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Glider Instrumentation and Plumbing

Glider Instrumentation and Plumbing. NCSA Safety Seminar 11 Feb 2006. Poor vs. Good Instrumentation. Ultimately to get the most on of your glider you need to know and understand the instrumentation and what it is actually telling you, not doing so, could lead you to make wrong decisions

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Glider Instrumentation and Plumbing

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  1. Glider Instrumentation and Plumbing NCSA Safety Seminar 11 Feb 2006

  2. Poor vs. Good Instrumentation • Ultimately to get the most on of your glider you need to know and understand the instrumentation and what it is actually telling you, not doing so, could lead you to make wrong decisions • Understand of TAS vs. IAS • Executing Best Speed to Fly • Identifying real lift

  3. Pressure Ports • There are 3 main types of pressure ports on gliders • Static • Altimeter, airspeed, vario • Dynamic • Ram or Pitot (pressure increases with speed) • Bernoulli venturi (pressure decreases with speed) • Total Energy = Static + Dynamic • Hybrid Bernoulli + Static • Dynamic + Static

  4. Static • True static is a measure of the atmospheric pressure surrounding the glider as if it was not moving • Usually a simple hole on the fuselage or the side of a tube normal to the air flow • Slipping and skidding can effect the reliability of this measurement • Multiple static ports can reduce this problem

  5. Dynamic • Always greater or lesser than the static when the glider is moving, measure of motion • Most common is Ram and is usually a large or small hole directly pointed into the relative wind • Comparing the static to the dynamic is a direct measure of airspeed • As the air density changes with altitude, indicated airspeed (IAS) is slower than true speed (TAS). How does this relate to VNE, maneuvering, stall speed? • "To convert IAS to TAS multiply the your altitude, in 1000s of feet, by a factor of about 1.5 to get the percentage increase to apply."    e.g. TAS @ 88 knots at 6500 feet = 88 + 8.8 = 97 knots. The factor increases with altitude reaching about 2 at 30 000 feet.

  6. Bernoulli pressureP + ½ r V² = constant • This pressure is always lower than the static when the aircraft is in motion • Very rarely used to measure airspeed these days • This effect is the most common used in compensating static pressure to give a Total Energy . Pure geometry between ports can achieve this.

  7. Grob 102, SS plumbing • 1 Dynamic Ram • 8 Static Ports ( 3 independent groups ) • 1 Total Energy • The point here is that it can be complicated and good intentions can lead to bigger problems TE and Pitot 4 static ports 4 static ports

  8. SS details • Airspeed • Dynamic from tail and separate static • Altimeter • Separate static • Sage Vario • TE from tail + ½ liter flask • Cambridge Electric Vario • Separate static + dynamic • Does not use TE from the plane and does its own TE using the pitot and true static, tunable

  9. Checking for Normal • Airspeed behaves normally with angle of attack, side slip, skidding, etc….?? • Air speed, altimeter, and vario does not change with vent open or closed • Total energy compensated vario shows only glider polar response in still air

  10. What to Look for • Pure static (in still air) • Vario swings with pitch and speed changes • Pull ups show positive rates of climb (stick thermal) • Very difficult to identify thermals, center lift, and adjust speed to fly • TE compensated (in still air) • Push over shows only glider polar sink rates (MaCready Zero) • During pull ups, vario never goes above minimum sink rate, always stays negative • Under and over compensation, tuning is possible • All of our gliders should have this, the hardware is there and if it is set up properly it should work. In general leaks are killers. Response time is also tunable with gust filters combined with the right volumes. • Netto • Adds additional compensation to TE that removes the polar sink rates • Only shows the air mass motion at any speed • To my knowledge, our club does not have a glider with this type of compensation • Modern instrumentation can switch between TE and Netto automatically while transitioning between thermaling and cruise. • Very , very nice for identifying thermal on a high speed run

  11. In Summary: • When you and your glider are working in harmony with the outside conditions, great things can happen • The experience can be both predictable and fun beyond belief • Please take the time to familiarize yourself with the instrumentation on board and learn how to make the best possible use of it • Also, understand whenit is giving correct information

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