Flying With Water Ballast

In my last article, we discussed what wing-loading is and how it affects the glider. Essentially, it is the aircraft's weight divided by the wing area & is a crucial factor in the cross country performance.  In this article, we’ll delve into the intricacies of wing loading, addressing key considerations related to aerotow operations, communications between the parties involved, take-off and landing & the general overall impact of water ballast.

Aerotow with Water Ballast

When taking off with water ballast in your glider, there are several considerations to keep in mind to ensure a safe and efficient operation.

Communicate with the tow pilot.  First of all, you’ll need to inform them of the presence of water ballast in your glider; this allows them to adjust the tow speed and their low-altitude handling appropriately. Forget to inform them, and you might see them trying to climb away while you’re staggering to even get off the ground, dragging the combination down in a dangerous situation (a potential double stall) resulting in an accident into the end fence.

Calculate tow speed. It's a tough one to answer because the number of different glider types out there is wide and varied, but typically, you’ll want to be about 10kts faster than your typical no-water-ballast tow speed.  If you find the glider struggling to maintain station, then you can always ask the tow-pilot for “ABC, plus 5kts” or “ABC, 5kts less”, why like this? Because they can adjust the tow speed relative to their own ASI.

Balance your wings. Communicate with your wing-runner too! Some gliders have tanks in their wings and will be completely full of water, requiring no balancing. Others will have internal bags and be partially filled, which require up to a minute to balance the water in the wings.  Regardless of the above, it’s important to equalise the water to a hands-off state.  Why? Well, if you were to miss this step, when the wing runner lets go of your wing, it’ll potentially slam into the ground, causing a ground loop or a scratched underwing while you try to pick up the wing with the opposite aileron.  

Low-speed control of the glider. You’ll want to be prepared for potential changes in the gliders handling characteristics during the aerotow, particularly in the low-speed region. The aforementioned point and the responsiveness of some glider ailerons are particularly poor at slow speeds.  There are techniques where one can begin the take-off roll with the airbrakes half extended, thus spoiling the airflow over the ailerons & increasing their responsiveness.  When you have positive control, then close & lock the airbrakes. What are the risks? That you forget to close and lock them! This can be because it’s your first time using this technique or you’re experienced, and something has distracted you, so use this with caution.

Ground Roll Length. It’ll be slightly longer, as the glider requires more speed to generate the necessary lift. Add in wet and long grass, and it’ll become even longer. So, the glider-tug combination should be aware of this and ensure a sufficient runway for a safe take-off.

Landing with Water Ballast

Typically, it’s something you shouldn’t do, but it’s not something you can not do. For example, if you can't stay up and need another tow, you may want to land with water ballast. Many factors are involved when making this decision; let's talk about them!

Is it your glider, a club, or a borrowed glider? If you aren’t the owner, what is their policy? Everyone has different opinions, and you should respect it. Landing with water ballast should be done with the utmost care and requires carefully assessing the conditions and what you’re trying to achieve.  

Only land with water ballast when:

• Conditions are predictable, namely, wind
• Smooth surface
• The approach is without obstacles
• You know what the AFM says regarding approach speed

Jettison water ballast before landing when:

• Unpredictable conditions, gusty winds
•  Rough surface
•  Challenging approach due to undulating terrain or trees on final approach, which could cause a wind shear
•  It’s just a regular day of soaring, nothing to be gained

Reasons for landing dry:

• Less chance of a gear collapse
• Less fatigue on your gliders structure
• Less chance of a ground-loop
• Won't block operations due to your long landing
• You don’t know what the AFM says regarding stall or approach speed with water ballast still on.

If you choose to land with water ballast, you need to be aware of your increased stall speed & how this will affect your circuit operations.  In the aircraft flight manual, you’ll find information on the desired approach speed with water ballast – respect it & adjust your operations accordingly.  You’ll also want to land as smoothly as possible, so ensure you have adequate runway length. Ensure that you don’t float so much that you cause a genuine stall onto the field, causing a gear collapse. Be aware that the handing characteristics will change, and you’ll have more inertia and a higher ground speed when touching down than usual.  Nothing to be feared, just something to be aware of.

When beginning to fly with water ballast, I always suggest that you start small and work your way up to the maximum take-off weight of the glider.  So start with 50 lts generally, then 100 lts, then potentially up to reach the MTOW. Each time, you’ll see the handling and performance change, but your skill set will match it.  It’s a lot of fun, I definitely recommend you try it!
 

Banner Photo by Mika Ganszauge

 Adam Woolley was born into the gliding world, being the 3rd generation in his family. Going solo at 15, his thirst for efficiency in soaring flight & quest for a world championship title to his name has never wavered. One big passion is sharing his experiences & joy with other glider pilots all around the world. Adam is an airline pilot in Japan on the B767 & spends his off time chasing summer around the globe. He has now won 7 national Championships & represented Australia at 5 WGC's & 1 EGC.