HPA

This is my winter project. I started it weeks ago - months, maybe: about the time that Bruce's HPA went dark.

I have now finished 'Phase 1' - the construction of a crude proof-of-concept model, and flight thereof. It's the last bit that's taken ages - mostly just one flight before wind, rain, dark or cattle stopped me, then many days before the next chance. The model could appear to want to fly, then next flight, days later, would collapse in a heap and look like it could never fly. I got a couple of approx 20 second flights, but wanted another one or two, preferably on camera, to convince me to proceed to 'Phase 2' - a properly-constructed and finished scale model. At last I have achieved several flights over the last 3-4 days, and I'm now [almost] convinced to go ahead.

The actual build of this test model was surprisingly quick, especially given the huge amount of research needed to get the shape right. More of that later.

The video,  https://youtu.be/nBDo7I6QxFM

shows seven flights over the last 3-4 days. Well - most of them are not flights, really, just crashes. I've just glued them end-to-end with no text on screen, so I'll describe them here.

1) Oops - I noticed a broken strand in the right motor while winding, but thought I might get away with it . . . err, no. You might spot the right nacelle breaking away on 'landing': that's normal.

2) The model has almost zero 'decalage' and it doesn't care whether it keeps going up . . . or keeps coming down. Perplexingly it also demonstrates good stall recovery at other times.

3)Worried by the proximity of cattle and wanting to keep 'em in sight, I didn't gauge the breeze carefully enough and launched downwind. The model didn't achieve climb-speed.

The remaining flights are all from today.

4) What was that? It's way too pitch-sensitive. I need to add noseweight but I'm too miserly.

5) See? That's what adding a tiny bit of down-elevator gets you . . .

6) Hey - it flies! (Sort of.)

7) Hey - it flies for more than twenty seconds! (Sort of.)

The still images attached are 1) A screenshot taken from video flight 6, when it happens to be straight-and-level for an unusually long time . . .about 0.14 seconds . . .:D

2;3) The model after the last flight. The last picture is an art-study, entitled 'Picture of Mossie with Moo-Cows'.

Those cattle have been really annoying. They're young, bored, and hungry. Any activity on the field gets them ready for a stampede. I could only fly today because the farmer had just spread hay on the field and they're too busy eating to worry about destroying model aeroplanes.

Stephen.

Wow what a great project Stephen. Looks like it's making good progress too from the video

That looks like a challenge to get flying, Stephen. I would imagine that twin rubber powered models would be a hand full. Two motors of slightly different power deliveries with two large props upsetting stability - definitely fun.

Young hungry cows - hope they are friendly.

John

That first picture brought me up short - I rather like it.

Very impressed that you're having a go at a Mossie; I had a NoCal Mosquito that I managed to get exactly (numbering from the left) one good, circling flight out of. All the others were all over the place, it had a mind of its own. I eventually came to the conclusion that it had not enough tail area and too much camber. I still have the props and motor sticks somewhere, your efforts are inspiring me to have another go at it.

Andy

Hullo fellows - good to see the familiar names convening again.

I have to say I don't have a clue regarding the trim of the model - like John says, I believe the power output of the motors will be slightly different, and what's more continuously varying as clumps of rubber break up, or brush the nacelle structure. The whole tail is completely blanketed by the slipstream. The sharply-tapered wingtips will want to stall (no washout). To my mind the CG looks adequately forward - but with the couple of degrees of down-elevator indicated, the wing and tail have almost the same incidence.

The reason I'm prepared to push things further is that I made a Westland Whirlwind years ago that behaved in a sedate manner. It occurs to me though that the Whirlwind had a high-set tailplane . . . might make a big difference if it's out of the propwash . . .

Yes the heifers are very friendly - but boisterous, and they'll test anything new by snuffling and licking and nibbling it - including model aeroplanes.

Andy, since I had no part in the composition of that photo - it just came about by pure happenstance - I think I can say that I like it too, without sounding conceited. The winter sun, the silhouette, the stark winter trees . . .  I hope you resurrect your NoCal model.

Stephen.

Great project Stephen, look forward to reading about the construction techniques you've used on this one.  Are the ailerons pendulum-controlled or simply adjustable?

Mike

Yes, pendulum ailerons, Mike. I think they're responsible for the wing-rocking when the model is hovering on the stall. There's probably a tip-stall and the ailerons correct, then maybe some hysteresis-type overcorrection. I have a non-scale pendulum model I made for an article in Aeromodeller Magazine, and after adjusting the pendulum setup (can't remember what I did), it flew whole flights with the wings rocking, even tho' nowhere near stalling. Kind of cute, but not very scale-looking. Pilots waggle their wings to say hullo or goodbye or whatever, but not for the whole flight! (Well, except me when I was a student, probably.)

FWIW here's a   video  (https://youtu.be/oSazIxF6pns)  from 10yrs ago (can't believe it :o ) of my Whirlwind, flying like wot a lady oughter. It was bigger than this Mosquito.

I opted to make a Mosquito test model because for me, a Mosquito was just too speculative a venture to merit a detailed, finished model from the outset. Those sharply-tapered wings; almost no dihedral; all that mass hung out on the wings creating loads of roll inertia . . . for the same reason I didn't intend to start a Mosquito thread on HPA unless and until it had flown more than say, 15 seconds, and looked capable of more.

But apart from proving basic viability, a huge advantage of a test model is that it can be flown over hard and rough ground even when untrimmed. Who cares?. All the flights of this model have been over hard-frozen or just slightly thawing ground. I'm pleased that my initial concerns over the design's ruggedness have been amply dismissed, with the cavorting model hitting hard, including one treestrike: a very low branch from which the model fell to ground. Sometimes a nacelle detaches on landing - the means of pinning them in place being very clumsy and 'afterthought' on this model. Another big worry was whether the prop blades would withstand landings. Again, yes - to my mild surprise and great relief. There has been one broken blade - in fact on flight no.3 in the video, when I launched downwind and the model accelerated onto the ground. The broken blade was the first thing to contact the ground. Luckily it snapped in a way leaving a large surface area for re-gluing and the repair took a minute or two with thin CA. See the blade lying on the worktop in the attached image.

Stephen.

DeHavilland Mosquito

Sun Jan 11 2026  10:00 AM  local time here in Windsor, Ontario, Canada.

    Hi Prosper Stephen!  Thanks so much for those videos -  it was great action there.  It is good to see those FF rubber trimming videos.    :)

    In Pic #1,  I also see about 30 blackbirds,  maybe  European "Rooks"  or  Crows (?),  content to witness those entertaining flights,  whilst sitting atop those leafless trees.

    Yes,  those cows do look menacing ....

Lastwoodsman
Richard

I think you are correct about the more efficient high mounted tail of the Whirlwind. A larger tail would certainly help but would possibly need to be much larger than scale.

A thought though - what if the tail is enlarged slightly and set at a positive angle to the fuse centre line with the wing slightly more positive - the idea being to have the tail flying a little higher above the wing wake with it's nacelles etc.

A quick test with a profile model may prove whether this is worthwhile attempting in more detail.

By the way that's a nifty freewheel setup on your prop!

Good luck.

John

Having still got my 40" span Mosquito, I can confirm that a larger tail does indeed help them to fly, but they still remain knife edge.

I added some very crude additions to increase the tailplane and tail fin area, to prove it was worthwhile perusing. That was around May 2025. It was a great success, so I made new larger tail surfaces, and even managed to make them lighter than the originals! It was so close to finally being trimmed last year, but it ended up sustaining damage (again!), got repaired and it's been sat waiting for trimming again because the weather in 2025 just wasn't in free flights favour.

Funny thing though, I've seen my Mosquito display the same characteristics in the air as your 1/24 version, despite mine not having working ailerons!

Got some better propeller blades as well for 2026, but they can wait until it's trimmed. Assume you're running counter rotating props as well?

Hi Richard, good to hear from you. Those birds - had they been birds - could well have been rooks, though more likely jackdaws. However in fact the shapes are the remains of the flowers or seed pods of the ash tree. They cling on all winter, it seems. I will keep an eye out to see when they drop - Spring, I expect.

John's and Mark's talk of enlarged tailplanes has got me scared. I'm not sure I could face that. First of all when weather and cattle allow I'm going right thru the repertoire of downthrust v. elevator; noseweight, and prop-pitch changes too, perhaps. On the face of it the tailplane is a good size - nearly 19% of wing area, which is what Monty Python would have called "lookshury". It's decently thin (about 10% thickness to root chord) and looks a decent shape in terms of efficiency.

