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S u p e r b i r d S u p e r b i r d Small 19-powered full-performance RC helicopter is simple

conversion of the Du-Bro Whirlybird. It is fast, simple, realistic,and inexpensive. / by Ed Sweeney

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Top: Carlin Tobin's conversion isa bit more ambitious. He made allthe changes shown in this articleand even fabricated his ownHughs 300 body for it. Note hisuse of a commercial four-bladedcooling fan and his big homemadeengine heat sink. Above: Com-pletely assembled Tobin's modelwill be a charmer. The little heli-

copter can handle the heavierbody and needs lots of noseweight so the Hughs 300 shape isquite ideal. Right: Dave Grey ofDuBro Products, creator of theoriginal Whirlybird, admires theconversion. He found the new mod*el quite easy to fly.

S u p e r b i r d S u p e r b i r d Why not build a small copter? I had

a noisy Du-Bro 505 and, without themotor on top, it looked sharp. I hadmastered the 505 in calm weather andknew its limitations. I had numerous RCcar motors, clutches and shafts in myworkshop, so I played around with the505 frame/body and came up with ashaft-drive system for the model, but

would it work? After many conversations with DaveGrey, John Burkham and Gene Rock,the mechanical parameters for a heli-copter using only the power of a typicalRC 19 engine were determined. Lessthan a month later, the prototype wasready to fly. In about a year it hasflown over 200 hours and many, manychanges have been made. My goal hadbeen to build a 505 conversion as closeto the original design as possible. It hadto be practical, durable and repairable.

These objectives were finallyachieved. The model, as simple and asinexpensive as a shaft-driven helicoptercan be, requires only average model

building skills. If you have a 505 andknow how to fly it, here's a neat way tofind out just how well helicopters canfly.

Without question, the Du-Bro 505helicopter has been made and flown bymore modelers than any model chopperto date. It is still the least expensive kitfor a workable helicopter. The 505 is agreat trainer machine, but it does actsomewhat top-heavy. It is not a veryrealistic looking machine though, and itsperformance is limited. The model usesa 40 located atop the rotor shaft drivingits own 10-6 prop one way and spinningitself and the main rotors the other.This method of powering the helicopteris known as torque reaction. It is idealfor learning to handle a helicopter incalm weather or indoors. Throttlechanges give instant altitude control andno sudden swing of the tail. So, if youwant to get into helicoptering, use the505 in stock form. Once you have mas-tered it, try either the conversion heli-copter presented here or buy one of thebig expensive and scale kits.

Our little helicopter will perform just as well as most of the big models;being smaller gives it many advantages.The Superbird can cruise at 35 mph inforward flight, and it loves to fly in awind. It is small and quietgreat forbackyards that intimidate the largermodel copters. It can be transported insmall autos (like VWs) without remov-ing rotors, costs very little additionalmoney (if you have a 505 now), is ex-tremely durable, uses only a 19 forpower, and most of its components arereadily available as stock items.

The conversion uses the 505's framebody mechanical systems and all fit-tings, to which a motor mount, clutch,shaft, more durable tail rotor system,and a new rotor head are added. Beltsand pulleys are the transmission. A con-version will cost you about $30 and anengine.

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This article makes two assumptions:First, that you already have a Du-Bro505; second, that you have masteredflying the 505. The conversion machineis the smallest actively flying four-channel RC helicopter around todayoffering full performance and this iswritten as a conversion project.

The conversion is a shaft-driven,semi-rigid rotor helicopter. The enginedrives a clutch via a belt and the clutchdrives the main shaft through anotherbelt. Overall gear reduction here is 12.3to 1. The large white bevel gear from

the 505 is attached directly to the alu-minum pulley which was belt drivenfrom the clutch shaft. This drives the505's original small, white bevel gear. Atthe end of the tailboom, another set ofbevel gears gives an additional 1 to 2gear ratio increase for an overall mainshaft-to-tail ratio of 1 to 8. When themain rotor rpm peaks at 1300, the tailrotor spins at 14,000. The loading islight, but at this speed balance is impor-tantalmost critical. Normal speeds are1000 rpm and 8000 rpm.

