[Search for users] [Overall Top Noters] [List of all Conferences] [Download this site]

Conference vmszoo::rc

Title:Welcome To The Radio Control Conference
Notice:dir's in 11, who's who in 4, sales in 6, auctions 19
Moderator:VMSSG::FRIEDRICHS
Created:Tue Jan 13 1987
Last Modified:Thu Jun 05 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:1706
Total number of notes:27193

203.0. "equipment installation" by PNO::CASEYA (THE DESERT RAT (I-RC-AV8)) Thu Jul 06 1989 16:09

Some thoughts on equipmenet installations.  It should occur to all of us
that the best built model has little chance of success if the various systems
are not well and correctly installed.  As a rule, the difference between a good
and a shoddy equipment installation is just forethought and a little extra time.
In fact, it takes little extra time to do a good job as opposed to a slipshod 
one, yet it can be (and often is) the difference between a long-lived, trouble 
free model and one plagued with inherent, built-in problems from the outset 
which will inevitably crash due to faulty installation(s), IF it survives the 
first few flights.

A good installation begins way back during the construction phases.  What better
time to get all systems properly fit and installed than when the airframe struc-
ture is wide open and accessible?!  _THIS_ is the time to plan and pre-install
the engine, fuel tank, all servos and associated built-in linkages.  Somr hints/
suggestions/recommendations:  "Think ahead!"  Such things as throttle and nose-
wheel steering linkages should be routed such that minimal, preferably no inter-
ference with the fuel tank results; I prefer the use of flex-cable inside nylon
tubing for throttle and the same tubing housing small ID music wire for steering
linkages.  These are routed as near the fuse side as possible.  The tank is then
located such that the fuel-feed line from the tank stopper is dead level with
the upright engine's needle-valve.  (For inverted engines, the feed line should 
be slightly lower than the needle-valve; for sidemounted installations, align
the feed line to be level with the venturi centerline.)

"Good enough" simply ISN'T when it comes to tank installation!  A poorly located
tank will cause severe reliability problems with the engine which makes the 
model vulnerable to damage or worse as a result of unexpected engine failures.
Nowadays, I recommend against fuel-filters in the feed line as they present just
one more place air-leakage and resultant engine problems may occur.  Instead, I
recommend having a filter on the pickup in your fuel can and another in the
tubing from your fuel-pump output.  Further, you can use a filter-stlye clunk in
the fuel tank.  At this point your fuel has been triple-filtered by the time it
reaches the engine and another filter in the feed line would be redundant!

Hinges:  Here we have my least favorite part or construction.  Lately, I prefer
Robart steel-pinned hinge point hinges for their ease of centering/alignment and
installation; what could be simpler than drilling a hole, filling it with epoxy
and stuffing the hinge in the hole?  While many are sold on the new "Simple"
hinges that are paper thin, slip into an X-acto knife slot and are secured with
a drop or two of CYA, I can't yet bring myself to trust these as I have obser-
ved failures of this hinge, regardless to the advertising hype to the contrary.
Whatever you prefer, use a good quality hinge and install it precisely; the con-
trol surface should move with total freedom, no slop, no binding.  This minimiz-
es the mechanical load on the servo and reduces current draw, thereby extending
battery life.  

Control linkages:  I strongly recommend AGAINST using the EZ vaiety of quick 
connectors to connect control rods to servo output wheels for critical controls,
i.e. elevator and ailerons.  These items are fine for throttle, rudder, steering
etc. as a failure here doesn't constitute a serious threat to the model.  How-
ever, I refuse to trust them to controls, the in-flight loss of which will al-
most certainly guarantee a severe or total crash.  For critical controls, I 
recommend using a direct connection of the pushrod to servo output via a "Z"-
bend...I guarantee _THIS_ connection won't fail.  Second choice here is a clevis
safetied with a slice of fuel tubing or tightened copper wire.  Anything less is
inviting disaster!  Remember Murphy's Law: if it can, it WILL!!!  The same type
of connection, preferably the "Z"-bend is recommended for connecting pushrods to
bellcranks., etc that will be buried within the airframe...you want to avoid
the necessity of performing surgery on the structure to access a bellcrank in
order to repair/correct something that was poorly done in the first place.

And, what about the bellcrank mounting screw upon which the device pivots? These
_MUST_ be safetied too as their failure means the loss (or jamming) of a vital 
control and probable loss of the airplane.  Do NOT fail to use all washers and
locking hardware and SECURE the nut by means of Loctite, CYA, solder, RTV or
whatever...just be SURE that the nust can't come off accidentally.  Control
horns should, ideally, be firmly mounted to a plywood base built into the struc-
ture and the screws safetied as above.

