Defining the location for the cockpit rails
The location of the front ends of the cockpit rails is not comfortably defined on the horizontal in any of the Avro drawings I have found to date. The height above datum is given clearly at 44 ins. But the horizontal value depends on the structure of Former E around this area and relates to the Former E Extrusion itself, the packing pieces and the side panels, all of which are shown below.
The next stage of the work after this will be to draw the cockpit rails with the correct curve/twist and location for their front ends. The actual attachment of the cockpit rail front end to the parts shown here is quite pleasing. I look forward to putting it all together.
Images 1 to 5 following are all viewed from the same position: from the rear and from below former E.
Former E consists of two elements, the extrusion and the angle. The angle is bolted on to the front of the extrusion and forms the base for the construction of the nose section. The cross sections of both are illustrated below in a separate image.
The small instrument panel support angles, Avro 5/D.1745, are floating in Image 4. They join the inner front sides of cockpit rails and the instrument panel shown in Image 5.
The packing pieces, Avro 2/D.1675, are in three segments, ‘af’, ‘bc’, ‘de’, and are wedge shaped with the thin edge to the front. The divisions between the segments are suggested in the following image. The height of the thick end of the wedge for ‘af’, the top element, is constant at 3/8 inch. The middle segment ‘bc’ tapers from 3/8 inch at its top down to 9/32 inch. The lowest segment ‘de’ tapers from 9/32 inch down to 0.06 inch. The height of the thin edge is constant at 1/16 inch through most of the length of the 3 segments, but reduces to 0.06 inch similarly to the thick edge towards the bottom of the last segment ‘de’.
I’ve some concerns about two previous posts of mine.
First in relation to my post no. 80 20th Sept in this thread. I was not thinking properly.
The cross-sections of the stringers I envisage to be like this.
That is: a strip of flat aluminum is rolled into the shape shown where the bulb corresponds roughly to the centre line of the strip. I do not have any source that confirms this for the Lanc. But I have seen cross-sections of stringers produced currently which suggest this as a strong possibility for the Lanc.
Now look at a section from the drawing i attached to the above post.
The technique used to produce the end piece of the stringer is first a joggle to clear the flange of former K and then the disappearance of the bulb. The bulb can be removed either by unfolding the stringer completely and cutting off the surplus or by flattening the bulb. Unfolding and cutting would weaken the joint considerably. My best guess is that the bulb was flattened.
What this means is that my own drawing is in fact following the production method used, flattening the bulb.
So the misgivings I expressed in that post are in fact not justified. The only departure from the Lanc is that the stringer bulbs are solid not hollow. This is unimportant.
Is this argument good?
Second, following on from my posts 87 28th Oct, 88, and 91 dealing with the Bowden cable of the Harness Release Mechanism and the spiral sleeve which controls the release.
The problem I had was the projection of the development curve, shown in red here, onto the 1/2″ dia hollow cylinder in such a way that the projected curve was tangential to the circular end points of the spiral slot.
The straight line given in the 2D development here will form a curve on the surface of the cylinder when projected.
I was forced to approximate this curve in order to make the curve a tangent to the ends of the slot. So, basically, I lost the 2D straight line property if the projection was reversed back into 2D. This seems to me to be wrong.
At the very least I drew one of an infinity of curves satisfying the tangent property when the curve I required was unique.
This makes me feel uncomfortable. The problem is not this particular Lanc drawing. It is a defect in my technique, a limitation on my ability. Can anyone suggest the correct technique here.
Incidentally, without the tangent property at the end points, a projection of the drawn curve normal to the axis of the cylinder onto the inner surface of the cylinder destroys the circular end points.
Mhhh!! Some comments would be very welcome
Mike
See what you’ve had me do. QldSpitty!!!
Back to the nose section to see what can be done with the complicated joints of stringers 13, 15 to 19 with the round former K.
The bulb at the end of the stringer design used is in fact hollow. The stringer is folded in half more or less and the bend is developed into the bulb.
