Greyhead

I don’t know about bombing a target, I’ll be happy if the bombs stay attached until I “flick the switch” and then they actually release from the model!

It makes sense that they would produce standard bombs; in the photo of them mounted in the “vertical” bomb rack you can see that they have the mounting brackets that are used on the SE5a bomb rack but they do nothing in this one.

When I turned the nose section I included the “collar” around the end, having removed it from the rest of the wood I mounted it onto a cocktail stick and made a series of slots in the collar using the Dremmel with a thin cut off disc. I cut a strip of 1/64th ply about 1/8" wide by 3" long, put it in one of the slots protruding the correct amount onto the nose section and gave it a drop of cyano, I then trimmed off the excess length and repeated the procedure. When all the lugs were in place I gave the whole lot a good “cyanoing” then sanded the lugs down to the diameter of the collar.

It sounds more complicated than it was to actually do; it had to be easy because I wasn’t going to go to too much trouble as I have serious doubts that I’ll be able to produce rubber nose sections with such fine detail.

Greyhead

This is a compilation of posts “lost” because of the hacker attack

I intended to make a mould for the nose section from Plaster of Paris but a trip to our local chemists drew a blank; they even tried to order some from their supplier with no luck. During a recent decorating episode, which involved a fair amount of repair work to the walls in preparation for emulsion painting, we used Polyfiller, it seemed very similar to Plaster of Paris so thought I’d try it.

The plug was prepared by dripping molten candle wax all over it, heating it up with a hot air gun re-melts the wax and most of it drips off leaving a very thin layer. I mounted it on a plastic base with a wall of Plasticine and then gave the lot a spray with WD40.



The Polyfiller was mixed quite thin and carefully poured in to fill the mould. It’s not as quick setting as Plaster of Paris; it took about 2 hours to harden and be ready to remove the Plasticine and the base, then another couple more to dry before carefully easing out the plug.



It has actually turned out surprisingly well; there are a few places where the Polyfiller has broken away in between the lugs but to be honest I expected a lot worse. It remains to be seen whether or not I can use the mould to produce acceptable rubber nose sections; I still have my doubts.

There was a reply from Alan2525 about the type of rubber



Alan

I have not idea what sort of rubber I’ve used; I bought it years ago from the model shop, I think its intended use was for making moulds for casting Plaster of Paris figurines. It’s very soft with a “natural” colour; you melt it over a low heat then pour it either into a mould or over a plug dependant upon whether you’re making a male or female item, and then just let it cool and set.

Grahame

Being thermo-plastic it was easy to “touch up” the mouldings using a precision screwdriver heated over a candle flame. They’ve been glued to a 1/64th ply base with cyano and given a coat of black paint.



The finished parts are not perfect but I’m not going to too much trouble as they are “throw away” parts and as such will be attached to the bombs with double-sided tape for easy replacement, I’m sure they will need replacing after just a few “bombing runs”. I might make a set of better finished parts for static display.

smcouch77

Those ends look really fine! I need an extra set too. I'll make a set with this kind of end for dropping and touch up the others for static. Thanks!
Steve

__________________
Life's too short to fly ugly airplanes!

Greyhead

An assembled bomb partly painted.



I really uploaded this image to check the new “gallery”.

This is the biggest photo that can be used.

OK sorted it out now; I'd linked to the thumbnail not the full size image. Well it was new years eve!!

Greyhead

The bomb release mechanism on the SE5a is very complex, no surprise there then! Although of course it is a proven design there is no way I could duplicate it in miniature so I’ve had to design from scratch

Steve used 4 different length pins to hold the bombs, being a control line model he was able to use a 5-way switch to control the release mechanism but I only have either the retract channel or, if I invest in a new 8 channel receiver, a proportional channel. A proportional channel would be the easiest to work with but I don’t like the idea, if I turned the knob a bit too far a bomb might almost but not completely release then with vibration it could release itself at an unplanned time, which could be dangerous, or at the very least loose me a bomb.

I will use Steve’s idea of different length pins and having decided that the “bang / bang” retract channel it will be, I need some way of “stepping” the release mechanism. I got my thinking cap on and came up with an idea inspired by the timing gear in a clock. I made a mock-up to see if it would work in practice.

The main release bar has 5 indexing pins spaced at 5mm intervals and will eventually have 4 bomb release pins each 5mm longer than the previous.



The release cam has a slot cut out from the centre; before an indexing pin is released from one end plate by passing through the slot the other end plate is in a position to "catch" the next indexing pin.



This is a series of photos showing the sequence as the servo moves the release cam arm backwards and forwards from one extreme to the other; the release bar steps by 5mm with each operation.



At the moment I’m using an elastic band, the spring tension will need to be worked out when it is actually releasing bombs, I hope!

Bunkerbarge

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.

__________________

“Dirty British coaster with a salt-caked smoke stack, Butting through the Channel in the mad March days"

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.