Showgirl - the beginning

LAST EDITED ON Dec-12-03 AT 12:27 PM (CST)
 
Just thought I would walk you guys through my design process as it happens. Here is a cardboard cutout from my initial CAD sketch for a new design. The model is a .15 powered forward swept flying wing. For UC aerobatics, of course!

I did a rough hand scrawl to get the look I wanted, then started in drawing. I scanned the side view into photopaint hit "copy", opened my CAD drawing and hit "paste". Lock that layer, and then trace over the scrawl. Scaled it up and down, distorted the length until the look and moments were what I wanted.

Finally, I printed it out and glued the sketches to some thin cardboard, and here you are with a first, 3-D look at what I have in mind.

You are doing something very interesting. The OTS-legal DMECO Sportwing is a sweptforward aerobatic flying wing. It flys very well and is capable of the OTS pattern with a 15 if kept light enough. It is too small and the wing is too thin, of course. It would make a good 1/2A airplane with structural mods to keep the weight down. I'm thinking of making another (my fourth) for a TD 09. I've also fooled with drawing up enlarged versions, but havn't done anything concrete with them. Keep us posted. I have an old MAN article from the 40's on sweptforward flying wing design if you want a copy.

Sure, I would love to have the article. I do have the plans to the Sportwing, and have seen one at VSC. The fuselage is awfully wide for even an .09 size engine. And if you cleaned the design up, it is no longer OT legal. Sigh!

Larry-

As you may remember, I have compiled a 450 page bibliography of material relating to flying wings (yes, you're in it). Unfortunately, learning about UC stunt and other responsibilities have really slowed work on the 7th edition (6th is sold out), but I also have 5 file drawers full of reports, articles, patents, etc. So, if there is anything in particular you want along these lines, please let me know.

SK

That is one very interesting design! Looks more like a bird than any plane I've seen, although the Freebird (British design) came close.

I'd be interested to see where the bellcrank goes, and how you manage the leadouts...

Tim

In addition to having seen a Sportwing fly, Don Butman has a forward swept design that dates from 1948 that is a LOT better. He flew a replica of it at my Leprechaun contest one year. In addition, I have seen the big one fly. And then Larry Scarinsi published a 1/2A fsfw called the "Streak" in MAN in the '50s. Always loved that design.

Finally, I have a model of my own, called the Frite Streak that was kitbashed from a Brodak Baby Lightning Streak. I fly it when we do demos at airshows.

The elevators are split and driven by a single bent wire running in "Lucky Boxes". Exceedingly smooth action even with the 24 deg. bend in the hingline. Balance is exactly at the root leading edge, easy to find!

Stab-less too?

I dunno. But I think that dog might HUNT!

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"Ninety-nine per cent of the people in the world are fools and the rest of us are in great danger of contagion." -Thornton Wilder

I think that title is just a little too racy for this forum!

How about "Let us pray".

I have a Sportwing lying around.

Rescued from a garbage can, actually. So I was told. Currell

VERRRRY Interesting! Why not call it the BOOMERANG? Is the concept to launch it yourself, and it will return to you? Wireless U-Control? Kidding aside, It is a nice looking creation. I hope it flies well for you.

A swept forward wing is dynamically unstable (inherently), in fact, that feature was exploited on the X-29 fighter design. You'll need a computerized control system to make it appear stable.

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I suppose if the wing is located far enough aft, it can be made stable enough to fly.

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"Lord, what fools these mortals be!" -Shakespeare

years ago, I built a forward sweep design. It had a profile fuselage and a built up wing. It looked great but---it was so unstable it could not be controlled. three short flights was all it lasted, hunting is an understatement. Those wings being swept so far forward will move the cg forward and will require a great deal of nose weight.

Good luck

Mike

>A swept forward wing is dynamically unstable (inherently), in fact, that feature was
>exploited on the X-29 fighter design. You'll need a computerized control system to make it
>appear stable.

A moderate amount of forward sweep is easily handled though. The REAL problem lies in aeroelastic effects. These tend toward pitch divergence (e.g. tip flexes up, thus creating more upward pitching moment). You can make these very unstable, but they don't HAVE to be.

Forward swept types can be designed with several advantages. In a forward-swept design the c.g. "problem" is not really a problem at all. It allows a longer nose, with more room for a tank than your average tailless type, and more important, it lengthens the "tail" moment. Forward sweep moves the a.c. forward away from the (centered) elevator. With the elevator further behind the a.c. and therefore the c.g, you get more control authority and more pitch damping to contend with the forward tip lift. The elevator can be smaller and therefore doesn't compromise the lift over as much span as on other tailless types. On a full sized or R/C model plane, instead of using elevons, ailerons can be placed at the c.g. so that adverse yaw can be handled with differential, wheras elevons can't be handled that way. Last of all, swept forward wings inhibit tip stall and reduce tip vortices, making the wing more efficient and safer, without incidence washout. On full sized sailplanes, a moderately sized vertical stabilizer has been found to handle the forward swept wing's inherent yaw instability easily on moderately forward swept designs like Marske's "Pioneer" and "Genesis II". Overall, the forward swept tailless type has more advantages than many realize; it just must be proportioned, AND STRUCTURED, carefully. In my opinion, it is the best tailless configuration for all but the low-aspect-ratio designs.

Larry Renger (Designman) is experienced with forward swept tailless types, having also designed the R/C slope soarer "Toucan" , manufactured by DCU of Anaheim, CA. David Garwood reviewed this markedly forward swept model as handling well (FM, 4/95).

SK

Why not develop a line of these in four sizes as they did in the 50's and call it the "Chorus Line". Just a suggestion.

There is hope yet for my idea.

Being a star trek fan and fully appreciating the wonderful models of the various space ships; I have this weird idea to build a Klingon Bird of Pray and run it through the pattern with its disruptors blasting all the bystanders coming over the wingover. The configuration begs for a pusher configuration; perhaps a K&B 35 that can use regular props by running clockwise to eliminate that problem. The bird of pray is a swept forward configuration. Any taker's on this idea?

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler

Umm, that's Bird of Prey. Prayer has a rather different effect...