The skill level in building and flyingfits three chopper types. From simple tocomplex, they are torque reaction (likethe 505), shaft-drive throttle only for

lift control (most kits), shaft-drive andcollective pitch (Kavan and Graupneronly, at present). If you are new to heli-copters, work up the ladder of complexskills; don't try to learn at the top. Ifyou take my advice, converting your505 to shaft-drive is a perfect secondstage. That's exactly what this Super-bird is for.

Construction To begin converting your 505, com-

pletely disassemble the model down tothe basic frame. You will reuse abouthalf of the parts in the conversion. Ob-tain a K&B Veco 19BBRC (or similar)and order parts from Stock Drive. Listof parts and appropriate addresses are in

panel at lower right of this page. Findmiscellaneous parts at local hobby shop. Only two wood parts are shown on

the plans. The major rotor head partmay be bought at Sears. (The plans withthis issue are full-size as printed.) Theseare the upper adjustable and lower(fixed) clutch shaft bearing blocks. Thefirewall and engine bearers are cut to fitthe original frame which you alreadyhave. Firewall is 3/16" (or 1/8")plywood located at the backside of theframe uprights between the tailboomblock and gear block. Engine bearers(1/2 x 1/4" cross section) simply glue tothe firewall spaced to suit your engine.Seal the completed frame with surfacing

resin or epoxy and cover with a verydurable paint (K&B epoxy or Hobby-poxy).

Originally, the clutch gripped theshaft it was intended to drive. On ourhelicopters the clutch is drive-pin en-gaged. Notice the two slots in the plasticshaft/bearing which enabled the clampto grip its shaft. After cutting the clampoff, extend the two slots 1/8" insideand below the metal clutch bushing.Also widen the slots to suit your drivepin. Trim the plastic shaft/bearing flushwith the steel bushing. Such locationprevents the pin from escaping. Natural-

Top: This layout of parts shows general relationship of each part. Note especially body nosesection cutout for clutch and radio, receiver, servo and battery positions. Above: Posedtogether, an original 505 meets the converted model.

PARTS LIST

1 30 groove alum. 1/4" pulley l/5th pitch 1/4" hole 1 10 groove alum. 1/4" pulley l/5th pitch 1/4" hole 1 6 l / 2 x 1/4" steel shaft 1 7 x 1/5" P 1/4" wide belt 1 10" 1/5" P 1/4" wide belt

Set Plastic Bevel Gears 2 ea. 1/4 ID 3/8 OD ball bearing flanged 4 ea. 1/8 ID x 1/4 OD ball bearing flanged

All the above parts are available in one package No. HK105 for $16.39. 2 ea. Rocket City nose gear bearing3 ea. I.B.M. large clevises1 ea. Delta heat sink blank (black) 1 ea. Curtiss clutch assembly 1 ea. 3V2" Sears turnbuckle (3V2" alum, part)

SDP Handbook of Commercial Drive Components (No. 71) is $1.49 ppd.

Curtiss-Dyna Products Corp. Box 297 Westfield, Ind. 46074

American Aircraft Modeler 45

6A3-30DF02508 6A3-10NF03708 7X1-08065 6R3-0350025 6R3-050025 1M3-Y3216 & 32 7Y55-F3725 7Y55-F2512

Stock Drive Products 55 South Denton Ave. New Hyde Park, N.Y. 11040

Delta Systems P.O.Box 754 Bridgeton,Mo. 63044

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S u p e r b i r d S u p e r b i r d

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S u p e r b i r d S u p e r b i r d ly the pin must not scrape the bushingeither.

