Author Topic: forward swept wing (Read 1831 times)

Steven Kientz · « **on:** October 24, 2008, 02:44:50 PM »

Has anyone toyed with a forward swept wing? I have seen several R/C planes, but was curious as to how a C/L plane would behave? I assume some(all ?) of the peculiarities of a swept wing would be reversed?
I was thinking of a flying wing( no taper), twin rudders with a stabilator between them.

thanks
Steve

Jim Thomerson · « **Reply #1 on:** October 24, 2008, 02:59:55 PM »

Take a look at the Dmeco Sportwing. Barry Baxter has plans. There is a photo of one of mine on the PAMPA website under Old Time Stunt. http://www.control-line.org/DesktopDefault.aspx?tabid=23

I've also seen a photo somewhere of an airplane like you describe. I think it would fly fine.

Ralph Wenzel (d) · « **Reply #2 on:** October 24, 2008, 05:44:29 PM »

Henry Nelson (Yeah, that Nelson), designed a .15-size combat plane with forward-swept wing back in the '70s called the Venom. Good flier with a ST G20/.15, but rather small by today's standards. Of course, modern .15's put out a bunch more power too.

Pretty sure I still have plans, if you're interested . . .

JIM SHAMBLIN · « **Reply #3 on:** October 24, 2008, 10:00:39 PM »

In the late 40's, I competed against someone with a sweptforward wing. It turned so fast I built several myself.The smaller one was powered by a Torpedo 29 and weighted about 32 oz. Even without flaps, it really turned great. A larger one with an Atwood 60 was perhaps the best stunt plane I built. Unfortunately, I crashed it a few days before the last contest I entered before going to college. The next time I flew I was 72, quite a long lapse, lots of things have changed. I need to try one again.

John Miller · « **Reply #4 on:** October 24, 2008, 10:37:15 PM »

Larry Rengar, known as "Designman on some of the forums, has a nice little design. I forgetwhat he calls it, but it has a swept forward wing. I think it has been published somewhere.

Howard Rush · « **Reply #5 on:** October 24, 2008, 10:42:25 PM »

I've messed with them. They have some interesting properties:

The root tends to stall before the tips. This is usually a virtue.

Rolling moment due to sideslip is positive (I think), but whatever it is, it makes the airplane less sensitive to wind direction. This is good for combat planes, because you can better maneuver them upwind.

Yaw moment due to sideslip is unstable, so they tend to oscillate or worse in yaw in tight turns. A good-size fin will cure this.

If the wings aren't rigid, they are subject to two aeroelastic phenomena: 1) torsional diversion, where the wings just twist off above a certain speed, and 2) a roll instability above a certain speed caused by the leadouts twisting the wing.

Steven Kientz · « **Reply #6 on:** October 25, 2008, 04:23:54 PM »

Do you think a foam wing would be rigid enough, or is a built up wing the way to go? I'm considering a 40" ws, powered by a TT .36. I currently fly off of grass so no landing gear is needed. The R/c model I saw had a very long forward fuselage, likely needed to get the CG right?
ralph, I might take up your offer of plans if I get stuck as how to proceed.

Thanks
Steve

Patrick Rowan · « **Reply #7 on:** October 25, 2008, 10:51:51 PM »

Back in the day I watched Henry flying his 35 sized fast combat Venom. I have a set of plans for it. Thin air foil.

This would have been about 1970.

L0U CRANE · « **Reply #8 on:** October 27, 2008, 10:24:28 AM »

Steven,

I understand your question as about wings with both the leading and trailing edges swept forward...

However, on a technicality, even a Ringmaster wing has forward sweep! Sweep angle is measured at the quarter-chord line. A Ringmaster, Flite Streak, or any other wing with a straight LE and a forward tapered TE is mildly swept forward...

When you get to a layout like deBolt's Sportwing, you really got forward sweep... Several of Bill Werwage's stunt designs have a forward sweeping flap hingeline, btw...

A foam core wing sheeted with, say, 1/32 balsa, or glassed and vac-bagged, or either or both, in combo with CF reinforcement, should stand up to just about as much as any other way to do things. Do it strong, though. A thing called aeroelasticity does exist. Roughly, it deals with the tendency of airloads to distort the pieces we are moving through the air.

A radically forward-swept wing layout, pulling a lot of lift, can tend to twist at the tips towards MORE lift, which feeds on itself to go worse. A swept-back layout, pulling a lot of lift, would more likely tend to twist towards unloading the lift - reducing the load.

When the sweep angles are moderate, it doesn't make a whole lot of difference, but at extremes, it might just. Renger's SkySport has definite, but not radical, forward sweep. It was in Model Aviation last year, I believe.

Steven Kientz · « **Reply #9 on:** October 27, 2008, 01:51:23 PM »

I've only drawn a few sketches so far. Some have the tips ahead of the prop disc. My concern with a built up wing is how to tie the spars together. I feel a center section is needed, with the wings angled from there. With the foam wing it would have to be cored for the leadouts, way past my building experience.
Maybe I should stick with conventional wings for a while. Once I get a few more planes off the board, maybe I can tackle this project.
By the way, the picture that started this was in MA 9/2008 page 39, electric powered Talon.

