Starting on the Rotol Gearbox Path of Discovery

For years I have had a general knowledge of the SG3 Rotol Gearbox fitted to the Vampire Mk.30 and Mk.31. Years ago Alan Allen in the UK sent me a digital copy of the SG3/1 manual for the Nene Vampire and that was the starting point for learning more, but without getting my hands the real thing, I didn’t have good reason to get into the thick of it, having many other things demanding of my time.

In 2020 I had the chance to examine two SG1 gearboxes and make a simple comparison with the SG3/7. I knew even less about the SG1, so embarked on the process of figuring out their application. One had the data plate with Type ID on it: SG1/18. The other appeared to be identical. It turned out they were from the Gloster Meteor; the driveshaft pointing directly out of one of the main gearbox apertures plugs directly into the front of the Rolls Royce Derwent. The SG1/18 fits into the right-hand intake for the Derwent of some marks of the Meteor. This gearbox is set up to carry a generator – something like a Rotax KX, HX or 02 – and a Dowty hydraulic pump.

The original Vampire Mk.30/31 gearbox was the SG3/1 with the driveshaft located on a forward face, the other mounts were taken up by B3X Mk.III vacuum pump, KX-B generator, Hymatic compressor and Lockheed Mk.VI hydraulic pump. When the vacuum pump was deleted (by RAAF mod 175 or DHA mod V.191), the gearbox was modified as the SG3/7.

Comparing the SG3/7 illustration from the Vampire Mk.30/31 manual with the photos of the SG1/20 below, you can see how different the drive input is.

So having a need for a couple SG3/1 or SG3/7 gearboxes, I started to wonder about how common the SG3 and SG1 are – whether an SG1 would be a starting point for building an SG3.

After a little googling and looking at the various suppliers of scanned manuals, I found the AP.2240A Rotol Gearbox schedule of spares for the Meteor – from the very handy Aircraft Reports. Excellent!

Looking at the basics, it was easy to see that several of the assemblies that make up the SG1/18 are indeed common to the SG3s of interest. After trying to kid myself otherwise, it became obvious that the main gearbox cover is NOT common, although a cheat might be possible. BUT – what about the main casing itself? I’ll come back to that.

In November 2020 my friend Chris sent me an email with a photo of a ‘thing’ caked in mud and looking rather worse for wear, and asked ‘would I be interested?’ Well, that got me excited! He eventually managed to source two SG1/20 gearboxes for me!

So what’s the SG1/20? Similar to the SG1/18, but, importantly and usefully, also carries the set-up for the Hymatic compressor. It was fitted in the left-hand inlet of some Meteor marks.

The basic drive assembly for the compressor is common to the SG1/20 and SG3, but the SG3 also has a mounting adaptor because of the different location on the gearbox where it is attached.

By working through the parts lists for the SG3/1 and SG1/20 and the section drawings for each, I have been able to show that there are a lot of common drive assemblies plus the oil pump, and other parts. This is shown in the drawing below.

Orange highlights: common parts; Yellow – the cover that doesn’t match; No highlight – not sure!

Are the main casings the same? They certainly don’t have the same part number. But the main attachment bolting pattern matches and given how the various assemblies fit, I think the casing of the SG1/20 will work for the SG3. It is clear that Rotol introduced design improvements over the years but retained commonality, and it is also apparent that the casings often have bosses in the casting that may or may not be in use for a particular assembly. I think it is likely these casings will do the job.

It wasn’t until mid-June this year that I picked up the gearboxes. First thing: Clean and protect!

The suggestion was to start with high pressure water but I was worried about the water getting inside. I took the 3 hour per gearbox gentle clean instead! This is exterior only – will need to do something about the interior after lockdown – just an inhibit of sorts as I won’t be disassembling until I actually have what I need to make at least one SG3. Below are a couple of photos – one gearbox before cleaning, and the two after.

There is no Mystery of the Missing Generator

About time I put this one to rest. The answer behind this puzzle is that the generator was there. Past tense! I just didn’t know what the guts of one looked like. I didn’t understand that there are the remains in the photo, and I had been put off the scent by the state of the Rotol gearbox fitted to Camden Museum’s A79-14. This gearbox has a blanking plate over the generator position and the Dunlop pressure reducing valve (AHO19682 – for the Canopy Seal line) and its mounting bracket (L002109A) attached on the blanking plate, as if the blanking plate should be there for a serviceable aircraft. (Although I would certainly mount the bracket over the blanking plate if I had just removed the generator – to keep it all together.)

The Generator position on the gearbox of A79-14

Below is the image from AP.1095C Vol.1, Sect. 5, Chap.9, that made me see the light. Notice the long bolts that run much of the length of the generator, holding the casing and mounting together. This is actually for the KX, but is much the same for the KX-B.

A79-536: Now that I know…

Air Diagram AD 4551 and Junction Box 1

In an effort to identify modifications incorporated in to Vampire FB.9 R1382’s Junction Box 1, I went searching for a later revision of Air Diagram AD 4551. We already had issue 3; this came from Gina’s Vampire library. My general Google search came to nothing. Not really surprised!