For the terminus end of pushrods, the most acceptable termination/connection is
via an adjustable clevis; I try to use nylon against metal and vice-versa for 
the purpose of minimizing mechanical noise.  To properly install, set the con-
trol surface at neutral, then adjust the pushrod length such that the clevis is
in the center of its adjustment range when attached to the horn.  This assures
that you'll have plently of adjustment in both directions to work with when it
comes time to trim the model.  Again, safety the clevises against accidental
opening using a slice of fuel tubing as a small, tight rubberband to hold the 
clevis closed.  I should add here that I make every effort to avoid metal-to-
metal contact _anywhere_ on the model.  Unlike the radios I flew in the early
years of proportional R/C, today's state-of-the-art radios are supposedly im-
mune to mechanical noise but I prefer to adhere to the old, well-founded no-no's
and decline tempting fate as long as it's so easy to do so.

While still on the subject of pushrods, a word or three on exiting them from the
fuselage.  Install pushrods such that they can exit the fuse in as straight a
line as possible.  One easy way to accomplish this is to cross the pushrods in
"X" fashion so that they have a straight shot at their control horns without the
need for bending the rods.  Bending the rod to exit the fuse should be avoided
as this introduces slop in the linkage and exposes the affected surface to spon-
gy response, flutter, etc.  If a bend simply cannot be avoided, use as shallow
an angle of bends as is possible and _NEVER_ use 90-degree bends as this is the
worst possible case for the problems just mentioned to occur.

Pushrods:  My favorite pushrod material is fiberglass arrowshaft; it's light,
bulletproof and easy to adapt to our purpose.  Kits are commercially available
for foolproof termination of the arrowshaft to the clevis wire.  Next on my list
of preferred pushrod materials is 1/4" dia dowel, then 1/4" square hard balsa.
While it's fairly easy to install and many modelers use it, I do not recommend
_any_ of the "ny-rod" types of pushrods; temperature sensitivity is the biggest
reason for my dislike of this material...also, if one isn't careful when instal-
ling the "all-thread" rod into the ends of the inner ny-rod, he's inviting a
catastrophic failure.  Also, I don't care for the use of flex-cable for _any_ 
flight controls for two reasons: 1. it's too easy to wind up with spongy con-
trols and, 2. I prefer to avoid having long lengths of wire running about inside
the airframe as it can spook the radio through the secondary antenna effect.

The entire engine,tank and radio system should be completed and checked out
_before_ the airframe is completed.  This is the easiest time you'll have to 
detect and correct any deficiencies as may exist.  There should be NO servo buz-
zing!  This is usually the result of a too tight or binding control surface.
DON"T let it go; this buzzing is increasing the draw on the battery tremendously
which is a potentially dangerous situation.  Correct it NOW!  If everything ap-
pears perfect and the buzz persists, try another servo...sometimes they're too
tight around neutral which results in buzzing under the slightest load.  Your
local radio service center or the manufacturer can correct this symptom and
you should have it attended to as this is an unhealthy condition.

Wheel collars:  Anywhere a wheel collar is used, precaution should be taken to
assure it will stay put.  Losing a wheel on takeoff (or in flight) can mean
severe airframe damage when the aircraft is landed and the wheel-less axle digs
into the ground...this can be especially true on grass.  To safety a wheel col-
lar, simply file a flat spot on the axle where the setscrew will come in con-
tact.  Use of Loctite on the setscrew will add some insurance as well.  The use
of a filed flat is also effective to keep the nosewheel tiller (steering arm)
from slipping on the nosegear strut, a condition that can be very aggravating
and even hazardous.

Most of what I've mentioned above is nothing less than good ol' common horse
sense but you'd be surprised (or maybe you wouldn't) at how many modelers vio-
late one or more, perhaps even all of these installation practices.  You might
even recognize a violation or two on yer' present model as you read this.  I
don't propose that these are the ONLY ways to do things in every case but I'll
guarantee you this; if you strictly adhere to the guidelines I've laid out
above, your chances of experiencing a catastrophic failure due to equipment 
installation will have been reduced to as near zero as is possible.  It's dif-
ficult enough flying our birds without incident even when everything's perfect;
why stack the deck against yourself by doing a poor job on systems installation?
T.RTitleUserPersonal
Name		DateLines
203.2Set idle so that you can Kill EngineLEDS::WATTTue Apr 26 1988 09:0511
    Dan,
    	You mentioned having to reset your idle trim.  This is a good
    idea.  Try to set it up so that you can kill the engine by pulling
    all the way back on the idle trim and so that the engine idles well
    somewhere in the middle of the trim setting.  That way, you can
    kill the engine if something like this happens in the future.
    Anker is right, trainer 40's do fly fast.  The symmetrical airfoil
    leads to this.  Also, they sink fast when you slow down.
    