Prepare the clutch by surfacing thebell (instead of the shoes) with leatheror cork lining. Recess the spring bygrooving the shoes with your Dremeltool, then tighten the spring by remov-ing about 3/4" of spring coils. This is astarting point; the spring must be ad-

justed later to suit your engine's idlespeed. The 505's aluminum engine counter-

weight can be machined to make thenew flywheel/fan assembly. Any ma-chine shop will do this for a nominalfee. Also have them shape and drill thealuminum main shaft head piece. Do allthe thread tapping yourself. You willuse 4-40 and 1/4-28 NC taps. Also makeand attach the fan blades and the ninesteel pulley drive pins.

To prepare the 505's large white bev-el gear, cut it flush on its backside, cen-ter it on the bare bottom of the 30groove pulley, then attach it with twoor three screws to lock the parts to-

gether. Prepare the clutch shaft with itsflats, hole and threads. Now assembleentire power train as shown in thephotos. The clutch must be just lowenough to clear the landing gear mount-ing screws; locate the engine height onthe frame accordingly. Engine is securedwith long 4-40 bolts into blind nuts atthe firewall. Upper pulleys are locatedaccording to the tail drive bevel gearmesh. Your original 505 bevel gearsystem can be used temporarily to ad-

just gear mesh properly. Upper pulleytension should permit only 1/32" move-ment on one side of the belt. Lower pul-ley can have 1/4" movement on oneside. Shim the clutch shaft or engine toachieve these tensions. Mount the ser-vos. They are positioned almost exactlywhere they were on the 505 but movedforward by the width of the lowerclutch shaft bearing block. The cycliccontrols are not spring loaded as on the505; make them solid. Install all push-rod systems for throttle, cyclic and tailrotor controls.

Using your old 505 body parts, reas-semble the forward section containingthe battery and receiver. Provide cut-outs as necessary for the clutch. Onlysmall sections of the lower rear bodycover are used.

Now reinstall the landing gear andswashplate. Prepare the aluminum rotorhead main piecemine was an alu-minum Sears and Roebuck turnbuckle.Bend the coning angle into the turn-buckle ends as diagramed, then tapholes for the modified Rocket Citynose-wheel bearing parts. The drawingsshow how the Rocket City bearings arecut, drilled and modified. With theDremel Moto-Tool, cut away the insidelower edge on the turnbuckle to allowadequate teetering of the assembly. Butdo it after preassembling the head. Youwant to maximize the teetering move-ment, but cut away as little of the turn-buckle as possible.

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1 The modified frame showing firewall,engine bearers,lower clutch bearing mountwith servo rails moved forward.

2 Preparation of the clutch including aheavy-duty return spring. Note drivepin groove in center of clutch ballbearing.

3 Clutch shaft assembled with bearings,pulley and belts.

4. Entire power train installed on a finishedand epoxy-painted frame. Upperclutch sha ft bear ing mount is secured bybolts and can be shimmed for optimumbelt tension adjustment.

5 The Veco engine fitted with theflywheel/pulley/fan which can be made fromthe original model's engine counterweight.

6 Rotor head parts in "exploded" view.Sears turnbuckle is main piece. RocketCity bearings are the black plastic parts.

7 Complete rotor head system shown here.Number of washers on the flybardetermines the controlstability/sensitivity.

8 Underside view of assembled rotor headshows how the turnbuckle is cut away tomaximize flybar tetering movement.

9 Building the rotor blades is easy. First,splice the spruce leading edge to thebalsa trailing edge stock. Then plane andsand to airfoil shape. (Note two airfoilsshows on plans to suit conditions. Takethe shaped 5/32 mw arm and insert itinto a cutout in the blade. Epoxy the wirein place and then epoxy the "L" shapedcutout over it.

10 After resanding, the blade is ready forMono-Koting and matched set balancing.These are very durable blades.

11 Top view of rotor head with swash platefollower properly aligned and linked tothe flybar. "Servo paddles" are pitchedby the control. They aerodynamicallymove themselves up and down for cycliccontrol.

12 Tail rotor system is similar to originalmodel's unit, but much stronger and ball-bearinged. Note brass center piece in thelarge gear.

