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Hawaii Sailplane Challenge

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Hawaii Sailplane Challenge

Postby Wilbur1 » Mon Sep 12, 2011 4:07 pm

This idea has been floating around in my head for some time. After some testing I think it might be possible, if the winds are right.

Here's the planned route, which is subject to change:
Image

Begin: PHDH - Dillingham Airfield - postponed until I figure out the route
End: HI25 - Kaalaiki Airstrip
This is open to any sailplane, but I'll be testing with the ASK 13. Other sailplanes might be better/worse for this trip.

The distance will be about 300 miles / 475km. I need to do some math/testing to see if the water crossings are even possible. More on this later...

I'll be testing each night this week at about 23:00 UTC.
Last edited by Wilbur1 on Tue Sep 13, 2011 1:06 am, edited 1 time in total.
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Re: Hawaii Sailplane Challenge

Postby Kabuki » Mon Sep 12, 2011 9:55 pm

The North Shore of Oahu is renown for sailplane and hang gliding conditions. On a (very) typical day, the winds are out of the northeast at 15-25 kts, and when strike cliffs ("pali") head on, creating powerful, consistent updrafts. There is a legend -- which may be true -- about a battle where warriors were thrown off the pali, only to be blown back into battle by the strong winds. There is at least one hang glider launch site near the west end, and it's common for flyers to make several traversals of
20 miles or so, until they get tired, and land on the beach far below.

There are also similar high cliffs on Molokai, but they drop directly into the ocean -- no place to land, other than the Kalaupapa peninsula. On the Big Island, I have heard of somebody taking off from the top of Mauna Kea (13,796 elevation) and flying down to land on the beach at Waipio.

But I've never heard of someone gliding from one island to another. There is a pronounced venturi effect between islands, and no updrafts, no thermals. Your route also takes you on the exact wrong side of Haleakala (East Maui), where there is a pronounced downdraft on the leeward side. One real life challenge for hang gliders is to
take off at the top (10,000 ft) and fly to the southernmost tip of the island. It's tailwind all the way, and the last couple miles are over ranch land punctuated with prickly pear cactus and rough lava rock. I've heard it's been done, and it's like AGL < 100 feet all the way.

What I would like to see is a realistic modeling of the wind conditions on the North Shore (Oahu) pali, which is indeed a gliding playground. I've glided in a sailplane
in flightgear (can't remember which) and it's pretty nice, but I was not (am not) proficient enough with modeling the winds and thermals to make it realistic.

Another challenge is to take off from Hilo (PHTO) and fly on a heading of 242-245 degrees for 40 miles. It will take you from sea level to the top of the most massive mountain in the world. Do it in a Piper Cub at an AGL of 500 ft. It's just a slow, boring slog over nearly featureless terrain. The slope is so gradual, you hardly know you're climbing. Above ~5,000, it's all black lava. It's difficult to tell if you're flying level in certain directions, because of the slope. The Big Island has some pretty good canyon flying on the northeast end, also.
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Re: Hawaii Sailplane Challenge

Postby Wilbur1 » Tue Sep 13, 2011 1:05 am

Thanks for the info!

I'd like to use current METAR weather, but there's the chance of pulling info from a station on the other side of one of the mountains. (This explains why I'm currently crashed on the side of a mountain in California.)

I also found a nice visual representation of the avg winds on all of the islands. http://hawaii.gov/dbedt/ert/winddata/

After some math I also realized you would need at least 4000' of altitude to run between the first stretch of water. That's going to be difficult. Time to re-think this plan. :mrgreen: So this is postponed for now.
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Re: Hawaii Sailplane Challenge

Postby Thorsten » Tue Sep 13, 2011 6:53 am

What I would like to see is a realistic modeling of the wind conditions on the North Shore (Oahu) pali, which is indeed a gliding playground. I've glided in a sailplane
in flightgear (can't remember which) and it's pretty nice, but I was not (am not) proficient enough with modeling the winds and thermals to make it realistic.


Maui happens to be one of my testbeds for placement of thermals (because the terrain changes radiacally over short distances), but since I've never been there, I am down to plausibility. Here are some recent developments of how the conditions are simulated right now.