    Charlie
203.4HARD OR SOFT BRASS TUBING.....??UPWARD::CASEYATHE DESERT RAT (I-RC-AV8)Mon Apr 23 1990 12:2659
    Re: .-1. Ajai,
    
    Thanx for the previous saga.  Now I remember why I always enjoyed yer'
    chronicles and have missed them so much.  I appreciate the "fix" but
    you gotta' keep 'em coming now or me and Shiva will have to get
    together and do a little more conspiring.  (Isn't Siva also an
    accepted spelling? I'da sworn I've seen it spelled that way although
    still pronounced Shee-vah.)
    
    On the brass tubing problem, yes, some sorta' chemical/electro-chemical
    reaction with the fuel hardens and brittles brass tubing to the extent
    that is will just break of its own accord.  I've had the identical
    experience you described and witnessed it many times as well.  However,
    that was back in the days before the _bendable_ brass tubing became
    available...the stuff you can form to desired shape with yer' bare
    hande.  I've not had a single problem with tanks rigged with the
    bendable tubing and the Sullivan tanks I generally prefer have come
    with this type tubing for years (as least I _thought_ so).  Was the
    brass plumbing in yer' tank the soft, hand bendable brass tubing or the
    very hard, rigid variety?  If the latter, be sure to replace with the
    former and you should replace the pickup line at the same time even
    though it hasn't broken yet...if the overflow broke, rest assured this
    one will too.  BTW, an alternate to the bendable brass is copper tubing
    though it tends to turn green and corroded looking in time and should
    probably be replaced with some regularity.  The bendable brass is
    definitely to be preferred.
    
    I don't believe I ever came across the excessive clunk wear you
    describe.  Wonder if you got one of inferior manufacture or quality. 
    Mayhaps it'd be a good idea to replace this item at the same time you
    replumb the brass tubing.
    
    Someone (is it Ace?) is just now announcing a new spage age plastic
    tubing which can be permanently formed/bent under the low heat of a 
    Monokote heat gun and used to replace all the metal tubing in yer' fuel
    tank.  Sounds good if'n it works but it's too new for anyone in the
    field (that's us'ns) to have any knowledge of or experience with it yet.
    
    On the subject of my possibly leaving DEC the end of June, that remains
    a possibility but is perhape a bit less likely than it first appeared
    to be.  Reponse to the buyout was so overwhelming here that many jobs
    have had to be posted to fill the positions that are required to staff
    the new plant structure.  Always opting for the bird-in-the-hand, I've
    applied for a position and should know within the next day or two
    whether I got it.  If not, more jobs are due to be posted between now
    and June 29 and I'll apply for anything I'm qualified for and/or would
    be interested in doing.  I'll keep y'all posted as developments er...,
    ah..., well....develop regarding my going or staying with DEC.  Believe
    me, I'd prefer to stay; I intended DEC to be my last job when I hired
    on here almost 11 years ago and I'd still prefer that to be the case. 
    Time alone will tell but I'd sure like to get just 5-more year years in
    so I could at least qualify for retirement bennies should this bridge 
    have to be crossed again. 
						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)
203.3soft and hard brass and tank innardsUPWARD::CASEYATHE DESERT RAT (I-RC-AV8)Tue Apr 24 1990 18:5646
    Ajai,
    
    I suspect the tubing you used as a replacement vent might well be the
    hard stuff.  The soft brass stuff is pretty easy to distinguish from
    the hard stuff; it'll bend almost as easily as copper tubing with
    little tendancy to kink until the bend radius becomes quite acute.  The
    hard stuff, on the other hand, _can_ be bent with the fingers but with
    noticeably greater difficulty and drastically increased resultant
    kinking.   The soft stuff can be laid across the index and 2nd fingers,
    then readily bent by applying pressure with the thumb of the same hand
    just like you could do with copper...the hard stuff is considerably
    more resistant to this test.
    
