What's the connection between servo selection, and a brief how-to regarding the classic silk-and-dope model airplane finish? As occasionally happens, we detour through the unexpected coincidences of life before reaching an answer. It began simply enough with an email asking . . .
Q. Which servos do you recommend for a
Great Planes Christen Eagle II biplane?
A. As it happens, I reviewed this 29% ARF for modelSPORT
in 2003 and I still got the similar size sister to this model, the Pitts Special. mine is equipped with a 50cc engine. Anyway, this size biplane flies great and for mere mortals engaged in sport-maneuvers, all that's needed are eight DS90DLHV servos (four on aileron, two on elevator, plus
one each on throttle and rudder).
- Now discontinued, this Great Planes model is lovely with a 50cc twin
Variations on a theme, or how
mini-class servos fit the story
I answer variations of the above question regarding which servos are best for such-and-such a model every day, and that should have been that. This time we took a different path, but before I continue, and in anticipation of queries regarding the now discontinued Eagle and Pitts models, let me point you to a very suitable alternative.
If I stuffed mine in the ground tomorrow, because it's so much fun I'd replace it with the lovely PAU 27% Pitts Challenger. A hair smaller at 27%, this model is also designed for 40-50cc engines and while I'm partial to the all-red Oracle version, PAU offer one trimmed in yellow as well.
- Super maneuverable this 27% PAU Pitts Challenger is a gorgeous 50cc ARF
So back to the story, things were going innocently enough when later
that same day, buried within a followup message, I mentioned thoughts of
taking my Pitts to another level by using DS160CLHV mini-class servos.
At 160oz-in, these are roughly 2X stronger, easily 3X faster, and come in at about 1/2 the weight. Since minis are more thrifty than standard size servos battery-wise, along with a lighter
flight pack I'm thinking the smaller avionics package may shave nearly a pound off the AUW of the model, or enough for even a duffer like me to feel. Anyway, mini-to-standard adapters, part number PDRSM2S make using minis, instead, quite easy.
- aluminum screws because we're serious about weight loss also!
Not ten minutes later, ring, ring, it's the phone. Same
fellow with more questions. We chat a while before an off hand
comment regarding a black color scheme sparked a memory of a
conversation from 15 years ago. Shortly after the review came out, a
guy called seeking engine advice. That call was memorable because he
shared his plan to strip the gorgeous white MonoKote/multi-colored
feather scheme because he didn't want his to look like everybody
else's Christen Eagle. Wanted black instead of white. Fact is, the Eagle scheme in black looks really sharp.
- Templates for the eagle motif were included with the experimental kits!
Anyway, it takes an individualist to buy an ARF professionally covered in
MonoKote, only to immediately strip and redo it. This requires dedication
and a certain panache. I immediately recognized a kindred soul and we
hit it off. Anyway, for a while, he and I were speaking
For example, once we detoured into using UltraCote instead
because MonoKote because the latter can be a be-atch to trim without
a ton of little bubbles under the feathers – or – by using a
chemical activator for the adhesive. UltraCote, on the other hand, is
dead-nuts easy to layer without bubbles. Somewhere along the way I
half joking suggested using silk and dope. he did and it turned out gorgeous. As I related this, the
call fell silent long enough for me to go, “Hello?” thinking
the tower had dropped the call. Nope, the silence was the guy collecting his
thoughts before blurting out a name. Same guy. His Dad. Small world,
Fast forward fifteen years and I'd lost
track of him. So I find myself explaining to the son some of what I'd
explained to his Dad; basically sharing a few tips for doing old
fashioned silk-and-dope finish. His Dad had done a good job with my
verbal instruction (subsequently sent pictures, but sadly, I've long lost
them). Anyway, yesterday the son calls again; this time regarding details
for repairing the covering. Mentioned some damage (old silk can be
fragile). Basically, he needed to effect some repairs. Wondered if I
could help if he visited and brought the model. Nope, no way do I
have time, and sentiment aside, things around here are like Mach 2 with my hair on
fire because we're working to finalize a new submicro servo.
Then hesitantly, he asked if I had any of the emails. Implied was; would I mind sharing the messages between me
and his Dad (perhaps confusing me with a priest or a doctor regarding
confidentiality)? Since I'm neither padre nor sawbones, I didn't
think confidentiality applied. Especially because a) I didn't mind
sharing and b) the other guy is dead so who would object? Naturally, I said, “Sure!”
