Glider Instrumentation and Glider Instrumentation and PlumbingPlumbing

NCSA Safety SeminarNCSA Safety Seminar

11 Feb 200611 Feb 2006

Poor vs. Good Poor vs. Good InstrumentationInstrumentation• Ultimately to get the most on of your Ultimately to get the most on of your

glider you need to know and understand glider you need to know and understand the instrumentation and what it is the instrumentation and what it is actually telling you, not doing so, could actually telling you, not doing so, could lead you to make wrong decisionslead you to make wrong decisions– Understand of TAS vs. IASUnderstand of TAS vs. IAS– Executing Best Speed to FlyExecuting Best Speed to Fly– Identifying real liftIdentifying real lift

Pressure PortsPressure Ports

• There are 3 main types of pressure ports There are 3 main types of pressure ports on gliderson gliders– StaticStatic

• Altimeter, airspeed, varioAltimeter, airspeed, vario

– DynamicDynamic• Ram or Pitot (pressure increases with speed)Ram or Pitot (pressure increases with speed)

• Bernoulli venturi (pressure decreases with speed)Bernoulli venturi (pressure decreases with speed)

– Total Energy = Static + DynamicTotal Energy = Static + Dynamic• Hybrid Bernoulli + StaticHybrid Bernoulli + Static

• Dynamic + StaticDynamic + Static

StaticStatic

• True static is a measure of the True static is a measure of the atmospheric pressure surrounding the atmospheric pressure surrounding the glider as if it was not movingglider as if it was not moving– Usually a simple hole on the fuselage or Usually a simple hole on the fuselage or

the side of a tube normal to the air flowthe side of a tube normal to the air flow– Slipping and skidding can effect the Slipping and skidding can effect the

reliability of this measurementreliability of this measurement– Multiple static ports can reduce this Multiple static ports can reduce this

problemproblem

Dynamic Dynamic • Always greater or lesser than the static when the Always greater or lesser than the static when the

glider is moving, measure of motionglider is moving, measure of motion• Most common is Ram and is usually a large or small Most common is Ram and is usually a large or small

hole directly pointed into the relative windhole directly pointed into the relative wind• Comparing the static to the dynamic is a direct Comparing the static to the dynamic is a direct

measure of airspeedmeasure of airspeed• As the air density changes with altitude, indicated As the air density changes with altitude, indicated

airspeed (IAS) is slower than true speed (TAS). How airspeed (IAS) is slower than true speed (TAS). How does this relate to VNE, maneuvering, stall speed?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 "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."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     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.with altitude reaching about 2 at 30 000 feet.

Bernoulli pressureBernoulli pressure          P + ½ P + ½  V² = constant V² = constant • This pressure is always lower than the static when This pressure is always lower than the static when

the aircraft is in motionthe aircraft is in motion• Very rarely used to measure airspeed these daysVery rarely used to measure airspeed these days• This effect is the most common used in This effect is the most common used in

compensating static pressure to give a Total compensating static pressure to give a Total Energy . Pure geometry betweenEnergy . Pure geometry between

ports can achieve this.ports can achieve this.

Grob 102, SS plumbingGrob 102, SS plumbing• 1 Dynamic Ram1 Dynamic Ram

• 8 Static Ports ( 3 independent groups )8 Static Ports ( 3 independent groups )

• 1 Total Energy1 Total Energy

• The point here is that it can be complicated and The point here is that it can be complicated and good intentions can lead to bigger problemsgood intentions can lead to bigger problems

TE and Pitot

4 static ports

4 static ports

SS detailsSS details

• AirspeedAirspeed– Dynamic from tail and separate staticDynamic from tail and separate static

• AltimeterAltimeter– Separate staticSeparate static

• Sage VarioSage Vario– TE from tail + ½ liter flaskTE from tail + ½ liter flask

• Cambridge Electric VarioCambridge Electric Vario– Separate static + dynamicSeparate static + dynamic– Does not use TE from the plane and does its Does not use TE from the plane and does its

own TE using the pitot and true static, tunableown TE using the pitot and true static, tunable

Checking for NormalChecking for Normal

• Airspeed behaves normally with Airspeed behaves normally with angle of attack, side slip, skidding, angle of attack, side slip, skidding, etc….??etc….??

• Air speed, altimeter, and vario does Air speed, altimeter, and vario does not change with vent open or closednot change with vent open or closed

• Total energy compensated vario Total energy compensated vario shows only glider polar response in shows only glider polar response in still airstill air

What to Look forWhat to Look for

• Pure static (in still air)Pure static (in still air)– Vario swings with pitch and speed changesVario swings with pitch and speed changes

• Pull ups show positive rates of climb (stick thermal) Pull ups show positive rates of climb (stick thermal) • Very difficult to identify thermals, center lift, and adjust speed to flyVery difficult to identify thermals, center lift, and adjust speed to fly

• TE compensated (in still air)TE compensated (in still air)– Push over shows only glider polar sink rates (MaCready Zero)Push over shows only glider polar sink rates (MaCready Zero)– During pull ups, vario never goes above minimum sink rate, always stays negativeDuring pull ups, vario never goes above minimum sink rate, always stays negative– Under and over compensation, tuning is possible 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 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 it should work. In general leaks are killers. Response time is also tunable with gust filters combined with the right volumes.gust filters combined with the right volumes.

• NettoNetto– Adds additional compensation to TE that removes the polar sink ratesAdds additional compensation to TE that removes the polar sink rates– Only shows the air mass motion at any speedOnly shows the air mass motion at any speed– To my knowledge, our club does not have a glider with this type of compensationTo my knowledge, our club does not have a glider with this type of compensation– Modern instrumentation can switch between TE and Netto automatically while Modern instrumentation can switch between TE and Netto automatically while

transitioning between thermaling and cruise.transitioning between thermaling and cruise.– Very , very nice for identifying thermal on a high speed runVery , very nice for identifying thermal on a high speed run

In Summary:In Summary:

• When you and your glider are working inWhen you and your glider are working in harmony with the outside conditions, greatharmony with the outside conditions, great things can happenthings can happen• The experience can be both predictable and fun beyond The experience can be both predictable and fun beyond

beliefbelief• Please take the time to familiarize yourself with the Please take the time to familiarize yourself with the

instrumentation on board and learn how to make the best instrumentation on board and learn how to make the best possible use of itpossible use of it

• Also, understand whenAlso, understand when it is giving correct informationit is giving correct information