How to tell my instructor to increase glidespeed with headwind?

"Nik" wrote in message
ups.com...
Ok, my instructor did a simulated engine failure in the pattern; winds
were around 20kts in the air and 13kts on the ground. Did everything
perfectly; however after we took off again, he told me to maintain 65
kts next time, and I totally disagreed.
The manual says 65 kts for best glide speed; however that is in calm
air. As a glider person, I know adding about 1/2 the headwind component
will give the greatest distance.
After the flight I pulled up the Glider Flying handbook online and it
says:

"...it is apparent that flying a faster airspeed as the headwind
increases will result in the greatest distance over the
ground. If this is done for the polar curves from many
gliders, a general rule of thumb is found, namely, add
half the headwind component to the best L/D for the
maximum distance."

But even after telling him that he said that doesn't apply to power
planes, also saying that manuals never give best glide, and there has
to be a reason for that.

Do you guys have any ideas on how I can really convince him? Any good
sources?


I found this link very helpful
http://www.auf.asn.au/emergencies/aircraft.html
terry

"T o d d P a t t i s t" wrote in message
...
"mike regish" wrote:
That's wrong, too. Flying at minimum sink will get you the longest time
in
the air-like you'd want if you had a tailwind and needed the distance.
Minimum sink is slower than best glide.

You only fly at min sink for better distance when the
tailwind is infinite. At any slower tailwind speed, you fly
somewhat faster than min sink, but not as fast as best
glide. Generally, if you turn downwind, you will be able to
glide quite far and will have more fields you can reach, so
getting the absolute maximum distance is less important than
picking a good field and setting up a good pattern.

I could think of other reasons to fly minimum sink
1. More time to get the engine restarted
2. If flying over tiger country .. you get to live longer :)
terry

wrote in message
ups.com...

Dave Doe wrote:
In article ,
says...
On Thu, 2 Nov 2006 22:02:09 +1300, Dave Doe wrote in
:

fly at 65kts, and you get the longest time in the air

That is incorrect. Flying at best glide speed will give you the
maximum (no wind) distance over the ground just as Vy (velocity along
the Y axis: best rate of climb) does. Flying at minimum sink speed
will give you the most time before landing just as Vx (velocity along
the X axis: best angle of climb speed) provides the maximum height in
the shortest time (regardless of wind).

If the best glide speed is 65kts in a C172, what is the best min. sink
speed?

According to Kerschner, best glide speed (for distance) will be
around 1.3 Vs and minimum sink speed will be around 1.1 Vs. If the
airplane stalls clean at 50 kt, the minimum sink will be 55 kt and best
glide 65 kt.
But pay attention to the calibrated/indicated airspeed chart in
the POH. Airspeed indications are usually off quite a bit near the
stall.
One could go to altitude and do some gliding at various
stabilized airspeeds and find the one with the lowest rate of descent
on the VSI.

Another rule of thumb is lowest sink speed is 90% of best glide speed. So
for the C172
best glide 65 best sink 58.5
terry

d&tm wrote:
I could think of other reasons to fly minimum sink
1. More time to get the engine restarted
2. If flying over tiger country .. you get to live longer :)

Flying over water, but so far away from land or any visible ships that
where you fly to will not really made a difference... What you need is
more time in the air to broadcast a Mayday for as long as possible...
And possibly more time to get your survival gear ready...

On Thu, 02 Nov 2006 19:40:16 -0800, Peter Duniho wrote:

You seem to be disagreeing with something else, and not something I
actually wrote.

Okay. I'd missed that you qualified it with "during the flight".

- Andrew

On 3 Nov 2006 10:45:01 -0600, T o d d P a t t i s t
wrote in
:


You only fly at min sink for better distance when the
tailwind is infinite. At any slower tailwind speed, you fly
somewhat faster than min sink, but not as fast as best
glide.

http://www.glidingmagazine.com/CommD...d=178&RootId=0
McCready theory usually uses the formula

Sink rate = a x V^2 - b x V + c

where a, b and c are the parameters to fit. This formula has the
advantage that it makes the math much nicer, but the disadvantage that
it is just plain wrong, in the sense that it says that sink rate
increases like V^2 at high speeds, which it doesn't - it increases
like V^3, which is much faster!

In article ,
says...

wrote in message
ups.com...

Dave Doe wrote:
In article ,
says...
On Thu, 2 Nov 2006 22:02:09 +1300, Dave Doe wrote in
:

fly at 65kts, and you get the longest time in the air

That is incorrect. Flying at best glide speed will give you the
maximum (no wind) distance over the ground just as Vy (velocity along
the Y axis: best rate of climb) does. Flying at minimum sink speed
will give you the most time before landing just as Vx (velocity along
the X axis: best angle of climb speed) provides the maximum height in
the shortest time (regardless of wind).

If the best glide speed is 65kts in a C172, what is the best min. sink
speed?

According to Kerschner, best glide speed (for distance) will be
around 1.3 Vs and minimum sink speed will be around 1.1 Vs. If the
airplane stalls clean at 50 kt, the minimum sink will be 55 kt and best
glide 65 kt.
But pay attention to the calibrated/indicated airspeed chart in
the POH. Airspeed indications are usually off quite a bit near the
stall.
One could go to altitude and do some gliding at various
stabilized airspeeds and find the one with the lowest rate of descent
on the VSI.

Another rule of thumb is lowest sink speed is 90% of best glide speed. So
for the C172
best glide 65 best sink 58.5
terry

Thanks guys.

--
Duncan