Okay, who watched the two hour Mythbusters special last night? 

I'm just curious how you restrain a 747 at full thrust...I guess the flight crew that did the engine runs was standing on the brakes the whole time?

I know that there are some jets (and I don't know that the 747 is one of them   ) where you would have to tie the aircraft to something on the ground when it's at full power, otherwise it will move forward, tires screeching...  

Set the Parking brakes.........................................

Quoting KELPkid (Thread starter): I'm just curious how you restrain a 747 at full thrust

Paperwork. It can stop ANYthing.   

2H4

Quoting KELPkid (Thread starter):

The procedure we always followed with 747's (and 767's) was to only run a single engine up to take off power at a time. The parking brake was set and all the landing gear chocked. If an outboard engine was run up to take off power, you might add a little power to the opposite outboard engine to try and balance things up. Nonetheless, whenever any engine was run up to take off power, you would get appreciable swinging and scrubbing on the nose-gear tyres.

Regards, JetMech

Quoting JetMech (Reply 3): The procedure we always followed with 747's (and 767's) was to only run a single engine up to take off power at a time. The parking brake was set and all the landing gear chocked. If an outboard engine was run up to take off power, you might add a little power to the opposite outboard engine to try and balance things up. Nonetheless, whenever any engine was run up to take off power, you would get appreciable swinging and scrubbing on the nose-gear tyres. Regards, JetMech

Ah, makes sense.

Well, last night on TV, the Mythbusters destroyed both a Lincoln Town Car (painted up as a taxi) and a School Bus by pulling both of them behind one of Kalitta Air's 747's as it was at full takeoff thrust on all 4 engines... Rather spectacular seeing a 20,000 lb. school bus get blown into the air and then flipped over, I must say  

Plus they appeared to only have the outboard engines on at anything more than idle.

Mark

Quoting Mark5388916 (Reply 5): Plus they appeared to only have the outboard engines on at anything more than idle. Mark

How do you get at that? It looked like the grass was getting blown back equally behind all the engines...

When that much air is moved at that velocity, you're not going to notice much difference if the power settings are different.

Quoting KELPkid (Reply 4): and a School Bus

Who was the manufacturer?

Quoting LASOctoberB6 (Reply 8): Who was the manufacturer?

Not that I know my school buses, but the chassis was a '68-'72 Chevy...couldn't tell you who made the body, except that it wasn't a Bluebird  

I've run a classic at max TO, all 4 engines, before for a leading edge overheat issue (basically grasping at straws, but that's another thread). Since this was a cargo aircraft, we decided that we needed the normal ballast fuel (30K in the center) and we went with about 200K in the wings. Set the brakes and made all kinds of noise for 5 minutes. That much weight, the aircraft didn't even bounce around too bad.

Hi KELPkid, Buzz here. I'll second the motion (or lack of it) that Fr8Mech had. I don't run the 747 series so I won't speculate on those.
About 10 or 12 years ago UAL made that Jet Blast educational video with a scrapped out work truck dragged on a cable behind a 767-300 at takeoff power... truck tumbles into San Francisco Bay. Something similar happened one night previous to that, a DC-10 vs. Airport Maint. Toyota pickup truck. But the guy had to swim back.

Our Jet Run Handbooks (JRH... the taxi-run mechanic's book of common prayer) specify a fuel load on the Boeing airplanes to keep the skid marks from occurring. For a 737-300 it's about 20K lbs, a 757 gets more than 24K lbs - assuming one engine at takeoff power. With both wings full of fuel (737) the airplane is fairly steady. A 757 bounces with some force, it's hard to write legibly (light turbulence?) due to all the air going under the tail. But it still stays in one spot.

Fi-Fi the WonderJet (A320) has no minimum fuel load, we have to get a willing individual to chock the main gear to keep from moving. I've noticed that even with the green system pedals held down sometimes she still squirms forward slowly (before we had the chocks policy).

