Suls Record Trainer

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After an absence of 45 years, control line aeromodelling returned into my life. No longer 049 Cox engines and 12-foot dacron lines but 1.5cc diesels and 45-foot braided wires. To bystanders it may all look a bit childish but that changes once they are hands-on in the circle.

After this Record Trainer, built from a hand-me-down plan, many L/C models are going to follow for sure. This particular model was available as a kit in the 60's and early 70's, supplied by a Netherlands company named Suls.

These pictures were taken on a wonderful, sunny day on the Almere club's field.

what the kit used to look like ...

Although my first Record Trainer is still serviceable I am inclined to become jealous when I see other people's concours-standard work. Wanting to experiment with a lighter model, this example was built. It is about 30% lighter than it's yellow-and-red predecessor and sports plywood nose cheeks that are original Suls kit components. Some extra decorations are pending.

Not intended for the “Record Cup” competitions (10 cc tank capacity rule), the model has a 35 cc Brodak tank that was modified to “uniflow” type .

Another variation on the Record Trainer theme is the ENLARGED version – in this instance 115% of the original. Power is to come from the Webra Record's big brother, the 2,5 cc “Winner”. For comparison, the standard-sized model is placed over the enlarged one.

In the case of my big trainer the wing is no longer a simple sheet affair but a deep, hollow profile with flaps. The fuselage is not a balsa profile but made of redwood.

After re-reading Ron Moulton's iconic “Control Line Manual” it was decided to create a fuel tank that fits between the engine's backplate and the wing leading edge in order to keep the fuel line as short as possible. Reason for this is that my models often suffer from fuel starvation when performing stunts.

Instead of the usual wedge-shape this tank will be a simple box affair, the idea being to keep the fuel line close to the fuselage and cancel out as much centrifugal and gravitational force as possible. I find it helpful to make a card prototype first. The sheet metal is from a biscuit contaiiner. Good tin snips are a boon when it comes to following the score lines.

Sharp folds make for a better result. The tools are somewhat improvised but that makes modelling more fun.

Here the box tank starts to take shape. Holes for the various tubes are made prior to the folding process and the card prototype is especially reassuring in this step. Notice that the tank is made up from a single piece of sheet metal. There are pro's and con's to this, but I often struggle to keep loose side pieces in position while soldering.

All piping faces the front of the model where the motor is located and the airstream comes from. The two tubes on top of the tank are a filler vent (which can be blocked off before takeoff) and a pressure inlet (Uniflow principle).

My first flapdriver, soldered up from all sorts of leftovers. The U-shaped connector, that links the two flaps, hinges through a brass tube soldered to a saddle that in turn sits on the trailing edge of the wing (see next picture).

Wing trailing edge with flap driver mounted.

Christmas is upon us and the Winner Trainer is decorated too.

Just a few more coats of clear dope to go before the final assembly is taken to hand.

The Webra Winner 2,5 cc engine had spent decades in a shed after a hard life in combat models with its previous owner. In spite of all the nicks and the cut down needle, it runs beautifully.

If you look closely, you can see the piano wire tail skid. The original design does not have this feature, but the forward location of the wheels leads to the tail slamming down in hard landings and that can crack the slim fuselage if there is no shock absorption.

This is my first model with flaps. The secondary push-pull rod is a strip of bamboo with short pieces of wire at each end.

The primary push-pull rod is a piece of bicycle spoke that runs through the wing. The bell crank is tucked under the wing where it should be and the “up” arm is the rearward one, which is supposed to be good for yaw in aerobatics.

Once satisfied with the flying characteristics I will discard the rather complex adjustable guide for the leadouts.

Here the original 1,5 cc model is placed next to the 15% enlarged version.

In the meanwhile, trainer number one still soldiers on. It is such a pleasant model to fly that one is inclined to try more than one is capable of and as a result the fuselage is often severed. Below, yet another repair has been completed: after adhesive come nylon patches and epoxy for additional strength.

Repeated repairs have marred the finish somewhat and the model reminds one of the type of vehicle found on used car lots back in the 60's.

The lightweight Record Trainer was not a succes. It's low wing loading made it unstable in even the best of conditions but especially the thin wing was an issue as it twisted and flapped, creating much resistance. In order to tackle the problem the wing is doubled with a crossgrained lamination that stiffens both chord and span.

The laminated wing turned out to be the next issue because it warped horribly. Ultimately it was removed entirely and replaced by a new wing from stiff 6 mm balsa. In the picture below the new wing is covered both sides with white tissue (for additional strength) after receiving 3 coats of sanding sealer. After the tissue + decorations 6 coats of clear dope are applied. When applying the tissue and dope the wing is flipped over before each application and always pinned to the builiding board in order to prevent warping.

The model is back in one piece. Besides the wing, the fuel tank was (once again) revised, the leadouts were renewed and the spoked lightweight wheels replaced.

For the hell of it wheels were made from a plywood/balsa sandwich and bushed with brass tubing. The ultralight spoked wheels seemed to act as an airbrake and did not really appeal to the eye.

Because the elevator horn is placed on top of the elevator in order not to snag in the gras when on the ground, the leadouts are switched so as to bring the “up” control to the rear position: this is the common situation and leads to less mistakes when connecting the lines tot the model.

It appears that the closer the fuel tank is to the engine, the less issues there are with engine cutouts during manouvres. I look forward to trying out the refreshed model.