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Author Topic: Junkers 87 B-2/R-2  (Read 2958 times)
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TheLurker
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« Reply #75 on: November 07, 2019, 03:04:39 PM »

Huzzah.  A fin & rudder.

The hinges are some lovely thin tin-foil from a supermarket (Sainsbury's for - southerly - Englandlandshire based readers) quiche base. It comes in at about 115g/m2.  Not many years ago you could have used the foil casing from most pies to repair the bodywork on a car so, "Huzzah! for cost-cutting measures" say I.  I daresay most own-brand pies and quiches have similarly thin tin-foil bases these days.

In lieu of cigarette papers the rudder/fin spacing was set using three layers of 80gsm glued together, the top spacer was 2 layers and the spacer for the stab. slot is 1/16" + 4 layers of 80gsm.  The stab. spacing may be a bit too much, but I wanted to allow for a couple of layers of tissue over the 1/16" framework.  If needs be I can always pack the slot if it is too deep.

Will be covered with pre-shrunk & doped tissue. Used this construction on my Peck M-10 and it worked pretty well.

Pics.  Finished article and a couple of in-progress shots showing spacers in situ.
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abl
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Andy Blackburn



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« Reply #76 on: November 07, 2019, 05:21:29 PM »

So, let's see... that's 5 points for converting a sheet fin/rudder to built-up construction, and at least 1 point for having a moveable rudder. I've said this before, but I have an uncomfortable feeling that this is going to cost me...
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TheLurker
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« Reply #77 on: November 09, 2019, 04:13:01 AM »

... and a stabilizer.  

Mr Barnes-Norway is preening himself on having implemented his wizard wheeze of making the final fuselage formers ever so slightly overlong at the top so as to provide a key for the fin.  The rest of the staff in the drawing office think he's too far too full of himself over such a trivial idea and are wandering around muttering about pride going before a fall.

That's the sheet tail dealt with.  Not sure whether to deal with the canopy or the wings next as both will be slightly different to the kit supplied bits.  The canopy will be plunge moulded.  No, I'll rephrase that.  I'm going to try to plunge mould the canopy.  Not having used the technique before the result could prove amusing.

The plan is to make the canopy plug from laminations, see the attachment, for three reasons. One, I guard my stock of block jealously. Two, I'm rubbish at carving and three, the canopy has three distinct sections.  It has been pointed out by the CD that this could result in some unsightly lines on the resulting canopy.  However I think it's worth the experiment as I can always fall back to a three-section plug if it all goes horribly awry.

The wing?  Well it looks like we need a complete new wing.  The image shows what I intend to build compared with the kit version.  The planned wing is a closer, although not exact, match to the prototype's proportions.  The inner, anhedral, section also changes slightly, but the differences are not so marked.
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abl
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Andy Blackburn



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« Reply #78 on: November 09, 2019, 09:36:08 AM »


>  It has been pointed out by the CD that this could result in some unsightly lines on the resulting canopy...

They might not be too bad if you use balsa cement and clamp the joint to reduce the glue thickness to a bare minimum.

A.

P.S. is there anything on this build that you've not changed from the original plan?  Smiley  I think you've safely exceeded the points required for the full Monte breakfast, as long as it flies for at least 12 seconds.
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TheLurker
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« Reply #79 on: November 09, 2019, 01:10:58 PM »

Quote from: abl
P.S. is there anything on this build that you've not changed from the original plan?  Smiley
A number of Lurker Industries' inter-departmental memoranda have surfaced.  Two of them may shed some light on the situation.
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TheLurker
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« Reply #80 on: November 23, 2019, 02:02:43 PM »

It has been remarked upon in the Drawing Office that there is a regrettable tendency to molly-coddle pilots these days with unnecessary and weighty luxuries such as enclosed cockpits.  The elder of the McPhail brothers, James, is particularly irked by the extra weight incurred , but he is regarded as rather too purist even by the exacting standards of the rest of the staff in the Office and he refuses to be persuaded that there are aerodynamic advantages to a well designed canopy.  It is probably as well that he is considering retiring.

Or...
First experiment with plunge moulding the canopy today.  Not a roaring success, but there are grounds for optimism.

In brief.
Some evidence of lines, but they're very faint and a bit more polishing of the plug should deal with that.  If I were better at shaping block it's not a technique I'd use again as it's rather time consuming.

May have to exaggerate the steps at the front and rear sections of the plug to get a crisper step in the moulded canopy, see the profile pic.  Suspect that wouldn't be an issue with vac. forming.

Gun "bubble" works better than I thought it would. Again I suspect vac. forming is what's really needed to pull the material tight to the plug, but there's definitely a bubble.

Need to cut a proper mounting plate for the blank, the test today was with a rough cut bit of hard-board to see if a hot-air paint stripper would be a good enough heat source.  It is.  I think I may need a bigger gap around the plug as I got a very uneven draw of the sheet.  One side and parts of the top are paper thin and wrinkle on sight.  Maybe even some heavier gauge sheet.

