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Author Topic: How many square inches can I make an Ackrobat wing?(Akromaster!)  (Read 8671 times)

Offline frank mccune

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How many square inches can I make an Ackrobat wing?(Akromaster!)
« on: January 29, 2015, 09:16:21 AM »
    Hi All:

    I am wanting to increase the wing area on a Sig Acrobat to enable me to use a Magnum .15 engine. The standard Acrobat is about 220-250 square inches and is great powered by a Fox .15 slant plug. I imagine that I will also have to increase the tail to achieve about 20% of the total wing area.  I think that the Magnum has a lot more power than the Fox thus the question.

    I have a stash of foam wings that I can cut to achieve the correct number of square inches for the wing.  Perhaps about 270 square inches would be a good number.

    Any suggestions?

                                                                                    Tia,

                                                                                    Frank McCune
« Last Edit: January 29, 2015, 04:42:38 PM by Bill Little »
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Offline Tim Wescott

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Re: How many square inches can I make an Ackrobat wing?
« Reply #1 on: January 29, 2015, 10:08:58 AM »
If you also stretch the fuselage then you'll have an entirely different plane.

Why not save the Acrobat for an old 15 or a new 10, and just build something bigger for the Magnum?
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Russell Shaffer

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Re: How many square inches can I make an Ackrobat wing?
« Reply #2 on: January 29, 2015, 12:35:36 PM »
What you can do easily is to not cut the leading and trailing edges shorter.  The instructions ask you to saw them off but if they are left full length you gain quite a lot of span.  You have to make some more ribs and extend the fixed flaps but it isn't too hard.  We are talking about the Akromaster, the little one?  Everyone confuses the names on these two planes. I have one flying with a ball bearing Super Tigre   that probably isn't much less engine than your Magnum. 
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Russell Shaffer
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Just North of the California border

Online Brett Buck

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Re: How many square inches can I make an Ackrobat wing?
« Reply #3 on: January 29, 2015, 04:03:48 PM »
Quote from: frank mccune on January 29, 2015, 09:16:21 AM
    Hi All:

    I am wanting to increase the wing area on a Sig Acrobat to enable me to use a Magnum .15 engine. The standard Acrobat is about 220-250 square inches and is great powered by a Fox .15 slant plug. I imagine that I will also have to increase the tail to achieve about 20% of the total wing area.  I think that the Magnum has a lot more power than the Fox thus the question.

    I have a stash of foam wings that I can cut to achieve the correct number of square inches for the wing.  Perhaps about 270 square inches would be a good number.


   Keep going! More like about 350-370. I flew a variant of a Magnum 15 on my 36 ounce plywood-rib Skyray 35  (398 square inches) and it perfectly flyable, not as good as a it was with a 20FP or "New" 25LA, but better than with a Fox 35. 270 is about the size of a Shark 15 and that is WAY too small for a modern, unmodified 15.

   You are really designing a new airplane. 375 square inches, flapped, shoot for around 30 ounces all-up. Wimpact Jr.

   Brett
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Offline Tim Wescott

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Re: How many square inches can I make an Ackrobat wing?
« Reply #4 on: January 29, 2015, 04:12:34 PM »
What do you want out of the plane?  Fun?  Competition?  The best performance you can get out of that size engine?  How comfortable are you with scratch building?

A Sterling S-1 Ringmaster built light, or a Williamson Ringmaster (they're entirely different planes), should work for sport/fun/Old-time, and there are S-1 kits out there.  I have an FP-20 on a 34 ounce S-1 Ringmaster that got 475 points in Classic last year.  34 ounces is terribly porky for an S-1: if the weight were reasonable it would do great with a smaller engine.

If you have an electronic copy of the Skyray plans you could scale them down by 4% all around and hit Brett's 375 squares goal -- I might go down a bit more, because that porky S-1 isn't the only really heavy aircraft I've built.
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline frank mccune

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Re: How many square inches can I make an Ackrobat wing?(Akromaster!)
« Reply #5 on: January 30, 2015, 04:54:23 AM »
     Hi All:

      Thank you all for the replies.

      The plane is already to put together as it has been for the past 3 plus decades. Lol In lieu of the Fox .15, I thought that I would go modern and install a Magnum .15.

