Today's Message Index:
----------------------
1. 04:16 AM - Re: Adequate rod ends (Michael Perez)
2. 05:06 AM - Re: Adequate rod ends (Jeff Boatright)
3. 10:39 AM - Re: Adequate rod ends (Bill Church)
4. 11:47 AM - Re: Adequate rod ends (KMHeide, BA, CPO, FAAOP)
5. 11:53 AM - Streamlining Struts (Bill Church)
6. 02:36 PM - Re: Adequate rod ends (Gary Boothe)
7. 02:56 PM - Re: Adequate rod ends (Jeff Boatright)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Adequate rod ends |
Bill, you sir, are right on! That is what-I was looking for. Thank you fo
r taking the time and effort to do that for me. (and the list)
-
I am not a big fan of aluminum fasteners as well, usually. However, they do
have there place. Wing struts are not one of them. I may use aluminum on t
he center struts, but that is yet to be determined. The aluminum solid ends
I have been looking at cost more then their steel twins.- For each strut
, I will more then likely use one threaded, solid rod end for each. So, for
the center section, I would only need to buy 4. Not sure it is worth the a
dded cost to buy 4 aluminum fittings...I doubt the weight savings would be
much. But, then again it ALL adds up over the entire project. Like I said,
TBD on the center section. You have convinced me on steel for the wing stru
ts. Thanks again.
---
Message 2
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Adequate rod ends |
Ryan,
Thanks for the reply and link. You are describing in part what I'm
thinking. The negative g-loading causes compression of the strut. The
strut then bows, and like a straw, can eventually snap. Once the
bowing starts, loads are no longer 100% in parallel with the former
line of the unbowed strut. In a sense, some of the load is now from
the side, a bending load. If the rod end shaft is part of the strut
diagonal, it will also be subjected to those loads.
All of this pondering on my part is because the plane is already
built and I'd like to add more dihedral. The easiest thing to do is
to back the rod ends out to lengthen the distance between wing as
fuselage strut attach points. But easy doesn't mean safe. Like
anything on a plane, changing what has proven to be safe into some
other configuration demands much consideration.
Thanks all for your thoughts,
Jeff
>Jeff,
>
>I could be wrong on this, but I believe the "collapsing" that the
>jury struts eliminate results from negative g-loading that places
>the struts in compression. Let's say the Piet is flying through
>smooth air. The wing is making lift, and thusly "lifting" the
>fuselage. The struts would then be in tension. If you fly through a
>downdraft and experience negative g's those struts would now be in
>compression, and that would be where they are susceptible to
>failure. Here is a link to a short article about model airplanes:
>
><http://www.fly-imaa.org/imaa/hfarticles/const/v2-4-69.html>http://www.fly-imaa.org/imaa/hfarticles/const/v2-4-69.html
>
>I know that they are not the same as a real airplane, but it does
>simply explain the idea.
>
>As far as the loads on the strut being the same as the loads on the
>rod end fitting....well, they may be transmitted the same but the
>piece probably would not react the same. One is a hollow
>steel/aluminum tube, the other is a solid metal fitting.
>
>Finally...I posit a situation. The service manual for a J-3 provides
>rigging instructions (according to the table of contents). But they
>may not provide such specific data as how far out the fork can be
>unscrewed. They know exactly how long the strut/fork combination is,
>because they manufacture it. They specify a standard set of
>instructions for rigging the airplane, and if things need to be
>adjusted they are relatively minute adjustments. They don't need to
>worry about thread engagement on the fork end, because they are
>dealing with very small adjustments. Thusly, even if engineering
>calculated the minimum thread engagement that may never have made it
>into the maintenance manuals, as there was no reason for that to
>have ever come into play when rigging a Cub (unless it has some
>serious issues).
>
>Maybe that would be the case, I don't know. Just throwing that out
>there. As you said, even if you could find the data it's for an
>entirely different airplane, and you probably shouldn't use that
>standard without some solid analysis. Personally I would think one
>of the preferable things to do in the situation of a Piet is to look
>at what others have successfully flown, preferably for many hours,
>and choose which of those to emulate. Determine how long you want
>your struts to be, and build them so that they have maximum thread
>engagement.