On UltraCote and buying a new model
It helps I'm a pack rat and don't throw
anything away - emails included. So I dug them up and forward same.
And this brings us full circle to a few thoughts regarding how to
cover a model airplane using silk-and-dope - the classic model
airplane finish – as promised!
I've put my notes in better order
and this time, include a few thoughts about MonoKote vs. UltraCote.
What got me started on this last bit? And why do the differences
between the two popular film coverings matter? Well, it's like this;
recently, I saw a very pretty model airplane online. Pretty enough to
feel the urge to get one.
Frankly, this happens a lot but this
one is special. It's a 69” Turbo Raven by Extreme Flight
which has a bird motif. I really like the trim scheme. Folks, this thing is gorgeous (and it's an ideal candidate
for our DS160CLHV mini-class servos because the designer is clearly
playing the weight game to win).
- Playing to a genius level this top-designer means for this model to be light!
By playing to win I mean the designer, Cody Wojcik paid more than lip service to reducing the AUW.
Moreover, he's obviously thinking outside the box else he wouldn't have considered minis for the application. In a word, he's very astute and fully groks the reality of what modern
mini-class servos bring to the table in the way of performance.
Frankly, this is a rare thing. I often refer to it as thinking around corners.
Gaston Glock did it when he created his Glock
pistol using a plastic side frame. Now it's common because Smith &
Wesson and everybody else offer something similar. He was first.
Henry Ford thought around corners also when he created the moving
assembly line. Now everybody does it. Anyway, believe me, this
designer thinks outside the box!
Other designs in this size specify the safe
choice, standard size servos. Yet Cody ditched those for mini-class servo. Why? Simple, it's because minis like our DS160CLHV and DS175BLHV have got the power and speed to extend the performance envelope of the aircraft whilst reducing weight. This is a big deal, believe me!
Meanwhile, I touched on it but the other thing I
find irresistible about the Turbo Raven is the bird-pattern with
which it's trimmed. It results in a relatively complex finish. There
was, however, a question. Is it covered entirely with film, or is the
trim scheme painted on? Painting trim film coverings are a shortcut I
abhor. Enough so I won't buy a model done that way because effecting
a proper repair is nearly impossible since the paint can't be easily
matched. Once I confirmed it was done right (e.g. the trim is done in
film), I ordered one. Note; Extreme Flight
even makes it easy by sharing the UltraCote product codes for all the
colors of the covering. Nice touch!
On how MonoKote came to dominate
UltraCote, of course, is a polymer film
similar to MonoKote. For those not in the know, when Top Flite
introduced MonoKote it displaced silk and dope from it's prominence
as the preferred finishing technique of balsa wood flying models.
This happened seemingly overnight but in reality, it took about a decade to
effectively displace the old technique. When I became an RC modeler
in the early 70s the process was well underway but because total
dominance wasn't fully established until the late 70s, I cut my teeth
with silk and dope. This, largely because my mentor was old school
(gunnery sergeant with the Marines in Vietnam – he was my senior by
15-20 years). He was a very picky guy from whom I learned the
importance of details.
Anyway, silk and dope was (and is) a
tedious finishing process for model airplanes process (and my Mom
hated the smell). The point being, making the switch to MonoKote
didn't take a lot of convincing (for me or virtually every modeler of
the time). Only now dead curmudgeons (like my mentor) persisted with
silk and dope.
Note; to this day, a few modelers still do it, but it's a small number, perhaps fewer than 1% of models are done this way. The rest
are covering in film. Or maybe silkspan attached with nitrate. Especially on models with fully sheeted wings (foam core wings were new back then also). Anyway, on
models with no open spans between ribs, the paper covering (silkspan
vs. genuine spider silk) was often color-sprayed with Hobbypoxy or
Ultrapoxy instead of dope. Also far more laborious than MonoKote,
this process was significantly faster than dope but different because
epoxy is handled and sprays in a completely different fashion (and
only needs two coats). Still a lot more work than MonoKote, but in
common with silk, better looking . . . but I digress.
Thus, for the modeling masses, MonoKote
was the no-brainer of all time. Basically, the whole job of finishing
the model was reduced from weeks of tedium to a matter of hours. Then
it was ready for the equipment install just like we do with ARFs
Anyway, like pretty much everybody else, after my first
experience with MonoKote I never went back. In fact, I took to
MonoKote like a duck to water because it was so much less work and
looked good enough. Good enough means I could easily overlook the
fact it wasn't as a nice looking as a well executed silk-and-dope job
because I am somewhat lazy. You may be thinking, 'John, you're
exaggerating and making a bit much regarding how much work was
involved in silk and dope.” I'm not.
