Hillson FH 40 (Slip Wing Hurri) retrospective.

[TheLurker]

This retrospective was originally posted at HPA II in Feb. '24.  I've made a couple of minor edits, mainly to be explicit about dates.
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To begin at the beginning...

I'd got well and truly stuck with both the Zanonia plan and a Peanut MKI Hurri so I thought I'd put them to one side and do something simple and quick to let the sub-conscious bit of my brain chew the over, especially the Zanonia.  That was in September 2023.  Quick?  Oh well, never mind.

The Hawker Hurricane is one of my favourite aircraft and when I came across the FH40 experiment some years ago it was immediately added to the, "Really *must* Build One" queue.  Being an idle sort I bought VMC's (waves at Arnie) MFM MK I Hurri kit three or so years ago with this is mind.  I'd previously used the kit as the basis for K5083 so knew my way around it and was confident it would make a sound basis for what I had in mind, that and it was only thirty odd quid for most of the bits I would need.   

If we accept the commonly available histories as accurate, there is some dissent, L1884 was a Block 1, Hawker Aircraft Ltd. machine built between 15th of Dec '37 and the 6th of Oct 1939. It was shipped to Canada and was in service with the RCAF as 321 by the 22nd of May 1939 at Sea Island BC. It returned to the UK with units of the RCAF in 1940 and it was struck off charge on the 20th of May 1940.

The available pictures aren't clear enough to be certain, but as an early L series airframe it would have orginally been fitted with fabric wings(1) and 5 spoke wheels (L & N serials) and it still had its fabric wings when Hills received it for his experiments in 1943.  What happened to it in the 2 years between being SoC & allocated to Hills is... unclear.  However as it wasn't in active service I am going to make the following assumptions.

(1) Block 1 aircraft from L1976 onwards were factory fitted with metal skinned wings.  Those already in RAF service with fabric wings were fitted with metal skinned wings when they underwent major repairs or refit.

This is a build retrospective rather than a build in progress because I saw no point in boring everyone with something that stood a good chance of not even making it to the trimming stage.

So, what needed to be done?  Well first off a new upper main plane, so a bit of tracing of kit rib profiles and some tweaks like laminated tips. Then some mods. to the centre section.  The kit sets the outer panel dihedral on the outermost ribs of the CS.  This wouldn't work because I needed to have those ribs vertical so I could mount the interplane struts against them.  Cue two new CS main spars, one for the lower main plan, one for the upper and a dihedral gauge for the outer panel root ribs.

What else?  Well, I decided that I wanted, laminated outlines, elevators and a rudder so a little bit of scribbling gave me some new drawings for the tail assembly.

We're still not quite done with tweaks. I thought it would be interesting to make the radiator boat closer to scale than the kit sub-assembly, but I didn't want to vacuum form it, I'll tell you why if you're bored enough to ask. This that meant puzzling out how I could do it in balsa *without* carving 'cos I can't carve my way out of soggy paper bag.   Fortunately I have a number of (more than 6, but fewer than 10, OK?) 1/72 MK I Hurri. kits to hand and while mulling this problem over I thought I'd see how the Airfix designer had solved the problem and with some minor adjustments I had a "two box" balsa variation of their solution that works surprisingly well.  I think the result is quite passable. It won't stand scrutiny by a Hurri obsessive, but passes the "Doesn't look off to the casual gaze." test.

Wheels.  I've gone with the 5 "spoke" pattern (the kit comes with a 4 spoke pattern hub) on the assumption that as L1884/321 still had its original fabric covered wings and had been "off the books" so wasn't being flown or subject to anything but the barest minimum of maintenance so could quite feasibly still be fitted with its factory issued wheels.

Thought I'd done with changes to the kit?  Hee hee, not a chance old cock. The last change was the introduction of a ballast space. You can only really do this if you're prepared to infill the nose, but it's worth the effort.  When I built my K5083 I extended the lower keel and left the front lowermost panels open so that I could slide in Pb after trimming. It worked, but it felt (still feels) like a bodge.  The other change was a couple of extra lengths of strip & some infill at the top of the dog kennel.  When I covered K5083 I could *not* get this area covered without dips & wrinkle, despite 2 or 4 goes at it.  It was better for 321, but there's still room for improvement.

Why is it grey & green rather than dark earth & green?  Interesting you should ask that, it's the result of a discussion I had with Andy Blackburn.  There are no colour photographs so it's balance of probabilities.  Although RCAF 321 was struck off charge in 1940 and would almost certainly have been dark earth / green when it was parked at the back of a hangar; spares, for the use of, RAF regs in 1943 (reference please AB) for flying airframes, when the F.H.40 was bolted together, mandated the grey/green scheme.  It is very difficult to be certain from the few photographs there are, but if you squint right you can just about convince yourself it's grey rather than dark earth.

The prototype yellow undersides are highly likely given that the fuselage carried the yellow prototype "P".  On which; the RAF's insistence on surrounding the yellow prototype "P" with a narrow yellow circle is a proper pest.  Don't they know how difficult it is to recreate this in tissue?

Late 2025 Update. 
At the time this was first posted Andy couldn't find any more than a general comment regarding the appropriate scheme in his library, but this past summer I found and bought a second hand copy of, "British Aviation Colours of World War Two"  (volume 3, ISBN 0 85368 271 2, first published 1976) from my local Oxfam shop. The bulk of the book is a set of Air Ministry Orders specifying the official colours and disruptive patterns to be used.  For the FH 40 the relevant order and section is AMO A.664 3 (iii) which runs....

