Hawker P1081 the 'straight through' Sea Hawk

[Simon Chaddock]

I have decided to build the complete Sea Hawk based set!

As I explained the original Sea Hawk fuselage had inadequate strength for 'transonic' flying and the bifurcated exhaust did no favours to the Nene's static thrust so Hawker decided to kill two birds with one stone and build a complete new fuselage for the second P1052 swept wing Sea Hawk prototype. An added bonus was there was sufficient space to incorporate an afterburner, although called reheat at the time, to further improve the available thrust.

No question of what bit was new but doesn't that tail look rather Hunter(ish)!

Although the nose, centre and wings are still P1052 the long duct will make the construction sequence slightly different. In fact the total length of the inlet, EDF and exhaust duct will be a whopping 745 mm long unit. Rather than insert it into a complete fuselage half shell it should be possible to actually use the duct as a 'spine' and simply build the fuselage around it. 

It is the method I used to build my Depron Folland Gnat.

It does rather mean you need the full duct complete before any construction start can be made.

Unfortunately I do have a spare 55 mm EDF so not much progress until that is delivered.☹️  

 

 

[GrumpyGnome]

You sure are a glutton....

[alan p]

11 hours ago, GrumpyGnome said:

You sure are a glutton....

That is a understatement.

Where does the edf fit in the christmas tree, wings can be used to hang the decorations on!!

You have definitly got your teeth into this subject, more strength to your arm you build these quicker than I build a wing.??

[Simon Chaddock]

Gents thanks for the kind comments.

After a bit of thought I decided I could get on and build the inlet part of the duct as it is that which determines the exact position of the EDF.

Actually the intakes were not as wide as those on the standard Sea Hawk so the design did need a slight "tweek".

There are actually 5 parts. The centre, each leg and a bell mouth for each inlet.

It occurred to me the large flat areas would benefit from flued on external stiffening ribs.

The inlet duct is printed in grey PLA with a single 0.3 mm thick wall. With the stiffening ribs it weighs 20g all up.

The ring in front is a test of two short short sections of 55 mm exhaust duct glued together to check the fit.

 

 

[GrumpyGnome]

Love your 3d printing. In 3 years I have successfully printed..... a white 'benchy' boat, a pink 'benchy' boat, a small civilian pilot (VERY heavy). I must learn how to use it properly.

[Simon Chaddock]

Still waiting for the 55 mm EDF to be delivered so all I can do is cut out some of the fuselage formers.

They will have to have their centres cut out to fit around the duct - when it can be built.

 

[Simon Chaddock]

At last the new 55 EDF has arrived so I can proceed to make up the duct but first the bell mouth has to be cut off the EDF.

The now shortened EDF wit he inlet and the first of five Exhaust sections.

  

After over 4 hours more printing the full duct against the fuselage plan.

The nozzle at the end reduces the duct to about 95% of the FSA.

Given the EDF is in virtually the same location as the RR Nene was in the full size it is likely the long exhaust duct probably cost nearly as much thrust as the Sea Hawk's much shorter bifurcated one.

I have not yet be able to find out how much extra thrust the after burner unit actually delivered. Probably not a lot compared to what is expected now.

Now at last I can actually start to build the P1081!

 

[Simon Chaddock]

The first two planks go on, one on each side, with a 24" rule for size.

The planks are not glued on vertically like that but does make a more dramatic picture. ?

 

[Simon Chaddock]

The planks are not difficult to bend, the curve of the fuselage is very gentle, but they do need quite a bit of sanding and 'manipulation' to get a good adjacent fit.

After some hours work including waiting for the glue to dry about 1/2 the planking is done.

 

The problem is that is the relatively easy bit!

I shall have to leave some of the fuselage un planked to be able to run the elevator and aileron servo wires through the fuselage formers.

Soon the fin and tail plane will have to be added. The tail plane is the same as the P1052 but I think this time I will use an individual servo for each elevator.

Edited August 9, 2021 by Simon Chaddock

[Simon Chaddock]

With the wing roots added, at least on the upper surface, it actually starts to look like something.

The underside root skins have to be left off so the aileron servo wire can be run through the fuselage. 

The base of the fin is on too.

It actually goes down through the fuselage top skin and it glued to the duct to ensure it is rigid as it also has to carry the tail plane.

Tail plane next which will include the individual elevator servos. 

 

[Simon Chaddock]

The tail plane with two servo added.

 

For structural reason the servos needed to be as close in as possible which meant they were symmetrically opposite (like ailerons) so a servo reverser was required.

The individual servo wires run down through the fin with one wire to a small and light servo reverser taped to the duct.

The wires are then combined and a single wire run through the formers to what will be the cockpit area.

To my relief it all works as it should.

Wings next. This will allow the aileron servos wires to be run through to the cockpit and then at long last I will be able to finish planking the fuselage.  

Edited August 14, 2021 by Simon Chaddock

[Mike Chantler]

Simon,

I'm planning on doing similar for a 50"  PSS F86 using two puny 4.5g  0.6 kg cm servos in the tailplane.

