quorneng

I was given about 20 sheet of 500 x 1200 5mm thick XPS in both grey and green. It was being used as a underlay for laminate flooring.
Most definitely not Depron being much softer yet more brittle but at least a bit lighter.

I judged that with a reasonably compact subject it would be possible to make an EDF using just the strength of the XPS with no reinforcing so hopefully it would be really light.
I happened to have a spare but rather old and low powered (by todays standard) 55 mm EDF but also light and quite efficient at turning its modest Watts into thrust,
The Hawker Sea Hawk has some features that appeared to suit my criteria. Straight wing, so slow flying, and with both its inlet and exhaust bifurcated it meant a substantial wing root at the point of maximum bending.
The scale inlet and exhaust area showed an appropriate difference to suit an EDF so the scale was set that the twin exhaust area was 95% of the 55mm SFA to give a good static thrust. It would have a span of 1050 mm.
The next task was to use 3D printing to create both the inlet and exhaust duct. I hoped printing would create an efficient profile given the low power of the EDF.
As I hoped the exhaust duct gave a gradually reducing section from the 55 mm EDF diameter to the required exhaust nozzle areas.

'Vase' printed in PLA as a single piece with a 0.3 mm single wall.
The inlet proved to be harder as the Nene turbojet used a double sided compressor so although the wing root inlet area looked adequate the duct was very short and certainly not a 'direct path' airflow as required by any EDF

Again a 0.3 mm single wall but it had to be printed in 3 pieces glued together
Compared to the exhaust I was concerned it would be restrictive to the EDF. I could see why the Sea Hawk is not a popular EDF subject despite its generous diameter fuselage..
The complete duct now glued onto the EDF. .
.
On test it gave just over 11 oz thrust at 25A on a 3s. The Sea Hawk was going to have to be light to work at all.
Next is the fuselage centre section which contains the complete duct. I chose to build it it as a planked half shell over the plan.

The end result is light but rather fiddly to do although with the thick 5 mm planks it should end up plenty rigid enough.
Once the half shell is complete it can be lifted from the plan and the complete duct inserted exactly half way into the shell.

Fortunately XPS is easy to both trim and to add to so getting the duct to fit exactly into the formers was not too much of a chore.
The duct is then glued in and the other half of the formers added.
At this point I started to have second thoughts as the the practicality of this build.


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solentlife

If its anything like the stuff we have over here ..... smooth surface one side ... grooved on other ? I found it makes good formers as its stiffer or for laminating to Depron for added stiffness. But on its own - was prone to easy fracture ...

Sanding produced a fine powder that got everywhere !!



I did use it to produce my SE5 .... and that has survived ...



Laminated fuselage is really strong ...





Watching with interest ......

quorneng

Solentlife
Yes it is the smooth/rigged stuff and it is a bit brittle but I am building a hollow structure so will hopefully be very light with adequate strength for its weight.
It will of course be a belly lander which on grass which greatly reduces any shock loading, up to a point!

A little more progress.
Completed the skin on the centre section and started on the wing root fairing.

The EDF wires have been extended forward to what will be the cockpit but a portion of the root skin will have to be left off to be able to run the aileron and elevator servo wires when those bits are built.

quorneng

Still pushing on.
The skin around the LH inlet completed.

The same around the LH exhaust.

Note the small piece of 3 mm white Depron over the exhaust duct.
I concentrated on one side as I was working out what to do as I went along. The RH side should be easier.
Once the centre section is complete next will be the wings. They should be very simple, just a complete top and bottom skin glued down over two XPS shear webs to give the scale(ish) wing section. No spar or wing ribs. It will rely entirely on the strength of the foam skin.
Once the glue is dry the ailerons can be simply cut out. The aileron servo will be 'inserted' through cut outs in the wing underside and the servo wires passed down through the hollow wing.
To be even more extreme I have determined that using Technicqll glue a simple edge to edge butt joint is as strong as the foam itself.
Provided the two surfaces line up exactly the wing will be simply glued on to the centre section.
Just as well the Sea Hawk has a reasonably thick wing.

solentlife

Foam spar is fine ... my SE5 has exactly that with NO wood or CF at all ...



White 3mm depron top skin formed over the foam 6 x 6mm spar





Years later ... even after a few bad landings / even a nose in ... that wing is still good.



I modified from his flat plate wings ... and it literally can fly slower than I walk !

quorneng

The LH wing. I had to start with one as didn't have enough clamps to do two at once!

Just top and bottom one piece skins, all identical.
Very simple in theory but not quite so easy to do in practise as a significant area of the inside of each skin has to be sanded down to give a fine trailing edge.
The aileron is cut out and the wing tip glued in place.

