Spars and Cessna Engineering
Mark Bench
series do not seem to have a full length spar spanning the wing. They
do have a strut that, I suppose, is attached to the spar of each wing
and aide in structure. However, 210's do not have that strut. I'm
curious if anyone knows how the structural forces are absorbed on a wing
without a full length spar and if 210's differ structurally from 172's.
Cessna's are reputed as not having spontaneous wing separation (like a
Malibu I've heard) or any in flight failure. What exactly, about the
design, makes this a sound engineering design? As a starting point, I
know that most of the forces are absorbed by the skin structure.
-Mark
Larry Fransson
In article <377BD7F5...@sabre.com>, Mark wrote:
>The engineering of Cessnas has always intrigued me. 150, 170, 180
>series do not seem to have a full length spar spanning the wing.
Are you referring to the fact that the wing bolts to the fuselage? Or are you
thinking that the spar does not run all the way to the wing tip?
>They do have a strut that, I suppose, is attached to the spar of each wing
>and aide in structure. However, 210's do not have that strut.
The strut braced wing is known as a semi-cantilver wing. The 210, without the
strut, has a full cantilever wing. Like so many things in aircraft design,
deciding between a semi-cantilver and a full cantilever requires making a
compromise. If you brace the wing with a strut, you can save some structural
weight, and weight is everything in aircraft design. On the other hand, if you
don't brace the wing, you've got extra structural weight, but you don't have
the extra drag created by the strut.
>I'm curious if anyone knows how the structural forces are absorbed on a wing
>without a full length spar and if 210's differ structurally from 172's.
>Cessna's are reputed as not having spontaneous wing separation (like a
>Malibu I've heard) or any in flight failure. What exactly, about the
>design, makes this a sound engineering design?
The 172, even with the struts, still must have some sort of spar carry-through
structure. I don't know the specifics of how the 172 is put together, but I
would imagine that the carry-through structure is there primarily to absorb the
compression (and, to a lesser degree, tension) forces that come from the
interaction of the wing and strut - essentially pinned truss elements. This
would also mean that there must be some structure to carry the tension forces
at the point where the struts are pinned to the fuselage. To keep it all
together would require more structural elements between the point at which the
wing attaches to the fuselage and the strut attach points. This might seem
like a whole lot of structure, but the way I'm envisioning it, it would involve
six truss elements - elements that carry forces that act only in tension and
compression, without any bending - and two beam elements - the wing spars,
which carry the bending forces in the wing. Four of the truss elements form a
square that surrounds the fuselage - probably somewhere around the door posts.
The other two truss elements are the wing struts, pinned at the bottom of the
fuselage structure and at their attach point to the spar - each spar being one
beam element that is pinned to the fuselage structure. Truss elements, because
they absorb only tension and compression forces, can be relatively light. Beam
elements, on the other hand, are necessarily heavier because of the requirement
to absorb bending forces. This is probably where the weight savings comes in.
You can apparently save a lot of weight by using a structure that acts only in
tension and compression instead of having to absorb a lot of bending forces.
This is probably highly oversimplified, but I believe the basic principles I've
presented do apply.
Lost yet? That probably wandered a little bit, because I'm recalling things I
haven't had to think much about in almost ten years. If I had the reference
materials handy, I could probably work up some kind of engineering analysis
that would show the weight difference between a strut-braced wing and a full
cantilever wing.
>As a starting point, I know that most of the forces are absorbed by the skin
structure.
Not quite. Bending forces, which will normally be the majority of the forces
acting on the wing, are absorbed by the wing spar and associated structure in
the case of a strut-braced wing. The ribs are there to transmit twisting
forces to the wing skin, which absorbs those twisting forces through shear
(that's sheAr, not sheEr) forces in the skin panels.
Larry Fransson
Seattle, WA
"Pilots are just plane people with a different air about them."
Roger Long
actually quite efficient. One of the Cessna models, I think the 210, went
from struts to a fully cantilevered wing design and actually got slower.
The increased weight of the strutless wing slowed the plane down more
than the drag of the struts. Besides, without the struts, what do you push
on? Where do you put the little step to check the fuel? Struts rule.
