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Hawker P1121

That is not a typo it really is 1121 so what was that?
The answer - it was started but never completed being cancelled by the infamous 1957 white paper
This is the full scale mock up that Hawker built.
Impressive -a sort of Supersonic Mach 2 Hunter.
So I set about building one out of Depron with a 4.5" ducted prop like my Skyray.
The fuselage was built in 3 sections each as a half shell with formers.
But only clad internally to create the duct.
Note the reinforced double former to carry the spar round the duct.
To make maximum use of the available space the duct changes section down the fuselage.
The wing has no ribs just a spar and 4 spacers.
The completed fuselage - minus the outer skin. To supplement the chin duct two cheat holes were added in the position of the rocket hatchs just behind the cockpit.
The all flying tail would also be an elevon so no ailerons.
I did wonder if I could even finish it let alone that it might fly.
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No EDF just a PID (prop in a duct) just like my 36" Skyray.
That works because the plane is big (duct is 4.5", 114mm diam) and very light so it needs a much smaller motor than the same size EDF would and thus a smaller battery (1500mAh 3s) and servos.
Even a small high revving prop (4.5x4.5) is about twice as efficient as an EDF so despite the small battery the flight times are reasonable.
The P1121 will have a bit less wing area but should be aerodynamically a little bit more efficient than the delta Skyray. On the down side the fuselage and the duct are 50% longer so there will be rather more skin drag and I have never tried an all flying tail before or anhedral on a wing. :eek:
We shall see.

Next the electrics and motor have to be added but exactly where?
with the battery in the nose and servos resting on the tail plane the motor was positioned on the fuselage to give a balance point just ahead of the main undercarriage position. The fuselage was then chopped in half at that point!:eek:
Doing it this way only gives an approximate CofG position but hopefully there was enough room in the cockpit to move the battery about when the airframe was fully complete.
The motor in its streamlined 'pod' with thin hardwood supports.
Intalled in the fusealge.
The tailplane pivots round a fibreglass tube spar.
Keeping the battery to ESC leads short meant 3 long (18") wires to the motor. Appropriate silicon insulated wire actually weighed nearly half as much as the motor itself.
In fact the insulation contributes nearly 50% the weight of the cable. Depron itself is a very good insulator and built into the fuselage it does not have to be flexible either so solid copper conductors at half the weight!
The radio and ESC squeezed in between the duct and the skin.
Installing all the RC gear and wiring is a bit easier when the fuselage has no skin but if you ever want to change anything......


Stuck in Sunny FL
Staff member
I find the bare copper to be an interesting approach. I wonder if the weight savings will be worth the risk to the equipment.
With all the basic now sorted the airframe could be skinned so building everything in.
As the external profile is a bit more complex than the smooth duct it took rather a long time to do particularly round the tailplane.
Although the plane is over all not much bigger than the Skyray the cockpit and canopy are only half the size indicating just how big the P1121 was.
Next comes the issue of what colour. Had the prototype been completed it would probably have been left aluminium so against my better judgement I thought I would try silver emulsion.
On the one piece wing skins that retained the natural Depron skin surface it worked well enough.
But on the planked fuselage with its mryiad of joins and sanded surfaces was a nightmare to get anything like an even finish without resorting to many coats of what is a pretty heavy paint. In a word it did not work well.
Fortunately the camera does lie!
For contrast it seemed reasonable to give it a red fin and spine.
But does it actually fly? Well yes and no.
Its maiden flight was short. It had virtually no roll authority.
I just managed to keep it flying level enough to land with minimal damage in the next field.

It needed ailerons, which is what the original had, but the lightweight 'build it all in' came back to bite!

The wing is so thin that even a tiny 3.7g servo on its side will not fit between the skins so has to lies flush with the under surface.
At least the rib-less wing construction makes it relatively easy to feed the servo leads through the wing although the same could not be said for the fuselage with its many formers. A lot of access holes are required.
At least with its relatively thick skin an inserted Depron patch is virtually as strong as the original skin.
At the same time the tailplane spar was replaced with a bigger one that had a tiny spring loaded 'pip' pin at its end. The flying surface is simply pushed over the spar until it 'clicks'. It takes a surprising large pull to remove it.
As the aileron servos are virtually on the CofG there is no real overall change and the weight increase is just 1/2oz to 17oz ready to go.
Smooth and gentle it is surprisingly forgiving to fly. No speed merchant but at least it now has a passable roll rate.
The Depron skin acts as an effective sounding board so under power it lets you know its around! ;)
It glides nicely but that big chin intake really does not like sliding on the grass! :eek:
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6 months from start to first maiden working every but not all day.
Then another 3 months of rework to install the ailerons (and wait for the right weather!) for the first true flight.
But to be fair with its tri-furcated inlet and long variable cross section duct it is about the most complicated Depron structure I have yet attempted.