|
R/C Model Aircraft
Questions And Answers
As author and publisher of "Basic
Flight Instruction," an authoritative R/C flight instruction book and
training manual, I receive
literally hundreds of E-Mail questions from R/C fliers from all over the world.
Please note that my book has answers to virtually all your questions
about learning to fly R/C, choosing your first R/C airplane, and most other
topics essential to the beginner. So for these type of R/C questions, please purchase a copy of my book.
Click on the banner below to order a copy for your very
own...
For all other R/C model aircraft questions, please send me an E-Mail.
Your R/C questions are all very important to me
and I try to respond to each and every one of them. Answers to some of the more
common questions are posted below.
~Andrew S. Rosz
Question From Bill: How can I obtain an AMA
application?
Answer: By clicking on the link below.
The AMA application
will open as a .pdf file that you can print out and use. Please note that you will
need Adobe Acrobat Reader installed on your computer to open this link...
Note: click "Cancel" if prompted for a
password after clicking on the link below.
http://modelaircraft.org/templates/ama/PDF-files/902.pdf
Question From Howard:
Is there a rule of thumb as to
where the balance point should be located for an R/C airplane to handle properly?
Answer: For most R/C airplanes, the balance point (CG) should be
located about 1/3 the distance back from the leading edge of the wing to the trailing
edge. This is usually under the main spar of the wing plus or minus about a quarter
inch or so. To test an airplane for proper balance, place a finger from each hand
under the main spar on each side of the fuselage and lift the plane off the ground.
A properly balanced airplane should tilt slightly forward. You definitely DON'T want
a tail heavy airplane. All R/C airplanes should be a bit nose heavy in order to fly
properly. Once you observe how the plane flies for the first time, you can always
shift some weight around and/or add weight as needed to achieve the proper balance.
Question From Jeff: I am thinking about "scratch-building"
an R/C model aircraft from a plan. Do you have any idea where I can get any plans
off of the internet?
Answer: I'm sure there must be many model aircraft websites that offer
plans for download or sale, but I don't personally know of any. However, both Model
Airplane News and Model Aviation Magazine routinely advertises
their catalog of R/C aircraft plans in every issue. You can pick up a copy of either
magazine at your local newsstand. Or, once you become an AMA member, you get a Model
Aviation Magazine subscription included with your open membership. Please visit www.modelaircraft.org for more information.
Question From Ed: I have a new Airtronics VG4R radio Channel 60.
My question is using channel 60, the last one on the end; will I pick up
interference from what ever is used on the frequencies after 72.990 MHz?
Answer: Probably not. The FCC assigns channel usage in
such a way where there is adequate band separation between two different applications.
In all my years of flying R/C, I have never heard of anyone having problems with
either Channel 11 or Channel 60 due to their location at each end of the useable R/C
frequency range. Accordingly, you should have no problems.
Question From Greg: I read somewhere that you have obtained
patents for some of your model aircraft designs. What's involved in getting a patent
and I'm wondering just how much one can develop design principles applicable to
"full-sized" aircraft by experimenting with models? Are there any rules
regarding compensating for weights and thrust due to the differences in air pressure and
density from a "mini" model airplane as compared to a "full-sized"
one?
Answer: Patentable items include a design, the way something
works, and/or a method of manufacture. Indeed, if someone obtains a patent on the
way something works, patent law would protect that invention regardless of its scale.
As for using models to predict specific flight characteristics of the way a
"full-size" version might fly... not likely. The dynamics of the forces of
flight are simply much too great between full-size aircraft and models. You just
can't scale down the numbers and expect things to work. I guess you could if you
could also scale down the size of an O2 or an N2 molecule!
But
of course, that is not possible. This also explains why so many "scale"
models (exact miniature versions of a full-size version) fly like crap compared to their
full-size counterparts. The models I design have all been designed to fly great as
models. Through revision after revision, and a lot of trial and error,
one can learn how to blend just the right amount of each design
characteristic in creating the perfect flying model. Indeed,. my designs probably
wouldn't even fly at all if they were scaled-up to a full-size version.
Question From Mike: I have two pre 1991 approved AM radio sets.
Can they still be used?
Answer: As long as your radios have a "Gold Sticker"
attached to the back of them... This "Gold Sticker Standard" is the current FCC
requirement and indicates that your radios conforms to the current "Narrow Band"
transmission protocol. If your radios do not conform to
this standard, using then could potentially shoot down other fliers in the air.
Fortunately, most older radios can be upgraded to the newer
"Gold Sticker Standard." Please visit your local hobby shop to learn more
about how to get this done.
Question From Cono: I have a Waco-E bi-plane that I
recently picked up at a garage sale. I didn't get any instructions or building
manual with it so how can I determine if the CG is correct?
