Today's Message Index:
----------------------
1. 04:41 AM - 106 years ago today-prelude to flight (helspersew@aol.com)
2. 06:23 AM - Re: 106 years ago today-prelude to flight (Wayne Bressler)
3. 07:52 AM - Push/pull tubes and rod ends (Michael Perez)
4. 09:22 AM - Re: Push/pull tubes and rod ends (Jack Phillips)
5. 12:06 PM - Re: Push/pull tubes and rod ends (Michael Perez)
6. 01:04 PM - Re: Push/pull tubes and rod ends (Michael Perez)
7. 01:12 PM - Re: Push/pull tubes and rod ends (helspersew@aol.com)
8. 01:55 PM - Re: Push/pull tubes and rod ends (Bill Church)
9. 01:57 PM - Re: Push/pull tubes and rod ends (Pieti Lowell)
10. 02:05 PM - Re: Push/pull tubes and rod ends (David Paule)
11. 02:09 PM - Re: Push/pull tubes and rod ends (Ryan Mueller)
12. 02:36 PM - Re: Push/pull tubes and rod ends (Bill Church)
13. 02:43 PM - Re: Push/pull tubes and rod ends (Gary Boothe)
14. 03:00 PM - Re: Re: Push/pull tubes and rod ends (David Paule)
15. 04:48 PM - Re: Push/pull tubes and rod ends (Jack Phillips)
16. 05:26 PM - Re: Push/pull tubes and rod ends (chase143)
17. 07:04 PM - Re: Re: Push/pull tubes and rod ends (Jack Phillips)
18. 07:39 PM - Re: Push/pull tubes and rod ends (Pieti Lowell)
19. 08:13 PM - Re: Push/pull tubes and rod ends (Clif Dawson)
20. 11:27 PM - Re: Push/pull tubes and rod ends (Robert Ray)
Message 1
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| Subject: | 106 years ago today-prelude to flight |
>From the diary of Orville Wright.
Saturday, Oct. 24,1903
Kitty Hawk, N.C.
Had strong wind from northeast during night, with some rain, which continu
ed during day at velocities of 25 to 40 miles. We put in the uprights betw
een surfaces and trussed the center section. Had much trouble with wires
made up at home, which for some reason unexplainable failed to fit. Wind
at 7 o'clock this evening blowing 45 miles. Air very damp and cold.
do not archive
Message 2
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| Subject: | Re: 106 years ago today-prelude to flight |
I could read these every day. Please don't stop! This is great stuff!
Thank you for sharing.
Do not archive
Wayne Bressler Jr.
Taildraggers, Inc.
taildraggersinc.com
Sent from the phone that made the Blackberry obsolete.
On Oct 24, 2009, at 7:40 AM, helspersew@aol.com wrote:
> From the diary of Orville Wright.
>
> Saturday, Oct. 24,1903
> Kitty Hawk, N.C.
>
> Had strong wind from northeast during night, with some rain, which
> continued during day at velocities of 25 to 40 miles. We put in the
> uprights between surfaces and trussed the center section. Had much
> trouble with wires made up at home, which for some reason
> unexplainable failed to fit. Wind at 7 o'clock this evening blowing
> 45 miles. Air very damp and cold.
>
> do not archive
>
>
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| Subject: | Push/pull tubes and rod ends |
I am trying to figure out what size and material tube to use to go from the
control stick to the elevator bell crank.- I see in the Bingelis books,
he talks about heavy wall aluminum threaded tubing.- Since I am all about
saving weight on my plane, I would prefer aluminum. The plans call for 1/8
" cable, which-is rated between 1760 and 2100 lbs. I would hope that a tu
be/rod end combination that rated at these numbers would work.- So, I am
trying to figure out what size tube and threaded rod end will give me the 1
760-2100 lb. rating.-- If someone can prvide a usable formula, I may be
able to figure it out myself.
-
Thanks group.
Message 4
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| Subject: | Push/pull tubes and rod ends |
Are you planning on re-designing the entire elevator control system with
pushrods, requiring a pushrod attached to each elevator, a pushrod from the
bellcrank to the rear stick and a pushrod between sticks? It probably will
require an additional pushrod and bellcrank to enable you to pass underneath
the rear seat (where the cable from the stick to the bellcrank makes a bend,
with the plans showing it just passing through a hole drilled in the wood -
I added a pulley here).
If so, figure out the yield strength of whatever alloy of aluminum you
intend to use, then determine what area will be required to withstand the
load (1760 lbs, if you want to equal the cable strength) without exceeding
that stress level. Use the formula Stress = Load divided by Area (s = P/A),
and solve for area (A) since you know the load (P = 1760) and you know the
stress (s = yield strength of your alloy times whatever safety factor you
feel like throwing in). Once you know the area, then determine what wall
thickness and tube diameter will produce the required area. Of course,
there will be machined fittings required on each end of the pushrods, and
rod end bearings to reduce the amount of slop.
As an engineer, I have to wonder why are you doing this? The cables work
well. Any arrangement with pushrods is going to be much more complicated,
due to the geometry of the airplane. Pushrods will end up being far more
expensive and heavier. I don't understand what advantage you are trying to
achieve here, other than to be "different". You could accomplish that by
painting it Pink.