Next the aileron servo is glued in via a cut out in the lower wing and servo wire passed though the wing it is ready to be glued onto the centre section.

Note the large area of the wing root fairing left open to pass the servo wire through the formers
The wing is so thin that the aileron servo lies flush with the wing underside.
A modest amount of light weight filler is used to 'blend in' the joint.

In fact the XPS is so soft that the smooth surface readily picks up the odd 'ding' even during construction!
Now to do the other wing.
. .

solentlife

Yep .... when I was cutting - even when one hand was resting on it - I had dents from thumb / finger tips !

Sadly - the green foam sheet is not so easy to buy here now .. the shops now only take telephone orders and you collect at door - I don't speak Latvia - so cannot order, and second even before lockdown - I didn't see it on the shelves anymore - it was replaced by cheaper stuff that looked more like coarse woolly cork ...

Looking good as always Q.

quorneng

The RH wing under construction. It needs a lot of clamps!

The RH wing added to the centre section.

It had to sit like that over night for the glue to dry.
Time to start the rear fuselage. A fairly simple concept as half shell over the plan.

Although the relatively thick foam made planking the sharply tapered profile not so easy.
Again I resorted to bit of 3 mm Depron to line the exhaust cut out.

Lightweight filler again proved its worth.
Eventually the rear fuselage could be glued to the centre section.

Note there was quite a bit of corrective work required to get a smooth top fuselage line.
Next will be the 'tail feathers'. These like the wing will be two skins over a sear web but all in 3 mm Depron.

The big question is whether rather inefficient ducting will provide enough thrust for the relatively big but light airframe
This shows just how tiny the 50 mm EDF is relative to the Sea Hawk's rather portly fuselage.

I could have used a bigger EDF but then scale inlet and exhaust duct areas would be seriously restrictive..
I am now starting to see why the Sea Hawk is not a common EDF model.

quorneng

The tail feathers components in 3 mm Depron

The elevator line is straight the halves can be connected with a short glass fibre tube.
The elevator servo is buried in the lower fin. The rudder is fixed.

Once the extended elevator servo wire, like the aileron wires, is passed through all the formers to the cockpit area the final areas of the fuselage skin can be closed up.
Just the section still to do.
The intention is to make the removable canopy the only hatch to access the battery and rx. Everything else is permanently built in and will have to be cut out for access.

quorneng

Started to build the nose section. Like the rear fuselage it starts planking a half shell over the formers.

When the half shell is as complete as it can be it is lifter and the other side completed.
It can then be glued on.

The canopy windscreen frame is printed and then 'filled in' with 3mm Depron.
The big nose cone is also printed.

A screen dump of the CURA picture showing its single wall 'vase' printed structure.
It is light at just 3g and although certainly not crash proof it is simple to print an replacement.
Just the canopy/hatch to do.

solentlife

You are a master !!

Don Sims

Another fantastic build.

quorneng

To ensure there is enough room to get at the battery the canopy hatch is wider than the canopy itself.

The battery will be positioned a bit to the LH side in the cockpit to counter the weight of the fingered 30A ESC in the RH cockpit wall.
The ESC fingers stick though the foam into the airstream just ahead of the air intake.
The canopy hatch is built 'in situ' and cut out when dry.

The hatch is retained by a peg at the windscreen and a magnet at the rear.

The Navy paint scheme is relatively simple. Dark Sea Grey upper and Sky Blue under.
The only issue is to achieve the required shades in Match Pot emulsions!


Household emulsion (US latex) paint although entirely foam safe has a very matt finish so a light spray of 'rattle can' clear lacquer gives it a suitable 'sheen'. Needs to be several 'mist' layers as it is only the paint coat that stops the lacquer eating the foam.
With an 1800mAh 3s on board it weights 539 g (19 oz).
Not too bad for a 1040 mm (41") span EDF but with only 250 g of thrust it will have to rely heavily on its aerodynamically clean airframe.
We shall see.


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solentlife

Fingers crossed !

quorneng

Well it does fly!
Gentle and sedate with adequate power, a bit like the full size.
Mild aerobatics included
Hawker put some swept wings on a Sea Hawk as the P1052. They even did some carrier trials wit it but decided against production.
Even more surprising is it still exists in the Fleet Air Arm museum but not a permanent display.

I wonder?

solentlife

Yet again - Master !!

Very nice.

