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Airplanes & Rockets

Kirt Blattenberger, Webmaster - Airplanes and Rockets

Kirt Blattenberger

Carpe Diem!

(Seize the Day!)

Even during the busiest times of my life I have endeavored to maintain some form of model building activity. This site has been created to help me chronicle my journey through a lifelong involvement in model aviation, which all began in Mayo, MD ...

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1996 - 2026

Webmaster:

Kirt Blattenberger

BSEE - KB3UON

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Starting Free Flight
Annual 1960 Air Trails Hobbies for Young Men

Annual Edition 1960 Air Trails
Annual Edition 1960 Air Trails Cover - Airplanes and RocketsTable of Contents

These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

While credit is not explicitly given to a particular author for this "Starting Free Flight" article in the 1960 Annual issue of Air Trails magazine, Cal Smith's name is on the drawing, so it might be him. It was an era when many modelers were transitioning from gasoline-fueled ignition engines to the newer glow fuel type. Smaller and lighter engines and proportionally smaller and lighter models quickly became popular both because smaller fields could be used and the costs were lower, thereby providing greater affordability to no more people. The same change was true for other forms of modeling - control line and radio control airplanes, boats, and cars. An evolution in configurations of engine, fuselage, wing, and empennage was occurring as well based on decades of experimentation by the hobby's pioneers.

Starting Free Flight

"Starting Free Flight, Annual 1960 Air Trails - Airplanes and Rockets

Key wing to pylon saddle with short dowels or small wood blocks to keep wing from shifting.

Use prop size recommended for your 1/2A engine: 6D-2P (6" diameter, 2" pitch), 6D-3P, 6D-4P are best.

Put prop on backwards for test hops. When adjusted, fly with same type prop. Changing props changes thrust, requires trim adjustment.

Limit engine run on first flights. Fuel tanks can be eye dropper or fuel line coil. Reduce fuel space on some engine tanks by inserting hardwood blocks.

Correct looping tendencies with down thrust. Most models have down thrust built-in. Use thin metal or washers under engine mount to change thrust line.

Check model balance by supporting on fingertips. Pylon types should balance about 75% of chord.

Test glide by hand launching with nose down slightly. Stall (top dotted line) corrected by raising wing trailing edge and/or tail leading edge. Use thin card for shims, add 1/64", 1/32" a bit at a time. Dive (bottom dotted line) corrected by raising wing leading edge and/or tail trailing edge. Good glide shown by heavy middle line. Do test gliding over high grass if possible.

Put prop crossways to avoid breaking.

Correct steep turn tendencies with opposite side thrust.

Free-flight construction must be light but rugged. Surfaces should be as warp-free as possible. Check alignment of all parts from front, back, side and top.

Thin aluminum trim tab on fin is useful for glide and power trim on some models. Wing tips may be warped to act as ailerons. Tilt stab for turn adjustment. Model turns toward high side.

Modern free-flights can make VTO (vertical take-offs). Light dowel or aluminum tube serves as stand. Usually hinged to fuselage to streamline when airborne.

Contest flying requires a de-thermalizer to bring model down at five minutes. Popular design is pop-up tail. Stab is rubber loaded to swing up at trailing edge. Timed fuse burns through rubber band over hooks at T.E. releasing tail. String limits travel to about 35°. Model "sinks" fast in level attitude.

A Half-A (or 1/2A) free-flight model probably offers the beginner more flying thrills for the smallest investment than any other phase of model building. (Half-A class means a model powered by an engine not over .05 cubic inch displacement - which is smaller than the "A" class.)

Today's free-flight models are a far cry from the six foot giants of the early 1930's. Gas engine powered free flight really got its start about this time when Maxwell Bassett of Philadelphia installed Bill Brown's first .60 cu. in. "Brown Jr." in his big semi-scale "Fleetwing" and sent the model aloft for two hours 35 minutes to set a national record. Fuel load permitted then was measured in ounces and an engine run limited to a few seconds was unheard of.

Through the years since then the gas engine has undergone constant improvement. Power has increased, smaller size engines have been developed. Ignition systems using heavy batteries, coil and condenser have given way to the now familiar glow plug. Gasoline and motor oil fuel mixtures have been replaced by the potent glow fuels. As power plants were improved free-flight model design changed to keep pace. Early free-flight models were practically all high wing cabin jobs copied after real planes. Flights were slow and sedate by today's standards. Then in 1939 Carl Goldberg designed the "Zipper," the first pylon type which set the style for years to come. Here was a design that could handle a lot of power when properly adjusted. It climbed like crazy and would soar like an eagle. Generally, "pylon" type means the wing sets atop a thin, flat mount high above a boomstick like fuselage.

Model flying performance improved so that it became necessary to shorten engine runs to prevent fly-aways. Present rules limit engine runs to 20 seconds for R.O.G. (rise-off-ground) and 15 seconds for hand launch. Even limited to this extent today's free-flight model can climb hundreds of feet in this relatively short time. Since the object of free-flight is to climb the highest and glide the longest, a free-flight model combines the best features of a powered plane and a sailplane. It must be capable of flying in a high speed climb under power and then soaring well after power ceases. This has led to a highly specialized model design combining ruggedness and light weight. To control the red-hot power of the modern engine and still attain a good glide requires a compromise of adjustments. Free-flight adjustment is about as controversial a subject as you will find in all of modeling. We cannot hope to cover it all here. We will, however, try to touch on the basic rules of adjustment a little later on.

