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80% Akromaster for Cox .09 engines

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80% Akromaster for Cox .09 engines

Post  coxaddict on Thu Aug 06, 2015 6:15 pm

Decided to follow Marks's suggestion and build a scaled down version of the Sig Akromaster for my Cox .09 engines.  A 27" wingspan turns out to be about an 80% sized Akromaster.  Should turn out to have about 148 square inches in wing area.   I couldn't do an 80% leading edge so I just used what I have on hand and shaped the airfoil accordingly.  The ribs were CA glued on the edges and shaped on a disc sander. I then cut the spar notches with a razor saw. I'll do a dry assembly to mark the location of the bellcrank and the holes for the leadouts.  

Tight lines
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Re: 80% Akromaster for Cox .09 engines

Post  batjac on Thu Aug 06, 2015 6:22 pm

Cool! Should be a great project. I looked at the pictures before reading the text and thought, "Hmmm... Those ribs look awfully fat." But I see now why. Being fat, it should help with aerobatics. Looking forward to seeing the build progress.

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Re: 80% Akromaster for Cox .09 engines

Post  akjgardner on Thu Aug 06, 2015 6:29 pm

Thats a good way to make ribs.Its amazing how fast you can build a wing using that method.
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Re: 80% Akromaster for Cox .09 engines

Post  Cribbs74 on Thu Aug 06, 2015 7:07 pm

148 sq"?

That's .049 territory. Maybe 90% would work better.

Just a thought. An .09 will definitely fly it with authority!
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Re: 80% Akromaster for Cox .09 engines

Post  JPvelo on Thu Aug 06, 2015 7:28 pm

Beautiful work on those ribs. I look forward to watching this build.

Jim
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Re: 80% Akromaster for Cox .09 engines

Post  Mike Mulligan on Thu Aug 06, 2015 7:33 pm

Those are beautiful ribs. I'm going to have to try that, especially since I really,really get tired of cutting out all those ribs... tongue

Mike
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Re: 80% Akromaster for Cox .09 engines

Post  Marleysky on Thu Aug 06, 2015 8:01 pm

MMMMMMMM,  FAT RIBS.....who's got the BBQ sauce??  
Nice way to cut sand ribs quick, looking forward to the set up and build pictures.
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Re: 80% Akromaster for Cox .09 engines

Post  RknRusty on Thu Aug 06, 2015 8:38 pm

Your wing is about the size of my Baby Streak. It says on the box; Recommended for .049 to .09, so it might turn out to be a real rocket. my oldest Baby Streak is getting heavier with age, maybe I should bolt my .09 to it and see what happens. Dang, I got a new idea! Double Dang, I got too many new ideas!
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Re: 80% Akromaster for Cox .09 engines

Post  NEW222 on Thu Aug 06, 2015 9:12 pm

Ok, I'll bite after the comments. So, how did you cut those ribs out so nice and straight(unless there is a picture of you and your method that I do not see). I have read a few ways of doing them, but have not had much success. Thank you.
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Re: 80% Akromaster for Cox .09 engines

Post  NEW222 on Thu Aug 06, 2015 9:15 pm

Ok.  Sorry, please disregard my last post.  I was looking at it again and see you did describe how in the first paragraph.  I see pictures then I forget to read, cause a picture is worth a thousand words, isn't it? Laughing My bad.
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Re: 80% Akromaster for Cox .09 engines

Post  coxaddict on Fri Aug 07, 2015 3:02 am

Separated the ribs and marked them 1 to 14 and used a blue marker on all the top rib spar grooves, to orientate the ribs top and bottom.   Cut the leading and trailing edges to 27".   Mark 1" on both sides of the center line then then 2" spacing on both sides of the center line.  Make the grooves on the leading and trailing edges using 2 hacksaw blades taped together. draw a line with a marker as a depth gauge stopping the cut at the line.  I like to leave material on both ends, say in this case 1/2" after the last rib to anchor the wing tips, not having to depend on tip braces for strength.  Assembled the wing with no glue so I can position the bell crank and lead out wire holes. This wing has no drawings to go by so everything needs a trial fit before gluing.

Agustin Jr.I Love This Forum!
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Re: 80% Akromaster for Cox .09 engines

Post  batjac on Fri Aug 07, 2015 3:31 am

coxaddict wrote:Decided to follow Marks's suggestion and build a scaled down version of the Sig Akromaster for my Cox .09 engines.  A 27" wingspan turns out to be about an 80% sized Akromaster.  Should turn out to have about 148 square inches in wing area.  

The test fit is looking good! Thumbs Up

Since the original Akromaster has a wing of 250 square inches, shouldn't an 80% scale bring it to around 200 square inches?

But, even if it is lower, that fat wing will absorb more power and have a little more drag than the normal thinner 1/2A wing and slow it down some.

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Re: 80% Akromaster for Cox .09 engines

Post  getback on Fri Aug 07, 2015 10:31 am

Agustin Jr. That is really looking good Sir , got the original size that I need to get started on or I want make the fly this year , wish I could build as quick and sharp as you . Thanks for the lessons , Eric Very Happy
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Re: 80% Akromaster for Cox .09 engines

Post  gcb on Fri Aug 07, 2015 11:00 pm

A couple of suggestions:

First, if you haven't already covered your wing...cut a small hole in each rib so pressure will equalize or you may get a "puffed up" look on the wing as your plane sits in the heat.

Second, you keep saying Cox .09 engines but you should find the TD much more powerful than the Medallion. I would suggest a Medallion on this plane, a TD should pull a full-size SIG Akromaster.

Of course these are only suggestions, you may like the smaller one with a TD. Good luck either way.

George
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Re: 80% Akromaster for Cox .09 engines

Post  coxaddict on Sat Aug 08, 2015 2:29 am

Thanks for all the observations and suggestions.
 George Thanks for the idea for the vent holes in the ribs.  Didn't think about that.  My green Ackromaster has no holes in the outboard wing.
I knew going in that this wasn't going to be an exact replica of the .15 sized Ackro but that's the beauty of scratch building.  I got the idea of a thicker , fatter airfoil watching on YouTube  indoor control line flying.  The planes are huge and fly very slow.  Check it out!  
The fuselage is 1/4" medium hard balsa with 3/8"x 1/4" hardwood engine bearers. By insetting the .09 I was able to allow for mounting a Norvel  .049/ .061 forward in the nose!
Just waiting for glue to dry.


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Re: 80% Akromaster for Cox .09 engines

Post  getback on Sat Aug 08, 2015 11:24 am

Nice job on the engine rails , that is one fat wing hope to see a flight report when its done . Your cooking now ! Eric Smile
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Re: 80% Akromaster for Cox .09 engines

Post  gcb on Sat Aug 08, 2015 2:46 pm

coxaddict wrote: I got the idea of a thicker , fatter airfoil watching on YouTube  indoor control line flying.  The planes are huge and fly very slow.  Check it out!  
The fuselage is 1/4" medium hard balsa with 3/8"x 1/4" hardwood engine bearers. By insetting the .09 I was able to allow for mounting a Norvel  .049/ .061 forward in the nose!
Just waiting for glue to dry.

Agustin Jr.  

Each airfoil is designed to fly at a particular velocity. Since you have thickened yours so it will fly slower note also that you may need to fly on shorter/lighter lines or add additional out-thrust to the engine to hold it out on the lines.

Easy to overcome if you are expecting it...there is no free lunch. Smile

George
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