an introduction to radio control sailplanes

8/8/2019 An Introduction to Radio Control Sailplanes

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Introduction to the Hobby ofIntroduction to the Hobby of

RC Model SailplanesRC Model Sailplanes

Copyright (c) 2

002 by Bill Kuhl. Right is granted to use thismaterial for non-commercial purposes. All other rights arereserved.


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Introduction -The Hobby of RC

SailplanesIs This a Hobby for Me? Some reasons it might be:

You can start out fairly inexpensively.

It is clean, quiet, and environmentally friendly.

You can have success as a beginner, but there arealways new challenges as your level of proficiencyadvances.

With a dependency on atmospheric conditions there is a

good deal of randomness, you never really get it allfigured out.

It can be very educational; you learn about meteorology,aerodynamics, and strength of materials as you advance.


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The Origins of SoaringThe first creatures to soar upon slope and thermal liftwere large winged creatures a couple hundred millionyears ago. With wingspans well over 20 feet andweighing well in excess of 100 pounds, huge muscleswould have been required to maintain flapping flight even

with the denser air of that time providing more lift, so it isthought these creatures flew exclusively in lift by jumpingoff mountain tops.

In more recent times

large soaring birdssuch as eagles andhawks, rely on findinglift for much of theirflight.

Paul NatonImage


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The Origins of Soaring

Public domain image of one of the Wright Brothers gliders.

The Wright Brothers spent years experimenting with glidersbefore attempting powered flight. Much of their effort wasspent developing more efficient airfoils and perfecting theircontrol system before building a powered plane.


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Advances in the HobbyThere Has Never Been a Better Time to Take up Soaring

A Few Good Reasons Why:

Reliable radio equipment available at low cost. Size and

weight of equipment available makes planes practical thatwere not 10 years ago.

High quality kits and Almost-ready-to-Fly planes at areasonable cost.

Composite construction materials available

Important technical information made available toeveryone.


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Radio Equipment

Computer radios will handle manyfunctions such as flaps, ailerons, and

spoilers, capable of mixingcombinations of functions. As youprogress through the hobby, mostlikely this is the type of radio systemyou will want. Prices around $500 andup.

Two or three functionradio equipment is

available for $50 to $100.

Close-up compact radioinstallation in discus launch

sailplane, complete plane weighsunder 10 ounces.


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ARF - Almost Ready to Fly

High-quality sailplanes areavailable at a reasonable cost.The Primera A.R.F. glider that Iam holding, came completely

constructed of wood andcovered with plastic covering,required only minor assembly ofmajor components. Receivedthird place in two-meter division

at 2001 Southwest Classicflying this plane.


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Sailplane Design & Construction

Design is related to creating a light, strongstructure with minimum drag. Because ofthese goals, many planes use composite

materials to get maximum strength fromminimum amount and weight of materials.

The wing of a sailplane launched by electricwinch must be able to withstand a forceequal to up to ten times the weight of theaircraft because of the stress placed on thewing during a zoom launch.


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Laser Cut Pieces

Many of the balsa wood kits come with laser-cut piecesthat come out of the wood sheets much easier andcleaner than the die-cut procedure used in the past.

Laser cut pieces are veryaccurate, although theedges of the wood isbrown from burningprocess.


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Composite Materials

Carbon or carbon fiber is found in various forms such as

strips, rods, and woven into cloth.I

t has a high strength toweight ratio, but the primary strength is in tension.

Kevlaris a trade name

for this materialdeveloped by DuPont.Used in sailplanes fordent resistance, it alsoused in the making of

bullet-proof vests.


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Composite Construction

The Allegro Lite spar construction consists of end grainbalsa sandwiched between carbon fiber strips. This iswrapped with kevlar tow (loose fibers) and then paintedwith a slow curing epoxy.

Note:sheeting,leading edge,and trailingedge have notbeen added, to

show sparassembly ofmid panel.


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Free Information & Plans

Significant advances in model sailplane design were made free fordownloading in the form of plans over the Internet by Dr. Mark Drela,professor at MIT. These designs utilize composite construction or balsawood construction with clever use of hi-tech materials such as carbonfiber and kevlar.

