Carl Goldberg Tiger 60 ARF

You have to wonder why a company like Carl Goldberg Models even bothers to submit a product like the Tiger 60 ARF for review (Ed Note: Because I begged them to submit it, that’s why. I like the airplane and know that Sport Aviator readers would love to fly it.). After all, everybody already knows that the Tiger is a great flying airplane; in all three sizes. The wood kit that has been available all these many years is a good one that goes together quickly and sturdily. In an era when actual builders’ kits are getting hard to find on the hobby shop shelf, the Tiger kits still sells very well. Under those conditions, the best that an ARF based on this design could do is to not mess up a good reputation.

Most reviews are written after a handful of flights have been put on the new airplane: such are the pressures of the traditional print deadline. But the Tiger 60 ARF described in this review has a full season of flying under its belt. The airplane is now close to eighty or ninety flights old, and the soundness of the pre-assembled structure can finally be determined.

In short, the Tiger 60 ARF succeeds, and the Tiger’s excellent reputation remains untarnished. Nothing has come unglued, none of the landing gear mounting blocks have loosened, the firewall and nose-gear mounts are solid, and the airplane is still a pleasure to fly. Now, this reviewer has had ARF airplanes in the past that were somewhat lighter than this one, but they have generally suffered from a variety of structural failures in all of the areas listed above.

As a result, these areas were watched like a hawk as the flight count racked up. Other than the loss of one piece of white Ultracote pinstripe from the fuselage side near the exhaust, somewhere around flight fifty, the airplane is literally as-new. That’s another good point. If for some unimaginable (?) reason your Tiger ARF gets, shall we say, damaged, the covering is Ultracote, and you can easily get matching covering for repairs.

Now that you have had fair warning that this is going to be a favorable review, it’s time to go into the details.

Construction

Photo 1

Reviews have always begun with the ritualistic opening of the box, and this will be no exception. One of the best parts of any project is admiring all the bits after bringing the box home! The Tiger 60 ARF was shipped with a cardboard over-wrap around the box and arrived with no damage to any components.

The internal packaging, complete with corrugated cardboard dividers, is shown in photo 1. Hinges, control system hardware, a motor mount with spinner, and landing gear hardware were all bagged and included. All the hardware included with the kit was used in completing my Tiger 60 except for the engine mount.

Since I believe strongly in protecting my airframe and radio system from vibration damage, a Dave Brown Products’ Vibra-Damp Sport Beam soft mount was substituted. In addition to vibration protection, this change from stock was dictated by the noise sensitive environment at my home field, although the included engine mount looked entirely satisfactory. (Ed. Note: As Dean points out later on, so-called “soft mounts” limit the amount of noise an aircraft makes. Any airframe acts like an amplifier to increase the sound of an engine since the entire airframe is vibrating. When using a soft mount, the airframe is insulated from the engine, vibrates less, and therefore produces less noise.)

After a quick survey reading, the instruction manual checked out as complete without spending a whole lot of extra print to describe every last bit in mind-numbing detail. I mean really, some of these things actually teach you how to tie your shoelaces! As it turns out, even the boredom-inducing zillion page instruction manuals have errors, but I only found two omissions in the manual for Tiger 60 ARF.

      

Photo 2                       Photo 3

The wing is made in two pieces that plug together using an aluminum tube main spar. This would allow one to transport the wing in two shorter pieces for convenience. But unlike most plug-together wings, it mounts to the fuselage with the traditional twin dowel pins at front and a pair of bolts at back. The bolts hold the wing together once it is bolted to the fuselage.

I would recommend that you fuel-proof the exposed plywood root ribs for longevity sake if you intend to transport the wing this way. I epoxy-glued the wing halves together permanently because I have no problem with transportation and it served the same fuel-proofing purpose.

This is the first of two omissions in the otherwise excellent manual, by my count. The book neither specifies gluing the wings together nor fuel-proofing the root ribs. But I think that you should do one or the other. The book does recommend that you hinge the ailerons, install the servos and linkages before joining the wings, and it is right. This is more convenient.

