Topic: Hawker P1121 EDF Build

As I mentioned in the M52 build thread I had hoped to start this back in February, but we unexpectedly lost our flying site at the end of January and my building/flying mojo went with it!  However, I continued tinkering with ACAD and after several iterations I decided on using a 70mm size higher powered fan which in turn fixed the size.  Intake and exhaust areas are very close to scale wrt the fuselage/fin, but the tail plane and wing are 105% to get a reasonable wing area and hopefully allow hand-launch.   Length-1280mm; wing span-756mm; wing area 19.6 dm2.   All-moving tail plane, conventional ailerons, no rudder.

The full sized one would have had small anhedral on the wings and a marked dihedral on the tail plane, but I will be going with 3 degrees wing dihedral and a flat tail to make rigging and control easier. 

A few weeks ago I gained access to a CNC router and my enthusiasm was re-ignited.  I have been learning how to use/control the machine and generating 3-D models for the intake and exhaust ducts, I also used the formers to do the fuselage, just because I could!  Anyway, if the balsa skinned fuselage looks half as good as the renderings I’ll be very happy.  I’m still amazed how modern a 50+ year old design looks.

Last night we felt confident enough to try a first “proper” 2-D cut using the CNC router.  Still a lot to learn, but the parts were accurate and although the edges were not as clean as they could/should be, the bits were useable.  I used the same principle I used in the M52 with a 3/32” internal balsa frame built over the plan covered with 1/16” sheet.  To add a bit more stiffness the grain on opposite sides is at 90 degrees.  A little filler/sanding is required and then they will be glassed.

Back to ACAD work this weeked

Been looking forward to this one  Nice CNC work!

Looking forward to this one also Pete
Happy to hear your mojo is restored,we need your input on here mate.
Any news about an alternative site yet??
John

Been looking forward to this one  Nice CNC work!

Thanks.  I'm pretty happy with the CAD side of things now (this is the third one I have done), but we are on a steep learning curve with the machine and doing the CNC cutting ourselves.  Seems that you can read-up everything going, but in the end it is all down to experience.   
I'm working on the next set of parts so we can cut them next week and build some more knowledge before moving on to making the 3-D ducting and canopy tools.

Looking forward to this one also Pete
Happy to hear your mojo is restored,we need your input on here mate.
Any news about an alternative site yet??
John

Hiya John
I would say my mojo index is currently running at 7.5 
Our group leader is talking to a Farmer about a potential site today.......   But we have identified 3 other possibles so I'm sure something will come up soon.
When are you down this way again?  Tea and buns will be ready and maybe a pint down the Blue too.

Am already considering colour schemes, but am going to have a struggle relating it to the FAA.  I have a 1/72 plastic vac-form kit and I got potential RAF colours from that. 
One thing for sure, this build won't be a quick as the M52, but the same invitation applies though, anyone is very welcome to chip in about anything.

Pete

And the Saro?

Soon Pete,soon
John

Afraid that the SR177 still not fully checked out, but we do have a new flying field as of yesterday.

Have been rather busy at work since the last post, but have managed to slowly continue building experience using the 3D software and the CNC machine.  As a first exercise we made some NACA duct plugs for vac-forming.  Tried Balsa and MDF: MDF gives the best finish off the machine, but Balsa can be cut far quicker.

Moving on to more demanding work I decided to make the canopy plug next.  There is only a limited depth of cut depending on the length of the tool shank, so thicker items have to be sliced into manageable sheets.  It took many hours to generate the 3D canopy from just a side, a plan view and 2 cross-sections.  This was sliced into 25mm thick files and then glued together with PVA. 
Dope, sanding sealer and filler-primer were applied, sanding between applications to get a smooth surface for vac forming.  I added some tape to generate a frame work then we had a practise with styrene then immediately made a canopy and finally made another styrene mould to fill with plaster of paris for future canopies  - the vac-forming process quickly causes the balsa plug finish to deteriorate.

