Scale Soaring UK

Another prototype build from a one of Jilles’ excellent plans.
Lots of drawing rolls have arrived, plus a full set of laser cut parts from Cliff Evans to make up this 1/3 scale primary glider which includes lots of rigging wires and scale pulleys for the control surface operation.
The servos are largely hidden and the Rx is buried within the pilot’s body
All parts have been checked against the Bill of Materials & identified on the highly detailed plans.
Just awaiting delivery of a large pile of stock wood before starting the build.

For a Primary glider there are an awful lot of parts

Ooooooh! I will be following this build.

The wood has arrived (for both the SG38 and ASK21), so I have just made a start on the rear fuselage
A lot of the spruce strip is for the SG38.

I have just cut the dozen or so core wooden parts for the rear fuselage structure, so will make those up into the basic framework (complete with Carbon strip strengthening) tomorrow.

Booo, killjoy..

First up in the build is the rear fuselage frame.
This is built up with the top, rear & bottom rails laminated from various lengths of spruce & thin carbon strip as can probably be seen from the cross sectional liquorice allsort stripe appearance in the pic.
The top & bottom rails will plug into the rear of the forward fuselage 'A' frame assembly.
There are still numerous diagonals, gussets, sheave mountings etc. to be added.

Rear fuselage construction now complete apart from metal fittings and tailplane fixings.

I am now moving on to the forward fuselage where the first job has been to make up a steam bending template for the box structure lower rails. Once the rails have been shaped, the basic structure should go together pretty quickly.

Moving on to the forward fuselage, the plan advises starting by building up the basic fuselage box structure as shown on a section of the drawing.
I started by splicing together lengths of standard 36" long spruce to make the curved lower rails, then steam bent these to shape with the aid of a simple MDF sheet template (profile taken from edge of a laser cut side sheet).
The various laser cut formers etc. are then glued into place to make the basic structure.
The shaped hardwood nose block holds the tow release pin guide tube and has slots to take a 12x12x2mm aluminium U channel.
The photos show the structure placed in a mirror image jig to hold the lower rail in shape whilst glued to the formers. (the yellow tape is used as a release layer to prevent the rail from sticking to the template.)
The other photo shows the assembly less laser cut the top & bottom sheets which will be added once the aluminium channel has been fitted up front.

Looking quite interesting and great work again from Jilles

Fuselage lower box structure now assembled to the state shown on the plan for the initial assembly.
The release servo position is up front & the rudder servo just behind. The elevator servo will be mounted in the seat base. All servos will be hidden by the fuselage side plates/seat base in due course.

Next step is to start constructing the 'A' frame parts.

Mast assembly construction has progressed to the point where I can check how the rear fuselage fits.
A slight hiatus on the forward part of the mast whilst we sort out a couple of missing tabs slots to enable the wing assembly to interlock correctly.
(CAD doesn't always produce what is expected!)

Its probably worth noting that there are an awful lot of wooden pieces which need to be assembled to make up the overall fuselage, so a builder needs to be very careful to make sure he carefully notes all of the drawing notes and supplied cross-sections to make sure the various items are assembled in the right order and place.
Jilles has done a very good job in providing a detailed plan which appears to mimic the full size construction and finished appearance.

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).

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
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).

Thanks Pete, just over 12 inches long then

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

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.

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.

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.

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.

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.

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).

Elevator now dry hinged to check fit & movement.
Can fit tailplane LE skins next, but the rest will probably be left until the various rigging/horn fittings have been installed.
Meanwhile, I tried fitting to the rear fuselage/mast sections to see how large it is becoming

Hi There Peter,

Beautiful work, I really do enjoy building as much as watching them get built, especially from a set of nice drawings.

Steve

Many thanks for the compliment Steve.
A bit more done today, so will hopefully post some photo showing the installed rolled ply rudder & elevator leading edges tomorrow.
Peter

Peter & Jilles strike up a good team. Nice work and well done to both parties

Thanks Vince.
Here is a photo of the tailplane once the rolled ply Le has been fitted (using the white glue & ironing technique).
The tip rolled ply sections need to be applied as separate pieces as they taper towards the tip at that point, where as the central part can be done in one piece.
Balsa tip blocks complete the process.
Still a lot of 0.4mm ply cap strips to be added.

