Ambrosini SAI.7
Ambrosini SAI.7
1939 IV Raduno Aero del Littorio
1939 FAI World Speed Record 302.58km/h
(Category C, Powered, Multiseats, 6.5 - 9L, 100km closed circuit, no payload)
1939 IV Raduno Aero del Littorio
1939 FAI World Speed Record 302.58km/h
(Category C, Powered, Multiseats, 6.5 - 9L, 100km closed circuit, no payload)
Comparison profiles that are guiding the work. Little out there to work with, but this will do. Test measure of the kit against the lower profile benchmarked quite close, so has given some confidence ..
Nice solid one piece wing. Wheel wells to be covered over as I’m planning this to be another ‘in flight’..
Slightly ‘puffy’ form to the fuselage, sort of ‘bulging’ at the panel-joint seams. Cockpit opening rough & nose detail indistinct, but no worry as these to be heavily modified ..
Upper wing, nice form, sharp trailing edges, very feint engraved panel lines …
Wing upper panel lines scribed & surface smoothed. Fuselage rear joined, front minimally so, merely to hold alignment as the nose will be sawn off.
The wing root fairings on the fuselage halves were rough, unevenly edged & wildly out of alignment. The worst raised bits have been carved off and new styrene edges shimmed in …
Wing root fairings were so lousy that alignment of primary parts was not happening naturally. So a boxboard jig was devised to hold in place while the epoxy cured. Jig also used to guide reset of wing root to wing edge … next is putty to fill those crevasses!
Working on the starboard wing root ..
Plane was ply construction, while wing roots are seen in photos as overlaid metal fairings. So I’m using dymo tape to maintain a slight lip on edges (& protect the adjacent surfaces from sanding)
With wing roots done, guide tape applied for the heavy surgery ahead .. time to dig out the razor saw
OK, I’m definitely committed!
Look how thick those resin fuselage walls are! Out of scale, sure, but for now helpfully stable. Will clean up the cut edges tomorrow …
The kit SAI.207 has the long nose housing a V12 motor, whereas the SAI.7 was fitted with a shorter V8 ..
.. the V8 is an inverted Hirth 508D which is air-cooled, so it’s quite visible through the open cowling mouth, no radiator to hide it. This is the same motor as fitted to the Messerschmitt Bf-108 .. [edit - my error! only the first handful of 108’s used the Hirth, production versions used a similar configuration Argus motor. Oh well, carry on!!]
Using an Eduard Bf-108 kit from the stash for measurements, I’m underway fabricating a copy of the motor .. the block is largely done, cylinders underway ..
Progress on the scratchbuilt inverted V8 …
Landing gear wells were quite different between 7 & 207. I can’t say if these kit 207 ones are accurate or not, in any case need to blank them off ..
Templates transferred onto thick sheet stock, which were then CAed in with a bit protruding all round
Some epoxy putty for blending adjacent & then much sanding down to merge in the kit openings. Then a new template for scribing SAI.7 racer wheel well door arrangement …
And done (until primer punctures my hubris!). I will be mounting the aircraft in-flight, so that’s the extent of undercarriage work completed. (This exercise revealed that the kit wheel wells are pretty rough, non-symmetrical & off-centre .. of note for anyone building the base kit 207)
Correction time! Argus = 90deg V but Hirth = 60deg V. Soooo .. deep breath & start sawing
Fiddly work …
Dusted off
Another boxboard jig - at 60deg V - to hold the cylinder banks at new splay. Next will be to fashion a styrene wedge to fill the centreline of the block, before reshaping the block
OK so, I’ve caught up after my error. Here’s the re-sculpted block, new gearbox, & 60deg cylinder V .. one scratchbuilt Hirth 508D ready for paint & pushrods!
Remaining wing underside scribing now done too.
Blocking out basswood to be carved as bucks for vacforming. Two on top for canopy, one below for cowling.
Early SAI.7 profile not only differed from kit SaI.207 forwards as canopy, but also along spine back to tail fin. A plate of styrene fixed along the spine to guide future putty work.
Cowling block first ..
And we’re underway! Very pleasant whittling away time & timber …
Time for the canopy blocks to catchup to the cowling. Adhesive guides trimmed to reveal the timber ..
And some meditative time later, a large portion turned to shavings and powder ..
The goal of this phase being to bring the top of the block to the final profile.
A definitive centreline ridge line is now drafted on. The discipline now is to protect that. Next will be shaping the sides down to meet the fuselage.
.. some time later .. separate bucks for clear & opaque plastic
Bulk shaped. Next & final bit will be the nose ..
