BuiltWithNOF

MIKE ROACHíS SOPWITH AVIATION COMPANY

SAUNDERS-ROE DUCHESS BUILD DIARY

1. Making a start on the fuselage
2.
Sheeting the hull
3.
Tail design and build

There is a picture of this project in the S-R Princess book by Bob Wealthy, and googling the name brings some more.  Isnít it beautiful? With a 129í wingspan It would have been about the same size, performance and carrying capacity as the DH Comet, and would have been just as elegant. The reason I have chosen to model it in 2008 instead of the Princess is that it is smaller and a lot simpler, and I just donít want the pressure of trying to produce a large and complex 6-motor model to the Chilliwack 2009 deadline.  But no wood cutting until the Catalina has flown!

My aim is to take the finished and flown model to the May 2009 Chilliwack fly-in, flying with Air Canada and a couple of boxes of excess baggage.  Iíve had some very generous offers of accommodation and assistance. First, some thank-you notes in advance:

The Christchurch and District MFC at
www.cdmfc.org for encouragement and practical help, especially the Ashley Fliers Group; Andrew, Clive, Ken and Trevor.
Ivan Pettigrew at
http://www.geocities.com/ivansplans/ for inspiration and advice on building large flying boats.
Luke Z, the Kansas Flier, moderator of
http://www.rcgroups.com/forums/showthread.php?t=710485 the thread devoted to Ivanís Plans at RC Groups, and all the contributors to the thread.
Rudderman 98, who started the Princess Discussion Group at
http://www.rcgroups.com/forums/showthread.php?t=681628 and of course all the distinguished modellers contributing to this thread.
Frank ďthe Hun in the SunĒ vanJaerschsky at Comox BC
Bob Wealthy at Solent Aeromarine Enterprises for the Princess GA, the book and the video.
George Dixon from Cowes on the Isle of Wight, builder of a 144Ē PSS Princess.

5 June 2008. In the traditional way, Iíve made a start on the 100Ē Duchess by making a chick glider version which although quite small does 3 things: it marks the start of the project, establishes whether the thing flies and gives some idea where the balance point is going to be.

Do you like the seaplane analogy?

17 June. The basic fuselage took quite a lot of 5mm square! The four formers are 10 x 4mm sheet with more 5x5mm strip joiners between the sides, which are parallel between F5 and F15.

The strips running down the sides are 5 x 4mm triangular, to provide a glue line for the curved side sheeting. where it meets the lower hull.

This structure was built upside-down and the next step is to re-attached it to the board and steam in the taper front and rear and secure F1 and the tailpost, then fix all the V formers under the hull and sheet the ďseaplaneĒ part with 2mm. It should then be rigid enough to remove from the board and have a closer look at the formation of the step (rather tricky) and the passenger compartment sheeting. The top can then wait until the wings and tail are built, so that the battery position can be more accurately estimated.

The formers are simply 10 x 4mm balsa strips.  This method of keeping the sides apart is simple and strong, and saves all that tedious and wasteful cutting out of plain sheet formers. The strength is all in the right directions, too.

The diagonal bracing can be knocked out once the fuselage is sheeted. Iíll also put some diagonals top and bottom, so that the shape stays as intended!

The fuselage is actually 6Ē longer than my building board, so there was a little bit of shuffling about to get the final tail section in place. The cross-section is narrower at the top than the bottom.  The sketch shows why. On the 3-view, the lower hull is shown as having vertical sides (the LH side of the drawing) but in my new capacity as Chief Designer, Saunders-Roe Ltd, Iíve added a slight flare, to reduce spray on take-off and landing, and provide a slightly larger hull surface.  These are the sections F10 to the sternpost. You can see why the triangular strip is needed, to provide a support for glueing the curved passenger compartment sheeting
The dashed curved line is my best guess at the shape immediately behind the step.  Photos will make it much clearer and Iím assuming it followed the Princess pattern. As CD S-R, I suppose I should know these things!

The stern glued together and pegged tight. Thatís the Catalina wing itís resting on: where am I going to store this lady?

What passes for grass in the Sopwith Mike household, with the ďnose and tailedĒ fuselage.  I was trying to work out where the battery might end up (between F1 and 3, I expect) and plotted the CG of my little chuckie (2/3 root chord) onto the plan. The fuz as it is balances exactly on that point!

One of the penalties of rolling you own is that apparently simple construction can take much longer than expected because things just donít turn out as expected.  This is certainly true of the planing hull, and this view represents the third iteration of former shape!  I abandoned the reverse chine of the Catalina because it just did not look right and then had two goes at getting the authentic scalloped shape to fit properly.  The model in the background is a Sopwith 3-Seater.  Of course.