As I haven't got any really suitable thin board for the draw plate the plan now is to make a start on the wings and come back to the canopy when I have.

Pics.
Front, rear and side view of the test piece. You can see clearly that the rear step in the top line is more of a slope than a step.
Test piece very roughly cut down and perched on the fuselage to assess the "rightness" of it.
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« Last Edit: November 23, 2019, 02:20:45 PM by TheLurker » Logged
abl
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Andy Blackburn



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« Reply #81 on: November 23, 2019, 02:38:19 PM »

Dunno what thickness acetate you used, I normally use 10 thou on a canopy that size. Also, I find I have to leave a decent-sized gap around the plug (maybe 1/8") with rounded edges on the plate in order to get a decent canopy. I usually get best results by just shoving the acetate with the base under the grill and then pushing it over the form when it's steaming and gone properly floppy - I've never been able to get a decent result with a hot-air paint stripper, I'm a bit too cack-handed with it so bits of the acetate tend to overheat and bubble.

Had you considered moulding the gun "bubble" separately and then attaching it afterwards with dope or similar?...
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TheLurker
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« Reply #82 on: November 23, 2019, 03:23:54 PM »

Quote from: abl
I usually get best results by just shoving the acetate with the base under the grill....
Mrs Gordon, the Staff Canteen Head Cook, is not kindly disposed to staff from other departments encroaching on her domain.   The last time canteen equipment was put to uses other than catering was when one of the junior members of the establishment tried to dry off a freshly cleaned bike chain in an oven. Reader may wish to note that the smell of paraffin is not regarded as particularly pleasant by cooks.   Odd people cooks, everyone knows that, after benzene, it's quite the nicest smell.

Quote from: abl
Had you considered moulding the gun "bubble" separately and then attaching it afterwards with dope or similar?...
I hadn't.  I rather think I'd make a complete pig's ear of it if I tried.
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FreeFlightModeller
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« Reply #83 on: November 23, 2019, 07:01:54 PM »

Benzene?! It was taken out of circulation at my old school over 40 years ago. Considered quite a carcinogen now I understand. (About the same time as the chemistry teacher stopped walking around the class with radioactive isotopes...)
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flydean1
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« Reply #84 on: November 23, 2019, 08:57:40 PM »

As I recall, nitro-benzene was a key ingredient of the old "This Is It" UC racing fuel.  Went to many a speed meet "way back when" and luxuriated in the fragrance of "shoe polish" fuel.
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TheLurker
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« Reply #85 on: November 24, 2019, 04:21:32 AM »

Quote from: FreeFlightModeller
Benzene?! It was taken out of circulation at my old school over 40 years ago.
That'd be about right.  We were still using it in undergrad. labs in the early/mid 80s but it was "fume cupboard only" use and very, very rarely used at that. IIRC* toluene was the preferred alternative for use as a solvent.

Quote from: FreeFlightModeller
Considered quite a carcinogen ...
No "considered" about it.


*I may not. It was a long time a go and I was spectacularly rubbish at chemistry. Smiley
« Last Edit: November 24, 2019, 04:36:19 AM by TheLurker » Logged
billdennis747
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« Reply #86 on: November 24, 2019, 04:44:30 AM »

(About the same time as the chemistry teacher stopped walking around the class with radioactive isotopes...)
I think ours did that too but we were more interested in playing marbles with pools of mercury.
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FreeFlightModeller
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« Reply #87 on: November 24, 2019, 05:20:00 AM »

Lurker,
Yes, toluene was the substitute.

Bill,
Eee ... you were lucky. We had to make doo wit' asbestos fibres pulled from mat and put in t'bunsen to make flame turn orange.

How are we all still alive?!
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FreeFlightModeller
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« Reply #88 on: November 24, 2019, 05:29:18 AM »

As I recall, nitro-benzene was a key ingredient of the old "This Is It" UC racing fuel.  Went to many a speed meet "way back when" and luxuriated in the fragrance of "shoe polish" fuel.

I'll have to look that one up .... in my youth there was not much finer than the whiff of rapidly burning Castrol R 2 stroke oil!
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Squirrelnet
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« Reply #89 on: November 24, 2019, 06:39:03 AM »

I still use Castrol R in an old bike I have , as you say Russ the smell  Grin

 
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FreeFlightModeller
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« Reply #90 on: November 24, 2019, 07:57:39 AM »

I've always been the "smellee " rather than the "smeller" if that makes sense?! As much as I have always loved bikes, my glorious collection only runs to a Suzuki ts50er and an Aprilia 125 Futura! The latter was worthy of Castrol, but ran on fully synthetic.

Anyways ... back on thread .... what did a Stuka smell of!  Roll Eyes
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billdennis747
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« Reply #91 on: November 24, 2019, 08:24:26 AM »

Lurker,
Yes, toluene was the substitute.