13 Complete tail rotor installed onhelicopter uses same spring-loadedcontrol system as on original model. Itworks surprisingly well, but keep itlubricated. Gears handle quite a load.Keep checking the gear mesh and solderjoints for safety's sake.

14 The snap clutch provides overloadprotection for the bevel gears and tailrotor blades. It also permits spliningaction of the tail drive shaft. Heavy wallPylon Brand surgical tubing tensions theclevis against the larger square tube.

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Above: Cutaway was seen in Fred Wolff's fantastic article in Popular Mechanics last year. Wethank them for letting us reprint it here. Below: This cutaway is his adaptation of the originalartwork showing conversion's mechanics.

S u p e r b i r d S u p e r b i r d The turnbuckle bolts are RH and LH

threaded respectively. Cut 1/2 in. fromeach and center drill each piece for 5/32hole. This hole takes the 5/32 musicwire blade mounting loopmake onefor each side. Solder these wire loopparts securely in the threaded sectionsand cut to equal lengths. Now just screwthese assemblies into the turnbuckle.

The set screws will later lock the threadsto hold the proper collective pitchsetting.

Build your main and tail rotor bladesas drawn and shown in the photos.Incidentally, I suggest that you coverthe blades (including tail rotors) withtrim MonoKote. The servo paddles (asHiller calls them) in this model use thesame lifting section airfoil and chord asthe main blades but are only three in.long each. When the paddles are made,epoxy a five-in. length of 1/8" ID brasstubing in them. The flybar is to be 22in. long of 1/8 mw. It is bearinged in ashort length of brass tube inside thelonger nose-wheel bearing. Wheel collars

pinching the 5/32 OD brass tubes lockthe paddle assemblies to the flybar. Theflybar is weighted with brass or steelone in. dia. washers with 5/32 hole. Thenumber of washers is varied to suitflying conditions and control reactionsdesired.

50 December 1973

Note especially the linkage from throttleservo (installed) through the frame, acrossthe frame and down to the engine.

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Above: The Superbird in flight with Dave Grey at the transmitter. He likes to fly so close inhovering that you can reach out and touch the helicopter. Below: Stylish body houses four-channel radio entirely inside. External fuel tank shows when to land without disaster.

A short Du-Bro nose-wheel steeringarm links the flybar, via a pushrod, tothe swashplate. The swashplate followermust be straightened and will be posi-tioned parallel with the rotor blades,not parallel with the flybars as on the505. A length of 4-40 bolt added to thearm, with one of those neat Du-Broswivel links and its clevis, completes thisassembly. Add two new holes in theswashplate follower to give 1/2 and 2/3of original control. Link the pushrod tothe inner hole. When all parts are as-sembled, you now have the model com-plete with body, frame, power system,radio system and rotor head. Thethreaded joint of the aluminum rotorhead piece and the shaft must be extrastronguse a lock nut and "Loctite"compound. Be sure the piece is properlyaligned on the shaft in relation to theswashplate follower. Next is the tailrotor drive shaft and system.

You will find the tail rotor systemeasy to make if you realize it is verysimilar to the 505 system, but muchmore durable. The square tubing locksthings together with less dependence onsolder joints. Some of the work is quiteintricate, so be slow and plan yourwork.

Not shown in the drawings is a1/16" wheel collar set into the large tailrotor drive bevel gear. Drill out the gearto snug-fit the collar. Drill all the waythrough the gear's hub into the collar'sset screw area. One long set screwthrough both parts will lock them to-gether. Also, drill and tap for anotherset screw in from the other side. Thesmall bevel gear is secured on theknurled section of the tail rotor shaft.

The tail rotor blades are mounted viabolts in the large IBM clevises. Underimpact the blades pivot in the clevis.This clevis has a short brass tubesoldered inside it as-its pivot bearing.The clevis is controlled exactly as on the505, but a new wire control arm is madeto suit the clevis's larger diameter. There is one critical step. A tinylength of 1/16 ID brass tube retainseach blade mount clevis on its axle. Ifyou overheat the joint, you might soldereverything together; not enough heatand the joint might fail causing a bladeto fly off!

