| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 282.1 | combination of closed loop with conventional | SPKALI::THOMAS | | Thu Apr 02 1987 10:52 | 14 |
|
Verry good picture, but a suggestion is that if possible
you want the two wires from the rudder to be attached to a
180 degree bell crank. The a stiff rod connection from this
bell crank to the servo arm. the reasoning is that you
eliminate and adverse strain being put of the servo gear
train. This system is also typical on most pattern birds.
regardless how sloppy a system is set up you always get a
positive restonce from the pull of the servo. Since with
this system you have a pull on both sides the responce is
positive on both sides. Slop is a factor that you need to
be sure that you eliminate.
Tom
|
| 282.2 | More on closed loops | NOGOV::BODDINGTON | Andrew Boddington, RE02 F/M8, 830-4557 | Thu Apr 02 1987 11:17 | 9 |
| I have used the closed loop connection system on a couple of 1/6th
scale WW1 aircraft, they look realistic and work well. The wire
used is fishing trace line (wire with plastic coating) with the
ends being secured with a small piece of crimped aluminium tubing.
I somewhat disagree with .8 - I have always understood that the
closed loop system puts less strain on a servo gear train than a
push-rod. The reason being that the strain is applied alternately
on both sides of the servo rather than always the same side.
|
| 282.3 | Spring is here | TONTO::SCHRADER | Share and Enjoy! | Thu Apr 02 1987 16:14 | 7 |
| RE: .8, .9
How about a small spring attached at the center of the servo
arm/wheel and a point forward of the servo to take the side force
off the the servo output bearing???
GES
|
| 282.4 | avoiding slop | BASHER::DAY | I might as well be parking cars | Fri Apr 03 1987 10:03 | 15 |
|
re .8
I've seen that system used,but you will
introduce a certain amount of free play with the servo arm
to bell crank linkage.... whereas a properly set up loop
will have none.
bob
|
| 282.5 | closed loop linkages | ROYCE::HORNBY | | Fri Apr 03 1987 12:03 | 68 |
|
For Information...
Some Thoughts on close Loop... for reference see back to 81.6->>
Standard arrangement of close loop using nylon coated fishing
wire trace. Watch out for symetry which will help to minimise servo
strain in both pivot point (*) and length of arc
Fig 1
+-----------//------+ --+
+-----|-+ | Rudder OR \
| * | *====== *=====
+-----|-+ | (or elevator) /
+-----------//------+ --+
------------------------------------------------------------------
---+ ---+ Differing radius
BUT NOT | (pivot off centre) *==== to servo
------- *====== ---+ connection
|
---+
To reduce strain some additional precutions can be taken.
Fig 2
+--/\---
+-----|-+
| * | Where --/\-- is made from thin piano wire
+-----|-+ say 20SWG (or AWG)
+--/\---
__ /\ _
detail L____/ \____+----------
Fig 3
+______+--------//
+----|-+ |
| * | * where a pushrod is used
+------+ | to a separatley pivoted arm
+--------// In this case additional tension
can be placed on the C.L.
Fig 4
(this one I'm not so sure about ...anyone like to comment)
+------//
+----|-+
+-/\/\/\-------* | Spring used to "take the strain"
+----|-+ Ref note 81.??
+------//
Comments anyone...!!
Trev
|
| 282.6 | my pennies worth | BASHER::DAY | I might as well be parking cars | Fri Apr 03 1987 12:49 | 49 |
| re .0
---+ ---+ Differing radius
BUT NOT | (pivot off centre) *==== to servo
------- *====== ---+ connection
|
---+
This is VERY important on a
loop system.I found out the
hard way on my Acro Wot.. The
wire not being pulled goes baggy,
and rudder flaps about.
Fig 4
(this one I'm not so sure about ...anyone like to comment)
+------//
+----|-+
+-/\/\/\-------* | Spring used to "take the strain"
+----|-+ Ref note 81.??
+------//
If you use a decent ballrace servo and ensure that the wire
is only tight enough to keep the rudder in position this
shouldn't be necessary...
The wire can be run through a tube to acomodate strange shape
fuzs..
bob
|
| 282.7 | Steel wires instead of nylon | BRSRHM::CLEMENT | | Tue May 07 1991 13:25 | 22 |
|
hello all
I am a belgian glider designer, builder and pilot !!
