Sterling Schweizer 1-34

[Pete B]

I bought this kit on Ebay a couple of years ago and it's sat on the wardrobe ever since. There's a temptation to keep it as an 'investment', particularly the way vintage kit prices are going, but, heck, it was made to fly, so I'm going to give it my best:

The prototype was an ali-skinned sailplane which first flew in 1969 and became a popular club aircraft, although not produced in great numbers. It hasn't got the curviness of later glass models but it has a certain appeal, with very clean lines. Here's a couple of photos of the full size:

The model is 98 1/2 inch span, to a scale of 1:6 and has a design weight of 2 1/4lb. With a wing area of 615 sq ins, a wing loading of around 8.5 oz/sq ft indicates that this could be a bit of a floater, rather than a sledge. Let's hope so!

 

I'm still making decisions about certain aspects of the model, which was designed for anything from rudder-only to full-function radio. Not having a convenient slope site, I'd originally planned to put a brushless in the nose but, having to rule that out due to lack of adequate space (and not wishing to be run out of town by the purists!), I've decided to put an tow-release in the nose and find someone with a tug, or just get in the car and drive the three hours down to the Pyrenees..............

 

Given the age of the kit, the balsa is in excellent condition, although the ply is a bit, shall we say, agricultural and has become a bit flakey. Nothing a bit of adhesive cannot rectify, though. The die-cutting is largely good on the balsa although some of the ply parts needed a bit of assistance and the flakiness didn't help on the more intricate cuts.

 

The plan had yellowed so I went to a copy shop in the UK and had it printed off to preserve the original and I was very impressed with the result. I can now do as I wish with the plan and pinholes, glue stains etc, are not an issue

 

The original uses a single aileron servo with pushrod and bellcranks but I shall use a pair of Vigor VS-12 ultra-slim servos mounted at the bellcrank position. Again, the original has a fixed centre section of 26 inches, with the outer sections plugging in with a tongue and dowel system, but I'm wondering whether it may be better to construct the wings in a single length and split them at the fuselage for transport. I've also yet to decide whether to keep things simple by using spoilerons to assist landing or construct the dive brakes as per the picture above. I'm sure I'll be needing some advice!

 

Anyway, enough chatting, on with the build............

 

Pete

[Pete B]

There's a lot of balsa and ply in the kit and separating and grouping the parts took a little while. It was useful as it allows one to become familiar with the parts and, by constant reference to the plan, the construction becomes a little clearer. That's not to say I haven't made the odd error, though...........

 

Dealing with the die-cutting, particularly the ply, made me appreciate just how things have advanced and how fortunate we are to have CNC and laser cut kits these days!

 

A certain amount of pre-assembly is recommended. If you look closely, the trailing edge of the ribs has a lug, used as a guide for the trailing edge strip and this is cut off after assembly. My lack of familiarity with the system, together with the lack of clean die-cutting, led to some of the lugs breaking away and I'll have to tidy these up before I start the wings. In the foreground is the wheelbay and skid, with ply reinforcement on the ribs for the joining dowels:

Anyway, leaving the wing construction aside, I decided to go in at the deep end and start with the fuselage. The instructions recommend constructing the cockpit and nose section vertically, on the edge of the bench. I was bit sceptical about my abilities to square this up but surprisingly, with a lot of juggling, it worked, and it seemed to go quite well:

I'm using aliphatic resin, cyano and epoxy for the build and the cyano certainly helps wih a quick fix! The fact that there's only about 30mm clearance inside that birdcage of stringers behind the nose bulkhead dictated that an electric motor wasn't going to fit inside.

 

The fuselage sides were then constructed. I made the first, reversed it over the plan, and with a sheet of polythene over that, constructed the second directly over the first to ensure that both were identical:

 

Next, the sides were married up to the aforementioned birdcage, clamped and pinned and left to dry. The front end of the fuselage side took some wetting to fit to the nose curvature without splitting :

Once dry, the remaining formers and stringers were fitted, applying them in matched pairs to keep everything straight and true:

That'll do for tonight - more tomorrow.

