TE compensation problems

Hi

The varios in my club's Discus CS report extra sink when pulling up and extra lift when pushing down. Its as if the needles have mass intertia and are affected by the vertical acceleration of the glider (which of course they dont (for this discussion) but its a good analogy). It can be as mush as 2-3 meters depending on the stick force. Unfortunately I have not flown any other gliders recently with a quality vario system so I dont have anything to compare it with, however I am fairly sure that the compensation should be better then it is.

Idealy the vario should show the sink/climb rate I would acheive at a transient speed as if I was actually cruising at constant speed. (I dont want to get into a netto discussion here cos I dont think it is relevant)

The varios are a Winter and a M Nav on separate bottles (of course). I fitted a brand new ILEC TE probe (long boom) in the hope that this would fix the problem but it didnt. I have checked for leaks - none, and there are no gust filters or other gizmos in the tubing.

I have been trying to work out what factors could cause this behaviour. The first one that I can think of is obviously the compensation built into the TE probe. Since I am now using the best probe there is (according to some) then I have ruled out this posibility. It should not be necessary to bend the probe since it is factory calibrated and this setting is always correct (ie independent of glider and instruments etc).

So what other factors can cause this. The next factor I can think of is if the tubing (from the probe) is being accidentally squeesed by something (e.g the pilot's weight through the seat) reacting to G forces. The tube would be squeesed during a pullup causing pressure to go up and the vario needle to go down). I have checked for this and cant find a problem.

Then there are the aerodynamic efficiency changes of a pull/pushe which no doubt have an effect but I am guessing that these are smaller then what I am seeing on the vario. Nothing can be done about these effects. Or can one tweak the factory calibrated probe to compensate for this as well? Either way I am fairly sure that this is not the main cause of my problem.

Does anyone know of any other factors I should consider?

Hi Peter,

There must be something wrong; Aerodynamic efficiency changes will not give you errors anywhere near this magnitude. My best advice is to check and double-check again for leaks. Even the most minute leaks that do not reveal themselves when testing with e.g water will make vario's go haywire. (been there, done that..) - And since it's both the mechanical and electric vario, I guess we can rule out simple misadjustments.

Good luck, Lars Peder