Don Sims

It flew great and seemed to float along forever on the landing. Another well done model! Thanks for posting your build.

quorneng

Thank you for the kind words.
The Sea Hawk did fly well but what you can't hear on the video was the rather convoluted inlet path causing some change in the EDF note at high angle of attack so I considered redesigning the inlet to give a less disturbed path.
Rather than simply build another Sea Hawk, extracting the old duct would completely destroy the fuselage anyway, I decided to build the swept wing version P1052. The fuselage was identical so it really was just a case of building another. The wings were very simple to make anyway and I happened to have a another spare 55 mm EDF.
I judged that if the EDF was moved back the inlet geometry could be significantly improved which would more than compensate for any loss of thrust from the slightly more acute bifurcated exhaust geometry.
Much of the CAD design could be simply adjusted so printing a complete new duct was not to much of a chore.
The P1052 duct.

The duct in the Sea Hawk.

The EDFs were not identical but the new duct was not short of thrust.
That was the interesting bit next the rather more tedious build another airframe.
At least I would have both flyable for comparison.
The P1052 first flew in November 1948 and 3 were built. Two to fly and one for structural testing so it was quite serious proposal.
There is even a picture of a P1052 with a hook added landing on HMS Eagle in 1952.

quorneng

On with the construction of the Swept Wing Sea Hawk P1052.
Built in the same way as the Sea Hawk so I more or less knew what each step would involve. This time I also printed an inlet bell mouth which significantly stiffened the opening.

As before the complete duct inserted into half the centre section.

The completed centre section showing the inlets.

The picture does rather highlight just how 'bulky' the fuselage is compared to the exhaust area.

The rest of the fuselage is pure Sea Hawk except the tail plane which ended up being swept like the wing.
There is a quite a story as to how this happened.
Structural testing of the 3rd airframe suggested the standard Sea Hawk rear fuselage would need strengthening to withstand the full performance potential of the swept wings.
Although both the P1052s had flown Hawker decided to leave the first flying to continue testing but simply replaced the rear fuselage of the second with a completely new design with a straight through jet pipe and a redesigned fin and swept tail plane. It was given a new type number P1081.
Just out of the shop and unpainted.

Still basically a bulky Sea Hawk fuselage but its tail assembly does now look familiar and rather Hunter(ish).
The redundant rear fuselage was indeed strengthened and given the same swept tail plane as the P1081. it was then re fitted to the first P1052 to allow it to reach its full performance. Neat!
First flown in June 1950 the thrust benefit from the single exhaust did give the P1081 a higher performance and was expected to be able to go supersonic in a dive unfortunately it only lasted 10 months. In a high speed dive Hawker's chief test pilot lost control and ejected but was killed when the ejection seat failed to perform correctly. Not the first test pilot to die testing in the early 1950s.

quorneng

The swept tail plane of the P1052 presented a bit of a problem due to the acute hinge line and the fact I already installed a single servo in the tail before thinking about it.

Eventually solved with a rather inelegant combined rod & cross link. It should be adequate as it is a 'lightweight'.
The wings were built in exactly the same way as the Sea Hawk but simply using swept skins.

The swept wings of slightly smaller span make the Sea Hawk fuselage look even fatter!

solentlife

I know you would already consider this ... but ...

that elevator cross link - it will need to be very stable to avoid it twisting under the elevator resistance on the long arm outer part ....

quorneng

Solentlife
I agree but it appears to be adequate. At the stall limit of the servo at least one half of the elevator moves.
The nose/cockpit is a direct copy of the Sea Hawk.


As with the Sea Hawk the hatch part is slightly offset so it gives access to the battery which will be offset to the left to counter the weight of the ESC in the RH cockpit wall.
It will be painted in standard RN colours, as the full size P1052 is currently, although when originally first flown it was painted a very pale green/blue typical of Hawker prototypes of that era.

quorneng

About the most difficult part of the paint scheme is keeping a neat line between the very contrasting colours.


Self adhesive decals, although not quite the right size, and a paper printed cut out serial number.
As for the Sea Hawk given a tight spray of clear lacquer for a bit of 'sheen' and to make sure the markings stay on!
Slightly lighter than the Sea Hawk and more thrust so it should fly but of course the exact CofG will have to be guesstimated.
The Lemon stab rx does help to reduce stress on the maiden.
We shall see.
Whilst building this an alarming thought crossed my mind. What if I built the P1081, the same but with a straight though jet pipe and then the prototype Hunter.
I would then have the complete 'development' set!

quorneng

As I hoped the P1082 Swept Wing sea Hawk" does indeed fly.
The rather better static thrust to weight ratio combined with the improved breathing of the inlet duct as speed has given it quite a performance edge over the Sea Hawk.
Probably its best party trick is an unassisted slide take off which it does really quite well.
A single circuit flight!

Don Sims

Great takeoff and smooth landing. lad to see it flies.