Personnaly, I use closed loops not only for the rudder but also
for the elevator ( T shape, Vshape or + shape). I use very thin steel
wires (about 1/10 mm diameter). I don't like nylon wires because
they don't resist to UV radiations, the length varies with temperature
and with the tension you apply. I do that from about 5 years without
any problems. The advantage for me are that there is no play and
also that the weight is much less than the classical rod! In my
models, the steel wires are free inside the body of the glider and
only guided a few centimeters, close to the servo. With steel, it
is important to be sure that the wires are NOT able to enter in
contact with each other in order to avoid radio interferences
Philippe CLEMENT
the highest flyer
|
| 282.8 | Details on the ends please | KAY::FISHER | Stop and smell the balsa. | Wed May 08 1991 12:01 | 12 |
| > <<< Note 282.7 by BRSRHM::CLEMENT >>>
> -< Steel wires instead of nylon >-
How do you fasten the ends of your wires on the servo horns?
Do you crimp them with brass tubing?
What do you use for rudder horns?
Bye --+--
Kay R. Fisher |
---------------O---------------
################################################################################
|
| 282.9 | pull-pull excerpts from 399.* | ABACUS::RYDER | perpetually the bewildered beginner | Sun May 12 1991 10:46 | 174 |
| The following came from the generic glider topic. Because many of the
entries covered more than one subtopic per entry, a simple move of the
entry to this string would not have been satisfactory. So most of the
following are excerpts, not complete entries.
Note 399.256 by ELMAGO::TTOMBAUGH 20-DEC-1989 -< Foam & Fiberglass revisited >-
My MTS bird ....... The only "exotic"
features will be Kevlar pull-pull cord for rudder actuation and
carbon fiber rods for both stab pivot and wing rods. These also
work well on my Pulsar, but can't be justified on a cost basis.
Note 399.435 by NEWOA::NEALE 2-NOV-1990 -< Geometry of closed loop controls >-
I have a question about the use of closed loop rudder controls, as used
in the Osprey. The books tell me that you should always set up the
servo arms and control horns to get the correct throw of the control
surface with the maximum servo travel, so as to obtain the most
accurate control from the servo. The use of rate switches is a
"second-best" because you lose servo definition. However, with a closed
loop system you need to set up the geometry so that servo arm
connections and control horn connections are the same distance from
their respective pivot points, to avoid the cables loosening/tightening
as the servo moves. But this means that you must restrict the servo
travel using rate switches, in order to set the maximum control surface
travel, as servo arms and control surface will turn through the same
angle.
I guess that the geometrical requirements are the most important (and
anyway, with my current level of flying skill I don't suppose that
servo positional definition makes much difference!) but I am curious
from a theoretical point of view how you reconcile these two opposing
aims. Anyone have any comments?
Note 399.436 by ELMAGO::TTOMBAUGH 2-NOV-1990 -< Of flaperons & closed loop rudders >-
I'm using closed loop rudder control with kevlar string on a ~ 120"
sailplane and it is the best rudder system I've ever tried.
Don't worry about the theory of angles and all that. Just
keep as straight a line as possible between the servo arm and rudder
horn, make sure the cable isn't rubbing on anything, or sleeve it
if it is, set the string tension equal on both sides of the servo
arm when the servo is in neutral, and go for it. Of course
the string will go slack on one side when turning. So what?
Trying to avoid this won't buy you a thing except wasted time.
Try it, you'll like it.
Note 399.437 by HPSRAD::AJAI 2-NOV-1990 -< An off the cuff remark? >-
Couldn't help noticing, that if the string goes slack on one side, you
will have "backlash" or sloppy/floppy controls, as the surface won't
respond going the otherway until the slack is taken up.
Then again, the air pressure on the surface would help move the control
surface until the slack is gone from the other side.
Note 399.438 by ZENDIA::REITH 2-NOV-1990 -< I'm a believer >-
I had this system on my first Panic fuselage. The big problem I ran
into was that the edges of my exit guide tubes weren't as smooth as
they should have been and this chewwed on the Kevlar lines over time.
