Slope Soaring Without Mountains
(Why R/C is a good excuse to go to the beach)

 

Whooosh!

This sailplane graphic was graciously stolen
from some model sailplane company's website!




INTRODUCTION

Believe it or not, slope soaring is entirely possible here in sunny Florida, despite the fact that within 30 miles of the coast the ground rarely gets more than fifty feet above sea level. While our thermals in the summertime have been known to lift small houses off their foundations, the cooling seabreezes that form much of the year are a convenient source of lift along our beaches. Slope soaring is not difficult for anyone who is capable of flying a model sailplane safely. It also offers some unique qualities and opportunities not found in thermal flying. This section will cover a beach environment like we have in Florida, but applies also to any slope with a bit of flat area in front... hills, mountains, large flat-sided buildings, highway overpasses, etc.

The thing that most people will probably notice first is how easy it is. The lift is usually constant and easy to stay in. You need bring nothing but a plane, your radio, sunblock (let's be careful in the sun!) and perhaps a reclining beach chair... bring a cooler and you can really make a day out of it. There are no hi-starts, winches, or motors to worry about. You can bring the kids with little fear they'll be in the way of the airplanes.

Like anything else, there are cons along with the pros. First is the obvious one... you can't slope soar if you don't have a wind off the water. There is, however, usable lift when the wind is coming close to parallel to the shore. (See the diagram for an explanation). The wind may also be too light, which will not let you be able to stay up, or it may be too strong, and your plane will have to be ballasted or may not be able to fight it. Landing on sand will buff your Monokote to a dull haze quickly, and I have lost a brightly-colored Gentle Lady forever by crashing in palmetto scrub so thick it swallowed my plane up forever. Some sites have too many people around for safe flying (particularly in the summertime), or it may be difficult or inconvenient to get to a suitable site. (See map below for Brevard county slope-soaring sites.) But like any other endeavor in R/C, once you know what you are looking for, most of these problems often are easily solvable.

"Of course, I suppose killing people IS a scale-like maneuver for a WWII bomber."
- Scott Black on EFLIGHT



HOW IT WORKS

Slope soaring has been used by birds for eons and was used by glider pilots long before methods to detect inland thermals were discovered. Anytime there is an obstruction to the wind, such as a hill, dune, building, or tree line, the wind has to get around it somehow. Immediately in front of the obstacle, the wind is forced upwards to get over the obstacle. This rising air is usable by flying objects as a means to counteract the pull of gravity. Unlike thermals used for most inland soaring, slope lift depends almost entirely on the prevailing wind, rather than on solar heating and air temperatures. Thus, slope soaring is possible (even improved) by conditions that hinder or prevent regular thermal flight. Sometimes, slope lift can be combined with thermal lift, depending on the topography and weather at your flying area.


EQUIPMENT

First of all, you need an airplane (duh...) I have flown for a long time with that most common of sailplanes, the Goldberg Gentle Lady. My first one (the one that got eaten by the palmettos) didn't have spoilers. The one that is, shall we say, "dearly departed" (named Splat Cat) had large spoilers of my own design. This is not absolutely necessary, but it is a tremendous help - on most days that are worth soaring at all, the lift is so good it is very difficult to land without killing some of your lift! I have a 59-inch hand-launch ship from DJ Aeroworks called the Chrysalis, modified into a pod-and-boom type configuration. (Interested? Read all about it!) This type of ship does well on those light lift days when a 2-meter Gentle Lady isn't terribly exciting. On the other hand, sometimes things don't go so well. I recently built an all-EPP flying wing called a Boomerang, the idea beign to get into the air quickly and easily while my other planes were down for repairs. As of Late February 2000, I can honestly say that I have had virtually no luck with it whatsoever! I have covered it twice (the second time involved a complete re-taping in an attempt to straighten out severely warped wings, they came that way in the kit) but after a few test flights with the newly straightened wings, I'm still having no luck... the thing is just downright squirrely in both roll and (especially) pitch, regardless of the CG, exponential, or control throws I've tried. I must say that I'm a bit baffled as to the problem, but I suspect that it's something I'm doing (or failed to do) rather than the design, and I also believe it's caused by several problems that are all aggravating each other. I've heard from several other people who have had great luck with the Boomerang and I've also flown a Zagi-400, a similar design, with no problems at the IRKS field. At this point I plan to try adding a tail on a boom (or booms) in order to make things less sensitive. Who knows, maybe I could try a canard or something too. Couldn't hurt to play around with it, the EPP bounces and the current iteration isn't capable of sustained flight. I believe that any flyable sailplane can probably fly well on a slope, although a plane that can't handle high winds in thermal flying shouldn't be expected to handle them on the slope as well as a dedicated slope-type ship. However, since a part of sloping is trimming the plane out to match the wind speed, even a Gentle Lady can slope-fly on days you'd probably not even bother to take it to the regular flying field. Dedicated slope planes are often heavier than other gliders and may not be flyable very often in places (like Florida) where there are rarely winds higher than 10-15 mph, although this certainly isn't the case for all slope planes.

