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Author Topic: Short wingspan F1A  (Read 2645 times)
corm
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« on: August 02, 2012, 04:03:17 PM »

I was wondering if a short wingspan F1A  (under 2m,  chord 165 mm near joiner) would be a good idea to have for the UK conditions?
Intended airfoil  would be B6356b modified to 5% camber. 

Any thoughts on such design?
Example here:  http://www.f1a.info/models/plans/f1a/fric/Fric_Vetrak.gif
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Baz599
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« Reply #1 on: August 03, 2012, 09:25:19 AM »

I have a 'Flashback' glider which is 66inch span and it performs well. 'My Hobby Store' sell the plan number G1331 I think the cost of the plan is about £12. It is of the 'clasic' balsa construction not carbon wing construction.  However, at the end of the day it is all about putting the model in the good air, put a short glider in lift and a long one in sink and the short one will do better.
« Last Edit: August 03, 2012, 09:53:34 AM by Baz599 » Logged
CHE
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« Reply #2 on: August 03, 2012, 01:55:36 PM »

The old adage is still true : "A two minute model in four minute air is better than a four minute model in two minute air".

I have a model about 2.15m span (usually known as #44, sometime by other descriptions) that I use most often in the UK. It uses a modified 6356B with a sharp nose and less camber as used by Quanstrom in the '79 champs. The design was in Aeromodeller some years back.

I've built more models to this basic design than any other and #44 (and the later #45) performs well in thermals but extremely well in wind. The 'shortness' of the wing helps circling in wind but it must have a composite structure or it will distort in the gusts. In my view the Flashback suffers in this respect due to its wood and tissue form but the basic geometry is obviously very capable.

I  think tapered centre panels just complicate things and I wouldn't go for the design shown for that reason.

Other good designs are Horeisi's 811 (used by Bill Colledge for many years) and Peter Allnutt's Czechmate, which I think is also called the W-Hobby Junior. I think Vasily makes a carbon version of the latter which would be a good starting point in my view.

Of course the winner of the last two windy British Nats was Jim Arnott with a W-Hobby Sija. The winner of the more presdigious Scottish Nats is too shy to say but I believe the model he used was numbered 44 ...........

CHE
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corm
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« Reply #3 on: August 03, 2012, 02:32:11 PM »

So the conclusion reached so far seems to be make something with straight centre panels - would you go for 150 mm chord or 160 mm - 165 mm ?

I am really thinking about strong wing conditions.

I bought Andy Crisp's PDF e-book, so I have all drawings of Flashback versions.   

I like carbon construction, but need to say I've not built many of them and I use a lot of prefabricated components.

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Baz599
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« Reply #4 on: August 03, 2012, 04:05:04 PM »

If you are looking at windy conditions I have come to the conclusion that for windy weather a carbon spar with a ‘proper’ hardened wing joiner is the only answer, even if it is not a carbon ‘D’ box configuration. It may be me who is too ‘vicious’ with my models on the line, but I have bent several 10swg wing joiners in strongish winds. I have a Lively Lady wing with the tips squared off, the wing construction has stood up to windy conditions, but 10swg joiners are definitely it’s weak point, (although it is an 82inch wing). Unless it has to conform to a Classic class design I would think about modifying the spar to a carbon construction and use a proper wing joiner (just my opinion you understand).
Unfortunately, the Sija is no longer available as a kit from W Hobby.
« Last Edit: August 03, 2012, 04:06:54 PM by Baz599 » Logged
CHE
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« Reply #5 on: August 04, 2012, 05:39:50 PM »

The reason some of the wood models survive is that they wash out at higher speeds than normal straight tow and offload the line tension. The risk is that they flutter of course which is why a carbon d-box is so much better - it doesn't wash out (as much) but correspondingly line tension is increased so you need the strength of a carbon spar and a good sized joiner to cope.

You can get wing joiners from a few sources. My #44 and #45 use a single 6.5mm joiner which suits the thicker section very well. Thinner sections will tend towards 2x5.5mm to give you the bending stiffness albeit at increased weight.

Interestingly the 6356b is making comeback; there are a few in the UK using slick covering and no turbulator in order to present a reduced drag model - thos gives better height gain with limited loss of glide performance.

In answer to the question about wing chord, I wouldn't go above 150mm for constant chord inner panels.

CHE
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martynk
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« Reply #6 on: August 07, 2012, 02:33:42 PM »

Hi CHE

<snip> using slick covering </snip>

What do you mean be slick? Can you expand on that for me please?

Thanks

Martyn
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Martyn
corm
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« Reply #7 on: August 07, 2012, 05:57:56 PM »

Using something like Oracover but much lighter - semitransparent plastic film - I guess...
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CHE
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« Reply #8 on: August 08, 2012, 08:06:43 AM »

Yes, Ocracover (Profilm in the UK) is the Usain Bolt of the covering world at the moment. Highly recommended for bottoms .........

CHE
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martynk
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« Reply #9 on: August 09, 2012, 02:51:34 PM »

Yes, Ocracover (Profilm in the UK) is the Usain Bolt of the covering world at the moment. Highly recommended for bottoms .........

CHE

So - if no turbulators - what are you putting on the top to keep it laminar?

Martyn
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Martyn
corm
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« Reply #10 on: August 10, 2012, 01:32:41 PM »

Just a  remark that couple years ago  before LDA era the idea was to put on the top Vlies, to keep it rough.  I cannot comment on the latest developments.
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CHE
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« Reply #11 on: August 10, 2012, 04:04:07 PM »

The LDAs do use trips (thin strips of tape maybe 1mm wide by 0.2mm thick) on the top and somethimes bottom surfaces to keep the flow attached past 50% chord.

Yes, rough upper surfaces can help, the question is how rough to get 'best' turbulation and performance.

Maximum lauch height is probably with a clean wing but the glide is often unstable.

CHE
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accipiter
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« Reply #12 on: August 30, 2012, 08:48:18 PM »

 I have built and flown extensively the 2m Vetrak with a carbon dbox and mechanical circle bunt system.  Suits windy conditions well, safe circle tow too. Thermals tightly. Robust. No hassle and max enjoyment. Well until it flew out of sight.

In my experience B6356b can be less robust at the wing tip, than thickened sections from Stamov and Titov.  Don't bother with a LDA wing section if you want to fly in the UK. Stick with icarex nylon wing covering, as it does not puncture on stubble and withstands pole when stuck up a tree.

You could carbonize Mike Woodhouse's "Whiffler" Free Flight Supplies plan.  Alternatively I have a Sija wing kit, W Hobby uncovered short B6356b and/or other short F1A wings for sale.

In summary have 2 x 2m winged F1a's plus a copy of Igor Yablonsky's F1a short bunt model for UK flying for max enjoyment.  See Martin Gregory's website for carbon d box wing construction.
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corm
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« Reply #13 on: September 01, 2012, 07:53:38 AM »

Vetrak  (design from D. Fric) has  B6356b airfoil with less camber and I believe less thickness of the airfoil on the tips. I know this design for couple year, but never had time to  build it. 
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DaddyO
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« Reply #14 on: September 23, 2012, 04:49:09 PM »

Ha! I knew eventually my models would come back into fashion  Grin
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