Control Line: Aerobatics
Wynn Paul
Three-bladed props
Two stunt fliers have gained moderate notoriety lately by using homemade three-bladed props. Bob Hunt won the 1978 World Championships using his own three-blader made from Rev-Up 12-5 blades; he also competed and finished sixth in the 1979 Nationals with this type of prop. Gene Martine also made up several three-bladed props to use with his HP-40s and Max 40s.
Both men are excellent machinists with thousands of dollars’ worth of machine tools at their disposal. Bob’s father, Jim, is a machinist and small-parts producer by trade; Gene is a machine-shop teacher and possesses exceptional skills. The average stunt flier should not attempt to put together a three-bladed prop. Considerable skill and safety consciousness are required to machine the front and back plates, to fit the three blades together, and to balance the prop — these operations are very exacting.
It is my opinion that only a few other qualified persons in the United States could successfully and safely construct a three-bladed prop. I do not anticipate Bob or Gene marketing their products: they are expensive and potentially dangerous. Bob has stated that one of his three-bladers was broken on a takeoff, shearing off one of the blades while the hub assembly did not come apart. It’s not worth the risk. Several expert stunt pilots question whether there is a large increase in performance using the three-blade prop, and certainly it takes a very strong engine to pull the three-blader. If all you have is a drill press and a hobby lathe, don’t try to build your own trick prop — you’re asking for trouble.
Supertigre 46 spray bar modification
Mike Mustain suggests an improvement to the Supertigre 46 spray-bar assembly to improve fuel flow and needle-valve setting. He notes the spray bar is designed for Supertigre’s sprinkler system; when the needle valve is relocated (as most fliers do), the fuel is atomized too soon.
Mike’s modification:
- Drill the length of the spray bar with a No. 53 drill so fuel flow is constant to the spray-bar venturi hole.
- Then drill the spray-bar venturi hole with the same No. 53 drill.
- Pass the No. 53 drill through the spray-bar lengthwise again several times to remove any burrs from the venturi hole. The internal threads will not be damaged by the drill if done carefully.
Mike says this modification will add power, greatly aid in setting the needle valve, and help achieve one-flip starts. Second-place Nats finisher Bill Werwage tried the needle-valve trick and reports it does help in setting the needle.
Support equipment
Lines, clips and handles
Line thickness is governed by the rules, but you might try some solid lines since reduced diameter can mean less drag. Be certain to loop the ends as required by the AMA rule book.
Clip recommendation:
- The best clips to use are the one-piece Pylon clips, item No. SU-LC-122, rated 110 pounds test. These clips are strong and won’t slip. (I have never seen the other type of line clip fail, either.)
Handles: you’ll see many commercially made handles and a lot of handmade designs fitted to the user’s hand. Common types include:
- E-Z-Just handles (small and large) — still available in hobby shops though no longer produced. (Production ceased after a lawsuit involving a boy electrocuted near overhead electric lines.)
- Control Specialties In-flite adjustable handles.
- Bob Hunt’s high-density foam handle (now marketed by Flying Models) — wide spacing and a very good cable.
- George Aldrich handle — lightweight, strong cable, available in several colors.
- Fox steel handle with a large wooden grip and two line-spacing positions — the wooden grip can be sanded and carved to fit your hand.
- Bob Baron’s adjustable handle design — featured in MAN (August 1970) and Model Aviation (April 1977); basis of the model marketed by Gene Martine of Custom Master Products, Jacksonville, Fla.
- Sullivan Products plastic handle with nine adjustments.
Cable testing: Richard Byron had cables tested and found they broke around 100 pounds pull — very good. Still, check cables from time to time, as there are instances of cables breaking at the outlet plastic handle. If you build your own handle, be certain to pull-test it thoroughly before use.
Electrical equipment
Electrical setups range from a plain 1.5-volt battery and two alligator clips to purpose-built connectors and rechargers. Options include:
- 1.5-volt cells with alligator clips (simple and cheap).
- Du-Bro “Kwik Glo” glo-plug connector No. DU-KG-147.
- Wet cells (usually about 2 volts and rechargeable) — will often blow out a weak plug, but they are effective.
- Fusite GloBee Fireplug and Charger — retail about $39.95; rechargeable, built-in ammeter, indicates flooded or burned plugs, and holds a charge well.
- Tatone “Pocket Booster” — a hand-on connector that eliminates wires.
- Prather “All in one” — NiCad battery, plug tester and battery tester combined (about $29.95).
Many fliers build a unit into their flight box with an ammeter and one or two 1.5-volt cells or a wet cell so the plug can be tested on the ground. Check local hobby stores and catalogs for current options.
Fuel transfer
Common methods of transferring fuel from a gallon can to the model tank include:
- Old-fashioned fuel bulbs.
- Plastic fuel bottles with squeeze bulbs.
- Manual feed fuel pumps attached to the cans.
- Electric fuel pumps.
Caution: some synthetic fuels will attack the parts of plastic fuel pumps and reduce them to putty. Choose pumps and tubing compatible with your fuel.
Tachometers
Many fliers use a tachometer to set engine RPM on the ground rather than relying on ear or partner judgment. Popular choices:
- Heathkit tach (favored by Bob Baron).
- Royal Pro-Tach (used by Gene Martine).
Under differing weather and humidity conditions, using a tachometer is a good idea.
Miscellaneous
I suggest obtaining catalogs (including Radio Control catalogs) and going through them carefully to find useful equipment and new products.
For information on stunt or P.A.M.P.A. contact: Wynn Paul 1640 Maywick Drive Lexington, KY 40504
Transcribed from original scans by AI. Minor OCR errors may remain.