Photo 4

The twin aileron servo installation is becoming pretty much standard these days. While this is generally a good technique, such an installation with worn out or undersized servos (too low a torque rating) can lead to all sorts of flying problems. More about that later. The aileron servo installation is easy and … well, sexy. The servos are attached to the inside of the servo bay hatch cover with the output arm protruding through. Once the hatch covers are screwed to the wing, all that protrudes is the servo arm and pushrod. It really is classy looking!

Once the wing can be bolted to the fuselage, it can be used as a reference for gluing the tail feathers onto the fuselage. Here is one place where I deviated just a little bit from stock. The wing is retained with a pair of steel bolts with blind nuts in the fuselage. In my opinion, ¼ – 20 Nylon bolts in CAA-soaked wooden threads resist loosening under vibration better than steel on steel, so the change was made.

An important alignment step at this point is to make sure that the wing is square to the fuselage as viewed from the top. You check this by measuring from the aileron hinge line near each wingtip to the tail-post. I like to use my Bob’s Alignment Gadget, but a pair of long sticks that are rubber-banded together will do as a substitute. Just slide the two sticks until the length is right on one side, and then use it to check the other side. As it turned out, when I bolted up the wing with the hardware included in the kit, everything was square. Now that was a pleasant surprise! Based on the rest of workmanship in the kit, I suspect that you’ll find the same, too. I should add that there wasn’t a warp to be found in any of the feathers, as well. Tidy … the workmanship was tidy, and from me that’s a rave. 

    

Photo 5                      Photo 6

Once the wing was bolted in and properly lined up, I partially removed only one bolt, punched the blind nut out so that it fell into the fuselage, and then removed the bolt. Then I drilled through the wing and fuse hold-down bock with a 3/16” drill bit. A 3/16th inch hole is a good size for tapping a ¼ – 20 thread into wood. Next, I ran a tap through the entire mess, and then threaded a Nylon bolt into the hole. Repeat the process for the other bolt, and then remove the wing.

The threaded holes in the wing were reamed out to ¼” using a stepped propeller reamer. Standard stepped reamers make holes that are 3/16”, ¼”, 5/16” and 3/8” in diameter. This maintains concentricity as the hole is opened up. Then soak the new threads in thin CAA, and wait for it to thoroughly cure before chasing the threads with the tap one final time.

After fitting the elevator joiner wire and hinging the tail feathers, it is time to glue them to the fuselage. Remember this spot! The UltraCote should be trimmed back as much as possible, without exposing wood after the glue-joint is made, so that the stab glues to the lite-ply fuselage sides as well as to the horizontal plate between them.

In order to make it easier to get the tail feathers straight, I found it easier to glue the stab in with slow-drying epoxy first, fitting both fin and rudder in a separate operation. The temptation may be to do this with some fast-curing glue, but this is one of those times where there is no substitute for epoxy with at least one-half hour of working time.

Before gluing the vertical fin, do make sure to remove a narrow stripe of covering from the top of the fuselage, the length of the dorsal fin. I should add that there is no need to mount the tail first, before hinging: just mount the stab first and then the fin and rudder. After the tail feathers are mounted, the control horns are fitted in line with the pushrod exit holes.

Photo 7

Remember the spot above? This is the only other glitch I found in the instruction manual. If you mount the rudder horn far enough forward so that the clevis holes are properly lined up with the hinge line, then the back corner of the fuselage will interfere with the rudder horn at extreme left throw. The tempting thing to do is to bolt the horn to the rudder farther aft. But this upsets the rudder throw, making travel to the left and right unequal. Filing a notch into side of the tail-post was an easy fix. I found a little red poster paint to make things pretty and fuel-proofed the area with a thin coat of epoxy.

The canopy and canopy floor get installed with small screws. After the landing gear was mounted, I had a completed airframe that stood on the workbench all by itself. Progress stalled just a while, as I took some time out to admire the clean lines of the Tiger.

