Balanced field length and Balanced V1

[Driver 170]

I've done some research and the more i read on this subject the more i get confused.

I know the basic definition of a Balanced Field Length; Balanced field means stop and go distances are the same (very basic)

But i just can't picture what an Unbalanced Field length is... does it mean the runway ASDA and TODA aren't equal? ie the clearway and stopway doesn't match up.

And also i'm lost at what Balanced V1 means.

[Driver 170]

Forgot to mention, i'm reading the 737 performance reference handbook

[Rick777]

Ideally your field length will be unbalanced with the accelerate stop distance less that runway length. With a balanced field an engine failure at V1 gives no margin for error.

[Driver 170]

So what are the advantages of using both? Also whats the difference with Balanced V1

Cheers.

[chksix]

I'm interested as well since that part of the book is hardest to understand for a non pilot.
As I understand it you try to balance the field length to maximize TOW...:confused:

[Driver 170]

What i know about FBL is you don't balance it with speeds but its rather the characteristics of the runway ASDA = TODA and they both are equal. Ie the CWY is equal to the SWY.

Yeh its a hard subject to get your mind around. I'm studying the 737 performance reference handbook to help me understand the 737 NG and also find it interesting :)

I'm sure FBL you are at your Max weight for the field length and only one V1 is available.

But i'm unsure at what Balanced V1 means and vice versa?

[Driver 170]

Below i have posted up two Balanced Takeoff Graphs and the description of each, but finding it slightly hard to understand them or get my head around it. This is all self teaching and never had any classroom or experience at this level.

The first Diagram is Balanced V1 and the second is BFL. can someone kindly in simple terms explain the both or give a definition as well.



http://i1022.photobucket.com/albums/af345/filthybeats1/Photo%2005-03-2015%2020%2027%2028.png

http://i1022.photobucket.com/albums/af345/filthybeats1/Photo%2005-03-2015%2020%2027%2032.png

[chksix]

Those two screens are great. Suddenly it clicked in my head what it all means. I wonder if he rephrased the explanations vs the ones in my edition of the PRH?

The top one is assuming you can vary your TOW. The other one is working with a fixed TOW and trying to optimize V1 vs takeoff distance.

A rated pilot better jump in here :}

[Driver 170]

Yeh that would be great if someone could jump in and offer there experience :)

I'm having trouble with something; in the GENERAL description part on the first line it mentions, selection of V1 is dependent on the TOW and on the second bullet point it explains further and this time mention maximum TOW? So is Balanced V1 worked on a given TOW like it says on the first line, or the maximum TOW like it says?

[Skysurfer007]

Don't think to complicated.

Balanced V1:
1. If V1 is to high the aircraft is not able to come to a stop before the end of the runway with an takeoff abort just prior V1.
2. If V1 is to low the aircraft is unable to make the 35/15ft obstacle at the end of the runway when continuing with one engine after V1.

Balanced field length:
The balanced field length is the shortest field length at which a balanced field takeoff can be performed.

From this basic statements you can do all sorts of considerations such as to obtain the maximum takeoff weight for a given runway length or the shortest runway for a given takeoff weight or the minimum thrust for a given weight and runway length etc etc..

Cheers,
Berni

[Driver 170]

Thanks Berni, i've been reading BFL is the characteristics of the runway is where ASDA=TODA? Is that correct? And you don't balance it by moving speeds.

[Driver 170]

So a Balanced V1 would be where ASDR=TODR?

[Driver 170]

I also read this,

Optional unbalancing; Balanced V1 requires the lowest runway length (balanced field length), but if the actual runway is greater than the balanced field length, a range of V1 is available.

I thought a BFL is where ASDA=TODA so how come the runway change the BFL?

[Driver 170]

Oh wait there is a Balanced field the same as Balanced field Length? Thanks