Topic: Hawker P1091 EDf Build

Well I have done it again and started building yet another EDF whilst I still haven’t properly finished or flown the previous projects.  I had planned to clear everything away during the summer and get the assorted bits and pieces needed to do my 1:9 scale Viggen (for a Stumax 110-52 EDF on 12S) next winter………………………..but once I got my hands on the fan I couldn’t resist making a start and have actually done quite a lot.  Unfortunately the 120Amp HV ESC failed during installed testing and had to go back to the USA for repair, so progress has now ground to a halt until it is returned.  I should have turned to the Vulcan and P1154 design, but whilst thumbing through “British Secret Projects – Jet Fighters Since 1950” I came across a small 3-view of a potential Hawker Hunter development, the P1091.  It looked a suitable candidate for my “planes that never flew” theme so I did a few what-ifs in ACAD and the numbers looked good for a 70mm fan.  PDR recently acquired a pre-owned WestWings Hunter so that prompted me to look at adapting the kit for the delta wing.  Scaling the P1091 3-view to match the WW Hunter fuselage diameter the wing area came 25% bigger than the Hunter, so hand launching should be OK.  It was an easy job to loose the extra fuselage length behind the TE, but the nose and intake area would have involved a lot of work, so I stuck with the kit dimensions.  Length will be 857mm (33.75”), wing span 663mm (26.1”) and wing area 20.8dm².  Power from a Wemotec minifan and HET 2W-20 on 4S with an 80Amp ESC – all stuff I already lying around from previous donor aircraft.  I also have 2 x Hitec HS65MG servos spare, but I think I’ll go for something bigger as the elevons are fairly large and I have a feeling that it could turn out to be quite fast.
The last .png shows my wing outline in blue, but it doesn't show up too well.

I e-mailed Peter S at WW to let him know what I was going to do to one of his kits and he very kindly sent me the front fuselage formers and a .dwg of the remainder.  This has helped massively and given me a good start on drawing the new formers F8 - F12 to match the wing root.  I have drawn 90% of the wing and have made a start on the formers, hopefully I will get them complete by Tuesday evening so I can cut the ply parts on the CNC router and the balsa bits on the CNC laser cutters I have access to.  Having spent several months learning 2D and 3D cutting on the router, I’m having to start again with the laser.  By means of a learning test piece I did the fin structure with it yesterday.  It is basically quite easy to set to work because the computer sees it as a printer rather than having to convert the vector drawings to g-code, however the difficult part is in getting the power, speed and focus point right to get a clean cut.  Yesterday I didn’t get it correct and ended up with tapered and burnt edges, but as it will be hidden I used it anyway.  1/32” hard balsa covered with 1/16” medium sheet, just like I did with the SR177, M52 and P1091.  Classic Hawker shape following the same lines as many other designs.
 
I have a few days off next week before Weston Park and I hope to get the construction largely complete by then - have to really because there is a Buccaneer kit heading my way in a month or so 

Watching with interest....

Same here, nice one Dizz

Cracked a lot of ACAD stuff last night but still have some tweaks to add to the wing ribs so they will have to wait until Thursday, however everything else I need to change has been done so I called in on the way home and did some cutting.  Finding it difficult finding the best settings for the laser and wasting a lot of balsa, but did manage to achieve some 1/16” balsa sheeting for the rear fuselage skin.   Went back to using the router for the 2mm ply modified fuselage formers.  Made the forward fuselage frame (stock) this evening – each side is built over the plan then glued together.

Was away over the weekend, but before I went I made the 2 fuselage halves.  You can see the ACAD modified rear fuselage that looses 2 formers printed and stuck over the plan.  I have some more drawing to do next to make an angled rib for the air intake.

Looking good Pete 

Cheers Jamie.....
I was away over the weekend, but before I went I made the 2 fuselage halves.  You can see the ACAD modified rear fuselage that looses 2 formers printed and stuck over the plan.  I have some more drawing to do next to make an angled rib for the air intake.