>
>Ryan
Message 3
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Adequate rod ends |
Jeff,
I think I understand the question now. You are concerned about buckling.
In compression, the strut assembly will act like a column. The longer an
unsupported column is, the more prone to buckling it becomes. If the
compression forces on the ends of a column are large enough (based on the
specific geometry and physical characteristics of the column), once the
column starts to buckle, it can suffer a catastrophic collapse. This type of
failure can be avoided by a couple of methods. One is to change the
structure of the column (larger profile, thicker wall thickness, different
materials, etc), and the other method is to provide some intermediate
support(s) to effectively shorten the unsupported length of the column. The
second of these methods is recommended for the Pietenpol. This is achieved
by the addition of jury struts. The lift struts on the Air Camper are about
eight feet long, but with the addition of jury struts, the unsupported
length becomes roughly half of that. Since the relationship between buckling
force and column length is an inverse square, reducing the length by half
means that the forces required to buckle the new shorter length increase by
a factor of four (likewise, if the length of a column is doubled, the force
required to buckle the longer column is only one fourth). The jury struts
do very little in ideal flight conditions - straight, level flight, in calm
air, followed by a perfect, soft-as-a-feather landing on a smooth-as-glass
runway. The only possible problem under these conditions would be if the
airflow over the lift struts were to cause the struts to flutter, or
vibrate. The addition of the jury struts will help to alleviate this
situation. In this instance, the jury struts should be attached at a point
that is NOT the midpoint of the strut length, as attachment at the midpoint
can allow harmonic vibration to occur, and multiply. Unfortunately, most of
us have to live in the real world (except for one weekend in July each year,
at a small airport in southern Wisconsin). That real world includes
turbulent air, and occasional hard landings and rough runways (or fields)
among other things. These conditions all have the power to impart negative G
forces on the plane and its occupants. When the Air Camper is put into
negative G conditions, the wings (especially the 3-piece wing) will tend to
pivot downward, putting the lift struts into compression, rather than
tension. When the lift struts are in compression, they begin to act like the
columns mentioned above. Unsupported, the lift struts might collapse when
subjected to these negative G forces. The consequences are nasty if it
happens on the ground, but likely fatal if occuring in flight. So, jury
struts are a good thing to have on an Air Camper.
Now, with respect to your question, as I mentioned, the calculations to
determine the "side loads" the strut ends might encounter are difficult to
determine. But, just out of curiosity, I did a few calculations to try to
determine how much longer your lift struts might need to be extended, in
order to give the wing the dihedral you are desiring. I randomly chose a
dimension of 2" for the dihedral (seems about right). Since the lift struts
are attached at roughly half way between the fuselage and the wingtip, and
the struts are angled at approximately 30 degrees, the resulting lift strut
will only need to be extended by approximately 1/2". I'm not sure, but I
think that Cub lift strut ends are 7/16" (correct me if that's not right).
The forces required to bend a 7/16" diameter bolt would be huge. I would
think that your strut attachment brackets would get ripped out of the plane
before the strut ends would fail (the old "weakest link in the chain", once
again).
The short answer is that I don't think that extending your strut ends an
extra 1/2" is going to put you at risk (provided the threaded rod is long
enough to keep the threads properly engaged).
Anybody have a differing view on this matter?
Bill C.
Message 4
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Adequate rod ends |
Well Explained!
-
Ken Heide
-
--- On Fri, 10/31/08, Bill Church <eng@canadianrogers.com> wrote:
From: Bill Church <eng@canadianrogers.com>
Subject: RE: Pietenpol-List: Adequate rod ends
#yiv179383659 BLOCKQUOTE {
PADDING-BOTTOM:0px;PADDING-TOP:0px;}
#yiv179383659 DL {
PADDING-BOTTOM:0px;PADDING-TOP:0px;}
#yiv179383659 UL {
PADDING-BOTTOM:0px;PADDING-TOP:0px;}
#yiv179383659 OL {
PADDING-BOTTOM:0px;PADDING-TOP:0px;}
#yiv179383659 LI {
PADDING-BOTTOM:0px;PADDING-TOP:0px;}
Jeff,
-
I think I understand the question now. You are concerned about buckling.
