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Oct 28, 2010, 04:02 PM
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Hawker P.1121


Having seen glimpses of this aircraft in various reference books, in mock-up form and under construction, I came across it again in an RAF Year Book, loaned to me after a chance meeting with a retired RAF pilot. A Mach 2.5 capable design, in this publication an artist’s impression pictured it at low level, in camouflage scheme, in company with a TSR2.

The TSR2 got to fly before being cancelled, whereas Hawker’s P.1121 was cancelled whilst partly constructed. The part-built airframe is in storage at RAF Cosford. Intrigued by the design - not to mention its cancellation - I decided to try and research it fully enough to build an RC flying model. Born in the 1950’s, this likely ‘Hurricane II’ was a typical piece of Hawker thoroughbred design – and well ahead of its time.

My internet search turned up Steve Bage's beautiful little free-flight Jetex model and Steve, despite my being a stranger to him, very generously made-available a GA to go with my Barrie Hygate drawing and his design (very many thanks Steve). I had hopes that this would mean a shortcut to a fast build, but my need to base the design around the edf and ducting installation ultimately meant starting again with a ‘clean-sheet’, or should that be ‘clear-screen’?!

Having got the basic tracing done in Corel (all known information then available on screen) I got down to some design decisions on size, power-plant and build-methodology. I wanted a design that would fly on its wing which would mean a lightweight build, with no so-called ‘lite-ply’. I also wanted to use a 4s power-system for the same reasons. I reasoned that because this was such a streamlined design, that if light-weight were achieved, this should allow a slightly larger build than the norm, thus giving a decent wing area and wing loading and a decent-sized model.

The decision came down to 1/14 scale; giving a span of 31.5”, a length of 55.5”, and a gross wing area of 2.4 sq ft. At say, 24 ozs per sq ft that would yield an auw of around 58 oz / 3.6 lbs. Around 21 ozs of that would be power-train weight...

The power system would be a Minifan with a 4s Mega or Het motor, to give a static thrust of a little under 3 lbs. Put another way, the power system would draw something like 50 amps giving around 700 watts or around 200 watts per lb. If the weight exceeded 3.6 lbs, the airframe should still cope with it. I stuck with the 1/14 scale dimensions, areas & and layout and a detailed design commenced.

I measured fan and Lipo weights and came up with a moments diagram to decide fan and Lipo placement. Without a good idea of the structure density of the airframe, this was always a ‘best-guess’ but luckily it has turned out OK for the 4s system envisaged. Surprisingly, (to me!) I became aware that I was not the only one engaged on a model design of this rare aircraft and that this was also to be for a 70mm edf unit and that Pete, its designer, was proceeding rapidly on the RCMF site.

Having achieved a finalised design, I had cut-ready files available about five months ago. I was pleased with this, my first full aircraft CAD design, but I was expecting to subject it to my usual slow build-pace. Then, whilst in conversation with a good friend, I broached the subject of his performing a test-build of the design upon my behalf. He very unwisely volunteered… As a result, the P.1121 has already had its first motor runs and has just about reached build completion. What progress! Thanks Scott – and yes, we are still talking..!

The airframe is now just about structurally complete and is now back with me for details, preparation, glassing and then the colour scheme and final setting-up, before the maiden. I’ll put up more posts and add photographs in a rough sequence here.
Paul W.
Last edited by paulbw; Oct 28, 2010 at 04:16 PM.
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Nov 03, 2010, 02:56 PM
build like there is no 2moz
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From the laser cut components the airframe of the P1121 was fairly quickly and easily assembled.
The first stage was to lay the central spine, and the left hand formers and stringers. Once happy, these were sheeted with 1/16th balsa creating a strong half shell.
Into this was added the mounting for the All Flying Tail servo and operating bell crank. The straight sections of inlet and exhaust were formed with pro-skin, whilst a lost foam method was used to manufacture a glass fibre intake. These were fitted, along with the battery tray, and internal wiring.
The second half formers were then added, and once happy that the craft was straight and true (and the required hatches had been implemented (motor, battery, servo, bell crank) the second side was sheeted.
All the tail feathers featured a built up core skinned with 1/16th balsa, whilst the wings are of a light, but conventional construction and went together easily on the aluminium joiner tubes.
From here all that remained was fitting the fan, and the ESC (mounted through the skin for cooling) and manufacturing the distinctive dorsal strake.
The overall build went smoothly with the majority of components fitting perfectly first time.. A Pleasure to Build, and hopefully a delight to fly.
Scott

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