Should I be scared -- C172 over Gross

On Apr 22, 10:16*am, tman inv@lid wrote:
tman wrote:

, and also the day turned out to be +20F hotter than I thought
it would. *I've experienced that heat not only hurts the planes
performance, but the pilots too. *Oh yeah, a slightly gusty xwind too.
Pretty happy I planned on leaving one pax behind.

If you look very closely at the take off performance data of a 172
( which I have) you will find that higher temperature actually
improves performance, for the same air density. Now I know that
contradicts what we get taught in flight school, and while it is
generally true that when temperature is lower the air will be more
dense , the atmosphere is a dyanmic system and pressure and
temperature can vary independantly. So it is possible to have the
same air density , or density altitude at 2 different temperature and
the day with the higher temperature wil give you better performance.
It is related to engine performance and the best explanation I have
got is that at the same density on a higher temperature day, the
pressure will also be higher ( since density = PM/RT where M is
molecular wt, R is gas constant, P and T press and temp), and the
higher pressure provides a greater driving force to suck air into the
engine. If you do the same analysis on the landing distance you see
no such temperature effect because landing distance is not power
related , only lift related.
In the next few days I will get around to providing a link to this
data, but you can easily prove it yourself if you have the Cessna
takeoff distance tables..
Terry
PPL Downunder

terry wrote in news:303fdf2b-7e83-4b08-aaf8-
:

On Apr 22, 10:16*am, tman inv@lid wrote:
tman wrote:

, and also the day turned out to be +20F hotter than I thought
it would. *I've experienced that heat not only hurts the planes
performance, but the pilots too. *Oh yeah, a slightly gusty xwind
too.
Pretty happy I planned on leaving one pax behind.

If you look very closely at the take off performance data of a 172
( which I have) you will find that higher temperature actually
improves performance, for the same air density. Now I know that
contradicts what we get taught in flight school, and while it is
generally true that when temperature is lower the air will be more
dense , the atmosphere is a dyanmic system and pressure and
temperature can vary independantly. So it is possible to have the
same air density , or density altitude at 2 different temperature and
the day with the higher temperature wil give you better performance.
It is related to engine performance and the best explanation I have
got is that at the same density on a higher temperature day, the
pressure will also be higher ( since density = PM/RT where M is
molecular wt, R is gas constant, P and T press and temp), and the
higher pressure provides a greater driving force to suck air into the
engine. If you do the same analysis on the landing distance you see
no such temperature effect because landing distance is not power
related , only lift related.
In the next few days I will get around to providing a link to this
data, but you can easily prove it yourself if you have the Cessna
takeoff distance tables..
Terry

Yeah, you'll get about 1% per 5 deg C on a typical normally aspirated
lightplane engine under those circumstances.

Bertie

On Apr 24, 9:31 am, terry wrote:
On Apr 22, 10:16 am, tman inv@lid wrote: tman wrote:

, and also the day turned out to be +20F hotter than I thought it would. I've experienced that heat not only hurts the planes
performance, but the pilots too. Oh yeah, a slightly gusty xwind too.
Pretty happy I planned on leaving one pax behind.

If you look very closely at the take off performance data of a 172
( which I have) you will find that higher temperature actually
improves performance, for the same air density. Now I know that
contradicts what we get taught in flight school, and while it is
generally true that when temperature is lower the air will be more
dense , the atmosphere is a dyanmic system and pressure and
temperature can vary independantly. So it is possible to have the
same air density , or density altitude at 2 different temperature and
the day with the higher temperature wil give you better performance.
It is related to engine performance and the best explanation I have
got is that at the same density on a higher temperature day, the
pressure will also be higher ( since density = PM/RT where M is
molecular wt, R is gas constant, P and T press and temp), and the
higher pressure provides a greater driving force to suck air into the
engine. If you do the same analysis on the landing distance you see
no such temperature effect because landing distance is not power
related , only lift related.
In the next few days I will get around to providing a link to this
data, but you can easily prove it yourself if you have the Cessna
takeoff distance tables..
Terry
PPL Downunder

You can play with your C172 N weight and balance here
http://home.new.rr.com/trumpetb/alph/wb172N.html

one little nit (?). doesn't the empty weight of an a/c include full
oil, making no need to add it to the equation? I know the "basic empty
weight" of my 172 includes full oil... I don't add the weight of oil (or
unusable fuel)...


george wrote:
On Apr 24, 9:31 am, terry wrote:
On Apr 22, 10:16 am, tman inv@lid wrote: tman wrote:

, and also the day turned out to be +20F hotter than I thought it would. I've experienced that heat not only hurts the planes
performance, but the pilots too. Oh yeah, a slightly gusty xwind too.
Pretty happy I planned on leaving one pax behind.
If you look very closely at the take off performance data of a 172
( which I have) you will find that higher temperature actually
improves performance, for the same air density. Now I know that
contradicts what we get taught in flight school, and while it is
generally true that when temperature is lower the air will be more
dense , the atmosphere is a dyanmic system and pressure and
temperature can vary independantly. So it is possible to have the
same air density , or density altitude at 2 different temperature and
the day with the higher temperature wil give you better performance.
It is related to engine performance and the best explanation I have
got is that at the same density on a higher temperature day, the
pressure will also be higher ( since density = PM/RT where M is
molecular wt, R is gas constant, P and T press and temp), and the
higher pressure provides a greater driving force to suck air into the
engine. If you do the same analysis on the landing distance you see
no such temperature effect because landing distance is not power
related , only lift related.
In the next few days I will get around to providing a link to this
data, but you can easily prove it yourself if you have the Cessna
takeoff distance tables..
Terry
PPL Downunder

You can play with your C172 N weight and balance here
http://home.new.rr.com/trumpetb/alph/wb172N.html

On Apr 24, 9:57*am, george wrote:
On Apr 24, 9:31 am, terry wrote:

You can play with your C172 N weight and balance herehttp://home.new.rr.com/trumpetb/alph/wb172N.html- Hide quoted text -

- Show quoted text -

Thanks for the link George, Did you write this? Its a nice piece of
work , but as another poster mentions, oil should be included in the
MT wt, as should unusable fuel. As you prolly know I wrote my own in
Excel which can be downloaded (along with some other applications) at
http://www.straightandleveldownunder.net/index.html

Mine, I think is more idiot proof ( it had to be , I wrote it
basically for myself) and gives clear error messages if any
parameters are exceeded. It includes oil and unusable fuel in the MT
wt, but you still enter total fuel as that is what you measure when
you dip your tanks.
Terry
PPL Downunder

On Apr 24, 10:49 pm, terry wrote:

Thanks for the link George, Did you write this?

No! I'd like to have though

Its a nice piece of
work , but as another poster mentions, oil should be included in the
MT wt, as should unusable fuel. As you prolly know I wrote my own in
Excel which can be downloaded (along with some other applications) athttp://www.straightandleveldownunder.net/index.html

Mine, I think is more idiot proof ( it had to be , I wrote it
basically for myself) and gives clear error messages if any
parameters are exceeded. It includes oil and unusable fuel in the MT
wt, but you still enter total fuel as that is what you measure when
you dip your tanks.
Terry
PPL Downunder

Thanks Terry.
I found it while looking up Weight and Balance for the same mark of
C172 I flew (ZK-CFD)
But I'm going to link to your one and run the same numbers