 

Pete

Edited By Pete B on 01/02/2011 01:44:09

[Stephen Grigg]

Going well interesting to see a vintage glider going together

[David Ashby - Moderator]

I agree Pete - can never understand why some collectors sit on piles of old kits, there's only so many times you can lift the lid off and, as you say, t'was meant to be built and flown.

 

Look forward to seeing this come together.

 

 

[Pete B]

I just hope I don't screw it up, David - replacements aren't easy to come by.........

 

Progress continues with the tail elements (there - I've avoided the use of the word feathers!). The spars need to be planed and sanded to a tapering section before the components are assembled, jigging them on scrap balsa where appropriate:

 

Having sanded the structures to the profile shown on the plan, they were sheeted with 1/32 balsa, with just a few pegs to keep everything in place and warp-free:

Trimmed and sanded, they look like this:

 

They can now be tucked away safely until I'm ready for them. The next post will be a ponder about whether I significantly alter the wing structure or go with it as per the plan.

 

Pete

[Alan Cantwell]

full marks to you sir, for building a collectable kit,

although i know  of kits  passing  to collectors, i can never see why they do this, boxes, maybe, but balsa is balsa, just differant shapes, NICE subject, much updating to be done with the build?

Edited By Alan C on 01/02/2011 18:24:09

[Pete B]

Thanks, Alan, I just hope I can do it justice! All the contents are totally familar and the stripwood and sheeting is of very nice quality.

 

The most significant improvement, I suppose, would be the move to individual servos rather than a single servo/ bellcrank system for the ailerons. The hardware supplied is of good quality but I shall use metal clevises rather than nylon and a balljoint on the cranked rudder horn, that and the elevator horn being enclosed within the fus. It's a bit of a shock to have to do all the wire bending, though - we've been spoiled with modern kits and ARTF's!

 

I've been giving some thought to the wing construction and attachment. The plan shows a 26" wide centre section which is constructed separately and permanently mounted on the fuselage:

The outer panel has a ply tongue and two 1/4" dowels which fit to the centre panel:

 

I had considered building each wing as a complete half, as I was doubting my ability to make a good neat job of the dowelled connection. I also had the servo wire connection to consider as well.

 

However, having studied the plan and satisfied myself that the components fit well together, I've decided to go as per the plan and I shall use MPX connectors to link the servo wires at the joint.

 

As I mentioned in an earlier post, I'd like to instal airbrakes. The scale location is at the trailing edge of the innermost 3 rib bays of the outer panel. The wing section is rather thin there and I'm not sure I can come up with an adequately small hinge and pivot system. The other alternatives are to use a non-scale commercial retracting airbrake just behind the mainspar, or just settle for a spoileron system to reduce the lift. All ideas considered and appreciated!

 

Pete

 

 

[Terry Walters]

Come on Pete you must have nearly finished it by now!

 

TW

[Pete B]

Hey, no heckling, Mr Walters - I'm trying to do a passable impression of BAeS.....

 

If you must know, I've entered a period of deep ponderance, essential when one is faced with apparently insoluble problems.........

 

No glue has passed the nozzle for two days now..........well, that's not strictly true. A combination of lack of close observation of the illustrations on the plan, the incomplete die-cutting of finer profiles and too-enthusiastic application of the balsa-hatchet when removing the ribs from the sheets means that a good number of the trailing edge profile tabs, which position the t/e lower sheet, have had to be manufactured before I can lay out the wing for assembly. This is very tedious but necessary:

As you can see, there is a considerable undercamber on the wing and I need to get it right.

 

The undercamber and the slimness of the wing profile also presents other problems. As I've already mentioned, I'm replacing the pushrod-driven ailerons with individual servos and I need a wiring connection between the wing inner and outer sections.