Quote from: OZPAFset at a positive angle to the fuse centre line with the wing slightly more positive - the idea being to have the tail flying a little higher above the wing wake with it's nacelles etc.

I see what you mean John. I'm not sure that the tail could be raised a worthwhile amount without the fus. taking on a ludicrous flight attitude (and adding lots of drag). However, I don't know - perhaps only a small adjustment would 'make the difference'.

Quote from: MarkI've seen my Mosquito display the same characteristics in the air as your 1/24 version, despite mine not having working ailerons!

That's interesting Mark. Maybe it's just the inertia of the heavy nacelles then. Even absent dihedral, there is a roll-damping effect - the downgoing wing has a greater effective angle of attack, and so more lift, and obviously the reverse for the upgoing wing.

No, both props rotate clockwise. There is lots of torque, which thus far I've controlled by a fair bit of downthrust in the right prop. This trick I remember learning from Tom Arnold - he mentioned it donkey-years ago on HPA and I didn't forget despite not ever using it. As I recall the Whirlwind needed no thrustline adjustments.

Stephen.

    Hi Stephen,
                Another Beautifully made model as expected. Just to add to your list I've always found 50 or so extra winds on the outboard motor gives a twin a positive path to fly, Just a thought.
                       Dave

Thanks Dave, that's a good tip. Now that the model seems to be behaving, to some extent (see below), I'll try that.

I've made some progress :). First, lots of downthrust on both props. Second, noseweight - an arbitrary 4.5g, which happens to be the weight of a little slab of lead I found, and stuck under the nose with carpet tape. A couple of short flights indicated an improvement, tho' it was too breezy to be sure. So this morning in dead air I wound about half turns and the model climbed well and made its first steady orbit. Then with nearly full turns and with camera, the model made a much wider left-hand tour, thankfully just staying within the field boundary.

Vexingly, the video didn't 'come out'. It's really hard to hold the camera and the model in one hand - much harder than for a single-engine, because there are two props being blocked by one's fingers and constantly trying to escape - fingers that are needed for the camera too. I must have moved the zoom lever, because the vid. was not zoomed and the model was a little scrap in the distance most of the time - and what's more blurred almost totally. At this wide angle, the autofocus didn't know whether it was meant to focus on trees, clouds, model or what.

There were just 3-4 frames with the model in focus so I've attached a pic cut from one of these frames. I guess the wider angle at least gives an idea of the height reached. In both flights the model began to stall a lot towards the end, suggesting less downthrust but more down elevator.

The second flight was 27sec. The model always lands with plenty of turns still available so I'll be trying 1/4" motors instead of the current 7/32". But for now I'm at last fully convinced that it's worth going ahead with a detailed and finished model. Man, I've got to make the tail lighter! This model doesn't even have a tailcone or tailwheel and it still needs noseweight.

Stephen.

Great flight pics.  I use a gopro copy on a headband then once adjusted properly all I have to do is watch the model in flight and it pretty much stays in the focal frame.  It might look a bit ridiculous, but it seems to work.

It's good to hear that you have tamed the Mossie Stephen. It looks very atmospheric in that photo.

John

Hi pedwards - I've often thought of a gopro copy - not just for modelling - but I can't figure out how they handle data storage. I mean my portable camera can generate .mov files of multiple gigs in less than a minute at high resolution - so what happens when you gopro a 1/2hr walk in the countryside, even at medium res.?

Hi John -

Quote from: OZPAFBy the way that's a nifty freewheel setup on your prop!

top marks for noticing, but I wonder if you can divine how it works from the photo? I invented this early in my aeromodelling days, probably about the time I joined HPA. It's very unobtrusive IMO but does involve a tricky mechanical solder which I don't look forward to.

Flight Report

Yesterday had almost zero wind all day, and the cattle weren't around much. The motors had been 20" 7/32" Tan SS - 2 loops of 1/16th and one of 3/32. I replaced them with 4 16" loops of 1/16". I made some adjustment to the rudder to anticipate the extra torque but it wasn't nearly enough. On about half of the motors' safe turns the model took 2-3 seconds to rear into a barrel roll to the left, over the vertical and dive almost vertically onto the frozen ground. It bounced backward. I did that pained, wincing "oh well . . . there goes that, then" thing, but amazingly the model was hardly damaged :o. I had to repair a tailplane spar, a bit at the back of a nacelle, some cracked sheeting at the front of same nacelle, and the pendulum arm had snapped under the momentum of the 1 gram bobweight. I even had time for another try before dark - just 350 turns per motor, with the downthrust on the left motor halved, and a bit more right rudder and down elev.

That worked well. The power increase has transformed the model. It did rock its wings a bit at one point, but okay. The flight ended with a tightening right spiral though. Against the torque there's plenty of right aileron and some right rudder - so no surprise it spirals right as turns run out. I'll have to play with thrustlines to manage torque if poss. It was fairly pitch-stable, and flew at a believable speed too, so I can almost forgive the need for noseweight.

Today I gave it 400 turns and it sailed off - lovely! Except that it sailed off towards a 'built up area'. Thankfully captured by a shrub, not smashed into a wall. No damage except the right aileron needs to be hooked up to its link to the bellcrank. And the ever-increasing potential danger of me teetering at the top of a wobbly stepladder. The model was 10-12ft up.

Stephen.

Over the years I sometimes considered a Mosquito model. I would dig out my Plans Service drawing and peruse it. Nope. Not nearly enough wing for that fat fuselage and those fat nacelles. Too damn curvy. Then recently I thought what the hell, and started looking online for information and images. I noticed right away that the Mosquito 'bodies' (fuselage and nacelles) didn't look very curvy or fat. Well it turns out that yet again I was fooled by believing drawings. Surely I'd abundantly proved to myself aaayges ago that nearly every drawing out there is rubbish?

Actually arriving at a believable shape involves much much poring over many many images. The three examples attached below were very useful, and actual measurements from a NACA Report, and videos, and 'walkaround' image collections including inside views showing fuselage frames. I can't claim my conclusion is correct but it's a durn sight better than my Plans Service drawing, which I bought as a teenager, and '3-views' in books like Squadron/Signal monographs.

Stephen.

I only know of one accurate drawing for the Mosquito. I was fortunate enough to be allowed to measure certain areas of a Mosquito at the DH Museum, which were then converted to the scale that my drawings are in - perfect.

The Mosquito plan I used for my build also had the scale sized fin, wing and tailplane area.

When I remade the fin and tailplane, I also increased the depth of the airfoil section as well on the tailplane. It's a lifting tail, and oh my word did it have a massive effect. It caught us off guard and the Mossie came down heavy. Good job I've got well practiced at the repair work! Ha!

Regarding your propellers, how have you set the pitch of the blades? Are they x amount of degrees at x distance?

They use the mini sd cards so you can get a pretty large 64 gig card.  Mine came with multiple batteries so you can change out if you need more power.  The only issues I have with them is you can digitally zoom when you edit the mov but the camera itself won't zoom.  I also had one that held my phone which really looked ridiculous but took pretty good movies.  With phone you can use verbal commands. "Shoot" will take a picture.  "Start video" will take a movie.

Ah, I see. If you've got a lifting tail, then presumably it needs to have lots of area, and it also adds to the total lift, which should make for a very buoyant model. Measurements from a real Mosquito - can't beat that!

The blades are currently 26°at 75% diameter. The blades are set simply by the slots they mount into - the slots cut into the hub/spinner. Pitch can be varied by heating the blade at the root until it can be twisted, or by removal from the slot and re-working the slot to a different angle.

I hope your model finds some long grass this year.

Thanks for the info pedwards.

Stephen.

I'm making the wings first.

The wing section is RAF 34, with the 'Piercy Mod' according to NACA - but they don't tell us what that mod is. The true RAF 34 has some reflex towards the T.E. but in no Mosquito photo can I see any reflex, so I'm taking that to be the mod.

The wing section retains the same thickness/chord ratio from root to tip rib.

I used to be shy of tapered S&T wings because I couldn't get my graphics program and/or printer to scale the ribs properly. I start with one rib drawing, photograph it then upload the .jpg to my PC and open it with the graphics program. Then I duplicate the rib image and rescale it to the correct chord and thickness for its position along the wing - and so on for all the ribs. The printer would print out a page of ribs all innocent-like, but on checking them the original one in the series would be dimensionally correct but the others would all diverge from the correct taper and thickness. I've tried several times over the years.

