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Author Topic: Junkers F13  (Read 1603 times)
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Rhys
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« on: January 20, 2019, 05:12:33 PM »

Greetings All!
This marks a new beginning here. Haven't built in a while. Thought I'd take a stab at what seems to be a fairly straight forward, and simple enough plan to get my feet wet again. The subject is Otto Reuter's design of Junkers' F13 - the inline version. The plan architect is Michael J. Heinrich. Though it seems to be more like a "dime scale" design, it appears, with a slight bit of adjustment to be a decent flyer with Voodoo 10 and Zombie Profiler. Accompanying this are pics of what Iv'e completed thus far. Although it's not much at least it's somewhat in the direction of progress. I welcome all questions and advice, and would like to say thank you all for allowing me to join in with this forum Grin

Ive added a couple of pics to illustrate the "open cockpit" the F13 had - I didn't know this was the case in earlier drawings  (this pic is of the Rimowa Junkers F13 replete with radial engine)

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Rhys
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« Reply #1 on: January 20, 2019, 05:13:33 PM »

an additional pic
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DavidJP
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« Reply #2 on: January 20, 2019, 05:40:12 PM »

Nice idea - I think some aspects of the construction will prove interesting so onward please. And pictures.

I wonder why the open cockpit - does not look difficult to have enclosed it?
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Pete Fardell
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« Reply #3 on: January 20, 2019, 05:43:46 PM »

Uncanny- I've just been looking at Junkers F13 pictures here: https://www.modelflying.co.uk/news/article/the-corrugated-catalyst/26585
as I've long been tempted by it. I like the look of the Michael Heinrich plan too. Following with great interest!
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Rhys
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« Reply #4 on: January 20, 2019, 06:17:06 PM »

Thanks for the kind words David. I too wondered why they stopped listening to their engineers when it came to the forward cockpit. 'What...windows you say? They attract bugs, get dirty and obfuscate your vision ahead! The answer is no you you silly Schwachkopf. No window for you! Perspex? What in the devil is that? Now leave me alone, I have some wicker chairs to design'
and...
Pete, thanks so for the link to modelflying.co.uk  Some wonderful photos and drawings. I can really use the information. I appreciate your lending a hand.

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flydean1
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« Reply #5 on: January 20, 2019, 10:11:53 PM »

I believe many of the early airliners had open cockpits for the crew and enclosures for the paying customers.  It was felt that pilots couldn't properly "sense the lift in the air" if they were comfortably protected from the slipstream.

Sort of like making schoolboys sleep in dorms with windows open in the winter to "build character".
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Rhys
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« Reply #6 on: January 20, 2019, 10:16:59 PM »

Just a bit more. So small, makes the going slower Undecided

Cheers,
Rhys
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Rhys
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« Reply #7 on: January 20, 2019, 10:34:57 PM »

Very true Flydean. I imagine it was a continuance of "how things were done" during that era. I recall a film/video of Generalleutnant Adolf Galland where he stated that he and most of the pilots of his time (prior to the closed cockpit days of the Spanish Civil War) preferred to fly in open cockpit airplanes. He stated 'You could not only hear the enemy, you could smell him from afar'.
Looking at the closeup pic I posted of the pilot area on the Rimowa F13, it does seem they would have little difficulty bailing.  Truly slight comfort for the paying customers. Just a thought.
In the link Pete posted, which was quite good indeed, the author spoke of the F13 having the sad notoriety of being one of the first commercial 'airliners' to crash. It is surmised the wings broke away and then the empennage after the plane dropped at high speed after dealing with a high altitude weather front. The wings just simply weren't built to take the stress of that incline of a dive.

Thanks for looking in, Flydean
Rhys
« Last Edit: January 20, 2019, 11:15:37 PM by Rhys » Logged
Graham Banham
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« Reply #8 on: January 21, 2019, 02:32:48 AM »

Nice delicate design. Having built several peanut sized models with the powertrain you describe, the best you are going to do with a 40mah lipo is a powertrain weight of 6g: more with a higher capacity cell,  so the structure has to be really light. I found the most important things to remember are you cannot re-prop a Voodoo 10: the diameter you have is the optimal it will take, so a bit of prop blanking is ok but not too much. Rules out a lot of radial subjects, sadly.

You can get close to the 20g max auw for the motor, but performance can be marginal: a low wing loading and low drag is crucial. Slight downthrust is good, but give it plenty, and i mean plenty, of right thrust.