Bill,
Eee ... you were lucky. We had to make doo wit' asbestos fibres pulled from mat and put in t'bunsen to make flame turn orange.

How are we all still alive?!
No idea. Another wheeze was dipping fingers in ether and lighting. Found out by practical means that acetone isn't the same as ether.
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Pete Fardell
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« Reply #92 on: November 24, 2019, 09:41:20 AM »

Don’t forget turning on and lighting a gas tap (with no Bunsen attached) to make an instant flame thrower with a useful 6 ft range.
Our physics teacher used to carefully remove the radioactive substance from its lead-lined box with tongs. However, by the end of the lesson he’d misplaced the tongs so he’d  put it back in with his fingers (but very quickly, before any radioactivity could rub off!)
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billdennis747
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« Reply #93 on: November 24, 2019, 10:46:19 AM »

Don’t forget turning on and lighting a gas tap (with no Bunsen attached) to make an instant flame thrower with a useful 6 ft range.
Our physics teacher used to carefully remove the radioactive substance from its lead-lined box with tongs. However, by the end of the lesson he’d misplaced the tongs so he’d  put it back in with his fingers (but very quickly, before any radioactivity could rub off!)
Yes we all did it in unison as Mr Thrasher (oh yes) turned back to the blackboard. It looked like the opening credits to Dallas.
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TheLurker
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« Reply #94 on: November 24, 2019, 01:13:04 PM »

My, my.  What a bunch of ne'er-do-wells and tearaways you all were.  I'm not sure that my mummy will let me play with such bad boys any more.  Smiley

On gun "bubbles".

I wasn't happy with the rake of the rear canopy, not shallow enough, too near vertical.  So hacked off the existing bump and sanded in a more correct angle before attaching a new bump.  As the bump worked moderately well in the initial test piece I'm hoping that a less "vertical" presentation will give an acceptably good result.
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« Reply #95 on: November 24, 2019, 02:26:36 PM »

Our favourite trick was to blow down the gas taps in the physics lab so that all the bunsen burners in the chemistry lab upstairs would go out!
Ron
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TheLurker
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« Reply #96 on: November 28, 2019, 03:24:05 PM »

Another little deviation to keep the judges busy.  A bomb aiming window.  Thought I'd have a go a fitting it whilst other bits are settling.

Construction is dead simple.  The difficult bit is the modified keel with a dent in it which requires a degree of forethought.  The "window" itself is three bits of 80gsm paper.  Sidewalls are black ink, the window is silver crayon and the hinged cover panel is light blue crayon which is a fairly good match for the selected tissue for the underside. All held in place with smears of glue stick.  The camera is pretty unforgiving, but it looks reasonably convincing to the my (middle-aged verging on old) naked eye.

And just for the hell of it the first completed wing section, starboard outer.
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abl
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« Reply #97 on: November 30, 2019, 04:06:46 AM »

Sadly (for me, anyway), whilst that is self-evidently not a "significant" deviation (I mean, you can hardly see it and it's hidden from view most of the time - hardly more than enhanced decoration, really) most judges would whip out their green pens and assign some penalty points.  Sad

(If there are any kit scale judges reading this, please feel free to chip in and contradict - I need all the help I can get here!)

...
And just for the hell of it the first completed wing section, starboard outer.

As previously noted, I think you've safely accrued more than enough static points to earn a Full Monte breakfast at the Super Sausage Cafe, but I'm not going down without a fight. May I say, then, that the half wing looks exactly the same as the Albert E Hatful's original; well done on sticking to to plan, for once...
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TheLurker
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« Reply #98 on: November 30, 2019, 07:24:50 AM »

Quote from: abl
Sadly (for me, anyway), whilst that is self-evidently not a "significant" ...
Indeed, hence my use of the adjective, "little".

Quote from: abl
May I say, then, that the half wing looks exactly the same as the Albert E Hatful's original; well done on sticking to to plan, for once...
While it is customary to denigrate some of Mr. Hatful's plans for lack of scale accuracy, quite unfairly and unjustifiably given the relative paucity of good reference documentation available when they were drawn up as well as the commercial constraints required to make Keil Kraft's kits profitable and still provide something that almost anyone could build, it would be deeply worrying if the wing section did not look much the same.  However as noted in Entry No. 77, Attachment No. 4 (above) the wings are not exactly the same.  It will be seen that there is a noticeable difference in the sweep-back of the L.E., the shape of wing tip and the size and shape of the flaps.

Quote from: abl
I think you've safely accrued more than enough static points
I've lost track of penalty points garnered so far and there has been a troubling lack of comment from His Honour Judge (Jury & Executioner) Jack Plane so I really couldn't say.  Anyway the real test will be does the blessed thing fly?
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DavidJP
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« Reply #99 on: November 30, 2019, 12:10:44 PM »

Must confess that I find it slightly alarming that some of you later taught/teach and behaved in such an irresponsible way.  So is such behaviour permitted today? 

I applaud you Lurk on defending our Albert.
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