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Jilles Smits 1/3 scale SG38

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Peter Balcombe
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Location: Clevedon, North Somerset, U.K.

Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

With missing slots (cutting files to be amended) added, the central wing structure can be added to the pylon/mast structure.
The first bits are the F7 pieces either side of the rear upright, notching into the forward mast.

The forward mast lower side pieces are also fitted to the structure prior to adding the lower part doublers and closing up the mast box assembly (to be done tomorrow).
Attachments
F7 added to mast structure
F7 added to mast structure
Mast lower sides added
Mast lower sides added

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

Here you go then.
I have completed the forward mast assembly and added the wing root ribs.
That is a 1m rule for scale.
Although trying to be careful about getting assembly order correct to avoid locking parts out, I failed to put in 2 balsa pieces just above the wing root ribs whilst assembling the F7 ribs just inside each root rib :o
However, these are only to provide a glue support land for the mast top covering in due course, so was able to cut these where they rest on the crosswise former at the wing incidence pin location and insert later as two separate pieces.
It looks like I need to do a lot more work on the forward fuselage before I can put the side skins on in order to avoid more lock-outs! This will need me to start making some of the many brass brackets ;)

Tow release and rudder servos screwed into place the check fits, plus servo plate added for the elevator servo (this will be hidden under the seat assembly).
Attachments
Overall fuselage mockup
Overall fuselage mockup

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VinceC
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Re: Jilles Smits 1/3 scale SG38

Post by VinceC »

Thanks Pete, just over 12 inches long then

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

Vince,
Er, not quite ....
More like 2.092m overall length, 3.45m span and 810mm overall height ;)

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

I forgot to say earlier in this thread that although the Bill of Materials (BoM) lists the various labelled parts (NC cut & stripwood), I thoroughly recommend going though the BoM against the parts and drawings before you start any of the build.
The reasons for this are to (a) check off your laser cut kit parts, (b) identify where each item fits on the plans & (c) identify the stripwood required to be ordered, (d) split the NC parts into various build groups (e.g. fuselage, wings, tailplane, rudder).

I also noted the purpose of each part on my BoM to help later on.
In doing this, I identified a few items that had been accidentally missed off the NC cutting files and a couple of wrong quantities (drawings since amended), but also identified a couple of items which didn't appear to be mentioned anywhere on the various drawings.

Items which fell into this latter category are GUS1, V13 & V14.
Jilles has provided lots of additional information on the various cross sections provided, but the above parts don't appear to get a mention on any of them. So...
GUS1 is a small slotted gusset which is used when glueing the elevator servo tray ST2 to the top of the forward fuselage deck DKD. It will be apparent from the tab/slot which way around it goes on the front of ST2. A photo below shows GUS1 in place.

The V13/V14 items fit at the very lower rear of the rear fuselage (tail skid area).
A problem I find with CAD drawings is that there are so many lines on them that it is sometimes difficult to decide where some parts end, unless you have an infinite number of notes/sections to show what is going on.
This was the case when I was assembling the fin post, as although there is a drawing note on the skid area saying that CS3 (carbon strip) & V5 go to the bottom of the skid, it didn't mention the V6 strips each side of the CS3/V5/CS3 sandwich and also didn't mention the NC cut V13/or V14 pieces.
Once you realise that V13/V14 actually fit into this area, all becomes clear .... albeit somewhat belatedly for me ;)
The V6 parts stop at the lower level of the bottom rail (V2,V4,CS2). The V13 piece fits on the bottom of the V2,V4,CS2 rail, forward of the V5/CS3 sandwich, with the V14 pieces acting as doublers & going each side of the lowest part of the V5/CS3 strip.
I mistakenly took my V6 strips to the bottom of the skid and have had to cut the rear off each V14 piece to get them to fit in the remaining space.
Note that this area is further doubled by the two outer V15 parts, so I don't think it will be a problem.
The photos below show V13 & the 2off V14 parts (one of which has been shortened), the underside of the skid area, both before & after fitting the V13/14 parts.
Attachments
GUS1 location
GUS1 location
Rear skid underside
Rear skid underside
Rear skid void
Rear skid void
Rear skid filled
Rear skid filled

Jilles
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Re: Jilles Smits 1/3 scale SG38

Post by Jilles »

How many notes are required on a drawing. coming from a engineering back ground I would say probably never enough.
Even though this SG38 fuselage looks a simple frame from sticks and ply plate, the time spend on working out and detailing took approximate twice the time then for a standard fuse of previous vintage designs. On a scale like this lots of features has to be added to make it look scale, the final finish has to be kept in mind, ready available material and it has to be structural sound. If you create a drawing of your own design one takes some items for granted because they are already in your mind. That is why in an professional situation an other person(s) will check the drawings.
In this case Peter as a first builder is that check person. All findings and recommendations will be amended on the drawings as soon as the built is complete. so far Peter is doing a great job.
As I mentioned before on various occasions my designs are not for the beginner and some details are left to builders preferences.
Above is not an excuse for problems on the drawings but it shows how things work. Compared to 10-15 years ago we are spoilt with CAD drawings, NC cutting and modern composite materials, but that does not mean everything will be perfect. Remember the hand drawn more often than not inaccurate drawings, you had to cut everything yourself and make it fit, maybe we are loosing skills here in the process.

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

Please note that my build comments to date are not in any way, shape or form, a criticism of the design, especially this one which has so many parts due to the nature of the beast.
I know from my own very limited design experience, how difficult it is to cover every eventuality and even more so, to remember to cover every detail of every part.
Thus the first build is always likely to find a few wrinkles which can be used to remove these for future builds.

The SG38 is a lovely design & the solid nature of the fuselage construction is so different from the normal rounded shapes, especially as nearly everything is visible in the final product.
All credit to Jilles for producing yet another excellent design.

Jilles
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Re: Jilles Smits 1/3 scale SG38

Post by Jilles »

Hi all, nothing what was said about the SG38 details is by myself received as criticism. I just felt a need to explain why I am not 100% perfect like anybody else I guess
I have the same little problems with my Nimbus built that is going on now and reported at an other built thread on this forum.
Peter is one of the first that actually comes back to me with problems he found, I appreciate that because not many other do. Enough said get on with the builds.

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

Moving on ...
Construction of both the rudder and tailplane has started.
The rudder commenced by inserting the top & a lower rib (at the correct angle) into the rudder post, then glueing the carbon strip TE core in the rear NC cut notches. Once this had set, it was a simple job to add the remaining angled ribs.
Rudder top rail still to be added.
Once the LE riblets have been added, the LE will be wrap-around skinned with 0.4mm ply.

The tailplane structure is build largely from NC cut parts, so goes together very quickly.
Note that the angled rib ends ideally need to be bevelled to allow the rib pair tabs to fit into the spar slots (i also bevelled the edges of these).
The rear of the tailplane & inset elevators are next.
Attachments
Initial rudder construction
Initial rudder construction
Rudder framework
Rudder framework
Tailplane core
Tailplane core

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Peter Balcombe
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Re: Jilles Smits 1/3 scale SG38

Post by Peter Balcombe »

Elevator framework now built and the trailing edges now have their balsa facings epoxied on prior to profiling.
Elevator LE to be added & then profiled.
The rudder framework is also nearly there with the exception of the top rail (since added together with balsa backing of the LE between the ribs).
Attachments
Tail & elevator progress
Tail & elevator progress
Rudder with TE facing
Rudder with TE facing

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