The first wing has now been started and is going together very quickly once you have pre-joined the 2 main spar webbing parts (I fitted a 1/32" ply doubler over the rear of the join area) and spliced up some spruce strip for the upper main & rear spars.
Starting with a few ribs at either end of the main webbing, I glued the ribs (R5 outwards) onto the web & initially held them in place using a dry fitted rear spar. (The notched ply web and bottom building tabs ease this process.)
I then glued the upper 1/4" square main & rear spars into place to firmly anchor all the ribs - note that the spars need to be pressed right down as the remaining space above will be filled with balsa later).
The remaining root ribs can be added by fitting them into the above two spars, spacing apart using the separate web pieces - not forgetting to fit the joiner tube hole doublers to R1 & R4, otherwise the rib positions will not work out correctly above the plan
The aileron spar AS1 can also be fitted to the rear of the outer ribs - not forgetting to add the aileron servo plate at the same time.
Note that the aileron spar and the main (MSE) & rear (RSE) extension spars need to be fitted so that the upper surface slopes downwards towards the tip - note that some of the plan sections appear to show some tip parts upside down, but that is because of the direction the section view is made. The check is that R14 should slot in from the top.
The photos also show a couple of the spruce strip cross braces which can be slid into place via slots cut in the ribs. Note that these need to be firmly bonded to the ribs and the spar tops to add torsional stiffness. Web plates are added between top & bottom cross bracing strips later.

Great,job!!! We are looking forward for the progress.

I had forgotten that I hadn't updated the thread for a while!
The 1st wing structure is now more or less complete & awaiting aileron horns & bracketry before the 0.4mm ply skins are put on.
The 1st wing aileron is nearly complete, just needing the LE to be shaped.

Also, I have put together the 2nd wing structure over the past couple of days, including the aileron.
Still a lot of finishing work to do yet, but I now have all of the major structures complete

In the meantime, Wilson has delivered a 1/3 scale old timer pilot to Cliff, so I had better get on with the seat and the metalwork

Bravo, Peter! What kind of wood did you use to wings?

What's the best choice of wood for spars?

Sotiris,
At 1/3 scale all of the strip wood, including the spars is Spruce (as available from UK model shops).
Some strip lengths have to be made by splicing two standard lengths together (I use a 50mm long splice with epoxy glue).

Thank you Peter! Are the hinges Robart type?
I noticed that, the leading edges of elevator and ailerons are square shaped and the rear spars too.I wonder,how the control movement can be achived with so small gap. Any explanation is useful because the SG38 is my first building attempt.

Sotiris,
Yes, the hinges are all Robart pin hinges.
The first aileron built has its balsa leading edge strip fitted but not yet shaped into a ‘Vee’ to allow up & down movement against the flat wing rear hinging strip. The hinge rotation point is recessed back into the control surface.
The 2nd aileron build has not yet had its balsa leading edge strip fitted, still shows the internal backing strip.
This arrangement is the same on all control surfaces (I.e. flat hinging surface, angled control surface leading edge).

Peter,
I didn't know,about this configuration.Thank you,really useful!

Sotiris,
The attached part of my SG38 plan gives a picture off the hinge area.

Peter,
thank you very much
I have spent a lot of time of internet research for hidden details.

Build recommenced after the Xmas break.
First up is to make some of the many brass fittings, including those to tie the front & rear fuselage parts together, plus some rigging brackets.
Photos below show some of the brackets before after putting in place.

Coming along nicely Peter,
Where do you procure your brass from? Is it sheet or linear metres. I have been poking around a little to find a good price, however, I think bad ole ebay seems to be the place. No-one local can compete with the prices from the internet.

Anyway she is coming along nicely and I had better post an update for mine as well, A little slack and slow start to 2019.

Kind Regards
Steve

Steve,
The 1/4” wide brass strip is standard K&S metals which I can get, together with most Brass & Aluminium tube from a good UK modelling shop such as the Sussex Model Centre. The 1/4” strip is very convenient as a lot of the brackets are 1/4” wide, so just need cutting to length.
I have sourced larger brass sheet pieces in various thicknesses from eBay to make the remaining items.
Peter

Awesome thanks for that Peter. Unfortunately its getting harder and harder for the actual shops to compete in this online era.

