Scratch Built SE5a

[Greyhead46]

As this is a retrospective thread (don’t get me started!) I’ll begin at the end and post a photo of the finished model to hopefully whet your appetites.

 

I have the complete thread on my computer so could in theory upload the lot in one go but I think the true value of these threads in the interaction with other modellers to share information and techniques so I will allow time between posts to allow for any responses.

 

Hope you enjoy

 

Grahame

[Greyhead46]

With the decision made that my next scale model is to be an SE5a the search begins for a suitable plan; if someone has done all the hard work for you what’s the point in doing it all again and designing from scratch? I will use one of my trusty Laser 70s but was unable to find a suitable plan for this size engine so first some calculations from a simple 3-view drawing downloaded from the Internet.

The first thing to determine is the size; this may not be quite as simple as it seems, a flick through the plans hand book shows models of a similar design i.e. biplane with rigging wires, varying from 80” span for a 48 – 52 four stroke to 56” span for 80 – 90 two stroke (therefore at least a 90 four stroke). The method I use is to work out a minimum size that will allow the engine to be fully enclosed then go bigger to make it the correct size for commercially available accessories, usually wheels. My argument for this method is that you can never have too much power if you need it, but you can always use less throttle and a larger diameter prop to fly in a scale manner. In this instance it equates to 58” span for 5” Williams Bros. vintage wheels.

The next consideration is how scale? As I was going to have to redraw the plan anyway I chose the most accurate I could find, the plan was ordered and then reduced by Prontaprint. I intend to trace the outline then design my own internal construction as I hope to be modifying the plan to allow for some extra scale detail. Before any design work can start I need to confirm the viability of such modifications by making test parts / jigs etc.

 

One of the notable features on the SE5a is the transparent inspection windows for the aileron and elevator linkage. These need to incorporated for scale authenticity so I want to make them at least have the appearance of “working” if at all practical.
 

[Greyhead46]

Forgot to attach the photo.

Is there a way to edit previous posts to add photos etc?

Also can photos be insert in the text rather than all being at the end of the post?

 

Looks like there's a time limit for editing.

 

The first problem is the pulleys; at the scale I’m building they need to be 9mm diameter, I’ve been unable to find any available commercially so turned some from circuit board. I’ll not include a photo; after all, if you’ve seen one pulley you’ve seen them all! 

 

Edited March 6, 2023 by Greyhead46

[Greyhead46]

Next there are the control horns. These a quite thin and as such would be too weak cut from paxolin sheet, metal seems to be the only viable material. My first attempt uses wire with the “outline” in filled with balsa; this means that the holes don’t have sharp edges that would of course quite quickly cut into the control cables.

The photo doesn’t give the correct impression of the shape of the horn, because of perspective it appears to be a lot less tapered than it really is. Although this method seems OK I’m not really happy with it, I’m going to try cutting the horn from sheet steel then use a yoke to attach the cable but just how to make a yoke at this scale I don’t know.

 

Before I commit anything to paper, let alone balsa, I build a “virtual” model in my head, at least for the more difficult parts. It doesn’t always work but usually several ideas are scrapped before the final plan is drawn.

I’ve decided, as I’m going to use scale aileron controls, that the most practical solution is to make the top and bottom wings “plug in” as an assembled unit. Still trying to get some suitable carbon fibre tubes to use as both spars and tubes for the piano wire wing pins.

To keep the interest going I’ve started some of the “engineering” jobs that can be done before the final construction details are worked out. I’d previously made the aileron control pulleys so I’ve started on the shackles.

Here are the components:


With the body bent to shape and the split pin soldered into place I thick the finished shackle looks quite convincing. Remember that the picture above is about 4 times true size (depending upon your monitor), the pulley itself is only 9mm diameter.

Edited March 6, 2023 by Greyhead46

[john stones 1 - Moderator]

20 minute limit on edits GH.

[Greyhead46]

OK thanks, I'll just have to remember not to take a tea break until I've finished a post!

 

I've sorted out inserting the images into the text so that's all good.

