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Author Topic: CallAir A-9 for rubber power  (Read 372 times)
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Pete Fardell
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« on: June 11, 2017, 03:37:59 PM »

Thank you for all the input on my Ag Plane thread. I've decided to avoid the more interesting (some might say insane?) suggestions and stick with the fairly orthodox, but rarely modelled CallAir A-9. It'll probably be around 30" span for indoor, and occasional outdoor flying. I really like the look of this aircraft, and one reason for building it is that I found flying conventional monoplanes at the FF Nats at Barkston was rather more fun than generally failing to fly my less conventional Caudron and Antoinette models at the last two Indoor Nats! That's not to say I won't return to weird and wonderful subjects later though.

As the only top view photo I have is of a standard A-9 (and not an A-9B, or other variation) I thought I'd better stick with the only matching 3 view. So, my first job was to see if it bore much relation to the photos. Starting with the side view, I find that it is not TOO bad when compared to the photos, but already I am a bit out of my depth. Using Adobe Illustrator I traced two side views photos of my planned subject, scaled them to the three view drawing and tried to see if they matched. The first one (red line) is quite close, but a bit short in the tail. The second one (blue line) appears to be a LOT short in the tail. So obviously there is distortion, presumably due to the photographer's viewpoint, vagaries of the lens, perspective etc.
Don't really know what to do next. Do I just decide the three view is close enough to build from, or do I adjust my building plan to match a photo? If so, which one? I don't want to get completely bogged down but I do want a reasonably accurate model this time.
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CallAir A-9 for rubber power
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ZK-AUD
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« Reply #1 on: June 11, 2017, 03:51:30 PM »

I think I'd find a better 3 view.  Manufacturers drawings will exist somewhere.  These things are still flying so there must be manuals.  The wing section in the photos is nothing like the the one in the drawing and is much better for our purposes.  Our rule here is that you go with the 3 view.  But as I said I think you need a better one.
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Pete Fardell
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« Reply #2 on: June 11, 2017, 04:03:51 PM »

Thanks. Mind you, the rule here is that you (or rather the judges) go with the photos. Having said that, I do need a three view too.
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Prosper
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« Reply #3 on: June 11, 2017, 06:06:38 PM »

Quote from: Pete
Do I just decide the three view is close enough to build from
No, 3-views are garbage, always. You may need one for competing but that shows how silly competition rules are. ZK's right, you need better info just for your own peace of mind let alone competition rules.  Not trying to step on yer toes, but I did a quick search and the side photo below looks a better bet to me because although it's at a slight angle it's taken from much further away so there's less perspective distortion. So with a key measurement or two - like the wing chord for example - you can start getting some fairly accurate measurements from ratios. Making accurate drawings in this way is painstaking and needs lots of lucky photos - I'm sure you know this from your researches into previous models Smiley. I'm not sure you'll get enough useful photos of a subject like this. . .but you might!

Stephen.
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Re: CallAir A-9 for rubber power
Re: CallAir A-9 for rubber power
Re: CallAir A-9 for rubber power
Re: CallAir A-9 for rubber power
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Pete Fardell
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« Reply #4 on: June 11, 2017, 06:32:06 PM »

Thanks, Stephen- that's all really Useful info. I'd found that picture and there are several other good side views too, so from that angle at least it should be fairly easy to get close to accuracy, especially with your tip (obvious to others perhaps, but not to me till now):
... the side photo below looks a better bet to me because although it's at a slight angle it's taken from much further away so there's less perspective distortion.

Anyway, I won't re-draw the three view unless I really have to (ie if it's miles out) but will aim to get towards a photo evidenced building plan first and go from there. Surely once the outlines are right, the details  (lumps and bumps etc.) can be modelled directly from photos can't they?
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Pete Fardell
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« Reply #5 on: June 11, 2017, 07:15:53 PM »

For what it's worth, this is what happens if I put a hastily traced outline of the N7232V side photo over the drawing. Still doesn't quite fit but the tail and nose length are about right now.

