SE5a CONSTRUCTION BEGINNING TO . . .

[Greyhead]

Time for the ailerons; I’m not going to use the “usual” modelling aileron-to-aileron linkage method of a 2mm threaded rod with quick links for at least 2 reasons. At this scale 2mm rod is just too big a diameter and no full size aircraft that I know of uses anything remotely resembling a quick link!


The brackets are bent at 90º for attachment to the aileron spars and consist of a brass bush soldered to thin tin plate with a 1/16th ply “spacer”.





A bracket epoxied and bound to the spar.





The ailerons have one side and the leading edges covered and are then attached to the wings before the other side is covered. A twist of tinned copper wire soldered to the hinge wires and expoxied to the LE acts as a keeper and in this case also additional strength for the control horn.





When it comes time to fit the aileron-to-aileron link wire I’ll either cut an “inspection hole” (the full size has lots of them) in the appropriate panel or remove the panel altogether; I’ll decided which at the time, but at the moment I’m leaning towards removing the entire panel for ease of access.

[Guest]

Excellent modelling Greyhead.

[Guest]

Grahame, thank you for the jpg offer - I shall certainly take it up, when I get there! Some time ahead I think. I had actually looked for instrument details but without success. I was intending to rely on Shuttleworth.

LINNEY

[Guest]

Bunkerbarge, thank you for the encouragement. I will not load up the thread but I shall now make a few comments - even if I only arouse disagreement.

For a start, I don't have a large workshop (they are never big enough actually) but my main construction bench is about 10ft long. It is conventional Formica top but with a 1/2" layer of SunDeala board on top - expensive but it takes pins without any lasting deterioration. Then I cover the whole bench top with graph paper (imperial) and follow that with a layer of clear film. Any "droppings" will then wipe off.

When I am making an assembly then x and y alignments plus a variable angle "square" to give z direction are virtually automatic, taking no actual skill.

I actually adopted Grahame's suggestion of starting on the undercarrige - for no good reaon except that he suggests it! But I use a different technique. He bends the wires, binds them into position and solders the assembly. Firstly I pre-tin all the approprate parts of the wire using Baker's Fluid (Zinc dissolved in hydrochloric acid) as a flux for 60/40 solder (no flux core). Then I drew the outline of the assembly of the parts on to hardboard, held the parts flat down into position and and spot soldered them into position. A large iron and pre-tinning made the joining virtually instantaneous. The strength of the joints of course was not great but everything held together, in perfect position, whilst I bound them all up with pre-tinned copper wire. I then flowed flux-cored 60/40 solder all over the joints and job done. Alignment perfect. Next, I washed well with warm water to remove all Bakers Fluid and then meths to remove the flux core residues. Finally a spray coat of matt black to cover all the flaws and it looks O.K. I think. But if you have better ideas I would like to know please.

LINNEY

[Greyhead]

Linney

If you follow the link in post 5 of this thread there are some nice shots of the instrument panel and cockpit detail but to get the actual dials into a useable state still required quite a few hours of manipulation. Just let me know when you’re ready for the jpegs and I’ll scale them for 71" span and send them to you.

I’m most impressed with the sound of your “building board”; I envy you the space! As for the undercarriage, soft soldered and bound joints are perfectly adequate if somewhat bulky, I use silver solder wherever practical but it’s really down to personal preference.

Grahame

[Guest]

Grahame, that link in thread 5 has some of the best close up shots of the Se5A that I have ever seen. The colouring is also different from others, but personally I think I shall adopt the Aussie scheme, a sort of racing green. Interestingly, I see you have purchased Williams wheels but made the guns. I have also bought the Williams guns, should save me about a month I should think!

I am trying to attach a photo, failed last time but here goes with another attempt! Just to show I have at least started - but I shall be out of the UK shortly for a time, then back, then out again for longer so I may not do much more until early September. But no guarantees unfortunately!

But a question for you - or anyone else.

People talk about engines for their models but I fail to see the point. It is the propeller which propels the aircraft and it has to have sufficient diameter for the load which has to be pulled and provide sufficient speed (pitchxrpm) to give lift. If you can tell me what size prop this model needs for its size and weight and what airspeed is good cruising then I am well able to find an engine to perform accordingly. Selecting an engine then hoping to find a suitable prop always seems to me to be to be the wrong way round.

[ATTACH]15524.IPB[/ATTACH]

[Greyhead]

Linney


SE5a’s came in a multitude of colours, most were what we call PC10, which varied from bright green to almost black! Your question about engine size as against prop size is perfectly logical (you must be an engineer) and would appear to be the sensible way of going about things; all I can suggest as an answer as to why we do it this way is that it’s the way it’s always been done, probably because there never used to be much choice of pitch, only diameter, and it’s the way modellers understand. Not really an answer at all is it?


You didn’t seem keen on starting your own “under construction” thread because of your lack of experience but all I can say is that your last few posts would have made an excellent start to a new thread. I’m sure if you mention it to one of the moderators they could move them to a new thread to keep all your SE5a information / queries in one place. But no pressure!


Grahame


The ailerons are now covered with rib stitching / tapes applied and are “on hold” until it’s time to add the aileron to aileron wire, which will not be until the model is fully rigged and there’s a fair amount of work to do before then.


The interplane struts are given the same treatment as the undercarriage to get the desired finish. The top strut in the photo below has some damage from test fitting the bracing wire brackets; it would obviously have been better to make the brackets and do all the test fitting before I applied the stain, so why didn’t I do that!!!!! Age is a wonderful thing!