I have valuable off-road experience with a 737 during a high power run... and less than 7K lbs of fuel. #1 engine pushed me off the side of the taxiway. I keep a picture or two as an attention getter when I teach people to taxi. (yes, it's on A.net) Nothing like knowing what -not- to do. (grin) I got to type up a lesson on the topic, no real damage to the airplane... had it flying 3 hours later.

I guess if there's a tailhook the proper thing to do is to hook onto a pad-eye on the deck (or in the concrete). One of my flying buddies (F-102's) said that squadron policy was that when the thrust lever went forward, the brakes are off (you can't hold it).

Quoting FADECFAULT (Reply 1): Set the Parking brakes.........................................

That doesn't always work.


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Photo © Zubova Marina

Quoting KELPkid (Reply 9): Not that I know my school buses, but the chassis was a '68-'72 Chevy...couldn't tell you who made the body, except that it wasn't a Bluebird

I've been waiting for this: schoolbuses.net

Quoting Airfoilsguy (Reply 12): That doesn't always work

That's 'IF' they did have the brake set. I think you'll find out they did not.

Quoting EMBQA (Reply 14): That's 'IF' they did have the brake set. I think you'll find out they did not.

Wow, if thats the case someone will probably be looking for a new job.

Quoting Airfoilsguy (Reply 15): Wow, if thats the case someone will probably be looking for a new job.

I wonder if the French would prosecute in a case like that...I hear it's a crime to unintentionally cause aircraft accidents in some places  

Quoting Airfoilsguy (Reply 12): That doesn't always work.

Wow...... Looks like the parking brake might have failed.

I see the 747-400 MM now states you require a min of 70 Tonnes of fuel on board for high power runs

Quoting YWG (Reply 17): Wow...... Looks like the parking brake might have failed.

Early telex describing the accident suggests they were leaving the run-up area after the engine test, so the brakes weren't set by design.

Tom.

Quoting JetMech (Reply 3): The procedure we always followed with 747's (and 767's) was to only run a single engine up to take off power at a time.

I wouldn't consider that a good policy, symmetric power is just good insurance.

On the DC-10 -30's and -40's we had a minimum winter fuel load for run-up of 60,000lb, but if it was snowing or icy I would usually load 100,000lb. As far as symmetric thrust is concerned, we would have the opposite wing engine at 75 to 80% power minimum, with the JT9's you want to operate your opposite engine at just below bleed closure, that way if you had a compressor stall, you knew it was the engine that you had at high power.

If you were to run a 752 with one engine at high power, and one at idle, one might want to be ready for the nose to swing into the idling engine. I have had a few occasions where a light fuel loaded 752 started moving at high power with the brakes set. We didn't always have time to up load a lot of fuel when the airplane had an early gate.

Now with the A320's you had to have your feet on the brake pedals to insure that you had full braking pressure to the brakes when doing a high power run-up, what a great idea, felt like I was back running a Cessna 150 again.

Quoting Ex52tech (Reply 20): If you were to run a 752 with one engine at high power, and one at idle, one might want to be ready for the nose to swing into the idling engine. I have had a few occasions where a light fuel loaded 752 started moving at high power with the brakes set. We didn't always have time to up load a lot of fuel when the airplane had an early gate

We dump 75K in the 757's to do full power runs, can run with the brakes set without any problems just hard to read the EICAS screen, We had a 757 we where ops checking a PRSOV problem, same thing late to gate not time for fuel, accidently fell into the throttles (wink wink) I think we left 15 feet of rubber on the ramp, and we only pushed it to something like 1.35 EPR to get it the PRSOV to shift.

The best is the 777 there is a note and when I do check rides to sign off people for run/taxi quals, that states not to run the engine above 1.4 EPR on Pavement due to the fact it WILL pull up the pavement. When I moonlighted in Mojave I watched the GE 747 with the GE90 blow rocks and pavement a couple hundred feet back at full power.

David

Quoting Ex52tech (Reply 20): I wouldn't consider that a good policy, symmetric power is just good insurance.