I also took a yellow plastic newspaper delivery bag and cut a one-foot streamer, the same width as the red flag on my transmitter antenna, and taped it to the end of the flag. This is quite useful in determining the exact wind direction (the red flag is just too heavy and stiff to work well).



WEATHER CONDITIONS

Well, first of all you need wind. A good situation would be a 10-15 mph steady breeze, within 45 degrees of being directly onshore. You can fly in winds coming very nearly parallel to the shore, although this greatly reduces the effective lift potential, and thus you will have to work harder to climb. Steady winds are ideal, but gusty winds are usually perfectly flyable. For a plane like a Gentle Lady, your upper limit is probably about a 25 mph wind... and that gets pretty hairy. The lower limit would be a 5 mph steady wind right off the water. The less directly the wind is heading off the water, the higher the wind speed must be to get the same lift... although this effect is minimal within 45 degrees to each side of directly onshore.

Ideal Winds blow within 45 degrees of directly onshore

Rain isn't a problem if you and your model can handle it. Lightning storms can blow in quickly in Florida, and it can't be emphasized enough how deadly this can be! If you are at a remote site, fine, but be sure that you don't get stuck in the open with no access to your car or other safe shelter, just in case. High tides can be a problem if they shrink your landing zone to an uncomfortably small size. There have been times when I launched with plenty of beach available, but had to land near the dune because high tide snuck up on me! Beach erosion also can modify your available landing area, and of course don't forget the SPF 30+ sunblock... once you try slope soaring, you'll probably love it and spend a lot of time in the sun!!



SUITABLE FLYING SITES

The ideal flying site has a large area of flat land or (even better) water in front of it... and a steep slope that is directly perpendicular to the wind. Since mountains and seaside cliffs are scarce in Florida, we have to make do with what we have. Oceanside condominiums and hotels are often well suited for this, but simply flying over the natural dunes often provides enough of a rise to provide lift (and fun). The taller and steeper the object, the greater the effect it has on the wind, and thus the larger the area of usable lift will be.

As a slope pilot, there are three main areas to be concerned about:

  • The lift area extends from the front face of the slope or obstruction, up roughly along its vertical face to an altitude of roughly twice its height, out to about that same distance in front (upwind). If the wind is coming in at an angle, this area will be extended farther towards the upwind side of the building.
  • There is an area of little or no real lift that I call the dead zone that is found close to the ground or beach, and also in the "corner" where the front of the obstruction meets the flat ground. For gently-sloping dunes or hills, there may be little or no dead zone. This is the area where the wind stagnates, while the rest of wind blows over it. It is usually not particularly dangerous, although if you forget that there is little lift here you can be fooled into flying yourself to a forced landing due to lack of lift. It can be useful however as a calm area for landing in or sitting in, somewhat shielded from the icy blast of a wintertime gale.
  • The third area is the one that is dangerous, usually called the rotor. This is the turbulent area behind the dune line or building, where the air tries to come back down. It is best described as an area of sink from which it is difficult to recover, as the wind speed is typically high with no lift to give you the time to work it out. On the mega-slope sites out west, the rotor is known to eat airplanes. In Florida, it can eat them, but not by it's force, rather by the situation it puts the pilot in - having to land in what is almost invariably a bad place, such as palmetto scrub or a parking lot (just ask me how I know...) Just repeat to yourself: lift good, rotor bad!

Cross-Section of Wind Profiles on the Beach

These are only rough descriptions, every situation is unique and has its own idiosyncrasies. The only way to know for sure is to fly a site and find out!

