Bertie the Bunyip[_25_]
February 19th 08, 07:08 AM
terry > wrote in
:
> On Feb 19, 1:00*pm, Dudley Henriques > wrote:
>> terry wrote:
>> > On Feb 19, 10:02 am, "Bob Gardner" > wrote:
>> >> Back to basics. I have in my hand the POH for a 172Q. In section
>> >> 5, Performance, there is a whole page of data on stall speed vs
>> >> bank angle
> . For
>> >> example, at aeight of 2500 pounds with flaps up, indicated stall
>> >> speed
> is 50
>> >> with wings level, 54 at a 30* bank angle, 59 at a 45* bank angle,
>> >> and 7
> 1 at
>> >> a 60 degree bank angle.
>>
>> > easier to remember a formula
>>
>> > the load increase in a bank by a factor of *1/ cos( AOB)
>>
>> > since lift required is proportional to Vsquared
>>
>> > to maintain level flight the lift must increase in a bank by
>> > *square root of load
>>
>> > thus it follows the *stall speed in a level bank *must increase
>> > over
>
>> > the unbanked stall speed by
>>
>> > Square root ( 1 / cos (AOB) )
>> > which will give the numbers you have quoted from the POH.
>>
>> > At 60 degrees the load is 2g *stall increase by root 2, *after that
>> > the g's just take off. *75 degrees is 3.8g which is the limit of
>> > the average lightie.
>> > and a good reason why the timid types like Msx and me dont like
>> > stretching the evelope too far.
>> > Right Max?
>> > Terry
>> > PPL Downunder
>>
>> I am struck with this irrepressible twitch of unbridled American
>> humor as I envision some poor CFI up here using this explanation to
>> explain things to Mrs average housewife as she attends ground school
>> preparing for the written.
>
> As Lord Kelvin once said ( or something like this ) if you cannot
> explain a thing with numbers, your knowledge is of a meagre and
> unsatisfactory kind . Now I am not suggesting for one minute that your
> knowledge is unsatisfactory Dudley, I am sure you know the physics
> better than me, but up to a point I think there is a lot of truth
> in what Kelvin meant. Whilst I certainly dont advocate quantum
> mechanics or Tucker equations, where you can explain something with
> high school level maths or physics I believe this should be done. .
> There are many things about flying which are extremely difficult to
> fully explain with maths and physics, but banking at constant altitude
> is not one of them.
>
> The poster wants to know what effect banking has on stall speed.
Yes, but his question was phrased in such a way as to require an
explanation from first principles.
The math is incidental and not of a lot of use in flight.
However, the formula for acceleration vs stall speed is to multiply the
stall speed by the sq root of the acceleration. Assuming a constant
altitude is kept, a bank angle of 60 deg wil give 2 G the square root of
which is approximately 1.4. SO an airplane that stalls at 50 will stall
at 70 in a 60 degree bank. about 85 in a 70 (2.9 G) about 120 in an 80
deg bank (almost 6 G) and so on.
A 30 degree bank (about 1.15G) will increase the stall speed by about
1.07.
Call it 1.1 to take in to account the vagueries of aircraft handling..
Bertie
:
> On Feb 19, 1:00*pm, Dudley Henriques > wrote:
>> terry wrote:
>> > On Feb 19, 10:02 am, "Bob Gardner" > wrote:
>> >> Back to basics. I have in my hand the POH for a 172Q. In section
>> >> 5, Performance, there is a whole page of data on stall speed vs
>> >> bank angle
> . For
>> >> example, at aeight of 2500 pounds with flaps up, indicated stall
>> >> speed
> is 50
>> >> with wings level, 54 at a 30* bank angle, 59 at a 45* bank angle,
>> >> and 7
> 1 at
>> >> a 60 degree bank angle.
>>
>> > easier to remember a formula
>>
>> > the load increase in a bank by a factor of *1/ cos( AOB)
>>
>> > since lift required is proportional to Vsquared
>>
>> > to maintain level flight the lift must increase in a bank by
>> > *square root of load
>>
>> > thus it follows the *stall speed in a level bank *must increase
>> > over
>
>> > the unbanked stall speed by
>>
>> > Square root ( 1 / cos (AOB) )
>> > which will give the numbers you have quoted from the POH.
>>
>> > At 60 degrees the load is 2g *stall increase by root 2, *after that
>> > the g's just take off. *75 degrees is 3.8g which is the limit of
>> > the average lightie.
>> > and a good reason why the timid types like Msx and me dont like
>> > stretching the evelope too far.
>> > Right Max?
>> > Terry
>> > PPL Downunder
>>
>> I am struck with this irrepressible twitch of unbridled American
>> humor as I envision some poor CFI up here using this explanation to
>> explain things to Mrs average housewife as she attends ground school
>> preparing for the written.
>
> As Lord Kelvin once said ( or something like this ) if you cannot
> explain a thing with numbers, your knowledge is of a meagre and
> unsatisfactory kind . Now I am not suggesting for one minute that your
> knowledge is unsatisfactory Dudley, I am sure you know the physics
> better than me, but up to a point I think there is a lot of truth
> in what Kelvin meant. Whilst I certainly dont advocate quantum
> mechanics or Tucker equations, where you can explain something with
> high school level maths or physics I believe this should be done. .
> There are many things about flying which are extremely difficult to
> fully explain with maths and physics, but banking at constant altitude
> is not one of them.
>
> The poster wants to know what effect banking has on stall speed.
Yes, but his question was phrased in such a way as to require an
explanation from first principles.
The math is incidental and not of a lot of use in flight.
However, the formula for acceleration vs stall speed is to multiply the
stall speed by the sq root of the acceleration. Assuming a constant
altitude is kept, a bank angle of 60 deg wil give 2 G the square root of
which is approximately 1.4. SO an airplane that stalls at 50 will stall
at 70 in a 60 degree bank. about 85 in a 70 (2.9 G) about 120 in an 80
deg bank (almost 6 G) and so on.
A 30 degree bank (about 1.15G) will increase the stall speed by about
1.07.
Call it 1.1 to take in to account the vagueries of aircraft handling..
Bertie