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Author Topic: A1 International postal competition  (Read 2172 times)
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lincoln
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« Reply #25 on: December 09, 2020, 08:30:21 PM »

I think the Siesta (as found on Outerzone) is interesting, but I wonder how hard it is to shape the "undercamber " correctly, and whether it can be done quickly. Also whether that shape can be maintained over time if I don't find c-grain.
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« Reply #26 on: December 10, 2020, 12:31:16 AM »

The Siesta is interesting Lincoln.

On reading the supplement - I suspect that he has used a couple of spanwise strips chamfered on their LE and TE's so that they would approximate the undercambered shape, before sanding in the airfoil. If this is correct only 3 or so strips would be needed and I think it would be quite warp resistant.

John
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BG
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« Reply #27 on: December 10, 2020, 01:48:17 AM »

I agree with John, hard LE ad TE balsa (C-grain if you have it) with light wood for the core of the wing should be fine. If you sand the under camber in with a shaped sanding tool it should hold up with minimal change over time. The text seems to indicate that the designer uses dope to hold the under camber in. Again this should be fine if you always fly it in the same region and climate. Also the dihedral break serves to preserve the airfoil camber which also works in your favour. Should be an interesting build.

BG
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lincoln
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« Reply #28 on: December 12, 2020, 05:17:00 PM »

I imported the picture of the airfoil into CAD. Looks like most of the bottom surface is very close to a 14 inch radius circle. I'm not sure if that makes things any easier, but maybe I'll get a clever idea.
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billdennis747
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« Reply #29 on: December 12, 2020, 05:35:22 PM »

When sheet-wing wakefields were in voque, did they not use multiple strips, all slightly chamfered, to get the lower surface curve on a jig? Cuts down on the sanding!
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lincoln
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« Reply #30 on: December 12, 2020, 06:23:50 PM »

Does it really save time, though? I should think the precision required would take some time. Except maybe with a good table saw and the right skills. Am tempted to laminate 1/16" sheets, though that might make shaping the top trickier. The article says 1/4" balsa for the wing, but the airfoil drawing, imposed on cad, measures around 1/4" thick without any sanding.

I just noticed that the boom is a 3/8" birch or spruce dowel!! Never having seen a spruce dowel, I calculated for birch that the boom alone would require maybe 45 grams of nose weight and that total nose weight might be up around 80 or 100 grams. Is this common? Seems like a lot.
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« Reply #31 on: December 12, 2020, 06:27:26 PM »

Yes that's what I remember as well. Multiple is the right word and I imagine a fair bit of care was needed in sanding the bevels!

The model I was thinking of was Reiner Hofass's "Espada" which was used to win the 1981 Wakefield (Lothar Doring) and developed further to win again in 1985 - this time by the designer Reiner Hofass.

Very interesting period of model development.

John
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billdennis747
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« Reply #32 on: December 13, 2020, 03:02:43 AM »

Does it really save time, though?
Probably not  but unlike Siesta, I suspect the method was used by Hofsass et al to get some strength into a very high A/R wing. I gather they bent a lot.
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USch
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« Reply #33 on: December 13, 2020, 04:20:29 AM »

It was not so much the bending Reiner had to fight against, but the associated flattening of the profile. Indeed he was an early user of carbon rovings glued to the underside of the wing in cordwise direction.
About bending and dihedral, I remember Reiner saying that a lot of dihedral helped him to do without a wing wiggler  Cheesy

Urs
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« Reply #34 on: December 13, 2020, 07:22:19 AM »

In the late 1970s and early 1980s I built several solid balsa Wakefields with around 16 to 1 aspect ratio. Instead of the 5 strips of balsa used on the Espada, I used three wider strips (3/8" 1/4" and 1/8" front to back). Strips of basswood (linden/lime) were used at front and back. The balsa was ripped on a table saw to correct bevel and glued together. Sanding of the underside was done on an under camber-shaped form. For initial shaping coarse sandpaper was attached to the form and the wing panel moved side to side. Besides speeding up the work the coarse paper produced larger, heavier dust that didn't get in the air.

The wing was covered with tissue, No carbon strips were used. The one problem I had with the wings was flutter on the burst. Carbon strips top and bottom would have helped but the models were lost (pre-tracker era) and I moved on to wings sheeted top and bottom.

Regarding the Espada and its use of carbon strips I have seen two photographs of one of the models hanging in a museum in Germany. One photo is from below and the other from above. They show carbon on both top and bottom surfaces.

Right now I am working on another Vintage Wakefield, Carl Hermes' Alta from the 1964-65 Zaic Year Book. It features solid balsa wing and stab construction. On the wing three pieces (3/8" 1/4" and 1/8") are used. (This must be where I got the idea for the Wakes I built 40 years ago.) The Alta was designed as a quick, cheap (balsa was cheap then, not now) that could be easily be replaced when lost (again pre-tracker). In the interest of speed the underside of the wing was not sanded to give a smooth curve.

It is a quick model to build---much like building an oversize hand-launch glider. On interesting feature is a timer-operated flap on the left main panel that is held up for the first 3 seconds. It works much like a wing-wiggler to help keep the burst straight. No other auto surfaces.