I thought I'd give it one more go, and it worked! I use GIMP, and the scaling operation works in pixels by default. This time I chose the millimetres option, and that's what made the difference. I'd never thought to try this before because why would a computer program care what measurement units it works in? Mystery.

This time then, I printed out the rib shapes on thin paper, sprayed the back of the paper lightly with 3M Spraymount, cut each rib from the paper with scissors, then stuck each paper rib onto balsa, to be cut out with a scalpel. Then this rib was placed over more balsa to cut out its opposite-wing counterpart.*

The root rib of each wing is 1.6mm thick; 4 ribs are of 0.8mm and the rest are 0.5mm. The wood is medium/hard C-grain.

*I wrote this in a past tense as if I've done all this - but no. I'm referring to the process I used to make the test model. I've only just started this new model and cut the root ribs as per pics attached. I'll probably spend much of tomorrow cutting out the other ribs.

Stephen.

Cutting the ribs was not nearly so onerous a job as I'd feared - maybe an hour, if that. However I haven't yet cut the 657,343,556 little slots or notches to accept the multiple spars.

But first I've hit a snag. This is down to the leading-edge radiators between fuselage and engine nacelle. The long thin rectangular intakes in the leading edge have a small but characteristic cant to them, relative to the LE of the wing itself. They tilt up from fuselage to nacelle. In the test model I wasn't interested as this was one of many things not worth wasting time on, on a crude test model. Now I'm faced with trying to get it right. There are four ribs along this stretch of the wing, each one slightly smaller than the one inboard from it, but identical in shape. They have a forward extension to house the radiator. And because the radiator is canted, the curves of these forward extensions don't fair with the lines of the RAF 34 aerofoil.

Clear as gin, eh? Maybe some photos or sketches will make this clear. Will report back.

Stephen.

Stephen, keep the Mossie away from the cows.  They love balsa and doped tissue.  Something in the dope attracts them.  Lived on a farm as a kid.  My dad had a friend who flew models on our farm. Some of the cows snuck up to his car and ate one of his models that was still in the car trunk!

Gary

Thanks Gary, good story - well not so good for the aeromodeller, I suppose . . . I've noticed that the fast-growing young cattle have been extra-restive the last week or so - they charge round, head-butt each other, perform strange leaping stunts like they're trying to throw a rider, and have mass mooo-ing choruses. I think they must be reaching adolescence, in cow-years. Flying is off, what with them and the weather.

I've been kept from modelling for several days - still have a few wing ribs to finish.

Stephen.

Sun Jan 25 2026     Mosquito Build

Hi Stephen.    Here is a new video about the Mosquito. 
We have one almost restored,   in out local Canadian Aviation Museum here in Windsor,  Ontario Canada.
https://www.canadianaviationmuseum.ca/museum/aircraft/


Here is the new video:
How A Canadian "Wooden" Plane Became The Allies' Most Feared Aircraft    Jan 16 2026      23:06
https://www.youtube.com/watch?v=Nnq8pQDX5eY

Lastwoodsman
Richard

Thanks for the links, Richard.

Brrr! My workplace is around 10° lately - that's hampering my progress (Centigrade, BTW).

I feel I have to confess that my number of 657,343,556 rib notches to be cut was in fact a slight overestimate. In fact the number was about 170 - and as the ribs are cut in L/R pairs, that's 85 cuts. Huh - serves me right for using Governement Accounting software to calculate the intitial estimate.

The photos are self-explanatory, I guess. Pic 2 is staged to give an impression of how quick the notch-cutting is. Pinch the rib pair between finger and thumb, close to the cut for max. support, and stroke the razor saw backward - next!

Stephen.

Hi folks, a little progress here. I hope the work speeds up soon but things get in the way. The pic is of the 'working drawing' I made to figure out the wing for the test model. It uses rock-solid information - I have the fuselage width, the root and tip chord lengths, and the L.E. sweepback. There's lots of erasures and additions as I figured out a design. A couple of erasures and scribblings-out came because I used some info from the original Plans Service drawing I showed in post #16. Principally the trailing-edge extension of the engine nacelles (shape wrong; size wrong), and the outboard aileron rib (it's parallel to the a/c centreline, not perpendicular to the aileron L.E. as the Plans Service drawing has it).

While I think of it, the Plans Service drawing is labelled "Drawn by: XXXXX" and "Traced by: XX XXX". What's the difference between drawing and tracing?

The mainspars are of hard 0.8mm, tapering in width towards the wingtip. Pic 2 shows an assortment of tools for cutting rib slots in the trailing edge (medium 3.2mm balsa). The implement that's arrowed is a piece of thin plastic card with squares of abrasive paper stuck to either side. The last two photos show the importance of getting the ribs to fit properly in their T.E. slots. Not only can one encounter wavy-rib, but mal-positioned ribs can cause the mainspar to go wavy too - it's infectious!

Stephen.

Hi Prosper, fantastic to see your process, plese keep posting!

Pre 1980's, before the age of CAD, drawings were all done on paper by the designer in pencil. These drawings were often revised and changed through the design process, leading to what could be (depending on the fastidiousness of the designer) a pretty 'tired' looking piece of paper. Also paper is not a good archive material for a drawing that may be handled a lot and not necessarily treated very well!

When the drawing was approved by the chief designer for release, it would go to be traced, in ink on tough tracing paper, this work was often done by women. You could tell where they worked as the floor would be peppered by their heel marks where they stood at their drawing boards. (Where I worked as the floor was orange painted cork tiles). They would then 'spike' the paper drawing, which means tearing off the bottom RH corner and putting it on a spike, so everyone could tell what had been been traced. The inked tracing would be then submitted to the drawing stores. The original paper copies were destroyed.

One designer always made lots of graphite smudges on his paper drawings, so the others used a rubber to draw mushrooms in the smudges....

Malc.

Thanks malc for that thorough explanation - very interesting picture you paint.

Because work on this model has been so bitty, I haven't taken photos. I've reached the stage of glueing things together. The wing is in a simple jig that does nothing but hold the front spar (top and bottom spars in this case). I think I made this jig for a Martin-Baker MB.5 model, but it works for the Mosquito wing too.

There's a stiff strip of 0.8mm balsa fixed to a piece of white card. The strip has vertical strips alternating along its length - one behind; one in front; one behind . . . (green arrows). The spar/s are slotted into this arrangment, thus guaranteeing straightness in plan. The metal rule is just checking straightness in front elevation, and the card template is checking the angle of the ribs to the spar.

Stephen.

Today I did lots of 'spot welding' (dots of thin CA on each of the many joints in the wing); made the aileron shroud seen in pic 2, and a leading edge tip member - this is a bit of a burden at 0.2g, but has served very well in the test model, which has taken some thumping wingtip landngs without either tip breaking.

I used a long sanding block to give final shape to the ribs at the leading edge before it's sheeted, see pic 1 - actually the long sanding block is the dark thing at the bottom, propping the wing up.

Stephen.

Pic 1. shows the leading-edge sheeting bound to a mould. The sheeting is 0.6mm. I used light 0.8 or 1.0mm sheeting for the test model, to save time - but now I hope to save weight by taking the time to thin various parts. Also visible in the picture are the moulds or forms for the wingtips, along with the 0.6mm sheet blanks ready to be wetted and bound to the moulds.

Pic 2 shows the leading edge sheeting released from their binding, and 3) shows one of the wingtip sheets bound to its mould before drying. The curved ouline of the mould makes binding very difficult and it ends up as a mess of wrinkles and sticky tape.

Last picture is of the leading-edge sheet in place on the wing. Some judicious trimming will be needed until it fits snugly enough to be glued down for good.

Stephen.

Stephen,

Really enjoying following this build and flights of the testbed. The Mosquito is a favorite airplane and it's nice to see it done with your precision and craftsmanship.

Many thanks Oliver.

Yesterday I made the sub-spar that runs where the radiator face is - and forgot to take photos. I also did the coarse part of sanding the trailing edge to shape. Then today I've spent ages tying myself in knots over the radiator intake. I took the best measurements I could from suitable Mosquito photos but I'm not confident that it'll look right when finished. That's the difference between a quick test model and a properly-finished job - it takes twice as long bcause of piddly details!