The snap clutch on the tail rotordrive shaft is a unique feature. Becausethe new model's shaft is turning fasterand at a higher load, the brass-in-nylonbearings won't last and the gear meshmust be kept accurate, hence the ballbearings. The clutch has two purposes:First, it allows splining action when thetailboom flexes up and down. Second, it

releases overloads which result fromstriking the tail rotors into the groundby accident. Adjust the clutch laterusing thick surgical tubing to clamp theclevis on the outer brass square tube.This adjustment must safely handle themaximum flight loads on the tail rotor.With this feature, I have never lost abevel gear; without it, gears were con-stantly failing as a result of ground im-pact.

When final assembling the tail rotor system, make sure the drive shaft is

(Continued on page 79)

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S UPE R B IR DS UPE R B IR D(Continued from page 52)

straight all the way. Shim up or shortenany of the three supports to achieve this ifnecessary. Bevel gear mesh in front andin back are critical. Be sure that the teethfully engage, that the shafts are at rightangles to each other, and that there is nopossible slop when under load. Note that a1/16" collar is used on the tail drive shaftto locate the shaft at the rearmost bearing.

Now comes the balancing act. Balanceyour blades and paddles as individual setsremoved from the model. Balance theblades by bolting them together at the loopin the music wire. Set this on a flat surfacewith the blades at 180 degrees. Lightenthe heavy blade and/or heavy-up the lightblade. While the blades are removed,balance the flybar system. Whenreassembled you will have a balancedsystem. Set main rotor pitch using theoriginal 505 pitch gaugethe conversion'spitch is the same. You will have to removethe middle brace from the gauge to use it.The rotor blades must turn in the exact

same disc of rotation. Being a rigid-headed helicopter, an out of track bladecan render the head system useless.Bend or shim the parts to achieve correcttracking.

Balance the tail rotor by removing thecontrol input arm, but leave the spring andcollar in place. Remove large rear bevelgear. If the tail rotor is out of balance, theassembly will turn on the ball bearingsshowing which side is heavy. With plastictape, heavy up the light side. Reassemble.

Fore and aft balance of the helicopter isvery important. It must balance 1/8" aheadof the main rotor shaft. I used over sevenoz. of lead in the nose of my bird tobalance it. Incidentally, to locate CG, turnthe model on its side; don't guess the CGby hanging the model by the rotor head.

The controls should do the following:Forward stick tilts the swashplate down infront. Right stick lowers the right side ofthe swashplate.

FlyingNow it is time to fly. If you know the

505, you'll have no trouble. Don't botherwith trainer gears. They are nice, butheavy. A bsolutely don't use a tether.

Needless to say, your engine must be

broken in before helicopter use. Set theidle as low as possible with drive beltremoved. Use a needle setting at highspeed that is a bit rich. Attach the belt.Always start at low throttle-high trim.Set the clutch spring tension so therotors will fully disengage at engine highidle speed. Shorten the spring asnecessary. Advancing the throttle mustengage the clutch smoothly andpositively. Usually about 1/2 hr. ofrunning is needed to smooth the clutch.

The only screws that loosen with use arethe main rotor drive pin retaining screw(the one in the top of the shaft) and the

tail rotor assembly where it secures to

the tailboom. Keep checking thesefrequently.

Now start the motor and hold thehelicopter overhead, holding it under theback side of the swashplate. Run theengine up to 1/2 throttle to check forvibration. If there is any, inspect bladepitch, tracking and balance. If not, go tofull throttle to set the needle for a two-cycle run. Hold it for a minute to besure the engine won't sag as it heats up.The model should have a strong upward

pull.Check to see if the helicopter wants toswing R or L at the nose. Adjust tail rotortrims or stop and reset linkages. I can't tellyou what pitch your tail rotors need; thistest will guide you.

