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Last-modified: Dec. 4 1994
Greetings! This is the "Radio Control (R/C) Flying" help file, containing
information of general interest to beginners. This file is posted regularly
(every 28 days), and automatically.
If you are just starting out in R/C (radio controlled) flying, or just
thinking of it, be sure to read at least the Introduction and the sections
on Building/Buying, Learning to Fly and one of Gliders, Power or
Electric's. I have tried to address all questions a beginner may have;
if
your question isn't here, please send it to me so I can include for
the
next person needing help.
Remember, no amount of FAQ reading can substitute for an instructor!
Shamim Mohamed
shamim@math.isu.edu
============================== Cut Here ======================================
Authors:
W.A. - Wayne Angevine (angevine@badger.Colorado.EDU)
G.H. - Gary Hethcoat (gdh@dobbs.Eng.Sun.COM)
K.S. - Ken Summers (cs3871aa@triton.Unm.EDU)
J.P. - John Pitman (jrp@bohra.Cpg.Oz.AU)
G.J. - Greg Johnson (johnson@nrtc.Northrop.COM)
S.M. - Shamim Mohamed (shamim@math.Isu.EDU)
Thanks to the following for comments and reviews:
Dave Burritt (drb@druwy.Att.COM)
Jeff Capehart (jdc@reef.Cis.Ufl.EDU)
Warren R Carithers (wrc@cs.Rit.EDU)
Carl Kalbfleisch (cwk@boomer.Ssc.GOV)
Contents:
-Part 1
Introduction -- Beginning
R/C, radios
-- (S.M.)
Buying & Building -- Kits, ARFs and Scratchbuilding
-- (S.M.)
Learning to Fly -- Instructors, Pre-flight
checks -- (S.M.,G.H.)
Gliders
-- Launching, Staying Up, Recommendations and Costs
-- (S.M.)
-Part 2
Power (gas)
-- (G.H.,K.S.)
Electrics
-- Advantages, Equipment, Motor Specs., Recommendations --
-- (W.A.)
Helicopters -- Getting
Started, Controls, Radios... -- (G.J.)
Some Aerodynamics -- Speed, Turning, Stalls
-- (S.M.)
The rec.models.rc ftp site
-- to get plotfoil, airfoil data, circuit diagrams &c. --
Other Information -- esoteric supplies and materials
-- tuned pipes
-- (J.P.)
:::::: -- Introduction -- ::::::
Should I start with powered flight, or with a glider?
Depends on your preferences. I prefer gliders; that's where I started.
The
2m (6 foot wingspan) class is a good size---large enough to be easy
to fly
but small enough for easy transport. Beginner gliders are lighter,
fly
slower and are more acceptable to the non-flying community than powered
planes---no noise or mess. Gliders are also cheaper (at least the trainers
are) than powered planes---no fuel, batteries, starter etc. to worry
about. Electric Flight is silent and clean so finds greater acceptance
from neighbors etc. at the flying field, although some people feel
that
electrics are not robust/easy enough for beginners. There is a little
more
paraphernalia - you may need spare battery packs, but you can fly from
smaller fields. Power (with engines that use a fuel) will let
you fly
longer, and your model doesn't need to be as light as with electric
(so
it's likely to be easier to build); however, you may have to go to
a field
far from populated areas.
Whatever you pick, stay away from those sleek fast scale
jobs! They
look nice and fly hard, and those are the last things you want in your
first plane. Stick to the trainers - they might not look as glamorous,
but they will make you a much better pilot.
And the most important point - no matter what else, try
to find an
instructor! This is the one thing that may make the difference between
a
rewarding experience and endless frustration. R/C pilots are friendly,
and
most will gladly teach you for free.
Are there any organizations etc. I can join for information?
Ask at your local hobby shop---there may be a club in your neighborhood.
This is the best way to meet other pilots and find an instructor. Most
pilots will more than glad to help you out. If you can find a
club, for
an instructor, choose someone who is smooth in flying his/her plane
and
that you get along with. Remember, the ones best at flying (hangar
or
otherwise) may not always be the best instructors.
For U. S. residents, an organization well worth joining is the Academy
of
Model Aeronautics (AMA). They are the modellers' main voice where
it
matters---they liaison with the FCC, the FAA and Congress. It is an
affiliate of the National Aeronautic Association (NAA) and is the US
aeromodeling representative of the Federation Aeronautique Internationale
(FAI). Membership in the AMA also gets you $1,000,000 of liability
insurance, without which most fields will not allow you to fly. You
also
need to be an AMA member to participate in contests. Besides, you also
get
a magazine, `Model Aviation' which is rather good in itself, and it
keeps
you informed about the state of the hobby. So JOIN AMA!!! You can write
to: Academy of Model Aeronautics, 5151 E. Memorial Drive, Muncie, IN
47302-9252. Membership is $40 per year (and well worth it). Their phone
number
is 317 287 1256.
--- Radios:
Since a trainer needs only 2 or 3 channels, should I get one of the
cheap
radio systems?
Don't bother with the cheap 2 or 3 channel sets---get a
4-ch system.
It will come with NiCad rechargeable batteries and (usually) 3 servos;
this is the most popular and most cost-effective kind of system. You
can
put the main pitch control (elevator) and the main turning control
(in
this case the rudder) on one stick, which is how most people (and thus
most instructors) fly. The cheaper systems come with the controls
on
separate sticks and you will have tough time finding someone willing
to
teach you with that setup. They also use non rechargeable cells, which
can
get very expensive, and sometimes have corrosion problems at the terminals.
What is a "1991" system?
Strongly recommended! A "1991" system is so named because in 1991
the
radio control frequency regulations changed, which effectively made
the
"old style" radios unusable. The "old style" radios have a separation
between channels of 40 kHz. Today, a separation of 10 kHz is
needed, even
though R/C channels will still be 20 kHz apart---because the FCC in
their
infinite wisdom have created channels for pagers and such _between_
the
R/C channels, i.e. 10 kHz away from our frequencies. The Airtronics
VG4 FM
series is an inexpensive example, and is about $120 mail order. [U.
