"The Heart Of The Gnat"

[Renegadenemo]

I can't tell- is that a fuel system lurking underneath it already?

There's a filter bowl under there at least but somewhere I have a letter in which the purchase of the gnat is agreed with Donald and I'm sure the spare engine was part of the deal. Now I'll have to find it!

[Mike Bull]

Here's the letter- dated 20th July 1966, it's for 'Gnat Aircraft XM691 complete with Orpheus engine No. 711 - Dunsfold'.

Gnat letter.jpg

By this point Donald had already been loaned engine No. 709- the picture of it suspended above Bluebird as shown above was taken on June 26th.

[Renegadenemo]

That's not the letter I have or at least if it is, mine has been added to all over the place with scribbled notes.

[Mike Bull]

There's a similar document reproduced in Neil's book, complete with scribbled additions- page 34. Between the Air Ministry and Bristol Siddeley, it details that they have located two engines which 'should fulfil Mr Campbell's requirements'.

Point is though, Donald had 709 in hand before his purchase of 711 was even agreed. That still doesn't quite confirm which engine provided the fuel system, but the implication through the book at least is that 709 was on the way to being installed when Donald then had the opportunity to purchase the Gnat/711; that said, the offer letter speaks of some 'urgency' re. purchasing 711- maybe 709 had some vital bits missing?!

[Stuart Baker]

But do we know which of those engines the fuel system first came off of..?

I'd have thought the gnat would have its fuel system on it and the spare engine would be just a core. Any other assumption has to have the gnat delivered with important parts missing that were somehow left on a scrap engine.

A complete engine would normally come with its fuel system, although the main parts of the fuel system, e.g. pump, CCU, are all considered to be Line Replaceable Units. This means that they should be fully interchangeable on a deployed aircraft, albeit there may be some limited in-field adjustment required, such as ground idle settings.

When an engine is removed, cannibalising the fuel system to get spare parts is not normally the done thing, as this would render it impossible to inhibit the remaining fuel system parts. However, it is well within the bounds of possibility for a flight test engine that the complete system would be removed to be used elsewhere, or returned for evaluation. If it is all flight test stuff, then there are doubtless reports in our archives which reference most of the fuel system hardware, but it could take a VERY long time to find them.

We know that the fuel system which came off the lake bed contained at least one part which was for development flight test only (the ASC), and therefore would not have come from a production engine / aircraft - but I'm not sure if that helps you any. Most flight test aircraft in those days ended up having multiple changes of parts on the fuel system as the envelope was explored and the fuel system calibration was developed. Subsequently almost anything from the flight test inventory or production standard hardware could be fitted if an item was removed as unserviceable, so the concept of the "original" fuel system for an engine from this source is pretty meaningless.

All of this is very interesting, but I think we alreday have the most important piece of information here, which is that the fuel system parts which were on the engine at the time of Donald's last record attemt are the ones which were found at the bottom of the lake.

By the way, I'm sure that a few H&S types could spend hours discussing the workshop photo with the two engines and the man on the ladder as a case study...

[Renegadenemo]

OK - let's forget the fuel system for a minute.

If you look at the pic's from 66/67 it soon becomes apparent that they had only one oil tank and the stainless pipes that connect it to the pump and accessory gearbox. Only one set of igniter leads put in an appearance too. But what is perhaps most telling is that when they made the engine change following the failure of the inlet duct they abandoned the old engine with the inner and outer jetpipes detached. Considering that this meant removing hundreds of nuts (and tab-washers if it was put together properly) there must have been a good reason to go digging in there and all I can think of is that part of the turbine bearing lube system was needed for the engine swap too.

It seems to me there's only two ways this could have gone.

Either the spare engine came with everything and the plane arrived later with the engine out (so far as I'm aware you can't get the jetpipe and jetpipe-shroud off with the engine in-situ and whatever it was that was missing from under the jetpipes must have been gone from the plane) and loads of other bits nicked off it, or the opposite was the case.

It makes no difference which way around it worked but it would be interesting to find out?

Where's our resident historian? Neil...

[Mike Bull]

If you look at the pic's from 66/67 it soon becomes apparent that they had only one oil tank

Erm, no they didn't, they had a choice of two! Check out the taller filler spout on the oil tank fitted here on 709-

26 june 1966.jpg

So, 'our' oil tank- complete with it's cute little original dent and the shorter style filler spout- is something we can say for certain that came out of the Gnat.

[f1steveuk]

Never fails to amaze me. ALL the letters regarding the loan of a spare engine, and the purchase of the Midge/Gnat were given to me by Ken. When I went to return them he said "keep them, I certainly don't have a use for them and have copies if I do".

I've supplied a handful of copies and yet every bugger seems to have them!! Pointless excersise asking people not to copy things.

My next job today, emailing the Brooklands museum who are casually publishing a picture I own the copyright to.


Angry of Mayfair

[Renegadenemo]

Erm, no they didn't, they had a choice of two! Check out the taller filler spout on the oil tank fitted here on 709-

Interesting. Wonder why they didn't use that one then. It's a taller filler but not that much taller and where they cut the forward face of the parachute box away to clear it is quite low down so there's another four inches or so until you get to the inside of the outer skin.

None of this explains why they took the inner and outer jetpipes off when they did the engine change though. There had to be something in there that was either knackered or they only had one of them. If an example of whatever it was, maybe it was part of the turbine bearing lube system, was on 711 then why take the first engine apart to get at it during the engine swap? And if the item was missing from the aircraft, it surely must have been removed with the engine out. It may be as simple as them only having one set of nuts and bolts for the jetpipes.

I still say they didn't have enough parts for two complete engines and it wouldn't surprise me in the least if that seemingly complete engine on the stand was a spare core mated to bits snaffled from 711. If you look under the stand you can also see a pool of spilt fluid and a spanner so someone was messing with it.

By the way, the letter I have was given to me by Gina with another from some engineering firm in Manchester or Liverpool saying they could make K7 do 400mph but it would have to be painted green and renamed 'Greenbird 400'. I don't think he'd have gone for that somehow... I'll dig them out when I get a minute.

[Dominic Owen]

Pointless excersise asking people not to copy things.

My next job today, emailing the Brooklands museum who are casually publishing a picture I own the copyright to.


Angry of Mayfair

Steve, I know the feeling, although it's usually with pictures I've repaired/colourised/modified and others trying to claim ownership of the work: One cheeky sod once even posted a picture somewhere that I'd spent about 4 hours creating from a frame of video and tried to claim it was an actual photo from his own collection. When I pointed out the digital signature had my name as the creator, he tried to say it was from when I saved his version to my hard drive. In the end I had to point out that I'd written my initials in individual pixels, hidden in the centre of the image.
I still, to this day, have no idea how he got his hands on it because the two people I actually sent it to flatly denied forwarding it to anyone.