Jack Phillips
NX899JP
Raleigh, NC
Enjoying a rainy day by building the wings of my RV-10 in the basement
_____
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael
Perez
Sent: Saturday, October 24, 2009 10:52 AM
Subject: Pietenpol-List: Push/pull tubes and rod ends
I am trying to figure out what size and material tube to use to go from the
control stick to the elevator bell crank. I see in the Bingelis books, he
talks about heavy wall aluminum threaded tubing. Since I am all about
saving weight on my plane, I would prefer aluminum. The plans call for 1/8"
cable, which is rated between 1760 and 2100 lbs. I would hope that a
tube/rod end combination that rated at these numbers would work. So, I am
trying to figure out what size tube and threaded rod end will give me the
1760-2100 lb. rating. If someone can prvide a usable formula, I may be
able to figure it out myself.
Thanks group.
Message 5
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| Subject: | Re: Push/pull tubes and rod ends |
Push/pull tubes are used in all kinds of aircraft safely. All of which have
more aggressive performance then a slow, draggy, 80+ year old designed Pie
t. Yet most seem to think to make the switch to push/pull is a bad idea...w
hy? I know most just get upset because I stray from the sacred bible of bui
lding the Pietenpol...the prints. Yet non have legitimate reasons for not d
oing it...at least not any they share.- If you guys have facts for NOT us
ing them, please, do tell. To make a statement and not back it up is useles
s.
-
The Bingelis books talks about aluminum tubes-for push/pull...-you know
, the books everyone raves over. He also talks about how these systems-MA
Y weigh less then a cable system with the cables, pulleys, brackets, shackl
es, bearings, nicopress fittings, etc.-
-
If you could run a tube from the firewall to the rudder and support the len
gth along the way-with, say bushings,-there would be no flexing/bending
, yes?
-
I don't have the answers...yet, that is why I am here. I am looking for ANS
WERS, not opinion, guesses, or dialog on how this 80 year old plane built b
y a guy in his garage can't be improved upon with some common sense and som
e homework.
-
Here is what one engineer sent me:-
-
Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement)
-
For some generic heavy wall tube from McMaster Carr and a 1/4-28 male threa
d rod end, I get:- 1962 lbs. worse case with .500" thread engagement, 294
4 lbs. with .75" engagement.
-
The 7X19 SS cable is rated at 1760 lbs.- Using the controls in the Pieten
pol, can a person ever pull 1760 lbs. on the cable?- If they could, would
n't a wood structure fail first...I don't know...like the elevator itself?
- Since no one here seems to have heard of a control cable failure, that
must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control cable,
so what are the REAL loads on this plane and it's controls?- I think peo
ple get a little too extreme and have a plane built for mach 2 when it real
ly only flies at 70 MPH.
-
HOWEVER, my disclaimer...I have been wrong before and have abandoned other
"great" ideas that I have had, this may yet be another. But that decision w
on't be made until I have some facts, and some REAL numbers.
-
Anyone have another formula for pull out stress or bolt sheer?
-
Message 6
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| Subject: | Push/pull tubes and rod ends |
Jack, I got as far as finding the area using the formula you gave me. That
number is .11733.- I am not clear how to figure tube dia. and wall thickn
ess to this number.
Message 7
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| Subject: | Re: Push/pull tubes and rod ends |
Sounds to me like this push-pull tube idea is opening the preverbial Pando
ra's Box of "if I change this, then I must change that,.......... and that
, and that................
-----Original Message-----
From: Michael Perez <speedbrake@sbcglobal.net>
Sent: Sat, Oct 24, 2009 3:03 pm
Subject: RE: Pietenpol-List: Push/pull tubes and rod ends
Jack, I got as far as finding the area using the formula you gave me. That
number is .11733. I am not clear how to figure tube dia. and wall thickn
ess to this number.
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Message 8
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| Subject: | Re: Push/pull tubes and rod ends |
Whoa - what comments are you responding to Mike?
The only reply to your post that I saw was from Jack, and all I saw in his reply
were sound reasons explaining why the cables are a better system FOR THIS AIRPLANE.
As he stated, the geometry of the Air Camper will result in a heavier
and more expensive linkage as compared to the cables. Tony Bingelis says that
push/pull tubes MAY weigh less than a cable system. That will depend on the layout
of the airplane, and in this case, the control system has to go under the
seat, and then get back up into alignment with the elevators and rudder. Cables
can change direction with the addition of a simple pulley, where push/pull
tubes will require bellcranks - which one do you think is heavier? It is not possible
to run a tube straight from the firewall to the rudder in this airplane,
unless you have a properly sized and located hole in your torso for the tube
to pass through. Also, in THIS airplane, the elevators are separate entities,
so you would either have to redesign them so that they are tied together, or
run two push/pull tubes for the elevators.
To quote your original post "I'm all about saving weight on my plane". Jack's reply
explained that the push/pull system will end up being heavier than the cable
system. So what IS the motivation to change to the push/pull system?