S.
specific]
If you can afford it, a system that has a "buddy box" is a really good
idea. This is an arrangement where the instructor's radio is hooked
up to
yours, and he just has to release a button on his radio to take over
control, rather than wrestling the radio from your grip. If you do
this,
be aware that you need to get the same (or compatible) radio as your
instructor.
What about R/C rocket powered airplanes?
Rocket power for R/C aircraft is strictly regulated by the AMA; however,
R/C rockets are a popular hobby. You should contact the National Association
of Rocketry (NAR), and read the rec.models.rockets newsgroup. The FAQ
list
for that group may be obtained from sunsite.unc.edu by anonymous ftp;
get
/pub/ftp/pub/archives/rec.models.rockets/RMRFAQ/rmrfaq.*. Part 3 contains
information on R/C rockets.
:::::: -- Buying and Building -- ::::::
Should I start with plans and build my own plane from scratch, buy a
kit
plane with wood and plans included, or go with one of those everything
included ready to fly planes.
There are a few good trainers that are ready to fly (or almost ready
to
fly, aka ARF). ARF planes are usually heavy and hard to repair. The
new
generation of ARF kits is all wood and better built but more expensive.
The better kits have parts that are machine cut, the somewhat cheaper
ones are die-cut. You'll probably have to so a little more work with
a
die-cut kit, mostly in separating parts and sanding them.
ARFs vs. kits: this is a matter of opinion, but more people seem to
think
that kits are a better idea for beginners. Pro kits: you get valuable
building experience and are able to do repairs. Moreover trainers are
good planes to learn to build as well as to fly, and most of them are
cheaper than most ARFs. Pro ARFs: you can be flying sooner, and you
have
less emotional investment in the plane so when you crash you don't
feel
as bad.
However: regardless of what you chose, your chances of
a painless
education are greatly improved if you have an instructor---both for
building and for flying.
Remember, the plane you buy doesn't have to be good looking, it just
has
to teach you to fly! Many pilots after building a beautiful model are
so
afraid to crash that they never fly. Far better to have a scummy looking
plane that you don't mind crashing again and again and learning to
fly
than to have a slick model that you can only mount on a stand! After
you
are proficient you'll have plenty of time to build good-looking planes.
It seems to be the general consensus that there are enough decent kits
around that building from scratch is not really worth the effort unless
you are into design or obscure scale models. If this is what you really
want, you may find the "plotfoil" program (available from the
rec.models.rc ftp site and from comp.sources.misc archives) useful.
The most important thing you can do while building is to make sure that
everything is straight and square. This will result in a plane that
flies
consistently, predictably, and according to what you do at the transmitter
instead of constantly trying to turn! This means: make sure the fin
and
the stabilizer are at right angles; make sure the wing and stabilizer
are
at right angles to the fuselage (viewed from above); looking at the
side
view, the wing, stabilizer and engine (if any) are all at the angles
specified on the plans; and that the wing is built on an absolutely
*flat*
surface, to make sure it doesn't have any warps or bends.
Covering: for now, stay with Monokote. It's reasonably easy to apply,
not
too heavy, and fuel proof. (The label gives directions.) Also, if you
screw
up a bit and find that the wing is warped, sometimes you can fix it
by
twisting it and re-shrinking the covering to hold it in place.
Hinges: There seem to be as many opinions on this as there ways of
hinging! The important thing to watch out for - they should be strong
enough so they won't pull out, and the gap between the surfaces should
be
as small as possible. This is yet another place that an instructor
is
invaluable.
:::::: -- Learning to Fly -- ::::::
The most important point, one which cannot be overstressed:
*GET*AN*INSTRUCTOR!*
Here's what one beginner had to say:
I just started doing RC planes myself. In fact, yesterday I flew
my
plane for the first time (with an instructor). He took off for
me,
got the plane at a real high altitude and then gave me the controls.
I did OK (in my opinion) but did have to give him the controls
twice
in order to get the plane into stable flight again. I figured
the
controls would be sensitive but I did not realize HOW SENSITIVE.
I
only had to move them about 1/8 of an inch to turn.
There is no way I could have landed the thing without crashing.
By the way I am a full scale pilot. That did not help me at
all.
In fact I think it hurt. I didn't realize how much I use the
"feel
of the plane" when flying a real one. Obviously you have no
feel
whatsoever with RC planes.
You probably won't have any really bad (i.e. irreparable) crashes.
(Of
course, you'll still crash.) Also make _sure_ you have your instructor
check your plane thoroughly _before_ the first flight---as someone
said,
"it is much better to go home with no flights and one airplane than
go
home with one half a flight and many little pieces." This is really,
*REALLY* important.
--- Pre-flight Checklist ---
When your model is ready to fly, make sure it is thoroughly checked
over by
someone who has done alot of building and flying. When I say thoroughly,
I don't mean just picking it up and checking the balance and thumping
the
tires a few times. Every detail of setup and connection should be gone
over
in detail. If your instructor doesn't want to spend this much time
checking your plane, find a new instructor.
The importance of this pre-flight check cannot be overemphasized! Many
planes
are lost due to a simple oversight that could have been caught by a
pre-flight!
Here's a checklist:
_Before_the_first_flight:_
1) Weight
---is the model too heavy?
2) Balance
---Is the center of gravity (fore
and aft) within the range shown
on the plans?
---Is the model balanced side
to side? (right and left wings of
equal weight)
3) Alignment
---Are all flying surfaces at
the proper angle relative to each other?
---Are there any twists in the
wings? (other than designed-in washin
or washout)
4) Control surfaces
---Are they all *securely* attached?
(i.e. hinges glued, not just
pushed in)
---Are the control throws in the
proper direction *and* amount?
(usually indicated
in the plans)
5) Control linkage
---Have all linkages been checked
to make sure they are secure?
---Are all snap-links closed?
---Have snap-links been used on
the servo end? (They are
more likely
to come loose when used on the servo)
---Have all screws been attached
to servo horns?
6) Engine and fuel (if applicable)
---Has the engine been thoroughly
tested?
---Are all engine screws tight?
---Has the engine been run up
at full throttle with
the plane's
nose straight up in the air? (To make sure it
won't stall
when full power is applied on climb out)
---Is the fuel tank level with
the flying attitude of the plane?