When making your first takeoff,concentrate on the tail. Get it trimmedwhen it is about one ft. up; don't try totrim it during takeoff. Also, being a rigid-rotor helicopter, the cyclic controls areuseless until the model is airborne.

If the wind is calm, your 505 trainingwill help you keep the new model in onespot. Hover at about two ft. for mostearly practice. Don't make sudden throttlechanges. If there is a wind, learn to holdforward trim to stay in one spot. Notethat the power setting is less whenhovering in a wind and the tail stays aftmore steadily. (It acts like a rudder inforward flight.)

During this training period, use at leastfour washers on each end of the flybar.Set the control response for themaximum control. This combinationgives you the most stability and goodcontrol. Later, reduce control sensitivityto gain smoothness in hovering and atthe same time reduce flybar weight asyour skill increases. In calm weather thismodel can respond very fast withoutflybar washers, but in a gusty wind use allfour on each side.

Still you are only hovering. Forwardflight is easy and a real thrill. It is ex-tremely easy to begin forward flight-justpush forward stick and the model willaccelerate and climb. But slowing to land-that is, coming out of forward flight intoa hoveris quite difficult at first.

In forward flight the model behaves likea planeaileron and elevator do the flying(cyclic controls). You can almost ignore

the tail rotor control. Warning: Never gointo forward flight if it takes more than2/3 throttle to hover the model. Youcan cruise around in forward flight atyour hovering throttle setting orhigher. But if power is marginal,landings are abrupt.

As mentioned earlier, getting back tohovering is hard and can be disastrousunless it is done gradually. Here's theonly safe way down that I know. Keep insteady forward flight until about six ft.altitude while reducing throttle enoughto establish a slow rate of descent. Themodel must be moving forward, never

stopping With a helicopter you need less

power in forward flight or to put itanother way, you need lots more power inhovering. In this descent at a steady,slow forward flight the model will benearly level. Keep the rate of descentsteady with throttlejust like a plane.When you get to six ft. altitude and about20 ft. from the intended landing spot,level off with a touch of aft stick. Youshould have slowed to under five mph.

Now things get tricky. You must addpower as the model nears a hover, but

not enough to completely arrest theslow rate of descent. As far as I amconcerned, hovering is mostly donelooking down on my model; forwardflight is done higher up. So now thehelicopter is descending below six ft.;forward motion (in a calm wind) stopsand the chopper is hovering again.

Practice the above sequence only withplenty of fuel. Become very proficient indescending to a hover for landing. Why allthe fuel? Well, if you feel unsure of thedescent at any time, add power, pushforward stick, and go back into forwardflight like an airplane . It takes practice.

Once you have mastered takeoff,hovering, forward flight and landing,practice some aerobatics. Wingovers areespecially fun and easydo them aswith a plane, but at a steady throttesetting. Try a wingover with a full turn anda half for added spice. Two-bladedhelicopters can't loop or rollmy attemptshave ended in crashes.

I have also flown this little copter witha collective pitch rotor head, with whichsome modes of flight are easier, othersmore difficult. It has been flown with fullgimbaled rotor head, but again there areadvantages and disadvantages.

If you are trying to fly your model ata high altitude location or on very hotdays when the density altitude gets above4000 ft., or if your engine just won't putout enough power, make a change in therotor and paddle airfoils. Thicken both ofthem by 1/16". Either make new bladesand paddles or splice a sheet of balsa tothe bottom side and reshape them. In anycase, be sure to keep the rotor rpm up to1000 at hover.

If there is enough interest in these littleSuperbirds, we will publish other rotorheads for you to try. At the time of this

writing, about seven Superbirds arebeing built and flown by modelers. It is awell-developed and proven model. But, asimprovements are developed by all of us,they also will be published. Should therebe a problem, write me at AAM. I'm theeditor. I'll try to answer questions as bestI can.

If you need more information tobuild your model, note that a limitedsupply of expensive photo material onthis model is available through our PlansService. The photo set is $5.00 in-cluding first class postagewrite to medirectly for it.