Can Anyone Figure This Out??

[uwochris]

Hey guys,

I have 2 questions from an ATPL workbook I am doing now, and I can't quite figure out how they got the correct answers.

1. A/C empty weight: 7800 lbs.
Weight of pilots and their equipment: 380 lbs
MCTOW: 12,200 lbs.
Fuel in the tanks: 270 gal at 6.4 lbs/gal (270*6.4= 1728lbs).
MZFW: 10,400 lbs.

Question: What is the max payload for the a/c?

Options: 2350 lbs, 2292 lbs, 2672 lbs, 2220 lbs.

I get 2292 lbs, but the correct answer is 2220 lbs. I do not know how they got it. This is how I calc payload (MTOW- Empty weight- weight of pilots/crew- weight of fuel). The 2 equations given to calc payload are MTOW-(Fuel + BOW) or MZFW- BOW. When I use either equation I still dont get the right answer.


2. Which of the following factors causes the speed V1 to increase:
a) an increase in weight.
b) reverse thrust capability.
c) snow/slush on the runway.
d) an increase in the tailwind component.

The correct answer is a). I do not quite understand why this would cause the speed to increase (I can see how the runway used for t/o will be longer and how the required distance to stop would be increased). Also, why wouldn't slush/snow on the runway cause V1 speed to increase?

Thanks for all feedback,

Chris.

 

[uwochris]

Well, I figured out the answer to #1, but I still need some help with #2!

 

[eggman76]

Hey guys,

I have 2 questions from an ATPL workbook I am doing now, and I can't quite figure out how they got the correct answers.

1. A/C empty weight: 7800 lbs.
Weight of pilots and their equipment: 380 lbs
MCTOW: 12,200 lbs.
Fuel in the tanks: 270 gal at 6.4 lbs/gal (270*6.4= 1728lbs).
MZFW: 10,400 lbs.

Question: What is the max payload for the a/c?

Options: 2350 lbs, 2292 lbs, 2672 lbs, 2220 lbs.

I get 2292 lbs, but the correct answer is 2220 lbs. I do not know how they got it. This is how I calc payload (MTOW- Empty weight- weight of pilots/crew- weight of fuel). The 2 equations given to calc payload are MTOW-(Fuel + BOW) or MZFW- BOW. When I use either equation I still dont get the right answer.


2. Which of the following factors causes the speed V1 to increase:
a) an increase in weight.
b) reverse thrust capability.
c) snow/slush on the runway.
d) an increase in the tailwind component.

The correct answer is a). I do not quite understand why this would cause the speed to increase (I can see how the runway used for t/o will be longer and how the required distance to stop would be increased). Also, why wouldn't slush/snow on the runway cause V1 speed to increase?

Thanks for all feedback,

Chris.

My uneducated guesses.

1. The maximum payload in any config would be
MZFW - AC empty weight - Crew = 2220

Kind of a trick question, but this would be the max payload ever allowed onboard.


2. Isn't v1 related to stall speed and stall speed increased by weight? I don't know about slush part.

 

[banned username 2]

Fuel in the tanks: 270 gal at 6.4 lbs/gal (270*6.4= 1728lbs).

What kind of common fuel weighs 6.4 lbs/gal? AvGas is 6.0 lbs/gal and Jet-A is roughly 6.67 lbs./gal

 

[uwochris]

Falc,

It applied to Jet A1. Maybe the weight of the fuel was different because of the temp? 6.4 was the quoted weight though.

Chris.

 

[hawg2hawk]

First, let me say that whoever came up with the idea to use v speeds instead of plain english should be kicked repeatedly in the junk.

The FARs define v1 as "decision speed". Why they choose to call v1 decision speed instead of CEFS (critical engine failure speed), who knows. It's all very confusing, which I suspect is the FAA's intent. But I digress.

According to the FAR definition, at V1 the pilot can either continue the takeoff or abort in the remaining runway. Looking at just the "go" part of the equation, a heavier aircraft will have to be going faster to sucessfully continue the takeoff, so a) is correct.

