Ivan Pettigrew writes: "The fellow I talked to this past weekend, Glen Wilson, said that the vertical fins on the stabilizer were only really necessary on one side, because it was only when the critical engine failed (the left one) was it necessary to have them on the starboard side behind the operating engine. If they are on the port stab, it only to make the thing look balanced, but I can't see in the pictures if they are on the left side or not. Glen, who is also a pilot, said that he was not too impressed with things he had heard about the handling of the plane, and he was less impressed with the engineering department of Bombardier who had send them the drawing that were not accurate, and half the instructions in French when they were all supposed to be in English. He had worked on the project in the early stages, but not for the past year or two."

So it seems likely that only the starboard subfin was really necessary, and perhaps the additional area on the starboard side was a similar precaution.

Now that I have noticed that the starboard tailplane LE is extended forward, I think the large bullet fairing at the fin/tail join hides a hydraulic ram, which can trim the sibfins left or right during water pick-up. This would enable the pilot to trim out a crosswind without having to use the main "barn door" rudder.

Am I right? Does anyone know?

Ooops! I've had a good look at www.seawings.co.uk where there are some excellent walk-rounds including four different 415s, and it's clear that I was wrong (as was the little 3-view I was working from) and that the sub-fins are inclined to port to induce a turn to starboard, so that they counteract the torque from the engines. But this still raises an issue about scale fidelity, as I don't feel comfortable with such a large turning moment at 1/16th scale. So mine are now straight.

Well, not neuroses in the strict sense of the word, but you will see what I mean, I hope.

My new model is the Canadair CL-415 (now made by Bombardier). It has a number of interesting features: being built along the lines of a Norman castle being the main attraction, as it makes construction so much easier!

I have a few photos and "done so far" notes on my website.

But how far do you go in pursuit of even the most basic scale details? One unmissable feature is that the subfins are built at a 5 degree angle and will induce a turn to port. I've actually made the tailplane so that it accommodates this feature, but having done so, it looks ridiculous, not aesthetically but aerodynamically! I've checked on the main website, and the engines turn the same way as ours do, so to my bewildered mind, on a model, the subfins would just encourage the beast to spin in from 100ft, as the torque reaction would be adding to the turning effect. Or is my man-flu brain just too tired?

A feature relevant to Ivan's plan builders is that it has a real, full-span NACA cuff! Now this would be quite easy to build into the model (if I had not already made the wing, that is) by using a flat-bottomed section and extending the LE down a mm or two, then fairing in the resulting step with some soft balsa or even Depron.

Now, there is an interesting paradox in building a scale model (no, not whether ALL the rivets are necessary) but how you alter the basic structure to retain the features of the original, but use a non-scale modeller's airfoil and angle of attack. This is particularly relevant to flying boats, because to get a smooth take-off the wing chord should be at about 4 degrees to datum. Add to this the use of the thinner airfoil, and how do you build the nacelles and fuselage attachments so that they correspond closely to the original, which has perhaps one degree of incidence and a big fat airfoil? Answers on a postcard.....