A couple of other factors come into play. You have to have a place to fly from. Usually, fliers will stand on the top of a large hill, but on a Florida beach, you may end up standing either on a dune crossover or on the beach itself. Either one is acceptable, depending on what you feel like and the conditions. Remember, it is not good for the environment (and sometimes is even illegal) to damage the dunes or their vegetation by walking on them, so avoid this except in cases of emergency (lost airplanes) and then, be careful not to damage the plants. I have never tried flying from the top of a condo, but something tells me the landings would be almost impossible. A big factor with beach flying is finding a site that is safe. You don't want to have to fly over large numbers of beach goers, for hopefully obvious reasons. One or two folks on the beach is usually no problem, but you need as much (if not more) clear area to land in while slope soaring than you would need at a flying field (remember, you may not always be able to head right into the wind on landing). Rocky beaches can be flown on, but there is a greatly increased chance of airplane damage if you miss the catch. Even plain old sand is a bit abrasive on coverings, so after a while you'll probably want to try to catch the plane whenever possible.

My favorite sites are the beach access near the Perkins restaurant in South Patrick Shores. Just go about a mile south of the Pineda Causeway on A1A. There is a deck that is a great place to launch from, a flagpole to show the wind at a glance, reasonably tall buildings for a long way on both sides, and there are usually not too many people on the beach. There is also food nearby! My second choice is the Radisson Hotel near the corner of the Eau Gallie Causeway and A1A. Go to the beach access on the south edge of the hotel property. This building is very high and flat, however it often has a lot of people and the beach can get fairly obstructed by crossovers and rocks. There are some other sites that are a bit more remote in the south beaches, but I rarely fly them anymore... just too far to drive most of the time, although the desolation is kind of nice once in a while.

Two good slope sites in South Brevard County



FLYING ON THE SLOPE

OK, so you have a site that looks promising, with some nice dunes and a couple of 4-story condos. You have a glider ready (one you are comfortable with), batteries all charged, you've got your sunscreen on, and there is a nice, steady 10 mph wind right off the water. The beach only has a few scattered sunbathers, all of whom are a ways down the beach, so that's no problem. It's low tide, so there's plenty of beach to learn on. All's great, as far as you can tell.

Now what??

Well, first you have to get into the air. If you have a crossover to stand on, great... these make great "aircraft carriers." If you are actually on the sand, that's fine too - just get up near the dune line. If you are in front of a condo, you may wish to move off to one side of it, on the downwind side so that you aren't launching inside the dead zone.

Launching

To launch, check that both radios are on and the controls move properly, then just give the glider the ole heave-ho. If the wind is coming right off the water, you actually want to launch down the beach, not right into the wind (headed offshore), or at least plan on turning immediately towards the building or down the dune line. If the wind is coming more from one direction than the other, launch in the direction the wind is coming from. If you launch right towards the water, you often will be flying right out of the band of lift that is strongest directly over and in front of the dune line.

To gain altitude, you want to go back and forth, right over the beach just above or slightly in front of the dune line. Always turn into the wind, you will in essence be doing a long figure-8 pattern. If you are on a crossover, remember that anything that is at your eye level will appear to be lined up with the horizon. You may not climb very quickly at first, but just maintain gentle figure-8s and you should gain altitude. The key to this part is to fly smoothly, and don't lose altitude in the turns. When you are headed upwind, you will often see a sailplane virtually stop in midair. If you are trimmed properly, this is normal... you should be climbing even though the ground speed is low. When you go downwind, you will appear to fly faster but you will actually climb at the same rate (just cover a lot more ground while you do it, giving the appearance of less climbing).

When you first launch, it's not too uncommon to just not be able to stay in the lift and end up having to land on the beach. There are several causes of this. Assuming there really is lift enough to fly, what I do most often is get too close in to the building at too low an altitude, and get in the dead zone. All seems well, the air is quite calm, but you have little lift. The cure for this is to fly out farther towards the water (say, over the waterline or so) where there is lift at low altitudes. There is strong lift near the building near the top, but it dies near the ground... don't try to get to it too soon or you could end up walking! Another common problem is getting off to a poor launch that you just can't recover from. What can I say, it happens to all of us... try again. Remember, throw hard, throw up, but don't stall.

Flying

Once you are up, you can start trimming for optimum performance. This could actually be a matter of opinion. In lighter winds, I like to trim for a good climb at the expense of ground speed, since it's not hard to get up and down the beach. If the wind is heavier, I will often trim with quite a bit of down trim. This increases the plane's airspeed, since it is effectively in a dive. But since the wind is high, there is a large upwards lift component and the plane holds altitude relative to the ground. Aerobatics are also usually easier in higher winds, since there is more lift there to exploit and your plane is trimmed to fly faster. Just keep your plane pointed into the wind and you'll do well.