Lower fuselage box assembly now closed off using supplied side sheets and the upper outer side strips added.
Spruce strip to be steam bent for the lower strips.

Remaining side strips added, including a couple of top/bottom ones which will fit under the forward mast structure & secure this to the bottom box assembly. (Jilles, I am pretty sure that these 2 top/bottom strip on each side are the SP1 items shown on one of the plan sections).

The lower rear of the pylon assembly fits into the rear of the fuselage bottom box assembly (between the rearmost part of the 0.8mm ply side pieces) & the final triangular pieces have been epoxied onto the rear fuselage boom & checked that they will be able to be slid into place in the bottom box assembly in due course.
I currently am leaving the fuselage bottom box assembly separate at the moment due to the thought of trying to handle the total assembly in the overcrowded workshop.
In the meantime, I have made & fitted the 2 skid spring tubes & also fitted the brass plates where the tubes enter the bottom box.
Lastly, lamination of the skid has started. The skid is made from 8 laminations of 0.8mm ply, bonded whilst held in place round a simple former.

Skid now complete after taking out of the laminating jig, tidying up end and fitting the 3 brackets.
Test fitted to the fuselage bottom box assembly & now just needs the forward fuselage mounting bracket to complete the setup.

Front skid bracket now made & in place (photo later), but latest activity has been on making up the rudder pedal assembly.
Photo of the partially assembled unit shown below.
The nearby plates need to be silver soldered onto the angled ends, followed by the pedal themselves in due course.
The pulley wheel is for the elevator cable turnaround from the joystick.

Some excellent model engineering work there Peter, can I ask what you are using to silver solder - gas or electric?

Stephen,
I will let you know once I have found someone to do it for me
(Probably gas though)

Rudder pedal assembly now painted & assembled onto the forward fuselage assembly (bottom box assembly) although a touch-up of paint is needed to complete.
View of securing nuts & tow release pushrod also included.-
Note that the pre-bent tow release rod can be removed whilst the rudder assembly nuts are fitted if required.
The missing section of side skin also needs to be put in place before the two side fixings are put in place.

The 3mm ply rudder pedals and heel support strips are still to be fitted.

Stephen,
The results of the silver soldering are shown in the previous post with the assembled rudder pedal assembly.
A gas set with soft flame was expertly used by WMSA clubmate Steve Vincent (many thanks Steve) and it all went very well until the last joint.
I was pleasantly surprised that the soft flame didn’t disturb the work whilst being heated & the liberal coat of borax around the joint kept everything clean until the solder flowed.

Murphy’s umpteenth law decreed that the small brass pieces for the last joint deformed when heated, so had to be remade

Thanks for the update Peter, I must say it looks an exemplary job - in keeping with the rest of the build.

I think I will need to do some research on methodology prior to training myself up on the "blow torch".

Fuselage parts now all joined to make a 6ft long item!
The seat has also been made and the Wilson pilot tried for size.
(Still need to fit rudder pedal plates & heel rests)

Control surface cable sheaves can now be fitted on the fuselage sides, together with battery box, switch and BEC within the wing root area.

Looking well Peter, no hiding place or room for error with all that 'air conditioning'

Very impressive, the pilot looks fantastic!

Work has continued over the last couple of weeks to skin the tail feathers and make a start on the wing skinning.
The pics below show first wing assembly to check that they will plug together, and also to check that the root ribs are parallel.
Also shown are a couple of first overall assembly shots.
Rudder pedals now fitted & only bits left to initially fit are the control wire sheaves below pilot seat and on top tail boom rail.

Good,job!!!!!!!!!

Over the past few weeks I have finished the wing skinning and stained all of the skins and exposed wooden parts.
(Note use Wood stain, rather than Wood Dye as this gives a more uniform colour on both ply & balsa, even when the balsa has been sealed to prevent it fluffing up when wetted with stain).

