Correx prototype Gee Bee Sportster

by hellcat | February 23, 2015 | (12) Posted in Projects

The plane is built from 3mm Correx or Coreflute.made from extruded polypropylene

 I've increased the wingspan to 900mm from alibopos Alistair Potter's original 840mmm plan in  FT article, Gee Bee Sportster - swappable. The fuselage remained the same. My wing has no dihedral only under-camber back 150mm from the tips.

The motor cover and ply mount  with battery pod slide over the fusilage and are secured by bamboo sticks with caps made from diabetes novamix pens. 

Pop off undercarriage fits into wing and is made from coat hanger wire and correx spats a combination of stiffness and flexibility 

The motor is a little  monster Turnigy D3542/4 1450KV Brushless Outrunner  with a 9x5.5 prop, bit of over kill but it is what I have.  Battery is a 2600 3s Turnigy ESC 60 amps RX LM 6Ch DSM2 Compatible Receiver. servos Emax with metal gears

Motor 130 grams and battery 250 grams ESC RX undercarriage take it to 840grams or there abouts.

Elevator and Rudder servos are mounted at rear, I find that having my pushrod wires and servos visible and as close as possible to the horns makes for easy pre flight checking, maintainance and feels more responsive.

The ailerons and elevator dont need hinges or tape just slice the undersideof the Correx along the fluting

I live in a very humid climate and find foam board turns to mush overtime. I have also built with Depron but it is relatively expensive and still marks easy.Correx looks a good option, cheap and very strong. The plane suprisingly due to savings in less structural supports and less glue including no need for a wing spar for this size wing, came in on par with a painted foam board build.  The Correx  doesn't mark or dent like foam board while building and biro lines just wipe off with spirit or turps. The surface can be painted with turps based spray cans once etch primed or covered with coloured tape or signage film. the correx glues up well with hot glue UHU Selleys Durabond Gorilla glue and super glue. I did a lot of testing with those glues

And if I ever get a hankering for the smell and noise of nitro then no problem as the Correx won't be effected by fuel.

Pinkie the ex Bixler pilot recovered from our club field

 Performance

The  plane now called Lola flew on the maiden beyond expectations incredibly fast rolls loops and climbs vertical with ease. I used the 900mm flat wing which I cant fault. It was very soggy on the field and grass was unmown so lets just say she is a handful on landing in the long grass I will install flaps if needed. The landings looked hard but the correx is very tough so no damage at all just few paint scratches on the wing leading edge. The day was cloudy with rain coming across periodically in squalls our wet season post cyclone Marcia. My video man was not around but next Monday with a mown strip at the field will be the go

I will try to get video of a full flight test  as soon as the sun returns

Update 18/03/2015 the day was sunny and we put Lola in the air with her new motor a Turnigy D3530/4 1100KV Brushless Outrunner  70grams with a 9x6 prop recommeded by e calc. the old motor Turnigy D3542/4 1450KV Brushless Outrunner  with a 9x5.5 prop was overkill regarding power and weight.

I have posted a first video

 

which does not have any footage of her loops rolls and flying inverted as the video cam telephoto jammed. My fault as we did a much too close and personal flyover of the intrepid camera man.

But I do hope you enjoy the little video took off on half throttle turned straight to the wind minimum trim required plenty of power flew straight and true and rounded up a few of her bigger brothers. Will post more if there is interest and when the cameraman recovers his nerves.

I have decided to build a scaled up a 60 inch version as there is much interest from club members

My thanks again to Alistair Potter Alibopo for the plans and advice.

my email barberr@squirrel.com.au

Ross Barber

 

hi have just dry fit the geebee together made from 3mm coreflute dry fit with servos. no battery and motor yet 380 grams ive increased the wingspan to 900mm. motor and battery esc and rx undercarriage will take it to 800grams or there abouts. the motor is a monster. this coreflute really looks a good option cheap and very strong. doesn't mark like foamboard surface can be painted with turps based spraycans or or covered with colored tape or sinage film glues up well with hot glue uhu or selleys durabond gorilla glue and very small amounts needed if you want any piccies or movie for maiden when it happens here is my email barberr@squirrel.com.au - See more at: http://flitetest.com/articles/geebee-sportster-swappable#sthash.MBSiqQuK.dpuf

 

hi have just dry fit the geebee together made from 3mm coreflute dry fit with servos. no battery and motor yet 380 grams ive increased the wingspan to 900mm. motor and battery esc and rx undercarriage will take it to 800grams or there abouts. the motor is a monster. this coreflute really looks a good option cheap and very strong. doesn't mark like foamboard surface can be painted with turps based spraycans or or covered with colored tape or sinage film glues up well with hot glue uhu or selleys durabond gorilla glue and very small amounts needed if you want any piccies or movie for maiden when it happens here is my email barberr@squirrel.com.au - See more at: http://flitetest.com/articles/geebee-sportster-swappable#sthash.I1Wua7Vh.dpuf

