Dynamic Soaring 101, DS your RC Sailplane / Glider

Dynamic Soaring

Introduction:
So you want to learn how to DS your Radio Controlled Slope Glider... Well you came to the right place! This page is dedicated to the newbie as well as the advanced Dynamic Soaring enthusiast. I've been DSing for several years now and will document my understanding of this phenomena on this web page. My goal is to provide RC Pilots with the methodology to learn how to DS while maximizing the pleasure of the journey and the sense of personal accomplishment. It will be updated as my understanding improves or my beliefs change. I will also be introducing terms that will be new to alot of you that have come out of hundreds of hours joking around on the slopes. Jargin is always alot of fun. Use it and watch the reactions you get. email me if I've missed some good ones and I will attempt to integrate them into the text. This article will focus on two areas, understanding the air and going faster.

By: Norman Mertke

Understanding Air Flow that Allows Dynamic Soaring to Occur:
In order to harness the energy of the Dark Side you must first understand what the air is doing. This section focuses on defining areas of the air to allow for visualization of the optimal flight pattern..

Definitions:
Bait: Your worst plane that you won't mind crahing, the plane you throw out first to test conditions and verify the backside is functioning properly.
Clearing out the Squabs: This is vary difficult to explain with words, Video will do it best... coming soon!
Dark Side: The back side of the hill where the turbulent flow of the rotor allows the conditions of Dynamic Soaring to occure

Milestone #1, 10 circles in a row

Milestone #2, 80/100 mph (foam/glass)

Milestone #3, 100/125 mph (foam/glass)

Milestone #4, 150 mph

Milestone #5, 200 mph

Backside Separation:
Separation is highly dependent on hill shape and wind speed. The air will generally have laminar flow over the top and down the backside. As the windspeed increases the chance for separation increases. Wind direction is also critical. Conditions will improve as the direction becomes the more perpendicular to the face of the slope. Hill to hill performance greatly varies based on several key factors. The angle between the front and back side slopes as well as any flat or rounded tip are the largest influencers. Your basically looking for the smallest angle between the front and back slope and the smallest flat spot. The best spots can be difficult to impossible to land on. One last but potentially key feature would be an outcropping or disruption in the flow pattern that can assist the formation of the separation. (not shown in figures)

Figure 1
Laminar Flow over Hill Top

Figure 2
Backside Separation

Figure 3
Hill Features

Air Zones:
It is critical to understand the various air zones because they will be key in defining the flight pattern. Your target will be to do continuous upwind turn in clean air. Identifying where the boundary layer is will be key in getting below it on the backside. Watch other pilots fly, you can identify the boundry layer by the change in tone of the planes (change in air-speed) and by the waggle the plane makes when it go through. The plane will make a skipping or fluttering type noise if the pilot attempts to make the turn before passing completely through the boundry layer

Figure 4
Dynamic Soaring Air Zones

Getting your first 10 Dynamic Soaring circles in a row can be the most difficult and frustrating part about dynamic soaring. There are several key ways to minimize this frustration. Number 1, learn at a good DS spot. I spent way more time on this milestone than I needed to if I knew of the better spots in my area. As it turned out, I ended up identifying most of the DS-able hills that were close to me. Talk to the DS-ers in your area. Number 2, go out with someone who already knows what they're doing. Most DS-ers will be happy to coach you through your first circle and get you started. Number 3, focus on the basics and everything else will come on itself: a) Plane Setup, b) Dive in and Fly out, c) Frontside turn. There are 2 schools of thought on this. You can start with an inexpensive crash-tolerant foamy that is less efficient and more difficult to DS or you can go with the cruchy and start off vary conservatively. Personally, I generally push things too far and have more confidence in my abilities than I should for the crunchy route. If, on the other hand, you are vary methodical, good piloting skills and fairly conservative you may advance much more rapidly on a crunchy. I know of at least one individual that made it all the way up into the 160s (mph) before destroying his crunchy.