3. Camouflage
(i)   The temperate land scheme consists of dark green and dark earth.
(ii)  The temperate sea scheme consists of dark slate grey and extra dark sea grey.
(iii) The day fighter scheme consists of dark green and ocean grey.
(iv)  The desert scheme consists of dark earth and middle stone.

I think it is highly likely that the FH40 would have retained the "Day Fighter" classification of the Hawker Hurricane so scheme (iii) would have been used instead of (i).

If you can get hold of a copy of this book I can recommend it.  It can't take account of field and personal modifications to schemes, but if you're modelling a WWII RAF subject for which there is no good colour information at all it will at least provide you with the most likely colours for the subject together with serial and roundel colours, sizes and positions.

[TheLurker]

The tail assembly is completely new and uses basswood outlines because for this size of thing I find a single 1/16" x 1/16" or 1/16" x 1/32" strip of basswood far easier to work with than 1/32" laminations of balsa. 

The wing tips (upper & lower) were  also swapped to formed outlines and the upper spar extended & cracked as shown. 

Because the CS outer ribs have to sit vertically the inter-spar stiffener on the lower wing has to have the dihedral angle sanded into it. I didn't bother with it for the upper wing as it isn't subject to landing stress to the same extent.

[TheLurker]

The fuselage structure is largely unchanged.  The simplest changes are some extra bits of sheet & strip at the top of the dog kennel to make it easier to cover and a couple of supporting panels for the side bracing struts.

The only significant, and it's not that significant, change is the addition of the ballast space with a lid.

I couldn't resist making the aftermost former lighter though. Got to save that tail weight.

 

[TheLurker]

Think this is self explanatory.  Make two boxes bolt them together & sand to shape. search:/documents

[TheLurker]

Again no significant changes.  Five spoke wheels as mentioned in the opening post and I've used 3mm dried grass stem to represent the Oleo rather than the kit parts. Narrower stems would have been better, but I didn't have any to hand.

The UC doors are covered with Al and yellow tissue.

I've gone for Gun Metal (Humbrol 53) for the painted parts because I think it gives a better effect at small sizes than, say, Al.  I find matt / satin colours usually give a less toy-like appearance than the correct shiny ones.

[TheLurker]

The main thing to point out here is the use of a socket to receive the side braces at the fuselage with a matching plug on the braces.  It makes it infinitely easier to get the strut the correct size when fitting it.

The other wrinkle to note is the use of a couple of bits of thread glued to the main strut uprights. One at the top of the forward strut and one at the base of the after strut.  These allow, with the joint to the side brace struts set the depth of insertion so you can be confident everything is at the right height when fitting the upper main plane.

[TheLurker]

This is the third* go at the canopy.  I couldn't get the moulding to sit right as a one piece so gave up and went for an open cockpit 'cos  I could make that look about right.

Of course that meant I needed a pilot. The problem with many of the stock images (and I think it was Andy Sephton who pointed this out in the BMFA mag.) is that they sit too upright.  So after a fruitless search for a decent image I bodged together a side view of a helmet on a mannequin & a separate image of an Irvin jacket likewise that I found on an memorabilia site. There's no Mae West, but I choose to believe that the FH40 pilots wouldn't have bothered with one as all test flight operations would have been over land.


*I have spares.  I had fun with the canopy for K5083 so bought extras.  Just in case.

[TheLurker]

As is usual for my models it's a tissue only (ignoring bits like wheels & prop) finish.  There's nothing wrong with a painted or printed tissue covering, in fact they usually look far, far better, but I don't have an airbrush nor a printer capable of printing dope/water fast images so tissue it is.  It's also nice to show that you don't have to have expensive (ish) tools nor a dedicated workshop to build a reasonably convincing scale model.

Base cover is VMC's grey domestic water shrunk and with a single coat of 30% by volume of non-shrinking dope and the green is VMC's olive drab domestic pre-shrunk positioned by flooding with thinners and a single coat of 20% by vol. NS dope.  Needless to say this model is only for indoor use or for use out of doors in *dry* weather.

[TheLurker]

Rollout.

[TheLurker]

Current state of Play.

Well it did fly but it was declared a Cat. C write-off and struck off charge after a high speed CFIF* while trimming at Trinity for the '25 Indoor Scale Nats.

Squirrelnet has film somewhere of a moderately OK ROG flight. It might be in the March 24 Trinity newsreel on his squirrelnet28 youtube.

Andy Blackburn took the snap below of it during it's penultimate flight.

*Controlled Flight into Furniture

[g_kandylakis]

Looks repairable to me...

Lurk, I see nothing wrong with old threads reappearing. The original ones are lost, probably for ever. That does not mean they need to be forgotten.

Ah, Trinity, a fine place.
I already told you when we met, I am amazed you guys dare to fly scale models there. It is statistically certain you will meet one or more walls there. Makes for excellent trimming practice though.

[TheLurker]

Found it.

The FH 40 ROG ending in a stall is about 1' 50" in, but there's lots of other good models to see.

[g_kandylakis]

Very nice flight! Worth giving it a second chance...

(edited your post to make the video visible, wrote accordingly in the forum instructions)