Ahh, aerobatics. This is where the real fun starts! I'm sure most soaring pilots have gone out once in a while and blew a good launch on a few loops, rolls, spins, or whatever, only to think that it's a real shame to waste a good launch in order to have fun. Well, on the slope, you can do all the aerobatics you want. Re-launching is simply a matter of flying back and forth for a minute or two until you are back up! Even with a Gentle Lady, loops, rolls, and stall turns are a breeze on most days. (pun intended) Some of the full-house ships would be truly awesome. Just remember the chief caveat, don't do it over people and be careful not to get blown back into a building or get too low so that you can't get back. I usually perform aerobatics over the water (remember, the lift usually extends quite a ways offshore) and thus stay well away from danger.

Don't fly right overhead the whole time. This not only wears out your neck, but flying right overhead is disorienting. If flying by a building, try to get to one side so you can look down the beach at the plane. Be sure to keep an eye out for people around you. I'll let you discover the joys of flying with seabirds for yourself, or you can read about it here!

Landing

OK, sooner or later you have to admit that it's time to land. (Usually because either your batteries are gone or your neck is getting tired). You want to come into the wind as much as possible. There are two scenarios that commonly happen, one when the wind is within about 60 degrees of being parallel with the beach, the other when the wind is close to being directly onshore. The nice thing is that 90% of the time if you botch it up, you can go around again, you aren't forced down unless you get way out of the lift area.) Don't try to catch your plane from a dune crossover, I used to do this sometimes but I broke too many planes. Land on the beach instead. (The new EPP foamies are dang near impossible to break, even if you actually try to... so if you have one of these, then crossover catches become a realistic proposition.)

If the wind is coming down the beach, you want to kill altitude and use the lift right over the dunes to come home. Right over the crest of the dune, there is a lot of lift, but there is a rotor right behind it. It's probably safest to get a few feet in front of the dune. Go downwind a ways, maybe 50 yards or so, and lose altitude until you are no more than 20 or 30 feet high. You may want to dive, do a loop, use spoilers, whatever to get there, just keep in mind where the lift is (and isn't). Fly towards you, you may wish to trim for a slower speed just above the stall. Be careful, if you stall here you may do a good lawn-dart impersonation (sand is wonderfully gentle on planes trying to dive into it though, aside from the dulling of the finish.) By the time you are 10 yards away from yourself, you want to be near eye level. Just fly the plane to yourself and catch it. If you are too high, you may try a near-stall, diving usually will increase your speed too much to catch it safely (depending on the current ground speed). If you get too far off and still have some altitude, you may elect to do a go-around. Just keep flying down the dune line, climbing gently if possible, until you can safely turn around. Go downwind to where your approach started and try it again. Sometimes I even get out and just practice approaches, only catching it on the perfect ones.

If the wind is coming right off the water, you have to modify this a bit. Basically, you want to do the same thing but for the last few feet, turn to head right into the wind. This will allow your ground speed to drop to near zero, even though the airspeed is still high enough to prevent stalling. Spoilers are a godsend in the last 10 yards of this type of approach!! You may also want to stand a bit farther away from the dune for this one. If you are in trouble, try to get back up near the dune but don't forget the rotor / dead zone behind it!

If you are flying near a condo, this is good and bad. The dead zone usually extends onto the beach in front of the building. This makes landing a lot easier if you want to stand in this calm area and have a good approach. But, if you botch it, it's harder to go around. Overall though, this is probably the easiest and is definitely the best when the wind is really cranking. Be warned, though, the trim you set to fight the wind will bite you on landing if you forget about it... don't be surprised that you need a lot of up elevator all of a sudden when you get near the ground!!

Landed? Still have an airplane? :-) Of course you do, that wasn't really so hard was it. Pat yourself on the back and relax - that was fun wasn't it!



POST-FLIGHT DEBRIEFING

Well, there you have it, what you need to know to learn basic slope soaring. By all means try to find someone to help you out if possible, not that it's hard to do but watching someone who has already tried it will make all these words more understandable. Also, watch seabirds, especially pelicans. They slope soar the very same way as models, they're just better at it. Watch where they get lift (they don't flap then) and how they stay in front of buildings. They've been doing it for millions of years, you better hurry up and get started or you'll never catch up! :-)

I would like to hear from anyone interested in slope soaring in Brevard county. Please email me at merlin@ov-10bronco.net or catch me at the next IRKS meeting. Or of course you might see me at the beach, I'll be the one with a transmitter in my hand and a huge grin on my face! Till next time, may your launches be high, your thermals be big, and your landings on the spot!



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