I took the .dwg of the inboard ribs and did some stuff to generate a 3D model in Rhino then took a section where I want the intake support rib to run.  This section was then exported back into ACAD and I added some slots for the tabs on the intake formers.  At this point I realised that I had messed up on the depth of the wing thickness on the formers  (they are the same depth as rib 2 and don’t allow for the taper on the surface).  It is only 2mm max and I’ll be able to bodge that with some balsa strip. 
I printed the angled rib on card for a check fit and that seems OK, so I will use that as a template to cut 4 from 1/16” balsa (2 to go on the fuselage, 2 to go into the wing).
 
I'll be able to make the wings and elevons, but I won't be able to do anything to the fuz until the ducting arrives as that needs to be fitted before the fuselage halves are joined.........................as it happens I have heard that the Viggen 120A ESC should be back by the weekend 

Cut the angled intake ribs and glued to fuselage.  Then glued the wing root rib parts together on top of this to ensure a good fit.  Left wing structure built over the drawing, when the glue had dried I temporarily lifted it off the building board for a check against the fuselage which seemed ok.  With the wing pinned back flat on the board I added 1/16” and 1/32” balsa shear webbing both sides of the 1/8” square bass wood spars.   This has formed a box for the fuselage former tabs to glue into in due course.  (Rear spar has also had balsa shear webs fitted).

Slotted elevon spars and leading edges from hard 1/8” balsa, glued in place with medium cyano and Gorilla Glue one pin-width apart to help when I cut them free after glassing.  The wing skeletons proved to be pretty stiff and strong when I lifted them from the building board.  1/16” balsa sheet edge joined and then marked to show where the structure was to go.  This was then held in the correct position and secured to the skin by wicking thin cyano along all the edges.  Trailing edge and top of the spars all sanded level with a long perma-grit bar then balsa LE added.  Previously CNC’ed 4mm ply HS125MG mount glued in place and a slot cut for the horn – servos centred and screwed in place to be lost for ever once the top skin goes on.  Got carried away and added some lightening holes, not sure why other than I saw my Soft-Bore tools whilst looking for some elastic bands to mock-up the model. 

Seems like I have inadvertently made a balsa/ply Squall!  However.........................


if you substitute a sharp pointy nose for the Hunter cockpit and squint a bit there is a hint of the FD2.
Well there is for me anyway 

Is that a flat bottomed section?

Hi Pete,
Great to see another unusual subject taking shape. She is looking very good indeed and those are very professional-looking lightening holes! 
Paul W. 

Is that a flat bottomed section?

Not quite at the root - Don Ayres A7520, but it is at the tip - NACA-69 (not that it makes any difference at 85mm chord).  7.5% thickness along the span.
I did the wing using Profili Pro.


Pete

Hi Pete,
Great to see another unusual subject taking shape. She is looking very good indeed and those are very professional-looking lightening holes! 
Paul W.

I think they look good too Paul 


I'll probably get the wing/elevons glassed this weekend ready to fit, but then I'll have to wait for the ducting before I can go any further.  Woodsprings is actually next weekend (I got mixed up with something else later in July when we spoke the other day) and then the Viggen ESC should be back from CC, so not sure which will get priority - probably this because the Viggen is a winter build 


Going to assemble the motor/fan this evening.


Pete

Hi Pete,
That 'next weekend' date for WW's is for the public show?  The E-Fly being on the 21st August IIRC.  Out of interest, does the section incorporate reflex?
Paul W.

True genius buddy

Hi Pete,
That 'next weekend' date for WW's is for the public show?  The E-Fly being on the 21st August IIRC.  Out of interest, does the section incorporate reflex?
Paul W.

Yep, it is the 2 day public event; I'll be camping there with the fun fighter team for the w/e.  I'll be up for the e-fly-in too.  There was a section with reflex that caught my eye, but I have ended up using a pretty similar profile to all the others for ease of building (although I still don't have a clue how they fly yet  ).  The Typhoon, Squall and Mirage 2000 foamy kits don't bother with it and instruct to set up with 3mm(ish) of up at neutral and it would be easy to mould a wing with reflex from the start.  I think at the dimensions (Re numbers) we work with any efficiency gain wouldn't be noticeable/measurable. 
Whilst I was out with the hound this evening I was thinking more and more about the FD2, but I have ruled it out as it actually flew!  ........but......... there was a suggestion of a larger FD 2 seat interceptor for the FAA.  I'll scan a 3-view later - not that I'm in a rush to start anything new for several months (although there is a Buccaneer kit inbound in a few weeks).  Any how, we need to have a chat first and see if there could be a common project 

True genius buddy

I think you exaggerate Harry 


Dizz
PS There is an aeros comp at the Truro Club on Sunday but I don't think I'll be down - too much to do and not enough time.