Attention was then turned to the exhaust duct – after manually splitting the duct into left and right sides and adding an overlap for gluing it was the same process as the canopy, just bigger files. 

One side is finished and the other side will be completed tomorrow ready to vac-form on Tuesday.  This evening I started on the intake duct and all the cutter files are done.  Looks like it will take 3 ½ hours machining time plus an hour set-up to make the 4 slices, so will be making the intake stuff in stages.  Also there is an under cut on the front 40mm of the intake which will be done by hand.

Hey Pete, haven't you finished this yet? 

In all seriousness though, you're showing quite an impressive array of skills here. The canopy plug and ducting in particular looks excellent!

Cheers Jamie........I would say "bet it flies before your Meteor"  , but experience shows that I never seem to get around to flying them for a year after finishing!
Took me a while to get my head around surfacing in the 3D software, then we had to learn how to use the machine - 20% reading, 80% "playing around" gaining experience and trying different materials.  I'm very lucky to have free access to the machine though, and will be able to use an A0 scanner/plotter soon as well  
After I posted last night I realised that the intake will be too long for the vac former, so will have to have a re-think    Delayed BH Monday for me today (was working) so I'm off to finish the exhaust duct now which will then validate the way I have done the overlap on the 2 sides.

Pete

Hehe so when will your skills be available to purchase? 

Hehe so when will your skills be available to purchase? 

Depends what you want doing 

Hi Dizz,
Only just spotted your new thread and I'll certainly be following progress. Good to hear that you've secured a new flying field by the way.
Colour schemes will be more or less 'what-ifs' on this so maybe you can squeeze in some Naval influence?! 
Paul W.

Depends what you want doing 

2D stuff... flap and slat tracks. Can your machine route fibreglass board? 

Lovely aeroplane and continuing your "project cancelled" series. Have you flown the Miles M52 yet?

Hi Dizz,
Only just spotted your new thread and I'll certainly be following progress. Good to hear that you've secured a new flying field by the way.
Colour schemes will be more or less 'what-ifs' on this so maybe you can squeeze in some Naval influence?!  
Paul W.rnoon on the way home.

The new site is good news, but my EDFs deemed too noisy    Still great to have somewhere to fly though  

2D stuff... flap and slat tracks. Can your machine route fibreglass board?  

Easy-peasy.  Just a question of getting the right cutting/spindle speeds.  Did some Styrene sheet this afternoon on the way home.

Lovely aeroplane and continuing your "project cancelled" series. Have you flown the Miles M52 yet?

Afraid not, but it will happen  (one day!  )  There are a few more on my list after this one too.....................just need o pull my finger out and fly the already built ones!

Vac-forming the exhaust duct on Friday.

Not much to show, but exhaust ducting came out well and have made the first section of the intake duct plug.  Another couple weeks of ACAD and CNC and I'll be into building proper.
Dizz

Exhaust ducting has been vac formed.

It takes about 1hr 20 to machine each part that make up the plugs and I’m limited when I’m able to use the CNC router (work), so progress has been rather slow.  The complete intake duct was too long to fit in the vac-former so I had to electronically chop it up and re-do the 3D models.  Anyway, just one final lump of balsa to cut now and that will get done on Tuesday.  I can then concentrate on finishing drafting the fuselage and wing stuff.

The under-cut on the front intake section came out pretty good on the vac-former.  The depth of the “pull” and the sharp angle meant that the plastic is a little thinner than ideal in places, but it has worked.  Sides were taped together then a drop of MEK run down the overlap to weld the plastic together.  This has almost melted right through the thin plastic at one point on the top seam, but I have another set of parts ready to make a second section later.  I will also apply a strip of diamond tape down the outside of the joints to add a little strength to the seam.

Hi Pete,
You are making good progress - design-wise, this is definitely a case of starting with the ducting and adding everything else aircraft-shaped to it.
Your earlier comment reference edf 'too noisy to fly', I have to admit that I voluntarily stopped flying my 50mm edf Hawk, which sounded pretty much as I would imagine a baby elephant would with toothache...
Paul W.

