747-8 Test of Aborted Takeoff

[jollygreen07]

A4s (and other 18-wheeler drivers),

Is there any special braking technique for the MGW V1 Abort, or is it "mash on brakes, let anti skid do its magic, and NWS/Rudder/modulate brakes as needed to maintain centerline" sort of deal.

I've done a practice no-beta (no reverse or ground range pitch) abort in the Hummer, and it took damn near 5000 feet to stop from 15 kts short of V1, but I was going easy on brakes to not pop a tire.

Depends on the factors involved. In a hot, high, heavy scenario. I'm getting on the brakes. Low PA, temp, and high gross wt? As a good 2P my answer is what the boldface says "Brakes-As Required" but if i'm 7K' down a 13k' runway with the reversers roarin' I might try to save the brakes if I can. It's very situationally dependent.

 

[jollygreen07]

I know you just said your stopping distance doesn't account for thrust reverser usage but how much would you guestimate it cuts down on your stopping distance?

Because I'm bored on watch, I decided to look up exactly what the answer to that is. Assuming a standard day @ sea level @ MGTOW, no wind, no slope:

Non RVS CFL: 7600'
2 ENG RVS CFL: 7500'

We don't have data for 4 RVS but chart is pretty linear, so would come out to about 7400'.

So, long story short, not a whole lot of difference as per the book. Seat of the pants feeling, though? They add quite a bit. They are more efficient at high speeds where brakes are less efficent, so the quicker you pop them the more effect they have.

 

[81montedriver]

Because I'm bored on watch, I decided to look up exactly what the answer to that is. Assuming a standard day @ sea level @ MGTOW, no wind, no slope:

Non RVS CFL: 7600'
2 ENG RVS CFL: 7500'

We don't have data for 4 RVS but chart is pretty linear, so would come out to about 7400'.

So, long story short, not a whole lot of difference as per the book. Seat of the pants feeling, though? They add quite a bit. They are more efficient at high speeds where brakes are less efficent, so the quicker you pop them the more effect they have.

No shit. I kinda figured your turbofans might have a little more power in reverse than our props. Our figures tell us the same thing, that landing distance with max reverse vs no reverse only cuts down our landing roll by 200 feet.

However when you throw the power levers in max reverse at say 90 kts, you will definately be thrown forward in your seat.

 

[HAL Pilot]

A4s (and other 18-wheeler drivers),

Is there any special braking technique for the MGW V1 Abort, or is it "mash on brakes, let anti skid do its magic, and NWS/Rudder/modulate brakes as needed to maintain centerline" sort of deal.

That, ensure spoilers are deployed and full reverse.

 

[HAL Pilot]

Because I'm bored on watch, I decided to look up exactly what the answer to that is. Assuming a standard day @ sea level @ MGTOW, no wind, no slope:

Non RVS CFL: 7600'
2 ENG RVS CFL: 7500'

We don't have data for 4 RVS but chart is pretty linear, so would come out to about 7400'.

So, long story short, not a whole lot of difference as per the book. Seat of the pants feeling, though? They add quite a bit. They are more efficient at high speeds where brakes are less efficent, so the quicker you pop them the more effect they have.

I don't have the charts with me but in the 767 gouge is add another 50% to the length need for no reverse, spoilers or antiiskid (any one inop).

 

[jollygreen07]

No shit. I kinda figured your turbofans might have a little more power in reverse than our props. Our figures tell us the same thing, that landing distance with max reverse vs no reverse only cuts down our landing roll by 200 feet.

However when you throw the power levers in max reverse at say 90 kts, you will definately be thrown forward in your seat.

Hmm.. Well, our MGTOW is 340K. So our engines are putting out a shit load of thrust, they just have to move a heavier beast!

If you want to talk about landing distance, however. Adding the TRs makes quite a difference. Running normal data we still don't account for them.

 

[jollygreen07]

I don't have the charts with me but in the 767 gouge is add another 50% to the length need for no reverse, spoilers or antiiskid (any one inop).

I've often wondered what the differences between the 767 and the 707 were WRT handling characteristics. The two frames appear to be the most similar in the size/weight department off the Boeing line. I assume you guys take into account TRs in your CFL/landing distance calculations?

 

[HAL Pilot]

I've often wondered what the differences between the 767 and the 707 were WRT handling characteristics. The two frames appear to be the most similar in the size/weight department off the Boeing line. I assume you guys take into account TRs in your CFL/landing distance calculations?

No. Landing distance are calculated with spoilers, no reverse and max manual braking. That's why the 50% thing is a gouge figure, but we'd never use it to land on a shorter runway. Mostly it gives us an idea of where to plan our turn off, how's LAHSO going to affect us, etc.

Further, our performance charts all figure out a distance based on a landing weight. Missing spoilers, anti-skid or T/Rs add weight penalties and increase the calculated landing weight (for instance, manual spoilers increases our calculated landing weight by 35K). Increased landing weight increases needed runway length. There is no actual direct correlation between missing items and runway length.