Regarding your request for a formula, the thing to keep in mind is that in designing
a mechanism like a push/pull system, you need to analyze each component
and each connection in the system, and the loads that could be imposed on each
component. Those loads are used to determine the size and shape that each component
will assume. There are the different tubes that need material, diameter
and wall thickness to be determined, and the size of all the threaded connections,
and the design and positioning and fastening of the bellcranks, etc. It's
not simple. Not something that I would feel like spending a couple of days working
on - especially since there doesn't appear to be any benefit to changing
the system. Or do you know of a REAL benefit? (not just an opinion or guess)
Bill C.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269255#269255
Message 9
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| Subject: | Re: Push/pull tubes and rod ends |
Hosey Challis built his 8Th Piet, Challis Chafinch with a push-pull tube that operated
from the stick up to the wing centersection it eliminated the cross control
wires.
This is the Piet that I flew for many years, all worked perfect, is in a Museum
now in England
Pieti Lowell
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269256#269256
Message 10
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| Subject: | Re: Push/pull tubes and rod ends |
The equation you introduced is effective for the pull-out strength of
the threads in a hole. The "(shear load)" you mentioned is the shear
stress that the material can take, not the applied load.
A good (in fact, one of the best) sources for structural analysis is
free:
http://euler9.tripod.com/analysis/asm.html
It's not really for beginners, though, so be careful if this is new to
you. This is reasonably comprehensive.
While the Piet isn't an FAA certified airplane, it often makes sense to
use the certification requirements for determining the loads. Federal
Air Regulations, Part 23, covers this:
http://www.flightsimaviation.com/data/FARS/part_23.html
Control system loads are covered in 23.395 and more to the point in
23.397:
http://www.flightsimaviation.com/data/FARS/part_23-397.html
As you see, the control system doesn't need to be stronger than these
forces applied to the control stick. It's a simple matter to go from
there to the loads in any single part of the system.
Without looking at the system you are designing, but thinking only of
push-pull tubes, it strikes me that the major things to look at are:
a) the end fittings, which can get complicated. Look at the holes, the
pins, the clevis (if any) and the connection to the tube, including any
welds or fasteners, and their holes if there are any.
b) the tension strength of the tube, that is, accounting for any holes
or threads,
c) the compression strength,
d) the Euler buckling strength,
e) and finally the local crippling, sometimes referred to as D/t
crippling.
f) It's also important to make sure that the new system is no more
flexible than the old one. You'll need to know the effective modulus of
elasticity of the cabling, and that often seems to be around 11 x10^6
psi, based upon the nominal area. You can get better data from
MIL-HDBK-5, I think. There might not be much, though, I simply don't
remember. But the 11 msi value is ball-park.
I'm sorry that I don't have a handy link to MIL-HDBK-5H, the best source
for metal data, but after you download a copy, which should be free,
look at the end of Chapter 2 for steel or 3 for aluminum; chapter 2.8 or
3.11. There are handy graphs of element properties for tubes, which
include both forms of buckling. Incidentally, H is the best version. The
newer letters miss some of the data more applicable to general aviation
and are harder to use.
David Paule
----- Original Message -----
From: Michael Perez
To: pietenpol-list@matronics.com
Sent: Saturday, October 24, 2009 1:05 PM
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends
Push/pull tubes are used in all kinds of aircraft safely. All of
which have more aggressive performance then a slow, draggy, 80+ year old
designed Piet. Yet most seem to think to make the switch to push/pull is
a bad idea...why? I know most just get upset because I stray from the
sacred bible of building the Pietenpol...the prints. Yet non have
legitimate reasons for not doing it...at least not any they share. If
you guys have facts for NOT using them, please, do tell. To make a
statement and not back it up is useless.
The Bingelis books talks about aluminum tubes for push/pull...
you know, the books everyone raves over. He also talks about how these
systems MAY weigh less then a cable system with the cables, pulleys,
brackets, shackles, bearings, nicopress fittings, etc.
If you could run a tube from the firewall to the rudder and
support the length along the way with, say bushings, there would be no
flexing/bending, yes?
I don't have the answers...yet, that is why I am here. I am
looking for ANSWERS, not opinion, guesses, or dialog on how this 80 year
old plane built by a guy in his garage can't be improved upon with some
common sense and some homework.
Here is what one engineer sent me:
Pull out load = (1/3)(dia rod)(pi)(shear load)(length of
engagement)
For some generic heavy wall tube from McMaster Carr and a 1/4-28
male thread rod end, I get: 1962 lbs. worse case with .500" thread
engagement, 2944 lbs. with .75" engagement.
The 7X19 SS cable is rated at 1760 lbs. Using the controls in
the Pietenpol, can a person ever pull 1760 lbs. on the cable? If they
could, wouldn't a wood structure fail first...I don't know...like the
elevator itself? Since no one here seems to have heard of a control
cable failure, that must mean no Pietenpol has seen 1760 lbs. of force
on a 1/8" control cable, so what are the REAL loads on this plane and
it's controls? I think people get a little too extreme and have a plane
built for mach 2 when it really only flies at 70 MPH.
HOWEVER, my disclaimer...I have been wrong before and have
abandoned other "great" ideas that I have had, this may yet be another.
But that decision won't be made until I have some facts, and some REAL
numbers.
Anyone have another formula for pull out stress or bolt sheer?