DrDrela has also developed airfoils that offer performance gains formodel sailplanes. He has created a computer program XFOIL thatwill analyze airfoils for a variety of flow conditions. XFOIL is free fordownload for academic use.

DrDrela is also noted for setting the human-powered hydrofoil speedrecord of 21.3 mph in 1991 and the Daedalus human-powered aircraftthat flew 199 kilometers across the Mediterranean Sea.

Mark Drelas RC Sailplane Designs on the InternetMark Drelas RC Sailplane Designs on the Internet

Apogee Allegro Bubble Dancer SuperGee


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Where Can Model Sailplanes be

Flown?It is best to fly at an approved soaring club field as a member.If you must fly from private land, make sure to get permission.

Thermal Fields need big enough area for high start or winchand room to drift downwind over. As there is no glow fuel tobe spilled, often sailplane clubs are allowed to fly from sodfarms that power fliers can not.

Slope Sites - many concerns; access to the site, obstacles,and will there be consistent lift for wind conditions.

Safety is a concern, although noise should not be. Do not flyover populated areas.


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How Does a Sailplane Stay Aloft?

No matter how efficient a sailplane is, the glide path willalways be downward unless a source of lift is found. Lift is airthat is moving upward faster than the sailplane is descending,(sink rate).

Lift is found in two majors ways; slope lift - air movinghorizontal is deflected upward, or thermal lift - air rising fromthe ground because it is warmer than surrounding air.

Slope Lift Thermal Lift


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Staying Aloft - Thermals

Thermals - sailplane enthusiasts have such a fondnessfor the thermal lift that keep their sailplanes aloft, manysign their emails and letters with Thermals instead ofSincerely.

As the ground is warmed by thesun, thermal bubbles are formedand break way from the ground.These bubbles can combine andmature to form thermal columns.

Thermals will normally drift withthe wind, so the pilot circles thesailplane downwind adjusting tostay within the thermal.


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Staying Aloft - Slope Lift

Popular California Inland Slope

On large slopes such as this one, strong lift iscreated when the wind blows straight into theslope.


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Learning to Fly

Learning to fly RC sailplanes is easier than RC powerplanes because sailplane trainers fly slower but it is best tohave an instructor. The new bounce-able EPP training

sailplanes will survive all but the hardest knocks with nodamage.

BobH

aroldsTG

-3 EPP is a good lookingglider. Wooden gliders that are more fragile, willbe easier to thermal with if lighter.

E.P.P.

Expanded PolyPropylene foam


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Learning to Fly

Gentle Lady has been afavorite training glider formany years.

Many radio systems include abuddy box option, a cableconnects two radio systemsallowing the instructor to give or

take control from the studentsradio.


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How Does the Sailplane Get the

Initial Altitude?Slope sailplanes normally are thrown directly into the lift off hills or mountains.Thermal sailplanes normally need a fair amount of altitude to begin searchingfor thermal lift.

Methods Used to Reach Thermal Lift are:

Hand LaunchHand Launch - plane is launched in an overhand throw.

Discus LaunchDiscus Launch - plane is spun by wingtip and released upward.

HiHi--StartStart - stretchable tubing and length of string pulls sailplaneupwards like a kite, string detaches from plane.

Electric WinchElectric Winch - ground-based electric motor pulls sailplane up.

Electric Motor with PropellerElectric Motor with Propeller- electric motor in sailplane powers toaltitude, often prop folds for less drag.

Aero TowAero Tow - sailplane is towed behind a RC power plane.


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Winc

hL

aunching

Winch on theleft andretriever on

the right.

Pilot holds some tensionas the winch linestretches before pilotgive the plane a toss.

For most larger sailplanes, anelectric winch is the preferredmethod for getting a sailplane to analtitude of a few hundred feet.Electric retrievers are also availablethat pull back the winch line.


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Hi Start Launch

Paul Naton launching largersailplane by hi-start. Hi-starts are

available in a variety of sizes.

Hi-Start consists ofstretchable tubing,stake for anchoring inground, string, andparachute.


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Electric Powered Sailplanes

Paul Naton photo ofDieter Mahlein withhigh-performanceelectric poweredsailplane.