Latest free-flight trend to high thrust line design. VTO legs built onto horizontal tail and ventral fin.

 

A good place for the beginner to start in free-flight is with the 1/2A model. Kits and engines are inexpensive. Models do not have very complicated structures, are quickly and easily built and are a convenient size to transport and store. Flying performance leaves nothing to be desired. Many kits are for contest types, but there are also numerous scale kits available. Pick the simpler type to begin with. A contest ship can also be flown for sport. Since free-flight structures are relatively light care must be taken when building to have good alignment and warp-free parts. Every wiggle will affect the flying performance - so build 'em straight and true. In order to maintain light weight it is not necessary to cover the model with 29 coats of dope. This will only add extra weight. Five or six coats of dope is ample.

When your model is completed check it over carefully for good alignment. View it from front, side and top. Wings and tails should sit square on the fuselage. Any warps that have developed should be twisted out by holding that part over steam from kettle spout. Sometimes warps cannot be taken completely out of a structure and if they balance each other or are about the same on both sides they can be left alone. The next item to check is balance, Support the model on fingertips under each wing near fuselage. Pylon types generally balance from 50% of chord (distance from wing's leading edge to its trailing edge) to trailing edge. Cabin types about 1/3 chord point (one-third back from L.E.). Kit and magazine plans will show where model should be balanced. This should be considered a starting point since each model will vary a bit. Flying and gliding are final proof of correct balance.

When viewed from the side there should be a slight difference in angular setting of the wing and tail. The most desirable set-up should have wing at a few degrees higher angle than the tail. This arrangement determines proper glide. If this angular difference (decalage) is too great (5° to 10°) the model will climb too steeply and stall. If the angular difference is negative (tail L.E. at higher angle than wing L.E.) dive tendencies will increase as speed increases. When balance, alignment and decalage have been checked it's time to test glide the model. Do this on a calm day and preferably over high grass. Launch model slightly nose down. If it dives into the ground nose heaviness is indicated; it is corrected by raising the leading edge of the wing or trailing edge of stab, a slight amount. A fraction of a degree will make a difference. Try not to change settings radically from required decalage arrangement. Use match book covers and 1/32" thick wood for shims. If model still dives after changing wing and tail angles it may be necessary to add a bit of clay or lead shot to tail to get proper trim.

If model climbs and stalls when hand glided the angular difference between wing and tail should be reduced slightly or weight added to nose. These trim tricks will only take care of gliding - power flight will require further adjustment. The basic rule to follow is: Make glide trim changes with flying surfaces and make power trim changes with engine offset thrust. Obviously a model trimmed for good glide will tend to climb steeply when speeded up with power on. Steep climb and looping tendencies can be corrected by angling the engine down a few degrees. This is called down-thrust.

Most models have the firewall set at an angle so that down-thrust is built in, but minor corrections may be needed for a particular model. On radially mounted engines a bit of 1/32" thick metal or washers put behind top of engine mount will change angle. Strong turn tendencies are corrected by offsetting engine to side opposite to turn.

Pylon models generally tend to turn steeply to right so that side thrust to left is used. Cabin models tend to turn left so engine is angled to right slightly. Offset thrust adjustments are made after observing flight pattern during test hops. This is the critical point, if you can bring the model through the test hop stage intact you can refine the adjustments later for peak performance.

Make first test hops with prop on backwards to reduce power. Engine can be run rich to further reduce rpm. Shorten engine run to 5 to 10 seconds so that if erratic flight develops chances of crash will be reduced. Watch what happens during hop and make corrections immediately. Little by little as corrections are made flight pattern will become safe and maximum power can be used. Further adjustments will be needed to take care of added power.

Since pylon models tend to turn to right they are usually adjusted to climb in wide right spiral. Glide can be either way but natural tendency of model should be used rather than forcing turn in opposite direction. Glide trim can be adjusted with wing and tail settings as already mentioned and turn in glide can also be adjusted by tilting stab. Model will turn toward high side. Rudder trim tab will adjust glide turn but will also affect power turn. Glide turn should be flat and fairly tight so that model will circle and not drift straightaway downwind.

Always launch free-flight models into wind (unlike control-line which are launched downwind). Recent trends in free-flight design have been to high thrust line models. This design tends to turn left like cabin design under power.

Good straightaway climb can be attained with the high thrust design so spiral climb is less desirable. R.O.G. launching has given way to VTO (vertical take-off) with model climbing from a tail stand. This is pretty spectacular stuff when compared to lumbering ground runs of the "early birds."

Today's high climbing contest free-flight should be finished with some high visibility decoration so the timer will have no trouble keeping it in sight. Many modelers paint wing tips and tails with day-glo paint or put aluminum foil patches on fuselage sides to reflect sunlight.

Your field kit for free-flight should include: extra rubber bands for wing and tail hold-downs, extra props, fast drying cement for patching punctures and the usual fuel, boosters and extra glow plugs.

Your hobby shop will be glad to suggest a 1/2A kit.

Recommended free-flight kits might include.: California-Spacer, Midwest-Sniffer, Goldberg-1/2A Blazer, Berkeley-Mini-Hogan, DeBolt-Clipper, Guillow-Kiwi, etc.

So get down to the hobby shop and join the free-flight fans. You'll find plenty of model building fun and you'll get plenty of fresh air and exercise chasing that bird cross-country. Tree climbing practice will come in handy.

 

 

Posted January 22, 2022

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