Yeah I heard rumours about the butterfly not actually using the internals. Thanks Mike
Scott On 23 May 2014, at 2:07 pm, Mike Borgelt <[email protected]> wrote: > At 12:35 PM 23/05/2014, you wrote: >> The newer generation Varios still use TE but have inertial sensing as an >> adjunct to TE to assist with gust filtering. >> >> Regards, >> John Orton >> Mob: 0429357439 >> >> >> The inertial versions do (ie. ones that don’t use a TE tube). >> One other valuable feature I think is a good Artificial Horizon. >> >> I agree though that I would rather use external device (I use XCSoar) for >> glide computer (final glide, navigation etc). >> >> Scott >> > > > You don't need a TE tube to do a total energy vario based on pressure > measurement but there are many problems introduced by this which is why most > varios that offer this also can use a TE probe. The main problems are that > you are taking the difference between two large signals and if they don't > arrive at the vario at the same time you get large transient false > indications. The other problem is that a pitot and static source on a glider > are far more sensitive to yaw and pitch changes than is a good TE probe. You > may as well just use the TE probe. > > The so called "inertial" varios no doubt have the 3 axis accelerometer/gyros > and magnetometer built in (same kind of thing as in your iPad and maybe even > the same device, they are only a few dollars) but whether or not anything > useful is done with them is another matter. They may be there for advertising > purposes. I was advised to put them in the B600/B800 and advertise that but > not do anything with the data. If you buy a vario with inertial sensors ask > what exactly is done. It is a good bet that you will get some figurative arm > waving and talk of "Kalman Filters" without an actual good explanation. > > It is fairly easy to build a variometer (not TE compensated) using the > inertial techniques but a total energy variometer is far more difficult. Or > at least one that is a *good* vario with low zero point drift, like all > modern pressure transducer varios. The MEMS (Micro Electro Mechanical > Systems) accelerometers are pretty good but the gyros are fairly horrible. > They look good when you sit them on the bench and integrate the output to get > attitude (they measure *rate* of roll, pitch and yaw you need to integrate > these to get attitude changes from the start attitude) but are terrible when > moved around due to something called cross axis coupling and output noise > (no, the noise doesn't average out to zero). Been there, done that. > > Inertial measurement units that will work are still quite expensive, of the > order of USD10,000 for the bare sensor and even then by the time you do all > the reference frame transforms and put it in a dynamic flight vehicle (read > glider) you'll probably find the error budget has got out of hand. > > A human pilot filters out horizontal gusts by "seat of the pants" i.e. the > vario is now showing lift but did I feel the vertical acceleration? The > problem is that sometimes the onset of lift is very gentle and your push or > pull on the stick can mask it easily. Sure it is simple to use an > accelerometer to detect vertical acceleration but how do you remove the pilot > inputs on the stick? Removing them is what total energy varios are about but > by measuring the airspeed you make the vario respond very well to small rapid > changes in airspeed caused by horizontal gusts as well as small rapid changes > in vertical motion of the air. This makes the vario more difficult and tiring > to interpret. > > Anyway, our upcoming Dynamis system solves all these problems and can be > added to B600 or B800 variometer systems. > > Mike > > > > Borgelt Instruments - design & manufacture of quality soaring instrumentation > since 1978 > www.borgeltinstruments.com > tel: 07 4635 5784 overseas: int+61-7-4635 5784 > mob: 042835 5784 : int+61-42835 5784 > P O Box 4607, Toowoomba East, QLD 4350, Australia > > _______________________________________________ > Aus-soaring mailing list > [email protected] > To check or change subscription details, visit: > http://lists.internode.on.net/mailman/listinfo/aus-soaring
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