Monday, September 1, 2014

More from Saint Barthélemy Airport

Back in February I posted a video clip showing the diving approach to tiny Saint Barthélemy Airport in the Caribbean.  Courtesy of aviation enthusiast Cargospotter's channel on YouTube, here are two more videos from that island, shot from various vantage points and showing aircraft such as a DHC-6 Twin Otter, a Britten-Norman Islander, a Pilatus PC-12 and a Cessna 208 Caravan landing and taking off. I recommend watching both in full-screen mode.

I'm intrigued by the tendency of these relatively light STOL aircraft to 'float' after recovering from a diving approach like that.  In more than one landing, I was fully expecting the pilot to go around and try again, because his wheels didn't touch the tarmac until he was more than halfway down the runway!  Short landings indeed . . .



Will said...

It would appear that reversing props capability is the only reason that the strip exists. Wheel brakes alone would be very marginal for that short strip.

I'm thinking that someone could make some money designing and installing a near full span spoiler system for these STOL types. They need time to bleed off speed from coming downhill, which accounts for the float. Speed brakes would do, but adding big enough panels to the body would be a major pita, and take away internal space for the mounts/actuators.

They need to get the wheels down sooner, so they can start reversing asap. Not much braking distance margin for error. I suspect they are loaded lighter than normal, due to the minimal distance they have on hand.
I wonder how much head wind they deal with there? A missed approach going uphill might be more than the locals want to deal with, perhaps.

Inconsiderate Bastard said...

According to various Wikipedia entries, the runway at Gustaf III airport at St. Bart's is 2133 ft long (the entire island is 6,177 acres, or 9.6 square miles). FWIW, that runway length is not quite twice the flight deck length on a US Nimitz-class aircraft carrier. I'm guessing a good landing at St. Bart's is described as a "three-wire trap".....

I suspect the "float" you're describing is ground effect, which is an "air cushion" between the wings and ground which occurs starting approximately at an altitude equal to the aircraft's wingspan all the way down to touchdown, and is more pronounced on STOL aircraft, which have light wing loadings anyway. Miss D should have some insight on it, especially if she's flown Cubs and Super Cubs in Alaska. The solution is to learn how to fly through ground effect.

fast richard said...

That looks tricky. The winds look squirrelly and gusty. A short landing requires a slow approach speed which is hard to maintain on a steep approach. Gusty winds require a little extra speed for a safety margin. It is a difficult skill to balance those requirements. Good flaps or spoilers can help, but the pilot gets to show some skill on a runway like that, no matter what kind of aircraft.

Old NFO said...

Going 'downhill' increases airspeed, hard flare will cause a 'float' as you see... They don't want to do a 'stall' approach, because of the potential for shifting winds=crash... The other option is to just fly it on, but that would mean higher than normal landing speeds and more tire/brake wear. IB, one comment, the actual 'runway' on a carrier is the angle which is only 450 feet.

Roger Ritter said...

Another thing that would help with speed control/floating is to do a hard sideslip on the descent - but that sort of thing is frowned upon in scheduled passenger service!

Anonymous said...

We used a Twin Otter to get into sites in Northern Quebec. The only place to land was a butte, so we built the camp at the base of it.

Time to leave and we had more gear and three more folks going out than came in on the aircraft.

After two aborted takeoffs the pilot said the aircraft was too heavy and did anyone want to get off. I being the brightest person onboard volunteered and took my pack and rifle off the plane.

The pilot taxied as for back on the butte as possible and headed the Otter down the butte. He disappeared below the horizon like a B-25 raiding Tokyo and re-appeared a couple of seconds later.

They made Ft. Chimo in one piece and picked me up about 3 hours later.


Anonymous said...

Twin Otters were designed from day one for just this sort of thing. My second employer had bases in Frobisher Bay and Resolute Bay in the Arctic. In springtime they supported (and frequently rescued) adventurers who were trying to reach the pole by landing on whatever flat chunk of ice they could find.

A Twin Otter has Fowler flaps and flaperons, the ailerons act as flaps so the full span of the wing becomes a high-camber profile with the flaps down. In reverse thrust each engine produces 400hp IIRC.


Well Seasoned Fool said...

+1 IB on ground effect. Good coverage in the book every pilot should have.
by Wolfgang Langewiesche

BobF said...

I love watching good pilots flying a bird in the envelope it was designed for, especially when it flies in the face (some pun intended) of what we are used to seeing.

WV: you Gookel
Hey, enough of the name calling! :-)

Jim22 said...

I'd consider dumping the flaps as soon as the aircraft entered ground effect. That would put her on the ground quicker. It would also clean up the plane in the event of a go-around.