[john stones 1 - Moderator]

Yes I spotted you had GH. 👍

[Greyhead46]

“DON’T START TO BUILD UNTIL YOU KNOW HOW YOU’RE GOING TO FIX THE TAIL-WHEEL” is a quote from an article by a well-known scale designer / builder in one of the model magazines I read quite some time ago.

Whilst I can see the logic I’m afraid that I’m not that patient, although my plans are nowhere near finished some sections are complete, namely the front of the fuselage, and I want something to hold that looks like a piece of an SE5a!!

It might seem a strange choice but I’ve started the construction with the undercarriage. The reason being that the fixing is slightly complicated to allow for the tensioning of the front flying wires so I decided it would be easier to make the fuselage fit the undercarriage rather than the other way round.

The main legs use 2 pieces of 12 SWG piano wire, these needed some careful bending as they are quite a complicated shape, the rear support uses 1 piece of 10swg.

 

Before I can silver solder the pieces together I must make a jig to hold everything in the correct alignment.

 

The undercarriage jig is simply a length of 3x1 timber with a centre line; various screws and panel pins are used to hold the separate pieces of piano wire in their correct positions.

Unless you are exceptionally talented at wire bending and / or very lucky the joins will need a bit of tweaking to get a good fit. When all is ready the joins are held with a twist of thin copper wire, if you don’t do this the unequal expansion as you apply the heat will almost certainly “spring” the joins.

 

The silver solder flux is “active”, that is it physically cleans the metal as it gets to the correct temperature, but don’t use this as an excuse not to thoroughly clean the joins before you apply the flux and after soldering make sure that any flux residue is cleaned off as it is corrosive.

 

The thin copper wire will also be removed, as it does nothing for the strength once the join is soldered.

Just the anchor points for the bracing wires to be added and then the assembly can be clad with wood.

[Greyhead46]

With all the silver soldering complete (the large brackets are for fixing the undercarriage to the formers and will be bent to accurately fit when the formers have been made) it’s time to add the wood cladding.

The legs on some SE5a’s were wrapped with linen so hard balsa could be used for the cladding but the particular aircraft I’m modelling didn’t have wrapped legs, they were left as natural wood, so spruce is the material of choice.

As is sadly often the case these days my local model shop could supply me with an ARTF cloned SE5a but a sheet of 1/8 " spruce is another matter! The next best option was a length of “strip wood pine” from B&Q.

All the blanks are fret sawed out, the fronts routed to take the piano wire then clamped and glued using slow epoxy before the rears are routed so ensuring a good join.

 

I've got a couple of Black & Decker routers but the best way I’ve found to rout the blanks is to use an appropriate sized “ball ended“ router bit fitted to an electric drill in a vertical drill stand, adjust the height to cut half depth of the piano wire. Hold the blank in place and draw round the piano wire then rout down the middle of the lines. The bit doesn’t have to be exact size, once the router has done it’s job a piece of the correct gauge piano wire dragged down the groove will soon make for a good fit.

What better on a rainy Sunday afternoon than spending a couple of hours in the modelling room happily “Dremelling” away at the SE5a’s undercarriage?

 

The first coat of stain has shown up a few areas that require extra work so it’ll be out with the sand paper before the next coat. Then light sanding between coats to build up the “depth” of colour to represent the original hardwood.

[Graham Davies 3]

Inspirational modelling there Greyhead. Watching with great interest

 

Graham

[Greyhead46]

Hello Graham

 

Thanks for the interest, plenty more to come.

 

Grahame

[Greyhead46]

For such a high stress part of the aircraft the wood had to be close, straight grained. The way to simulate this is first to give the whole unit a dusting of matt white after the initial staining.

 

Then "stroke" the painted wood with 120 wet & dry in the direction of the "grain" that you want. Although not very clear from the photo, if you do ever try this technique you’ll find that it’s fairly obvious when you’ve done the right amount of "stroking" to produce the desired effect.

 

 

Then apply the stain, again in the direction of the "grain". This is only the first coat but I think it shows that the "grain" is now close and straight.

[Greyhead46]

Time to add a bit of metal work.

First the outline and fixing points are drawn onto thin card that is then covered with sellotape, which both strengthens and protects, before cutting out. The shape is then transferred onto litho plate as many times as required.