Message 11
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| Subject: | Re: Push/pull tubes and rod ends |
Mike,
I believe the statement you are referring to regarding weight is as follows:
"It is well to reflect on the fact that although individual cables are
lighter then push-pull tubes, the cable systems in high wing aircraft do
require the fabrication and installation of many pulleys, brackets and
guards. As a consequence the cable installation tends to become heavier and
more complex than *you would expect*."
No direct comparison is made to one being heavier than the other. A
nitpicking point I know....
Anywho...if you want a Tony B. statement in support of control cables you
can find it on page 120 of 'The Sportplane Builder' (the blue book):
"I marvel at the genius of the old time aircraft builder. His basic concepts
have hardly been changed or improved. Whatever improvements there have been,
it seems, are mostly in the development of improved designs and
sophisticated materials. The cable-operated control system is a good
example. It's as popular and as useful today as it ever was, and you can
find it in use on the most up-to-date aircraft as well as the oldest
antique. It's quite reasonable to say that using aircraft cables to activate
your controls surfaces gives you the lightest, simplest, safest, most
economical, and most effective way of doing the job ever conceived."
He then talks about cable specs for a paragraph or two. A bit farther down
the page he states:
"The advantages of cables are many. They are light, strong, and flexible.
They do not require line-of-sight routing, and slight deviations to bypass
structural obstacles present no problem. The cables can be deflected by
simple fairleads and even routed around pulleys to change direction. Try
that with a push-pull tube! Since the cable is light in weight, it can be
installed over considerable lengths without intermediate support.
Cable-operated surfaces respond instantly and precisely to cockpit control
movements because they are used in pairs and are stretched to the proper
tension by turnbuckles. This effectively eliminates all play in the control
system."
Etc, etc.
Tony B thinks cables work pretty darn good. So did Bernard Pietenpol, as he
designed his airplane with a cable operated control system, and in all the
years and all the other aircraft he built he apparently didn't see the
benefit to designing a push-pull tube control system for it. I'm not a
betting man, but I would feel confident in wagering that an overwhelming
majority of all of those that successfully built and flew Piets in the past
80 years used a cable control system as well.
I don't think the resistance to your proposed changes is because of some
"stick to the plans, just because" snobbery. I think it is because if you
build to the plans, the airplane will work (and work well). 80 years of
Pietenpol building has shown that to be the case. Are there certain
deficiencies here and there, or areas that can be changed to improve certain
things here and there? Sure, it's not a 100% perfect design. You can emulate
what other builder's have done, or come up with your own solutions. A wider
center section for more fuel in the wing, tilt the seat back for comfort, so
on and so forth. However in this case I don't see the need to "improve" this
area of the design. I can't recall having heard anyone with a properly
constructed flying Pietenpol say that the cable operated control is
deficient in practical application.
You don't have a flying Pietenpol (and neither do I), so we can't speak from
firsthand experience. We can compare it to other types of control systems,
and run the numbers, which is all well and good. But I would look at what
those that have well built and nice flying Pietenpols have to say about it.
What they have built and are successfully and happily flying (a cable
actuated control system) would indicate that it works well. Therefore, I
would also say that I fail to see how you can improve here; it just seems to
be a change for the sake of change. And if that is what you want to do, go
right ahead. It is your airplane, you can do what you would like with it.
Have a good day,
Ryan
On Sat, Oct 24, 2009 at 2:05 PM, Michael Perez <speedbrake@sbcglobal.net>wrote:
> Push/pull tubes are used in all kinds of aircraft safely. All of which have
> more aggressive performance then a slow, draggy, 80+ year old designed Piet.
> Yet most seem to think to make the switch to push/pull is a bad idea...why?
> I know most just get upset because I stray from the sacred bible of building
> the Pietenpol...the prints. Yet non have legitimate reasons for not doing
> it...at least not any they share. If you guys have facts for NOT using
> them, please, do tell. To make a statement and not back it up is useless.
>
> The Bingelis books talks about aluminum tubes for push/pull... you know,
> the books everyone raves over. He also talks about how these systems MAY
> weigh less then a cable system with the cables, pulleys, brackets, shackles,
> bearings, nicopress fittings, etc.
>
> If you could run a tube from the firewall to the rudder and support the
> length along the way with, say bushings, there would be no flexing/bending,
> yes?
>
> I don't have the answers...yet, that is why I am here. I am looking for
> ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built
> by a guy in his garage can't be improved upon with some common sense and
> some homework.
>
> Here is what one engineer sent me:
>
>
> Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement)
>
>
> For some generic heavy wall tube from McMaster Carr and a 1/4-28 male
> thread rod end, I get: 1962 lbs. worse case with .500" thread engagement,
> 2944 lbs. with .75" engagement.
>
>
> The 7X19 SS cable is rated at 1760 lbs. Using the controls in the
> Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could,
> wouldn't a wood structure fail first...I don't know...like the elevator
> itself? Since no one here seems to have heard of a control cable failure,
> that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control
> cable, so what are the REAL loads on this plane and it's controls? I think
> people get a little too extreme and have a plane built for mach 2 when it
> really only flies at 70 MPH.
