need for dial altimeter?

Transponders give Flight Level (assuming they are working properly), so
will give the altitude ATC are intereted in. That's how they know what
FL you are at when not talking to them.

At 12:52 26 September 2008, John Smith wrote:
JJ Sinclair wrote:

On the last home-built I regestered, the federallies required a
mechanical airspeed, altimeter and compass........nothing else. But I
have observed that the panel I am now flying has altitude displayed
all over the place, in two GPS's, in the SN-10 and in the
transponder.
The large altimeter takes up a lot of space and provides the least
important info..........................we can all estimate our
altitude for landing, can't we? The rest of the time its just nice to
know info.

Except when you're flying in the among controlled airspace, where
neither GPS altitude (geometric) nor transponder altitude (QNE) do you
any good. Loggers usually can give you QNH altitude, provided you set
them correctly and your battery isn't flat.

All kinds of good ideas. You may want to consider installing an EFIS.
The Dynon D10A fits in an 80mm hole. You get the full six pack plus!
It has an altimeter, airspeed, vertical speed, DG, T&B, attitude, OAT,
true airspeed, compass, HSI, and angle of attack. If you have a little
more panel room, you could consider an MGL Engima EFIS. It has a
larger screen and all of the above plus GPS and a moving map display.
The nice thing about the MGL is that it can display 9 different
screens - that you can create and edit yourself. Now you can create
the moving map display with airspeed and angle of attack on the left,
altimeter and vertical speed on the right, and compass at the bottom.
If you're doing a wave flight and get caught in clouds or want to file
IFR, select another screen that has the six pack in the upper left, an
HSI in the upper right, and a moving map display on the lower half.

Both units supply altitude encoding for a transponder. Also they
weight less than the instruments they replace. The Dynon has the
option of installing an internal backup battery that will run the
system for two hours. The MGL supports an external backup battery. A
small 2AH battery would run it for two hours.

If you want to take a look, the link to Dynon is
http://dynonavionics.com/docs/D10A_intro.html. The link to MGL is
http://www.mglavionics.com/html/enigma.html.

Charlie