If you can cast 'realistic' into a more detailed explanation of just what you'd like to see, we can certainly work on that. Wind-cloud-terrain interaction is, as of recent GIT, not so expensive as it used to be, which should in principle open the way for rather complicated modelling.

After some math I also realized you would need at least 4000' of altitude to run between the first stretch of water.


4000' are not too extreme, but you can't arrive at zero altitude (no lift on the ground), you need to correct for the winds,... Having flown in Flightgear around Maui, I think some crossings just may be possible, but others simply can't be done. Well, you can always aerotow up to 12.000 ft and then go from there...
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Re: Hawaii Sailplane Challenge

Postby Kabuki » Tue Sep 13, 2011 4:53 pm

Thorsten wrote in Tue Sep 13, 2011 6:53 am:Maui happens to be one of my testbeds for placement of thermals (because the terrain changes radiacally over short distances), but since I've never been there, I am down to plausibility. Here are some recent developments of how the conditions are simulated right now.


Man, that is gorgeous scenery! How did you do that? Maui sure doesn't look that good on my system.

Anyway, the clouds around Haleakala are typically very dense by mid morning on the north side (left in the pic). They don't "ring" the mountain, but hit it from the northeast and back up out to sea. Meanwhile, the tops, when they reach the height of the crater rim, spill over almost like a waterfall, down the leeward side of
the crater rim, and dissapate within the crater itself. The leeward side is typically cloudless, and gusty.

What's spectacular is how the clouds re-form on the leeward rift that runs from the southwest corner of the crater (the summit). At about 5 to 6,000 elevation, they form, almost as if they're coming right out of the mountain itself. The form something like a train of clouds that gets thicker as they head out to sea. It's really quite a sight to be standing on the mountain, and seeing the clouds form just a few hundred yards in front of you. The effect is like the sky spinning cotton candy.

Looking at the maps behind the link provided by Wilbur1, I can see it's happening at the edge of a very strong wind "apron" that edges to the south east coast
of the island. That coast is typically very gusty. It's also virtually uninhabited because (according to locals) the wind. It's dry, windy, and empty.

All the islands have lots of distinct microclimates, with dramatic changes in climate happening in distances of less than a mile. The valleys of west maui that open
onto the south-southwest shores have very pronounced winds that can be dangerous to motor vehicles, and a sailor's delight. I remember riding along the coast
road on a motorcycle, and as the road turned into a valley, the wind would hit you like a brick at first. The road would follow the side of the valley downhill,
but because of the wind, you'd slow down if you didn't add throttle. Then as you turned, the wind was coming from the outside of the turn, so you could go
a LOT faster than your eyes would allow you to think, and then ZIP up the hill with the wind to your back. If you didn't know how it worked, it could be
dangerous.

FWIW, most air traffic in Hawaii sticks to over the water to the north of the islands. I've flown a bit in an 8 passenger cessna (410?) and it's amazing how
the wind changes dramatically when you cross an invisible, but predictable "line". It gets really bumpy when you start flying over the land. Likewise, on a
sailboat, there's a "wind line" they talk about, and you can almost see it as you cross over it in a boat. One minute the water's smooth (with swells), and
the next minute, it's blasting.

BTW, when you cross those channels, don't forget that the winds are all crosswinds. I have a hard time imagining crossing from Oahu to any other island, or Maui to the Big Island. The sailing conditions there are likened to rounding the horn of South America. You can see whitewater from 30,000. The Hawaiian name for that channel is "alenuihaha", which means "use great caution".
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Re: Hawaii Sailplane Challenge

Postby Wilbur1 » Tue Sep 13, 2011 6:41 pm

Does Local Weather override all of the METAR(or custom) values in the regular Weather settings? Seems like it does. Is there a FG Local Weather For Dummies section in the wiki anywhere?

I wanted to use METAR data so everyone would have the same conditions, but it seems like it's not going to be accurate enough for a trip like this.
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Re: Hawaii Sailplane Challenge

Postby statto » Wed Sep 14, 2011 3:15 am

Kabuki wrote in Tue Sep 13, 2011 4:53 pm:Man, that is gorgeous scenery! How did you do that? Maui sure doesn't look that good on my system.