But in all honesty, sometimes - for the right plane - it's worth the effort. For example, his is orange silk finished in clear with cream trim and dark brown pinstripes on one of my Playboy models. When it floats overhead, the sun gleaming through the structure . . . it's magical, believe me!
-- Post war Playboy design is ideally suited to being silked
Silk-and-dope – the basic steps
Finishing a plane today is a matter of
a few hours with a covering iron. However, once upon a time, it
involved at least a week to 10 days (and two to three weeks wasn't
uncommon with intricate schemes). A silk and dope job begins
with brushing an adhesive coat of clear nitrate dope on the finely
sanded balsa structure.
You have to apply dope everywhere
the the silk will adhere on the perimeter of a panel. Every edge gets a light coat. Take special care to preclude runs
(especially on the ribs). Then after it dries, proceed to fine sanding of the wood you've coated with dope using 400-grit wet. This is then followed by
another light coat of dope. And this is the easy part!
Did I mention most wives (and my Mom
was definitely a wife) hate the smell of dope? Whether it's
nitrate or butyrate dope, it'll stink up the whole house. You can't even work in the basement! So the smell means finishing is an outdoor activity for most guys (summer or winter). Then there is drying time, a real time killer. Plus lightly sanding between coats everywhere silk touched the balsa
structure. All while taking great care not to sand on open structure
areas so as not to damage the silk's weave.
Where do you get silk? I
favor old fashioned Chinese silk. Look online for Habotai 5mm weight
class. I buy mine from Dharma Trading. Also, opinions vary regarding weight with some preferring the heavier 8mm silk - it's a judgment
call. What about dope? There are two types, nitrate and butyrate.
Note; it's important to realize butyrate can go over nitrate but not
vice versa. You'll only screw this up once, I promise. Anyway, there are tons of sources for dope like Randolphs, Brodak, Sig, even the full scale
suppliers like Aircraft Spruce. The internet can be your friend.
Tips and tricks – an overview
Both kinds of dope - nitrate and butyrate - have a purpose.
Continuing from my notes; once the nitrate dope on the wood structure is dry, the
next step involves trimming silk panels to size. Note, silk has a grain! The finished edge is the one that runs parallel to the span. Don't turn it 90° and use the cut edge for the span or it will sag in an unsightly way. This is a big deal, pay attention!
Anyway, after soaking
the silk in water and wringing dry (don't get too aggressive or you'll have to wet the silk again with a spray bottle), the silk panels are laid in position (and wet silk can be tricky to deal with).
Then you pull out wrinkles whilst spraying with 50/50
water-alcohol and using clear full-strength nitrate dope (and a
brush) for tacking the silk down around the perimeter of openings or complete panels. Note; what's actually happening when you do this is fresh dope melts existing dope so when it dries, the silk is fused to both old and new the same way fiberglass is used with resin. E.g the dope acts like glue the silk makes for a strong flexible surface. Done right it's ends up tight like a drum!
What's important about all this? Do not
induce a warp in the structure! And never allowing the silk to sag between ribs. Perfection is your goal and the Devil is in the details! By the way, there are loads of descriptions online
for doing all of this; Google is your friend because remember, this is just an
overview, OK? But ultimately, noting beats jumping in and getting started.
Anyway, once things have dried, a light
sanding, plus more clear dope where the silk adhered to the wood to
ensure it's well and truly stuck in place to the entire structure. This is de rigueur because if a silk panel pulls loose later you have to start all over. Plus take care to
'always' work with an eye to reducing the chance for a warp of the structure!
the perimeter coat dries and the silk is smoothly attached, you'll lightly brush a coat
of 50/50 nitrate-thinner (clear again) on all the silk. This will shrink it when it dries. The point is to work evenly
and on opposite sides at once to shrink the silk into place but
not warp the structure. I keep harping on this because it's important. When doing a stab, for example I'll work on one half but do the top and bottom at the same time to keep it from working. Then I'll do the other half of the stab. Take your time! Also, it's critical to not allow
puddles of dope to form on the underside of the silk at the open spans (e.g.
between ribs or over open tail feather structures). This is
important because it will look like crap!