       Since I can slide a foam wing of the correct size into the fuselage, I can make it any size that I want thus the question.  I have flown the Shark 15 with a Fox slant plug in the past, I still have three of them hanging in the attic, and I know that they are great fliers.  I wore out a Shark 15 by using a ST G 15 many years ago.  That too, was a great combination.  I am also planning of powering a Shark 15 with a Magnum 15.  That should be a great combination.  I also have a Shark 15 powered with a ST G20/.23 that is a great combination.  The ST G20/.23 is a sweet engine for Sport flying.

     One thing that one notices very quickly about flying the .15-.25 engines is that a gallon of fuel last a bit longer than using .40-.46 sized airplanes! Lol

                                                                      Stay well my friends,

                                                                      Frank McCune

       I fly Sport and a few crude Stunt patterns just for fun.   
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Online Brett Buck

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Re: How many square inches can I make an Ackrobat wing?(Akromaster!)
« Reply #6 on: January 30, 2015, 11:36:14 AM »
Quote from: frank mccune on January 30, 2015, 04:54:23 AM
     Hi All:

      Thank you all for the replies.

      The plane is already to put together as it has been for the past 3 plus decades. Lol In lieu of the Fox .15, I thought that I would go modern and install a Magnum .15.

       Since I can slide a foam wing of the correct size into the fuselage, I can make it any size that I want thus the question.  I have flown the Shark 15 with a Fox slant plug in the past, I still have three of them hanging in the attic, and I know that they are great fliers.  I wore out a Shark 15 by using a ST G 15 many years ago.  That too, was a great combination.  I am also planning of powering a Shark 15 with a Magnum 15.  That should be a great combination.  I also have a Shark 15 powered with a ST G20/.23 that is a great combination.  The ST G20/.23 is a sweet engine for Sport flying.

    I am a big fan of the Shark 15, having had 3 of them (no longer in operating condition...). I had one with a G20/23, too and it was fast as lightning. The original model (built by Lew McFarland) had an OS Max III 15 and was more than adequate. But the Magnum is even more powerful than the 23, and with the (recommended) stock muffler, a lot heavier.

   Do as you wish, of course, but I think you would be much better off with something substantially larger than 270 square inches.

     Brett
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Offline Trostle

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Re: How many square inches can I make an Ackrobat wing?(Akromaster!)
« Reply #7 on: February 01, 2015, 10:01:02 PM »
Quote from: Brett Buck on January 30, 2015, 11:36:14 AM
 
   Do as you wish, of course, but I think you would be much better off with something substantially larger than 270 square inches.

     Brett

I totally agree with Brett.  Consider this -  A good 1/2A stunt ship (the better ones that were flown at the unofficial 1/2A stunt events at the Nats were 200 sq in plus.  The better ones were around 220 or 230.  Now, there is one being built for the Norvel .061 (1cc) with about 250 sq in.  Light weight is important.  So it is for the .15 or .20  or .23 ships with 350 to 400 is not out of the question.

Keith
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Offline Mark Mc

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Re: How many square inches can I make an Ackrobat wing?(Akromaster!)
« Reply #8 on: April 26, 2015, 07:11:43 PM »
Sorry, piggybacking on Frank's thread here.  I finally got around to building an Akromaster kit I bought about 35 years ago.  After all those years, and all that time in changing temp/humidity, my trailing edge stock was very warped.  My local hobby shop didn't have the correct t.e. stock, and I didn't have any in my on hand supply.  So, I tried wetting the t.e. and clamping it while it dried.  Most of the warp came out, but a little is left.  It's little enough that I can get the rest out with a little creative application of heat with the covering iron when I cover it with Monokote.  I didn't cut down the l.e. or t.e. so I could get the extra 4" of wingspan.  But, trying to glue on the fixed flaps to the t.e. with the slight warp would be a pain.  I figured I'd leave them off and use scrap balsa stick to fill out the t.e. to soften the blunt edge.  I still come out ahead on square inches, but I was wondering what affect this would have on the c.g. position?  Worth bothering about?

Mark
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Offline Serge_Krauss

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Re: How many square inches can I make an Ackrobat wing?(Akromaster!)
« Reply #9 on: May 10, 2015, 01:05:04 PM »
With your higher aspect ratio, expect  a nicer glide, but higher susceptibility to gust upsets. I would not have sharpened the trailing edge, but would have sanded it to a flat vertical t.e. with sharp upper and lower edges. I'm not sure any more about wings at our Reynolds Numbers, but such "chopped off" trailing edges, with a small enough thickness to Chord ratio are supposed to work the best, according to tech reports I've seen in the past. I'm too busy now to follow up on that, but I have to think that an appropriate search on this site and SSW forum will get you some hits.
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