Master the dive in and fly out. The key here is to leave a decent safety margin for yourself while your trying to get comfortable. Your going to want about 15-20 mph winds for the best results right now. The target is to clear the boundry layer on the backside while maintaining enough altitude to avoid hitting the ground. You will need to go deeper for a larger off-the-deck height so make sure you have plenty of altitude to start with. Figure 5 displays a representation of the plane's bank angle relative to the ground plane. Moving from left to right takes you from the beginning of the turn to the end of the turn. The trick is to hit the green line where your off-the-deck height remains constant. Staying on the blue side is safer but will offen pop you over the boundary layer. Keep practicing until you can consistently hit the bottom turn and exit with more energy than you entered with.

First order of business will be to check your plane's setup. Check for slop in the linkages. Tight hinges are key to control. Take out those servo-savers and any other funky stuff. Stick to basics! If you can't afford to loose a servo you shouldn't be DS-ing. Sloppy control hinges will make your plane a beast to control on the turbulent dark side. As far as rates are concerned, at this stage all your really interested in is making sure it won't tip stall if you yank the elevator. A simple dive test from good altitude followed by full up elevator should tell you if your going to have problems. If you find your plane rolles out of the loop you need to back off you elevator throw. You may have to shitch holes on your servo control horn or elevator control horn if you do not have a computer radio with rates control. Next, check your roll rate. You want a decent roll rate, not an insanely fast roll rate.

Mastering the upwind turn is very similar to the downwind turn. At a good site and big air, you can be 50 feet off the deck and still get a good turn in. Focus on getting the plane to return to the backside at the same angle it came up at. There are 2 main areas to be careful of. 1st, there is usually a sheer that can develop in the 1st 10 feet off the ground ot the top line. If you go too low it will roll you over and you'll go straight into the hill. The 2 ways to overcome this is to fly further forward into the front side lift of to make your turn or fly higher off the ground. 2nd, DO NOT STAND IN THE PATH OF THE DOWNWARD LEG!!! This is probably the most dangerous place to be. Even expert DSers get caught by this shear area occasionally. If your caught in this you're going to get rolled over. If you hit it right, there won't be any amount of aileron input that will save the plane from going in.

Figure 5
Aircraft Turns

You should have a little confidence now in knowing where to turn. The focus now needs to be on control. Keep flying circles increasing the number of circles you can do in a row. Work on coming nailing the up line in the exact same place every circle. You will need to work on your turn diameters to control this. Releasing up elevator half way through the turn can allow you to move up and down the ridge line on demand. This will allow you to focus in the area where the air is working best.

Now that you have control of where your plane is on the ridge line it's time to start working on the angle your punching through the boundary layer. You want to hit the boundry layer in line with the wind direction. You'll know when this occurs when your plane no longer jerks as it goes through. This is a rapid up or rapid down motion as it hits the oncomming air. You need to hit this on the up line and the down line to really harness the energy out of the wind. When your able to hit this line on a couple of consecutive turns your ready! Time to start watching for some 20-25mph wind and the guys with the radar gun. Note, at a good site, you won't need to fly supper low yet. Keep that plane in one piece by maintaining a decent safety margin. Maximize your stick time, your really working on getting your reflexes to be second nature to what the plane is doing!

Figure 6
Beginner Flight Path

So now your getting some speed eh! Only problem is that plane is going so fast it's getting to be a bear to keep it under control. You've probably even scared yourself by now. First order of business is to learn how to make that plane more stable at high speed. It's all about reducing your rates. You can tell when your rates are too high by the way you correct the flight path of you glider. If your plane is over shooting your corrective inputs you need to reduce your rates. I've had glider rates reduced to as much as 25% to get the response I needed to fly a smooth line. Any seasoned DSer will be able to tell you when your rates are too high, listen to them and turn them down. Just remember to turn them back up for landings as the sailplane can become vary sluggish when the rates are adjusted properly. The faster you go the further the rates will need to be reduced. Now that you have your plane under control it's time to practice smooth circles again. Keep working on them and allow the plane to get lower to the ground. Being smooth is more important that getting so low as to start trimming the grass. 20-25 mph wind should get you there but 25-30 will make it easier. Pay attention to the radar gun callouts. You will be listening for jumps in speed. When you here them maintain your current turn locations.