When I built the second/lighter fuselage, I went with light wire cables
to help eliminate the fraying problem. Pull-pull is great and the slack
is minimal and taken up by ANY air pressure
Note 399.440 by ELMAGO::TTOMBAUGH 2-NOV-1990 -< Slack...but not slack-jawed >-
My statement about slackness has been bothering me all morning while
I was off doing other things. I didn't mean to imply that the slack
side of the line was so loose that it was lying on the bottom of
the fuselage 8^), I meant that it felt looser than the tight side
when plucked with the finger. This much slack doesn't cause any
slop in the controls. The Goldberg pull-pull set comes with outer
ny-rods and metal ferrules to slip over the end of the rods to prevent
fraying of the kevlar. The eyelets that interface between the kevlar
and the control horns are larger than necessary though, creating
a rather clunky appearance. Next time I'll engineer my own setup
and do away with the eyelets.
Note 399.574 by ELMAGO::TTOMBAUGH 8-MAR-1991 -< Kevlar pull-pull cord in a Chuperosa >-
Al Ryder contacted me off-line to ask about the methods I used to
install pull-pull cables in my Chup HLG. I'll answer here as it
may be useful to a wider audience, and also I can't connect to
Al's node right now.
I used the kevlar cord that comes in one of the Sullivan or Goldberg
packages. I glued ~ 1" lengths of the small diameter yellow nylon
guide tube, supplied in the Chup kit, inplace to serve as lead-throughs
whereever the cord passed through the bulkheads. I also glued two
pieces to the rear longerons where the cord exits the fuselage.
I threaded the cord through the tubing and got all the
lengths,clevises,etc. adjusted before covering. This is a pretty
straight-forward job, and to save weight I don't use adjustable
clevises at either end. Just stick the kevlar cord into the clevis,
push the end of a toothpick tightly into the clevis from the front,
hit it with a drop of instant CA, then cut the excess length of
toothpick off.
If you're using the vinyl coated kevlar then you don't need the
lead-through tubing in the fuselage, except at the rear exit points.
In a narrow fuselage such as the Chup, it's usually easier to mount
the rudder servo ahead of the elev. servo. and have both cords pass
by the elev. servo, keeping the elev. cable in the center.
In general, kevlar cord works much better than 1/32" wire cable
in pull-pull applications, especially in tight installations such
as the Chup. Much more forgiving as to routing, flex, binding, etc.
$ 7.00 for 20 ft. of the 85 lb. test vinyl coated kevlar cord from
Aerospace Composite Supply is the cheapest way to go.
Note 399.575 by TLE::SASAKI 8-MAR-1991 -< Have you guys tried Spectra? >-
You might try spectra in pull-pull cables. Spectra is a long chain
polyethylene that has similar characteristics to kevlar, but with two
distinct advantages:
o Spectra is slippery while Kevlar is highly abrasive.
o Spectra doesn't deteriorate as quickly with exposure to ultra-violet
light as Kevlar does.
Braided spectra can be purchased from kite stores. The last I checked
you could buy 135 feet of 80 pound for less than $15.
Note 399.576 by ZENDIA::REITH 8-MAR-1991 -< I've had the uncoated kevlar fray on my Panic >-
the only concern/question I have is if it stretches.
The uncoated kevlar tends to fray in normal use (rubbing over time
produces a fuzzball) I had given up on it and gone over to fishing
leader (wire). Haven't seen much coated kevlar out east yet.
Keep contributing Marty, you've got different sources than many of us
(guess it's time for a road trip to the kite store ;^)
Note 399.577 by ELMAGO::TTOMBAUGH 8-MAR-1991 -< Worth looking into >-
I've never had problems with kevlar fraying as long as it isn't
allowed to rub against anything. The coated version eliminates that
problem.
I sent for a catalog from the kite store in Colo. that Marty gave
the address for. Haven't received it yet.
If Spectra is made out of polypropylene fibers, rather than
polyethelene, then it should work very well. They use polypropylene
tow lines in full scale soaring and it doesn't stretch, abrade.
Polyethelene sounds ok though, if CA glue will stick to it and it
is available in small diameters, ~ .050-.060 ".