After again waiting for this to dry, it's
time to inspect and correct any defects. Basically, you're looking for any
imperfections. The goal is 100% wrinkle free. When you find a
wrinkle, you correct it by slitting the length of it using a single edge razor blade, then pat the new seam down with a brush loaded with dope to make it lay flat until it dries. Sometimes you need small
patches of silk to make repairs or clear up bad wrinkles. Have patience and stick with it until the job is 100% taut and wrinkle free.
Of course, there is always some light sanding between coats but by now you're using 600-grit paper (wet so it's almost akin to rubbing instead of sanding). Speaking of
intentional cuts with a razor blade to deal with wrinkles, there are also repairs; like where
you accidentally sand through the silk on a hard surface like a wing tip or rib. This is due to getting careless (sanding
can be a mind numbing job). So at a minimum, beyond a skillful touch,
silking involves a time consuming amount of detail work.
Break out the compressor
Finally, once the silk is perfectly
attached, the real work began. First, maybe brush on another coat of 50/50 clear but
more likely a coat of 50/50 clear mixed mixed with talc (to fill the weave). Add a few tablespoons to the pot of clear. Note; sanding this is perhaps the only fun part of the job. It makes tons of fine dust and the whole thing smells like a freshly changed baby's if you're using Johnson & Johnson baby powder as your source of talcum. I did and always like the mess I made with the fill coat.
Anyway, one that's been sanded smooth, you've well and truly killed a whole weekend with
an awful lot of tedium involving doping, waiting for things to dry, plus sanding (and heaven help you if
you sanded into the silk and fuzzed it up because this also weakens
the silk - plus it has to be repaired). This will sound strange, but I actually liked doing it because I'd get into a zone and just go!
Finally comes a thin coat of
silver. Yup, the first instance of breaking out the compressor and
spray gun. Now we add a lot of clean up time to the job because the spray gun has to be
disassembled and cleaned with thinner after each coat. Fortunately, these dry fast and if you're careful to not let paint dry on the spray tip you can get a lot done working from one wing panel to a stab or to ailerons, then rudder, then fuselage, etc until you're back to wing panels, and the cycle begins again. Once the weave is filled to your satisfaction, it's time to switch to butyrate for color coats.
Butyrate dope shrinks less than nitrate and is hot fuel
proof to about 30% nitro and impervious to exhaust oil (back in the day, castor oil but nowadays synthetics which can be hard on a finish). Fortunately, if you're working on a model that will be powered by a gasser or an electric motor,
you may elect to stay with nitrate dope the whole way because 'hot
fuel proof' doesn't matter.
Note; the component in nitro-fuel fuel you're especially concerned about is
the nitromethane but even the methyl alcohol can be an issue. Back in the day, my favorite brand of dope was by Pactra. Their Aero Gloss was what I liked and I used this exclusively for clear and for the color coats. However, I think they've gone by
Speaking of doping, a 'good job' means a
minimum of half-a-dozen color coats for a journeyman finish involving two to three white base coats on the silver, plus two coats for light trim colors like yellow, maybe a third for darker ones like red. Plus pin striping and all this followed by a couple
coats of clear.
Note, the folks using candies and flake, especially if shooting flames, may have applied many more coats plus a half-dozen of clear (plus 'lots' more waiting for
things to dry and sanding out to 800-1200 grit).
Finally, a few weeks
later - after a compound plus wax job - your model airplane is ready
for the field. So with respect to the question of is this a laborious
process? The answer is unequivocal . . . heck yes!
Tips and tricks
I alluded to my Mom hating the smell.
It's strong. Once you've been around it, dope has an unmistakable
smell (I rather like it but that could have been fueled by a teenager
drive to be contrary). Anyway, Mom hated it - her house, her rules,
so I worked outside.
Also, depending on humidity you needed to learn
a few tricks like working with banana oil to slow down the drying. In fact, there are lots of little
tricks involved. I was fortunate someone took a shine to me and
taught me a great deal. He was a pattern competitor and an artist
with a spray gun, and importantly, meticulous to a fare-the-well.
Note; the guys
on the pattern circuit back in the day flew very pretty airplanes (they even
cleaned them meticulously between flights). These days you really
only find this attention to detail amongst the control line crowd.