I decided to apply the Ceconite covering using dope (rather than the manufacturer's recommended adhesive) as I needed to get a uniform print-through of the underlying skinning & cap strips.
Therefore, i first applied a base coat of dope to the parts & then laid down a line of masking tape to define the boundary between the covering and exposed wooden finish.
The Ceconite covering is then laid in position and dope applied to attach it to all skinning/cap strips, rubbing the dope into the weave as necessary with a fingertip to ensure that the stained skins show through everywhere.
(I managed to recover lighter patches on the very first side by gently rubbing these areas with a cloth dipped in cellulose thinners to reflow the dried dope).
The Ceconite is doped over the edge of the masking tape. When dry the covering is trimmed around the edges and then along the masking tape line using a sharp blade. The covering can then be removed from the masking tape and this then carefully removed to leave a clean edge between the covering and stained wood. See photos below.

Tail feathers & fuselage covering is now done, so have started the wings today after installing the aileron servo & cable run.
First wing upper side covered this afternoon & aileron dry fitted to see what it will look like.
Initial shrinking has been done, but final go, plus dope sealing coats will be done once everything has been covered.

Getting there!
Control runs & rigging still to be sorted, plus hiding the Rx in a seat back cushion, hopefully avoiding the need for the pilot to undergo painful back surgery.

Oh! So that's what a wireless is?

Nice work Peter

Beautiful job Peter, very impressive - well done!

A small altimeter equipped Rx has been installed fairly neatly on the seat back & a blue foam pad cut to follow the seat-back curve and with a slot for the RX & cables.
The plan is to cover the pad in material to ressemble a full back cushion & the pilot will cover the Rx when in place

Attention has now turned to fixing the pilot figure (kindly supplied by Wilson) onto the seat using shoulder & lap straps as on the full size.

The full size has attachment points for the shoulder straps on/on the rear of the main mast roughly level with the top of the seat, whilst the lap straps attach via wire strops to points near the aileron cable attachment bar mounted on the top of the fuselage box, just behind the mast base.

I decided to make up two simple brackets, attached to the rear of the main mast & on the top of the fuselage box as shown below. M2 clevises and C/L adjusters allow easy removal and minor tension adjustment, with small piano wire loops (easily made with a K&S small wire bender) linking the harness straps to the C/L adapters.

The photos below show the general arrangement with the initial C/L wire loop strops, and then with the replacement piano wire ring (like a key ring loop) links.

A rigging day today, with 10 out of the 14 wires now made up (lower wing mid & rear).
Meanwhile, the control stick has received its handgrip and Cliff''s 3D printed top stopper has been fitted (photo when paint touch up has dried).
Seat back cushion has received its covering of material & is attached using Velcro.
Nearly ready for balancing & final weighing

And the completed joystick with cord grip

Beautifully done Peter, great attention to detail!

I'm guessing that your heart may be fluttering a little on the maiden ..........

Cliff Evans wrote: ↑30 Apr 2019, 17:17 Peters will not be but mine might be!!!

I am always available to help.

AEB

An initial balance indicated that I needed to put around 1.5Kg up front to a achieve the recommended CoG position (151mm from wing LE).
As the internal ballast box will only take 500g, the rest is located in 4 cylinders mounted on additional brackets in a manner very similar to that used on the full size.
The photo below shows the arrangement mock-up.
The rear brackets are bolted to each other through the fuselage, whilst the front brackets have since been silver soldered to the nose bracket and will also have a bolt through the fuselage in addition to 4 of the original 6 servo screws.
The bracketry & weights are currently in the paint shop.

External ballast bars painted & fitted with just a couple of spots of paint on the fixings now required.
About ready for what is hopefully the final assembly & balance check before handing over to Cliff for addition of the minimal registration lettering and then the maiden flight

Nice work Peter and a good solution to your CG problem

Just about done

Although it's not my type of model Peter, I have enjoyed your build. Best of luck with the maiden and I look forward to the pictures.
Brian.

Congratulations!!!!!! I enjoyed your job and the (full scale) appearance in flight!!!!

Here are some pics of the SG38 at the last MW event...

Great German site about "School Gliders" Some good info and pics.

https://www.schulgleiter.de/