---Is the carburetor at the same
height (not above) as the fuel tank?
---Is the fuel tank klunk in the
proper position and moving freely?
7) Radio
---Has a full range check been
performed?
---Has the flight pack charge
been checked with a voltmeter?
---Have the receiver and battery
been protected from vibration
and shock?
---Is the receiver's antenna fully
extended and not placed within a
fuselage with
any sort of metallic covering?
_After_repair:_
The checklist should be gone through again, with particular attention
to
the areas that were worked on or repaired.
_Before_*EVERY*_ flight:_
1) Start the engine (if applicable) and test the entire throttle range.
Run
it at full throttle with its nose in the air for 15 seconds
or so.
2) Check the receiver flight pack with a voltmeter to ensure enough charge.
3) Check the control throw direction for all surfaces. It's very easy
to
do a repair or radio adjustment and forget to switch these.
If you can't find an expert that is willing to teach you, it is best
to
start with a 2-3 channel model with a long wingspan and alot of dihedral.
The ideal thing to start with here would be a 2 channel glider. If
you
MUST start with a powered plane, a 6' foot powered glider, like the
Piece
O' Cake from Dynaflite is a good way to go.
:::::: -- Gliders -- ::::::
A 2 channel (rudder+elevator) polyhedral [see below] glider is just
about
the easiest way to learn to fly, and is highly recommended. Once you
can
handle that you can move up to rudder-elev.-spoiler-flap competition
ships or (on the slope) rudder-elevator-aileron-spoiler aerobatic ships.
Sailplane plug (aka religious sermon): ... don't think glider flying
is
just "launch, glide back"---It's very easy to get 30+ minute flights
and
about 1000' altitude. Remember, power flying is limited by the
size of
the fuel tank (about 10 minutes) and gliders are limited by the receiver
batteries (about 2 hrs). And glider flying is *much* more challenging
(my
opinion, of course), while at the same time being easier to learn.
And no
fuel costs, no starting hassles, no cleanup afterwards... Also,
many
cities have ordinances prohibiting model engines, which means the flying
fields are outside city limits. BUT, since sailplanes don't have
those
nasty, messy smelly things, we can fly in any large enough area!
Are most gliders hand launched, or do they have a small engine to get
them up?
Gliders are usually launched by a "hi-start"---a section of rubber with
about 500' of line. It is hooked to the plane and pulled back---the
rubber then pulls it up kite-like. (It is NOT like a catapult launch!).
Launches of heights up to 500' can be obtained on a good day. The launching
procedure is simple---keep the elevator neutral (for now) and keep
it
flying straight. At the top the glider will just fly off the line.
A small
engine can also be used but it creates a lot of drag which is very
detrimental to gliding performance. Hi-starts range from around $20
for
light-weight models to $100 for heavy-duty ones.
Winches are also used---it's very similar to a high-start except that
you
(the pilot) always have control over the line tension so you can usually
get better launches. It does take more skill, though; as a beginner
you
don't need to worry about winches just yet.
Flying at the slope you just chuck the plane into the wind---that's it!
How do sailplanes stay up?
Since a sailplane has no engine, it follows that it must always sink
through the surrounding air. The trick then is to find some air that's
going up faster than you'll sink through it... and for our purposes,
there are two kinds of such air:
---air heated locally will tend to rise. The heating could be
by the
sun on a parking lot or a bonfire or a ....
This is called "thermal
soaring"---the columns of rising air are called
thermals. This needs
some skill/experience, and mostly involves
smooth flying and a good
idea of how your plane reacts. An easy way
is to just follow more
experienced fliers (some of which are birds)
into them.
---wind striking a slope will rise to go over it. You just fly
in front
of the slope where the air is going up. With
a steady wind this is
easy to fly in, with challenges provided by
aerobatics etc. This is
called (surprisingly) "slope soaring." Landing
is more challenging
while at the slope unless you have a large
field or something at the
top.
Recommendations:
Sailplanes:
6' or 2m class: (recommended)
Carl Goldberg Gentle Lady, Dynaflite/Craft-Air
Drifter II, Airtronics
Olympic 650, SIG Riser, Great Planes Spirit,
etc. These are all
polyhedral ships with rudder and elevator
controls. All are highly
recommended.
Carl Goldberg Sophisticated Lady: basically
a souped up Gentle Lady,
it is in general not recommended---it's heavier
and the T-tail
structure is very easy to break, even on a
slightly rough landing.
100" or standard class:
These models fly better but are more cumbersome
to launch and transport,
and are also slightly more expensive. Try
Dynaflite/Craft-Air Butterfly,
Airtronics Olympic II, SIG Riser 100 etc.
These are basically scaled up
versions of the 2m ships above.
Costs:
What kind of cost am I looking at for a solid training glider or
powered plane, with all gear?
$200 is in the ballpark. $120 for a 4-ch radio, $60 for a 2m glider,
covering and other supplies. ARF Gliders---$100 + radio + supplies.
Powered planes: about $350-400---$120 radio, $70 plane, $120 engine + supplies.
(By "supplies," I mean things like rulers, knives etc.)
================================ End of Part 1 ==============================
Archive-name: RC-flying-FAQ/part2
Last-modified: Dec. 7 1994
============================== Part 2 ========================================
:::::: -- Powered (gas) -- ::::::
Even though "wet" power is called "gas", it's not the same as car
gasoline. Model fuel is usually a mixture of a lubricant (synthetic
or
castor oil), methanol and nitromethane. The power plants are usually
called engines, as opposed to electrics, which use motors (see below).
Engines are available in 2-stroke (louder, cheaper, and more powerful
for the same displacement) and 4-stroke (a more scale sound, less
vibration, but more expensive). Engine displacements are usually
measured in cu. in. the US (A 60 engine = 10cc [actually 0.61 cu. in.]).
Compared to beginner's gliders, powered trainers are more difficult
to
master. This means that everything about instructors and equipment
checks goes DOUBLE for powered planes. There are many, many ways a
beginner can make mistakes and destroy a model that he/she has spent
alot of time and money on. With the typical powered trainer, going
it
alone is foolhardy and will likely end with a destroyed model and a
very disappointed modeler.