Anyway, my friend and mentor is long dead and he never switched to
MonoKote and because he never asked, I never told him I had (but I suspect he'd have been a little disappointed in
me). Anyway, I switched to MonoKote. No regrets. Not
On actually using UltraCote
The point of all this being - yes
Mildred, there's a point - when UltraCote came out, I found my skills
with MonoKote let me adapt to using it quite easily. Not as easy, I
am told, going the other way around, e.g. from UltraCote to MonoKote
(been told plenty of time that if you're skillful with UltraCote there are
tricks to learn before becoming equally adept with MonoKote). The
latter is not necessarily harder but it's definitely different
because it goes on at higher heat and is a lot more work to get
around compound curves like wingtips.
Anyway, if you're still with me, I'll
share this last bit and quit. MonoKote came along and made some guy a
tidy fortune. What was a nice kit-business (nice but labor intensive
because kitting models is a lot of work) changed Top Flite, the
company. Basically MonoKote was a single product that made it
different from all the other kit makers of the day - something of a
one-trick pony ideally suited for widespread distribution.
was a better mousetrap at a time modelers were hungry for an easier
way to finish a model airplane than the laborious silk and dope
process. And believe me, with maybe four or five silk-and-dope
finished models under my belt before switching to MonoKote, I could almost do it in my sleep! The point being, my thoughts regarding silk and
dope aren't mere theory but something I know good and well how
to do! And maybe because I know how much sheer work it involves, I give thanks to the creators of polymer films
every time I cover a new model!
So back to what wound me about the axle
with whether the Extreme Flight Turbo Raven is an all UltraCote
finish or has sprayed panels . . . the thought of giving up UltraCote
for a prepainted covering job didn't cut it with me. Yes, it would
actually stop me from buying the Turbo Raven had that been the case.
Hmmm, seems I've become the curmudgeons of my day!
Anyway, I'm glad
the knowledge of crafting a good silk and dope job remains in my bag
of tricks but I don't really miss it despite Chinese silk and various brands
of dope remaining readily available. Polymer heat shrink film with
color adhesive simulates the old fashioned silk and dope job well
enough that from the 1970s it's totally dominated the field for
finishing your model airplane. Deservedly so.
Nothing breeds copy cats like
someone else making a pot of money. Competitors to MonoKote soon
surfaced. From England there was Solarfilm. Horizon Hobbies has
Oracover (a German product), which they rebranded as UltraCote. And
now that Horizon has bought out Hobbico they own the two most popular
products. Meanwhile, Solarfilm is all but defunct in the USA and perhaps England as well with the advent of ARF models.
However, the end result with any of the films is functionally
identical. Anyway, applying UltraCote isn't the same as applying
Monokote. While both are a heat shrink polymer sprayed with color
adhesive and sold on a 6' roll, UltraCote shrinks and goes around
compound curves better and at a lower heat. UltraCote is a tiny bit
heavier than MonoKote but unless you're flying competitive free flight this
probably doesn't matter (and in which case you'd be looking at other films
that are lighter).
One downside of UltraCote is it's
softer than MonoKote and thus, it scratches more easily. It's also
got a slightly duller shine than MonoKote. Some like this better.
Again, a judgment call. UltraCote is also easy to paint because paint
adheres well. Just because I pooh-poohed painted trim doesn't mean I
don't recognize there are times a places where painting the whole
plane which has been covered in film sometimes makes perfect sense. As a wise old wag once said, it depends. Anyway, both
UltraCote and MonoKote do a superb job of simulating a silk and dope
job without the smell and in a fraction of the time.
Me? I use either interchangeably
because to know one is to know the other (with just small adjustments
of your technique). And both produce a decent finish. But there's
no mistaking either for a good silk and dope job up close.
That said, the market has spoken and for the vast majority of us, film is definitely decent enough for most, me included - and coming
full circle - I'm very pleased to learn the EF Turbo Raven model is
100% covered in UltraCote film. Fortunately, the
saintly and long suffering Lynn won't object to my getting yet
another model airplane. How do I know? It's because I once overheard
her putting a snooty gal in her place at a party.
This gal was was definitely being snarky when she wondered out loud what it must be like to live with a man who has never grown up (referencing me and my
'toy' airplanes). Lynn, without missing beat drolly said, “I don't mind because his models have wings instead of legs plus he's
always home at night.” You could have heard a pin drop because it
was common knowledge that gal's husband (an advertising exec) was
fooling around with one of their clothing line models on the side, but again, I
Finally, if you're wondering, will I strip down the Turbo Raven and recover it in silk? Nah, not a chance! Comments, thoughts, questions? Fire