Spitfire PR XI

1 year 10 months ago #1040 by chris
Hi Carl
I have a saito 62 if you won't it to put in the spit ?

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1 year 9 months ago #1044 by Carl
The turkey has finally all been eaten and I have managed to extract myself from the comfort of the armchair and have ventured back into the garage to check on progress of the Spitfire. Sadly, the model fairies have not been busy in my absence so there has not been any progress. I have also got my right hand in a cast so can't do a great deal. An accident when mountain biking, a steep hill, a wet track, lots of gravity and a lack of skill then met a tree!
I have managed some work, I dry assembled the fuselage and have dry assembled the center section of the wing to see how it all fitted together. Some photos are below. I have also fully assembled the rudder. I can cut balsa left handed but as yet can’t sand anything and I don’t want to risk removing essential balsa that would only make more work later.




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1 year 9 months ago #1045 by Carl
The fuselage is assembled in two halves, each half built on the plan and then glued together. The front two formers are made of ply with the remainder made of balsa. They are of good quality and are well made, all the pieces fit together well. The formers are held together with top and bottom longerons and then stringers are added to the sides of the fuselage to add rigidity to the structure. Ply doublers are added to the lower sides of the fuselage from the second former to just aft of the wing trailing edge. The whole fuselage is then sheeted with 1/16” balsa.






A tasty set of ribs are provided, the centre section ribs are all the same profile and consist of four ribs with the middle two having ply doublers. The Spitfire has dihedral outboard of the centre section and this is achieved by the huge ply dihedral braces.




Well that is the progress so far, I hope you all had a great Christmas and that Santa brought you lots of goodies that will soon be making an appearance at the flying field.

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1 year 9 months ago #1052 by Carl
I have made some more progress this week. The plans have been flipped over and I have assembled the other side of the fuselage. The two halves mate together very well which is probably more by luck than judgement as it being assembled by a one armed bandit at the moment! The fuselage profile was cut out for ease of use on my workbench. I turned the plan over then redrew the lines that I could see through the plan. The next job is to glue the two halves together. I have a jig that I used to build my Typhoon that will clamp the two halves together and mainain alignment and produce a straight fuselage. I have finally ordered a permagrit sanding block and bar which should enable me to sand the correct profile even with only one hand.





Well, just a quick update for this morning before I head out to the garage to join the fuselage halves together.
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1 year 8 months ago #1053 by Carl
The fuselage sides have now been joined together and it is starting to look like a Spitfire! I dry fitted the fuselage sides first using the frame I made to ensure the fuselage is straight and not twisted.




I then squirted glue in all the appropriate places and clamped the two halves together. I used an aliphatic wood glue that would enable me to position the two halves and align them as accurately as possible. Clothes pegs were liberally applied to hold the top and bottom longerons together. A couple of friction clamps were used to join the ply formers at the front of the fuselage solidly together.




Hopefully, the fuselage halves are now joined with no bends or twists!


I have also bought a couple of permagrit sanding blocks. I had previously made my own sanding blocks but they wore out quite quickly and became easily clogged. Although expensive I have found them very good, they are accurate and don't clog. They can rip balsa if you are too vigorous but sanding has so far been accurae and quick.


I have sanded the tailplane and fin to profile and have roughly cut the excess material from the moulded cowl. There is 1/2 inch balsa infill between formers 2 and 3 which I have started and sanded roughly to shape.

The next job is to fit the fin post and balsa mounting plate for the tailplane. Maybe tonight? My next homework is to prepare the talk for Tuesday, hopefully will see you all there!
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1 year 8 months ago #1057 by Carl
The PR XI was a development of the Spitfire using a combination of features from the marks VII, VIII and IX. It was the first variant to have the option of mounting two vertical cameras in the fuselage behind the cockpit. The camera installation was quite versatile, enabling a selection of different camera mounting options known as configurations, they were labelled G, W, X and U. I am not sure whether the labels themselves had any meaning but I have found examples of the U type and G type as follows. The U probably stands for universal. The G type is the only configuration with an oblique camera; this also requires an aiming reticule on the canopy side.





The PR variants flew much longer missions than fighter Spitfires and so the engine used much more oil, the oil tank was therefore enlarged and this resulted in a longer bulge under the engine. This bit of detail I won’t be including in the model as the cowl is already moulded for the Mk 9. The fin of the PR XI was also larger and more pointed than conventional Spitfires, this I might attempt to replicate as it is a relatively simple profile change.
A total of 471 PR XIs were built, the first 260 were powered by the Merlin 61, 63 or 63A engine. Thereafter the Merlin 70 was used which was the high altitude version of the Merlin. PR Mk XIs were capable of a top speed of 417 mph at 24,000 ft and could cruise at 395 mph at 32,000 ft. The typical mission was flown between these two altitudes however in an mergency they could climb as high as 44,000ft. This was not an altitude that pilots could sustain for any period as they would suffer from decompression sickness (the bends!) and would even become hypoxic (oxygen starvation). The oxygen system they were using during the war could provide 100% oxygen but above 33,000ft even this was not enough without a pressurised cockpit. The PR XI was unpressurised.
During my training in the RAF we were put in a decompression chamber and taken slowly up to 24,000ft, they would then rapidly decompress the chamber up to 45,000ft to simulate an explosive decompression in our aircraft. The oxygen system we used in modern fighters had positive pressure oxygen which literally pumped up your lungs for you. The hard bit was breathing out when you had to overcome the pressure of the oxygen. This is obviously the opposite of how we normally breathe and is quite exhausting over extended periods. We then in pairs removed our oxygen masks and performed written tests. I only lasted about 45 seconds before I was ordered to put my mask back on. On inspecting my written work most of it was utter rubbish, I had an effective thinking time of about 15-20 seconds before my writing was illegible. Other effects I remember were that my vision became black and white and I got severe pins and needles around my face and finger tips. On replacing the mask it was like emerging into sunshine as my colour vision returned. One unpleasant side of the explosive decompression is that any gas in your body rapidly increases in volume and then tries to escape. This includes the sinuses, middles ear, lungs, your intestines (the most noticeable and unpleasant effect) and even air pockets in tooth cavities that could cause acute toothache instantly.
One purpose of this training was to enable us to recognise the effects of hypoxia in ourselves before we became incapacitated. I am glad to say that I benefited from this training on a high altitude flight during a NATO exercise over the south west approaches to the UK. We were on a high-low-high profile to attack a fleet of “enemy” ships, on the outbound leg at 45,000ft I started feeling strange and realised the pins and needles in my face were exactly as I had felt in the decompression chamber. I was able to switch to an emergency oxygen supply and recover without any further incident. After landing the technicians found that the main oxygen system was only providing normal air mixture instead of 100% oxygen. Fortunately, this was a rare event and the only time I recall suffering from hypoxia in flight.
Back to the Spitfire: I plan on replicating the PR XI with the ‘G’ camera configuration, this should be quite straightforward, I will just cut out three circles in the correct places and fill them with clear plastic!
I have made a little progress today with the cockpit floor glued in position and the fin post finally attached. Sorry no photos as yet but will post more tomorrow.
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