Hi Pete

Having see the drawings on your laptop, it's good to see some construction going on.  Looks like some nice CnC cutting.  I'm fired up again about my Hunter now!  Be in touch! 

PB

Cheers Paul.  The inside to out approach worked with the M52, speed of progress on this one is being driven by learning the CNC machine and work commitments.

Going to try cutting ply next week Pat.  I have some new bits on the way to try as well, so by the time you are ready we will be too.

Back to this week's efforts:

The first side is made from 2 x 25mm thick slices and finished the same way as the previous plugs with sanding sealer and filler/primer.
 
I tried a different finishing method for the second intake in an attempt to avoid the paint sticking to the plastic when vac-forming if too much heat is applied.  After the dinks were filled and the plug was wiped over with 600 grade wet & dry, the surfaces in contact with the plastic were smeared with medium cyano.  Once it had hardened the plug was rubbed back and a further layer of cyano applied.  This was finished off with a final wet and dry rub down and extra fine wire wool.  The surface is rock hard and very smooth, will find out if it works any better under heat and pressure on Tuesday.  Various types of tape were used to mark cut lines – the primer half has extra tape to create an overlap step.  

I had a couple of hours free last Thursday so I made a 3D model of the nose cone and the associated cutter files.  It only took an hour yesterday to machine the 3 slices from scrap block then it got the cyano hardened finish.  Am rather pleased with it actually, the intention is to hollow with a dremel permagrit bit before fitting, but for the time being I have an Armour Piercing nose  
 

Am very pleased with the intake vac-formings too.  The cyano finish is the best one to use, the plug just dropped out without any effort.
As I already had the ACAD drawings to make the plugs I cnc’ed formers for each end of the ducts to help with assembly alignment. 
MEK down the join overlap and diamond tape over the top.  Once the join had set the formers were removed and the ends cleaned up. 
Intake duct the same way and temporarily mated to the front section.  Once installed in the fuselage the ends will be trimmed to length against the formers.

Discovered the other day that the P1121 was going to be named the Hurricane II. 
Tracked down a RAF Year Book 1976 on e-bay last weekend with a "what if" feature that covers the SR177, P1121 and TSR2. 
Pete

Hi Pete,
It is that self-same illustration that got me interested in doing a P.1121: I was loaned that year-book some 18 months ago by an ex-Lanc pilot that lives locally. The 'what-if' feature was pretty strong I thought - not that it changed anything!
Paul W.

After nearly 4 months when work and doing stuff for other people (building and finishing fun fighters) took priority I have managed to get back to my P1121.  I was out of the country with work for the first 3 weeks this month and I was able to crack and finish the CAD stuff.  Got some time on the CNC machine today and started cutting wood.  Also printed the fuselage and wing plans on a large A0 printer.  There are another 5 sheets to go and hopefully will be able to do them next Monday or Tuesday, so building will start soon 
Whilst I was away I picked up 4x Cyclone Red 4300kV 64mm EDF units and they will go in this winter's project - a big bomber 
Pete

Glad to see you are back on the case mate! Hunter project has stalled at the moment... 

Hi Pat - this one took a bit of a back seat over the Summer too, but get your skates on and I'll be able to cut it at Christmas when I do the "bomber"
Anyway I got the last of my CNC'ing done last night and also printed a full-size plan to build over.  Confession time – should have printed it earlier as it is going to be rather large for a 70mm fan (wing area is fine though, maybe ok for hand launches )– time to re-visit the power plant and up the Watts a bit.  I spent this evening releasing the parts and sanding off the tabs.  Formers are a good fit on the keels and a test fit of the ducting looks good too, but I need to open up the stringer slots on the edges of the formers to fit the bass wood I have (I thought it was 2mm square, but it is 2.5mm) and adjust the fan bearers to give better clearance on the Wemo mini fan shroud.  Building proper starts again this weekend with the fuselage.
Colour scheme dilema as well: I quire like the Dark green/slate grey/light grey one as in the apinting above, but brand loyalty keeps bringing me back to FAA dark sea grey on top with white undersides (Sea Hawk).  Still, not the decision time yet and I probably wont be at the painting stage for another 4-6 weeks so plenty of time.

