Sterling Cessna 180 "restoration" - build blog from Outerzone plan download

[GrumpyGnome]

That brings back memories.  "Wee MacGregor's in control!" Just as well as I wasn't in the early days.... 

[Martin Harris - Moderator]

Composite aluminium/piano wire undercarriage made and fitted to its mountings. 
 

 

As this was the first stage of actual fuselage construction and I had my glues to hand, it would have been rude to stop there so I added the basic structure to the rear. 
 

Next will be to add the keel piece visible on top of the pile of wood destined to form the curvaceous nose - no fancy moulded plastic cowls in the good ol’ days!

[Martin Harris - Moderator]

Out of the jigsaw puzzle, something resembling a Cessna has started to emerge. 

 

I've started the extensive fuselage skinning - I’d forgotten that the entire model, other than the vertical sides which are 1/8 sheet, is covered in pre-cut and dampened 1/16” balsa but it’s so much easier tacking the sheets with cyano (something that wasn’t generally available when I built the original) while the aliphatic dries than following the instructions to use balsa cement and pins as I must have done in 1974.  Unlike the re-drawn formers, the cutting patterns on the plan are pretty accurate so I’ll stay true to the original rather than planking the double curvatures which would have been my natural choice.

 

It's a little annoying that the parts aren't drawn as accurately as they could be as they are essential - the plans being designed for building the kit rather than scratch building. Various notches have been omitted or are drawn the wrong size so there's a lot of remedial work involved - I don't recall any of these difficulties when I built the model from the die crushed kit so these errors must have been introduced by the Openzone contributor but it's all part of the fun...

[Dwain Dibley.]

"Die Crushed" I love that .. LOL

You are making a splendid job of the Cessna in my opinion Martin, despite the little setbacks, which as you say are "all part of the fun"

Watching with interest here at Dibley towers.

D.D.

[Danny Fenton]

Coming along well Martin, and quite quickly!

[Martin Harris - Moderator]

Thanks for the nice words gents. I just wish my builds looked as neat as some of the ones I see on other people’s build blogs (present company included). Mine always seem to be full of glue stains and adjustments!

[Martin Harris - Moderator]

Went fishing today - caught a whopper!

More seriously, today’s project was cutting, dampening and gluing the extensive 1/16 sheeting. 
 

 

Next step?  Probably the removable cowling. 

[john stones 1 - Moderator]

She's a sturdy little thing, still 3 ch then ? And what's power plant Martin ?

[Martin Harris - Moderator]

Sturdy but all 1/8 and 16th materials.  Looks quite dumpy at this stage of the build but the instructions reckon it's based on factory drawings so it should be reasonably accurate - and it looks quite like the real thing in a similar state...

 

       

 

I'm using a Leo 15 which was in my engine drawer - should be more than enough power as the .15s it was designed around weren't a patch on more modern engines.  IIRC, the mounting dimensions are the same as an OS15 if there are any problems with the engine but it was running well when I had it in a 12th scale Bf109 combat model about 10 years ago...

No plans to build a aileron wing at the moment although there's always the option of making an alternative version later and improving the scale appearance with reduced dihedral.  I'm debating whether to build it with the original 'laccy band wing retainers or update it to nylon bolts.  The cabin sides are only put in place to capture the look of the Cessna for the photos so I haven't actually got to the decision point

[Stephen Jones]

Looking smart. 

[Martin Harris - Moderator]

Spent a couple of hours on the basics of the removable cowling. 

 

 

 

 

 

 

 

Electric aficionados should look away now as the cover won’t be staying like this for long.  

 

 

 

... ‘cos this needs to poke its head out into the fresh air!

 

[Martin Harris - Moderator]

...and here we are, traditional sticky up engine with no possibility of cooling problems!

 

 

 

 

 

 

 

                                            

 

 

 

 

 

 

 

 

[GrumpyGnome]

Looking good....... I am a big fan of upright engines unless going for real scale look

 

GG

 

 

[Eric Robson]

Nice job Martin, engines always seem to behave better mounted that way.

[Martin Harris - Moderator]

There have been a few comments about the speed of progress - well, all good things must come to an end I suppose and today has been a bit frustrating. 
 

I started off by filling in a few details on the removable top cowling and fitting mounting blocks for the screws that will hold the most important part of the “restoration” - the original metal front cowl. 

With these done, I could then position the engine to get the prop driver in the correct place. This was where the troubles started.  What could be simpler...sharpen a 3mm screw to a point, use it to mark the first hole, carefully place the point of the drill in the dent and drill it.  Drop in a screw, mark the next hole, remove the engine, drill and repeat twice more. Precision ensured...
 

Result? 4 rather randomly spaced holes!  I’m at a loss to explain it but the drill must have wandered off in the grain somehow. 
 

Anyway, a needle file in the holes in the rock hard bearers eventually sorted this and then my hasty progress really came back to haunt me. Because I’d sheeted the nose, there was no access to fit the nut plates. I decided that there was insufficient width to use small Tee nuts and made some square steel nuts which I silver soldered to brass plate, put long screws through the nuts, buttered the plates with epoxy, pulled them into place until the epoxy just started to set, whipped out the screws, mounted the engine, tightened the screws, loosened and tightened them slightly several times in case the epoxy caught them - and then repeated for the other side.  It was a lot fiddlier than it sounds!

 

Did I mention that I ran out of gas for my blowtorch half way through the silver soldering?  Luckily I had an essential mission to perform that took me past Toolstation so was able to pick some up. 
 