>
>
> HOWEVER, my disclaimer...I have been wrong before and have abandoned other
> "great" ideas that I have had, this may yet be another. But that decision
> won't be made until I have some facts, and some REAL numbers.
>
>
> Anyone have another formula for pull out stress or bolt sheer?
>
>
> *
>
> *
>
>
Message 12
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| Subject: | Re: Push/pull tubes and rod ends |
Here's a link to some photos of the Challis Chaffinch that Lowell referred to.
http://www.shhas.co.uk/GALLERY_files/photos/Challis%20Chaffinch%20Test%20Flight/image_14.html
The aileron push/pull tube can be seen on the right side. Interesting to note that
it is officially not a Pietenpol Air Camper - it is a Challis Chaffinch. The
builder made a number of visible changes - including the shape of the empennage,
a widened center-section (although the fuel tank appears to be in the fuselage).
Undoubtedly there are other changes that are not visible. I would think
that any builder building their EIGHTH copy of a plane might have a few ideas
about ways they would like to change things.
Bill C.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269260#269260
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| Subject: | Push/pull tubes and rod ends |
Michael,
I'm not an engineer.not even college educated, so I cannot answer, directly,
the question you raise about engineering push tubes.
So what bothers me about this post?
First is an emotional response - that to someone who feels that Mr.
Pientenpol was, ".a guy in his garage." and that you can improve upon his
design with ".some common sense and some homework." I am sure that I'm not
the only one on this list who reveres the designer of this airplane as a
genius! And, since you bring up the "sacred Bible", it is a near religious
experience for me, as I have wanted to build a Pietenpol for over 35 years!
You may as well be saying that Jesus was a fraud, or that my mother wears
combat boots! I'm pretty sure Bernard Pietenpol used both common sense and
homework, along with a wealth of experience and education.
My second response, after spending 30 minutes attaching the hand-hold at the
tail, was the realization that you, nor anyone, can "improve" his design.
All you can do is illustrate the genius and flexibility of a fantastic set
of plans. Plans that allow you to make many variations to suit your
personality (or cover your mistakes!). Have I made changes to that design?
ABSOLUTELY! Including push rods similar to, and inspired by, Peter in
Australia. But I am reminded of a friend of mine who lives in the woods of
Montana, who insists on a family prayer every time they cut down a tree. I
am grateful to the Man who designed and built this little plane, and know
that I cannot improve it.only personalize it!
Just a suggestion, as I am sure you are a decent person and obviously a
skilled woodworker capable of building a show piece and eventually
hob-nobbing with all the Pieters, a simple, "Thanks, Jack, I'll take that
into consideration," would have been far more 'politic.'
I look forward to the day than you & I can toast a beer (Pale Ale, of
course) to this incredible journey made possible by one man.
Gary Boothe
Cool, Ca.
Pietenpol
WW Corvair Conversion, mounted
Tail done, Fuselage on gear
(15 ribs down.)
_____
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael
Perez
Sent: Saturday, October 24, 2009 12:06 PM
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends
Push/pull tubes are used in all kinds of aircraft safely. All of which have
more aggressive performance then a slow, draggy, 80+ year old designed Piet.
Yet most seem to think to make the switch to push/pull is a bad idea...why?
I know most just get upset because I stray from the sacred bible of building
the Pietenpol...the prints. Yet non have legitimate reasons for not doing
it...at least not any they share. If you guys have facts for NOT using
them, please, do tell. To make a statement and not back it up is useless.
The Bingelis books talks about aluminum tubes for push/pull... you know, the
books everyone raves over. He also talks about how these systems MAY weigh
less then a cable system with the cables, pulleys, brackets, shackles,
bearings, nicopress fittings, etc.
If you could run a tube from the firewall to the rudder and support the
length along the way with, say bushings, there would be no flexing/bending,
yes?
I don't have the answers...yet, that is why I am here. I am looking for
ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built
by a guy in his garage can't be improved upon with some common sense and
some homework.
Here is what one engineer sent me:
Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement)
For some generic heavy wall tube from McMaster Carr and a 1/4-28 male thread
rod end, I get: 1962 lbs. worse case with .500" thread engagement, 2944
lbs. with .75" engagement.
The 7X19 SS cable is rated at 1760 lbs. Using the controls in the
Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could,
wouldn't a wood structure fail first...I don't know...like the elevator
itself? Since no one here seems to have heard of a control cable failure,
that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control
cable, so what are the REAL loads on this plane and it's controls? I think
people get a little too extreme and have a plane built for mach 2 when it
really only flies at 70 MPH.
HOWEVER, my disclaimer...I have been wrong before and have abandoned other
"great" ideas that I have had, this may yet be another. But that decision
won't be made until I have some facts, and some REAL numbers.
Anyone have another formula for pull out stress or bolt sheer?
Message 14
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| Subject: | Re: Push/pull tubes and rod ends |
Historically, the major benefit to a push rod control system compared to a
cable control system is that the push rod system has lower friction since
there's no need for the cable tension in the cable system. No preload
tension, and you've eliminated a major part of the friction. Also,
typically, they have rod-end or other bearings for the joints, again with
lower friction.
Another benefit is that they can be stiffer, but that's generally only
beneficial for larger, faster aircraft.
Push-rod systems are almost always heavier.