The bracing wire brackets are bent up from thin tin plate; litho plate wouldn’t be strong enough. Getting the correct shape to wrap around the struts working from the flat side view was a challenge but PhotoShop came to my rescue yet again, how did we manage before computers?





The top bracket in position.





This is what caused the damage to the strut, any damage will be repaired and the brackets painted before being glued permanently in place.

[wonwinglo]

No doubt about it,struts really make or break a biplane,whenever I see the machines at Shuttleworth it makes me marvel at the workmanship that has gone into making those struts,your model emulates them well Grahame and the finish is spot on,what are you going to do when you have completed this time consuming lovely project ?

[Greyhead]

Barry


I’ve no idea what the next project will be. I won’t start thinking about that until the SE5a’s finished, I don’t want to get “side tracked”. There’s still plenty to keep me busy for a few months yet, when the SE5a’s up and flying I’ll wait and hope for a flash of inspiration.


Grahame


I’m at that awkward stage in the construction; all the major components are complete so for now it’s just "bitting and bobbing" until it’s ready for the paint. To make matters worse nothing seems to be able to be finished, each part needs another so I’ve only got half finished parts.


Getting the end brackets to fit was a lot more difficult than I imagined it would be involving a lot of trial and error. I mentioned earlier that the ailerons are “on hold” and that now applies to the interplane struts.





I’ve made a start on the Aldis sight; the brackets are from 2mm diameter aluminium tube, the sight itself is plastic tube with brass ends.

[wonwinglo]

How is the weight feeling Grahame ? I know that you are ever conscious but it does creep up on you.

[Greyhead]

Funny you should mention the weight; I’ve just started the rather mundane, but nevertheless important, job of making the hatch for access to the radio gear and for rigging. The hatch is between the undercarriage legs so necessitated their removal, this is the first time I’ve had them off the model as a complete unit with wheels, bracing wires etc., etc. and they feel quite heavy; having said that they need to be strong to take my “less than perfect” landings! I like to save weight wherever practical but I never compromise strength where it’s needed, the finished weight has never been a problem with any of my biplanes, after all there’s twice the wing area but they still need a big engine, or to defer to Linney, a large prop, which equates to the same thing, to overcome the drag.

[Greyhead]

The reason for the hatch is obviously to give access to the inside of the model and as such it should be as big as possible; I’m sure we’ve all built models that involved extreme contortions of the fingers and much swearing to get the radio gear in.


To this end I’ve made the entire fuselage bottom between the undercarriage legs removable. It’s fixed permanently to the undercarriage, which is attached to the fuselage by a 2mm bolt at the front and 2 small screws at the rear so it’s very quick and easy to remove.





This is the “hole” left when the undercarriage is removed; I shouldn’t have any trouble delving into the “innards” through that!

[Guest]

Greyhead, firstly let me make quite clear that my experience with this sort of thing is almost zero so if I am talking nonsense then please politely put me straight.

Looking at it purely from an engineering point of view, I can lay claim to some experience there, holding the hatch in the way you describe seems a bit on the weak side. You have gone to all the trouble of making the undercarriage substantial to help it to absorb the odd heavy landing but this strength is not transmitted into the airframe by having a couple of screws on the centre line.

Imagine the worst case and you are landing with a degree of sideways movement, say against a crosswind. There will be a component of the force trying to push the wheels to one side. To resist this you should have your undercarriage struts attached to the airframe to prevent the leading strut from pulling away from the fuselage sides and trying to crease the hatch about the longitudinal centre line. There is also a possibility of a slight concave flexing of the hatch which will immediately allow the hatch to become loose and put a significant strain on your centre line screws.

I would have either put screws at each corner of the hatch or mounted four metal tabs, close to the undercarriage strut ends, to the fuselage sides with either a threaded hole or a captive nut so that you can locate a BA screw through the hatch. It will be firmly held at each corner then and transmit all the landing forces into the fuselage more efficiently. I also would think that machine screws or BA screws would be better than wood screws as they will last considerably longer and be more resistant to use. If your wood screw thread gets weak it could cost you the aircraft.

As I say only a suggestion but it doesn't look as strong as the rest of the model in your current configuration.

[Guest]

Hi Grahame. It' really looking good. Have you worked out how to attach the fairings to the landing gear.

Steve

[Greyhead]

All valid points as always Richard; a more in-depth explanation is called for!

The “hatch” itself has very little strength being made mostly from 1/64th ply so it is definitely the undercarriage that holds the “hatch” and not the other way round. The screws are really only to hold the undercarriage in position, the front wires go either side of a former and the rear wire fits into a slot in a cross-member, both of which are quite substantial being made from 4 layers of 1/8th ply and it is these that transfer the landing loads to the fuselage doublers. The 2 screws will indeed have to deal with any transverse forces but these should be minimal because from a practical point of view we never land, or take off, crosswind with a biplane of this size, it would be courting disaster to try, I think the undercarriage would be the least of your worries! Once everything is “lined up” the screw holes will be drilled out and a snake inner cyanoed in place to preserve the threads.

I hope this has gone some way to allay your concerns, it’s always better to raise issues like this; I hate it when after a model has crashed someone chirps up with “I thought that didn’t look right before you took off”. Well why the **** didn’t they say something at the time!

As for the bungee fairings, I’ve put some sponge rubber in the bottom and this seems to hold them in place whilst still allowing them to move and then spring back into position, which may well be useful during take off and landing.