Louis
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lincoln
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« Reply #35 on: December 13, 2020, 01:47:44 PM »

The idea of flutter in a rubber powered duration model is mind boggling. I'll have  to look at the Alta.

If flattening of the profile is a problem, I think that makes c-grain a requirement.

I am juggling various model priorities and variable motivation. Then I made the mistake of checking out the gliders on the Hummingbird web page... 
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lincoln
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« Reply #36 on: December 14, 2020, 03:59:00 PM »

In my wanderings on the net, I ran across the Ornungen S-1 glider, which, according to some rough measurements, qualifies as an A1. Apparently, the kit is out of stock right now, but they have a redrawn plan you can download:
http://byggmo.se/ornungen_eng.html

Plan has 1954 date, plus the design is in the 1956 catalog, but not in the 1953 catalog:
http://tmfk.org/etmfk.html
http://tmfk.org/antikrundan/semo1956/semo56.pdf
http://tmfk.org/antikrundan/truedsson1953/Truedssons%20modellflygind.%201953.PDF
--------------------------------
Graupner Hobby:
https://outerzone.co.uk/plan_details.asp?ID=12087
The instructions say 1954 on them. Plus it shows up in the 1959 catalog: https://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=5155
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lincoln
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« Reply #37 on: December 14, 2020, 07:53:25 PM »



a1 1951 thru 60 a1 stuff for contest

Hip Pocket is giving me a hard time. I'm getting the text up and will try to post attachments as feasible.

The Bantam is supposed to be from 1953 and is in the Truedsson (aka SEMO) 1953 catalog
http://smos.homeunix.net/modellregister/modell/40/

The 1955-56 Aeromodeller Annual has several A1 plans in an article by vanHattum.

Tomik A1 appeared in the November 1960 Letecky Modelar
a cleaner plan: http://www.sam119.sk/images/sam119/data/plany/Tomik.pdf

The Aurea A1 was supposed to appear in 1957 in Letecky Modelar, but I haven't chased it down yet.
http://www.sam119.sk/images/sam119/data/plany/Aurea.pdf

There was an A1 called Havran Gabis (the designer's name is to distinguish it from another glider called Havran). It was supposed to have shown up in Letecky Modelar in 1960, but I couldn't find it.
http://www.sam119.sk/images/sam119/data/plany/Havran%20Gabris.pdf
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lincoln
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« Reply #38 on: December 14, 2020, 08:18:09 PM »

Oops, I forgot this one from Modellflyg bladet 1958 #2
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lincoln
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« Reply #39 on: December 14, 2020, 11:35:29 PM »

Ran across another appearance of the Aurea, in Aeromodeller Annual 1958-59
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lincoln
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« Reply #40 on: December 16, 2020, 08:13:50 AM »

Jedelsky's minimalist design for an A1, an A2, and a power model in an article which is supposed to be from the 1962-63 Aeromodeller Annual:
https://www.rcgroups.com/forums/showpost.php?p=33411582&postcount=14721
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lincoln
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« Reply #41 on: December 19, 2020, 03:07:27 AM »

OOPS! Jedelsky's design is interesting, but it's from the wrong decade.

I thought I'd posted it, but the Tempo is from 1960 and has a Jedelsky wing. You can download it and a dated article at:
https://outerzone.co.uk/plan_details.asp?ID=9645
It was in the October, 1960 MAN. So a Jedelsky style wing is still possible for this contest. I checked some of the Jedelsky airfoils with Profili/Xfoil the other day. With a turbulator at, say, 35 percent, they look pretty good. For a model that has a Reynolds number of 40,000 at a Cl of 1, Profili seems to think the Jedelsky EJ-85 is comparable to the MVA 123 when above a Cl of 1. For the EJ-75, you have to get up to a Cl of 1.2, so there isn't a whole lot of range between good lift and stall. The BE6407E behaves much like the MVA section, despite the gross differences in appearance. The Jedelsky sections have a bit more pitching moment, but not by all that much.  I think the Tempo's section looks like the EJ85.

---------------

If you like impossible aerodynamics, you could always consider the Elmira Ed. The root rib section has a huge amount of camber and is pretty thick. I did a CAD trace and fed it to Profili, but the program usually barfed and I don't trust the results. The section does get more reasonable, I think, as you go out on the wing. And then there's the very stabby 1/8" steel wire sticking out the front.

https://outerzone.co.uk/plan_details.asp?ID=2723
« Last Edit: December 19, 2020, 04:13:23 AM by lincoln » Logged
Tapio Linkosalo
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« Reply #42 on: December 19, 2020, 04:08:49 AM »

While talking about Jedelsky designs, I have been thinking of suggesting "Balsar" as a add-on, or subclass in the A1 postal. The design is too young, but is in the nature of A1, being a straight-tow basic glider. As the model was kitted in Sweden in 1980's (or maybe already in the 70's?), it was also very popular in the Nordic countries, and my guess is that there are numerous Balsars in people's storages, collecting dust and waiting to get flying again. At least I have one or two in my cupboard.

http://smos.homeunix.net/media/ritn_arkiv/Balsar_Olle_Broman.JPG

http://smos.homeunix.net/modellregister/modell/401/382/

A1 International postal competition
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lincoln
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« Reply #43 on: December 19, 2020, 08:14:49 PM »

I did a bit more investigation into the Tempo airfoil. The version I traced off the plan made Profili misbehave. That doesn't mean it won't work. Comparing drawings of the Tempo airfoil and the EJ-85, the Tempo has even more camber. Possibly too much.