Next, because the radiator intake is narrower that the radiator face itself, I cut a piece of card the same size as the radiator face, to check that I could insert it thru the intake then erect it and press it against the sub-spar where the radiator face is. That's so's I know I'll be able to paint or draw (or something) a representation of the radiator and smuggle it into place after the tissue covering's done. Fine! It went in and sat vertical with a bit of prodding, snug against the spar. Duuuuh . . . how to get it out again? Hmmmm, hadn't anticipated that. The answer is that you have to destroy it in the process - see last pic.

Stephen.

Nice work Stephen

Quote from: Prosper on Feb 09, 2026, 06:23 PM...so's I know I'll be able to paint or draw (or something) a representation of the radiator...

.
May I draw your attention to my favourite trick for a radiator grille/mesh? Surprisingly convincing even when seen close up.  A very thin film of (spray on) varnish is needed to stop the pencil lead smudging.

That's ingenious, Genius! Kudos, as they say. It won't work for this project but I'll remember your wheeze for future use. The radiator here has only vertical elements and no grille as such except for the inmost little part. I'll probably try to render it pretty dark, as it looks in most pictures. Talking of which, looking out a picture to illustrate the radiator, I found this (pic 1), which I'd only glanced at during research . . . and now I'm really angry:

  After gawping at every image and every video from every angle I could find, I'd satisfied myself that the wing section of the portion of the wing housing the radiator is completely smooth - a continuous curve. Yet this drawing shows a distinct bulge on the lower surface. My belief that there was no bulge led me to make an intake slot which looks too narrow, to my eye

Quote"but I'm not confident that it'll look right when finished."

. Now, this is only a drawing - a sketch, so to speak - but it looks pretty authoritative. The bulge would explain how to make room for a wider slot. Too late now, unless I take a step back and rebuild this area of the wing.

Stephen.

Apart from the radiator business, I sheeted the leading edge. This was with 0.6mm soft wood, and I expect it will be thinned slightly more by the final sanding fair, prior to covering.

Pic 2) shows this sheeting from behind. I normally choose a mainspar position further back, say 1/3 of wing chord, and sheet ahead of this. That means the sheeting is glued to the mainspar. In this case the mainspar position is dictated by the way the engine nacelle mounts to the wing. It's further forward. So the L.E. sheeting extends behind the spar, and is glued to very thin spanwise strips (I think they're just too flimsy to be called 'sub-spars). I think this will be strong enough, and the spanwise strips should support the sheeting well enough that it doesn't sag between ribs due to tissue shrinkage. It worked OK on the test model.

When I first started contemplating the design I presumed that I'd have to cut away the mainspar where it crosses the nacelle, in order to give room for the rubber motor. When it came down to detailed design I was pleased to find that this wasn't necessary. Left of pic 2) shows where I've partially filled the gap between the mainspar strips, and added cross-pieces behind the spar. These will have holes in them to accept pins on the detachable nacelle.

Pic 3) is the inside of a wingtip skin. This is nominally 0.6mm too, but it's been somewhat crushed round the edge by the tissue that bound it to the mould or form. I hope it'll be strong enough. I don't remember edges this thin on the test model. Mind you, I won't be flying this model over entirely unsuitable ground as I have the test model. That has suffered both tips hitting hard and rutted ground multiple times with no breakage (final pic).

Stephen.

I've been unable to work on this since my last post, other than in bits of time here and there - which I've used to get the left wing to the same stage as the right - nearly done. There's now a switch of focus. I don't want to install the wingtips until all the multiple spanwise strips are in place. I don't want to install those until the pendulum aileron pushrods and bellcranks are in place. I don't want to install those until the engine nacelles are made and fitted. So next I'll be tackling the nacelles.

QuoteThe bulge would explain how to make room for a wider slot. Too late now, unless I take a step back and rebuild this area of the wing.

Regarding the radiator intake slot, I've decided not to modify it, though I'm not too happy with what I've got. After seeking through my picture collection again for useful evidence, I couldn't find any photo suggestive of a noticeable bulge under the wing . . .  but could find to the contrary, as the 'screengrab' attached seems - to my eyes - to indicate. With the cowlings off, the line of the underwing is cearly seen.

The ghostly hand swimming into the picture isn't in fact an apparition but belongs to one K. Weeks. The Mosquito is one of the 'new-builds' - a brand-new Mossie made from scratch. This does raise the question of what concessions and compromises the builders might make, and what gaps might exist in their knowledge. Maybe they have every de Havilland drawing and only use the original specs. Either way, the area concerned isn't one that 'comes out well' in period photos - at least at the perspective angles I'm looking for. So I'm going with the 'new-build' evidence.

Stephen.

Nacelle wrassling.

The nacelles are less curvy than drawings like to show. All in all when making the balsa plug for the test model, I had to spend a lot of time working out the shape, leaning heavily on photos with panel lines evident and on u/c doors. It came to light that the aft end is 'hollowed out' - see pic 2, and 3 shows this quite well. Drawing u/c doors on the plug, then sanding the plug and re-drawing, until the ink lines looked like the real thing in photos, was my method. Same for panel lines (Mosquito nacelles were of  metal, not wood).

To save effort with the test model I made a plug that was symmetrical and it had to serve for both left and right nacelles. This made working out the blending of nacelle and wing difficult. The wing taper in thickness, the extended inboard wing leading edge, and the dihedral, mean that the L and R nacelles are somewhat different in order to fit their respective wings. This time I'm hacking away part of the plug and will attach an extra piece specific to the L or R body.

Now see pic 4 which shows the balsa plug in the foreground and one of the test model's nacelles behind it. Look at the curves of the plug, then see how the model nacelle has failed to keep the curvature it had when initially moulded. It can't be down to tissue shrinkage because the fore part is flattened even though it has no tissue covering. I wonder if the exceptionally humid weather for weeks on end is a factor, and the model repeatedly landing on soaking ground. I suppose I need to provide more supporting structure - AKA more weight and more time.

Stephen.

it's a pity that you can't get away with just one nacelle,Stephen ;)  That's an interesting way of judging curvature  - using the shape of surface lines - undercarriage doors and panel lines.

I'm a lousy 3d carver/shaper- I usually resort to 3d dwgs and the use of the old "bread and Butter" approach. Your system is far more accurate as it doesn't depend on the accuracy of the drawings.

I think you should leave your work partly uncovered and displayed in a transparent box. :)

John

Quote from: OZPAF on Feb 23, 2026, 02:44 AMit's a pity that you can't get away with just one nacelle,Stephen

In the event, I saw that this wasn't necessary.

Quote from: OZPAF on Feb 23, 2026, 02:44 AMYour system is far more accurate as it doesn't depend on the accuracy of the drawings.

Yes, I think so, but it does need some basic 'solid' information, say nacelle length and width for example. All the rest can be discovered by study of many photos and getting ratios. A really good side-photo (good in the sense of not being distorted by the camera lens) can yield the basic shape and then the study of photos at different angles can show up 3D aspects like cross-sections. 
 

The picture shows the nacelle plug (which I made for the test model) with a razor saw in it - I made several cuts on the right side of the plug. Thin card can be pushed into the cuts and a pen can be run round the card where it meets the balsa. This yields a true cross-section as seen in the picture. These card cross-sections not only help in attaining an acceptably symmetrical plug, but also make the templates needed to shape formers for the nacelle internal structure.

Now I've gone further and sawn the nacelle plug right in half. Am I mad? Well probably. But that's not important right now. In fact as I hope to show in coming posts, this will make joining the moulded balsa sheet parts of the nacelle quicker and more accurate. It happens that the original saw-cut wasn't at all perpendicular to the plug's centreline, so when I completed the cut I had to add some balsa and sand it square - this can be seen as a thin balsa wedge in one or two pics. On top of that goes another 'endplate' of thick wood. This is just to stop all the handling and tissue-binding etc. from rounding off the edges of the plug.

Also see the 3mm 3-ply balsa slabs which were shaped to be the nose formers. Hard balsa, glued with aliphatic.

Now, binding balsa skins to the form. Each nacelle has three main panels - front, rear, and top cowling. At least that's the idea. It worked for the test model. However I'm already on my second attempt of a front skin. It's got to conform to some pretty heavy-duty double-curvature. The test model skins managed this with just a couple of wrinkles which had to be cut out. I think it all depends on the individual piece of balsa sheet used, and practice. That's the second attempt in the pictures, and it's drying in my hotbox as I write this - along with a rear panel. See that there are some wrinkles right at the nose (they're just visible as corrugations). These may well be acceptable - the wood shrinks and flattens out somewhat as it dries. We'll see.