- Find this article & others like it at www.FliteTest.com -

COMMENTS

Yogenh on March 20, 2015
I love it and would like to know if you have plans that you will post? I would like to know how to work with correx. Is it hard to work with and use this way? Thanks for the good work you did
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hellcat on March 20, 2015
Thankyou, first of all the plans are on http://flitetest.com/articles/geebee-sportster-swappable by alibopo. my main modifications to that were to just increase the one piece wing wingspan to 900 mm or 3 feet with no dihedral and therefore no centre jointing. The wing strut is a length of 3 mm core flute doubled. The wing still still has FT style under camber at the end. I mounted the rudder and elevator servos at the back on the outside as I do with all my models (much easier to service and for pre-flight checks. The engine POD I made is designed so the front cover slides over the body but you really don't need to go that far if you don't want to just use a standard FT style POD. When you want to make curved sections like on the top of the fuselage just score along the inside of the pieces along the core flutes.
Re: using 3 mm core flute correx I didn't find it too hard the main thing was to align the plans for each item parallel and square with the direction of the flutes. I think the trade-off instead of using foam board is that you get a very tough plane that lasts, the weight is comparable and is very cheap to make. Thanks again and would be happy to assist in any way. My email is in the bottom of the article.
Kind regards
Ross

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Yogenh on March 21, 2015
Thanks I will have to try to make some out of the correx. It dose seem to bet something that will really last a long time.
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HilldaFlyer on March 22, 2015
Simply - so cool. I like the colors - and by the way... that landing was better than most of mine.
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hellcat on March 22, 2015
thank you and that was one of my better landings too... lucky she bounces the correx is very tough really absorbs any shocks. really well.
kind regards
Ross
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gremlin88 on March 21, 2015
I really want to learn how to build with correx
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hellcat on March 21, 2015
Hi, this was the first correx plane I have built so if you have built a couple of ft models before you wont find it hard at all. my skills are basic my tools are simple. my previous planes have been made with foam board or depron just keep the snap off cutting knife sharp and you will need a small exacto style craft knife. The more you experiment with different materials and ideas the more fun.
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alibopo on March 22, 2015
Hi Hellcat - Great build, 'Lola' looks very nice on the ground and in the air! Without the dihedral, she probably needs a little bit more attention/pilot input than mine, but still looked plenty stable.
If your transmitter can manage the mix how about trying flaperons? Here's the link to my article and the flight video.
http://www.flitetest.com/articles/the-geebee-sportster-x-gets-flaperons
I found it made a big difference to slow-flying speeds. There's no getting around the problem of a 'relatively' rough surface, but at least a lower landing speed is gentler on the airframe if it is going to nose-over.
Cheers, alibopo.

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hellcat on March 22, 2015
Hi back yes you are right have to pay attention especially when I am more comfortable just doodling about. re landings our field is a swamp so is soft and hard in places lucky she bounces, flaperons look the go. I have been asked to build a scaled up model so will look at either flaperons as you suggest thanks for the link. I could do the mix,or maybe separate flaps.
will keep you posted
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alibopo on March 23, 2015
Hi Hellcat, dihedral definitely helps with more relaxed flying. I understand correx is made from the plastic polypropylene - which means it is a 'thermoplastic'. (It softens with heat and then sets when it cools.) If this is a single-piece wing, this type of plastic can be bent quite easily using heat. A typical source would be a hot-air gun, carefully applied the heat will allow the plastic to stretch or compress (above and below the wing) to allow the bend or curvature to form. The deformation required to produce a dihedral is very small, and if spread over a wider area to produce a curve rather than a fold, I doubt much strength, 'if any' would be lost.
Perspex-type materials (many early aircraft windscreens) actually become rubber-like when they are heated and have 'plastic memory' which means that when heat is re-applied they return to their original shape. Polypropylene does NOT behave like that. Once it's bent I think it will never go back to its original shape. Maybe a few careful experiments? Cheers.
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hellcat on March 23, 2015
It is very much this is great information to follow up on. And it would be worth the time. I have the original 840 mm wing and will try it and see how that goes. I will also start bending some flat sections and folding them into the wings. I can also see that it might change the way I make curved sections on the fuselage. Rather than slicing the inside then rolling and bending which works okay but makes a section with only half the potential strength I will try heating and bending. If it is looking good put an article up on the site. Kind regards Ross
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hellcat on May 29, 2015
hi just an update Lola's big sister maiden flight still using your basic plan scaled up. flew beautifully no trim needed 9% dihedral, Maybelline Scratch built Correx 58" wingspan 1450 grams RTF 3s 3600 battery
https://vimeo.com/129082488

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alibopo on May 29, 2015
Hi Ross - quick update - I was able to follow the link from 'within' your posted video of Lola to your VIMEO page to see Maybelline in flight. Very cool, I particularly liked the landing - nice and slow. You've got me interested in Correx! Cheers :)
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hellcat on May 29, 2015
Hi back glad you liked it I'm sorry the capture images were so small. It is a very nice plane to fly very responsive no foibles with great acrobatic qualities. I have found a better quality of correx produced here in OZ as well in several great colors 9$ for a 6x4' sheet. Have just started a 60" correx ugly stik based on a 48" one I have been flying. I redesigned the wing foil shape from a standard stik its a real hoot to fly so will see if bigger is better. Correx is a good alternative enjoy
regards
Ross
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alibopo on May 29, 2015
Hi, the new plane sounds brilliant! I tried the link, but it came up as page not found, which was very disappointing - I'd really like to see this new version of 'Lola'. You must post this as a new article, if it flies anything like my 'original' foam board version, its going to have great presence in the air. Looking forward to that. :)
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Correx prototype Gee Bee Sportster