At the joint with former K, one half of the sandwich is unfolded to give a larger amount of material to the rivet. For reason of machine & software limitations, I chose to make my stringers solid. The unfolding is not now possible. Now the stringers could be solid in some situations with some aircraft; but not the Lanc. A similar bulb/ball might be hammered flat to give the same effect. I’m somewhat uncomfortable as this is becoming art rather than engineering. However, it does suggest the problems in manufacture.
Here is an image of the whole nose section to give context. The arrow points to the area covered in the following two images.
Pilot’s Harness Release System
Sorting out the problems of the spiral sleeve
The spiral has two end points. These are round holes to the diameter of the pin for the majority of their perimeter. The spiral profile, outer and inner, must form tangents to these holes. This proved difficult, if not impossible, with standard projection tools. In the end, for the outer spiral profile, I had to do it piece-wise and form the best fit curve to the segments of profile I had projected. For the inner profile, I divided the curve into a number of points and did a standard radial project onto the inner surface of the cylinder. I confess I cheated somewhat with the detent bump. The surface created with the two profiles did not form a smooth curved bump. I should have redrawn, yet again, the inner profile. But life is too short and I used a fillet tool which did not quite produce the result I had hoped for. I think it is probably pretty close the the actual pieces made in production.
Here are two images showing the profiles and the end points, plus the detent profile.
Here are two more show the pin resting in each end point,
WHY!
This work had a purpose which was to show the working of the Pilot’s Harness Release and to provide drawings for the release control barrel which are missing and, perhaps, have been lost for good.
There are two areas involved in the harness release as shown in this image of the pilot’s seat:
The Bowden cable connecting the control mounted on the righthand armrest to the release itself on the top face of the seat behinf the pilot’s neck is not shown. Drawing cables and bungee cords that hang naturally is above my skill level. One day perhaps …
The idea of this release is that the pilot at verious times needs to be able to lean forward to reach various switches & controls. But, otherwise, he should be firmly held in his seat by the harness. The release unlocks the shoulder straps so that the pilot can pull forward the top part of his body against a powerful spring held in a long tube at the rear of the seat. The spring returns the pilot to the seat when he relaxes. At this point he can use the control to re-lock the harness to hold himself firmly in the seat under tension from the should straps.
Here is an image of the control exploded to show the indivifual parts. The pin is fixed and is welded to the outside of the bracket attaching the control to the armrest. The handle rotates the spiral sleeve within the barrel by 170 degrees from the locked position to the released position of the handle. The spiral converts the rotation of the sleeve into fore & aft movement within the barrel. Moving the sleeve to its aft position causes the bowden cable to withdraw the locking pin from the pin rim, shown in a following image, on the top of the seat. At this point the pin is held in the detent end point by the bump which caused me so much trouble. Moving the sleeve to its forward position releases the locking pin. The long spring returns the pin rim dome into the socket and the locking pin jumps home when it hits the rim. It is itself spring loaded.
Here are side and front views of the release control with the fully forward and fully aft positions of the sleeve supimposed.
To complete the story, here are front & rear views of the release mechanism itself.
How wrong can I be?
Thanks, guys, for the comments. This is a long, long slog. Your comments keep up my spirits.
I’ve been taking quite a break from the work while I sort out some other pressing things.
But I thought I’d do some interesting little bits that I could do quickly and easily.
Oh boy, how wrong could I be!
I thought I’d draw the rotating keyway shell or spiral sleeve that pulls or allows to relax the bowden cable controlling the pilot’s harness release. This rotates and moves against a fixed pin. The pilot rotates it with a handle and the keyway slot causes the shell to move forwards or backwards.
Here’s the drawing for it.
I’ve sweated blood over the keyway. It’s made even more difficult by the bump or detente.
It’s the sort of thing that would be much easier with a lump of ali and a file.
But a 3D drawing!
Grrr!
Mike
More on the former E Angle Piece and its stringer brackets
Unfortunately none of the Avro drawings, 21 … 42/D.1649, which deal with the brackets seem to have survived.
Using photos and the existing dimensions of former E, I have drawn a reasonable version of the bracket from 41 & 42/D.1649. This form of the bracket is used to support all the stringers below the fuselage datum line. 42 is the other handed version of 41.