From now on, it is just a matter of installing the engine and radio equipment. The airframe alignment steps above really should be done with as much care as possible, because when carefully built, the Tiger can live up to its impressive parentage.

Back when he was part of Carl Goldberg Models, Precision Aerobatics (Pattern) competitor Dave Patrick designed the original Tiger 2. Those of us who flew with him regularly back then used to tease him that the Tiger was the best Pattern ship he’d ever designed. While this is a bit of an exaggeration, the simple fact is that the Tiger is an airplane that, like most good competition aircraft, is both docile and maneuverable. The long tail moment that comes from the Tiger’s competition heritage gives it a “groove” that you will rarely find in typical Sport designs.

While we are not reviewing any radio or engine components, it is time to describe what went into the Tiger 60. The radio is my trusty Futaba 9ZAPS with S9250 digital servos on all the flying surfaces and an S3004 on the throttle.

The digital servos are probably overkill, but I would take care to use standard servos with at least a sixty ounce-inch torque rating on the ailerons. The holding power of digital servos really makes the difference with twin servo aileron installations. Unlike a single servo installation, flight loads and high “G” maneuvers can deflect both ailerons upward at the same time and they never seem to move the same amount. This causes “funnies” that you don’t need.

The only good solution is to use servos with enough torque that the unwanted deflection is almost zero. The rudder is large, so it could probably use a similar torque rating servo too. The engine chosen was a YS 61 FS two stroke with the stock muffler, mostly because I had it sitting at the ready. The only real substitution was the use of a Dave Brown Products’ Vibra-Damp Sport Beam soft mount instead of the stock glass-filled Nylon beam mounts. Otherwise, all the kit hardware was used.

The radio installation is an area where ARF assembly manuals often run into trouble. In this case, the predetermined lengths for the traditional wood-and-wire rudder and elevator pushrods worked out within the adjustment range of the heavy-duty Nylon clevises. Now that was a pleasant surprise.

The throttle, elevator and rudder servos dropped into the pre-installed plywood tray just like it says in the instructions. Granted, your choice of servos may require a little trimming, but mine didn’t. The aileron servo installation has already been described. The standard Futaba power switch was installed sideways in the provided notch at the front edge of the tray. A small piece of 1/32” music wire provides the necessary link to the switch from the outside world.

   

Photo 8                      Photo 9

The battery and receiver installation was finalized after mounting the engine and muffler, so that a preliminary balance point check could be done. The Tiger 60 ARF is not likely to come out nose-heavy with a two-stroke 60. In order to place the Center of gravity (CG) right in the middle of the specified range at 4-1/4” from the leading edge, the airplane would require close to a quarter-pound of nose weight. 

Without using any additional nose weight, a 7-ounce battery would be necessary. No problem! I like being able to fly all day, anyhow. SR Batteries make a high quality 4-cell, 1500-mAh Nickel Cadmium (Ni-Cd) battery that would also be appropriate for a quarter scale airplane. It weighs just less than 7 ounces, and is placed underneath the fuel tank, as close as possible to the firewall.

This required that a hole be cut into the tank floor (photo 8). A little high-speed cutting tool surgery opened a hole near the back end of the tank floor which would allow the battery to be inserted from the top, through the tank hatch. Photo 9 shows the battery installed, but without the necessary vibration isolating foam. Also take care to glue a small piece of wood to the firewall that keeps the battery from being impaled on the engine mounting screws!

Photo 10

The receiver was swaddled in foam in the space in front of the servo tray, finishing the radio installation.

The engine installation was, as mentioned before, not stock; but soft-mounting really ought to be more common considering the lower noise and vibration benefits. You can easily imagine the noise benefit. How many times have you drummed out a tune on the wing as you carried it out to the flight line? Engine vibration makes for a very powerful drumstick, and a good soft mount can take away better than 90% of its power.