Note 399.578 by TLE::SASAKI 8-MAR-1991 -< Spectra stretchess less than Kevlar... >-
Spectra is stronger in tension than Kevlar (for a given weight) and it
either has the same stretch characteristics as Kevlar (spectra 900) or
stretches less (spectra 1000). Now that Terry brings it up, I'm not
sure if it is a polyethelene or a polypropylene. CA glue does stick to
it, although I'm not sure how good the bond is.
I'll measure the diameter tonight, if I remember. The fibers are
smaller in diameter than Kevlar, at least in the braided state, ie, a
150 pound piece of Kevlar is larger in diameter than a 150 pound piece
of Spectra.
Note 399.639 by ELMAGO::TTOMBAUGH 2-APR-1991 -< RCSD...good info >-
The April issue of RCSD is a goldmine of info.
Bob Champines' article on making pull-pull controls for stabs has
saved me a lot of work. I will definitely use his T-tail scheme
on the Legend. I need to find a local source for small pulleys,
but this is an ideal application for the vinyl coated kevlar cord.
|
| 282.13 | Kevlar cord | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Mon Jul 01 1991 12:42 | 4 |
| Vinyl coated kevlar cord---Aerospace Composite Products, Irvine,
Ca.
.038" and .058" diameter. ~$9 per 20 ft.
|
| 282.14 | | SA1794::TENEROWICZT | | Mon Jul 01 1991 12:58 | 6 |
| Thank's Terry, I was just about to do a search when I logged in and
found your reply. Is 20' a minimum length or can you but it on a
roll? Also, do you ahve any ideas on the strength of each size?
Tom
|
| 282.15 | Kevlar tensile strengths | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Mon Jul 01 1991 13:16 | 6 |
| The ACP catalog only lists it in 20 ft. lengths, but they're pretty
reasonable folks to deal with and might cut you a longer piece.
.038" = 85 lb. .058" = 215 lb.
Terry
|
| 282.16 | | TLE::SASAKI | Marty Sasaki ZK02-3N30 381-0151 | Mon Jul 01 1991 15:23 | 4 |
| If you don't need the coating, buy the kevlar from a kite store. Kevlar
in 100 lb breaking strength costs around $20 for 300 feet...
Marty Sasaki
|
| 282.17 | | SA1794::TENEROWICZT | | Mon Jul 01 1991 15:58 | 13 |
| Thank's Marty, But I'm really interested in getting the one with the
coating. I have Kevlar presently on the rudder of the Calypso and
it is exhibiting the "fraying" that's been talked about. I plan to
use the coated kevlar on the LA-1 I'm in the process of finishing
and seeing as it will be on the rudder and the elevator I want the
added protection that the coated Kevlar will give me. I've actually
already ordered two packages of the .038 sized coated kevlar from
Aerosapce Composite Products of Irvine Ca. (714)250-1107. Price
is 5.00 for 7 meters of the kevlar. I should have it thursday or
friday.
Tom
|
| 282.10 | pull-pull homework documentation | ABACUS::RYDER | perpetually the bewildered beginner | Fri Jul 26 1991 11:06 | 141 |
| This note documents my homework in putting pull-pull linkage on both
controls of a hand-launch glider. My reasons for changing the design
from push-pull to pull-pull were: 10% to keep the tail weight down,
10% to correct an elevator problem observed by Terry Sweeney, 5% to
reduce drag (questionable), and 75% because I felt like it and wanted
the experience. The Chuperosa specific aspects will appear in another
note; this note is generic to any extremely light weight plane except
that the pulley information below is applicable mostly to mid-fin
flying stabs.
Cable material: (linear densities are in ounces per inch)
---------------
density
Steel rope:
0.032" diameter (part of Sullivan #507 push-pull kit) 0.00270 oz/inch
0.012" [steel] diameter, plastic coated fishing leader 0.00065
" " " , plastic melted off, estimated 0.0004
Steel rod: (applicable for straight pulls without bends)
0.015" diameter music wire 0.0008
Non-metalic: (excluding any guide tubing sold with it)
Kevlar, coated, 100#, (Sullivan #521 pull-pull kit) 0.00036
Dacron(?), Sig #507 1/2 A control line 0.00009
Spectra, 100# braided kite string 0.00024
There are arguments pro and con for each of these alternatives, but it
looks like weight is not one of the significant factors. The heaviest
would weigh only 0.03 ounces at most, even in a large glider.