.. bulk shaped, yet to be slimmed down all over to allow for vac-plastic thickness, and yet to add the ‘pinched’ reverse curve detail along the sides ..
.. so a bit closer
The cowl nose needs a neat circle at front where it will meet the spinner. I was concerned that it would be just so easy to accidentally whittle or sand off too much & compromise that circle. So to protect the circle I fixed on a screw of suitable diameter. Interesting to find screws not as regular as you might think! I used a circle template to select a true circle specimen.
Confirming the top spine profile blends down to the screw-spinner ..
Progressive lopping off bits ..
Sanding, sanding …
Sanding, sanding … concentration fading, so a pause here for tonight.
Faces blocked out, with sharp edges to be addressed next …
.. smoothed off cowling edges ..
Cowling as close to done as I think I’ll ever get it..
Front of cowling particularly challenging!
Timber work done. Cowling shaped, with the pinched, scalloped indents to canopy finished too. Final surface finishing & preparation for Vacform soon!
Cowling buck, varnished & polished, sitting on final tweaked version of plinth. Proportionally too tall, so needed to ‘export’ the webbing down below the useable part
Finalised cowling: vacformed part trimmed back; cowl panels laminated on externally; near to a dozen styrene strip, rod & tube reinforcements internally!
Works in parallel: scratchbuilt engine now painted, pushrods added & cylinder banks now glued together. Some more detail to come .
Canopy transparency done! Test fit together with cowling.
Canopy transparency done!
Kommentarer
33 7 June 2023, 01:14
Alex KFollowing with great interest. I suppose building a SAI.207 resin kit could be already interesting... but the fact you're going to backdate this and turn it into a SAI.7 racer is the icing on the cake! Respects and good luck!
7 June 2023, 18:50
greggles.wThanks for your interest Alex & Robert, hope to deliver another update soon ..
8 June 2023, 13:51
David CulpModeling with a saw! I always like projects that require sawing. It looks great, and I'll be following.
9 June 2023, 15:27
Ludvík KružíkI like extensive modifications, rebuilding and scratchbuilding. Your project looks very good. Interesting machine and great range of modifications.
I'm watching with great interest 👀
25 July 2023, 12:59
HSC1932Wow, so many different skills and techniques on display…how do you not run out of motivation with that much work?
25 July 2023, 22:27
greggles.wThank you all for taking the time to comment, most appreciated! HSC1933, your query re motivation has had me reflecting. I think it's two things:
One, my opportunity to 'do' the hobby is limited, sporadic & unpredictable, so I spend much more time wistfully thinking of what I might do, some day, whenever I next can. So a more involved project gives me more 'think' to mull over while waiting to 'do'.
Two, my family is beset with perplexing health issues & care needs. I spend much time trying & trying to help & support as needed, however it can often seem like we get nowhere or worse regress. So I take a lot of reassurance from the fact that these projects 'progress' - yes with effort, patience, pause & hold - but they do progress. For this reason my recent completions mean a great deal indeed to me!
26 July 2023, 12:06
Pierre Pierreit is super impressive may I ask what type of putty you are using ?
28 July 2023, 12:12
greggles.wThank you Pierre, very kind. The yellow(ish) putty here is Tamiya two-part epoxy 'Quick Type'. I'm relatively new to using it, but liking it so far. Though don't be too hopeful re 'quick' .. where applied thickly I have waited 12hrs or so before sanding. For some this might be irritatingly slow, but for me - a very slow builder - this is 'quick' enough!
28 July 2023, 12:23
Alec KWow, amazing project. Love that custom scratch work and thank you for the detailed and insightful narrative 👍
20 October 2023, 12:28
Pierre PierreThank you greggle! slow modeller too so i will try to put my hand on as it look dense and easy to sand.
20 October 2023, 13:00
Alec KCowling looks amazing. What thickness styrene have you used for vacuforming?
22 November 2023, 14:29
greggles.wThanks both! Alec, for this piece I used 0.5mm / 0.020" sheet. I'm still quite new to vacforming & am still loosing more parts than succeeding! This thickness is my starting point with the inevitable trial-&-error process. In this case it was 'good enough', although resulted in quite a thin lower / rear edge. In the photo showing the inside of the cowl, the top 'plate' held by the tweezers is non-vacformed 0.75mm / 0.30" sheet .. compare that to the vacform sides, which look about 0.2mm at most?
22 November 2023, 22:57
Alec KThanks for the info. I have had similar experiences, with each part requiring trial and error runs to get a good final part 👍
25 November 2023, 19:32