Tapio,
You have really opened a can of worms, though I guess I helped you do it. I see your Balsar and raise you an A/Wonder, a Graupner Junior, and a Baguley Asteroid (for which I have a kit).  Fortunately, it's not up to us.
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lincoln
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« Reply #44 on: December 20, 2020, 01:00:22 AM »

I was curious about the BMFA rules, so I copied down the URL that's in the blurb in reply #6 in this thread. It asks for a log-in. However, if I go to bmfa.org and click on "Contests and Events", there's a link to the rules.
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lincoln
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« Reply #45 on: December 20, 2020, 08:04:56 PM »

I was just perusing the rules. For those who are concerned about running fast enough, it says something about using a pulley. I don't know if I'm interpreting this correctly, though. In any case, with a pulley you're going to have less line available at release, I should think, unless you can kite it. Maybe someone can clarify?

I may be misunderstanding things, but the BMFA rules and the rules for this contest as pointed out in reply number 6 in this thread differ. Reply number 6 says that towlines are supposed to be 50 meters under a 2kg load. BMFA rules section 3.1.5.1 has them at 75 meters for classic gliders. 2kg load for gliders above 16 dm^2 (i.e. for A1 and slightly smaller), and 1 kg load for smaller models. That smaller load might mean a thinner towline could be used for small models, decreasing their disadvantage. Towline drag isn't negligible.  Speaking of towlines, be careful with the high tech lines like Spectra. The smaller diameter means they can slice you. Or, at least, that's true with 50 lb test, if memory serves.

It seems smaller models are legal. Maybe someone who just want to dip their toes in (like me) could consider one. For a really minimalist approach, we have Ron Warring's Half Scale A2.
https://outerzone.co.uk/plan_details.asp?ID=11822
If looks matter, but you still want something a bit more manageable, there's the Settebello:
https://outerzone.co.uk/plan_details.asp?ID=8930
I'm guessing a certain amount of washout will be required.

Also, the Glevum:
https://outerzone.co.uk/plan_details.asp?ID=10117

Speaking of date confirmation, maybe someone has it on the Cirro Sonic?
https://outerzone.co.uk/plan_details.asp?ID=5146
Or the Mercury Gnome?
https://outerzone.co.uk/plan_details.asp?ID=4478
I think it's easy to establish that these two are old enough, but how do you establish that they weren't made before 1951?

I'm going to post this while I see if I can find date confirmation on the Settebello. Otherwise, the computer will eat it.
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lincoln
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« Reply #46 on: December 20, 2020, 10:39:10 PM »

I couldn't dig up as much as I'd hoped on the Settebelo, and I got sidetracked a bit.

Settebello:
I can't find the actual publications, but it was supposed to have appeared in:
 La Scienza Illustrata, Sept. 1951
some issue of Il Vittorioso (a comic magazine??) 1955
http://www.riviste-di-aeromodellismo.it/
There are some other interesting Aviominima plans on Outerzone, but I suspect they're too big. Maybe the Briscola, if someone wanted to do some careful measurements. Awfully thick airfoil at the root, but if you have a small field... NOT a simple project.

Skylark, 1951:
https://outerzone.co.uk/plan_details.asp?ID=7998
Date is right on it. Another small glider, looks like a relation of the Sinbad.

Lil Nordnik (or is it Nordnick, they can't decide)
https://outerzone.co.uk/plan_details.asp?ID=8235

As long as I'm mentioning designs, here are some more normal sized designs on Outerzone:
Everest
Hatchetman
Santanita
Yeti II

I really ought to have been doing so many other things.
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lincoln
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« Reply #47 on: January 03, 2021, 09:07:34 PM »

Another source for more A-1 plans:
https://archive.org/details/modelarz_magazine?&sort=-date&page=2
Some of these are appearing on Hip Pocket already. The December 1956 issue has an A-1 on page 16, but I bet there are a bunch more in other issues.
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lincoln
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« Reply #48 on: January 05, 2021, 07:29:36 AM »

Ok, there aren't as many as I thought there might be, but I did find another one from Modelarz magazine. It's called the Myszka. I haven't done OCR and had Google attempt to translate this, and I speak no Polish. Taken from a scan found on Archive.org

Sorry about the fuzziness. Hip Pocket is bit counting and I had to shrink them.
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dosco
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« Reply #49 on: January 05, 2021, 08:16:55 AM »

There are some other interesting Aviominima plans on Outerzone, but I suspect they're too big. Maybe the Briscola, if someone wanted to do some careful measurements. Awfully thick airfoil at the root, but if you have a small field... NOT a simple project.


On that note, I really like the Stiletto ... unfortunately there is no date on the drawing.

-Dave
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