Stephen.

This is a fascinating approach Stephen - courageous as well. Cutting into a carefully shaped form!

John

Thanks John! I've done the cutting-halfway-thru-the-form a good few times before. It doesn't seem to be a problem.

Where was I? Oh yes. I found that when the bindings were unwrapped, the wrinkles at the front of the nacelle panel were still present, so I resorted to brute force. I rewetted the local area and used a hot piece of metal to iron the wrinkles. Hot enough to hiss at it brushes the wet balsa. The now barely-discernible wrinkles can be sanded out - see before and after pictures.

I moulded four of the six nacelle panels yesterday and the remaining two today. It's a slow business because of the depth of windings and sticky tape required - this slows evaporation so the 'mummies' need to spend a couple of hours in the hotbox. In most cases 45 min seeems enough.

I'm learning. Initially, and also with the test model nacelles, I bound the centre of the wet balsa panel to the plug first, then on to the front and back ends. I changed to binding first the ends, then the middle. Hey presto, no wrinkles or puckered lips at either end - but a couple of folds at the middle. To deal with these I turned to what I should have done all along: cutting relief slits, as I do with balsa/aliphatic double-curved panels. These need filling, but the overall result is better - no touch-and-go brute force.

The rear nacelle panels have concavities at the back, as mentioned previously. I used folded wads of kitchen paper* held to the wet balsa panels and bound tight with tissue, to force the panels into the concave areas.

*I'm guessing the term is understood across the English-speaking world - but if not, I'm referring to rolls of pulp paper, perforated to be torn off as squares, often coloured and embossed with patterns, utilised for numerous household (and modelmaking) tasks.

Stephen.

Each shell now has to be rebound to the form, and the relief wedges can be filled in. A sliver of polythene is slid and wiggled between the shell and the mould to allow gluing without sticking the shell to the mould. Then (the rear edge of the shell (top cowling in this example) is trimmed and sanded flush with the mould* - carefully so's not to erode the mould itself. At this point all datum lines are re-marked as necessary according to the marks on the mould. This is because the initial act of binding the wet balsa tightly to the mould almost invariably causes the wood to shift around a bit, and when the dry shell is unwrapped, datum marks will be misaligned.

*edit - the 'endcap' has been removed from the mould at this stage-it was stuck on with double sided tape - yukky but it works

There's a photo showing my Hole-O-Matic™  hole cutter - oh okay, it's just al.tube with the end bevelled to a sharp edge, which is twizzled between finger and thumb to cut thru the wood. Also a photo showing what the result is if a hole isn't cut at the top of a relief wedge: the wet balsa sheet can be all scrunched-up by the tight tissue binding to the mould. In this case I'll just have to use filler to level the craters.

More fotos from yesterday and earlier this morning. I forgot to mention that the last pic in post #46 where a shell is re-bound to the form temporarily, and the back edge is carefully sanded flush with the face of the form - that that illustrates the reason for chopping the form in half. Unsupported, each shell is as floppy as you like, and sanding the back edge evenly and squarely to make a strong all-round join with the front edge of the rear part of the nacelle is really difficult.

Anyway, the front shells are joined up (the joints are along a straight line so relatively easy to achieve) and now the 3-ply disc can be unpinned from the front of the form ready to assume its grave duty as the nose former in one or other nacelle. In the pic it's not glued in place yet: just showing off for the camera. The other 3-ply slab can now be pinned to the form, to be shaped.

Then I cut a template from thick card and lifted the perimeter slightly. This is pinned to a slab of balsa which has adhesive-backed plastic film on it (non-stick). I cut strips from soft 0.3mm balsa. Four strips, put under the water tap, stick together and can be coaxed into the template. This normally works without the strips kinking but there are kinks evident in the photo. In this case I don't care that much. When the strips have dried they are wetted out with thin CA.

Stephen.

Today's work:

I have a habit of cutting formers on top of the drawing of the former, and holding two pieces in together on the drawing and putting a dot of thin CA on the joint. Occasionally slicing a piece to size with a razor can damage the paper, and occasionally the CA can get onto the paper. It sure is quick though.

One of the laminated formers pushed into place inside the nacelle. It appears to be detached from the nacelle at the bottom but this is just due to the slope of the nacelle - it's in contact at the front. I'm too lazy to chamfer the laminated hoop to fit properly.

Making a laminated hoop on a socket. I used a single strip of soft 0.3mm balsa, and glued it to the 7/16" socket with a tiny dot of CA. I wound it round the socket under slight tension - this prevents the strip from kinking. Then another bit of CA to secure the end. Then break the tiny bond between the strip and the socket by pressuring it with a fingeranil, and the whole hoop can slowly be worked off the socket. When it's ju-ust in contact with the socket (necessary for it to keep its circularity), some CA is dotted around the hoop - enough to secure its shape without gluing it to the metal. Then it's removed entirely and dosed with CA. These aren't very neat examples, but should be good enough.

Stephen.

The circle thing is a trick I am definitely going to nick.

What a master class of alternative Modelling! I feel ashamed to say that I've tinkered in a similar hobby! 😅

Good to hear from you Mr Speedy. The truth is, all this is predicated on whether I can succesfully cover the model. Apart from the test model immediately preceding this one, I've never tried tissue covering over double-curved sheet surfaces, and I've never shown anything but basic aptitude in straightforward tissue covering. I might send the uncovered airframe to a recognised tissue guru, someone like Mike 'MKelly', along with a begging letter :D.

Lurk, I hope you try this. As you can see the difficulty is in holding one end of the balsa strip to your chosen cylinder until you've wound one revolution of the strip - whereupon the end is trapped. I think I've managed to do this without resort to glueing the end in the past - but anyway the whole thing needs practice and a stoical acceptance of a few failures.

Today I taped the fore/aft mould halves together again, to shape some longitudinal strips which are in effect, the longerons. This is hard 0.8mm wood but it still responds to wetting and modest heating (my hotbox seems to attain about 60° in typical ambient conditions) - see the twisted and curved item in front of the nacelle. I joined the shells of the port nacelle and cut one of the strips to fit between formers as seen in the picture through the snout of the nacelle - the strips aren't glued in place yet.

The nacelle as yet seems to have retained its curviness - no flattening out as has happened to the test model nacelles . . . The thing that's been bugging me is how to clip the nacelle to the wing. I did this in a basic model Westland Whirlwind - there was a sprung latch which made a lovely 'snick' when the nacelle was pushed home, and which was released by pushing a wire into a very small hole in the wing. But that was a larger and more roomy job than thissy Mosquito. For the test model I used a crude and very visible pin, which turned out to need three hands to install (one for the model, one for the nacelle and one for the pin). I want something less visible  . . . and less annoying.

Stephen.

QuoteThe thing that's been bugging me is how to clip the nacelle to the wing

Have you considered small magnets to the rear of the nacelles to complement forward locating pegs in the holes in the former near the wing LE?

John

Hi John, I must admit I hadn't considered magnets - at least not consciously. The thing is, I've had trouble using them to fix the cowling of a Sopwith Camel model. They're strong enough (2 off 3mm, clapping onto little steel plates) to secure the cowling (which houses the motor/gears/prop/capacitor) But, when it comes to taking the cowl unit off, I've found it's hard to grasp the airframe securely enough to pull the cowl off. All the struts, wires, details, what have you . . . there's nowhere to hold it firmly. Then again, if the magnets are held away from their steel plates by a fraction of a millimetre, their attractive force becomes insufficient.

So I think I dismissed them unconsciously, so to speak. I might reconsider, but at the mo I'm leaning towards a piano wire spring-latch.

I've got some work done today, but no photos.

Stephen.

I've hit a rather frustrating bit - making the rear part of the nacelle which remains fixed to the wing. The horizontal part let in to the trailing edge of the wing - that's fine. Easy. It's the sides that are the problem. On the test model these proved difficult but it didn't matter that they ended up looking horrible and botched, whereas it does matter om this model! This is taking more time than it deserves. Other than that I've been catching the right nacelle up to the left one - it's not far behind now. When I've got these jobs done I'll be all nacelled-out, and glad to get on with other parts of the model.

Stephen.

This is some next level building! 8)

Thanks Gravitywell - undeserved praise I suspect, but welcome all the same!