Electrical conductivity and its impact on antenna efficiency might be
more important, but I have no hard data. Jim Reith has observed
stretch in Dacron lines, so the Kevlar and Spectra lines would be the
choice if procurement is reasonable; the price per plane is zilch; the
price per package isn't. Various people have told me that each is
subject to abrasion. I decided to use Spectra.
I believe Spectra is a polyethylene. It is very slippery; a taughtline
hitch wouldn't hold, even when soaked with CA. A bowline with CA does
seem OK, but I don't have a duration test yet.
Cable sheath/guide tubing:
--------------------------
Dunkin Doughnut coffee swizzles split into two 0.0011 oz/inch
Tobin coffee swizzles (~ 1/8th in. diameter) 0.0015
Cheap plastic soda straws ("Unique"; ~3/16ths) 0.002
Chuperosa kit antenna tube 0.0061
Yellow sheath from a Sullivan #507 pushrod system 0.0017
Red (5/32) sheath from a Sullivan #521 pull-pull system 0.0060
Heat shrink tubing, ICO-RALLY HEATRAX #8501, 1/16 id 0.0018
The yellow sheath is too small for reasonable use compared to the
straws and swizzles. The heat-shrink tubing doesn't seem right for
guiding a moving string. I used the swivels.
Cable attachment/adjustment components and other hardware:
----------------------------------------------------------
ounces
Nylon clevis; C.G. #202 (takes a 2-56 thread) 0.0108
Steel clevis; Sullivan #507 kit item; 2-56 0.0317
Modified Nylon horn; Dubro #107 cut down drastically 0.0094
Eye bolts; 2-56; in the Sullivan #521 pull-pull system 0.0244
Steel nuts; 2-56; in the Sullivan #521 pull-pull system 0.0062
Nylon nuts; 2-56 0.0011
Nylon machine screws; 2-56 x 1 inch 0.0027
Threaded brass tubes; 2-56; (Sullivan #521 system) 0.0207
Threaded brass adapter; 2-56; (DuBro?) 0.026
Crimping thimble; (Sullivan #521 system) 0.016
Pulleys; 0.090 thick; d'mtrs 0.5, 0.3, 0.094; Delrin 0.0108
Brass tubing; 1/16th id, 3/32 od; 0.0163 oz/in
Pulley axles; 1/8th inch long 0.002
Elevator "rod" connection; 1/2 inch long 0.008
Steel rod; 1/16th music wire; 0.014 oz/in
Elevator rod; 2.25 inches long 0.031
Small drop of solder (such precise science!) 0.005
CA in a bowline knot in Spectra (more science) 0.0003
The Nylon clevis is a winner, and if you don't need adjustability,
Terry Tombaugh's jammed and CA'ed toothpick trick would seem perfect.
I tied the line to the control horn and used the eyebolts at the servo,
but next time I'll use the Sullivan threaded brass tubing to avoid the
mechanical clearance problems of the eyes in a small glider. In a big
glider it wouldn't matter.
Control horns are not created equal. The Dubro #107 set of two has a
left one and a right one; the holes line up when they are used as pairs
in a pull-pull situation. Another brand has two identical horns in the
package, so the holes don't line up. The article in the Sept '91 MAN
missed this point as well as several other points. For drag reduction
I cut down the DuBro horn to only one hole; the spacing happened to
match the arm on my Airtronics 94501 servo.
To connect the Spectra to the moving elevator rod in the Chup, I used a
short piece of 1/16th id brass tubing tied with a CA'ed clove hitch
knot in the Spectra. The clove hitch has the advantage of being an
in-one-side-out-the-other knot, but there is a slight tilt effect on
the elevator; next time I'll use a pair of Lark's heads. (There must
be a name for that pair.) The pulley arrangement works perfectly and
is entirely contained within the fin. I will admit that re-threading
the line takes more than a minute.
All in all, I'm happy with what I have. All objectives were met.
Alton
|
| 282.11 | Spectra availability | TLE::SASAKI | Marty Sasaki ZK02-3N30 381-0151 | Fri Jul 26 1991 13:56 | 18 |
| Spectra is a polyethylene. The molecules have a molecular weight in the
900 to 1000 range. Spectra has very little stretch, but under high
loads does exhibit creep.