I found a reference using NAA RecordSearch to ‘Vampire FB Mark 5 Electrical Installation’ by chance while I was having a look for something else on Vampires. The FB.5 and FB.9 are largely the same, the essential difference is that airconditioning (an ACRE 8 cold air unit) is fitted to the FB.9. I imagine that this file is in the Australian archives because the RAAF had a single Vampire FB.5, A78-3 (formerly RAF registration VV465).

So I ordered a digital copy in February; the order cost just under $40 including GST and took 12 days to process. That copy is available at the NAA here:

http://RecordSearch.naa.gov.au/scripts/AutoSearch.asp?Number=3398245&O=I

So it turns out that the file contains AD 4551 Iss. 3. The AD 4551 pages are scanned at a suitably high resolution and overall the result is very clean. I had a look through this just to make sure that Iss. 3 was Iss. 3! Apart from the NAA version not having some small hand mark-ups that our copy had, I didn’t see any edition differences.

When working through the Gun Firing circuit to convert this in to a wiring/routing diagram for Junction Box 1, I had trouble reading some pin IDs on our version. The hardcopy in Gina’s library is a bit tatty (some tears) and grimy; also in the original photographic repro process, the pages weren’t flat so some of the schematic is blurry.

Gun Firing circuit scanned from Gina’s version of AD 4551.

The GF circuit from the National Archives file.

So I took a look at the NAA version to see the pin ID and found a lot more than what I was expecting. There was in fact a significant difference in the actual circuit. The version we already had included Mod 3146. Looking at the circuit diagrams you should be able to see that they are fairly different. There may be other differences too, in other circuits. No idea yet if this was a relevant discovery for R1382, but at least the NAA file is now there for anybody who is interested or may find it useful!

Alternative Fuel Gauge Panel

Five years ago I saw a photo that showed a rather unusual single-seat Vampire fuel gauge panel. The regular panel, when you look at the front face of it is mostly just gauges, placards and the base panel which is made of Tufnol – fibre reinforced phenolic.

This mystery panel had been seriously messed with! The top line of gauges now sat in a folded aluminium part that was attached to the Tufnol. This component in itself didn’t make for a bad looking assembly, but overall it was rather rough looking.

What was this assembly? I thought it was a rough repair, but why so complicated? Why not just replace the panel!

Turns out there were two mods involved. Firstly (RAAF mod 160, DH mod V.204) the Mk.II 8-day clock was replaced by the V.308 stopwatch clock, with the centre fuel tank gauge moving to the old clock position, and the new clock being installed in the centre-top position. The folded aluminium part was required to reinforce the Tufnol that had been dramatically weakened by the much larger hole for the clock, and to provide sufficient space for it.

Somebody didn’t like that idea, so the larger clock was then moved over to the right hand instrument panel, and the centre fuel tank gauge was then moved  back to its original position. (RAAF mod 231, DH mod V224.)

I think that most aircraft bypassed this mess, with the larger clock immediately being installed in the RH panel, as the aircraft came in for servicing and mods.

However, it turns out that A79-14 is a case that was fitted with the mongrel panel (not the panel I originally saw); see the photo below.

Although I still don’t understand why the original panel wasn’t replaced during either mod, given how much work I imagine was involved, I think it is nice that this oddity is preserved. Perhaps for some lessons on how things should have been done properly the first time (new clock in RH panel straight up), or otherwise on the diversity in modifications in our remaining Australian-built single-seat Vampires.

Vampire arrives

On Wednesday 24th May, Vampire R1382 arrived to join Australian-built Vampires A79-175 and A79-733.

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Thanks to Gina and the guys at Steve Holland Transport and Turner and Central Cranes.

Dispatch

We loaded R1382 on to a semi on Friday morning, 19th May. The truck and load went back to the depot; no travel to NSW this week.

Brian, the aerodrome safety officer, and the almost empty hangar

Brian, the aerodrome safety officer, and the almost empty hangar

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Thanks again to Alwin, Catherine, Gina, Rod and the CVT guys, Brian from the Central Goldfields Shire Council, and the guys from Steve Holland Transport.

Disassembly of Vampire R1382 – Day 3

Wednesday: With the headache of trying to get the main gear up and over-centre, I forgot to take any photos! Below is a photo showing that day’s efforts, taken Thurs morning. One of the things that stopped us getting the gear over-centre was the door lock Teleflex, which was seized. Once that was freed, we still couldn’t get her the rest of the way (working on port gear first). Alwin then made an observation about the tyre and suggested we deflate it. That did the trick! The point being that the tyre normally is jammed against a rub strip attached to the cut-away rib that arches over the wheel-well. This is normally done by a ram and with a fair bit of inertia. I was lying on my back pushing the wheel up with my legs – slow and only human! After letting the tyre down, it was 5pm and we had one leg up so that was it for the day.

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