Finally  got the rear nacelle fairing thingy finished. And still the other one to do. It's not very satisfactory but it'll have to do. There are now two strips at the rear of the nacelle which engage with the fairing thingy, and a hooky-thing that slides into the rear spar when the nacelle is slid into place, ensuring that the nacelle can't drop down at the back. I've still the motor peg (or maybe hook) to sort out, and the latch to stop the nacelle flying off the wing . . . oh and of course some details . . .but subject to a final clean-up it's pretty much done.

Stephen.

After getting nothing done yesterday, this morning I decided to forget the nacelle rear fairings - sick of it - and start on the pendulum ailerons.

I have an oak block - once a sanding block - into which numerous small holes of different diameters are drilled. A 0.5mm piano wire pin is stuck into a suitable hole, and a long piece of 0.4mm wire has its end bent over. This bent end is inserted into another hole, and is taped down with masking tape. The long piece of wire can then be wound around the pin, as many turns as needed; released; ends clipped and turned up, and there you have yer bellcrank. Another one is wound the opposite way, for the other wing. The one pictured was wound clockwise, for the stbd wing.

Four more of these coils are made - this time of 0.34mm wire wound round 0.4mm pin, and with one end cropped off right at the coil, and filed smooth, so that there's just a coil with wire sticking out at one end. Two clockwise and two anti.

Since the cranks were wound round a 0.5mm pin, that's the diameter used for the pivot pins*. A pin is seen fixed firmly into a hard piece of 1.6mm balsa - this will be mounted to the relevant wingrib.

The pushrods, extending out from the pendulum in the fuselage, to the long arm of the cranks, are of stiff 0.8mm balsa - a broad vertical bar and a thinner strip glued to it to make a T-section. The edges painted with yellow Sharpie pen are the edges to be glued: I found by happenstance once that yellow Sharpie ink goes bright red when CA'd. This can be used as an indicator of successful CA bonding.

This installation needs four bearings for which I use thin aluminium - from one of those disposable food trays - in this case snipped and chopped rounghly circular. A 0.5mm hole is 'twizzled' through it, then it's punched into a cup made in a thick slab of plastic card, to make a dome. The dome is lightly CA'd to the base of the pivot pin.

I got some more done than this but will post pix tomorrow.

* I don't know the correct or formal names for all of these things so kind of make 'em up.

Stephen.

Amazingly neat work!! Well out of my league!!👍

Ta Mr Speedy :)

I reluctantly had to take up the nacelle rear fairing of the stbd wing. Oh boy. Another day wasted, with moulded sheet after moulded sheet provong inadequate. Today I reverted to a fix I'd been resisting all along - simply carving the shape out of soft block balsa. Only it's not simple. I'm creeping towards a result. The reason I disliked this way of doing things is the weight. My hunch is that it will weigh at least twice the sheet version.

The reason I could no longer ignore this fairing is that I made a pair of ailerons - but couldn't finish them until the wingtips are in place and finished. Can't do that until the many spanwise strips (pseudospars?) are in place. Can't do that until the nacelle fairing and pendulum setup is in place . . .

When I say 'can't', I mean 'shouldn't', really. Once those strips are in place working on the wing becomes much more awkward.

More soon I hope.

Stephen.

I meant to add these pics when I last posted, but didnt have time. The first shows the link or hinge between the pendulum bar extending from the fuselage along the wing, and the bellcrank. By using  wire coils wound in opposite directions for opposite wings, I find that the coiled wire rides on the bent wire of the crank - a simple and v. low-friction result.

Next is a closeup of another coiled wire and some thin al. from a baking tray. This al. is folded around the wire and crimped, and a hole is made thru the end. This then becomes the link between crank and aileron. The point is that the coiled-end wire can be slid in or out of the folded al. tab. This is useful because of the huge leverage at this end of the pendulum system. Whereas the pendulum might swing several centimetres either side of vertical, at the aileron end, a millimetre of movement of the link seen here will rotate the aileron considerably. The ability to slide the coiled wire in or out of the tab changes the link's length, which allows fine-tuning of the aileron's neutral (pendulum centred) position. When done, a drop of CA run into the al. tab will lock the wire. Thereafter, flight trimming of the ailerons will come from adjusting the system at the pendulum itself.

This is probably clear just the same as mud is clear . . . I hope to take some photos that explain things better.

Now back to the present. A picture showing the shaping of soft block rear nacelle fairing. The picture utterly fails to convey the exasperating nature of this job. I could make a whole new %***££ nacelle in the time it's taken to do this %**&& fairing. And it's not finished yet. Below the wing are two of the many failed moulded-sheet attempts.

Incidentally, the join between the removeable nacelle and fixed rear fairing copies a panel line on the ackshual Mosquito.

Finally, I meant to take a 'before and after' photo of the ailerons but this job advanced so smartly that I overshot, so one aileron is not fully 'before'. But then the other isn't fully 'after', come to that.

Stephen.

Yesterday I finished the stupid rear nacelle fairing. It transpired that I could thin the block balsa more than I'd anticipated. I thought that the very curvy shape, cutting across the grain of the blockwood, would make the part brittle and ready to snap. In fact not. It's still heavier than the moulded sheetwood though.

Clear of that ghastly trap, I've been able to get on with the pendulum system today. To mount an aileron, the wingtip needs to be finished - but I'm not ready for that yet. So I've temporarily glued a strip of scrap wood with a hole drilled in it, to the wing. The outer aileron hingepin can slip into that. There's a picture of the inboard part of the stbd aileron with piano wire hingepin, and also the wire hook which the crank-to-aileron link hooks onto.

Stop.

I do have a problem with nomenclature here. I'm okay with 'pendulum' and 'aileron': it's the bits in between, that join the pendulum and aileron, that I have trouble with. F'rinstance, the bar running along the wing from the pendulum to the 'bellcrank': I want to call that a pushrod . . . except that it's a pullrod too. The bellcrank isn't bell-shaped and it doesn't ring. Anyway, here's a clearer picture of the 'pushy-inny-outy coiled-end thing'. This component proved too long, and I've pushed the wire further into the crimped aluminium, to the length seen here.

A picture of the bellcrank pivot pin, lightly fixed to a wingrib. Now I've had the setup working, the position of this item seems good so I'll fix it well with CA.

The next picture is of that same part of the wing seen from underneath. It's hard to see what's going on, I admit. First, the aileron has to be removeable. Just in case. A slim plastic card rectangle with a hole in it is slipped onto the inboard aileron hingepin. The outboard aileron hingepin is slid into a hole at the wingtip, and then the plastic rectangle is spushed into the slot. The plastic rectangle projects out a long way for convenience: once the setup is tested and passed, I'll cut off the projection to a minimum.

Then a picture of the whole setup from above. With the crank neutral, the aileron's neutral. At this first fitting and testing stage there's still work to do - some bushings and washers, and endcaps.

Stephen.

That's a nifty hinge arrangement Stephen - light and practical.

As for a name for the pendulum transfer beam - how about "crank arm".

John

Thanks John! Crank Arm it is.

As well as working on the right wing pendulum aileron assembly, today I made a spring catch for the right nacelle.

This little catch relies on the springiness of two 0.5mm lengths of piano wire. The wires are mounted strongly behind the mainspar; they take a sharp 90° turn, go through the spar at the top, and extend forward, ending in the pawl or whatever it's called - the wedgy thing that makes the catch. Inside the nacelle at the top, I glued a balsa ramp (arrowed). This takes advantage of the laminated former making a natural strongpoint. When the nacelle is pushed into place under the wing, the pawl rides down the ramp under spring pressure, and clicks up when it travels past the ramp. This is pretty neat given that it's an afterthought. To release it I can stick a fingertip into the nacelle from the front, but intend to make a small hole in the top of the cowling, through which I can use a prodder to push the pawl down.

The last photo is rather indistinct, but shows the catch in place, doin' it's job.

Stephen.

Stephen,

I immediately thought of you and smiled this morning as I read this sentence in an article accompanying G.E Whitehead's 24" Nieuport 11 plans from the December 1972 issue of Aeromodeller.

"The sweepback of the wings combined with the small amount of (non-scale) dihedral provides plenty of stability without without recourse to such 'artificial aids' as pendulum control."

The cheek! What utter blasphemy, tacitly endorsing non-scale dihedral as canonical while condemning pendulum ailerons as artificial aids in the same sentence. Heretic! ;-)   

Keep fighting the good fight.

Quote. . .tacitly endorsing non-scale dihedral as canonical while condemning pendulum ailerons as artificial aids in the same sentence.