There's an often unanticipated benefit of building per the plans: it reduces
the chances of inadvertently designing in some unanticipated failure mode.
So if weight or simplicity or safety matters, follow the plans.
David Paule
----- Original Message -----
From: "Bill Church" <billspiet@sympatico.ca>
Sent: Saturday, October 24, 2009 2:55 PM
Subject: Pietenpol-List: Re: Push/pull tubes and rod ends
> <billspiet@sympatico.ca>
>
> Whoa - what comments are you responding to Mike?
> The only reply to your post that I saw was from Jack, and all I saw in his
> reply were sound reasons explaining why the cables are a better system FOR
> THIS AIRPLANE. As he stated, the geometry of the Air Camper will result in
> a heavier and more expensive linkage as compared to the cables. Tony
> Bingelis says that push/pull tubes MAY weigh less than a cable system.
> That will depend on the layout of the airplane, and in this case, the
> control system has to go under the seat, and then get back up into
> alignment with the elevators and rudder. Cables can change direction with
> the addition of a simple pulley, where push/pull tubes will require
> bellcranks - which one do you think is heavier? It is not possible to run
> a tube straight from the firewall to the rudder in this airplane, unless
> you have a properly sized and located hole in your torso for the tube to
> pass through. Also, in THIS airplane, the elevators are separate entities,
> so you would either have to redesign them so that !
> they are tied together, or run two push/pull tubes for the elevators.
> To quote your original post "I'm all about saving weight on my plane".
> Jack's reply explained that the push/pull system will end up being heavier
> than the cable system. So what IS the motivation to change to the
> push/pull system?
>
> Regarding your request for a formula, the thing to keep in mind is that in
> designing a mechanism like a push/pull system, you need to analyze each
> component and each connection in the system, and the loads that could be
> imposed on each component. Those loads are used to determine the size and
> shape that each component will assume. There are the different tubes that
> need material, diameter and wall thickness to be determined, and the size
> of all the threaded connections, and the design and positioning and
> fastening of the bellcranks, etc. It's not simple. Not something that I
> would feel like spending a couple of days working on - especially since
> there doesn't appear to be any benefit to changing the system. Or do you
> know of a REAL benefit? (not just an opinion or guess)
>
> Bill C.
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=269255#269255
>
>
>
Message 15
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| Subject: | Push/pull tubes and rod ends |
Michael,
I got behind in answering emails because I had to watch my alma mater
(Tennessee) almost beat the #1 team in the nation (Alabama). Final score,
Alabama 12, Tennessee 10 but it wasn't decided until Bama blocked a
Tennessee field goal with 4 seconds left in the game. So Bill Church
basically said the same thing I was going to say. Here is what I had
started to write before the game.
"Michael, you can certainly put a pushrod control system in. But the design
geometry is much different than the geometry that the Pietenpol has. For
example, the elevators of a Pietenpol are not connected to each other. Each
elevator has its own pair of cables to deflect it. If you run pushrods, you
will either have to find a way to connect the elevators, or run individual
pushrods to each side. More modern airplanes using pushrods are designed
with a single elevator horn internal to the fuselage, requiring a single
pushrod. They also typically have a control system that allows the pushrod
which connects the front and rear sticks to run under the floorboard so it
can then connect behind the cockpit with the psuhrod which runs aft to the
elevators. You can accomplish all this with your Pietenpol, but it will not
be easy, or cheap, or simple. The cable system is light, simple and
well-proven. You are attempting to solve a problem where no problem exists.
You are looking to "improve" the design. Where will the improvement be if
it costs more and weighs more and does no better job?"
I'm certainly no purist, and in building my Pietenpol I made a number of
changes to the "pure" Pietenpol design, such as widening the fuselage by 1"
(bad idea), widening the centersection by 6" (good idea), changing the
design of the lift strut fittings to incorporate the steel band that runs
under the belly (good idea), adding a baggage compartment behind the
firewall (good idea), adding a trim system modeled after Mike Cuy's (good
idea), incorporating the heat muffs into construction of the exhaust pipes
(bad idea). I'm all for making changes that intend to serve a purpose. The
airplane is yours to do as you please, but there are some changes that
really need to be well engineered. I'm a licensed professional engineer who
worked many years in the aircraft industry (my first job out of college was
working on the design team for the F-16), and I wouldn't want to tackle
redesigning the control system of the Pietenpol. I just don't see what
purpose such a change might fulfill, if it will make it heavier, more
complicated and more expensive (those rod end bearings are not cheap).
If you really intend to do this, the way you calculate the area of the
pushrod tube is to use the formula : A = p(Doutside2 - Dinside2)/4. While
you're at it, calculate the weight of the tube, then compare to the weight
of an equivalent length of steel cable. Be sure to add the weight of the
end fitting for the tube, and the rod end bearing at each end, plus all the
bellcranks that will be required, as well as the brackets and bushings to
support those bellcranks.
As Bill Stout, designer of the Ford trimotor is supposed to have said:
"Simplicate and Add Lightness"
Jack Phillips
NX899JP
Raleigh, NC
_____
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael
Perez
Sent: Saturday, October 24, 2009 3:06 PM
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends
Push/pull tubes are used in all kinds of aircraft safely. All of which have
more aggressive performance then a slow, draggy, 80+ year old designed Piet.
