Scale Soaring UK

The model as designed by Chris Williams as an A-Spatz or, as Chris describes it, a "Spatz 1" is at a scale of 1:3.5 giving a wingspan of 3.8 metres. Early examples built by Scheibe were designated A or B, followed by the later L version, it's difficult to find online sources for verification of the differences, most A types seem to be without a wheel, some have shoulder mounted wings, some top mounted and canopies seem to vary too. So, not easy to find a full size to accurately model, mine will probably end up as this:



To speed the build process I ordered the laser cut short kit and plan from Cliff at Laser Cut Sailplanes, the parts all neatly packaged and bagged according to their use - left wing ribs in one bag, right wing ribs in another and so on. Balsa sheet and strip, spruce strip and ply were sourced along with the electronics, covering material and various hardware to produce a complete kit of parts:


The Bridson jig was deployed and the laser cut former supports were glued to the adjustable angle pieces with CA before sliding in to position and checking for correct alignment referenced against the dimensions marked on the plan:


The 1.5mm ply keel was strengthened by adding 1.5mm ply doublers in the wheel box area before glueing both sides on to formers 2, 3 and 4 with aliphatic. This assembly was then dropped on to the jig where the 6mm square spruce longerons could be added:

StephenB,

Here is some inspiration for you. The model turns out very nice and is a great size.
The overall handling is very benign, enjoyable to fly.
If you have any questions or queries please reach out.

Dale Nicholls

Hello Dale, nice job!

Did you build from the plan or the laser cut kit? Any challenges in the build that you had to overcome?

Hi there Stephen,

my model was handcuff off the plans, so no laser cut parts involved.
I followed the plans in all respects and its a well conceived design as you would expect from Mr. Williams.
The only suggestion I would make is to update the elevator connection to a ball link fitting (as per his later designs) to make it easier to detach and attach the stab. The model flies very well and is an easy flyer.

I have many photos during the build so if you have a question please ask.

enjoy the build.

Dale

The spruce longerons were bonder in place with the main one requiring some steam bending around the cockpit area, a removable cockpit floor was fabricated from liteply to allow access to cabling and the tow release servo:



I then set about adding the ply plates that form the wing box area, here I encountered a problem - the top plate H2 was a little undersize so required some fettling:



I then discovered that F4 didn't have the hole cut to accept the bottom longeron and F8 was not opened out at all, so nowhere for the pushrod to go! Of course I didn't spot these issues until after I had bonded them, in but F4 was easily dealt with in situ with the Dremel and F8 was carefully removed and opened out on the scroll saw. Onward and upward after this, 6mm square balsa cross bracing added and the ply sheeting glued on to the top decking:



Tow release servo added, this will connect via a Bowden out to a Multiplex aero coupling:



To get as much weight as far forward as possible a battery box was fabricated from birch ply to take the 4200mAh NiMH, this was epoxied in place and additionally secured with screws which will also give the car body filler something to key to when forming the nose:



A ply plate with captive nut for the tailplane retention was glued in place, a "paddle" to operate the elevator was fabricated from piano wire and brass:



With rudder, elevator and tow release servos in place the next job will be to sheet the forward fuselage.

That looks like a very small and weak servo for a tow release, especially a Multiplex type with a retracting pin. When everything goes wrong on the tow you need a super reliable release system that will work under any load. As you have the space, may I suggest you fit a much more powerful servo.

AEB

How much torque would be right for the release John?

I have no experience of these but Multiplex describe the aero tow mechanism thus: "To operate the release all you need is a low-cost standard servo and
a length of 1.2 mm Ø steel rod running in a snake outer sleeve.

In my experience over a range of models, the MPX release works very well with a standard servo for models up to 22lbs. The advantage of this system over cam-in-a-tube variety is that very little movement is required to release, so the rod can be set in the innermost hole of the servo arm for max torque...

For testing the tow system , including the servo , you should be able to release by pulling the tow cable with a force equal to the weight of your glider. That's the rule, we apply for our GPR glider ( over 5 meters wingspan ) during the meeting.
Pat'

Stephen

I agree with all of the above. Min movement on the pin to get max torque from the servo and test the release to ensure it works (every time) with a pull at least equal to the weight of the glider.

AEB

Thanks for the advice chaps, much appreciated. I have found a Futaba S148 that will be going in!

Some further progress to update. I must say, things happen a bit quicker when there are few parts to cut out!