 

MPX connectors are the obvious solution but there is precious little free space on the sides of the facing ribs. The faint dots either side of the slot in the rib will be where 1/4" dowels run through the ribs and the slot is for the wing tongue. The connectors are positioned where the original wire pushrods would have passed through and will need very careful positioning - as it is, there should be a couple of spacers (part 93) occupying that position between the ribs and I'll have to modify that:

In short, not a lot of space to work with. I'd also hoped to use the scale trailing edge air-brakes but the corresponding 1/4" dowel gets in the way, so I'm left with using either non-scale Hobbyking airbrakes like these, which I have tucked away somewhere, or settling for spoilerons.

 

So, my ponderance will continue for a little while longer............and when I've plucked up the courage, I shall continue

 

Pete

 

[Pete B]

I've made some more progress with the inner wings. The near end in the picture is the outboard end of the wing, with a ply box built in to hold the corresponding tongue on the outer wing. It was necessary to insert some scrap ply between the top and bottom of the box to maintain separation whilst the aliphatic dried:

Both halves constructed, sheeting has been started on the left hand panel:

Once both sections had had the upper surfaces sheeted (wetting the balsa helped with the camber, particularly in front of the spar), they were left pinned down to dry overnight and I turned my attention to the electrics.

 

I found I had enough room between the front dowel and leading edge for the MPX connectors, so an appropriate aperture has been made in each facing rib. As I am keeping my options open for airbrakes in the outer wing section, I've provided a single +ve and -ve and 2 x signal wire feeds from the Rx.

 

This is the first time I've used the MPX system and soldering, with a point bit, was straightforward. Pre-tinning both the wire and terminals helped and with the reassurance of the mating half of the plug in place to avoid any misalignment of the pins, a second or two on each terminal was sufficient:

 

 

The finished plug with heatshrink on the terminals:

 

Inner wings top-sheeted, dry-fitted and with the servo wiring in place. The ply crutch sits inside the fuselage on final assembly.

 

It's surprising how much pre-planning has to be thought out before committing glue to balsa! Before the bottom surface can be sheeted, the MPX connectors need to be epoxied to the root ribs. Once the outer wing section are built, I can align both sections before securing the dowels and then finish the sheeting:

A closer view of the MPX connector. The female half is inboard and will be secured with a paste of epoxy and microballoons. The male half will be left to float in the opposite root until the wings are aligned, then finally fixed in position:

That's it for tonight - still pondering which airbrake system to use!

 

Pete

[Gary Binnie]

Nice and neat Pete.

 

How does the designed spoiler system work? Is there something about it that you don't like?

 

Gary

[Pete B]

Cheers, Gary. Therein lies the rub - there is no designed spoiler system. It is merely shown as a option for the builder

 

The full-size has divebrakes on the upper and lower surfaces of the wings as in this pic here:

I'll settle for the upper surface only - the full set is an engineering problem a step too far for me! The plan shows the scale location (blue hatched area) at the inboard end of the outer wing section. The dotted blue line is a wing dowel, so any servo will have to go in the left hand bay:

 

There isn't much depth to the wing behind the spar, although the servo is slim enough to fit without too much difficulty. I have to decide whether to connect from the servo arm to the external top surface of the brake (a la Hi-Phase) or try and fit the linkage internally to the underside of the brake:

With the ribs laid over the plan, you can see the space available between the servo and leading edge of the brake.

 

The external arrangement seems simpler and with a bit of fairing over the exit point, wouldn't look too bad.

 

Finally, the question of hinging the brake arises. Hatch hinges would allow for flush mounting of the brake but a check with HK shows them on backorder at present. Alternative suggestions for a neat hinging arrangement would be appreciated!

 

Pete

 

 

[Gary Binnie]

Oooh! That's tricky!!

 

I like the string arrangement as it is lightweight and fairly foolproof but that would be difficult to use with this three-piece wing design. Just thinking out loud but four servos in the wing with their cables is going to put the weight up a bit, possibly to the point where it is not a floater any more! Can probably take it at 100" span though.

 

From full-size experience rear mounted brakes/spoilers are not very effective compared to the same size surface mounted at 1/3 chord, they do look a long way back on the plan. It used to be a type conversion briefing point for pilots, i.e. watch out for overshooting on the landing approach. Not many gliders like this about now.

 

For hinging plain spoilers I just use posh Sellotape, Diamond Tape I think it is.