    I know it takes some fiddling to accomplish but yer' correct in yer'
    observation that the vent should protrude up into the bubble atop the
    tank without touching.  In fact, if it _does_ touch, it can cause all
    sorts of problems, vis-a-vis wear a hole through the tank or, much more
    difficult to find, a starving engine syndrome where the engine can't
    seem to be set rich enough not to go lean before the end of the tank. 
    This latter scenario occurs when the vent fits against the top of the
    tank tightly enough to effectively seal it off; since no air can enter
    the tank through the blocked vent, a vacuum is formed as fuel is drawn
    from the tank making it increasingly difficult for the engine to draw
    fuel, hence becoming leaner and leaner to the point of overheating and
    seizing up...all this potential hazard and/or destruction just because
    the vent is sealed off against the top of the tank.  To eliminate this
    possibility entirely, I strive to make the vent(s) fit as perfectly as
    possible with a visible gap between same and top of tank BUT, JUST IN
    CASE, I file a "V"-notch in the end of the vent adjacent to the tank
    wall so that, even if the tube should become pressed aginst the wall,
    air can still be drawn into the tank through the "V"-notches.  Simple,
    huh?!
    
    Yes, prop consumption is a very good indicator of relative flying
    prowess and, when you get to where you can't remember _when_ you
    installed the prop yer' currently running and have been doing lots'a
    varied flying, you can feel fairly confident that you've got the game
    figgered' out.  Congratulations on yer' ever increasing skill level.
    Sounds as if Charlie's gonna' make a pilot out of you in spite of
    yer'self!  ;b^)
						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)
203.1fuel tank vent modificationSA1794::TENEROWICZTWed Apr 25 1990 07:5010
    Al, I was this idea in MAN months ago. Cut a small length of fuel
    tubing (Blue line) app 1" long. On one end cut a V groove. Rotate
    the piece 90 degrees and cut a second V. You get kind of a crown
    effect with four points. Now leave the brasss tubing short of the
    top of the tank and slip on the 1" length of fuel tubing. This way
    you cannot pinch off the opening yet you get no chaffing from the
    metal tubing.
    
    
    Tom
203.5Velcro servo tape problemABACUS::RYDERperpetually the bewildered beginnerTue Jan 15 1991 05:2717
    Small gliders don't have room for servo trays, so the servos tend to
    be mounted directly and individually.  I've been trying different ways
    to do this, and I've had a problem.  A very coarse and stiff Velcro is
    sold as a servo mounting mechanism; I've used it, and it seems to allow
    too much play.

    Long ago I had epoxied two servos together, side by side, so they are
    now always used as a matched pair for rudder and elevator.  I recently
    mounted them in a Gentle Lady using this Velcro on the bottom of the
    pair.  I noticed that they could rock fore and aft on the Velcro with
    more than 1/8th inch of movement at the servo arm.  Is this normal?  
    It doesn't seem acceptable; I took it out and glued the pair to the
    balsa bottom of the fuselage for more rigidity.  (Removal will be no
    more difficult than removing that damn Velcro.  It may be sloppy, but
    it isn't wimpy.)

    Is this stuff good for this application?  Did I mis-install it?
203.6Not the best IdeaLEDS::COHENThat was Zen, This is TaoTue Jan 15 1991 09:5121
>    more difficult than removing that damn Velcro.  It may be sloppy, but
>    it isn't wimpy.)
>
>    Is this stuff good for this application?  Did I mis-install it?

    I Velcro the Rx and Battery.  This way I can shift them around to adjust
    the CG without having to rip the plane apart.  Velcro Servos?  Well,
    I'de look it it this way...  If my Rx or Battery flops around a bit in
    the plane that might make it a bit twitchy, but if my Servos flop
    around, they'll make it more than twitchy.  The plane will never stay
    trimmed, and there'de always be the risk that the Servos would pull
    loose on a hard maneuver, or lauch, or landing.

    The closest I've ever come to Velcro is double sided Servo Tape, and
    even that makes me nervous, 'cause the adhesive doesn't always stay well
    adhered to bare Balsa Wood.

    I wouldn't Velcro my Servos.


    Randy
203.7SiliconKAY::FISHERStop and smell the balsa.Tue Jan 15 1991 10:2016
>    The closest I've ever come to Velcro is double sided Servo Tape, and
>    even that makes me nervous, 'cause the adhesive doesn't always stay well
>    adhered to bare Balsa Wood.

I have been using silicon on my last several servo installations.
Just sand the surface of the plastic servo a bit and put a wad of
silicon (from your huge caulking gun) and push it in place.  Wipe off 
the excess silicon (weight) and wait 24 hours.  Works on wood or fiberglass.
Gives just a tad of vibration isolation - depending on how hard you
push and squeeze out the excess silicon.  I typically only leave
a thin (maybe 1/64") film and very little vibration isolation.