Sailplanes powered by electric motors are available in all sizes andperformance ranges. The weight of the motor and battery is not as muchof a handicap as it once was. Often it is helpful to be able to use electric

power to avoid landing off field.


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The Need for EfficiencyNormally flying in thermal lift and often under slope

conditions, there is no excess lift, so a sailplane needs to beas efficient as possible. This means creating adequate liftwhile creating the least amount of drag, known as theLift/Drag ratio.

Wings of sailplanes are normally long and narrow, the ratioof wings length (wingspan) to wings width (chord); isknown as the aspect ratio or AR. Wings with higher

aspect ratios have a better glide ratio, but require strongconstruction.


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Efficiency - L/D Glide Ratio

Half the drag results intwice the glide ratio.

Steeper glideangle result ofgreater drag.


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AirfoilsShape of the wing cross-section (airfoil) is a major

factor in the performance of the sailplane. Airfoils areoptimized for the conditions that the plane is mostlikely to be flown under. Factors such as speed,weight, launching factors, wind penetration, and sizeof aircraft are considered.

The following individuals have done considerable

research in developing airfoils for model

sailplanes and other applications:

Dr. Michael S. Selig University of IllinoisDr. Richard Eppler Stuggart Germany

Dr. Mark Drela MIT


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Airfoil Performance IssueIn designing airfoils,

desirable to avoid thelaminar separationbubble on the airfoilupper surface that canlead to high airfoil drag.

On the diagram thisappears between A & B.The picture below is ofoil sprayed on airfoil in

wind tunnel observedunder black light.

Image by permission of

Dr. Michael Selig


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Competition

Sailplane competitions of many types are very popular.Most competitions are low key with entrants moreinterested in the social aspects of flying with others withthe same interests. Tasks are simple enough that pilotswith only moderate skills can accomplish.

Competition is always alearning experience. Youcompare your plane andpiloting ability with others, andoften you find there is muchroom for improvement.

The following is only a small

sample of sailplane events.


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Thermal Duration Contests

Thermal durationcontests such as theSouthwest Classicheld near Phoenix,Arizona everyFebruary draw pilotsfrom all over the

United States as wellas many vendors.

Planes are launched off electric winches, pilots try to keeptheir planes aloft as close as possible to a specified time and

then land as close as possible to a small circle on the field.


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Discus Launch

Flight tasks are performed within a time window, normallyten minutes. Typical tasks might be to get maximum flight

time as close to a target time as possible with a limitedamount of throws. Penalty for each throw after specifiednumber of throws. The best score for round is given 1000points and the rest of the scores are normalized, this isman-on-man competition. There is a lot of strategy in

picking your air and less emphasis on landing.

Once known as Hand Launchcompetition, everyone has

switched to launching byswinging the plane by a wingtip.


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Slope Racing

Photo bypermission of

Gliderking.com

Sailplanes race between poles on a course thatruns parallel to top of hill. Racing requires very

smooth flying.


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Hand Launch Golf or DLG Golf

Pilots fly hand launch gliders between holes on a golfcourse using foam noodles that planes must land against.Some pilots have achieved one throw for each hole on the

course.T

he pilot may run or ride in golf cart between holes.


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ScaleI

n scale competition, models thatare replicas of full-size sailplanesare judged for appearance andflight maneuvers.

Scale flying points are judged byat least two judges. Each of the

ten maneuvers is scored from oneto 10. Flying score is added to thestatic score for the total score.

Bob Harold


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The EndThe End

Special Thanks to the following companies or individuals forallowing me to use their graphics images:

PaulPaul NatonNaton www.radioncarbonart.comwww.radioncarbonart.com

Robert BinghamRobert Bingham GliderKing.comGliderKing.com

Klaus K WeissKlaus K Weiss www.h.s.l.rcclubs.comwww.h.s.l.rcclubs.com

Steve HenkeSteve Henke Spring Fling ImageSpring Fling Image

Bob HaroldBob Harold Scale Competition DescriptionScale Competition Description

Dr. Michael SeligDr. Michael Selig Laminar Separation Bubble ImageLaminar Separation Bubble Image

http://www.scienceguy.org - Science Video & Resources

an introduction to radio control sailplanes

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