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vario help!!!


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ok, it seems no-one has the brauniger comp gps so il see if i can get my question answered anyway!

the unit has 3 altimters.

A1, A2 and A3 although it seem A3 just plot sthe difference between 1 and 2.

this is my question?

A2 is resettable to zero and therefore great for seeing my height above take off area.

A1 i believe is the height above sea level? which is critical for my safe flying height / resrictions etc.

however when i switch on, A1 gives a reading of say 1000ft, but can be altered by pressing the arrows hence not giving me a true reading??.. so

other than with a gps or other means, can my vario give me an accurate height above sea level whatever my location.. and if so - how?!!

i understand this may be a simple question to most folk, and i can determine the height from other means, but i just want to know if my vario can do it?

cheers

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i have d/loaded the manual, and can see how to put the pressure in, but how do i find the correct pressure for the day? airmet?

i have since found an os map with the correct height on it, so i could just programme it in, i just wanted to see if it will give it to me automatically, just in case i go to another location where i cannot ascertain correct levels above sea.

cheers

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I agree with Pete. A1 is normally calibrated either with the known pressure or a known altitude. A2 as you rightly say is normally used for QFE (zeroed at your take off field). I don't have one of these devices so I don't know what A3 is so am assuming you are correct about the height differencial.

Cheers

Mark

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i have d/loaded the manual, and can see how to put the pressure in, but how do i find the correct pressure for the day? airmet?

i have since found an os map with the correct height on it, so i could just programme it in, i just wanted to see if it will give it to me automatically, just in case i go to another location where i cannot ascertain correct levels above sea.

cheers

do you have a link for the down load and I will take a looksy?

Pete b

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i have d/loaded the manual, and can see how to put the pressure in, but how do i find the correct pressure for the day? airmet?

i have since found an os map with the correct height on it, so i could just programme it in, i just wanted to see if it will give it to me automatically, just in case i go to another location where i cannot ascertain correct levels above sea.

cheers

They will not do it automatically it has to be set manually

Pete b

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Well once you've calibrated it for the day at a known altitude then it will keep the pressure that you have set until you change it again. Pressure will vary throughout the country if you are travelling but not enough that you need to worry about it. Pressure can also change throughout the day in the same location but again don't worry too much about that unless you can easily recalibrate it. You should maybe work out what your altitude is at home then use that to calibrate in future before you leave.

When flying with a vario you have to accept that there is a degree of inaccuracy because of all this and make allowances if you are flying in areas with restrictions on height. Allow a couple of hundred feet on the safe side (although big pressure changes can make more difference than that).

HTH

Mark

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A1 is basically the altitude above sea level (this can be changed to regional pressure reading)

A2 set for airfield height (take off field).

A3 totals up all the metres climbed during a flight (not very useful for us)

Pete b

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Because the atmospheric pressure can vary at sea level, just the same as everywhere else?, so you have to be able to dial in your ACTUAL altitude wherever you happen to be, prior to T/O, or have access to the regional pressure setting that altitude is based on (often erroneously referred to as regional QNH).

Remember that most clearances will be granted on the basis of the ATZ QNH, so you need to be able to set that. I seem to remember that the Brauniger units won't let you alter pressure settings/altitudes once a flight has commenced, although I may be wrong on that point.

The only "altitude" setting that is fixed so to speak is in fact not altitude, but flight level, where the level is referenced to a fixed 1013.2 hPa

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Exactly which is why it may be useful to determine the altitude at your home so you can set that every time you leave for the flight. You will notice that on a daily basis your 'home' altitude will change as the pressure varies so where for instance you set your home to say 400ft you may find that if the pressure drops the next day your A1 altitude could now show say 520ft (I think I have that the right way round but the amount can vary dramatically) so you will need to drop the A1 setting back to 400ft as that is the known altitude. Vica Versa if the pressure were to rise.

The best way to check the altitude on your home is to go to a local landmark/hill that has it's altitude printed on a map and set your A1 altitude to that setting. Then go home and note what your A1 altitude says. This will be near enough your actual altitude. It won't be spot on but certainly close enough for our purposes.

You could do the same exercise from your normal take off field, or all of them if you have multiples.

Alternatively compare it to GPS altitude but these aren't known to be very accurate if I recall.

Bit of a chore to do first time but once done you shouldn't need to do it again.

Cheers

Mark

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Marks solution isn't a bad one, but the regional pressure setting is actually a forecast that estimates a minimum expected pressure value for the region, for a given time period. I believe it is updated hourly. During the day, the setting can change quite a bit. The value that you compute based on your observations of a known reference height and rthe current pressure, will not necessarily return the correct value for the regional setting.

Easiest way to check it is to listen into a local (largish) airfields ATIS on an airband, or even just listen out to any old ATSU in your area, they will give out the regional setting whenever someone moves out of their control into open FIR and needs to reset their altimeter to a suitable en-route setting.

I have also had a look at the Brauniger site, and certainly the IQ Motor that I have, won't let you change altimeter settings once the barograph is recording (ie, once airborne). They claim it is an FAI requirement, so I imagine all other models will have the same constraint. This is a bit of a pain if the regional setting changes while airborne, if you temporarily want to set an airfields QFE for a zone transit.

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