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  #351  
Old 05-13-2018, 04:41 PM
Algebraist Algebraist is offline
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ellipsoids and ellipses

Dear all

It struck me that for the 1/24 build things are not always as expected. For example the stage two thrust structure proved difficult (for me) whereas I was expecting the top of the LOX fuel tank of stage one to be impossible (but actually turned out to be straightforward).

So for a bit of relief he is some things related to the LOX tank

First a photo (from NASA) of the real things being manufactured



Mathematically speaking the top of the tank is an ellipsoid (3d version of an ellipse). New welding techniques had to be invented to make these and I believe they are the methods (essentially) that modern day cars are put together by robots.

So why have an ellipsoid top of tank? From a "space" point of view the most efficient tank shape is a cylinder. But that causes problems pressure-wise. Pressure-wise a sphere is best but that is not efficient/practical space-wise. Mathematically, a cylinder with ellipsoid end is one of the best compromises.

The ellipsoid is one of my favourite shapes. One thing I like is the fact that there are two special points "inside " an ellipsoid which have the property that any straight line passing through one of these points will, when it bounces of the wall of the ellipsoid, pass through the other point.

I must admit looking at the shape this does not seem possible but it is true. This mathematical property has helped loads of people have kidney stones "smashed" with shockwaves using a method called lithotripsy and usually uses a machine which makes use of this ellipsoid property. Here is a photo of such a machine



On a "fun" note here is a neat thing. The ellipse has a similar 2d property to the ellipsoid. I remember learning this at school and thinking you could have a type of bowling game with one skittle (pin) on an ellipse shaped lane. IF you bowled your ball exactly through that special point it would bounce off the ellipse wall and hit the skittle. However miss that point you would miss the skittle. Recently Alex Bellos (a popularist mathematical writer) had a type of snooker/pool table made which uses this ellipse princple.

Here he is explaining his table



And of course ellipses are critical to the earth moon system and the paths of apollo/saturn V to the moon!

This post went on a bit (probably as an antidote to the difficulties of the build recently)

Regards

Kevin
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  #352  
Old 05-13-2018, 07:10 PM
elliott elliott is offline
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Well, at least you're still moving in the right direction Kevin. Mum's the word about any alleged difficulties with the stage two thrust structure. Enjoyed your ellipsoidal musings too.
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  #353  
Old 05-18-2018, 03:09 PM
Algebraist Algebraist is offline
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Thanks Elliott, much appreciated

Regards

Kevin
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  #354  
Old 05-18-2018, 03:34 PM
Algebraist Algebraist is offline
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1/24 stage 2 continued

Dear all

I have been able to continue with stage two and have been working on the aft skirt. So I followed (almost) the same way as the 1/48 model. The only major difference is the fact that much thicker formers needed. So here are the outer ring parts

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12550.jpg

Then glued together, walls thickened, joining tabs added and former glued into place (top and bottom view below)

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12558.jpg 1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12559.jpg

I then added the printed part on the underneath of the former and then glued the thrust structure into place

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12561.jpg

Whilst doing this I was constantly checking how it fit onto the interstage. At the finish the fit is pretty good (I think). See what you think in the photo below

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12560.jpg

There is something the photo cannot show which is the parts are so large that the stiffness of the pieces is not perfectly rigid. This means that the interstage can flex about 1mm and the "recess" of the trust structure (ie the lip which goes over the interstage) also flexes about 1 mm. This means that the joint is not 100% rigid so you can very slightly move stage two about. However it does not come off the lip of the interstage. However all of stage 2 and above rests on this tiny thin contact area. Fingers crossed it is okay. I think the physical limits of the paper have been reached for the design being enlarged to this size.

The 1/24 model has now caught up with the 1/48 model. I intend to press on with both in terms of the main structure and leave the J-2 engines for now.

Current model height 2.1 metres (6ft 11 in)

Regards

Kevin
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Last edited by Algebraist; 05-18-2018 at 03:37 PM. Reason: spelling corrections
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  #355  
Old 05-18-2018, 11:10 PM
rifleman rifleman is offline
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i keep saying it but dam fine work my man just keep plugging away well done
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  #356  
Old 05-22-2018, 03:04 PM
Algebraist Algebraist is offline
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Looking ahead to the CM (1/24 model)

Dear all

I have been thinking about the suggestion of replacing the CM of the download with Ken West's (reduced) CM (which I have purchased).

Here is a quick paper outer of a reduced to 1/24 scale KW CM

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12490.jpg

The first thing that struck me was just how TINY the amount of only bit that could keep the 3 astronauts alive was, and then how titchy it was compared to the volume of the rocket!

However back to the model. I have decided to stick with the CM of the download which is designed Ton Noteboom. To my eyes, at this scale and the comparing what would be used I think Ton Noteboom's looks just as good. Also I like the idea of the "authenticity" of trying to do an enlarged version of all 1/48 model. Finally for me (and this is just about me), for this particular go at the model I felt a little uneasy "replacing" somebody's work who had freely donated their time and effort to help complete this great design.

There is no criticism of Ken West's CM (of course), nor of anyone who had done such a change (past, present or future).

I hope everyone is okay with that

Regards

Kevin
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  #357  
Old 05-22-2018, 03:31 PM
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1/24 stage 2 "States" ring

Dear all

The build on the 1/24 model has continued and I now reach the biggest ring of the rocket, the "States" ring

Here it is formed and also with Gunter and Wernher for scale

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12562.jpg 1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12563.jpg

The parts were so big they had to be split into two, so the ring is made of 8 bits. You will also notice that it looks slightly strange. That is because the panels without the word "STATES" on them have been replaced with plain white pieces of paper. For some reason it was not possible to match both the outlines of the rocket motors and the markings (very feint) on the surface of the ring

Another thing to point out is the download has two panels with markings for umbilical tunnels and two without (parts 7 and 8) whereas the actual rocket only has one umbilical tunnel (so you only want 1 part 7, rather than the two in the pdf, and you want 3 part 8 rather than the two supplied in the pdf).

I then attached the ring to the thrust structure, using the interstage as a "base" to support the thrust structure, remembering to ensure the panel with the umbilical tunnel is in the correct position (as shown below)

1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12574.jpg 1/24 Apollo/Saturn V (enlarged 1/48 Greelt et al version)-sdc12573.jpg

As you can see the model is starting to grow again

Current model height 2.30 metres (7 ft 6 in)

Regards

Kevin
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  #358  
Old 05-22-2018, 03:32 PM
Algebraist Algebraist is offline
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Quote:
Originally Posted by rifleman View Post
i keep saying it but dam fine work my man just keep plugging away well done
Cheers!

Kevin
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  #359  
Old 05-22-2018, 07:44 PM
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beckychestney beckychestney is offline
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Aye carumba!


(had to think of something to say other than "wow!" )
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  #360  
Old 05-22-2018, 09:45 PM
elliott elliott is offline
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You're continuing to make great progress imho Kevin. As far as the CM switcheroo goes, it's your model, build it however it pleases you. You can always build the West CM at a later date. Keep at it guy, you're doing great work!
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