Thanks
Steve

phil c · « **Reply #10 on:** October 28, 2008, 07:23:57 AM »

The benefits from sweeping the quarter chord forward balance out at 1-2 deg. of forward sweep. It makes the plane roll slightly away from you whenever your maneuver extends into the upwind half- Vertical eights, hour glass, clover. Downwind the plane rolls in slightly, which makes the transitions in the eights smoother. More than 3-4 degrees of sweep in the QC(a straight leading edge as in the Ringmaster) doesn't help much if at all.

Ward Van Duzer · « **Reply #11 on:** November 09, 2008, 07:46:52 PM »

We experimented a little with swept forward wings on a 1950's Sky Box. Increased the turn ratio enormously. Of course we were only 15!

Check out the skis!

Ward-o

Steven Kientz · « **Reply #12 on:** November 10, 2008, 04:05:47 PM »

I saw an interesting picture in Ted Fanchers column of Ma Jan. 1990. An Itailan named Franco Ballesio was holding an Astro with a forward swept LE. Anyone have any info on that plane?

Steve

Dean Pappas · « **Reply #13 on:** January 30, 2009, 11:02:33 AM »

Hi All,
Howard hit on something important here - "Rolling moment due to sideslip is positive (I think), but whatever it is, it makes the airplane less sensitive to wind direction. This is good for combat planes, because you can better maneuver them upwind. "

In RC Pattern, now that there are many rolling turn and rolling loop maneuvers, we see the hassles caused by pitch-induced yaw to roll couple. If you have ever felt the need to take tip weight out of the plane when going to a strong runway-wind site, then you have encountered this. Wing sweep, as measured at the one-quarter chord line is the cuprit. If the one-quarter chord line is straight from tip to tip you end up with minimal cross-couple. Of course, that would mandate a strongly swept forward flap hingeline.

regards,
Dean Pappas

minnesotamodeler · « **Reply #14 on:** February 10, 2009, 05:52:24 PM »

Nothing personal, Ward, but that is a singularly ugly airplane. "LAR" factor is nonexistent.

Ward Van Duzer · « **Reply #15 on:** February 14, 2009, 10:27:18 AM »

Don't like my "peppermint box"? Awwwwwww shucks

Ward-

don Burke · « **Reply #16 on:** February 14, 2009, 10:36:39 AM »

From what I understand, sweep forward works the same as sweep back. And 6 degrees of sweep gives the same effect as 1 degree of dihedral. LE sweep is advantageous in an airplane that has to fly both upright and inverted, gives the dihedral stability either way. Might be why George Aldrich and Bob Palmer started the trend to swept LEs.

Brett Buck · « **Reply #17 on:** February 17, 2009, 08:08:25 PM »

Quote from: Dean Pappas on January 30, 2009, 11:02:33 AM

ing sweep, as measured at the one-quarter chord line is the cuprit. If the one-quarter chord line is straight from tip to tip you end up with minimal cross-couple. Of course, that would mandate a strongly swept forward flap hingeline.

You can do it with a straight hingeline, but it looks pretty awful/chunky. I think the disadvantages of swept-forward hinge lines far outweigh the advantages, so I usually use a small amount of sweep.

Brett

afml · « **Reply #18 on:** February 17, 2009, 09:26:56 PM »

Quote from: John Miller on October 24, 2008, 10:37:15 PM

Larry Rengar, known as "Designman on some of the forums, has a nice little design. I forgetwhat he calls it, but it has a swept forward wing. I think it has been published somewhere.

Larry's 1/2A plane is called "Skyfire".

He has plans to several sizes of forward swept wing designs.

"Tight lines!"
Wes

Larry Fulwider · « **Reply #19 on:** February 18, 2009, 02:03:01 PM »

Quote from: phil c on October 28, 2008, 07:23:57 AM

The benefits from sweeping the quarter chord forward balance out at 1-2 deg. of forward sweep. It makes the plane roll slightly away from you whenever your maneuver extends into the upwind half- Vertical eights, hour glass, clover. Downwind the plane rolls in slightly, which makes the transitions in the eights smoother. More than 3-4 degrees of sweep in the QC(a straight leading edge as in the Ringmaster) doesn't help much if at all.

Phil gives one side of "normal" quarter chord forward sweep. The other side of normal sweep (rearward), like the aforementioned Nobler, is also normal.

Outside of those norms, take the time to do actual MAC calculations, as your eyeball for CG location will no longer be reliable. It may not be where you think it should be, jsut based on your experience.

Personally, I think you should always do those calculations anyway, but the further from the norms, the more important they become.

Larry Fulwider

Larry Renger · « **Reply #20 on:** February 24, 2009, 11:44:22 AM »

Here are a couple of my forward sweep designs. I have a new one designed at 250 sq.in. for a .061, it is a flying wing. Don't know when I'll get to tackle building it, though.