SE5a CONSTRUCTION BEGINNING TO . . . - Page 57

smcouch77 · 10-01-2008

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

alan2525 · 10-01-2008

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 · 10-01-2008

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 · 13-01-2008

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!

tigertc · 14-01-2008

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 · 14-01-2008

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

alan2525 · 14-01-2008

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?

tigertc · 15-01-2008

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

**Bunkerbarge** · 15-01-2008

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

Greyhead · 15-01-2008

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