I've not done any calculations, just winging it, so I'll be rather embarrassed if it fails to pull out of a steep dive on it's maiden(!) Looking at my servos I'm now thinking hmm... rather tiny looking.

 

Have you used this setup before? 

 

[Simon Chaddock]

Mike

Yes twice and vitually identical. A Sea Hawk and the P1052 the swept wing Sea Hawk

Even as EDFs they are light so fly relatively slowly. I am pretty certain the wings would fail before even the tiny elevator servo ran out of power.

My thinking goes like this.

The hinge is really free moving and with the servo close to the surface the linkage is efficient (no snake or long rod!) so virtually all the servo torque is available to deflect the surface.  A 3.7g servo generates 0.35 kg-cm of torque. The horn is 25% longer than the servo arm so the torque at the elevator is actually greater. The centre of pressure of the elevator is no more than one cm from the hinge line so at servo stall it would be resisting nearly half a kg of aerodynamic pressure from the elevator. Just imagine what would happen to the plane if such a force, equal to its total weight, was acting on the tail plane.

It works for me. 

[Mike Chantler]

Thanks, that's a good way to think about it. In that case I may need a bit more torque - but I can get 1kg/cm by going up to 5 cells so may do this to start.

[Simon Chaddock]

Slowly moving on with the wings.

Although basically incredibly simple structures with just 4 pieces each side but holding the thick skin over a shear web relies entirely on the glue which really needs 24 hours to reach full strength.

The trail edge joint is easy enough, apart from all the very messy sanding required to achieve a fine edge, it only needs a few eights to hold it down but no further progress can be made for 24 hours!

Puling the skin over the shear webs down to create a leading edge requires many clamps and metal strips top and bottom to prevent the clamps marking the soft foam. To make matters worse I only have enough clamps and suitable strisp to do one leading edge at a time so its 48 hours before the second one is done. This is stage of progress above.

Then the ailerons have to be cut out and the aileron servo installed with its extended lead running through the hollow wing.

Only then can the wing be glued onto the fuselage which again requires 24 hours to harden before the other side can be glued on.

From cutting out 8 simple pieces of sheet foam (4 identical and two pairs) to having wings fixed on the fuselage at least a week has to pass!  

 

 

 

[Mike Chantler]

There never seem to be enough clamps of the right type for the job lol

[Simon Chaddock]

At last some measurable progress.

The tail feathers are more or less complete.

And the wings are on and all the wires passed through the fuselage formers to the cockpit area.

A lot of filling and sanding will be required to achieve an acceptable surface finish.

Fuselage nose section next.

 

 

[Simon Chaddock]

After many hours the nose is now on.

Just the canopy/battery hatch to construct with quite a bit of filling and sanding as well.

At least in now begins to look like an aeroplane!

Edited August 23, 2021 by Simon Chaddock

[Simon Chaddock]

A little bit further withthe cokpit/battery hatch conctructed and give an initial coat of white to hid the grey as it will be painted a very pale green/blue overall as I beleive was the original when it left Hawkers. The exact shade is difficult to determine as it was only photographed in black and white.

As far as I am aware it only ever flown experimentally so never received any RAF or RN paint scheme.

Taken at what was then RAE  Farnborough.

Pictures are rare simply because it first flew in June 1950 and crashed 10 months later killing Hawkers test pilot in April 1951.

   

[Simon Chaddock]

Nearly there. First coat of the very pale green/blue of the prototype.

 

Under natural light it looks rather greener!

The blemish on the upper rear fuselage just aft of the wing is a moth that settled as I was taking the picture!

Actually there is still quite a bit to do.    

 

[Simon Chaddock]

Now decorated with roundals and the service number on the tail and underneath.

I rushed to try to get it to a complete appearance although unflyable state to take to the DVMFC to compare with the P1052 and Sea Hawk but the paint was not even dry.

Once completed and flown than maybe a Hunter at the same scale to complete the set?

 

[GrumpyGnome]

Looking good Simon!

 

Yeah, may as well do the Hunter.

 

Tried your ROG with my Viper - didn't move a millimetre! Probably the aft strakes digging into the short grass.....

[Simon Chaddock]

GrumpyGnome

I was surprised how easily the P1052 does a ROG.

Apart from being light that bulbous rounded fuselage certainly keeps the point contact down and it also allows the nose to lift a bit as the speed rises before it actually leaves the ground. The Sea Hawk on the other hand simply does not have the thrust.

I haven't tried with the P1081 yet although its long straight rear fuselage may prevent the wing from achieving the necessary AOA to lift off at an achievable slide speed.?  

 

[GrumpyGnome]

I'm looking forward to frost/snow.....

[Eric Robson]

2 hours ago, GrumpyGnome said:

I'm looking forward to frost/snow.....

I'm looking forward to some decent weather, not much about in the N.E. 

Simon,  following with interest in you models, I have built a lot in Depron but since it is hard to come by now I am going to try foam board when the building season comes.