Liteply to box in the wing joiner area and then sheeted with 1/32" ply making for a very robust construction:


The aforementioned lightweight servo was removed and replaced with a Futaba S148 positioned in the nose, cockpit floor was glued in place with a provisional location for the Rx which should sit neatly hidden under the seat:


Cockpit surround laminated from 6mm square spruce bonded in place after soaking in hot water to achieve the curvature, this near enough completes work on the front end prior to sheeting:


Work then commenced on the tail feathers with the fully sheeted fin and tailplane:


And completed with the rudder and elevator, just needing final shaping and sanding:


Battery is as far forward as I can get it (weighs 330gms), I'm wondering how much lead I'm going to need up front? Maybe Chris will know ..........

Dear Stephen,

I built the A-Spatz from Chris Williams in enlarged version with several modifications. Scale is now 1:3 with 4400 wingspan and 7,5 kg. Profile is Gö 549, it allows very slow airspeed.

It is a great flyer.

greetings from Bavaria

Hans

Rcscaler wrote: ↑06 Jul 2020, 11:50

Gorgeous!!

A little more progress to update after a lull in proceedings whilst awaiting fresh wood supplies.

Ply sheeting to sides, bottom and front top decking applied:


This was followed up by glueing in place a full length 6mm x 3mm spruce longeron which simulates the tubular steel structure of the full size. Fin was glued in place and the rear ply sheeting could then be added after running the snake outers to take the Bowden cables:

This more or less completes the fuselage for now:

Right hand wing commenced by laying down the 6mm square spruce spars. The spar material was sourced from DIY store at 2M plus length, it came 7mm square but was easily reduced on my Proxxon table saw, quicker and stronger than splicing standard short lengths. Trailing edge was formed from laminated spruce and balsa. The laser cut ribs fitted accurately with no fettling needed, to speed the process I bonded them with Deluxe Materials Superphatic:



Ply/balsa wing joiner box was epoxied in followed by 1/32" ply webbing the full length of the wing. False trailing edge was added and the D box was formed with 1/16" hard balsa sheet top and bottom. The basic wing structure was completed with 1/4" LE and block balsa tips:

Basic airframe now complete. Next job is the wing incidence pegs

Stephen

Very much enjoying your build threads but I'm intrigued . You're either British or have an amazing command of the language. Prey tell.


Ian

Ian, I am English through and through but currently reside in Hungary.

After a long break whilst building the SF-33 motor glider it's time to get back to work on the Spatz.

The setting up of the wings to the fuselage was a job I wasn't looking forward to but with a lot of patience, careful rigging, de-rigging and fettling, the required incidence was finally achieved with the aid of my homemade gauge. The brass main joiner and incidence tubes were bonded in and the wing root fairings formed using scrap balsa in-ills and car body filler with the wings in place to achieve a perfect join. This complete process took me a couple of days of work, quite tedious with the constant rigging of the wings but it paid off with a very clean final result.



The nose was then formed using ply formers to give the outline shape and filled with huge quantities of car body filler - around a kilo! This has me a little worried because the weight seems excessive, so much so that I've had to remove the large capacity battery I had installed. The model in its current state weighs around 4.3Kg. and the balance point is in front of where it should be, and this is without a battery. I have to add the canopy, film for the wings and Diacov plus paint for the fuselage. Plus a lighter battery.

Chris's design weight for the Spatz is 4.5Kg, mine is looking to come in at around 5Kg I think .................

Further progress on the Spatz, the noseblock had another dose of filler and a severe sanding to achieve the correct profile. A Multiplex tow release was then epoxied in along with a snake outer to take the piano wire to the servo:


I then started on the canopy frame, building from 4mm brass tube and piano wire soldered up in situ to follow the contours of the cockpit after first soldering in place two brass hinges. It was a little tricky to begin with ........


....... but as the frame developed it became more stable and less problematic when the iron was not so close to another joint:




Finally I had a completed frame:



The two top rails were attached to the finished lower part of the framework using brass saddles wrapped around the piano wire, inserted in the tube to give a solid dry fit and then soldered up:


A small brass plate was drilled, offered up to the previously installed canopy catch and soldered to the front rail to complete the framework and now ready for painting and glazing:


Meanwhile I've stripped everything I can out of the nose whilst I ponder on how to keep the weight down and achieve the correct CoG without adding tail weight!

After just over a year in build, with a "holiday" in between to construct the SF-33, she's finally finished.

Fuselage and fin covered in Diacov brush painted with Oracolor, flying surfaces covered in Easycoat "seconds".

Rx power is from two LiFe batteries connected through a Jeti V-Cable and located on a tray behind the CoG to help compensate for the excessive nose weight:


Final AUW is 5.25Kg, well over the design weight of 4.5Kg, giving a wing loading of just over 21oz. sq. ft. Should I be worried??



I'd like to maiden her from a slope in the UK, the Long Mynd or White Sheet maybe, but with the current travel restrictions, who knows when that will be ........

Should be fine, Stephen...the wing section will tolerate higher loads that that...!

Thanks Chris, that's reassuring!