Stretching occurs when a material elongates when stressed, and returns
to it's original length. Creep is when a material elongates, but
doesn't return to it's original length. Spectra kite flying line seems
to exhibit creep only after prolonged high loads. After extended use,
my 130 foot lines were roughly 6 inches longer.
I don't think that the loads typical in control linkages will cause
creep, but being able to adjust the length should allow taking up of
the slack if creep does occur.
I can supply Spectra to the group for 5 cents a foot plus postage. Just
drop me a note if you want any.
Marty Sasaki
|
| 282.12 | AUG91 MAN has how-to article | AKRON::RATASKI | Veni, Vidi, Vomui | Fri Jul 26 1991 16:45 | 7 |
| Just informational...
The lastest Model Airplane News has an how-to article on
pull-pull systems. Just has the basics.
-TomR-
|
| 282.18 | pull-pull in a bARF | BRAT::RYDER | perpetually the bewildered beginner | Wed Aug 28 1991 10:00 | 3 |
| The 10/91 issue of Model Builder has a reasonable article on pull-pull
linkage by Art Steinberg on page 44. It's in an unusual place, his
column on ARF's.
|
| 282.29 | Closed loop wires | BIS6::CLEMENT | The Highest Flyer | Mon Dec 23 1991 08:31 | 35 |
|
Hello Gliders Pilots and Builders
First of all I wish you a very happy new year, full of long and high
flights. I would like then tell you the bad story that happend to me a few
weeks ago: I have bulid a 2.80 meter glider with ailerons and a V tail for
thermaling. As I do from many years now, I use closed loop steel wire between
the servos and the tail in order to avoid any play or thermal dilatation. It
has always worked perfectly well except in this particular model. I think that
the length of the cables matches exactly a multiple of the wavelength I use or
something like that. Any way, the result is that I loose the control as the
distance between the transmitter and the glider reaches about 100 meters. Poor,
isn't it? I tryed a lot of solutions and found finally that the problem was
caused by the steel cables. Then I managed to find another non conductive
material to replace the steel. Nylon seemed to be a suitable solution but this
material is much too extensible so that the play remains unacceptable. Finally
I found the best material ever made by human science: the KEVLAR. One of my VAX
dear Customer is system manager in a tire factory: GOOD YEAR. And they use
Kevlar wires to build up the frame of certain types of tires. I talked to him
of my problems and he gave me some sample of Kevlar wire.
Dear Builders, this is the final solution! If some of you are interested, I
can mail you one meter or two of those marvellous cables. The cables are
available in lengths of approx 1.30 meter. Mail me your PRIVATE address and I
send you the cables. Notice that my VAX mail address recently changed from
BRSRHM::CLEMENT to BIS6::CLEMENT.
Philippe
The Highest Flyer
|
| 282.30 | Comes in the package | KAY::FISHER | If better is possible, good is not enough. | Mon Dec 23 1991 17:18 | 16 |
| > <<< Note 399.1168 by BIS6::CLEMENT "The Highest Flyer" >>>
> -< Closed loop wires >-
...
>I found the best material ever made by human science: the KEVLAR. One of my VAX
I just installed pull pull linkage in my Zero (yes Dan - still working on it)
recently and I used the Sullivan (I think) package which comes with Kevlar
cord. Worked great.
But I can't resist a bargain and will also send you my address.
Bye --+--
Kay R. Fisher |
---------------O---------------
################################################################################
|
| 282.19 | help for a beginner? | COOKIE::R_TAYLOR | Richard Taylor | Sat Jan 11 1992 03:30 | 43 |
| I just bought the Sullivan #521 pull pull cable. When I get home, I
discover that there are no instructions on what to do with all the
little bits that they supply. In particular, there are 5 brass? tubes
that are 1/2 inch by about 1/16. What are these for?
My intended application is for the rudder of the Spirit 100. The
instructions show something that is obviously ridiculous, so I have to
invent something better, and thought of trying pull pull.
My questions are:
1. How straight should the guide tubes be? Is there any problem with
the kevlar rubbing against the inside of the guide tubes? In my
application the tubes could not be straight.