If you can't find an expert that is willing to teach you, it is best
to
start with a 2-3 channel model with a long wingspan and alot of
dihedral. The ideal thing to start with here would be a 2 channel
glider. If you must start with a powered plane, a Sig Kadet is one
of
the more docile trainers.
If you have an instructor, but have not flown R/C before, you can start
with something a bit more advanced. In general, the larger the
plane,
the easier it is to see and to fly; but at the same time, the more
expensive it is. The most popular size is the so-called "40-size" plane,
with about a 50" wingspan and .40 cu. in. engine. The Great Planes
PT-20/40/60 series are good. You can build these with ailerons,
but due
to their large dihedral, they can also be flown without ailerons. It
won't hurt to have them built-in. Even though they will not be very
effective, they will get you used to using them. Other recommended
planes are the Midwest Aerostar and the Goldberg Eagle. Something with
a "tricycle" undercarriage, that is one with a nose wheel and two main
wheels, is the easiest to learn on.
If you have an instructor, and have flown R/C gliders, you might want
to start with something still more advanced, say a Great Planes Trainer
20/40/60 or the like. These have a fully symmetrical airfoil and less
dihedral. They are capable of more in the way of aerobatics, but are
trickier to fly due to higher speed and less stability.
:::::: -- Electric Flight -- ::::::
I didn't know that you could put an electric motor and batteries
in an airplane. Isn't that kind of heavy?
Modern NiCd batteries are pretty amazing. You can charge them
in 15
minutes, take power out of them at up to 50 amps or so, and do it all
day.
That capability is what makes electric flight possible. Electric
power can
be used for any kind of flying---gliders, aerobatics, even racing.
It's an
excellent choice for sport flying.
What are the advantages and disadvantages of electric flight
compared to wet power?
Electric power systems are heavier for a given power output. This
means
that planes must be built lighter, which may be more challenging
(especially for the beginner). That's really the only significant
disadvantage. The big advantages are that electrics are quiet
and clean.
To me, the biggest advantage of all is that electric flight is unusual
and
interesting.
What is the best way to get started in electric flight?
That depends on what you want to do and where you're starting from.
If you've never flown RC before, and you want to start with an electric
plane rather than a pure glider, I recommend an electric glider like
the
Airtronics Eclipse. This will give you the best chance to stay
ahead of
the plane. In the sport/trainer category, I hear a lot of good
things
about the Leisure Amptique.
If you know how to fly RC, you have a lot of choices. The simplest
and
most available electric power systems use six or seven cells.
These are
called "05" systems, and are very similar to the power system of an
RC car.
You can find all sorts of planes in kit or plan form which will work
well
with these systems. Outstanding examples are the aforementioned
Eclipse
and Amptique, old timers such as the Leisure Playboy and Astro Viking,
a
variety of semi-scale kits from Davey Systems, all sorts of gliders,
and
the aerobatic ElectroStreak from Great Planes. Any two meter
glider kit
can be easily adapted to six or seven cell electric by a moderately
competent builder. Just stick a motor in the nose, battery under
the wing,
and go.
If you want more performance, good ground handling, or just like larger
planes, there are larger power systems available, all the way up to
systems
which will handle a 60-sized power plane. The cost and complexity,
of
course, go up with size. Any reasonably well designed power plane
kit or
plan can be adapted to an appropriately chosen electric power system.
The
first step is to leave out half the wood---all power planes are grossly
overdesigned. Electric motors generate very little vibration,
which helps
you get away with lighter structures.
What are the elements of an electric power system?
The power system includes a battery, a motor, a control, and wiring.
The
battery is almost always made up of Sanyo NiCd cells in the appropriate
number. Motors vary from the simple, cheap "can" type (otherwise
known as
"540" or "550" style), through more sophisticated styles adapted from
RC
car motors, up to the cobalt powerhouses.
Controls can be a simple on-off switch controlled by a servo, a directly
controlled on-off switch, or a proportional electronic control.
If you are going to fly a glider or old-timer type plane with less than
a
500-watt motor, think seriously about getting battery packs made of
Sanyo
900 SCR cells. They are significantly lighter than the more usual
1200 mAH
(sub-C) cells and give excellent performance.
What do the various letters used to refer to NiCd cells mean?
A: SC is the basic cell. SC cells will take fast charging
and have
reasonably low internal resistance. SCR cells have lower internal
resistance and a somewhat flatter discharge curve, that is, they put
out nearly the same voltage from beginning to end of the discharge.
SCRs are best for high current drain applications. SCE cells
have
somewhat more capacity for the same physical size, but also have
higher internal resistance. They are best for low current drain
use (less than about 10 Amps.) The higher capacity of SCE cells
will not be realized at high current drains, and they will heat up
more than SCR cells.
Many kits nowadays come with a power system. In most cases, these
systems
are adequate for the application. It won't hurt to try what's
there to
start with, you can always experiment later. If the kit you choose
doesn't
come with a motor, of course, you'll have to choose one. If you
are a
beginner, go with the recommendations of the kit manufacturer.
If you are
an experienced RCer, you probably don't need my help.
For a six- or seven-cell glider or old-timer with a cheap motor, an
on-off
switch is sufficient control. For anything else, you will have
much
greater enjoyment with a proportional throttle. Get a high rate
control,
they are much more efficient at part throttle. There are several
good
brands out there, but I like Jomar for good controls at good prices.
What support equipment do I need?
You need a charger of some sort. If you are using six or seven
cells, any
RC car charger will do the job. You don't need peak detecting
or any of
that fancy stuff to start with. For larger packs, there are good
high-voltage chargers around. Check out Astro Flight and TRC,
among
others. Remember, the biggest enemy of NiCads is heat, so try and keep
those
batteries cool when charging. Expect to pay about $40.
How are motor sizes specified?
Motors are traditionally specified by a system which attempts to equate
them to wet engines. There are significant problems with this,
but they
probably aren't of concern to beginners. An "05" motor takes
a six or
seven cell battery and puts out 75 to 120 watts, and so on up to a
"60"
which takes 28 cells and puts out 1200 watts. Incidentally, there
are
about 750 watts in a horsepower.