Of course. We did try and balance up the power on both sides of the ship, but on a 767 for example, we preferred to have a bit of nose swing instead of two engines at high power settings. We are somewhat lucky as we never got icing conditions in Sydney. It also comes down to team work, in that the ground observer should be alert and call out any potentially dangerous aircraft movement to the flight-deck as soon as they see it.

Regards, JetMech

Hi Airfoils guy, Buzz here. Guess they're "hanging out" at the blast fence... pun intended. I've seen a few other photos of taxi mistakes... and I can sympathize.

I don't know if the 340 system is similar to the 320 parking brake system. If you want max clamping pressure on the brake discs then you release the parking brake and hold the pedals down. Last month "10-Speed" (his old nickname) and I were testing an A320 / V2500 engine for oil leakage after a seal change... half an hour at cruise power. We took turns holding down the toe brakes. Yes, we had the mains chocked also... but with one engine at 1.25 EPR and one at 1.3 EPR we didn't want to slide. At PDX's "Hush House" there isn't much room before you'd end up in a ditch.

It's a shame to see a new airplane end up like that.
g'day

Quoting Buzz (Reply 23): I don't know if the 340 system is similar to the 320 parking brake system

Hi Buzz, no it's not - full brake press is applied by the park brake.

Quoting KELPkid (Thread starter): I'm just curious how you restrain a 747 at full thrust...I guess the flight crew that did the engine runs was standing on the brakes the whole time

During a High power Ground run,The Parking brake set,With Hydraulics available  ,Aircraft having the Adequate Weight,ensured by Fuel uplift,Chocks in place & the opposite wing Engine running.

regds
MEL

Quoting Buzz (Reply 23): Yes, we had the mains chocked also..

  

Quoting HAWK21M (Reply 25): Chocks in place

Chocks?????? The last time I ran an airplane with chocks in place was when I was in the military. I know......I know.....safety first, but we had to be able to pull off the run-up pad at a moments notice, for a higher priority aircraft. It must be great to work for a government subsidized airline.

Quoting JetMech (Reply 22): We are somewhat lucky as we never got icing conditions in Sydney.

I can't remember the number of times we had to blow the snow off of the spot we wanted to position the airplane in for run-up, and then have to taxi back to park on that spot. I don't care how much fuel you put on a DC-10, the nose wheel steering is just about useless in 8" to 10" of snow. If you damaged the aircraft, our management team would back you up really well.........right into the corner, then tell their bosses, " We begged them not to do it".

Quoting Ex52tech (Reply 26): If you damaged the aircraft, our management team would back you up really well

Ah management. They put all the pressure on you to do a job quickly, and they always seem to be the first in line to kick your arse when it goes pear shaped because you were rushing   !

Regards, JetMech

Quoting KELPkid (Thread starter): Okay, who watched the two hour Mythbusters special last night? Big grin I'm just curious how you restrain a 747 at full thrust

Well..... that aircraft was not at full thrust. If you watch, they only power up the number 2 and 4 engine.

I think all of you know what this means....

If you get a 777-LR with nothing in it except for enough fuel for a few minutes, lock the brakes and select TO thrust, the plane would move forward.

Would it eventually be able to take off?

Because if it could, the conveyor belt thread just got a whole lot more interesting   

MONSTER THREAD

iwok

Quoting Iwok (Reply 29): Because if it could, the conveyor belt thread just got a whole lot more interesting MONSTER THREAD

Now I regret ever starting this thread   

Quoting Ex52tech (Reply 26): If you damaged the aircraft, our management team would back you up really well.........right into the corner, then tell their bosses, " We begged them not to do it".

Good One   

Quoting KELPkid (Reply 9): Not that I know my school buses, but the chassis was a '68-'72 Chevy...couldn't tell you who made the body, except that it wasn't a Bluebird

C'mon, we all know ThomasBuilt Buses are best 

Quoting FLY2HMO (Reply 33):

I wished I had one of those on a few occasions.

Quoting Alitalia744 (Reply 32): C'mon, we all know ThomasBuilt Buses are best

Hell yeah - 2000 Thomas 71pax on a Freightliner FL65 with a 5.9 Cummins is my whip at 630 every morning.