This image shows the upper half of former E with the shaded outline of what I believe would be the bracket in the position of stringer 1, the top centre one. I do realise that, in fact, something completely different is actually used to support bracket 1 in this location and I do have good Avro drawings for this. My drawing here is just to make an explanation of the problem a little easier.
The nub of the problem is that the horizontal – ish flange of former E changes its angle to the horizontal continuously from the top central position down to the fuselage datum line. At the top centre the flange makes an angle of 9.12 degrees below the horizontal, or as shown in the next image 80.88 degrees from the vertical. At the datum line the angle is much reduced to just 1 degree below the horizontal, 89 degrees from the vertical.
Here, normal cross-sections of former E are superimposed. That of the top centre and that of the datum line showing the differences in angle. Also is shown my drawing of the bracket in the top centre position.
The brackets need to be of different shapes to cope with the change in angle. So we have a family of slightly different shapes for the brackets. Normally, Avro usage copes with this in a single drawing which has just one parameter to define the differences in the family. In this case the parameter would be the change in angle at the various stringer locations.
I have wracked my brains to try to derive a drawing of the bracket which has just the one parameter of the angle difference to produce the whole family.
I think there are really only two options, starting with the bracket I have drawn at top centre:
The first is to rotate the top line of the bracket up to the correct angle for each of the stringer stations and fill in the gap. This gives the following image:
The second is to rotate the whole body of the bracket up to the correct angle and fill in to the vertical flange of former E.
As here:
The first increases the height of the bracket substantially and changed slightly the angle of the nose. The second changes the bend at the bottom close to the vertical flange of former E and mucks up the cut-out at the elbow of the former E cross-sections.
Of the two, I much prefer the second. the cut-out can be managed easily where the interior vertical & horizontal lines of the former cross-sections are tangents to the fillet curve of these. But the change in the bend at the bottom needs another parameter attached to the angle difference. That would be the length of the horizontal stub before the start of the bottom bend or curve.
So, I haven’t succeeded in producing a family of drawings each defined by the single angle parameter. Can anyone else?
The conclusion otherwise is that there were separate Avro drawings for each of the handed pairs:
21 & 22/D.1649
23 & 24/D.1649
25 & 26/D.1649
27 & 28/D.1649
29 & 30/D.1649
31 & 32/D.1649
33 & 34/D.1649
35 & 36/D.1649
37 & 38/D.1649
39 & 40/D.1649
41 & 42/D.1649
Also I have not been able to find the gauge of the material for these brackets. Presumeably, it is between 14G and 18G.
I hope this is of interest.
Mike
Ok, to terminate the stringer I followed the shape of the bracket.
The rule seems to be do a reverse curve of the same radius.
Mr Merry, thanks a bunch for your comment.
Mind you if you enjoy it that much, perhaps an emergency airlift to Argentina of Tetleys & Baked Beans might be called for.
Mike
Rolled flange
Here is a section of D.2430 for the front nose former K showing the attachment of a stringer to the former.
QldSpitty, this is what you mean, isn’t it? The flange is unrolled to give a greater area for attachment to the former as in the upper of the 2 drawings.
Sadly, I have gone for a solid flange, not a rolled one. The memory overheads are just too great. Not only that, I think a rolled flange would need a lot of experimentation on my part to achieve even a rough model. So I just cut the flange.
Probably this drawing is also an answer to my question in my last post. The end of this stringer is just square and there is no reason why the termination to the former E angle shouldn’t also be square. The inner faces of both formers K & E are square to the datum.
Thanks
Mike
Help please. What would be the industrial practice?
Unfortunately, I have not found any Avro drawing showing the shape of the rear end of the nose stringers where they join to the angle section of former E. There is quite a hefty bracket, not shown, for which I do have a drawing. That’s not the problem.
It is how the stringer end would be shaped to fit the angle section as done on the production line. Here I’ve made a perfect shape for the joint. I don’t believe for one minute the actual shape of the end of the stringer would be anything like this.
Can some kind soul, please, give me a rough sketch of what the actual industrial practice might be for forming the end shape. It doesn’t have to be from an actual Lancaster joint. Just some idea of how the blokes with hammers would fashion the stringer end shape for the joint.
Much obliged & thanks
Mike
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