Yet most seem to think to make the switch to push/pull is a bad idea...why?
I know most just get upset because I stray from the sacred bible of building
the Pietenpol...the prints. Yet non have legitimate reasons for not doing
it...at least not any they share. If you guys have facts for NOT using
them, please, do tell. To make a statement and not back it up is useless.
The Bingelis books talks about aluminum tubes for push/pull... you know, the
books everyone raves over. He also talks about how these systems MAY weigh
less then a cable system with the cables, pulleys, brackets, shackles,
bearings, nicopress fittings, etc.
If you could run a tube from the firewall to the rudder and support the
length along the way with, say bushings, there would be no flexing/bending,
yes?
I don't have the answers...yet, that is why I am here. I am looking for
ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built
by a guy in his garage can't be improved upon with some common sense and
some homework.
Here is what one engineer sent me:
Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement)
For some generic heavy wall tube from McMaster Carr and a 1/4-28 male thread
rod end, I get: 1962 lbs. worse case with .500" thread engagement, 2944
lbs. with .75" engagement.
The 7X19 SS cable is rated at 1760 lbs. Using the controls in the
Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could,
wouldn't a wood structure fail first...I don't know...like the elevator
itself? Since no one here seems to have heard of a control cable failure,
that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control
cable, so what are the REAL loads on this plane and it's controls? I think
people get a little too extreme and have a plane built for mach 2 when it
really only flies at 70 MPH.
HOWEVER, my disclaimer...I have been wrong before and have abandoned other
"great" ideas that I have had, this may yet be another. But that decision
won't be made until I have some facts, and some REAL numbers.
Anyone have another formula for pull out stress or bolt sheer?
Message 16
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| Subject: | Re: Push/pull tubes and rod ends |
Jack- BTW you did a heck of a job on the Fly-by-wire system on the F-16, but what
was with that second arm rest!? ;-)
Just to add my two cents: building a Pietenpol reminds me of the friends I have
refurbishing cars. Some refurbish to classic original condition (my favorite),
and some take a beautiful vintage automobile and refurbish it into a streetrod.
Sure, a Model-T ford or a 57' chevy with a 400hp V-8, glass pack exhausts
and racing wheels has a lot more power, but to me losses something in translation.
I don't think the term purist need have a negative connotation. Rather, it
is a tribute to the originator of this design, who through his brilliance and
adventurous spirit, created a successful aircraft design and unselfishly authorized
others to share in it. It's challenge enough crafting a Piet with all
the power tools available today, the Internet, and live samples at Brodhead ever
year (thanks guys), so save for the small changes like Jack mentions, I always
challenge myself to stick as close as possible to the original, reproduction
being the highest form of flattery, but thats just me.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269277#269277
Message 17
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| Subject: | Re: Push/pull tubes and rod ends |
Second arm rest? Which side? Right or left? The original versions
(F-16A's) had a fixed side stick that didn't move at all - just sensed
forces. Too many pilots had trouble getting used to that so they changed it
to have a slight amount of movement, but still it communicated with the
Flight Control Computer through 4 load cells at the base of the stick which
sensed the force the pilot was applying to the stick. There was an armrest
behind the stick to support the pilot's arm during high G maneuvers so the
g-forces wouldn't make him pull even harder on the stick. There was talk
about providing a second armrest on the left side to support the throttle
arm for the same reason, but that was not done before I left.
Jack
-----Original Message-----
From: owner-pietenpol-list-server@matronics.com
[mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of chase143
Sent: Saturday, October 24, 2009 8:26 PM
Subject: Pietenpol-List: Re: Push/pull tubes and rod ends
Jack- BTW you did a heck of a job on the Fly-by-wire system on the F-16, but
what was with that second arm rest!? ;-)
Just to add my two cents: building a Pietenpol reminds me of the friends I
have refurbishing cars. Some refurbish to classic original condition (my
favorite), and some take a beautiful vintage automobile and refurbish it
into a streetrod. Sure, a Model-T ford or a 57' chevy with a 400hp V-8,
glass pack exhausts and racing wheels has a lot more power, but to me losses
something in translation. I don't think the term purist need have a negative
connotation. Rather, it is a tribute to the originator of this design, who
through his brilliance and adventurous spirit, created a successful aircraft
design and unselfishly authorized others to share in it. It's challenge
enough crafting a Piet with all the power tools available today, the
Internet, and live samples at Brodhead ever year (thanks guys), so save for
the small changes like Jack mentions, I always challenge myself to stick as
close as possible to the original, reproduction being the highest form of
flattery, but thats jus!
t me.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269277#269277
Message 18
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| Subject: | Re: Push/pull tubes and rod ends |
You might also note that the airfoil is a 4412., shortened 2 Ft and with an 85
HP Cont it could cruse 105 plus. The center- section is 3 Ft. wide.
Pieti Lowell
Bill Church wrote:
> Here's a link to some photos of the Challis Chaffinch that Lowell referred to.