If anyone followed my M52 build this will be familiar, I’m going to be building form the inside out again.  Formers glued to 2mm ply keels over the plan.  The structure at this stage is rather fragile and due to slight warping of the ply keels it isn’t very true either.  This time I added triangular fillets to keep the formers perpendicular.  To add a little stiffness for handling I glued on a few 2mm stringers.  I learnt from building the West Wings Hawk a couple of years ago that even though the fuselage is pinned down whilst the stringers are added, when released the fuselage will bow, so I’m conscious of that now and try to avoid inducing bending stresses.

The intake area is quite complicated.  I have tried to make the lip as strong as I can to take the landing knocks with additional ply doublers and using the original’s full depth splitter.  I am using the same method of attaching the wings as the M52: 3.2mm square hard wood stub spars into pockets.

The left fan bearer will also carry the elevator servo (HS65MG).  Control will be via a short, well supported snake and ball joints.  I made the elevator bushes last time I had the lathe out, but I have a bit more work to do to the pivot rod and horn yet.  

Having got to this stage I glued the right hand ply keels to the structure and weighed it all down flat on the building board whilst the pva glue dried.  Gluing 2 thin parts together like that has straightened out the wraps and added enough strength to keep it straight whilst adding the ducts and other formers.

I trimmed the intake duct to fit around the splitter and eased the vac-forming into place.  I  hade only taped the front D-section in place at this stage to allow some room for manoeuvre.  Once I was happy with the fit I started adding the fuselage right side formers.  It was easy to keep the keels straight so I glued the duct in place. This immediately made the fuselage rigid and much easier to work on.  The duct is a very good fit around the d-section and the fan face, but it is a bit out on a couple of formers – not sure why because it should an exact fit all the way along.

The plastic has been cut/rubbed back flush with the ply – I am very pleased with the fit here.  I have wicked some MEK into the D-section joint and that has been left to set overnight.

2.5mm CNC’ed balsa was glued to the former to take the front of the fan shroud.  Next job is to make and fit the elevator gear.

Doh!

Have realised why those 2 formers don't fit the duct.  I used a radius tool in Rhino to smooth the transition from the slope to the circular run into the fan after I had already exported the cross sections back into ACAD.   
Too late to do anything about it now though.

Elevator horn from some scrap brass sheet soldered to the piano wire rod.  The bearing bushes were turned from ali bar and glued into the 6mm balsa supports.  Have used wheel collets to stop sideways movement.  The slot on the former had to be opened up to clear the ball link, but I knew I would have to make adjustments as the concept I had in my mind’s eye developed.  The elevator control rigged roughly square and at neutral which gives plenty of potential movement and I’m pretty pleased with it.  All will disappear forever when the fuselage is sheeted.

With that job complete I was able to install the exhaust duct and remaining rear formers. I also added the other forward formers and a 1/32” ply battery tray.  This overlaps the intake to help carry the loads from the cockpit through to the fuselage proper as well as providing something for the battery to sit on.

Got a busy week on at work coming up so wont be able to do any more until next weekend.

This evening I sheeted the nose and made a start on the fuselage (not a favourite task for me).  Am using 3/32” soft balsa and will use a permagrit bar to achieve a smooth, flowing surface before glassing.
I was curious to find out if the intake duct was stiff enough when the fan started sucking, so I just fired it up just now   There is a lot of air going down that intake!  All sorts of stuff started moving on the bench but fortunately nothing was ingested.  Even with it exhausting directly into the fan bay it felt as if there will be plenty enough thrust when it is properly installed and no sign of the duct collapsing.  I also did a quick check weigh and it looks like it will come out at about 1.7kg with a 44000mAh 4S pack.
Think I'll leave the sheeting for the time being so I can still modify inside the fuselage as I'm not 100% sure where I'm going to put the ESC (which will need and cooling air supply).  Wings tomorrow and then I'll finally be able to see what it will look like rather than interpreting a computer screen 

Ribs and 1/8” square bass wood spars glued together over the plan for both wings………that is all I managed to do today.  
Next building session not until Wednesday evening' so might be able to see what it looks like put together then.

