SE5a CONSTRUCTION BEGINNING TO . . . - Page 55

tigertc · 19-12-2007

Could you bomb parliament first?
Then do a tour of England taking out all the council tax offices?

Greyhead · 23-12-2007

At last I’ve made a start on the bomb rack, or to be accurate on the bombs; there’s no point making a bomb rack if I can’t make the bombs! Here’s a photo to show what I’m aiming for. (sorry, I just couldn’t stop myself!!)

I decided that the only practical method is to turn the bombs, but therein lays the first problem; I’ve not got a lathe. If you work for Health and Safety I suggest you don’t read the next bit. I "converted" my vertical drill stand into a make shift lathe, very Heath Robinson but it works.

I started with a length of curtain pole and I’ve now got the basis for one bomb, but I don’t think I would be able to produce all 4 bombs and end up with them all being the same; they’re quite a complex shape.

I’m thinking of using this one as a master for a mould and then making a set of bombs from casting resin. I’ve never used casting resin before so any tips / advice will be gratefully received.

One question that immediately springs to mind is “is it tuff enough to withstand being dropped from the model?” They will be released quite low, I’d think about 50ft and at relatively slow speed over grass. For safety I intend to mould the front black bit from rubber and the arming vanes will be removed.

smcouch77 · 23-12-2007

Hey Grahame! That looks just like my lathe! I cut out a pattern using the picture above and set it against each bomb as I turned them. They're not "factory perfect" but you can get them close enough. I drop mine from about 10' over pavement with only minor scuffing of the paint. Black rubber would fix that.

Greyhead · 24-12-2007

There was no chance of getting any casting resin until after the Christmas holidays and as Steve successfully turned his 4 bombs I thought I might as well give it go.

I’d turned the first one using a card template and found it quite a difficult and slow job; then I had a “eureka” moment, it does happen! I measured the diameters at various points along the length of the bomb, turned the wood as a series of cylinders and then simply tapered from one diameter to the next.

This produced the other 3 bombs very easily and quickly; just as Steve said, “ they’re not factory perfect” but certainly near enough for me and a lot cheaper than buying casting resin etc.

smcouch77 · 24-12-2007

AH! Ingenuity! the mark of a true modeler.
Merry Christmas, my friend. And a happy New Year!
Steve

Greyhead · 27-12-2007

Making the bombs as a series of cylinders was simple and quick, which is just as well because I’ve had the make a completely new set of bombs. It wasn’t until I came to fit the rear fins that I realised that the rear section of the bombs was about ¼" too short. It just goes to once again emphasise the old adage “measure twice cut once”!

So what went wrong?

I first tried to turn the bomb using a single template of the wood to be removed, this meant that before the template for the widest part of the bomb got close to the surface the deepest cuts had to be made and this made the work piece quite weak and impossible to work with safely. I decided to “split” the bomb into 3 sections; I made templates for the front and middle sections, the rear section is just a straight taper so didn’t need a template. To ensure that the curves “flowed” nicely I decided to make the templates overlap by a ¼" but somewhere I got the measurements wrong! Having turned the front and middle sections I simply measured the overall length of the bomb and tapered the rear section accordingly not realising that the front of the bomb was in fact ¼" too long. When I decided to turn the other 3 bombs I used the master, not the photo, to set the callipers and measure the distances so duplicating the error. When I discovered the error I remounted a bomb in the lathe and tried to correct it but that didn’t work at all so 4 new bombs it had to be. It’s not all doom and gloom though; at least I now have some “spare” bombs to practice on.

I found that cutting 2 slots as a cross to fit the fins made the rear section very fragile and I was afraid that I might break the “legs”, so I cut one slot first, glued in opposing fins made from a single piece of 1/64th ply, then cut the other slot and fitted the other 2 fins once again as a single piece.

The bombs have been filled and sanded but I’m not too concerned about a perfect finish, after all if everything goes to plan they will be dropped from a great height and are certain to sustain damage or even get lost in the grass!

I turned a plug for the nose of the bombs from which I hope to make a mould to produce them in rubber.

rjwood_uk · 27-12-2007

very nice work there. looks very convinsing!!!

is the hook sticking out the back the arming pin that would need to be pulled out before release?

did the SE5 have a bomb rack under it or where they just "thrown" out?

Greyhead · 28-12-2007

Richard

The decision to add the bombs was only taken recently after seeing the photo of Steve’s model; I’ve done very little research on the subject myself. I’m using information supplied by Steve; if it’s good enough for him then it’s good enough for me!

I’ve no idea what the loop at the back is for but I do have some general information:

The SE5a was developed well after the time of dropping hand grenades or bombs by hand from the cockpit or shooting at the enemy with a pistol. The load it could carry was limited so 4 bombs of 20lbs each was the maximum, either as 2 sets of 2 bombs, one under each wing or a rack of 4 under the fuselage just aft of the undercarriage legs. The bomb release, operated by the pilot, is the out of focus black lever mounted low down on the cockpit side.

Pulling it back released a bomb, pushing it forwards reset the ratchet system, pulling it back again released the next bomb and so on until all 4 bombs had been dropped.

Grahame

smcouch77 · 29-12-2007

The bombs look really great! How did you do the little "lugs" around the nose piece?
I think the loop on the tail was to hang the bombs on a rack used on bombers. I have pictures with and without. The drawings I have of the rack show the bombs with loops, but they're not attached to anything.

**Bunkerbarge** · 29-12-2007

Now you're into a whole new area of flying Grahame, trying to drop a bomb onto a target. That should keep you busy for a few hours and probably cost you a couple of bombs.

Maybe do it in short grass first!!

Lovely modelling job as always though. When is your anticipated maiden flight? I can't wait to see this model in the air.