I have soldered connectors and assembled the minifan with the HET 2W-20 I got from Giant Cod the other week.  I’m impressed that HET now ship the motor with a heatsink which takes the place of the thin ali centring ring I got with he last 2W-20 motor I bought for the 1154 in January.  It has a lip on one side that is a good tight fit in the fan centre-body, in fact with a smear of heat conducting grease on the motor it was a tricky job to get it fitted, but it is in now and not going anywhere.  It would also seem that I have got a minifan-pro with a dynamically balanced impeller as indicated by the blob of purest green for balancing.  I’ll do my usual bench test tomorrow and get some thrust/power figures for my spreadsheet.

Back to the FD temptation: from Project Cancelled - Derek Wood - page 65.

Seems I gave a bit of duff gen earlier - the FD III was a concept in response to an OD for a RAF interceptor.  However a bit more digging revealed the Fairey Lancer which was meant for the FAA.  I wasn't aware of this particular project so I'm going to do a bit more research.   

Back to the FD temptation: from Project Cancelled - Derek Wood - page 65.

Seems I gave a bit of duff gen earlier - the FD III was a concept in response to an OD for a RAF interceptor.  However a bit more digging revealed the Fairey Lancer which was meant for the FAA.  I wasn't aware of this particular project so I'm going to do a bit more research.

Well, you are allowed to build the odd Air Force jet you know!  I was idly thinking along those FD2 lines and got as far as 'it would need the droop snoot for those high-alpha carrier approaches' and that two engines over water would have been preferable - so maybe a 'new' design Naval FD is called for - not so very far away from the FD2/Type 221 in looks, but twin engined..?
OK; crystal-ball Met. is now below minimums...
Paul W.

Have done that with the P1121 - it is just a bit of brand loyalty 


Did a quick breaking-in run after breakfast.  Got to go out now so will post the results after lunch.

I only really managed to break-in the impeller this morning, although the fan is nice a smooth when running the blades still stretch as the witness marks indicate.  At rest there is just over a 1mm gap all around, but as you can see in the photo the blades have rubbed against the shroud in one place.  I started on 3S and moved up to 4S with short bursts of full power until the smell of melting plastic stopped.  Recently I acquired an infra-red thermometer and the motor only got up to 36 degrees C in use, but the heat soaked through after stopping and max’ed out at 45.  Not seriously hot, but does indicate the value of running at low power after being flat-out to dump the heat.  On 3S I got about 380W and on 4S 800W.  Thrust on 4S was ~1200g @ 53Amps, with the intake ring in place this increased to 1380g and current dropped to 49Amps.  I have charged a range of packs and will try and populate the spreadsheet tomorrow morning.

I finished sheeting the wings and realised that I should have used more ribs and a few more top surface spars to support the skin.  You can just make out the uneven surface in the photo and the lack of support was even more obvious when I applied the glass cloth this evening. 
Wing tips from scrap Ľ” balsa sandwiching a strip of 16”- unfortunately the tips have ended up a little on the thin side.  When the elevons are cut free and hinged this will allow an even clearance gap at either end.  Finally this evening I started glassing with 50g cloth and Zap finishing resin.  I prefer using this epoxy for small jobs because it goes off in a few hours and is then easy to sand for a couple of days afterwards before achieving the full hardness.  Hopefully the glassing will stiffen up the surfaces and tips to an acceptable level.

Back to the reflex question: one of the “features” of Profili is that is assumes that the trailing tapers to a point with zero height.  In reality of course the TE retains a thickness and because I build over the plan, even though I sand a slope on the bottom sheeting, the top surface ends up with a slight curve – I have no idea if it has any effect or not.  Here are photos of the M52, P1121 and P1091 tips. 