So: which bit of sheeting goes on first? For simplicty it has to be the side hull. It does not get in the way once on and it will add a bit of strength before the underhull contortions. However, I needed to form a rebate for the sheet to adhere to and used some 10 x 1.5 under the triangular section to achieve this.

The sheeted side.  This effect, where sheet conforms pretty well to a concave dual curve, had been noted on a smaller scale with the Catalinaís tip floats. The opposite curvature on the fuselage sides and top will be more difficult.

25 June. Off to Channel 4 to raid Johnís stock of 1.5 and 2mm sheet. The 2mm in particular seemed very good quality and much to my surprise one 24 gram sheet coped with the dual curvature of the chine with no problems.  I glued up all the edges with aliphatic, pegged and pinned the sheet in the right place then did all the tricky concave joints with superglue and kicker.  And I didnít even have to wet it. So far, so good!

What the sheet had to conform to.  The 5mm square longerons and keel were carved to follow the shape of the chine and provided the base for the glueing session. Most of the formers needed the superglue treatment because it was too difficult to secure the sheet with pins.

The step design on the project was rather more subtle than I was prepared to consider, so this diagonal strut supports the rear hull sheeting and allows the front sheeting to be glued on top and form the step, which you can see in the view below.

A fair amount of grunt was needed to force the 1.5 sheet into the tailpost, but Zap-O and Kicker were good friends at this stage.  The lovely flowing lines are caught in these views, and you can see that the half-round formers for the side sheeting are in place. I have a feeling that the only simple solution to the forward and rear side sections is to use pink foam.

As you can see, the grass has not received any attention since the basic fuselage structure was completed a couple of weeks ago.

The next ďproperĒ job is to varnish all the hull interior and glass the floaty bits

The black spot on the sheeting is a large fly!

The tail components are complicated by the need to reduce the overall dimensions in order to fit in my car and in an excess baggage box, so the upper part of the fin and the tailplane halves are to be detachable. This will also simplify storage at home, which is getting critical! The fin base straight-forward, but has to accommodate the all-moving tail (AMT) crank and the various tubes for the fitting the top fin and rudder.  I have it worked out on paper...:-)

The rather clumsy former above is to support and align the fin false LE and should have been designed-in at the start.  The fin sternpost alignment is critical and was checked by set-square. Incidentally, the little orienteering tie-pins were awarded in Bulgaria at the Masters Worlds and in Sweden in, oh, 1975. I use the marble blocks as weights and squares, and the colourful badges seemed appropriate all those years ago. Ahh, nostalgia.

This new photo also shows the method of attaching the AMT with brass tubes in the tailplane halves and wire connectors. There will eventually be 13 degrees dihedral each side

The fin in its embryo state. The upper section will detach for travel, with a bolt through the LE where the overlap is, and a wire in tube at the TE. The plan is to sheet the structure with well sanded light 1/16th, but fabric cover the rudder..

As you can see, it is getting increasingly difficult to photograph the model as it takes over all the available space in my room. There have been dark mutterings about ďa shed in the gardenĒ unless I take the Sopwith out of our bedroom where it is resting!

Since this picture was taken I have reversed the pivot point, in order to bring a bit more tailplane area in front of the pivot line. The proportions were 90% aft of the pivot, itís now slightly less than 75%, which will unload the servo and the snake considerably and reduce the possibility of flutter.

The tailplanes are sheeted on the upper surface, and the fin and rudder on both surfaces. I donít like having ribs showing on what is supposed to be a metal-clad structure but every gram at the tail is ten grams in the front end!  I took the sheet parts out to the garden and sanded off about 0.5mm, saving a gram. The undersurfaces will be film covered. Soft balsa LEs have yet to be fitted to all surfaces. The elevators are dummys. (Dummies?)

27 July. At last, some progress! A week as race officer for the Army Windsurfing Champs, a week decorating the kitchen and a week fiddling about and eventually the tail surfaces are fit to be displayed. The upper fuselage formers and the rudder and elevator servo locations are also fixed. Itís only when she goes out in the garden for her photo-call that I realize how big she is (and how elegant you are my dear, how elegant). I have cut the grass since the last outside pictures...

I gave a short talk to the Phoenix MAC a couple of weeks ago, and took along the fuselage, only to be met by a member who had worked as an apprentice at Saunders-Roe when the Princess was being built and the Duchess designed.  His finest memories were of a lad who didnít wash much being thrown into the test tank one night!

The rudder and water rudder can be seen clearly and using Robart hinges the gap can be hidden quite well.  The missing section is a fixed extension of the rear fuselage sheeting

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