...then I go to the airport, fly Pipers all day long, and come back for more bus action. Hell of a life.

-Meister

Is setting the brakes really that strong? I've accidently drove around forgetting I set my parking brake on. A 744 has 1/4th its weight in thrust, to hold the plane in place the brakes need to be that strong, preventing wheel rotation with 30k ft lbs behind each wheel. Heck if brakes were that stong, there'd be no need for reverse thrust, landing and takeoff distances would be the same, right?

Quoting Lehpron (Reply 36): Is setting the brakes really that strong? I've accidently drove around forgetting I set my parking brake on. A 744 has 1/4th its weight in thrust, to hold the plane in place the brakes need to be that strong, preventing wheel rotation with 30k ft lbs behind each wheel. Heck if brakes were that stong, there'd be no need for reverse thrust, landing and takeoff distances would be the same, right?

At some point, the forward thrust will overcome the friction caused by the stopped tires' contact with the ground, and the plane will move forward, tires screeching...as the mechanics and MX folks have alluded to in this thread, there is apparently a minimum weight that the aircraft needs to be at to run up the power on all 4 engines to prevent this.

Quoting Lehpron (Reply 36): Is setting the brakes really that strong?

Yes.

Quoting Lehpron (Reply 36): I've accidently drove around forgetting I set my parking brake on. A 744 has 1/4th its weight in thrust, to hold the plane in place the brakes need to be that strong, preventing wheel rotation with 30k ft lbs behind each wheel.

The parking brake on most cars is much smaller than the main brakes and only operators on the back two wheels. For aircraft the actuator mechanism is sometimes different but the physical brake is the same and it's huge. The brake is much more than capable of locking the wheel; the critical part is the wheel's friction on the ground.

Quoting Lehpron (Reply 36): Heck if brakes were that stong, there'd be no need for reverse thrust, landing and takeoff distances would be the same, right?

There is no "need" for reverse thrust...you can dispatch an aircraft with the thrust reversers inoperative and all the certification landing distances are done using brakes alone. Landing and takeoff distance would not be the same though...landing and takeoff speeds are not the same and one is governed by engine thrust while one is governed by braking power.

Tom.

Quoting Lehpron (Reply 36):

As others have pointed out, it is not the brake units themselves that are of concern, it is whether you have enough aircraft mass combined with the coefficient of friction between the tyre and tarmac that is critical.

Quoting Tdscanuck (Reply 38): For aircraft the actuator mechanism is sometimes different but the physical brake is the same and it's huge.

Exactly. On the 747 and 767, the park brake is merely a mechanical pawl that locks the brake pedals in the applied position. Thus, on a 747, the park brake involves the use of all 16 main brake units. IIRC, they get the full 3,000 psi but I am not 100 % sure   .

Regards, JetMech

Quoting Lehpron (Reply 36): Heck if brakes were that stong, there'd be no need for reverse thrust, landing and takeoff distances would be the same, right?

As Tdscanuck points, out the reversers are a bonus. The brakes are that strong.

Quoting Tdscanuck (Reply 38): The parking brake on most cars is much smaller than the main brakes

Actually, in most cases the actual brake is the same as the main brakes, but actuated by a cable or hydraulic line connected to the hand or foot parking brake lever.

but it

Quoting Tdscanuck (Reply 38): only operators on the back two wheels

Eitherway, even if all the wheels are locked if the plane is light, then the thrust will overcome frictional forces. For example if you take a lightly loaded 77W at ~450K lb the resulting wheel to ground friction is about 45-150K lb. If you hit this with a total of 230 ln thrust from two GE 90-115's, then plane will start moving even though its wheel speed is zero.

So if the runway was actually a slick treadmill......   

iwok

Quoting Buzz (Reply 11): keep a picture or two as an attention getter when I teach people to taxi. (yes, it's on A.net)

Mind letting a clutz like me know where to find these pics? I looked under your profile, but it says you don't have any pics uploaded ...

Thanks
Bren