Slush doesn't have as significant an effect on the "go" part of the equation as it does on the "stop" part due to increased stopping distance.

 

[NoahWerka]

#1: use BOW(Basic Operating Weight)= empty weight + crew.
7800( empty weight)+380(crew)=8180
MZFW =10,400
10,400-8180=2220

#2: V1= decision speed, or, go, no go, (continue and fly, or abort takeoff and still stop on the runway)
Remember: Lift=Weight
At 0 degrees (takeoff attitude) angle of attack, a heavier aircraft has to go faster to reach flying speed than a light one...therefore V1 is increased, as is V2 and Vr.
Contaminated(slush, snow,etc.) runways do not increase V1 because V1 is only related to weight. They increase the length of runway required because the friction(drag) created by the contaminates causes slower acceleration(longer to reach V1).

 

[mynameisjim]

2. Which of the following factors causes the speed V1 to increase:
a) an increase in weight.
b) reverse thrust capability.
c) snow/slush on the runway.
d) an increase in the tailwind component.

a) yes - while a heavier airplane needs a longer runway, it will have a higher V1 speed
b) no - reverse thrust is not used to calculate V1 and accelerate stop distances
c) no - snow/slush is a contaminate which lowers V1
d) no - wind does not affect takeoff speeds

 

[TransMach]

v1

Chris,

A is the "preferred" answer, but it isn't correct. V1 is an engineered speed. It is selected by the engineers to make accelerate-stop and accelerate-go roughly equal hence the term "balanced field". V1 can never be lower than VMCG ( you need to be able to control the airplane on the ground ) and VR can never be less than VMCA ( you need to control the airplane in flight ). The higher the V1 speed is, the longer the accelerate-stop distance, conversely, the higher the V1 speed is the shorter the accelerate-go distance.

Since it's a speed "picked" by engineers to make accelerate-stop and accelerate-go equal, the possible answers offered do not include a truly correct selection.

TransMach

 

[mynameisjim]

What do you mean by "picked"? I would prefer the term "calulated". Using the A320 as an example (its what I'm familiar with) the takeoff data cards are on pages that go by 5,000 pounds each. V1 increases as speed increases. That is all that is taken into account as far as the pilot is concerned. (as long as nothing is MEL'd)

 

[hawg2hawk]

http://clem.mscd.edu/~christib/wprof/fecourse/121perf.htm

d) no - wind does not affect takeoff speeds

Not directly, but it does affect critical field length, which affects V1.

 

[Weasil]

Chris,

A is the "preferred" answer, but it isn't correct. V1 is an engineered speed. It is selected by the engineers to make accelerate-stop and accelerate-go roughly equal hence the term "balanced field". V1 can never be lower than VMCG ( you need to be able to control the airplane on the ground ) and VR can never be less than VMCA ( you need to control the airplane in flight ). The higher the V1 speed is, the longer the accelerate-stop distance, conversely, the higher the V1 speed is the shorter the accelerate-go distance.

Since it's a speed "picked" by engineers to make accelerate-stop and accelerate-go equal, the possible answers offered do not include a truly correct selection.

TransMach

TM, not always true. V1 is not necessarily going to give you a "balanced field" A balanced field is desirable if runway length or surface condition are an issue. We regularly use speeds of V1/Vr ration equal to one giving better "go" performance than "stop" performance. This is because most of the runways that we use are almost twice as long as necessary in the event of a rejected take off.

If you want a balanced field you calculate a lower V1 speed than Vr. But you don't always have to use a balanced field. You just have to have enough runway/stopway etc.. in order to meet the longer of the "go" or "stop" distances. Whichever is longer.

As for the original question. a) is clearly the answer they were looking for as stated in previous posts.

An increase in weight results in an increase in Vr (usually calculated as as factor of Vs). If you increase Vr but do not increase V1 and an engine quits at V1 you now have more speed to gain before reaching Vr - thus increasing distance required. By increasing V1 you decrease the accelerate- go distance by reducing the amount of acceleration required to go from V1 to Vr and still make it to V2 by 35' at the end of the rwy.