I can see why accurate 3 view dimensions are essential for accurate building, but don't completely understand why judges need a drawing at all if they're going to go by the photos anyway. What do they do with it?
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Re: CallAir A-9 for rubber power
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Prosper
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« Reply #6 on: June 12, 2017, 03:30:56 AM »

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. . .why judges need a drawing at all if they're going to go by the photos anyway. What do they do with it?


I think I've read posts from Bill Dennis saying that there's a move in the UK to give priority to photos. It seems reasonable that judges need some quick reference regarding layout, and that's the job of a 3-v. The trouble is that 3-views are only passingly like the subject they represent. I'm mostly thinking of the small, black silhouette kind seen in sales brochures and annual directories and such, but frankly many 'scale drawings' embody inaccuracies which spoil or even ruin the scale appearance of a subject too.

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. . .once the outlines are right, the details  (lumps and bumps etc.) can be modelled directly from photos can't they?
No kidding - and accurately too, if you have the luxury of relevant and reasonably undistorted piccies. If I know that the Bloggins Skyking Mk.2 has a 4ft aft fuselage extension compared to the Mk.1, and I have a square-on picture of the middle of the 'plane, I might get the length of the undercarriage doors, which might then yield the engine nacelle length from another photo, which might provide the wingroot chord from an underside view. . .It's slow work and sometimes exasperating, but if used with the danger of photographic distortion ever in mind, can give you a better scale result than even draughtsmen with vaunted names come up with.

Stephen.
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Pete Fardell
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« Reply #7 on: June 12, 2017, 05:28:10 AM »

Thanks- that's encouraging.

I think I've read posts from Bill Dennis saying that there's a move in the UK to give priority to photos.
I think it goes a bit further than that; the rules state that photos already ARE given priority. In theory, good photos with an inaccurate 3-view should not necessarily get you marked down. On the other hand, if I was judging, a 3-view that bore no relation to the photos would really tick me off, and annoying the judges cannot be a good idea!

So perhaps I'll just bite the bullet, re-draw the 3 view and try and get it signed off first.
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Pete Fardell
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« Reply #8 on: June 13, 2017, 12:29:09 PM »

Made a start today. For this drawing I'm going to use a mix of Adobe Illustrator and freehand drawing. Illustrator suits me quite well because it's not proper CAD (which I still find rather onerous) but lets me do things like trace over photos and import pencil sketches and turn them into black line drawings. Not really familiar with all it's tricks so learning as I go.

My subject aircraft is now firmly decided as N7207V , aka 'Jaws', thanks to Mike(msc)'s very kind offer to try and get more photos from someone at the Elsinore Soaring Club where the aircraft is based.
Here are two of the photos I've already found of it. Note that one side is white, and the other yellow. The yellow side has metal panels on the rear fuselage and the white side doesn't. A lot of A-9s seem to have this asymmetry. I assume the panelled side is to enable access. This is just the kind of anomaly that makes ag planes so quirkily attractive.

Also, here's a screenshot my continued drawing experiments showing the tracings from two side views of another A-9 (N7232V as suggested by Prosper) superimposed over the evidently inaccurate side view I already have (which thanks again to Adobe Illustrator is now converted to a faint outline drawing rather than the silhouette it was to start with). The two photo tracings match each other pretty closely with any slight differences easily accounted for by the slightly differing viewing angles. I think I can get a decent side view drawn up on this basis and then extrapolate it into a top view drawing with the aid of more photos and published dimensions. Quite enjoying myself at the moment.

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Re: CallAir A-9 for rubber power
Re: CallAir A-9 for rubber power
Re: CallAir A-9 for rubber power
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Pete Fardell
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« Reply #9 on: June 13, 2017, 01:07:16 PM »

Just for my own peace of mind I added a third tracing (blue line) from another side view; this time of my subject aircraft. Everything still seems to match up quite well.
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Re: CallAir A-9 for rubber power
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