The stiff mounts, intended to reduce engine shake at idle, generally do not do a good job of isolating vibration and the ones that permit some shake at idle tend to be the best. Now, here’s a counter-intuitive little bit of information:

The way to eliminate shake at idle is not to make the engine mount stiffer but to make it even softer! Making the mount soft in rotation reduces the natural frequency of the wobble. If that natural frequency ends up being lower than the idle, then you get almost no shake! Ideally, you make the mount soft, without leaving the front of the engine so loose it wobbles side-to-side or up and down. The Dave Brown Products’ Vibra-Damp Sport Beam can be used with a nose ring to tame the wobble. But with a muffled 60 it has just not been necessary. By the way, DBP makes a suitable nose ring as well.

The soft mount required relocation of the bolt holes in the firewall, and just for security’s sake, the existing holes were filled with epoxy and short lengths of birch dowel. 8-32 blind nuts in the firewall accepted the threaded ends of the rubber cylindrical isolators, which are threaded hand-tight. Although I used ¼” long flat-head screws with countersinks to attach the Nylon “T” brackets to the isolators, 5/16” long 8-32 bolts will do nicely.

When those screws are tightened, the isolators will never loosen from the firewall. The “T” brackets were drilled and tapped for 6-32 screws and the engine bolted in. One thing to remember when doing a soft-mount installation is to route the throttle linkage in a straight fore-and-aft line from the throttle arm to the hole in the firewall. The stock installation in the Tiger made this painless. The hole in the firewall was in just the right place and the included wire-in-a-tube throttle linkage worked like a charm. When the proper throttle linkage geometry is used, the tendency of the throttle barrel to move as the engine rocks back and forth will be minimized. It doesn’t sound like much, but failure to do so can cause needless frustration … and we aren’t in this game to get frustrated!

Photo 11

The simple single-chamber muffler was likely to be just a little too loud for my home field, so an extension was made from ½” diameter, 1/16” wall thickness, Teflon® tubing and an angled rubber exhaust extension (photo 11). The Teflon tubing was found in the McMaster-Carr online catalog (website) (Ed Note: Type “Teflon Tubing” in their search engine and look for the PTFE variety.). The angled exhaust extension is available at any hobby shop.

The end of the extension was held in place by a short pig-tail of 1/16” music wire that was screwed to the bottom of the fuselage right in front of the wing. This works well at taming the bark in the exhaust note, provided the engine is propped down to 10,000 RPM or so. Later, as the airplane was dive tested to test its flutter resistance, I found out that the extension would “tune” in a steep full throttle dive. But for sane flying, it’s a simple way of taking the edge off of the exhaust noise. That pretty much completes the engine installation.

Photo 12

The Tiger 60 saves a few construction steps from the usual ARF routine since the wing can be assembled without gluing if you wish. But even when gluing the wing together, the Tiger 60 assembles quickly and easily since all the parts fit so well.

Flying the Tiger 60

   

Photo 13                        Photo 14

One thing I like about the Tiger 60 is that it is a larger airplane than the usual sport 40 size. It is easier to see and flies a little better then smaller aircraft. These photos show the larger size to best effect.

Photo 15

After cycling the batteries, double checking the control throws and direction (don’t ask me why that is so important!) it was time to go out to the flying field. Actually, this part is really anti-climactic. The Tiger, as described earlier is groovy, maneuverable, and stable as a rock.

Photo 16

Endless touch-and-goes without ever letting the nose wheel touch the ground are the airplane’s forte, and it looks good doing slow and point rolls right down the runway.

Photo 17

Photo 17 is a picture of the Tiger doing its “duck landing on a calm lake” impression, nearby. The landing speed is so slow that there is almost no ground roll to disturb the “lake”. The airplane really does make you look good, and if pushed too far, the stall gives you plenty of warning.

Photo 18

The inherent smoothness of its Pattern-inherited design gives one confidence to maneuver close to the ground where you can admire it. No … it is not a 3-D ship. So if that’s what you are looking for, go elsewhere.

I mentioned the dive test earlier. The Tiger has a stick-built tail that is not prone to flutter. No doubt, this is because firm balsa is used in the construction of the horizontal stabilizer and vertical fin. But even with a 10” pitch propeller, I could not get the airplane to even hint at control flutter in dive tests. Why do such a test? Well, for one thing, this is a review! The other reason will be discussed shortly.