>
> http://www.shhas.co.uk/GALLERY_files/photos/Challis%20Chaffinch%20Test%20Flight/image_14.html
>
> The aileron push/pull tube can be seen on the right side. Interesting to note
that it is officially not a Pietenpol Air Camper - it is a Challis Chaffinch.
The builder made a number of visible changes - including the shape of the empennage,
a widened center-section (although the fuel tank appears to be in the
fuselage). Undoubtedly there are other changes that are not visible. I would think
that any builder building their EIGHTH copy of a plane might have a few ideas
about ways they would like to change things.
>
> Bill C.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=269291#269291
Message 19
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| Subject: | Re: Push/pull tubes and rod ends |
As Michael has stated that he wants to thread the tube no one
so far has considered what that means.
The depth of those threads eliminates that much of the wall thickness
from the overall thickness of the tube for stress
calculations. So to get the strength you want you'r egoing to
have to have wall thickness to handle that PLUS the wall
thickness to take the threads. Now you've got this fat tube
half of which is useless weight unless you can lathe that
long length down. This assumes the threads are on the
outside. However, if they happen to be on the inside........
I have a tube joining my throttles that's off some I-know-not-
what, expensive military hardware. It's 1" dia and VERY thin
wall for most of it's length. If I put helium in it it would float
away. Then it narrows down to take a 1/4" threaded ball end which is
inside a 3/8" dia. weldment at the end. So tubes
can be made light but then KISS disappears from the
equation. :-)
Clif
"Creativity is allowing yourself to make mistakes.
Art is knowing which ones to keep." (Scott Adams)
Michael,
If you really intend to do this, the way you calculate the area of the
pushrod tube is to use the formula : A = p(Doutside2 - Dinside2)/4.
While you're at it, calculate the weight of the tube, then compare to
the weight of an equivalent length of steel cable. Be sure to add the
weight of the end fitting for the tube, and the rod end bearing at each
end, plus all the bellcranks that will be required, as well as the
brackets and bushings to support those bellcranks.
As Bill Stout, designer of the Ford trimotor is supposed to have said:
"Simplicate and Add Lightness"
Jack Phillips
Message 20
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| Subject: | Re: Push/pull tubes and rod ends |
Ask a Grega builder, I think it uses a tube.
Russell
On Sat, Oct 24, 2009 at 12:18 PM, Jack Phillips <pietflyr@bellsouth.net>wro
te:
> Are you planning on re-designing the entire elevator control system with
> pushrods, requiring a pushrod attached to each elevator, a pushrod from t
he
> bellcrank to the rear stick and a pushrod between sticks? It probably wi
ll
> require an additional pushrod and bellcrank to enable you to pass underne
ath
> the rear seat (where the cable from the stick to the bellcrank makes a be
nd,
> with the plans showing it just passing through a hole drilled in the wood
'
> I added a pulley here).
>
>
> If so, figure out the yield strength of whatever alloy of aluminum you
> intend to use, then determine what area will be required to withstand the
> load (1760 lbs, if you want to equal the cable strength) without exceedin
g
> that stress level. Use the formula Stress = Load divided by Area (s
> P/A), and solve for area (A) since you know the load (P = 1760) and yo
u
> know the stress (s = yield strength of your alloy times whatever safety
> factor you feel like throwing in). Once you know the area, then determin
e
> what wall thickness and tube diameter will produce the required area. Of
> course, there will be machined fittings required on each end of the
> pushrods, and rod end bearings to reduce the amount of slop.
>
>
> As an engineer, I have to wonder why are you doing this? The cables work
> well. Any arrangement with pushrods is going to be much more complicated
,
> due to the geometry of the airplane. Pushrods will end up being far more
> expensive and heavier. I don=92t understand what advantage you are tryin
g to
> achieve here, other than to be =93different=94. You could accomplish tha
t by
> painting it Pink.
>
>
> Jack Phillips
>
> NX899JP
>
> Raleigh, NC
>
> Enjoying a rainy day by building the wings of my RV-10 in the basement
>
>
> ------------------------------
>
> *From:* owner-pietenpol-list-server@matronics.com [mailto:
> owner-pietenpol-list-server@matronics.com] *On Behalf Of *Michael Perez
> *Sent:* Saturday, October 24, 2009 10:52 AM
> *To:* pietenpol-list@matronics.com
> *Subject:* Pietenpol-List: Push/pull tubes and rod ends
>
>
> I am trying to figure out what size and material tube to use to go from t
he
> control stick to the elevator bell crank. I see in the Bingelis books, h
e
> talks about heavy wall aluminum threaded tubing. Since I am all about
> saving weight on my plane, I would prefer aluminum. The plans call for 1/
8"
> cable, which is rated between 1760 and 2100 lbs. I would hope that a
> tube/rod end combination that rated at these numbers would work. So, I a
m
> trying to figure out what size tube and threaded rod end will give me the
> 1760-2100 lb. rating. If someone can prvide a usable formula, I may be
> able to figure it out myself.
>
>
> Thanks group.
>
> * *
>
> * *
>
> **
>
> **
>
> **
>
> *http://www.matronics.com/Navigator?Pietenpol-List*
>
> **
>
> **
>
> *http://forums.matronics.com*
>
> **
>
> **
>
> *http://www.matronics.com/contribution*
>
> * *
>
> *
>
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