The actual power output for a given voltage (number of cells) depends
on
the load. Unlike wet engines, electric motors put out more power
with more
load. If you don't like the performance you get from your plane,
you can
try a bigger propellor---up to a point. More power, of course,
means less
run time.
In the ideal world, motors would be specified by the total power they
are
capable of supporting and by the number of cells (or voltage) with
which
that power is produced.
What's a cobalt motor and why would I want one?
Rare-earth magnets, of which the most common type is samarium cobalt,
are
stronger for a given weight and volume than ferrite magnets.
Perhaps an
even more important reason for getting a cobalt motor is that they
also
have better brushes, bigger shafts, better bearings, are built more
carefully, and so on. For the serious electric flier, they are
worth the
extra expense.
Where can I get this stuff?
Electric equipment is somewhat specialized, and most hobby shops aren't
yet
sufficiently enlightened to carry very much. You can use RC car
equipment
for a lot of things (after all, they developed this stuff in the first
place) and your local hobby shop will have lots of that. If you
want to
get more sophisticated, get the catalogues from Hobby Lobby and Hobby
Horn
(both have ads in all the usual magazines.) Both catalogs contain
a lot of
detailed information that I can't fit in here. Hobby Horn has
good prices
on mainstream stuff. Hobby Lobby sells the lines of several European
manufacturers, and tends to have higher prices for fancier (or at least
more unusual) stuff. I haven't dealt with CS Flight Systems on
the East
Coast, but I read good things about them.
:::::: -- Helicopters -- ::::::
Getting started
How hard is flying heli models?
What are some good helicopters to consider?
Price to get going?
What are some good books?
What accessories should I get?
What about electrics?
Controls on a heli
What is cyclic? Collective?
What is gyroscopic precession?
What do the servos control?
What is the use of gyros and how do they help?
How about fixed-pitch versus collective helis?
Radios
How many channels do you need to control a heli
and why?
What are the radio options?
Can I use my airplane radio?
Flying
What's the deal on auto-rotation?
What about aerobatics?
How high do they fly? How fast do they go?
Getting started
How hard is flying heli models?
Getting the hang of flying an R/C heli is a fairly challenging undertaking.
It's like riding a bike: when you first start trying it seems impossible,
but with enough practice it starts to seem easy, like second nature.
It
may take 5 or 10 sessions to get to the point of being able to hover
with
some consistency. Helicopters provide a long sequence of challenges,
and
the corresponding satisfactions of mastering them. After hovering,
there
is forward flight, nose-in hovering and flight, auto-rotation, aerobatics,
inverted flight, etc.
What are some good helicopters to consider?
There are several good helicopters on the market. It's a bit like
Ford
people versus Chevy people: different people develop preferences for
different helis. Good ones to learn on include the Hirobo Shuttle,
Kyosho
Concept .30, and Kalt Enforcer. An excellent although somewhat
more
advanced heli is the X-Cell .40. Also, Shluter makes first-rate
R/C helis.
Check out the local hobby shops to see what the well supported helis
are in
your area, and if possible find where the locals fly. Hang out
at the
flying field for an afternoon or two, and see what the locals are flying.
Price to get going?
The helicopter itself will cost from $250 to $400 for a good starter
heli.
A radio will cost $200 to $450 or so. Gyro is about $70.
Engine is about
$130. Starter box, starter battery, etc. will probably be at
least another
$100.
What are some good books?
There are two excellent books. Paul Tradelius's book (available
through
Model Airplane News) is particularly good for beginners. He presents
the
material in an order and a depth that is well suited to getting started.
A
more encyclopedic book is the one by Ray Hostetler. This book
goes into
great detail on all topics, and is a book to grow into. Ray's
book mixes
beginner info and info necessary only for advanced pilots, and consequently
can be a bit overwhelming at first. There's a lot of stuff in
there that
you won't need to delve into for quite a while. I would recommend
getting
both of these books.
What accessories should I get?
There are a million accessories that you can buy. There are a
relative few
that are indispensable, or almost so. I'd put the following items
on the
short list: a prop balancer, a pitch gauge, a pair of ball link pliers,
and
a receiver battery tester. You will need a standard assortment
of tools
such as needle nose pliers, screw drivers, hex wrenches, etc.
You'll also
need a starter and starter battery.
What about electrics?
There are a couple of pretty good electric helis on the market.
One is
made by Kyosho (the Concept EP), and one is made by Kalt (the Kalt
Whisper). These machines are small, light, delicate, and squirrely.
Not
the thing to try to learn on. They are more novelty items for
experienced
R/C heli pilots.
Controls on a heli
What is cyclic? Collective?
On most R/C helis (and full-scale helis for that matter), the main blades
can change their (so-called) pitch angle. What this means is
that if you
sit the heli on a table and look at the tip of one of the main blades,
the
chord line of the blade can be tilted through a range of angles by
the
servos. In this sense, the rotor disk of a heli is a bit like
a
variable pitch prop on an airplane. If the heli is hovering and
you wish
to make it climb straight up, you increase the pitch of the main blades,
and increase the throttle so that the engine can overcome the increased
drag and keep the blades turning at the same speed. The increased
blade
pitch results in more lift, and so the heli climbs. (With R/C
helis,
unlike R/C airplanes, engine RPM's are supposed to stay the same over
(most
of) the throttle range. At high throttle the engine puts out
more power,
but there is a corresponding increase in the load on the engine due
to
increased main rotor blade pitch, and so the engine stays at the same
RPM's.) This overall increase in pitch that makes the heli climb
is called
collective control.
To get the heli to pitch forward or back, and to roll left and right,
there
are controls that are analogous to airplane elevators and ailerons.
These
controls are referred to as cyclic controls. The idea is to set
up
asymmetric lift on the rotor disk. (This is similar to what ailerons
do to
an airplane-one wing can be made to generate more lift than the other,
and
so the airplane rolls.) If there's asymmetric lift on the rotor
disk, the
plane of rotation of the rotor disk is going to change. For instance,
the
rotor disk (and the heli that is attached to it) might go a bit nose
down.
