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Old Apr 30, 2012, 02:41 PM
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WE're here now !Go to Sparky 175%

I gone
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Old May 07, 2012, 08:32 PM
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United States, NH, Nottingham
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Holy freakin' smoke

I have unleashed a maelstrom! Good, though. (Oops, please excuse the obscure sub-cultural reference to Kendall Morse's song "Moose Turd Pie") Actually, all the entries are educational for me. Thank you all. I will have to continue the thread a little longer by touching on air foil. The (52" W.S.) Mambo Special I built many years ago had a flat-bottom airfoil with a slight taper on the bottom near the L.E. (see photo); the Great Lakes Special has more flat surface on the bottom (see other photo). I could certainly modify the scaled-up rib profile to match, but not sure it would be necessary. Any comments?
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Old May 07, 2012, 08:59 PM
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Yeah -that little angle is called a "Phillipps entry" and it made a little less drag.
And we're still waitin'to see what you're scaling up.
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Old May 08, 2012, 01:48 PM
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Fred, something with a LOT less camber would be good for a scaled up version which I expect you intend to use for some minor to medium aerobatics. The airfoil as shown won't fly upside down all that well. To the point that you'll be hard pressed to make it perform any outside loops unless you use a LOT of down elevator travel.
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Old May 08, 2012, 03:25 PM
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Mystery Revealed

Sorry, should have specified sooner; it's Hal Krier's Great Lakes Special by Sterling. I love bi-planes. It was originally intended for 1/2 - A either single-channel (with a rubber band powered escapement, no less) R/C or C/L. If I do this, it will be powered by maybe .29 or .35. Some will scoff, tell me to go modern electric kit, but I am basically a mechanic who wants to do something a little different. I was wrong about the Mambo air foil - the bottom also curves up (slightly) toward the T.E. The rib profile of the Great Lakes model is a little "fat". When modifying it, should I start with the current bottom and taper up appropriately from there, or, should I start at the current bottom surface & "bulge" it down, making the ribs even fatter? The top wing of this model is swept, & the top & bottom ribs are the same, which gives the top wing a higher aspect ratio. I can't tell much about the wings of the full-scale plane from the photos I have found, but they do appear to be quite thin & symmetric, or nearly symmetric. Any suggestions? In the meantime, I will examine some other kit plans to get a better clue.

Thank you
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Old May 08, 2012, 04:04 PM
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Don't blame me! I was at an Airshow last weekend,and took some photos of a great lakes,but none of a rib profile...I do have some partials,which may serve to confuse us.
I guess this has been modified to a flat four,but I have no idea,really.
A full zoom on #4 leads me to believe it's semi-symmetrical-good for a model..
I have more detail shots-PM your e-mail if you want them.
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Old May 08, 2012, 04:19 PM
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An easier method once things require so much modifying is to go with something else.

I've taken a moment to sketch out an airfoil style that was made popular by Randy Randolph on a lot of his designs. They all share an approximate thickness of 12 to 15%. The most useful charactaristic of his home brew TLAR airfoils is that the rear lower portion is flat. This flat portion is shown by the small indicator lines on the sketch. By having this part flat the wings can be built on a regular building board without the need for any fancy jibs or packing yet the airfoils are of low camber value which makes them very aerobatics friendly for sport flying. Airfoils of roughly this sort of shape will fly inverted and do outside loaded maneuvers with little trouble. Not as well as symetrical airfoils but not badly at all.
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Old May 08, 2012, 09:44 PM
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More about air foil

Thank you guys! The Mambo's ribs were very much like the drawings; about 13%. Seems a little "fat" for a biplane model though, maybe a little too much drag for the lift provided. 12% looks about right. The photos are great, helpful for scaling, particularly the L.G.! Love this site!
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Old May 09, 2012, 06:23 AM
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Quote:
Originally Posted by jfredmoran View Post
Thank you guys! The Mambo's ribs were very much like the drawings; about 13%. Seems a little "fat" for a biplane model though, maybe a little too much drag for the lift provided. 12% looks about right. The photos are great, helpful for scaling, particularly the L.G.! Love this site!
just ask ?
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Old May 09, 2012, 09:40 AM
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United States, VA, Arlington
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I'll second Bruce on those Randy Randoph airfoils.

First off - big Randy Randolph fan here. I was lucky enough to meet him on several occasions and he was one of aeromodelling's best. Not many of us can cover our study wall in beautiful indoor rubber powered scale models, nor cover a hallway wall in our framed magazine covers. All of Raandy's models flew well - though he once, almost jokingly, told me that all his models were identical, just the sizes and shapes changed some!

Secondly - another TLAR section, by Bruce Tharpe and immortalised on his 'Four Star' series. I flew an electrocuted Four Star 40 for eleven years - by the time it wore out, only the wing section was left unaltered. Okay, it wasn't quite up to F3A pattern - which I have flown, albeit a while back now - but it would do all the good Sunday flyin' party tricks up to a knife edged loop.

If its readable, the attached jpg is a scan off the plan and a CAD tracing. Like Randy's section, it is flat at the back for ease of building. I have built models with this section using both 1/4" flat sheet ailerons, as per the Four Star, and tapered ailerons that match into the airfoil. To be honest, can't tell the difference come when I go fly.

Hope that helps

Dereck
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Old May 09, 2012, 05:27 PM
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Thank you more

Nice! I really appreciate the Info - thank you!
The Mambo had a lot of balsa in it; this one will be a lot lighter, since it is sticks & silkspan. I suspect thinner wings will be OK, maybe make a faster plane.
There are references in this group & others to plan services - any recommendations?
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Old May 12, 2012, 02:31 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Now defunct Radio Control Modeler published a lot of plans - sometimes three a month before they became a magalogue. Lots of good RC plans stuff of all sorts still available:

http://www.rcmplans.com/

Still around - Flying Models. Maybe the last true aeromodelling mag left outside of AMA's Model Aviation:
http://www.flying-models.com/

Model Aviation - all sorts of plans, big range too.

http://www.modelaircraft.org/plans/plans.aspx

Real odd stuff, leans to 'pretty old designs'
http://www.outerzone.co.uk/index.asp

Should keep you quiet for an hour or two

D
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Old May 12, 2012, 09:48 PM
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Busy for a while!

To quote Skyler (comic strip "Shoe") "You mean homework is for ever!?"
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