The shape can be cut out quite easily with kitchen scissors, not the wife’s best, it’s a good idea to buy a pair especially for this job. Once the shape is cut out turn it over for final sanding of the edge, this shows up any slight imperfections that would be “masked” by the drawn outline.

 

The fixings are embossed from the reverse side; “rivets” using an old ballpoint pen, the bolt heads using a nut soldered onto a bolt.

 

The undercarriage legs are looking a lot better now with a few coats of stain.

Edited March 7, 2023 by Greyhead46

[Frank Skilbeck]

On 06/03/2023 at 12:57, Greyhead46 said:

The first thing to determine is the size; this may not be quite as simple as it seems, a flick through the plans hand book shows models of a similar design i.e. biplane with rigging wires, varying from 80” span for a 48 – 52 four stroke to 56” span for 80 – 90 two stroke (therefore at least a 90 four stroke). The method I use is to work out a minimum size that will allow the engine to be fully enclosed then go bigger to make it the correct size for commercially available accessories, usually wheels. My argument for this method is that you can never have too much power if you need it, but you can always use less throttle and a larger diameter prop to fly in a scale manner. In this instance it equates to 58” span for 5” Williams Bros. vintage wheels.
 

 

If it's any help my 61" span Flair D7 flies fine on an ancient Laser 61.

[Greyhead46]

Hello Frank

 

The D7 doesn't have rigging wires so there is not as much drag as with the SE5a but having said that the model size relative to engine size seems to vary considerably with available plans. This is a retrospective thread, the model has flown and the Laser 70 was fine with a bit of wind to assist take off but marginal in a flat calm.

 

Hope you enjoy the rest of the thread'

 

Grahame

[Greyhead46]

The axle fairing is quite a complicated affair consisting of hardwood leading and trailing edges fixed to the undercarriage legs with metal covers top and bottom. The lower cover is fixed but the top cover is hinged for access to the axle and to allow for excess movement of the axle in the case of a heavy landing.

The lower cover is simple to make from litho plate; the strengthening ribs are pressed into a “mould” made from a piece of scrap spruce using soft balsa as a tool and the rivets embossed using a dress makers copy wheel

 

The LE and TE are joined with cross grain 1/16 balsa to strengthen the litho plate as this area will be subject to quite a battering during take off and landing.

 

To complete the unit I’ve got to make a “piano hinge” to attach the top cover, then the legs will have the inner litho plate added, the fairing glued and pinned in place and finally the outer litho plate added to the legs.

 

I decided not to make a separate “piano hinge”; there are two reasons for this:

1) The hinge will not be used that often so the litho plate will be strong enough.

2) The sections of the hinge are fairly long, about ½ inch.


The first job is to make the top cover allowing enough extra material to form the hinge and the front section, mark the sections then cut the front free. The cover is backed with 1/64th ply and the appropriate sections bent down, these will eventually be cut off but for now they will ensure there is sufficient clearance when the other sections are bent around the wire hinge pin.

 

 

Here is a photo showing the top cover completed with hinge wire in place; the front section is yet to be started.

Edited March 8, 2023 by Greyhead46

[Greyhead46]

The front section is bent around the hinge wire and then the completed top cover glued to the axle fairing.

 

With the cover closed......

 

and open.

 

With the axle fairing fixed in place the metal  work and bracing wires can be fitted then a coat of etch primer applied to the litho plate ready for a coat of PC10.

 

 

The tops of the legs need to be made an exact fit when the fuselage is made and the brackets bent to fit the formers.

Edited March 8, 2023 by Greyhead46

[Geoff S]

A master class!  I'd not appreciated how beautiful a mere undercarriage could be!

[Greyhead46]

Hello Geoff

 

Thanks for the reply and I hope you'll keep watching, there's a lot more build to show!

 

Grahame

[paul devereux]

Museum quality. Fascinating build thread.

[GrumpyGnome]

Wow.....

[leccyflyer]

Beautiful work Sir - very nice indeed. 😎

[DaveyP]

Watching this with great interest 👍

[Ace]

Fantastic realism  from basic materials and creative thinking 👏

[Murat Kece 1]

Museum sculpture!!!