In that case, the heli will transition out of a hover and start flying
forward. Similarly, the heli can be made to lean back (nose high),
left,
right, or any combination of these. The way this asymmetric lift
is set up
is to vary the pitch of each blade as it goes around. For instance,
say
you push forward on the cyclic control stick (the right one on your
transmitter, which does the same thing as an aileron/elevator control
stick
on an airplane radio). This will make the blade pitch down as
it travels
through the forward moving part of the rotor disk (usually the left
side of
the rotor disk), and it will make the blade pitch up as it travels
through
the backward moving part of the rotor disk (usually the right side
of the
rotor disk).
What is gyroscopic precession?
This is a counter-intuitive aspect of helicopters, that even many advanced
pilots don't clearly understand. In order to get the helicopter's
rotor
disk to tilt (for example) downward at the front, you increase the
lift on
the right side of the rotor disk and decrease the lift on the left
side of
the rotor disk. (This is assuming the standard clockwise main
rotor
rotation.) To see why this is so, consider the following example.
If the
heli is in a nose down attitude, the forward moving blade travels downhill,
and the aft moving blade travels uphill. The blades travel level
at the
front and back. To get a hovering heli to go into a nose down
attitude,
you need to encourage the forward moving blade to start going downhill
and
the aft moving blade to start going uphill. Hence, pushing the
cyclic
stick forward causes lift to be killed on the forward moving (left)
part of
the rotor disk and increased on the aft moving (right) part of the
rotor
disk.
What do the servos control?
There are usually five servos on an R/C heli. One controls throttle,
one
controls collective, one controls fore-aft cyclic (analogous to elevator),
one controls left right cyclic (analogous to aileron), and one controls
tail rotor pitch (analogous to rudder).
What is the use of gyros and how do they help?
The gyro is positioned so that it senses yaw. It then feeds small
inputs
to the tail rotor servo to counter the yaw that it detects. This
keeps the
helicopter from yawing to the left and right when you don't want it
to.
Left right movement of the left stick also supplies input to the tail
rotor
servo; so you and the gyro are both giving control inputs to the tail.
A
gyro is a MUST. It's probably not an exaggeration to say that
gyro based
stabilization of the tail rotor made R/C heli flying feasible.
It is
possible to fly an R/C heli without a gyro, and it's also possible
to
juggle seven balls. It's just darn hard! Furthermore, it's
definitely not
something you want to try tackling when you're just getting started.
Without a gyro, the heli can begin to whip around wildly as soon as
the
skids leave the ground. The heli will do a 180 degree turn and
you're
looking at an angry helicopter coming right at you before you know
what
happened. Definitely not something for a beginner to tackle.
How about fixed pitch versus collective helis?
Helicopters with collective are now inexpensive and reliable.
Every
reasonable modern heli, from beginner trainers up to FAI world beaters,
has
collective. In a fixed pitch heli, lift is controlled by varying
engine
RPM, just as in an airplane. This is an outmoded technology,
and you will
outgrow such a heli very soon. Virtually no aerobatics, no auto-rotation
(if the engine quits at altitude, the heli becomes a brick), not as
much
fun.
Radios
How many channels do you need to control a heli and why?
You need five channels to control a heli. You need one each to
control
pitch, roll, and yaw. You need one to control throttle, and you
need one
to control collective. You might think that one servo could control
both
throttle and collective, since they are related. There are several
reasons
this wouldn't work, however. The main rotor disk of a heli is
huge and
generates a correspondingly huge amount of drag compared to an airplane
prop. (If you think of the heli rotor disk as a big propellor,
its
actually pretty amazing that a tiny little .32 engine can turn it at
all.
There's about a 10:1 gear down from the engine to the main rotor, which
makes it possible for the engine to turn the main rotor.) So, you have
to
have fairly fine control over the relationship between the collective
pitch
(and corresponding drag) and the throttle setting. If you get
it wrong,
the engine bogs badly or races wildly. Also, auto-rotation is
an important
maneuver, and this entails control of collective pitch while the throttle
is set to idle. Finally, for inverted flight you want to have
full
throttle both at maximum up collective and maximum down collective.
What are the radio options?
Pitch curves and throttle curves: You can adjust the amount of servo
travel
at 0% stick, 25%, 50%, 75%, and 100%, both for throttle servo and
collective servo. This feature is a must.
Throttle hold: Flip this switch to practice auto-rotation; the throttle
is
reduced to idle. All the other controls still work normally.
Idle up: This is an alternate mode, usually used for aerobatics.
You can
set throttle and pitch curves, mixes, etc., and change over to the
different setup at altitude or whenever.
Programmable mixing: This neat feature lets you establish a relationship
between channels. One channel is designated as the input or master
channel. As the master channel varies, it causes small changes
to the
output channel. This is an advanced feature.
Revolution mixing: This feature causes increases in tail rotor as throttle
and pitch increase. This is useful to compensate for the increased
torque
the engine produces. I feel that this is a somewhat over-rated
feature,
and that it only really comes into its own when you're doing aerobatics.
Even then, a programmable mix may be better.
Electronic trim adjustment: similar to and augments mechanical trim
End point travel adjustment: sets where servos go at max stick displacement
Exponential: can be used to make cyclic less sensitive in midrange.
Can I use my airplane radio?
It is possible to control a helicopter with a 4 channel airplane radio.
You can master hovering and move into elementary forward flight this
way.
For anything beyond that, you will need a helicopter radio. If
you do try
to use a 4 channel airplane radio, build a Y-connector, and control
two
separate servos (collective and throttle) off the throttle channel.
Then
adjust control arms to get a form of mechanical throttle and pitch
curve
adjustment. It's not too hard to set a heli up so that it will
hover
tolerably well at mid-stick this way, and you can contrive to increase
lift
above mid-stick and lose lift below mid-stick.
Flying
What's the deal on auto rotation?
If a heli's engine quits in flight or you simulate this by going to
throttle hold mode, it is still possible to glide the helicopter down
safely. As the helicopter descends, the wind flows up through
the rotor
disk from below. At a low or negative collective pitch setting,
the wind
flowing up through the rotor disk keeps the blades spinning.
Heli blades
usually have lead weights epoxied into the tips, so as the blades spin
they
build up a fair amount of rotational inertia. When you are near
the ground
and ready to land, you add in collective to increase lift, and the
inertia
maintains head speed sufficient to execute a controlled landing.