Another thing is that if it won’t go with a V10, it’s unlikely it will take a geared V15, as the latter will very probably be too heavy, and may not fit in the nose: that’s when you convert it to rubber!

Good luck!
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Rhys
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« Reply #9 on: January 21, 2019, 12:01:54 PM »

Thanks so very much, Graham, for responding to my posts! I'm very flattered you fellas with so much experience and the many accolades you've received in competition  take the time to advise Grin
Okay...this is where I sound very ignorant. Most likely I am, so please pardon. What is "prop blanking"? Construction of wooden prop? And you mentioned..
"you cannot re-prop a Voodoo 10: the diameter you have is the optimal it will take" Do you mean the prop suggested by the manufacturer is the optimal prop pitch and diameter?
By the way, the span of the wing is 16inches. Will that make a difference in flight compared to a span of 13" for peanut?
I'm a bit of a novice so I'll have many questions.

Again, thanks for taking the time to lend your advice. I'm honored to receive it!

Rhys
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Graham Banham
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« Reply #10 on: January 21, 2019, 02:07:09 PM »

No problem Rhys.

The 63mm GWS prop supplied by Atomic Workshop and fitted to the Voodoo 10 is the 25mm pitch version, and has been matched to the motor to give the best thrust levels. There is another version of this prop available elsewhere with a finer 19mm pitch that unless you look closely is identical.

 By prop blanking, i mean the cross sectional area of the fuselage immediately behind the rotating propeller disc. If you imagine a model with a radial engine 50mm in diameter, then a Voodoo 10 propeller at 63mm diameter would only protrude 6mm or so beyond the outer edge of the cowling: insufficient to give enough thrust to fly. A ‘flat’ nosed radial aircraft also makes it difficult to add side and downthrust without the prop catching the cowling edge.

Regarding the F-13, i wouldn’t worry too much about the span. I’ve actually looked at this plan too in respect of V10 power as the fuselage is very small: it’s effectively a peanut with 3 inches more span. In this context treat it like a powered glider it terms of wood choice and resisting the temptation to beef up the structure and you should be ok.

When fitting the motor what i normally do is dispense with the mounting plate provided and have it a close push fit in the noseblock at the appropriate thrustline angles (around 1-2degrees down and 5 degrees right). Wrap a strip of masking tape around the rear half of the motor: then when it pulls forward under power, the masking tape ‘collar’ will stop the motor pulling out of the nose, but still allow it to be easily removable.

Looking forward to seeing it take shape!

Graham


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Rhys
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« Reply #11 on: January 21, 2019, 06:02:47 PM »

Thanks Graham, for the explanations and information. Sure keeps me on a straight and even path.

Rhys
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Rhys
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« Reply #12 on: January 23, 2019, 10:54:40 PM »

Sorry I've only been able to get this meager amount done but time constraints and of course the fact that this small of size is hard to assemble without destroying it keeps the pace at a crawl. I'm trying to stick with the plans and avoid the temptation of adding a bit/beefing up here and there. Actually when built, the structures are quite sturdy. Michael Heinrich really knows his stuff. I have so much to learn here and am fortunate to be in the company of many who have refined the art of building. Getting nearer to the fuselage. I have some thoughts about the cockpit structure but haven't come to a decision yet.



Cheers to everyone!
Rhys
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« Reply #13 on: January 23, 2019, 11:36:18 PM »

Nice work Rhys.

John
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Rhys
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« Reply #14 on: January 24, 2019, 12:15:02 PM »

Thanks John Grin  Certainly hope I can get some time to do serious weekend building.

On a different but unique note, yesterday I noticed one of my patients, who is in his later 70's, was wearing a t-shirt celebrating the April 1942 Doolittle raid on Tokyo. On mentioning my interest he stated that his father was a navigator on one of the participating B-25s. According to the son, his father's aircraft was one of the birds that made it the farthest into the China interior and was assisted to safety by Chinese residents and military. Talk about being in awe. I get to meet some really interesting in my line of work. Another I have had the pleasure of meeting piloted my favourite jet, the B58 Hustler and then on to the SR71.

I was able to find a site that described all of the participants in the raid. In particular, here is the bio on my patient's father  Grin
Thomas Carson Griffin

https://childrenofthedoolittleraiders.com/crew-members/team-members/griffin/

Cheers to all,
Rhys
« Last Edit: January 24, 2019, 01:28:56 PM by Rhys » Logged
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« Reply #15 on: January 24, 2019, 06:49:47 PM »

Fascinating bit of history - thanks Rhys.