2. Is there a problem if the axis of the rudder is not at 90 degrees to
the line of pull from the cords? In the Spirit the rudder hinge
slopes backwards and the guide tubes would emerge from the fuse below
the bottom of the rudder, roughly like this (side view):
_ _____
/ / /
/ VS / R /
/ / /
/ / /
cord -----------/-*_ /
where: VS = Vertical Stab
R = Rudder
* = control horn
I can see that this would introduce asymmetry in the geometry
and could strain the hinges.
3. I will have two servos side by side. Any suggestions on how I
handle the servo end of the installation? My initial thinking is
to have a tube run up each side of the fuse, but this would not be
very symetric at the servo end as one cord would cross from the
side to the middle of the fuse.
4. Anything else I should know/consider?
Richard
|
| 282.20 | Hope this helps | ZENDIA::REITH | Jim Reith DTN 226-6102 - LTN2-1/F02 | Mon Jan 13 1992 09:37 | 23 |
| The brass tubes are for crimping the Kevlar to keep it from slipping
the knot. Sounds like you got a spare. The rubbing and asymmetry will
introduce drag and stress on the hinges. Avoid as much of it as
possible. Round the ends of the tubes and make sure there aren't any
"edges" on them. I had a plane that frayed the cord due to rubbing back
and forth. I had much better luck after "trumpetting": the end with a
pencil point and a heat gun. Having the tubes on the sides of the
fuselage will cause drag when it comes back to the center to attach to
the servo. I also found that I needed to swap ends on the servo output
shafts so that one was forward and the other was backward to avoid
adjacent arms from rubbing.
My personal preference is as straight as possible and in tail heavy
conditions, only use segments of tubes as guides through formers and
sheeting (this makes it harder to replace the line if you need too). I
use a piece of music wire to align the tube segments until the glue
dries (trumpeting each piece) Make sure your servo mount is solid.
Sudden movement forward in a hard landing can rip your fin/rudder off.
Personally, I've been using .015" braided steel cable (a used roll of
C/L flying lines) in my applications recently. I've been able to crimp
the threaded brass couplers onto the servo end to allow adjustment (use
a lock nut)
|
| 282.21 | Reduce parts count and keep the line straight. | ELMAGO::TTOMBAUGH | Dangerously close to mawkishness | Mon Jan 13 1992 11:54 | 32 |
| What Jim said. Also, here's what I found to work well:
Avoid guide tubes as much as possible. A straight shot from the servo
arm to the rudder horn should be the goal.
Mount the rudder servo on the center line of the fuselage. This means
the rudder and elev. servos will be inline rather than side by side.
Use vinyl coated Kevlar cord, it eliminates worries about fraying.
It is only available from Aerospace Composite Supply, as far as I know.
Eliminate all brass tubes, crimping, etc. Ability to adjust line
tension at the rudder end is redundant. Put all your adjustment
at the servo end. This can be done by running the cord into the
hollow end of a brass threaded coupler, wedgeing it in place with
a toothpick and hitting it with a drop of CA. A normal clevis can
be used on the threaded end.
A simpler non-adjustable method is to use a nylon clevis with the
toothpick and CA trick as above.
Another adjustable method without using a clevis is to put a round
output disk on the servo. Thread the free end of the cord through two
of the holes in the disk, one cord on each side, and lock the end
under a set screw inserted in one of the disk holes.
This method eliminates clevises while still allowing adjustability.
The Sullivan/Goldberg pull-pull kite have about 90% more hardware
than necessary. Reduce that and you'll be on the right track.
Terry
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| 282.22 | vinyl coated Kevlar cord | RGB::MINER | Dan Miner, DTN:225-4015, HLO2-1/J12 (@ H11) | Mon Jan 13 1992 14:06 | 5 |
| > Use vinyl coated Kevlar cord, it eliminates worries about fraying.
> It is only available from Aerospace Composite Supply, as far as I know.
