or throttle control, and where we operate at a
variety of airspeeds and angles of attack, having an easily adjustable
incidence to the wing is less desirable than on a low-powered indoor
free-flight rubber model.

If you are planning to use functional wire bracing on the wing, and a stick
fuselage, mounting the wing on a pylon gives a better angle for the flying
wires. Without that, you would need some sort of structure sticking
downwards to provide a decent anchor point, and such a structure might be a
problem when landing. However, on an R/C model, if you have landing gear,
that gives you a good anchor point without the extra structure that a pylon
wing mounting requires. This is another example of how an idea that works
well in one application is not as helpful in another, only slightly
different application.

As far as stability is concerned, the effects are generally little or none,
especially if the pylon is open structure, not covered. Contrary to popular
belief, there is no such thing as "pendulum stability" for a high-wing
arrangement. When the plane is banked, the wing's lift vector banks with
it, so the vector's relationship with the C/G does not change, and
therefore creates no restoring effect.

The aerodynamic interaction of a covered, slab-sided fuselage or a covered
pylon with the underside of the wing can create an effect that acts like a
degree or two of additional dihedral, but for a stick fuselage and.or an
uncovered pylon this will not happen. We saw this when developing our
Roadkill Series Curtiss-Wright Junior and Piper J-3 Cub. The Junior needed
about two degrees more dihedral because its parasol-mounted wing did not
get the same extra dihedral effect that the Cub received from its high
fuselage.

There can be a weak influence on static pitch stability in positive-G
flight. One of the biggest drag producers is the wing, and positioning it
well above the C/G on a pylon or high fuselage does create a nose-up effect
if the airspeed increases. Of course it has the opposite effect when flying
inverted. Also, it does tend to move the major masses of the plane further
from each other, increasing the moment of inertia about the pitch axis in
particular, which would tend to hurt the dynamic stability.

There are some theories that placing the wing above and clear of the
fuselage results in cleaner flow over the wing center section, resulting in
less drag and more lift. However, I am very skeptical of whether this is
actually being achieved in the real world. The interference drag between
the wing and the fuselage top, the wing and the pylon, and the fuselage and
the pylon, the extra structural weight of the pylon and its supporting
structure, and the parasite drag and added whetted area of the pylon itself
all extract their toll. Also, on a powered aircraft, having the propeller
slipstream below the wing instead of in-line with it or above it, will tend
to reduce lift by increasing the air velocity under the wing. Altogether,
the net effects of increasing the amount of "stuff" hanging out in the
airflow by adding a pylon to put the wing significantly above the fuselage
most likely kills any benefit from supposedly reducing the disturbance
across the wing's center section. A little work on properly interfacing a
shoulder-mounted wing with the top of the fuselage should in most cases
accomplish about the same benefits, without the detriments.

BTW, you can see the effect of slowing the local airflow under the wing
(the opposite of what a low-positioned propeller slipstream does) in the
performance specs for full scale airplanes. The published stall speed with
landing gear extended is typically a little less than the stall speed with
the gear retracted. The drag of the extended landing gear impedes the
airflow under the wing, reducing the local airspeed, which, in accordance
with Bernoulli, increases its static pressure and therefore the wing's lift.

Structurally, a pylon-mounted wing is typically not a major issue on an
extensively strut or wire-braced arrangement, but a significant problem
area if the wing is cantilevered from the pylon with no extra bracing.
Besides all the usual forces and moments present in a conventional
arrangement, the pylon introduces at least two additional bends in the load
paths, and with them a number of additional torsional and bending problems.

Altogether, in most cases you would probably be better off from both a
structural and an aerodynamic standpoint without the pylon.

Visually the pylon can be helpful, especially on trainer planes such as our
Curtiss-Wright Junior. It increases the plane's overall "visual footprint",
and also adds some more visual cues to tell the pilot on the ground what
the plane's orientation is. For beginners this can be a significant
benefit. Also, the greater structural flexibility that is almost inevitable
in an open-framework pylon-mounted arrangement can help reduce the impact
stresses on both the wing and the fuselage in case of a crash or hard
landing. Typical crash damage will usually be just a strut end pulled
loose. Try to anticipate that and make the strut attachments easy to repair.

Other operational considerations can mandate a pylon-mounted arrangement,
such as the need to keep wings and propellers clear of the water spray on
the PBY Catalina flying boats. On models such as the "Mantis" series of
thermal duration R/C sailplanes it allows for a one-piece flap all the way
across the center section, eliminating end gaps that can increase induced
drag and reduce lift. Of course a conventional flap can be sealed against
the side of the fuselage with just a little extra work and forethought,
such as we did on our original "Monarch" 2-meter sailplane, without
introducing all the other problems that come with a pylon mounting.

Then of course some folks think pylon-mounted wings look "cool". To each
his/her own. In the case of the PBY Catalina I'd have to agree with them.
However, Neil, for a plane like you're contemplating, it's probably not
going to have any measurable net benefits for any objectively-based criteria.


Don Stackhouse @ DJ Aerotech
djaerotech@erinet.com
http://www.djaerotech.com/


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Old Oct 31, 2004, 08:11 PM
Neil Stainton
Guest
n/a Posts
RE: Aerodynamics Question - pylon mounted wing

This message from "Neil Stainton" <neil@itpartnership.com> brought to you by EFLIGHT!

Don, thank you very much for taking the time and trouble to answer my
question so authoritatively and generously. As always your post included
nuggets of extra information which also improved my general understanding of
aerodynamics. I found the landing gear extended lower stall speed
explanation especially illuminating.

Thank you again,

Neil.

-----Original Message-----
From: owner-eflight@ezonemag.com [mailtowner-eflight@ezonemag.com] On
Behalf Of Don Stackhouse @ DJ Aerotech
Sent: 30 October 2004 19:10
To: eflight@ezonemag.com
Cc: Neil Stainton
Subject: Re: [EFLT] Aerodynamics Question - pylon mounted wing

This message from "Don Stackhouse @ DJ Aerotech" <djaerotech@erinet.com>
brought to you by EFLIGHT!
<snip>
Altogether, in most cases you would probably be better off from both a
structural and an aerodynamic standpoint without the pylon.
<snip>

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