SE5a CONSTRUCTION BEGINNING TO . . .

[Guest]

Graham, you're obviously well on your way with this but if you decide on a differrent direction I would have a play with a model yacht sail winch. You could use that to pull in a wire that operates a slide with some sort of release mechanism attached.

The beauty of a sail winch is that you have a lot more travel to play with than you do on a normal aircraft servo.

[Greyhead]

Richard

I did consider using a “servo slower” to give me more time to play with after a bomb has been dropped, to lessen the chance of almost releasing the next, I hadn’t thought about a sail winch, which would give the same result. The problem I could see with this arrangement is that there would also be a delay after moving the servo channel control until the bomb was actually released.

Another idea I had was to buy a different control knob for the transmitter and arrange some form of indexing so I could confidently turn it a ¼ of a turn at a time.

One major drawback with both these methods is that I’d have to buy a new 8-channel receiver.

Grahame

[Greyhead]

Before I could start on the bomb rack itself I had to finish off that most useful of Christmas presents, a family size tin of Quality Street; for those who haven’t realised these tins also provide a good supply of flat tinplate. As a special favour, to help the better half keep to her new year’s resolution to watch her diet, I volunteered to take on the task myself!


The main body is made from the tinplate with a brass tube for the rear support. The release arm is made from 2mm threaded rod, the threaded section acts as the bearing in a length of tapped snake inner cyanoed in a brass tube. It will extend up into the fuselage through the large opening just behind the undercarriage legs to connect to the servo.





The release mechanism works a lot better now that a bearing supports the release arm.

[Greyhead]

The bombs are now finished, not without a few problems along the way!





I painted the rubber nose sections with Warbirds paint; I thought it would be OK because it is water based although it does have a couple of drops of a catalyst added to make it fuel proof, but it turned sticky after a few hours so obvious there was some reaction. I stripped the paint off but the rubber was still sticky, I’d got nothing to loose so I tried the old “trick” of dusting them with talcum powder, this time I painted them with “genuine” acrylic and there was no problem, I dusted them again, just to be sure, before the second coat.


I’d intended to attach the nose sections with double-sided tape for easy replacement but this also didn’t work very well so they are now epoxied in place.


The arming vanes are from tinplate soldered to a pin so these are easily removable.


They will be removed before dropping the bombs because not only could they cause damage they would also be damaged themselves.

[Greyhead]

Even this simplified bomb rack is quite complex and it still has the safety stops to be added.

[Guest]

It will make a great addition to an already awesome plane! How do you load the bombs?

Steve

[Guest]

This old SE5a is getting more and more technical by the minute! Lovely workmanship on that bomb rack mechanism! I'm really impressed by how fast you manage to put all these little scratch built bits together - the devil is in the detail! I always find working on painstaiking parts to be really irritating and normally have a box full of failed attempts after a couple of days graft!

Great Work as always!

[Greyhead]

I mounted the bomb rack on some scrap balsa whilst I adjusted the bomb cradles. This adjustment turned out to be quite critical; a balance between having the bombs loose and able to swing about or too tight to allow the release bar to move under the spring tension.





In fact it was so critical that I have had to number the bombs to ensure they are fitted in the same positions, the slight variations in the diameters of the bombs where the cradles support them was enough to cause problems.


The bombs are held in position by different length pins that pass through loops on the bombs, which themselves pass through slots in the base of the bomb rack. This photo was taken before any adjustments were made; the bombs are now equally spaced!





Steve


The bombs are loaded in the reverse of the order that they are released. With all the bombs released the release bar projects 20mm from the end of the bomb rack, I don’t think this will be too obvious “in flight” but if it is I’ll shorten the release bar and extend it with a length of piano wire. The first bomb is held in position and the release bar pushed in to engage the release pin through the bomb’s loop, the slot in the release cam is such that the previous indexing pin can pass back through it when the release bar is pushed in. The cam is then moved (at the moment by hand but once on the model by flicking the retract switch on the transmitter) to the other position. The release bar can then be allowed to spring back against the cam whilst the next bomb is put into position and the process repeated until all 4 bombs are in position.

[Greyhead]

The bomb rack is bolted to 4 small brackets fitted between the undercarriage legs; the release arm has a ball-joint soldered to it just inside the fuselage bottom and the control rod passes forwards between the undercarriage cross members and the fuselage bottom.





A mini servo to operate the bomb release is located in the engine compartment attached to the firewall by an “L” shaped servo mount.





Commercial “L” servo mounts seem to me to be very expensive for what they are so I make my own from “L” shaped plastic extrusion from B&Q; I bought a 6ft length for a couple of quid years ago and I’ve still got half of it left!

[Guest]

Words fail me when i try to say how good this is looking Grahame.

Cant wait for her to fly. Are sure about all the weight you are adding? I am no proffesional in these matters, but you do tend to keep adding things.

*Wates for kitchen sink to be added

[Greyhead]

Terry

Weight is always a consideration with scale models; because it isn’t a property with a “tipping point” it’s tempting to say, “it can handle another few grams.” The trouble is all these few grams add up and can end up as a few kilograms!

Of course given enough power anything will fly but as the weight increases for a given wing the flying speed has to increase to generate the extra lift required and it can get to the point where the model can no longer be flown in a scale manner, which really defeats the object of the exercise.

One advantage of these early biplanes is that because they didn’t have powerful engines available at the time, they were designed lightly loaded with lots of wing area, unfortunately the aerofoil sections are not as efficient as more modern ones but in practice weight isn’t usually too much of a problem, drag is what really saps the power.

Personally I don’t over concern myself with the weight, I just build as light as I can, allowing for sufficient strength, certain details have to be added to be scale and there’s nothing that can be done about it. The bomb rack on the other hand isn’t essential so if needs be it can be easily removed with 4 bolts, but I hope it’s OK as I think it will be a real “talking point” and increase the appeal of the model.

Grahame

[Guest]

Those pics of the Bombrack clamped to the shelf in your workshop gave me a big smile! Looks absolutely superb and certainly worth the extra bit of weight that they add to the model! Certainly looks very purposeful!

I wish I had a little bomb rack like that in my workshop for those times when the part just doesn't turn out quite how you wanted it!

When she's airworthy - I'd love a chance to see her in flight and a close up look! Any plans of a Scale Models meet?

:bravo:

[Guest]

Something bad happens when we try to organise a meet...we need to call it something else.

[Guest]

A 'Gathering', or is that a bit too Stephen King!!?

[Greyhead]

Alan

I’m not into competitions so the only place I’ll be showing the SE5a is the TMFC “Bring a Model Night” where we take our winter projects for other members to peruse and I’ll fly her from our field at Redmarshall.

It’s a long way from County Durham to Essex but if you’re every up this way drop me a PM and you’re more than welcome to come and have a look, you might even get a cup of tea if you’re lucky!

Grahame