Settle a bet: Mach speeds

"Al Gerharter" wrote in message ws.com...
1083 fps @ 59F, Sea Level, hypothetically dry atmosphere. STP, Standard
Temperature & Pressure. In std water, about 4800 fps. Al

SNIP
For quick and dirty (in one's head) cruise calculations I always used
1.0 Mach = 600 kts. (It's closer to 610 at -57F) but that let me, for
example, say .8M was 8 miles a minute. On the deck, about 670 (11
m/min). That and using fuel flow per minute (3000pph - 50ppm) gave me
rough figures. Of course, if things looked tight, then I used the
whiz-wheel. BTW, on the deck 760 mph is close to .1M (STP), so when
your car is showing 76 mph, you're buzzing along at about .1M. (For
interstate travel, 75 mph is 12.5 miles in 10 minutes . . . we just
completed about 6000 miles of driving where I used this sort of mental
T=D/R to predict ETAs thus boggling my better half. Same sort of calcs
can be used ina light plane such as C152 . . . 6gph = 1 gal in 10 min,
90KTS = 1.5 nm/min; 120(tailwind)=2 nm/min. As above, use the
calculator if things look tight. (If they do you've screwed up.)
Walt BJ

Walt wrote:
BTW, on the deck 760 mph is close to .1M (STP), so when
your car is showing 76 mph, you're buzzing along at about .1M. (For
interstate travel, 75 mph is 12.5 miles in 10 minutes . . . we just
completed about 6000 miles of driving where I used this sort of mental
T=D/R to predict ETAs thus boggling my better half. Same sort of calcs
can be used ina light plane such as C152 . . . 6gph = 1 gal in 10 min,
90KTS = 1.5 nm/min; 120(tailwind)=2 nm/min. As above, use the
calculator if things look tight. (If they do you've screwed up.)

Glad I am not the only one running continuous ETAS while cruising down the
Interstate :-) Drift gets to be a bitch though!
Habit! Ingrained by instructors who are really old farts now!

Rick Clark
MFE

(OXMORON1) wrote:
Walt wrote:

BTW, on the deck 760 mph is close to .1M (STP), so when
your car is showing 76 mph, you're buzzing along at about .1M. (For
interstate travel, 75 mph is 12.5 miles in 10 minutes . . . we just
completed about 6000 miles of driving where I used this sort of mental
T=D/R to predict ETAs thus boggling my better half. Same sort of calcs
can be used ina light plane such as C152 . . . 6gph = 1 gal in 10 min,
90KTS = 1.5 nm/min; 120(tailwind)=2 nm/min. As above, use the
calculator if things look tight. (If they do you've screwed up.)

Glad I am not the only one running continuous ETAS while cruising down the
Interstate :-) Drift gets to be a bitch though!
Habit! Ingrained by instructors who are really old farts now!

Speaking of winds and such, as an "old fart" flight instructor myself
(it's all downhill after 40, right?) here is a little homemade
question that I find many aviators both military and civil routinely
get wrong:

If you takeoff from airport "A" and fly 200 miles into a 20 mph
headwind to airport "B" at 100 mph (TAS) and then turn around and
fly back to airport "B" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Yea or nay?

(Correct answer gets a cigar and large bucket of his favorite
drink....)

Mike Marron wrote:

Speaking of winds and such, as an "old fart" flight instructor myself
(it's all downhill after 40, right?) here is a little homemade
question that I find many aviators both military and civil routinely
get wrong:

If you takeoff from airport "A" and fly 200 miles into a 20 mph
headwind to airport "B" at 100 mph (TAS) and then turn around and
fly back to airport "B" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Yea or nay?

(Correct answer gets a cigar and large bucket of his favorite
drink....)


Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

In other words, if you takeoff from airport "A" and fly 200 miles into
a 20 mph headwind to airport "B" at 100 mph (TAS) and then turn around
and fly back to airport "A" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Mike came back with:
Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

Glad you made that correction, I was still orbiting "B"

Rick

(OXMORON1) wrote:

Mike came back with:
Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

Glad you made that correction, I was still orbiting "B"

Heh. But now that you've flown back to "A" and landed, in order to
get the cigar and bucket of your fave drink you have to hazard an
answer to the question.

Rick

No, you are exposed to the headwind for a longer time. Any wind from any
direction will increase your round trip time. Al (a very old flight
instructor)

"Mike Marron" wrote in message
...
Mike Marron wrote:

Speaking of winds and such, as an "old fart" flight instructor myself
(it's all downhill after 40, right?) here is a little homemade
question that I find many aviators both military and civil routinely
get wrong:

If you takeoff from airport "A" and fly 200 miles into a 20 mph
headwind to airport "B" at 100 mph (TAS) and then turn around and
fly back to airport "B" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Yea or nay?

(Correct answer gets a cigar and large bucket of his favorite
drink....)


Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

In other words, if you takeoff from airport "A" and fly 200 miles into
a 20 mph headwind to airport "B" at 100 mph (TAS) and then turn around
and fly back to airport "A" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Mike Marron wrote:
Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

In other words, if you takeoff from airport "A" and fly 200 miles into
a 20 mph headwind to airport "B" at 100 mph (TAS) and then turn around
and fly back to airport "A" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Okay, I'll bite.

Looks like the no-wind solution is 4 hours, the headwind/tailwind
solution is 4.17 hours.

Just in case I win, I prefer Lagavulin 16. I'll skip the seegar.


Jeff

"Jeff Crowell" wrote:
Mike Marron wrote:

Oops!

The above question should read, "...turn around and fly back to
airport "A" now with a 20 mph tailwind at the same TAS."

In other words, if you takeoff from airport "A" and fly 200 miles into
a 20 mph headwind to airport "B" at 100 mph (TAS) and then turn around
and fly back to airport "A" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Okay, I'll bite.

Looks like the no-wind solution is 4 hours, the headwind/tailwind
solution is 4.17 hours.

Just in case I win, I prefer Lagavulin 16. I'll skip the seegar.

Al Gerharter was the first to answer correctly, but disqualified
himself by admitting that he's an old hand instructor so it looks
like you won indeed. Congratulations! A large bucket of Lagavulin
16 is on the way...

In other words, if you takeoff from airport "A" and fly 200 miles into
a 20 mph headwind to airport "B" at 100 mph (TAS) and then turn around
and fly back to airport "A" now with a 20 mph tailwind at the same TAS
will you complete the roundtrip flight in the same time as if you had
made the flight in no-wind conditions?

Okay, I'll bite.

Looks like the no-wind solution is 4 hours, the headwind/tailwind
solution is 4.17 hours.


Because you spend more time going against the wind and fighting it, than you
spend with the wind and benefitting from it, so thats why you lose time




Ron
Tanker 65, C-54E (DC-4)
Silver City Tanker Base