800w and 1.2-1.3 kg is not that bad but is not that great either. I am sure there should be fans that will run at 2g/W through their rpm band but they all seem to fall away badly when you get to a certain critical rpm. Not something that I understand well enough just keep seeing the same thing with pretty well any fan.

Had a check weigh before I started: all the bits in the photo come to 990g (includes 3200 4S at 366g).  Too much other stuff missing to make an accurate estimate on the final weight, but I think it is looking good for less than 1250g finished at the moment.  I ran the Wemo minifan on the test stand and have entered the results in the Spread sheet (attached).  Am happy with the results on the 60C 3200mAh 4S pack and will aim to use that for flight (some time next year! ).  Cockpit area has been sheeted and the nose vac-formings have been glued on which meant I could make the battery hatch.  The other glassing has been done and is now curing.  I can’t do any more now until I get the duct vac-formings, so plenty of time to decide on a colour scheme.

That's looking quite encouraging Pete 

With regards to the reflex effect on the wings; there's not much you can do there beyond actually sanding the skins to a sharp edge. One would need to dominate. You could do what you're doing now, then fix the wing to the edge of the bench* and work the top skin down perhaps using an aerosol dusting to show when you've removed the concave curvature.

*Perhaps using a couple of blocks fixed to the bench to hold the leading edge in a place which keeps the TE about a millimeter from the edge of the bench, so you can't accidently sand a scallop out of the TE's planform by going too far.

If it doesn't seem to be hurting them then they're probably best just left the way they turn out though 

Thats what I recon too - leave it as it comes out.  With all of them I have sanded the bottom 1/16 sheet with a long perma-grit bar to approx 1/32 with the TE lifted clear of the bench on 2 cutting mats, then glued the top sheet onto that, sanding the top surface in turn to leave a square TE approx 1/16th thick.  Any thinner and it (TE) becomes weak and can't stand being glassed and handled afterwards.
I'm on TG with a 20 minute delay now - nearly missed it!!!
 
PS
Had a thought - next time I'll try fooling Profili to generate longer ribs by entering a wider chord then required, but that might not work with a highly tapered wing though.  Just need to decide on the next subject and I'll be able to check out the theory 

Hi Pete,
I have also encountered T/E curl and the business of how to manage two 1/16" sheets as they merge at a T/E. The sheet will of course take a (repeatable) curl depending upon which face was last sanded. 
What made me think carefully was the slight but noticeable 'extra-length' that results from the overhung joint beyond the rib length as plotted.   I even drew this in Corel to try to decide what approach I'd take.  Pre-sanding the inner faces, with the sheet arranged along a bench edge, using a pre-marked line and a  ply rib-tail seemed to give the easiest solution.  I too would not want to see a knife-edge for the reasons you state.
Paul W.

4 potential colour schemes at the moment.
Thoughts anyone?
(I know the last BVM one isn't a Hunter, but I have done a FunFighter in those colours for a mate and I like the colour combo).


A set of duct formings have started their journey from WW in Helston and will probably arrive on Friday morning 

I like them all Pete, but I'd probably go for either scheme 2 or 3 - prototype colours,  or (of course)  Navy!
Paul W.

Strewth, I go away for an hour and 10 people have looked at them.
The duck egg green would probably be the most suitable, but a bugger to see (same for the FAA colours).  Am drawn to the Neville Duke scheme Paul, but with some white go-faster stripes - dead easy to paint with gloss red enamel (I have a 200ml pot) over red primer (I have a can) 
Got to crack on as the 120A Viggen ESC shipped from CC today.

Sounds like a decision there Pete!
Paul W.

I have got a minifan-pro with a dynamically balanced impeller as indicated by the blob of purest green for balancing.

Would that be a piece of purest green that you have transmuted from base materials - achieving the feat that baffled alchemists for generations?

PDR

Nothing will bring Jane Harrington back you know...

We shall now all bow our heads in her memory while the choir sing Handel's Requim to "Bob".

PDR

Would that be a piece of purest green that you have transmuted from base materials - achieving the feat that baffled alchemists for generations?

PDR

It is indeed the very same made by Sir Percy.

Thought so. Once again the devil vomits in my porridge bowl...

PDR