Photo 19

For extra quiet, I fly the airplane with a 12×10 APC propeller, and while almost as quiet a 13×7 APC Sport series propeller, it gives better acceleration on takeoff. When a 12×6 prop was bolted on at another flying site, the YS engine hauled the Tiger around very nicely.

    

Photo 20                   Photo 21

Inverted flight is stable and requires very little “down” elevator to maintain straight, level flight. Outside loops stay round and with the extra powerful YS engine, can be as large as you want them to be. (Ed. Note: The YS .61 engine was a special, very powerful “long-stroke” engine designed for Precision Aerobatic (Pattern) events back when 0.61 cu. in. was the maximum engine displacement allowed in competition. It proved to be THE most powerful production engine in this size range ever produced but is no longer available. But even with modern OS Max, Enya or Evolution .61 engines, the Tiger 60 will fly maneuvers large, smooth maneuvers.)

    

Photo 22                     Photo 23

The Tiger 60 flies knife-edge maneuvers well. With the CG in the middle of the recommended range, the Tiger 60 reviewed here displayed no pitching problems in knife edge, (unusual for a sport aircraft) but it does roll in the direction of applied rudder (very usual for a sport aircraft). The rolling tendency is not strong, and it can be tuned out with a computer transmitter in just a few minutes.

Did I mention that the Tiger 60 flies well inverted? Well…how about flying well in an inverted slow flight? It does, as photo 23 proves. The airplane remains stable and easy to fly even near the inverted stall. Even when stalling before entering an inverted (on purpose) spin, the Tiger remains easy to fly.

Photo 24

The Tiger 60 proved so much fun to fly that I forgot that this “wonder plane” still needs fuel to keep the propeller working. After a lot of flying time, the tank went dry. That was when I knew it was time to land. The Tiger 60 handled the power-off landing as well as it did every other maneuver.

Things I’ll do when I build another Tiger 60

While the instructions describe a tail-dragger conversion, I’d stick with the tricycle landing gear. Mainly because those nose wheel-high landings look so cool. At just over 7.75 pounds, the muffled sixty provides good horsepower. But I believe in the horsepower-to-wait principle. That is, “The more horsepower you have, the less you have to wait.” There are now a variety of 90 sized engines in 60 cases, like the O.S. 91 FX. Fifty percent more displacement with no packaging issues is a “gimme”. A 90 four-stroke with a 13-8 or even a 13-9 prop will really put a Tiger in your tank! I’m thinking of putting a tuned pipe on mine. I know that the added horsepower will not cause any problems, and I’d shy away from using anything under a two-stroke 60.

The only other thing I would do is to make the elevator a little bigger so that the control feel during low-speed and landings is a bit more linear. The stock elevators are about 1-5/8” wide, and I think I’d go out to maybe 2-1/4”. In that case, I’d be sure to use a strong elevator servo: one with at least a sixty ounce-inch torque rating.

In summary, the Tiger 60 ARF stayed true to its wood-kit heritage. Dave Patrick outdid himself designing this airplane and Carl Goldberg kept his excellent tradition going strong when they built the ARF version.

That’s pretty much it, maybe if the local club does get that electric-only flying site in the township park just one mile from my home, I’ll be back to describe the Tiger electrification project. Bye.

For more information on this excellent choice for a second airplane, click here. 

Specifications Manufacturer: Carl Goldberg             Length:           62.5 in.                                                        Wingspan:       70 in. Wing Area:     855 sq. in. Wing Loading: 20.9 oz./sq. ft. Weight:           7.75 lb.Airfoil: Symmetrical Radio: Futaba 9ZAPS                          Servos: 4 x Futaba S9250 1x S3004   Engine: YS .61                                                Cost: $200.00

Special Airframe Features Extremely easy to fly yet aerobatic; Attractive; Easy to build straight.

Short URL: http://masportaviator.com/?p=763