Wherewhendid dual speed on ias come from

Steven P. McNicoll
Steven gave a wonderful presentation as to the conflict of statute
and nautical miles to be used in the U.S. during the 1950s to 70s. What he
failed to give us who the genius was to come up with both sets of numbers on
our airspeed indicators.

The main push for a KNOT measure of aircraft speed came from the use of DME
in military aircraft which was always slant range to a
military VOR known as a TACAN."

It may be of interest that the use of Distance Measuring Equipment
or DME was derived during the last few months of WWII from a radar set known
as the APQ-23. The -23 was able to give an odomenter like read-out as to
the exact slant range distance from the bomb release point to planned impact
point. The trigonometry to do this was electronically done by using taps
taken from wire wound resistors. So difficult to do that there were only
six APQ-23s in the Pacific when the war ended. Getting both statudte and
nautical distances would have more than doubled the complexity of the -23 .
Hence the conflict between AOPA and the military in Steven's email.

As a corporal, I had the APQ-23 installed on my Supersonic Trainer on Tinian
to simulate flights in the vicinity of Nagasaki
for radar bombardment practice. The Nagasaki chart I used and
the manual to the simulator are on my web site. The manual displays the
equipment and I have written explanations of the pictures.
www.whittsflying.com
On the home page click on the sixth blue line down: Gene Whitt's WWII.
Page 8.935 is the WWII aeronautical chart can be expanded and moved. Go to
right side.
Page 8.935 is annotated pictorial Supersonic trainer manual.

The APQ-23 was standard equipment in the post-war B-47 jet bomber.

Just a couple of comments on the nautical vs statute miles thing. I
hope this hasn't been covered. I like nautical miles becuause you can
use your thumb to index finger to get a 30 nautical mile distance on
any longitude line (60 if you are using WAC's) and then use that to
measure distances elsewhere on the map. No need for a ruler.

The other thing is my Husky has as it's primary markings on the
airspeed indicator in statute miles. Now it was built in 1996. At first
I said "what the heck?". But typical cruising altitudes around Colorado
flatlands are 6-8000'. (Not bad altitudes elsewhere either). And it
just so happens that statute miles indicated is pretty close to Knots
True at these altitudes! Shazaam. (I've always been dumbfounded by the
number of students that have no concept of knots true. Its what matters
if you are actually trying to GET somewhere!).

Anyway, just thought I'd share.

"Gene Whitt" wrote in message
et...

The main push for a KNOT measure of aircraft speed came from the use of
DME in military aircraft which was always slant range to a
military VOR known as a TACAN."


TACAN development began in 1947, the military switched to knots and nautical
miles in 1946.

(I've always been dumbfounded by the
number of students that have no concept of knots true. Its what matters
if you are actually trying to GET somewhere!).

No, isn't that "knots made good"? After all, wind is an issue. Moreso
for sailing, where the currents and tacking also matter (but I'm not a
sailor so I know not of what I speak, which has never stopped me before!)

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Yes, usually called Groundspeed now. This is what the GPS gives you.
Still Knots True is what gets you there, NOT Knots Indicated. Of course
you have to factor in the headwind component.

Of course the only difference between Knots True and Groundspeed (in
knots) is the headwind/tailwind component.

"Steven P. McNicoll" wrote:

"Gene Whitt" wrote in message
et...

The main push for a KNOT measure of aircraft speed came from the use of
DME in military aircraft which was always slant range to a
military VOR known as a TACAN."


TACAN development began in 1947, the military switched to knots and nautical
miles in 1946.

When did the airlines in the U.S. switch to knots?

Gene Whitt wrote:

The main push for a KNOT measure of aircraft speed came from the use of DME
in military aircraft which was always slant range to a
military VOR known as a TACAN."


Picking at nits: The azimuth portion of a TACAN facility is not a military VOR;
rather it is a somewhat different method of providing bearing and operates at
UHF frequencies.

There was quite a contest between TACAN and VOR/DME for the military. The Air
Force was willing to go with VOR/DME. The Navy placed both a VOR/DME and a
TACAN aboard a ship and demonstrated that the TACAN would operate around the
superstructure of a ship with far lass degradation than the VOR portion of a
VOR/DME. Thus, for that reason the military went with TACAN.

So, we ended up with all these duplicate civil facilities (VORTACs) to satisfy a
Navy requirement at sea.

The main push for a KNOT measure of aircraft speed came from the use of
DME in military aircraft........

Not exactly. Naval aircraft had used knots long before that.


TACAN development began in 1947, the military switched to knots and nautical
miles in 1946.

No, the *Air Force* switched to knots. See above.

vince norris