 

Another alternative is to use the Graupner 93 airbrake set, good diagram here:Graupner 93

 

They are torque rod operated, you could mount the servos in the inner panel or use a single one in the centre section although that would be tricky as it's mostly built and awkward to cut any new holes. They are relatively heavy being plastic, I've got a couple of sets if you want photos of the parts.

 

Spoilerons sounds good to me!! I've got three 100" gliders without spoilers (or ailerons) and havn't lost them yet!!

 

Not very scale but flip-up canopies (imagine a crocodile with its mouth open!) have been used as well as 'one-shot' trailing edge brakes.

 

I was just thumbing through some old Aeromodeller magazines in the loft and found an advert for your kit, distributed by Ripmax it was £34.75 in 1978. Bit of trivia for you!!

 

I'll keep thinking, something might come to me!!

 

Cheers

 

Gary

[Pete B]

The price back then is interesting, Gary - it seems that the £50 I paid for it kept ahead of inflation, I guess - but I think I got a real bargain in terms of today's kit prices - there's a lot of balsa and building in the box!

 

The Graupner set is interesting, although it now seems to be out of production from what I can establish. The small amount of dihedral I have at the wing root would cause a few issues with the linkages, I think. Installation would be interesting, to say the least

 

I've made a start on fixing the ribs to the lower spar this evening and can make some progress before I commit myself. The solution may just evolve during construction. I have a set of the HK pop-up airbrakes which may be a better option for efficient braking, as you suggest. Not the same quality as the Graupner items but with care may be fine.

 

Your interest is appreciated.

 

Pete

 

 

[Gary Binnie]

I think the Graupner units are still available from Germany but I had a search and it looks like nobody is stocking them over here. They come up on eBay quite often.

 

The Mini-Nimbus from the late 70s was designed to take them, even down to pre-cut holes in the ribs. Should be my next build project, once it gets warmer in the shed!

 

The wing torque tubes have brass ball ends with flat sides (like a Bondhus Allen key) that fit into plastic drive sockets in the fuselage, that makes the wing root connection and allows for dihedral, quite clever really.

I've had a go at most aspects of aeromodelling (some successful, some not so successful!) but I have drifted fairly solidly towards gliders over the last couple of years, especially designs from the 70s and 80s. Known as the 'nostalgia' class in the states!

 

Cheers

 

Gary

 

[Pete B]

Having prevaricated for a long time on the brake/spoileron question, I've decided to go for the non-scale pop-up brakes on the grounds that fitting the scale dive-brakes was excessively complicated, they were likely to be less effective, and that I had the brake set anyway.

 

The wing went together without too many difficulties and I used anything that came to hand to keep it flat as it dried............

One critical part of the wing construction was the setting of the dowels. Once the holes had been drilled in the ribs I was committed but fortunately only a very small amount of easing was required to keep the facing ribs aligned and there is a good sliding fit for the tongue and dowels:

 

A dry run with the brakes tested the system:

 

The ribs were recessed to set the top of the brake 1/16" below the wing sheeting:

The underside shows some bracing and the servo fitted:

Careful application of epoxy fitted the sheeting to the top surface of the brake:

The brake open:

More to follow.........

 

Pete

[Pete B]

Meanwhile, when setting up the dowels, I was able to start the fitting of the MPX connectors for the aileron and brake feeds. I've run only 1 +ve and -ve feed, with 2 signal wires, from the Rx - the outer wing has two of each leading to the relevant servos. I fixed them using 5 min epoxy with a bit of lightweight filler, which made a thick paste -easier to keep under control!:

The female side was fitted first and once I was happy with the dowel setting and the wing parts were joined, the male side was inserted into the female and was fixed with the epoxy mix, resulting in an accurate fitting:

 

The wing joint:

Sheeting, stringers and cap strips have been applied to the outboard wing:

 

Hard balsa has been used to make the servo access covers:

The two parts of the wing section. Aileron still to shape and fit and then final sanding:

 

Just another outer wing to start, now...................