In compression, the strut assembly will act like a column. The longer an un
supported-column is, the more prone to buckling it becomes. If the compre
ssion forces on the ends of a column are large enough (based on the specifi
c geometry and physical characteristics of the column), once the column sta
rts to buckle, it-can suffer a catastrophic collapse. This type of failur
e can be avoided by a couple of methods. One is to change the structure of
the column (larger profile, thicker wall thickness, different materials, et
c), and the other method is to provide some intermediate support(s) to effe
ctively shorten the unsupported length of the column. The second of these m
ethods is recommended for the Pietenpol. This is achieved by the addition o
f jury struts. The lift struts on the Air Camper are about eight feet long,
but with the addition of jury struts, the unsupported length becomes rough
ly half of that. Since the relationship between buckling force and
column length is an inverse square, reducing the length by half means that
the forces required to buckle the new shorter length increase by a factor
of four (likewise, if the length of a column is doubled, the force required
to buckle the longer column is only one fourth).- The jury struts do ver
y little in-ideal flight conditions - straight, level flight, in calm air
, followed by a perfect, soft-as-a-feather landing on a smooth-as-glass run
way. The only possible problem under these conditions would be if the airfl
ow over the lift struts were to cause the struts to flutter, or vibrate. Th
e addition of the jury struts will help to alleviate this situation. In thi
s instance, the jury struts should be attached at a point that is NOT the m
idpoint of the strut length, as attachment at the midpoint can allow harmon
ic vibration to occur, and multiply. Unfortunately, most of us have to live
in the real world (except for one weekend in July each year, at a
small airport in southern Wisconsin). That real world includes turbulent a
ir, and occasional hard landings and rough runways (or fields) among other
things. These conditions all-have the power to impart negative G forces o
n the plane and its occupants. When the Air Camper is put into negative G c
onditions, the wings (especially the 3-piece wing) will tend to pivot downw
ard, putting the lift struts into compression, rather than tension. When th
e lift struts are in-compression, they begin to act like the columns ment
ioned above.-Unsupported, the lift struts might collapse when subjected t
o these negative G forces. The consequences are nasty if it happens on the
ground, but likely fatal if occuring in flight. So, jury struts are a good
thing to have on an Air Camper.
-
Now, with respect to your question, as I mentioned, the calculations to det
ermine the "side loads" the strut ends might encounter are difficult to det
ermine. But, just out of curiosity, I did a few calculations to try to dete
rmine how much longer your lift struts might need to be extended, in order
to give the wing the dihedral you are desiring. I randomly chose a dimensio
n of 2" for the dihedral (seems about right). Since the lift struts are att
ached at roughly-half way between the fuselage and the wingtip, and the s
truts are angled at approximately 30 degrees, the resulting lift strut will
only need to be extended by approximately 1/2". I'm not sure, but I think
that Cub lift strut ends are 7/16" (correct me if that's not right). The fo
rces required to bend a 7/16" diameter bolt would be huge. I would think th
at your strut attachment brackets would get ripped out of the plane before
the strut ends would fail (the old "weakest link in the chain", once
again).
-
The short answer is that I don't think that extending your strut ends an ex
tra 1/2" is going to put you at risk (provided the threaded rod is long eno
ugh to keep-the threads-properly engaged).
-
Anybody have a differing view on this matter?
-
Bill C.-
-
=0A=0A=0A
Message 5
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Streamlining Struts |
The recent discussion regarding the various methods possible to
streamline round struts caused me to remember an article that was
published in an issue of To Fly, the magazine that was published by the
now defunct Sport Aviation Association that was founded by Paul
Poberezny (in an effort to return to the original ideals of the EAA). As
the magazine is now out of print, and since the following article used
to be available on the SAA website, I figure it would be okay to scan a
copy and share it with the List.