If you have the old scenery, get the new scenery (thru TerraGear only). If you have the new scenery, those textures are improved from when the new scenery was originally released.
Custom Scenery available from http://www.stattosoftware.com/flightgear
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Re: Hawaii Sailplane Challenge

Postby Thorsten » Wed Sep 14, 2011 11:15 am

Anyway, the clouds around Haleakala are typically very dense by mid morning on the north side (left in the pic). They don't "ring" the mountain, but hit it from the northeast and back up out to sea. Meanwhile, the tops, when they reach the height of the crater rim, spill over almost like a waterfall, down the leeward side of
the crater rim, and dissapate within the crater itself. The leeward side is typically cloudless, and gusty.


Aehm, north is to the right side of the pictures (where the vegetation is). The code really rings Haleakala only when there's no wind, if you put in 20 kt, you get the spilling into the crater and a pronounced lee.

The problem in making the leeward side cloudless is that a bias that is strong enough to do so kills off clouds in lees in other regions of the world too strongly. I can do a complete wipe, but I have the feeling that is too harsh, so maybe a more differential condition on the strength of the lee (currently it's just local gradient from 2 points) would work - but any more sampling of terrain costs performance.

Backing up to the sea is currently not in the code. It would also require a third terrain point to 'look ahead' what terrain is coming (currently I am only looking back where the cloud came from). But it can be done.

The form something like a train of clouds that gets thicker as they head out to sea. It's really quite a sight to be standing on the mountain, and seeing the clouds form just a few hundred yards in front of you. The effect is like the sky spinning cotton candy.


Do you have any pictures of that? I have some trouble visualizing how it works to the degree that I could extract the math to simulate it.

I'm also staring a bit at the wind maps - it seems the surface winds are especially strong whenever an obstacle has just been crossed, but much weakened before it. I'll have to stare a bit more to get a feeling for how the airflow actually goes.

The valleys of west maui that open
onto the south-southwest shores have very pronounced winds that can be dangerous to motor vehicles, and a sailor's delight.


Any general rule to simulate that needs to probe a lot of terrain... Funneling of descending winds by a valley requires you not only to get the gradient, but also some sample points perpendicular to the gradient to see how persistent your terrain pattern is...
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Re: Hawaii Sailplane Challenge

Postby Kabuki » Wed Sep 14, 2011 7:41 pm

Thorsten -- Yeah, North is to the "other left" of the pictures, AKA "the right" :oops:

Code: Select all
I'm also staring a bit at the wind maps - it seems the surface winds are especially strong whenever an obstacle has just been crossed, but much weakened before it. I'll have to stare a bit more to get a feeling for how the airflow actually goes.


That's the "venturi effect", and it's how carburetors work on cars. One of the most amazing demonstrations I saw was in an educational film, where it was
observed with people crowding through a doorway. As they exited the doorway, they briefly sped up for a few steps as they spread out.

I'll try and find some pictures of the clouds on the leeward side of Haleakala... stay tuned. BTW, I think it's amazing that you're able to do this at all with pure
math and physics. This is the kind of thing meteorologists were wishing they could do not that many years ago. I would have thought some kind of "contrived"
model would do the job. Isn't that how thermals work in flightgear?
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Re: Hawaii Sailplane Challenge

Postby Johan G » Thu Sep 15, 2011 6:46 pm

Off topic
Kabuki wrote in Wed Sep 14, 2011 7:41 pm:One of the most amazing demonstrations I saw was in an educational film, where it was
observed with people crowding through a doorway. As they exited the doorway, they briefly sped up for a few steps as they spread out.

People generally tend to move like particles. I often think of (simple) aerodynamics when I'm in more populated places, provided enough of them are taking the same route. You get Venturi effects, and sometimes even eddys (sort of) as people tend to be waiting for others against walls and pillars, away from the stream. :wink:
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Re: Hawaii Sailplane Challenge

Postby Wilbur1 » Fri Sep 16, 2011 1:13 pm

I'll be trying out the North Shore (starting at PHNG) today and tomorrow. Look for me on the FG live map. http://mpmap02.flightgear.org/

I've also found a couple great 3-point trips in BC and California. If there's some interest I'll post up the routes.
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