Just one of those days and hopefully back on track tomorrow. 

[Danny Fenton]

We all have days like that, fortunately not often. I have been known to try and stare a problem to submission for many hours. I blame insufficient coffe exciting the little grey cells.

[Martin Harris - Moderator]

I’ve decided to go my own way a little with the wing fixing and delete the old fashioned rubber bands in favour of a tab and plastic bolt. 
 

The piece of 1/8 balsa linking the top of the cabin sides looked rather dubious anyway so I’ve remade it in ply and run a 3/16 spruce member under it to stiffen it, and complete a hoop up from the floor and glued to the fuselage sides. Reference to the picture of a full size fus that I posted earlier more than justified my idea and even allowed me to pay homage to the like minded designer with “scaleish ” 1/16 ply triangular gussets at the top corners to complete a nice rigid structure for only a small weight penalty. 
 

 

I think at this stage, it would pay to build the wing centre section to ensure a strong and suitable wing location. 

[Martin Harris - Moderator]

I know I’ve taken yet more time off my long term Tempest build but did I pick up the wrong plan?

 

[Martin Harris - Moderator]

... well no, but I have made a start on the centre section and redesigned the centre rib to provide an anchor for the leading edge to update it from the original banded on wing. 
 

I also needed to knock up a new small building board to allow the rib to sit on the plan.  You can see the special hole to accommodate the tab more clearly in the previous picture.
 

 

...and the aliphatic is now drying ready for tomorrow. 
 

[Dwain Dibley.]

Clever.

D.D.

[Martin Harris - Moderator]

Just as you think life is ticking along nicely, something always crops up to spoil the party!  This time it's the BMFA News!  Perhaps I should have followed the lead that some people claim and thrown it into the bin unread...

 

Anyway, I happened to peruse Mike Woodhouse's article where he warns against using plastic film on structures designed for tissue covering as the skin was designed to be a stressed part of a rigid structure.  Guess what I was planning on using?  Having looked at the wing drawing, there does seem to be a lack of torsional strength designed in and yes, the original kit included Silkspan tissue....

 

 

Bearing in mind that this is a quick "whim" build and not intended to be a high quality / leisurely constructed project, any thoughts on the following ideas?

 

1. Ignore it and continue as planned - possibility that the wings will suffer flutter. Maybe just build the wing as per plan and assess the torsional rigidity when it's finished and before covering.

2. Cover with tissue and dope as designed - lack of resilience to hangar/transport rash.

3. Cover with tissue and then film cover over it - unknown technique and possible warpage problems when applying heat as I don't think it can be used on a pinned down structure.

4. Redesign structure to add a D box* - 1/16 sheeting and shear webs wouldn't add much weight but I've already cut out and shaped all of the ribs. ? 

5. Add diagonal bracing between the spars.

6. Something else!

 

* Possible D box scheme using existing (modified) ribs/structure

 

 

[Bob Cotsford]

How about tissue over laminating film?  I've not tried it but one of the claims for it is that it's supposed to give the rigidity of tissue with improved puncture resistance.

[Danny Fenton]

I have also heard that tissue over laminating film adds more tension. I am sceptical but have not tried it.

I believe the issue is the bond with the surface, dope soaks into the surface, and its true the structure is much stronger than using conventional iron on films.

 

This was an article published many years ago, but is the proof behind the suggestion.

 

 

 

 

 

 

 

I covered mine, back in the day, in Nylon.....

 

Cheers

Danny

Edited March 20, 2021 by Danny Fenton

[Martin Harris - Moderator]

Thank you both.  The article looks very interesting and I shall examine it in detail. 

 

I decided to build the tailplane - or stabilizer as the plan insists on calling it - and of course this was also designed for tissue covering. 

 

 

 

I decided to add a small amount of additional stiffness with a minimal number of triangulated trusses and cover it with film to see how it feels - it’s a relatively small investment in time and materials which may give an indication of the likelihood of similar measures (less weight critical so a little more substantial) being effective on the wing. 

Starting to look the part! Additional stiffeners can be seen here. 

 

 

P.S. Alasdair's final comment in the article above makes interesting reading!

 

Edited March 21, 2021 by Martin Harris - Moderator
P.S. added

[Nick Cripps]

Martin,

Mike Woodhouse's article rightly points out that use of film in place of tissue can reduce the torsional strength of the structure and could lead to flutter if the underlying wooden structure is insufficient to resist the likely aerodynamic loads. However, he is talking about competition models where the structures are pared back to the minimum in the pursuit of performance which clearly isn't the case for the simple Cessna.

 

It looks to me that the thick leading and trailing edges, along with the relatively deep section  and low aspect ratio would probably be strong enough for the sort of speeds and conditions the Cessna is likely to encounter and film would be sufficient. Having said that, I think I would try out the tissue over mylar (or lam film) as championed by PatMc and others on this forum and suggested by Bob C above. Alternatively, diagonals between the ribs would give a good increase in stiffness without too much weight gain (and which seems to be your preference).

 

The Alasdair Sutherland article, while very good in itself, does not consider torsional strength of the structure, only bending strength which, in a wing structure, is provided by the spar(s). It has to be said that the single beam spars, centred at mid-height of the wing section, are not the most efficient but were quite common on older designs. It would be better with a decent D-box design which would address both torsional and bending strength but then you wouldn't be building the Sterling Cessna 180 you remember from your youth.