John
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Rhys
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« Reply #16 on: January 25, 2019, 10:39:33 PM »

Just got in from work. Fix a sandwich and some tea and got this finished before I turn in. This is just a small beginning to what I hope will be a productive weekend of building. We'll see Wink

Cheers,

Rhys
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« Reply #17 on: January 25, 2019, 11:11:21 PM »

Coming along very nicely; impressive detail work on the joints. What kind of knife/blade are you using, with the green handle?
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Rhys
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« Reply #18 on: January 26, 2019, 12:08:39 AM »

It's a disposable surgical scalpel. Thanks for the compliment indoorflyer Grin My progress has really been slow and I hate to put so little up for view at a time but I do want those to know I'm still working at it. You can probably get the scalpel on amazon or on a medical supply site.
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Dan Snow
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« Reply #19 on: January 26, 2019, 07:51:59 AM »

I'm enjoying following this build Rhys, I just might have to add it to my bucket list!!

You're right about finding scalpels/blades on Amazon. I  have my Dads Uber knife and I bought a pack of #11 scalpel blades on Amazon for $7 plus shipping. I find them sharper than an Xacto #11 but not quite as durable.

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Rhys
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« Reply #20 on: January 26, 2019, 12:36:27 PM »

They are indeed not as durable, particularly the tip which has a tendency to bend as it's very thin. Flesh and tissue are much easier to cut than some stubbornly grain balsa. I always make a VERY GENTLE 1st cut that outlines the part, then follow with 1 or 2 more that finishes things up. This keeps the tip from bending while also keeps the blade from angling and making an angled slice.

Thanks for dropping by, Dan Snow. Pleasure making your acquaintance.
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Rhys
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« Reply #21 on: February 02, 2019, 08:46:14 PM »

Well, you know what they say about "good intentions". My "intentions" were sailing along fairly well with the building of the F-13 fuselage but as fate would have it, I fell upon sour circumstances. Trying as I did to build straight & square, it finally came time to remove from the building board and behold I beheld a banana in my hands. So, I'm redoing the fuse from the very beginning and trying to pay attention to my methods. I initially used CA to secure the cross spars but that, I'm certain was my problem. Any slight amount of torque or misalignment would be instantly locked in by the cure of the glue. This time I'm using cellulose glue (Duco). Hopefully this will give me adequate time to align everything before it sets.

My original scale only measured to the whole gram, so I bought one that measured to the 100th of a gram. The purchase came with a peculiar story...and a story that made me a bit nervous. The salesperson at Walmart stated they had no scales that measured that accurately but one of our local pawn shops probably did. On a visit to the shop, the proprietor showed me what I was looking for. I removed it from new in the box to make sure my purchase was certain when he stated ... 'now that's an accurate scale there but it's not anything that you can rely on to make an honest trade', I was puzzled. 'Trade? What do you mean?' He reached under the casing and from a drawer, took out a box and opened it up revealing a very nice scale.  Telling me 'I can let you have this one for only 150$ since it's the last of two in the store'. 'That's abit pricey when I only want to weigh balsa wood, I retorted. He again spoke, 'well, it's worth every penny. Especially when you're weighing things like weed, meth'. " Hey,' I said nervously I'm only wanting to weigh balsa'. I chose the 15$ scale, paid cash and left the store in quick step. Yes, the scale was wrapped, sealed and new in the box and NO I don't do drugs ......but the scale, works fine.

Rhys



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flydean1
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« Reply #22 on: February 02, 2019, 11:31:30 PM »

That's similar to the treatment I got when I bought my Ohaus triple beam balance.  I think the seller was selling weed, and was concerned that I might be competing.  Assured him that I lived over 30 miles away, and he didn't buy my model airplane story.

The Ohaus has been relegated to obscurity due the proliferation of very accurate and inexpensive digital scales.
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Rhys
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« Reply #23 on: February 03, 2019, 12:22:30 AM »

I too remember the triple beam Ohaus scales when I was doing R&D with Kraft Foods. They were state of the art technology at the time. The electronic digital are for certain more accurate but then, where's the artful execution of the dance in that
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Rhys
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« Reply #24 on: February 03, 2019, 02:05:41 PM »

A few pics of a slow process. So far I haven't broken any wood. Yet Undecided

Rhys
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