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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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Kirt Blattenberger

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Academy of Model Aeronautics (AMA) Plans Service - Airplanes and Rockets

Starting Control Line Flying Scale
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.

This "Starting Control Line Flying Scale" article in the 1960 Annual Edition of Air Trails magazine is still a good primer on how to go about getting into scale flying model competition. Some of the contest rules have changed over the decades since, but the basics are the same. The table of model sizes and engines might need to be adjusted for electric powered models, but in the scale world there are still many modelers who use internal combustion engines - especially in the large airplanes. A quietly humming motor does not give quite the same real-world affect as a screaming engine. Even with all the research going into full-scale electric aircraft, we're still many moons away from have a viable military fighter, transport, or commercial commuter. The drawing is by the famous Cal Smith (as is the cover image), but the text of the article is not attributed to any named author. BTW, this 1960 Annual edition has a few other "Starting" themed articles on other realms of modeling. 

Starting Control Line Flying Scale

If kit or "mag" plan model, use size engine recommended. Use prop giving best performance, even though not exact scale. Upright or side mount engine is better than inverted mounting. Provide cooling air inlet and exhaust.

Lead fuel vent well overboard and cap filler tube to prevent fuel marring finish.

Balance at 20% to 25% of wing chord. Bellcrank pivot should be behind balance point.

Biplanes should balance at midpoint of line connecting 25% chord point of both wings.

Add ballast to nose or tail if needed to make model balance properly. Typical examples shown.

Attach parts such as wheel pants, cover doors, bombs, rockets or auxiliary fuel tanks firmly or make removable for flying.

Flying scale models have long been the top favorites in air-modeling. There are more kits manufactured and sold and more magazine plans presented for scale models than any other type. In competition, while other phases of flying such as free-flight attract more contestants, everyone turns out to see the scale event.

Here is where more careful attention to craftsmanship and time consuming patience is lavished than anywhere else. All too often the beginner attracted to flying scale modeling is scared off by the sight of a beautiful model plowing up the macadam. Sure, some crackups are inevitable, but many are preventable. Too often so much attention is paid to the "scale" that the "flying" suffers.

Locate balance point of tapered wing on average chord at 1/4 span line.

So let's start at the prop and work our way back and discuss the most important ingredients for successful flying scale modeling. First of all it must be remembered that every scale model presents its own particular set of problems. There is no really perfect scale model but control line flying minimizes most of the risks resulting from a design that is not readily adaptable to scale flying. Some aircraft when scaled down have wheels that are too small, tails too long or noses too short. but the basic requirements of control line design must be incorporated into the model or it will not fly correctly. Proper power for given size and weight model and proper balance and trim make the difference between crack-up and good flying.

Choose a model of reasonable size to start with. Tiny Half-A (.049 cu. in. disp.) powered scale jobs may be real cuties but are difficult to fly off anything rougher than a ballroom floor. A ship with about 30" wingspan and a .19 engine is a good workable size. Leave the 10' giants alone until you gain plenty of experience. If you are building from a kit or mag plan the size engine will be specified. Use that size! The designer has done the necessary test work for you already, so take his advice.

Mount bellcrank and leadouts level and close to thrust line and C.G. vertically.

"Starting Control Line Flying Scale Size Weight Table, Annual 1960 Air Trails - Airplanes and RocketsOn multi-engine models unless engine cut-off is used, put larger tank on inside so that outside engine will cut first to permit controlled partial-power let-down.

This "ideal" beginner's flying scale model is no particular airplane but would have such features as: Reasonable size spinner, apple cheeks for engine cowling, straight flat midwing, single strut landing gear, big wheels, simple bubble canopy and many straight lines. Racer type shown closely approaches the ideal model.

Make sure entire control system works freely. No binding or sticking should be tolerated.

Make every effort to keep model from becoming too heavy. When scale details and many-coat finish add excess weight, control and flying performance usually suffer.

Use the size prop recommended by engine manufacturer. This may not work out to exact scale size, but appearance will suffer only slightly while power will not be impaired. Avoid mounting engine inverted to prevent flooding, making starting difficult. Use sidewinder and upright mounting whenever possible. Since engines in scale jobs may be buried in a cowling be sure there is adequate space for cooling air to get into and out of cowling to prevent over-heating. Provide plenty of room for attaching booster clips to glow plugs. If you wish to cover over glow plug install a small booster clip permanently on plug and lead wires out of cowling at some convenient place.

Install the fuel tank as close to engine as possible and be sure fuel line is free from kinks and sharp bends. Mount tank as in a stunt model if wedge type is used, with center of tank level with needle valve. If a rectangular tank is used, top should be level with needle valve. Extend overflow tube through bottom of model so raw fuel will not mar finish. If possible provide a cap for filler tube so that fuel won't slop out in flight. A short length of plastic tubing melted and squeezed together at one end makes a simple cap. You may wish to use a balloon tank for your scale model. Since this type tank has no overflow vents raw fuel won't spill on model.