Weston Aerodesign carries it too.
|
| 282.23 | I Think I'm In Trouble... | SELL1::MARRONE | | Wed Jan 15 1992 14:50 | 19 |
| After reading the last two notes I got concerned. You see, when I
decided to install a pull-pull system on both the rudder and elevator
of the Super Aeromaster, I didn't see how to make straight runs from
every point back to the servos. So I used the red tubing and snaked
it thru the fuse as necessary to get around obstructions. I did
want to make each run as straight as possible, and in the case of the
rudder, both lines are almost straight. However, the elevator was
another story. I had to make a fairly radical bend in the tubing
coming from the top elevator horn, so I know there will be a
substantial amount of rubbing on this line.
I will be using the Dubro Kevlar kit for this, so the last two notes
have me concerned. Seeing as there is not much I can do now to change
it as the fuse is completely finished, am I in for a lot of trouble?
More advice needed.
Thanks,
Joe
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| 282.24 | Our comments were simply the best possible method, not the only | ZENDIA::REITH | Jim Reith DTN 226-6102 - LTN2-1/F02 | Wed Jan 15 1992 15:31 | 7 |
| If you used the red tubing from radio compartment to fuselage exit, you
can always retrofit the coated Kevlar or steel cables. You also should
be able to trumpet the ends (the Kevlar won't melt) with a heat gun and
pencil. The big concern is whether there's any binding in the linkage.
This will stall/rob power from the servo and cause extra drain. If it
moves freely, leave it alone and watch for fraying (and replace it when
you see it)
|
| 282.25 | A Sigh of Relief! | SELL1::MARRONE | | Thu Jan 16 1992 20:08 | 19 |
| Re: -.1
Thanks, that's a relief. I know it's not the perfect solution, but I
was hoping it would work well enough. My original concern with a bent
guide tube was that the Kevlar might be abrasive enough to cut through
the red tube over time. That could be solved with a smaller diameter
tube inside the original one, but you could probably make this kind of
repair only once.
As far as trumpeting the end of the tube to prevent rubbing, I never
thought of this method. Instead, I placed small hollow metal rivets
inside the end of each tube and CA'd them on. These rivets have a nice
smooth surface and a radius at the flange end so that they will prevent
the Kevlar from scraping against the raw end of the tube. I've never
used this technique before so I won't comment on its effectiveness
until its in use. I just hope it works.
Regards,
Joe
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| 282.26 | Another useful piece of hardware... | RANGER::REITH | Jim (RANGER::) Reith - LJO2 | Thu Feb 13 1992 10:00 | 8 |
| Last night while picking up some balsa at the local hobby store, I
spotted something that I thought looked useful. Dubro sells some
"rigging couplers" (Cat. No. 201) which are a length of 2-56 thread
with a hole drilled through them sideways at one end. The C/L flying
wire I'm using in my pull-pull linkages will fit nicely through these
and a nylon mini clevis from CG fits and doesn't require a locking nut.
I'll be putting these on the Alcyone to allow adjustment and removal
of the rudder (possible due to the use of the Legend style hinging).
|
| 282.27 | Yet more useful hardware.. | ELMAGO::TTOMBAUGH | Naked in a cave in the Jemez | Thu Feb 13 1992 14:21 | 5 |
| And while you're busy Legendizing the Alcyone, you might want to
look at using a 4-40 bolt as the rudder horn. Also easily field
repairable. It saved me in Az.
Terry
|
| 282.31 | Good source for Kevlar | KAY::FISHER | If better is possible, good is not enough. | Thu Feb 13 1992 15:37 | 24 |
| Speaking of pull pull linkages.
I've recently received my free Kevlar sample that
Philippe "The Highest Flyer" Clement has offered.
I was quite surprised to see how much he sent and couldn't
believe it was Kevlar. Also was curious as to what it came
from. After a bit of a language barrier he told me that it
is the cord from racing tires. I compared it side by side
to the Kevlar cord that I had purchased with the pull pull
setup I have and it looked almost the same - a bit thicker
and more twist to the cord. I did a poor man's test on it
and it was stronger than my store bought stuff.
Anyway I think anybody is a fool that doesn't get their mail off to
Philippe. He sent me about $100 worth of the stuff and NO - you can't
have a strand of mine. I'm going to protect it like the last ice cream
cone on the planet. Send mail to BIS6::CLEMENT if you want some.
You will be in Kevlar Cord heaven.
Bye --+--
Kay R. Fisher |
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