BTW, a single 3/8 inch wire cable has about the same drag as the entire wing
of a Cessna. Streamlining does a lot. Now you know why
the glide angles of those old cable stayed planes and ultralights are so
steep.
I've heard more than once that the 172 is the only production airplane never
to suffer an inflight break up. Does anybody have the definitive facts on
this?
Mark Bench wrote in message <377BD7F5...@sabre.com>...
>The engineering of Cessnas has always intrigued me. 150, 170, 180
>series do not seem to have a full length spar spanning the wing. They
>do have a strut that, I suppose, is attached to the spar of each wing
>and aide in structure. However, 210's do not have that strut. I'm
>curious if anyone knows how the structural forces are absorbed on a wing
>without a full length spar and if 210's differ structurally from 172's.
>Cessna's are reputed as not having spontaneous wing separation (like a
>Malibu I've heard) or any in flight failure. What exactly, about the
>design, makes this a sound engineering design? As a starting point, I
>know that most of the forces are absorbed by the skin structure.
>-Mark
>
Alan Golden
Assoc. at www.cessna.org. I took one of their courses on the 182 a few
months ago,(I own one), and they really went into a lot of detail on the
wing structure. The strut braced wing is very strong, and they said that at
least the 182 has never had a wing seperate in flight. I don't know about
the 172, but the wing is similier but a little smaller. The 206 also has a
strut braced wing, and is very strong. One of the reasons C182's lift so
much weight, is the weight savings by using struts to brace the wing. But
check out the CPA. If you e-mail me directly, I can send you an exploded
diagram of a 182 wing.
Alan
N98SL
Rod Farlee
They are just very rare. A 172 broke in NW WA in the 1970s, and a 182
over SE AZ in the 1980s, as I recall. Both in thunderstorms after loss of
control. They predate what the NTSB has online.
All Cessnas have a "full length spar", right out to the wingtip rib. The
177 empty weight is 50 lbs more than a 172. That's the added weight of
the wing root castings, stronger spar, and deeper spar carry-though
structure (in the cabin roof), required without the strut.
All these also have a small rear spar, on which the flaps and ailerons
are mounted. The 177 and later (strutless) 210s also have a thin
forward spar, running behind the leading edge D section and in front
of the fuel tanks.
I assume the skin is loaded only in shear?
- Rod Farlee
Howard Eisenhauer
um, landed it upside down. The spars each bolt to a support on the side of
the cabin roof, & theres an eccentric bolt near the trailing edge to
adjust the angle of the wing relative to the fusalage. If you ever go to
the national Air & Space museum in Washington they've got a 152 "Au
Naturale" stuck up on the wall where you can see all the dirty little
details on how everything goes togeather. Once you remove the struts the
wingtips fall down & hit the ground.
It actually looks pretty funny (as long as it ain't Your plane :))
On the planes that are strutless the spar does indeed go all the way
through, such as the 177 Cardinal, where the front seats are a little
further ahead of where they are compared to a 172 in order to keep the
occupants of said seats from banging thier heads said spar.
Mark Bench (mark....@sabre.com) wrote:
: This is a multi-part message in MIME format.
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: The engineering of Cessnas has always intrigued me. 150, 170, 180
: series do not seem to have a full length spar spanning the wing. They
: do have a strut that, I suppose, is attached to the spar of each wing
: and aide in structure. However, 210's do not have that strut. I'm
: curious if anyone knows how the structural forces are absorbed on a wing
: without a full length spar and if 210's differ structurally from 172's.
: Cessna's are reputed as not having spontaneous wing separation (like a
: Malibu I've heard) or any in flight failure. What exactly, about the
: design, makes this a sound engineering design? As a starting point, I
: know that most of the forces are absorbed by the skin structure.
: -Mark
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: --------------074356547FE56D583D75CA24--
--
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Larry Fransson
In article <19990702154822...@ngol01.aol.com>, rodf...@aol.com
wrote:
>I assume the skin is loaded only in shear?
Good assumption. It takes all the twisting loads that way. Obviously, there
is some tension and compression as the wing bends, but that's what the spars
are for.