All too often the scale fan becomes so engrossed in crowding scale details onto his pet that he ignores the basic requirements of balance, trim and control. These factors cannot be ignored or that first flight may result in a beautiful wingover with no pullout - splat! Don't hesitate to add a bit of lead ballast to nose or tail to make model balance properly. C.G. should be located at 20% to 25% of wing chord. On tapered wings locate this point on the average chord taken at 1/4 span location on wing.

Biplanes should balance at mid-point of line connecting 25% chord point of both wings. This applies to wings of equal chord. Unequal chord wings require a more complicated method to locate C.G. correctly. But make such a model a bit on the nose heavy side to be safe. The bellcrank pivot and line leads should be located slightly behind the C.G. and lead outs can be angled back slightly to help keep lines tight.

Another important factor concerning bellcrank location frequently overlooked is its vertical location. Because scale models come in high, low and mid-wing types a good rule to follow is: keep bellcrank and leadouts level and as near thrust line and center of gravity as possible. Even if this means having leadouts exposed rather than buried in wing. A typical example of incorrect location is in a cabin type where lead-outs are run through wing. This suspends the model well above its Center of Gravity point causing it to bank inward when under way and maybe to fly into circle with loss of control.

The entire control system should be free from any binding or sticking because stiff controls cause loss of control. Pay particular attention to leaving room for elevator horn travel in buried installations. Lead out guides should be clear of cement and dope.

Finding the right size wheels to fit any scale model may be tough. It is best to use nearest size larger than scale so the mode) will roll well during takeoffs and landings. Even smooth concrete may have expansion joints swelled by heat that can trip up a model with small wheels.

To wear pants or not to wear pants? If your scale design has wheel pants they should have adequate clearance inside around wheels. The pants should be attached firmly so that they cannot be knocked off during rough landings. This requires a knotty bit of building, but a little extra effort here will make a more durable model. Other external details such as wheel cover doors, bombs, rockets and auxiliary fuel tanks should be either "nailed on" tight or made removable for flying. A model shedding parts in flight is an unnerving sight and can even cause a flyer to get so excited he loses control of model.

Probably one of the greatest problems encountered with scale models is weight. They just naturally seem to wind up being overweight. So make every effort to keep weight of model within reasonable limits. Avoid hard wood and brass details, use balsa and aluminum wherever possible. That contest winning finish can also be the source of considerable excess weight.

Some builders use auto primer as undercoating for dope finish. Auto primer contains lead and should be well sanded to lighten load. Use talc-dope filler for a good lightweight undercoating. Cover planked areas with tissue rather than silk or nylon to help save weight. Since model weight and wing area govern the amount of power needed to fly properly, the following table will serve as a guide to determine the correct engine size. The table can only serve as a "rule of thumb" since individual scale models vary greatly and exceptions may be necessary.

For multi-engine models: Select engine indicated by weight and range and divide disp. by number of engines required. An example: A five foot span B-24 model weighs Sibs. (80 oz.). This weight falls into the 48 to 128 oz. range, therefore .60 is engine size indicated, .60 divided by 4 equals .15, or .60 divided by 2 equals .30. The model can be flown with four .15's or two .29's. In actual practice this B-24 model (weight 72 oz.) was flown with two .19's because of propeller clearance problems.

With the recent upturn of interest in multi-engine models the flying scale modeler has found his problems increase in direct proportion to the number of engines involved. There are several factors that require particular attention to get a big B-25 or B-17 flying successfully. Because it is practically impossible to tune all engines to exactly the same RPM, a "beat" occurs that sets up some pretty unusual vibrations throughout model. Engine mounts and nacelles must be extra strong and tied into wing structure adequately or they will crack loose causing all kinds of ruddy ned . Excess vibration may cause fuel flow problems because of foaming in tanks. Baffles and shockproof mounting may be required .

Fuel tank size should be large enough so that when one engine is started it will not drain its tank before the other engine is started. A helper standing by topping off the tanks can solve this problem. Unless some sort of engine cut-off is used it is a good idea to have inside engine tank larger than outside engine tank. Then the outside engine will cut first and inside engine will keep the model pulling on lines. On many multi-engine models an inside engine cutting first can cause disaster. The best provision is for cut-off of all engines at the same time so that glide to landing can be made rather than partial power let down. A third line or bellcrank-operated fuel cut-off similar to that used on team racers does the job nicely.

Adequate propeller clearance on multi-engine models is always a problem. Frequently it is necessary to use cut-down "clubs" to clear fuselage side or ground. These are difficult to start and engines really scream causing unnecessary vibration. If possible avoid cut down props and three or four-bladers since they are difficult to balance and are real knuckle-busters. Fit the correct size prop to the engine wherever practical (based on maker's say-so).

There are scale kits of every size and type available, no particular one can be recommended in preference to any other, but to start with, pick a simple-engine type. Lay in a large supply of patience and elbow grease and join the flying scale fans. Great sport ... if you remember to thoroughly test fly your model before you go to a contest!

 

 

Posted June 26, 2021

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