 

Pete

 

 

[Terry Walters]

That's all looking very good Pete - puts my building to shame! Keep it up! Raining today so I expect a lot more in the blog!

 

TW

[Pete B]

Well, it's been a long time since I last posted on this thread but I haven't been idle. A lot of progress has been made but, about a fortnight ago, it seemed to be becoming a bit of a chore, so I turned my attention to the Druine Akrobat, which went together rather more quickly and can be seen here, if anyone is interested......

 

Anyway, to the Schweizer. I left off having made one outboard wing. The other, and the ailerons went together a bit more quickly, and it was then that I realised I had made a bit of a bloomer. In this photo, you'll see that the wing dowels are mounted in the inboard wing, and they should have been fixed to the outboard wing. No problem structurally but it makes transporting the fus assembly a bit more difficult than it should be.....Doh!

It was time to turn my attention to planking and sheeting the fuselage. Before I did so, I installed the interior fittings such as snakes, servos and tow-release, whilst access was possible.

 

I started by fitting the tow release to the rear of the front bulkhead, intending to attach a towline via the convenient hole in the nose. It wasn't until recently that I've found that is an air vent and the tow release should be at the front of the skid, below the nose..........double Doh!

 

Whilst the likelihood of me using the tow release is low, I'm now a bit concerned that this could pull the nose off, so I'll stick to sloping it!

At the other end, the rudder and elevator fittings would be sheeted in and inaccessible, so a metal clevis went to the elevator horn (behind the tailwheel wire) and a balljoint coupling to the rudder. One of the greatest problems was working out a sequence of assembly, which required the tail assembly to be covered and installed before the fuselage was fully sheeted and covered:

The mainwheel was installed at this time, too:

Back to the planking. Starting at the nose, I made a bit of an error in not tapering the first few strips:

..........but I realised my error and got better at it. This was a very slow process, using aliphatic resin, wedging and pinning a few at a time until the dried. The plan were soaked in hot water to encourage the bend. It took about 4 days to work around the nose!:

Better post this now...........

[Pete B]

The nose having been planked, it was on to the rest of the fuselage, again wetting the sheeting and using lots of pins:

Finally, having sheeted most of the fuselage and having covered the wings, there was a chance to see it looking like a sailplane:

Lots of planing and sanding was to follow and the fuselage from the rear of the wing seat forward has been reinforced with glass cloth and epoxy.

 

Covering trimmed where necessary, the tailplane and fin assembly were epoxied to the fuselage.......

....together with the upper sheeting around the fin:

The rudder and elevator connections were made and sheeted in, with everything sanded nicely.

The fuselage, with the exception of the top section from the cockpit to the tail, was then covered in Oracover, the centre wing assembly then being epoxied to the fuselage.

 

The over-wing fairing was then constructed and sheeted:

The servos, together with an Orange Rx with satellite, have been installed and just final detailing and fitting out of the cockpit is to be done:

The wings are complete, with access panels for the spoiler and aileron servos:

Here she is, earlier today, with just the cockpit and canopy, together with external marking, yet to be done:

 

Final piccies in the next couple of days, then I'd better find a slope!

 

Pete

[David Ashby - Moderator]

Very nice Pete

[brad lang]

Pete,

Have your I flown yours yet? What's your weight ?

Brad

[Pete B]

Hi Brad,

Well, I'm ashamed to say it still hasn't flown - a lack of a suitable nearby slope has been just one reason but having recently purchased a motorhome, I'll be looking at getting out and about as the weather improves, so no more excuses!

I plundered the Rx from it to use elsewhere so it needs setting up again and I'm thinking of replacing the cheap servo-driven spoilers with leccy versions but that could wait until after the maiden.

I'm confined to the UK for a while longer yet but once I'm back out in France I promise I'll turn my attention to it!

I measured the AUW with NiMh flight pack at 3lb 2oz - I build a bit light, that's for sure!

Pete

[brad lang]

[brad lang]

 

Yes,it took me awhile....maiden soon.....about 4.3lbs.

 

Edited By brad lang on 22/05/2017 11:20:09