How do you fold a wing?

Which way do you fold the wing, Up or fore - aft.  Is the wing high or low?  Bi plane or Monoplane.  These have to be answered before you can make these decisions.  Sometimes the best approach is to hinge the wing where it makes sense and then pin the spars with a bolt and multiple lug clevices ( kind of like interlacing your fingers. )  the simplest approach was that used by Grumman to fold their wings for carrier decks.

That's a big topic, but like many things in aviation, there's not a lot that hasn't already been tried by someone, sometime.  For light aircraft, look for articles on the 1920s Lympne light aviation contests in Britain in the Flight archives online or in Richard Riding's book Ultralights:  The Early British Classics.  But those are for wings foldable for strorage, not for the road.

Folding is one thing, making the folded wing secure enough to be roadable at highway speeds is quite another.  About the most elegant solution I have seen are a couple of high wing designs in wich the wing swivels 90 degree to project ahead, but again, that wouldn't be very secure in on the road.  The roadable aircraft is an attractive dream but a very problematic reality.

Take a look at www.terrafugia.com for an LSA with folding wings.

Check out the wing folding on the Glastar and Sportsman 2+2.

 http://www.glasairaviation.com/

-Dj

I found some pictures of the Sportsman.  It's wings appear to swing back from the root without twisting by pivoting on a vertical hinge near the back of the wing root and the base of the strut.  That simple articulation accomplishes two goals of a roadable aircraft:  that it be narrow enough, and that it minimize lift and drag while moving forward in the road configuration.

True, but I'd settle for roadable at city streets speeds.

Go to www.mustangaero.com and check out their folding wing option on the Mustang II. I know of one builder who keeps his plane at home in his garage and takes it to the airport on a trailer. There is a link on that website where you can look at his plane. His name is Bill S. I can't spell his last name off the top of my head.

If you’re looking for simplicity you might look at how the Taylor Coot Amphibian does it. Basically Molt used a little homemade U-joint between the spars at the point he wanted the wing to pivot. Since it’s a cantilever wing there are three pins (bolts) to pull from the spars. I was thinking about using that idea on a different airplane only with an automotive driveline U-joint for the actual rear spar attachment (which is where I wanted it to pivot). If you wanted the U-joint on the front spar it would have to be a strut-braced wing. (Or could you have a strong U-joint for say the bottom spar attachment with a bolt at the top? Dunno.) I had a system figured out for automatic connection of the control surfaces and no wing tanks. Not fancy, but simple.

What mechanism do they use to keep the wings extended in flight while being able to fold on the ground?  Is it patented?

Take a look at the KitFox folding wing.  The rear spar and the front spar are attached to the fuselage with hefty clevis pins.  Pulling the front pin allows the wing to fold back along the fuselage.  The control linkage for the flaperon is designed so that when the wing is folded the flaperon swings up out of the way of the fuselage.  Simple braces are installed to support the wings by the tail feathers, and the airplane can then be rolled onto a trailer, or even towed behind a vehicle for short distances.  Travel for more than 10-15 miles needs to be by trailer, or if the speed is going to be higher than about 30-35 mph.  Many people have built covered trailers to move their aircraft across country.   Even without the braces, the folded wings take up less hangar space by quite a lot.  Here's a link to several websites that might help:  

http://www.kitfoxaircraft.com/; http://www.teamkitfox.com/Forums/.  

Mike

The Dyke Delta has a wing fold that secures the wing so that it has been towed clear across the country at highway speeds. However, the wings of the roadable aircraft I have seen are too big for the mission. Stall speed should be in the Lancair, Thorp  T-18 range. If the cruise speed isn't at least 200 mph, what's the point? The whole idea of a roadable aircraft should be to save time. The smaller the wing, the easier it would be to fold. But, why fold at all? Very short span wings (<8 ft) have been successfully flown. See the Stits Fly Baby or Baby Bird. An acceptable (to me) roadable aircraft would be a snug tandem 2 seater- as in Firestar ll- with a high wing, very low aspect ratio, maybe with a canard- front tires at the tips (Dragonfly, Q2) but steerable. Would have a small auxiliary engine for city street  speeds driving a single rear tire. Ought to be fun.

I recently completed my Sportsman in the TWTT program in Arlington and needed to get it to Oregon, where there is no sales tax, most immediately. So, I flew it the 100nm allowed by the temp airworthiness certificate and then trailored it the rest of the way. Folding the wing is as simple as pulling two safety pins and two structural pins from the leading edge spar, just inside the passenger compartment and folding on the hinge at the trailing edge spar. You do have to remove the cabin top covers, which requires a screw gun. The plane comes with a support strut kit that supports the wing while folding and pin and tang couplers at the tail, once the wing is folded back against the fuselage. This whole folding process only takes about 10 minutes and allows the plane to be trailored, with an 8'-4" width. Simple tension straps, that can be purchased at the local hardware or Home Depot store can be used too strap the plane on a trailor. I saw a Sportsman hosited onto the upper deck of a large yacht, with its wings folded recently...pretty coool! Got the plane, working on the yacht!

Folding the wing is one way to achieve a necessary change from the landing configuration to the driving configuration.  I want a low stall speed in the landing configuration.  I want to drive at city traffic speeds into a breeze without generating enough lift to pick up the vehicle or make it unstable.  While driving, I don't want to be tipped over by a side gust of wind or the rush of air from a passing vehicle.

OTOH, I'd rather not have to fold the wing, and I invite any suggestions for other means of spoiling the lift.

I like your description of an acceptable roadable aircraft.  Why would it be preferable to make the front wheels steerable rather than the rear wheel?

If you don't fold the wing, then you have a severe limit on wingspan, and have to make up for it by extending the chord or having multiple airfoils.  My understanding is that the longer the chord, the higher the speed at which the wing begins to stall, so I don't think extending the chord is an option.  The Terrafugia Transition has a 27.5' span and a small canard on the nose.  To generate the same lift in an 8' span would take at least 4 wings, right?

If you want to drive at city traffic speeds- 45 mph- into a breeze- 20 mph- then the stall speed of the wing should be at least 65 mph- Lancair range( 82.5 sq ft wing). There are many aircraft with a wing loading above 25 lbs/sqft of wing area. An 8 ft span and 10 ft chord main wing mounted on pylons above the "fuselage"  with the rear pylon(s) adjustable to change the angle of attack would reduce/ eliminate the wing affecting the handling of the vehicle at road speeds. A tractor flight engine mounted on the leading edge would allow the use of engine power to accelerate the airflow over the wing. I've seen video of a roadable aircraft with an 8 ft span wing, however it was a low wing and was not very controllable in roll. A full-flying canard might be an easy way to have flight controls that also could nail the vehicle to the ground  when appropriate.- it might even be possible to separate the 2 sides for roll control as well. This provides structure for the front axle with steerable tires at the tips, so it will steer like a car -see Molt Taylor - then have a single relatively large rear tire to handle the landing and  auxiliary engine loads. There have been and still are 3 wheeled vehicles of this configuration- check out the Can-Am. Everything I'm proposing has already flown- just not all on the same vehicle( that I know of). Last, but not least, a parachute a la Cirrus just in case...