>From the data presented, one can easily see how beneficial it is to use
streamline tube or, if round tube is used, to streamline that round
tube.
Bill C.
Message 6
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Adequate rod ends |
Bill,
You are a treasure! Even I could understand that..
Gary Boothe
Cool, Ca.
Pietenpol
WW Corvair Conversion
Tail done, working on fuselage (endless metal parts!)
(12 ribs down.)
Do not archive
_____
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Bill Church
Sent: Friday, October 31, 2008 10:38 AM
Subject: RE: Pietenpol-List: Adequate rod ends
Jeff,
I think I understand the question now. You are concerned about buckling.
In compression, the strut assembly will act like a column. The longer an
unsupported column is, the more prone to buckling it becomes. If the
compression forces on the ends of a column are large enough (based on the
specific geometry and physical characteristics of the column), once the
column starts to buckle, it can suffer a catastrophic collapse. This type of
failure can be avoided by a couple of methods. One is to change the
structure of the column (larger profile, thicker wall thickness, different
materials, etc), and the other method is to provide some intermediate
support(s) to effectively shorten the unsupported length of the column. The
second of these methods is recommended for the Pietenpol. This is achieved
by the addition of jury struts. The lift struts on the Air Camper are about
eight feet long, but with the addition of jury struts, the unsupported
length becomes roughly half of that. Since the relationship between buckling
force and column length is an inverse square, reducing the length by half
means that the forces required to buckle the new shorter length increase by
a factor of four (likewise, if the length of a column is doubled, the force
required to buckle the longer column is only one fourth). The jury struts
do very little in ideal flight conditions - straight, level flight, in calm
air, followed by a perfect, soft-as-a-feather landing on a smooth-as-glass
runway. The only possible problem under these conditions would be if the
airflow over the lift struts were to cause the struts to flutter, or
vibrate. The addition of the jury struts will help to alleviate this
situation. In this instance, the jury struts should be attached at a point
that is NOT the midpoint of the strut length, as attachment at the midpoint
can allow harmonic vibration to occur, and multiply. Unfortunately, most of
us have to live in the real world (except for one weekend in July each year,
at a small airport in southern Wisconsin). That real world includes
turbulent air, and occasional hard landings and rough runways (or fields)
among other things. These conditions all have the power to impart negative G
forces on the plane and its occupants. When the Air Camper is put into
negative G conditions, the wings (especially the 3-piece wing) will tend to
pivot downward, putting the lift struts into compression, rather than
tension. When the lift struts are in compression, they begin to act like the
columns mentioned above. Unsupported, the lift struts might collapse when
subjected to these negative G forces. The consequences are nasty if it
happens on the ground, but likely fatal if occuring in flight. So, jury
struts are a good thing to have on an Air Camper.
Now, with respect to your question, as I mentioned, the calculations to
determine the "side loads" the strut ends might encounter are difficult to
determine. But, just out of curiosity, I did a few calculations to try to
determine how much longer your lift struts might need to be extended, in
order to give the wing the dihedral you are desiring. I randomly chose a
dimension of 2" for the dihedral (seems about right). Since the lift struts
are attached at roughly half way between the fuselage and the wingtip, and
the struts are angled at approximately 30 degrees, the resulting lift strut
will only need to be extended by approximately 1/2". I'm not sure, but I
think that Cub lift strut ends are 7/16" (correct me if that's not right).
The forces required to bend a 7/16" diameter bolt would be huge. I would
think that your strut attachment brackets would get ripped out of the plane
before the strut ends would fail (the old "weakest link in the chain", once
again).
The short answer is that I don't think that extending your strut ends an
extra 1/2" is going to put you at risk (provided the threaded rod is long
enough to keep the threads properly engaged).
Anybody have a differing view on this matter?
Bill C.
Message 7
| INDEX | Back to Main INDEX |
| PREVIOUS | Skip to PREVIOUS Message |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Adequate rod ends |
Bill C,
Great synopsis of the issues and a very useful analysis of the
real-world scenario. Thanks so much, I'll stand you a beer at B'head.
Jeff
Other Matronics Email List Services
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|