M.
to have a full cantilver wing (strut-less), the wing spar must be tip to
tip carry through (i.e. one spar spanning both wings). If that's what
you assume, it's not true. Most of the full cantilver wings don't have
tip to tip carry-through spar. Planes like Bonanza, Cherokee, Boeing
jets and DC3s all have full cantilver wings without carry-through spar.
Mooney is one of the famous exception that has a one-piece wing with tip
to tip carry through spar.
--Mike
Mark Bench wrote:
>
> The engineering of Cessnas has always intrigued me. 150, 170, 180
> series do not seem to have a full length spar spanning the wing. They
> do have a strut that, I suppose, is attached to the spar of each wing
> and aide in structure. However, 210's do not have that strut. I'm
> curious if anyone knows how the structural forces are absorbed on a wing
> without a full length spar and if 210's differ structurally from 172's.
> Cessna's are reputed as not having spontaneous wing separation (like a
> Malibu I've heard) or any in flight failure. What exactly, about the
> design, makes this a sound engineering design? As a starting point, I
> know that most of the forces are absorbed by the skin structure.
> -Mark
>
> ---------------------------------------------------------------
>
> Name: mark.bench.vcf
> Part 1.2 Type: text/x-vcard
> Encoding: 7bit
> Description: Card for Mark Bench
Steven Levin
: Mooney is one of the famous exception that has a one-piece wing with tip
: to tip carry through spar.
Some of the less-famous light planes that also have this are the Piper
Comanche and Apache/Aztec, as well as the Beech Musketeer/Sundowner/Sierra
line.
Steve
Matt727
the Center Wing Section and also as the Wing Stub has a front spar a rear
spar and baffles for the fuel. In the case of the 747 there is also a
midspar which carries through the center wing section. All Boeing jets are
like this.
Matt
Seattle, Washington
747-400 Wingline
M. wrote in message <378101...@my-dejanews.com>...
>Reading between the lines, I sense you made the assumption that in order
>to have a full cantilver wing (strut-less), the wing spar must be tip to
>tip carry through (i.e. one spar spanning both wings). If that's what
>you assume, it's not true. Most of the full cantilver wings don't have
>tip to tip carry-through spar. Planes like Bonanza, Cherokee, Boeing
>jets and DC3s all have full cantilver wings without carry-through spar.
Steven & Rise Estergreen
I've only seen one Bonanza with the wings off, and it's been awhile, but I'm
sure someone will correct me if my memories of it are not accurate. Here's
what I remember: the wing spars do not extend into the fuselage at all. There
are four large bolts that bolt each wing root to the fuselage. There are a
couple of "serrated" areas on the fuselage that the wing is clamped against
with these bolts. Shims are used to correct wing rigging/construction errors.
As you can imagine, the condition and proper torquing and safetying of these
bolts is critical.
M. wrote:
> Reading between the lines, I sense you made the assumption that in order
> to have a full cantilver wing (strut-less), the wing spar must be tip to
> tip carry through (i.e. one spar spanning both wings). If that's what
> you assume, it's not true. Most of the full cantilver wings don't have
> tip to tip carry-through spar. Planes like Bonanza, Cherokee, Boeing
> jets and DC3s all have full cantilver wings without carry-through spar.
> Mooney is one of the famous exception that has a one-piece wing with tip
> to tip carry through spar.
>
Roger Halstead
There is a one piece spar and then there are those that bolt to a "carry
through", which is what Bonanzas and many others do.
The serrated area is part of a casting mounted on the carry through and is
not an actual part of the fuselage. I believe you will find that the only
alignment is the positioning on those serrated areas (with the matching
serrated ones on the wing.) which is to get the angle of incidence correct.
I doubt that shims would be permissible.
Aircraft like the 421 Cessna use a clevis like arrangement to attach to the
carry through..
Roger (K8RI)
http://users.tm.net/rdhalste
Steven & Rise Estergreen <sle...@molalla.net> wrote in message
news:37885A1A...@molalla.net...
Bob Gardner
removed--it is the rare bird that has a one-piece spar. I researched Part 23 and
found one mention of the word "spar," but several instances of the word
"carrythrough." Must be a popular concept with manufacturers.
Bob Gardner