Har har :D

Yes orthodoxies can be very puzzling, in whatever facet of life. Artificial? Last time I looked, aeroplanes had ailerons which move up and down l. Most scale free flight model aeroplanes don't - isn't that more artificial than having them? My pendulum systems are made of balsa and bent wire - why would this be artificial as applied to ailerons, but apparently acceptable in all other areas of modelling?

Anyway, I must stop before I go into a rant and nurse forces me to take another of her 'little tablets'. Mind you, I'm tempted to make a basic Nieuport 11 with scale dihedral - it looks the same as a Camel dihedral-wise, and the lesser dihedral stability of the lower, dihedralled, wings of the Nieuport (because of their smaller area) might be well compensated by the sweepback. The Camel is very stable.

First, I must correct my last post - I said my nacelle latch was installed on the right wing whereas the photo clearly shows it's the left. I get muddled.

Photos show the pendulum components fully installed in the - uuh left? right? Left wing. Just about visible are the little plastic card endcaps on the pivots. With this done I could fit the 1,459 thin balsa spanwise strips (we-ell, five on top, three on the bottom in fact). In fact the whole, conjoined arrangement of crank arm, crank and aileron linkage can be smuggled into the wing after the cage of mini-spars is fitted. I did this on the test model. But it's a murderous job.

Note how the mini-spars wave somewhat from rib to rib - that's from my inaccuracy in cutting the slots in each rib. The 0.4mm balsa strips are pushed into a slot in a rib by pinching the strip either side of the rib and gently coaxing the strip into place - finished by tamping it down with some square-ended object.

Now I can get the other wing to the same stage and fix the wingtips.

Stephen.

Stephen,

If you do a Nieuport 11 I'll be tuned in. There is just something I love about that airplane.

Your work looks wonderful as always.

Quote from: bcarterIf you do a Nieuport 11 . . .

But when I think of it, I've got so many models to attend to - 3 or 4 unfinished projects and a couple of finished-but-untrimmed models, and a couple of experimental bulds i want to tackle . . . Aaiiiy - not enough time!

The wingtips. I trimmed the prawn cracker-style wingtip halves. Note how thin the wood is at the very tip (arrowed). The other arrow in the picture: see the billet of timber forming the leading edge - see how the leading edge continues a straight line well past the last rib. However, in front elevation the taper does begin from the last rib outboard.

Well, at some point I noticed that the billet of timber wasn't sanded very fair, and blithely gave it a few sweeps with a fine-grade sanding block. Then I glued the bottom skin in place. I saw that there was a slight gap between timber billet and skin, but cheerfully went ahead and stuck it down anyway. Then I went to peruse photos to see the position of the wingtip navlite transparency, and got an uneasy feeling. Back with the model I could see that I'd sanded away the correct wingtip curve. Hence the gap between billet and skin. It's much too rounded.

Great steaming idiot. I now have to remedy matters (time and faff) - I haven't decided how yet.

Stephen.

{quote]I now have to remedy matters (time and faff) [/quote]  I made the other wingtip for practice, then repaired the faulty one with an almighty bodge, as ugly as they come. But it's under the skin, so who knows? I certainly don't :).

There's quite a bit still to do on the wings/nacelles, but now I'm turning to the tail surfaces.

Stephen.

Quotemade the other wingtip for practice, then repaired the faulty one with an almighty bodge, as ugly as they come. But it's under the skin, so who knows? I certainly don't :).

I'm actually amazed that you can match preformed panels with the shaped LE, full stop.

Where is your English wheel to modify the curvature of the panels. :D ?

I remember reading an article quoting DeBolt stating that the Curtis P40 wings were built from the outside inwards. The Skin was laid up in jigs and the ribs attached to the skin. I wonder how many gaps there were between the ribs and the skin.

John

Stunning!

Thanks Australia :).

John, shaping that billet of wood isn't so hard - after all the plan taper and curve are known and can be inked onto the initial blank; likewise the front elev. taper and curves. The cross-section of the inboard end of the piece is also known, coz it's the same as the nose-shape of the rib it butts against. That same shape is used to make the balsa tip mould that the skins are bound to for shaping. So with a bit of careful sanding the billet should have the same curves as the moulded skins. Close enough for this kind of a job anyway. That's why I ws so cross when I ruined the shape of the stbd billet by some brain-in-neutral last minute sanding.

Yesterday I just had time to make the tail surface skins/shells/prawn crackers. They're all from nominal 0.5mm soft C-grain. I find crossgrain generally better at adopting and holding moulded curves. Pic 2 shows the balsa moulds (foreground). The Mossie's tailplane had a symmetrical section so only one mould is needed for left and right surfaces. Note that the lines of the fin and tailplane are inked on the moulds. I dose the L.E.s of moulds like this with CA to strengthen them. Tissue binding needs to be firm, and sometimes can squash mould L.E.s, if of soft wood.

Pic 3 shows a freshly-bound stbd fin skin and a wet blank applied to the tailplane mould. The skin is glistening wet. This wet, there's the advantage of it sticking to the balsa mould - which helps placement while it's bound - but the disadvantage that such a wet article weakens the 'wet strength' tissue and it can easliy tear under the stress of binding. This is not precious Esaki of course but craft tissue used by lamp-makers: about twice the weight of Esaki.

After a sojourn in the hotbox, when the parts are unwrapped, I ink the correct finished outline of the skin on the skin, using the aforementioned markings on the mould, while the skin is still in intimate contact with the mould. It's hard to ink a freehand line along the leading edge, so I rub the side of a pencil lead gently along the L.E., which leaves a faint grey mark to guide the ink pen.

Stephen.

Onto the control surfaces. The first picture is an X-ray image of the test model's fin and rudder. I took this because I have no drawings of the rudder, and needed to see it in order to 'reverse engineer' it for this model.

I do have a drawing of the tailplane/elevator, which is slightly modified because of the way the elevator meets the fairing on the Mosquito tailcone - more on that later. The series of photos is the best I can do - without a headcam - to illustrate the construction method.

Broadly speaking this involves cutting strips of wood (in this case quite hard, straight-grain 0.8mm (1/32"). A strip is laid on the drawing and sliced with a razor - used in the guillotine sense. The cut end is squared off with a brush or two of sanding block, the strip is pushed against another strip and CA'd. That's probably a poor explanation but I hope the piccies help. Note that the photos were taken scant minutes apart - this is a Supa-Kwik method. I anticipate that the rudder will follow as quickly.

Really eagle-eyed viewers might just notice that the elevators somehow don't quite have the full streamlined, curved elegance that is the Mosquito's essence. Yes, I suppose they could do with a going-over with trimming knife and sanding block :D.

Stephen.

I've added some thin balsa sheet to the 'balance horn' area of the rudder - this should hold the tissue to a nice convex curve. Also three hinges, made of baking-tray aluminium folded in two. The slits thru the spar, to hold these hinges, are made with a piece of razor stuck into the end of a bamboo stick. The fin spar is only 0.8mm thick so has doubler blocks stuck onto it to anchor the hinges.

The join of the two fin skins, along the leading edge, is just about visible.

There are two additional little blocks of balsa glued inside the fin leading edge - one is to anchor the pitot probe, and one to anchor the aerial wire - if I ever fit one.

I had hoped to get further than this today, but there it is. The construction of the tailplane/elevators is so similar to what's shown here that I'll just crack on and not take photos.

Stephen.

I glued the tailplane skins along the leading edges, but got no further because I decided that I really ought to have the fuselage - or at least the rear fuselage - ready before finishing the tailplane. This so that I can achieve the best fit between the two. So for the last couple of days I've been modifying the fuselage mould. I've split it into three main parts, for the same reason that I split the nacelle mould: exact joins between different skins are much easier to make. I hope to show this in photographs.

The fuselage mould was carved from many bits of odd block balsa stuck together. I used to make big moulds like this from expanded polystyrene, but never liked it - neither the hot-wire cutting nor the sanding. I found that packs of irregular block balsa offcuts were cheaply available, so took to balsa instead. But I looked at balsa block prices recently - blimey! Costs a fortune! I presume this is the wind turbine effect  https://eia.org/press-releases/ill-wind/ 

I made a separate mould for the bomb bay doors. That's because the subject I want to represent had the 'pregnant cat' bomb bay. From all my photos there's no really good indication of the curve of these doors. The pesky engine nacelles always obscure that area in photos. I think my first iteration might be a bit too curvy - but I'll see how it looks when matched up to the rest of the fuselage. What's seen in the photo is that first attempt, moulded in two halves and joined along the centreline. Note the red line - this comes from drawing a yellow Sharpie pen along the edge of the balsa skin before joining - whereupon it turns red when touched by cyano. This then gives a clear indication of the completeness of the joint. Mostly I use cyano in a sort of 'spot weld' fashion, but sometimes a totally glued joint is needed. The bomb bay skin is then loosely bound to the mould to encourage it to keep its shape until the time it's fixed to the rest of the fuselage.