Answer: Determining the CG on a bi-plane can be a bit
tricky. Unlike a single-wing aircraft, you can't just lift the plane up to determine the
CG and expect to get a reliable result.
Most bi-plane owners adjust to the correct CG position by observing the
way the plane flies... especially at slow speeds. So after you take it up for the
first time and get it trimmed out, get up nice and high then cut the power completely...
and see what it does. If the tail sinks, it's probably tail heavy. If the nose
sinks, then it's probably nose heavy. But if it falls off to the right or left
without either the nose or tail sinking, then the CG is probably in just the right
location. Keep in mind that if you discover it's tail heavy, you will need to keep
your airspeed up during your landing. The last thing you
want is a tail stall on a slow approach to the runway.
Question From Don: I am putting together an Easy
Sport ARF using a typical 4 stroke engine. I am having difficulty connecting the
throttle linkage to the carburetor. Do you have any suggestions?
Answer: Indeed, many people have trouble connecting a
throttle linkage to the carburetor. I have found that the BEST way to attach the
throttle linkage to the carburetor on a typical 2 or 4 stroke engine is to use a 2/56 Ball
Link. Several companies make them, and all work equally well... and kiss you
throttle linkage troubles goodbye.
Question From Dan: I
am designing a homebuilt aircraft and would like to build a scale model for
testing purposes. How does one scale the power and weight to give an
accurate representation of the aircraft?
Answer:
Unfortunately, there is no "size to power" relationship that can be
used to correlate model aircraft engine size to full size aircraft engine
size. If this were so, then a typical Cessna 150 would woud have the
equivalent well over 3000 hp. In other words, most (if not all) model
aircraft have a considerably higher size to power ratio as compared to
full-size aircraft. Considering this fact from another perspective, if a
particular model were built with the same size to power ratio as its larger full
size cousin, it would be grossly underpowered resulting in only minimal (if any)
control while airborne... sort of like an early Wright Brothers flyer.
Question From Bob: I’m
designing an building an R/C plane from scratch. How do I determine where
to attach the wing to the fuselage to achieve the proper CG?
Answer: Turn
the finished wing over (wheels side up). Using a non-permanent marker,
measure (and mark) a point on each half of the bottom of the wing, three inches
from where the wing halves meet and 1/3 the distance from the leading edge to
the trailing edge. Now measure (and mark) a point for each wing tip in the
same manner estimating the 1/3 distance as accurately as possible. Next,
use removable auto pin striping tape to connect each of the two marks on each
half of the wing. The pin striping tape is your precise CG and desired
balance point at any given point on the wing. Next, lightly attach the
wing to the fuselage with rubber bands in such a way so that the wing is
moveable and re-positionable on the fuselage. Now get someone to help you
for this next step… With the wing attached as described above, the fuel tank
empty, and the plane sitting right side up on a level surface, place one finger
on the pin striping tape near the wing tip and have your helper do the same on
the other side of the wing. Working together, slowly lift the plane
slightly off the ground (about six inches or so) and see if the nose lowers only
about 2 to 3 inches before coming to rest. If so, your plane is properly
balanced and you have found the precise location on where the wing should attach
to the fuselage. If this is not the case, then re-position the wing on the
fuselage until you do get this slight 2 to 3 inch nose drop when the plane is
lifted off the ground with only one finger supporting each wing tip on the pin
striping tape. Once you find the correct location to attach the wing to
the fuselage, you are ready for the final check... And this step you can do by
yourself. Using only your index fingers on each hand, place them on the
pin striping tape on each half of the wing about 6 inches from each side of the
fuselage and again lift the plane slightly off the ground. See if you get
the same 2 to 3 inch drop. If you do, then your plane has been perfectly
designed and it's flight behavior will be consistent when flying at both high
speeds and slow speeds. If however the nose drops more than it did when
supporting the plane near the wing tips, then it will tend to rapidly fall out
of the sky when flying at slower speeds. If on the other hand it drops
less than it did when supporting the plane near the wing tips, then it will tend
to plow through the sky at slower speeds only to lose virtually all control when
flying at or near stall speed. Accordingly, you will need to “fly your
plane in" with a bit more air speed on landing approaches as is typical of
most high performance designs.
Having said all this, it should be a
primary goal of every model aircraft designer to build a plane whose CG is
consistent throughout the entire length of the wing. But with the
tremendous variety of R/C models and designs now available, this is not always
the case which is perhaps the main reason why some planes seem to fly better
than others. Ask any experienced modeler and I'm sure he can give you a
list of the really good designs and a list of the planes you should stay away
from. Not surprisingly, most of the well known model manufacturers market
their share of both good and bad designs. So when building or choosing a
new plane, never overlook the importance of a proper CG and always take the time
to get it right before taking to the air. This way, you’ll have a model
that will simply fly better, especially on landing approaches and when flying at
slower speeds.
Back
|