Bye          --+--
Kay R. Fisher  |
---------------O---------------
################################################################################
203.8Radio Shack hold down tapeELMAGO::TTOMBAUGH20/20 Vision&amp;walkin&#039;round blindTue Jan 15 1991 10:2421
    Al,
    If you are using the stuff that has the little stalks with the knobs
    on top, then this can be sucessfully used to hold down servos.
    This isn't actually velcro although you have to look close to see
    the difference. If it is impossible to pull the servo loose by pulling
    straight up, then you have the right stuff. If it gradually pulls
    loose with a scruunching,ripping sound (I love this technical talk)
    then you have some species of velcro and it will never work well
    for servo retaining.
    
    Radio Shack sells the stalk and knob stuff as "superstick hold down
    tape", or something like that.
    
    A thin coat of epoxy must be applied to the bare wood to allow the
    tape adhesive to stick properly. This goes for double sided foam
    tape too.
    
    I sometimes use a scrap piece of ~1/4" balsa, a moderate press fit
    between the servo and fuse. side, to prevent servo rocking.
    
    Terry
203.9YOU MIGHT TRY PFM.....UPWARD::CASEYATHE DESERT RAT (I-RC-AV8) 551-5572Tue Jan 15 1991 11:0130
    Mind you, I've never tried this so I take no responsibility for it but
    there's a new "miracle-glue" out from Innovative Model Prod's called
    PFM and one of its recommended uses is for mounting servos.
    
    PFM is an RTV (silicone rubber) type adhesive with some advantages; it
    dries clear, dries faster and can be removed without damaging surfaces
    to which it is applied...you just lift the edge a bit with an X-acto or
    whatever, then grab it and peel it off.  It's recommended for
    installing bulkheads in glass fuselages, installing canopies, mounting
    servos, etc. ad nauseum.  A _HUGE_ tube of PFM sells for $9.95. 
    
    I got a sample tube from Greg Namey and have tried it for a few
    test-type applications, e.g. securing the 4-way vacuum valve/switch for
    my retracts and tack gluing the retract air lines out of the way in the
    wheel wells.  So far, I'm satisfied that PFM does all it's advertised
    to do.  The advantage I see in using PFM for servo mounting would be
    the fact that the adhesive can be peeled off later without "glucking" up
    either the servo or the mounting surface as is the case with RTV and/or
    the numerous other silicone calks.  (I love that technical talk
    too, Terry.)
    
    In any event, it sounds like it's worth a try.  I think the uses for
    PFM are too numerous to list and will increase in time as useage
    becomes more widespread.  Looks like real good stuff to this hombre. 
						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)
203.10HPSPWR::WALTERTue Jan 15 1991 12:367
Al R:  I don't understand why you can't use regular rails to mount the servos.
It seems to me if the fuse is big enough for the servo, then by definition you
can glue a wood rail in too. It's a lot stiffer than tapes or RTV, and the 
servo can be removed easily. I think the servo mount should be as stiff as 
possible to eliminate trim problems.

Dave
203.11never again with knob/knob "Velcro"BRAT::RYDERperpetually the bewildered beginnerWed Jan 16 1991 07:0530
    The stuff I used was symmetrical knob/knob from Tower.  (I believe the
    trade name Velcro applies to asymmetrical hook/loop material.)  So I
    probably used the stuff that Terry has used successfully.  Failure and
    success may be a matter of bottom vs side mounting.  The moment arms
    would differ by at least a factor of 4.  The throttle servo is still
    side mounted with this stuff, and I don't recall a slop problem.

    Whatever, now once burned I won't ever use the stuff again.

    When I re-installed those two servos, I used PFM adhesive --- much as
    Kay and Al suggest.  I would expect the balsa to rip out when the time
    comes.

    Randy, I have to admit that I didn't seriously consider rails.  I
    should have.  The initial installation used a side-saddle servo tray
    that could hold only one servo, hence the epoxy between the servos. 
    When that tray ripped out in a crash, I tried the knob/knob tape.  I've
    used rail installations; I just didn't think of it here.

>    Is this stuff good for this application?  

    I think the answer is a qualified "no".  I'm inclined to use it again
    on the side of a throttle servo to minimize servo stalling.  Nahhh. 
    The difference between idle and cut can be too delicate.  The answer is
    an unqualified "no".  

    I now have five inches of stuff that could attach a spare tire to the
    side of a truck.

Alton