In
theory. ;-) Auto-rotative glides and landings are beautiful to
watch. A
helicopter can sustain as much as a 4:1 glide ratio in auto rotation.
What about aerobatics?
Helis can do awesome aerobatics: loops, rolls, pirouettes, you name
it. My
personal favorite is inverted flight. If looks 'way cool to see
a
helicopter hovering inverted right above the grass. I've seen
guys do
aerobatics routines flying the whole thing BACKWARD. With a helicopter
you
have unbelievable versatility.
How high do they fly? How fast do they go?
Helicopters can go so high they are out of sight. Being able see
the thing
in order to control it is the only limit on how high they can fly.
R/C
helis can go 60-80 MPH or more.
:::::: -- Some Aerodynamics -- ::::::
The aircraft can rotate around three axes: the fore-and-aft axis (or
the
_roll_ axis); the span wise (nose-up/nose-down) axis or the _pitch_
axis;
and the nose-left/nose-right, or _yaw_ axis.
Speed:
The cross-section of the wing has a shape called an _airfoil_. It has
the
property that when it meets the air (usually at some small angle, called
the _angle_of_attack) it generates an upward force (lift) for a small
backward force (drag). The amount of lift (and drag) depends on the
airspeed and a value called the _lift_coefficient_ (and a few other
things like surface area and density of the air). If the plane is in
unaccelerated flight, the upward force (approximately equal to the
lift)
is equal in magnitude to the weight of the plane, which is a constant.
It
thus follows that the total lift generated by the wing is always constant
(at least in unaccelerated flight). [One example of accelerated flight
is
turning---see below]
The above mentioned _coefficient_of_lift_ (abbreviated Cl) depends on
the
angle of attack. Usually, as the A-of-A is increased, Cl increases;
to
keep the lift force constant, speed can decrease. So to fly fast, we
decrease Cl (and A-of-A); to slow down, increase Cl (and A-of-A). Since
the wings are fixed, we alter the A-of-A by pitching the entire plane
up
or down. This is done with the elevator. The elevator is thus
the speed
control.
Turning:
To turn a body moving in a straight line, a sideways force must be
applied to it. For a plane, the best method for generating a force
is to
use the wings. To get them to act sideways, we roll the plane: now
part
of the lift is acting sideways and voila! a turn. To roll the plane,
we
use the ailerons (the movable surfaces at the wing tips). Also, notice
that now since part of the lift is acting sideways, the lift force
in the
upward direction is reduced; but the upward component of the lift needs
to be equal to the weight of the plane i.e. we need a little
more lift
from the wings, which we can do by increasing Cl---i.e. by pulling
a bit
of up-elevator. That's why to turn in a plane you push the stick sideways
in the direction of the turn and then pull back a bit to keep the nose
level.
What happens if you try to turn with the rudder alone? The application
of
the rudder will cause the aircraft to yaw, and it will continue to
travel
in the same straight line (more or less), skidding. (Think of a car
on a
perfectly slippery road---if you try to turn just by turning the wheel,
you'll skid but won't turn). So we need a roll to turn.
But most of the trainers we see don't have any ailerons! How do they
turn? They use a configuration of the wings called _dihedral_ (or,
for most
gliders, _polyhedral_).
Flat
Dihedral
Polyhedral
~-_
_-~
-------O-------- ~~~----___O___----~~~
~~~~~~~----O---~~~~~~
^
^
^ ^
^
0 angle between small angle
between small angle between 2
wing
2 wing panels
2 wing panels
panels and also small angle
within
each panel (Gentle Lady)
OR
0 angle between 2 wing panels
and small angle within each
panel (Olympic 650)
When we apply rudder (say left rudder) to a plane with dihedral, what
happens? The plane yaws; the right half of the wing then sees
a greater
angle of attack than than the left half:
/ / / / / / <--- airflow
direction
._______________________.
|___________|___________|
left wing right wing
(You can try this out if you don't believe it: take a piece of paper
and
fold it slightly, like dihedral; then look at it end on, but slightly
off center, i.e. from the point of view of the approaching airflow.
You
will see that you can see more of the underside of one half than you
can
of the other.) And what does an increased angle of attack do? It
increases the Cl and the lift generated by that half! So we now have
the
right wing generating more lift and the left less; the result is a
roll
to the left. With polyhedral we get the same effect, only to a larger
extent.
The Stall:
If you try to fly slower and slower by pulling back on the stick (i.e.
applying up-elevator) you will reach a point where the plane "falls
out
of the sky" or the stall. What happens is that an airfoil will only
"work" up to a certain angle of attack. When that angle is exceeded,
the
airflow above the airfoil breaks up and the result is an increase in
drag
and a drastic decrease in lift, so that the wings can no longer support
the plane. The only remedy is to reduce the A-of-A i.e. to push the
nose
down. This may be a little difficult to do when you see your plane
falling---the natural tendency is to pull back on the stick, to "hold
the
plane up."
A development of the stall is the spin. Volumes can be written about
it,
and have been; go to the library and check any book on introductory
aerodynamics.
If you want to know more about Aerodynamics as it applies to Model
Aircraft (the small Reynolds' number regime, as it is sometimes called)
check "Model Aircraft Aerodynamics" by Martin Simons [Argus Books,
ISBN 0 85242 915 0].
:::::: -- The rec.models.rc ftp site -- ::::::
Nur Iskander Taib <ntaib@silver.ucs.indiana.edu> has been kind enough
to
establish an ftp site for the use of the rec.models.rc community. Use
anonymous ftp to log in to "bigwig.geology.indiana.edu" and go to the
directory called "models" . You will find subdirectories called
"airfoil", "faq" and "circuits". These contain, respectively:
plotfoil---a program to plot airfoil sections on PostScript
printers.
It can also draw spars and sheeting allowances, and can
plot airfoils of arbitrary chords (on multiple sheets). It
also includes a library of airfoil data, including many
from Soartech 8.
faq ---contains this FAQ file.
circuits---circuit diagrams for modeling applications,
including
"smart" glow plug drivers.