Now that your getting good at this it's time to get into the 150 club! This requires a whole new level of knowledge and control. First I'll explane the power zones and how to find them. First of all your going to need to find the smooth air. Make your turns at various locations up and down the ridge line looking for where the plane's flight path is most stable. Obviously you need to be in a power area but the smoothest air will usually be in the best spot.

By now you have a really good feel of the backside and are fully addicted to this type of flying. This is where my competence level ends as I've only flown 207mph with a Super-Tron. It's all about being at the right spot at the right time with the right plane. Plane construction becomes a major factor at this point. Use of Bait is extensive and your going to find out about "Clearing the Squabs" There are vary few planes that are able to achieve these speeds without major upgrades so be prepared to start hacking those beutiful moldies. This is the complete list of upgrades I believe work.
Radio Gear Upgrades:
   - Servos are critical, use digital servos with minimum 50oz torque for ailerons. I like the JR-DS368
       servos since I've seen them go over 250mph. I hear the Airtronics 94761 is a good choice too.
   - 6V battery is a cheap upgrade and it ups your servo speed and torque!
   - Use heavy duty wire on everything, you don't want a voltage drop during those hard turns.
Linkage Upgrades
   - Maximize your mechanical advantage by using short horns on your servo and long horns on your
     control serface. You should not need to reduce your rates for normal flying and if your dropping them
     below 35% for high speed DS your not taking full advantage of the servo torque
   - Minimize sloppy linkages. Add a dab of CA on clevis threads to eliminate thread slop.
   - Improve Linkage strength - Your linkages should be as straight as possible to keep them from
     buckiling. Pushrod tubes must be supported for the full length of the fuselage
Aileron Upgrades (Aileron twist is a major problem at speeds over 160mph, they need to be rock solid)
   - Tighten hinges lines if you don't have live hinges. Silicon hinges won't cut it! Use more hinges, at
      least double what your used to or under and over hinges using strapping tape.
   - Push on the ailerons at thier ends with about a pound of force. If they twist more than 1/32" they
      need upgrades. An aluminum tube on the leading edge of the control surface works great!
   - Set up your aileron throws so they move twice as much up as down. This will help you keep the nose
     pointed down during flight path adjustments.
Mass Balancing (Critical for softer airframes)
   - Wing tip weight can be added to offset fuselage weight.
   - Leading edge weight can be added to offset wing twist.
   - Be careful with these, they allow the plane to go faster without more strength leading to much more
     violent structural failures.
Site Conditions
   - High altitude helps but is not a requirement at this speed.
   - High wind speed, there will be a limited number of days in the year when the wind will be strong
     enough to achieve these speeds. Keep an eye on the weather and be ready to take a vacation day when
     the opportunities exist. The more times you fly at high speed the more comfortable it will feel and the
     better you'll get. Oh yeah, be prepared to loose planes!.

Milestone #6, 250mph:

Vary few people have attained this speed and there's only 4 places in the world where it's been done. Parker Mountain, Castle Ridge and Mission Ridge and Eagle View. Still working on this one myself. I'll write more when I get there.

Now your going to need to dial in the angle you pop through the boundry layer. The plane won't shake or shudder when your hitting it square. If it jumps up you have a positive angle of attack and you should hit it at a lower angle ie. a slight touch of down elevator. If it pushes down, a little more up before going through is appropriate. Remember to keep sufficient altitude to be comfortable with your plane while finding the spot your going to fly. "Bait" is often used at new sites to find these power spots, especially on big days as their locations tend to change based on wind direction. Now you need to dial in your down wind turn. Your going to play with turn hieght and radius to maximize your speed as you listen for the radar callouts. Once you've got it dialed in, do the same for the upwind turn.