I did a little last night and have spent a couple more hours on it this evening.  1/16” hard balsa sheer web has been applied to both spars whilst the structure still pinned to the board, also tip blocks and fillets.  
Big push tomorrow and over the weekend.
Anyone feel free to chip in if you want 
Pete

I'm still watching Pete, I've just had nothing to add as yet! 

Any further thoughts on fan size / power loading from your initial "ooh it's a bit big" moment?

Hi Pete,
Still here too - that’s good progress you've made.   The airframe really starts to come alive once the power-plant has run, doesn’t it?  Can I compare notes and ask what scale you decided to proceed at?
Paul W.

I was beginning to feel a bit insecure with lots of people watching but not saying anything 

Have been back on the build for a week now and should get the wings built this w/e for sure and possibly the fuselage sheeted too depending on the weather and if I can get out or not.  I need to crack on because I have another build that I'm itching to start 
I am going to use the ARC 28-47-1 motor in a wemo mini fan and a 4S 4000 30C pack.  I ran it on the test stand 9 months ago and the figures in my little black book are 1030W steady and 1300g thrust.  Here are a couple of photos for comparison with a Graupner Typhoon and a P3 EF-16, so t will be big, put not massive.
Will be 1220mm long with 750mm wingspan and wing area of 20.2 dm².  I'm guessing a wing loading about 85gdm^-2 - my EF16 is ~73gdm^-2.  I increased the wing area from scale so using the fuselage length quoted in British Secret Projects - Jet Fighters since 1950 the scale is 1:15.75 Paul.  That was arrived at by adjusting the 3-view in ACAD until the intake and exhaust areas based on the fan roughly matched up with the drawing.  My model intake is 3 mm too tall against scale, but nobody would have known until reading this 

Stub spar guides from scrap balsa.

Bottom surfaces made up from 1/16” medium-soft balsa sheet edge joined using the clear tape and cyano method.   Both surfaces sanded smooth with a rubber sanding block before accurately marking the rib and spar positions.  The TE was chamfered with a razor plane and the sanding block to accept the top sheeting idc.
The front of the tip blocks shaped to match the last ribs, then the assembly was glued in place on the sheeting with pva and cyano.  Wings left weighed down flat on the building board for glue to set.  
The leading edges were squared off with the long Permagrit bar and tops of the tip blocks shaped with a razor plane/Permagrit/Wet and Dry paper.

Decision time tomorrow whether to go with the production dog-toothed LE and a Strike colour scheme or do a duck egg green prototype.

Hi Pete,
It’s interesting to compare design decisions.  All my numbers are in imperial I’m afraid, scale 1:14 – wing area 2.4 sq ft, span 31.5”, length 55.5”: although my drawing is in Metric…
As you’ll recall, mine was in the design-stage when you mentioned the aircraft on your M52 thread but it has now progressed rapidly from screen to model, due to my having entrusted the plan and laser parts to a friend of mine for a check-build (hence the rather more rapid progress than I’m used to making!) 
On the test rig, the Het 2W20/Minifan unit is giving a static thrust, measured by my wife’s electronic kitchen scales, of a little over 1200g, from a 4 amp 20C pack (this needs upgrading).  The fan first ran in the airframe two weeks ago but I still haven’t got round to re-checking the installed performance. The airframe is complete and has now come back to me for prepping and glassing.  I've gone for the saw-tooth wing and will probably do a development prototype colour scheme in silver.
Paul W.