Another site is ickenham.isu.edu. Go to the "pub" directory. These files
(among others) are available:
README contents of the ftp site
rc.flying.faq{1,2} this FAQ file
plotfoil.tgz source code for plotfoil (gzipped tar archive)
plotfoil.zip MS-DOS executables for plotfoil and ghostscript
If you have a WWW program (like Mosaic) you can use this URL:
"http://ickenham.isu.edu/~ftp".
Other FTP sources:
Sometimes people have trouble getting to bigwig. Plotfoil
is also
available from comp.sources.misc, which is archived at many sites,
including sites in France and Australia. Get Volume 31, parts 28-30
(archive name: plotfoil). Contact your administrator, or read
the periodic
posting in comp.sources.misc for more information on how to reach the
nearest one.
This FAQ is available from rtfm.mit.edu, the news.answers
archive. It
is in /pub/usenet/news.answers/RC-flying-FAQ/part*.
These two sources are guaranteed to be up-to-date, since
it is all
done automagically.
:::::: -- Other Information -- ::::::
SOURCES:
Materials:
Composites - carbon-fiber, glass, epoxy and other composite
materials are
available from:
Aerospace Composite Products: P.O.Box 16621, Irvine, CA 92714. +1 714
250 1107
Carbon fiber tow, rods and strips; glass cloth, kevlar,
Spectra, rohacell.
Fibre Glass Development Corporation: 800 821 3283.
Glass fabrics, resins etc.
Composite Structures Technology: P.O.Box 4615, Lancaster, CA 93539 800
338 1278
CF, glass cloth, rohacell, kevlar. Recommended by some
for good prices and
lighweight materials.
TUNED PIPES:
Tuned pipes are a means of boosting the power of two stroke
engines.
They are not all things to all engines, but when properly set up they
can
be very effective.
If you have ever played a note by blowing over the end
of a piece of
tubing, you are using the principle involved. This is that any tube
has a
natural resonant frequency, usually dependent on its length, and the
speed of sound in air. This means that some oscillations will die away
quickly, but one in the right range will resonate, and be strengthened
in
force, when the wave---length matches the resonant length of the tube.
As a pressure wave in the sound reaches the end of the pipe, a reflection
is set up, and moves back up the tube. This occurs at the end, whether
open or closed, and at changes of section or taper. Now, if we arrange
a
length of pipe as a muffler for a two stroke engine, we will find that
at
a certain rpm, the pipe will resonate, and boost the engine's rpm up.
This is because the reflected pressure wave arrives at the exhaust
port
just in time to push some fuel/air mixture that was about to be lost
out
the port (due to timing overlap), back into the cylinder, where it
will
be burnt, producing more power than without the pipe. All we
have to do
is arrange the length of the pipe so that the boost in rpm occurs at
a
rev range that is useful to us with the relevant load (propeller).
It
may be that the engine cannot produce enough power to turn the fitted
prop at a useful speed. Some engines have port timing that cannot benefit
usefully from any pipe.
The major factor in setting up a pipe is the length for
a given
propeller and rpm range---some examples are given later. Some different
designs of pipes will produce different lengths, because of the effects
of diameter, taper angle and type of end reflector. Many pipes also
have
a muffled section which hides the rear cone or reflector's shape.
Here
are the basic questions to ask yourself before trying a pipe:
is the engine likely to benefit---if it is
a sport type engine, less
likely, but ask around.
If it has a name for power (e.g. ROSSIs, YS, the
hotter OS) almost certainly.
is the aircraft capable of handling extra
speed?
is the pilot capable of handling extra speed?
what prop and rpm range are you aiming at?
Let's get started. Record the static rpm on the prop of
your choice
with a muffler before doing anything else, so we know where we are
starting from. Try to get a starting point for the length from
a similar
set up if possible, and fit your pipe. If you have a choice, get a
header
that is a bit (1") longer than you think you need---it is easier to
shorten than lengthen the header. Now start the engine and tune
for
slightly rich from peak revs. Note that this may require a richer setting
than usual, as we (hopefully) are producing more power than before.
If we
have fewer revs than with a muffler, something is wrong---if your mixture
is correct, the pipe is probably too long. Try shortening the header
(or
pipe if more convenient) in 1/4" increments until the revs start to
rise.
If the pipe is too short, the motor will run harshly, and the needle
setting will be unstable and critical---add 1/4" spacers between the
header and the pipe. Now to fly it. If it is not visibly faster in
the
air, try a shallow dive. If there is a distinct jump in revs and speed,
the pipe is too short, and the `coming on' is caused by the prop
unloading in the dive and coming up to a resonant rpm. If however the
dive produces no change, but the vertical performance is better, the
pipe
is too long. Note that the references to `short' and `long' are
relative---the pipe cannot improve the speed over all rpm ranges, and
you
will have to decide what the most appropriate compromise for your case
is
yourself. Most fliers do not need to have the engine speed up while
descending, only to slow down in level and upward flight, so most
adjustments will be aimed at improving level and upward flight.
Remember that pipes will vary in their boost and tolerance
of
non-optimum length.
The lengths given below are from the exhaust port face
to the high
point of the two cones of the pipe, or if muffled, usually to the point
where the muffled section joins the first cone.
Prop
Length Rpm
OS 46 SF MA 10x6 345
mm 14000
OS 45 FSR MA 9.5x6 305 mm
15000+
(10x6 cut down)
OS 45 FSR MA as above 305 mm
16200 (exhaust port lifted 1.0mm)
ROSSI .60 MK 11x7.5 375 mm
YS .45 MA 11x7.5 320
mm
These examples used a variety of pipe makes, but I have
found that MACS
pre tuned pipes are hard to fault---i.e. they will come up straight
away.
Some other types and makes of pipes will differ---GRAUPNER pipes will
give bigger boosts, but are MUCH more critical on almost every parameter
---length, prop, plug, fuel etc.
Don't forget to record what you try so you don't repeat
mistakes or dead
ends in your trials. I have found good muffled pipes, properly set
up,
frequently are quieter than mufflers, especially when set up long with
big props---the best result I have had was an OS 46 SF with a 12x6
and a
pipe about 40mm(1.5") longer than for a 10x6, measured about 85db (at
3m/10ft) over grass, and in the air it was inaudible if there was
anything else in the air.
================================ End of Part 2 ==============================
