Aviation maths for Pro !!

[Paul[_1_]]

I'm trying to find out a formulae regarding the gap between Takeoff
Distances by POH and real-life measures. I did the maths for wind,
temperature, pressure altitude, runway slope, weight, etc. It's quite
detailled and effective...

But...

The only calculation I don't know how to "translate" is the difference, in
feet, between the POH speed and the speed I did during the test.

For example: If my airplane took off at 1050 feet on the initial roll, at 62
knots, how many feet will I need if left the runway at 56 kts ? POH states
it requires only 699 feet at 56kts for the same factors (temp, press, etc)!

Thank you

Paul

[WingFlaps]

On Feb 13, 7:23*am, "Paul" > wrote:
> I'm trying to find out a formulae regarding the gap between Takeoff
> Distances by POH and real-life measures. I did the maths for wind,
> temperature, pressure altitude, runway slope, weight, etc. It's quite
> detailled and effective...
>
> But...
>
> The only calculation I don't know how to "translate" is the difference, in
> feet, between the POH speed and the speed I did during the test.
>
> For example: If my airplane took off at 1050 feet on the initial roll, at 62
> knots, how many feet will I need if left the runway at 56 kts ? POH states
> it requires only 699 feet at 56kts for the same factors (temp, press, etc)!
>

I think most of the POH takeoff figures are not theoretical
calculations but the results of actual tests. As such they are
affected by factors outside aerodynamics -runway surface roughness,
tyre performance and pilot skill being factors in rolling distance. In
other words I don't think a simple equation will give you the "right"
answer. For a first order approximation consider kinetic energy build
up.

Cheers

[terry]

On Feb 13, 5:23*am, "Paul" > wrote:
> I'm trying to find out a formulae regarding the gap between Takeoff
> Distances by POH and real-life measures. I did the maths for wind,
> temperature, pressure altitude, runway slope, weight, etc. It's quite
> detailled and effective...
>
> But...
>
> The only calculation I don't know how to "translate" is the difference, in
> feet, between the POH speed and the speed I did during the test.
>
> For example: If my airplane took off at 1050 feet on the initial roll, at 62
> knots, how many feet will I need if left the runway at 56 kts ? POH states
> it requires only 699 feet at 56kts for the same factors (temp, press, etc)!
>
I think you will struggle to find a simple calculation ( or a
difficult one for that matter) . why dont you just try testing your
takeoff distance at the same speed as the POH reccomends? May I ask
what aircraft you are flying? and what did you find with your
mathematical studies, and did you read my earlier thread on
"Confusion with Cessna take off distance " where I found that after
converting pressure ht and temperature to density altitude that there
was still a temperature effect on the take off distance required. I
would be interested to know if you saw something similar wtih your
data?.

Terry
PPL Downunder

[Bertie the Bunyip]

On 12 Feb, 18:23, "Paul" > wrote:
> I'm trying to find out a formulae regarding the gap between Takeoff
> Distances by POH and real-life measures. I did the maths for wind,
> temperature, pressure altitude, runway slope, weight, etc. It's quite
> detailled and effective...
>
> But...
>
> The only calculation I don't know how to "translate" is the difference, in
> feet, between the POH speed and the speed I did during the test.
>
> For example: If my airplane took off at 1050 feet on the initial roll, at 62
> knots, how many feet will I need if left the runway at 56 kts ? POH states
> it requires only 699 feet at 56kts for the same factors (temp, press, etc)!
>

I've got a couple at home and I'll check for you when I get there, but
like I told you before, it all depends on the approach the engineer
takes and you're not going to get any real precision out of them