This bomb bay has considerable double-curvature and I used reasonably stiff balsa, which led to three wrinkles in the skins from the initial wetting/binding/drying process. I cut these out and inserted balsa patches, circa 4x4mm. One of these is just visible (arrowed) in the picture.

Stephen.

Today I reshaped the nose mould to make it suit a bomber Mosquito. I had to revert to holding the nose mould up against pictures on my PC screen to see how good (or bad) the match was. Hardly ideal but the best way available. It's not just about comparing the outline, but also comparing shape, by drawing lines on the mould (the little side windows are a good example) to see if they match the same lines on the photo. In the end the nose needed quite a bit of reshaping and is now about 6mm shorter than it was, which means a slab of balsa added to the back of the mould to restore the correct length. I then plunged a test of the Perspex nose. It looks like the side windows can be obtained from the same plunge as the nose bowl.

I then made a bomber canopy mould, and likewise tested a plunge of this. It clearly needs a good bit more shaping yet. It doesn't look right.

Stephen.

It takes a good eye to see those differences Stephen - and a fair bit of artistic capability.

It's a fascinating journey.

John

Quote from: OZPAF. . .a fair bit of artistic capability.

S'funny you say that, John. About 18yrs back, I started to teach myself painting (aeroplanes of course :) ), and thought that the best way of seeing how light bounces off an object would be to make a model of said object and place it in the same relation re. sun, sky, clouds, whatever, as the subject I wanted to represent in oils. That's what went and gone an' got me into this daft hobby :). I ended up dropping painting. Mainly due to eyesight troubles, but partly because this daft aeromodelling thing sucked up all my hobby time.

 Adding a plate at the rear of the nose mould means that it doesn't match the fuselage main section behind it - see the photo. Luckily I dodge a bullet here, because the sides are parallel, so they do meet each other properly, and the main discontinuity is at the top - where the cockpit is, so there won't be any wood there anyway. The discontinuity at the bottom is slight and I sanded it fair.

After reshaping the canopy mould somewhat I tried another plunge. Better but not quite there yet.

Meanwhile . . . what has the farmer done to my flyng field? It's been sprayed with pesticide, sprayed with slurry ('muckspreading'), and yet still has cattle on it, fed with hay. It's a churned-up, dead, smelly mess. Normally at this time of year it's lush green. I have a nasty feeling that it's going to be ploughed up - maybe soon - and planted with maize.

Stephen.

That doesn't bode well for your flying field Stephen! Whatever is planted there will just become a new challenge to miss :) 


John

Moulding these nose skins was something. 3+ hands required to do the binding. It meant that the top and bottom skins had to be done individually - on less curvy moulds I would bind a left+right or top+bottom in pairs, to save time in the hotbox. That's approx 1hr for stuff like this, whether it's just one skin or two. I did manage to bind the left and right as a pair, so saved 1hr. Incidentally I measured the temp in the box - something I haven't done in years. 82°! That's going some. No wonder these parts are holding their curves nicely after unbinding.

The top and bottom skins had to have slim 'relief wedges' cut out at the front in order to bend to the curvature of the mould.

Today came the tricky job of shaping the edges so that they fit accurately. This is one of those 'sand a fraction off just here; check the fit; repeat' type ops that takes time. I stuck a thin strip of Sellotape to the mould to stop the skins from sticking to the mould, and commenced to join the skins until only one seam remained. I thought I had shaped the edge of this so that the skins fitted to the mould tightly at the front. I glued this seam 'in the air' - off the mould: easier to manipulate the join. But when I put the finished nose onto the mould it was loose at the front. I had to cut out additional relief wedges in each side panel and glue them closed, in order to get the right circumference at the nose. Those relief wedges have to have slightly curved sides.

The balsa skins and the PETG nose transparency are formed on the same mould. But the balsa skins are much thicker than the plastic. Approx 0.4mm thicker. So there'll be a step between the two when the transparency is fixed in place. Hmmm. Heck, I don't even know how I'll fix it yet. One of the things i wanted to find out from the test model is the vulnerability of the nose with regard to landing. As I'd hoped, the nose turns out to be well protected by the nacelles and props. So I hope the light structure of the nose will suffice in this model too.

Stephen.

QuoteI had to cut out additional relief wedges in each side panel and glue them closed, in order to get the right circumference at the nose. Those relief wedges have to have slightly curved sides.

Good grief Charlie Brown!! :)  The final result result looks very neat!

QuoteThe balsa skins and the PETG nose transparency are formed on the same mould. But the balsa skins are much thicker than the plastic. Approx 0.4mm thicker. So there'll be a step between the two when the transparency is fixed in place. Hmmm. Heck, I don't even know how I'll fix it yet.

A balsa hoop ring under the end of the fuse may allow it to be sanded gently down to the line of the transparency without it being too obvious?

John

Quote from: OZPAFA balsa hoop ring . . .

Yes. That was the kind of thought I was having before turning to the rest of the fuselage (got to keep the whole thing moving roughly in concert). I did use the balsa form to plunge mould a 1mm plastic card 'nosebowl' - that might come in handy - and also I stuck one of the existing test plunges back on the balsa form, and then plunge moulded another transparency over it, which of course has a larger radius . . . that was fun - I didn't know what would happen - would the hot PET melt the PET stuck to the form, and generally make a complete mess? No, it worked fine. So there are 'options on the table', as we jet-setting business magnates like to say.

Also yesterday I made the other fuselage panels - Two forming the main section and two the rear fuselage. These were a doddle compared to the nose  - there's very little double-curvature involved. Today I wielded the long sanding block to get the long edges ready to meet, whereupon the top seam is glued with thin CA. The end-caps of the moulds are unscrewed so that the skins can be clamped back on the mould (fingers being the clamps) and each end of the skins is sanded carefully flush with the mould (pic 3). That's why I cut the original one-piece fuselage mould into three: by allowing the ends of each fuselage section to be sanded exactly flat, the butt-joints between one and the next are easy. The skins at this stage are springy/ floppy - trying to sand the ends flat and square freehand is difficult and time-consuming.

There's work to do on the internal structure, which I've started but no pix yet. Mostly careful measurements, and dealing with the difference from the test model caused by the bulging bomb bay of this Mosquito variant. The picture with the long sanding block shows some thin card slotted into a razor-saw cut in the main fus. mould. The cross-section this provides is for the critical main former (the one that bears the wings and also the pendulum).

Stephen.

Starting on the internal structure: making various templates for the four fuselage formers. I may choose or need at least one in the nose, but I hope not. Of the rear formers, one is light but has a stiff crossbrace, and the tail former is fancy. The fin spar slots into its forward face, and the tailplane spar presses into its rear face. All the flying the test model has done is with the fin/rudder not fixed to the airframe: the fin can be drawn from its slot. Positioning these formers for fitting involves skewering the former on a bamboo stick, in the case of the tail former, and pushing the crossbrace into a split end of the same stick, in the case of the mid-section former. Then lots of tamping and hooking (bent piano wire) to align the former. The weight of the little tail former worried me - it's stiff 1/32  0.8mm. The test model is irritatingly tail heavy . . . but the former turns out to weigh only 0.15g, so no grounds for complaint I suppose.

Stephen.

.

Your multipurpose rear former( 0.15g - getting a bit heavy there Guv.) is clever Stephen and I like your skewer assembly approach.

Will the elevators be hinged as well as the rudder?

John

Oops - I'm back after an unscheduled absence. I hope to get on with this model now. I've started on the main formers. The one on the left has a strong crossbrace because it's located where I will hold the model for launching. I learned from the test model that this was the natural spot for a balanced launch (as much as I can ever achieve a balanced launch that is . . .). The former I'm assembling on the right is The main former - the one that holds the wings and the pendulum.

John, yes the elevators are articulated and yes the tail former/slot/spar arrangement could be lighter ;).

Stephen.