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Hello, I was just wondering, I was watching a 737 takeoff yesterday and when they advanced the power I noticed the tail especially the leading edge of it shakes from the thrust of the engines. Obviously the 737 is a very safe aircraft but does this cause any long term damage or fatigue? Also second question, ehat did they actually change in the rudder system that prevents another disaster like the ones they had in the older models? Thanks!

I know they say the 737 is a dog, but this is ridiculous.

Maybe it had to do with the air movement around the tail during take off and not the aircraft itself? Manufacturers do design the extremities of their aircraft to wobble as they move through the air. That actually makes it easier on the airframe itself; similar to how a skyscraper is designed to sway in high winds. I know stress tests for the wings are required and once they reach failure it is a very dramatic episode. It wouldn't surprise me if they have a similar test for horizontal stabilizer failure in the same fashion they do wing bend tests.

The 777 does this as well, in fact most airplanes will. The components are designed to be flexible precisely in order to prevent damage - so you will probably find that a fully rigid tail would fatigue at a greater rate than one with some "give"

They changed the rudder PCU valves - google 737 rudder to find more info.

Didn't they also increase the approach speed so that if there is a rudder hardover the pilots will have enough control authority to keep the plane from continuing the roll?

Not sure about the approach speed, but pilots were trained once the hardover situation was understood (before the cause was found) in how to safely recover the airplane if it happened (by applying opposite aileron), and it was this training that helped the Eastwinds flight safely recover from the event. Even at the speed they were going, they could very easily have gotten into an unrecoverable situation w/out the training.

dtwpilot225 wrote:

Hello, I was just wondering, I was watching a 737 takeoff yesterday and when they advanced the power I noticed the tail especially the leading edge of it shakes from the thrust of the engines. Obviously the 737 is a very safe aircraft but does this cause any long term damage or fatigue? Also second question, ehat did they actually change in the rudder system that prevents another disaster like the ones they had in the older models? Thanks!

If the tail didn't shake, it would lead to more fatigue cracking. During High Power engine runs, the whole airplane is bouncing so much, it's hard to read the instruments.

https://www.youtube.com/watch?v=ZqM0HXtlSAE

https://www.youtube.com/watch?v=cEgiqCZLJqQ

https://www.youtube.com/watch?v=ChS3p3G44NQ

Quick pic of rudder system changes

Phenomenon is more acute with application of reverse on landing...quite striking sometimes how much the tail will shudder...


Faro

Caltech, that second video was amazing. Thanks for sharing!

question related to the high power test runs in the videos: how are brakes and chocks able to keep aircraft from moving when the engines are at TOGA thrust levels?

DFWflightpath wrote:

question related to the high power test runs in the videos: how are brakes and chocks able to keep aircraft from moving when the engines are at TOGA thrust levels?

One could just say --because they are but....

In normal production Boeing airplanes with high thrust engines 747,767,777 & 787 are not taken to full thrust in the chocks to prevent possible damage. The first time the engines see full thrust "on wing" is during a taxi run up to about 80+/- kts prior to the initial B-1 takeoff.

By far the most spectacular horizontal tail movement at high power was a 757.

spudsmac wrote:

Didn't they also increase the approach speed so that if there is a rudder hardover the pilots will have enough control authority to keep the plane from continuing the roll?

No the speeds were not increased for rudder hard over The speeds were increased because the airplane has geometric limits with flare and to reduce the risk of tail strikes.

DFWflightpath wrote:

question related to the high power test runs in the videos: how are brakes and chocks able to keep aircraft from moving when the engines are at TOGA thrust levels?

Not only might they not be at full power, but I believe it's only one engine at a time. I could be wrong though.



This has always been my favorite engine run up video. You don't see the entire aircraft, and it's not even an HD video, but good god this engine screams!! The condensation and little tornados inside the engine look like some sort of black hole or time warp lol. The engine shakes like crazy. I don't know how they can make engine mounts that can handle this kind of power. Watch at 2:20, it's pretty cool they reduce power then push it back up to what seems like very high thrust settings and you just get a real sense of the amount of power.

https://youtu.be/waDeveWle54

spudsmac wrote:

Didn't they also increase the approach speed so that if there is a rudder hardover the pilots will have enough control authority to keep the plane from continuing the roll?

Yes, good memory....Reference https://en.wikipedia.org/wiki/USAir_Flight_427

trnswrld wrote:

DFWflightpath wrote:

question related to the high power test runs in the videos: how are brakes and chocks able to keep aircraft from moving when the engines are at TOGA thrust levels?

Not only might they not be at full power, but I believe it's only one engine at a time. I could be wrong though.



This has always been my favorite engine run up video. You don't see the entire aircraft, and it's not even an HD video, but good god this engine screams!! The condensation and little tornados inside the engine look like some sort of black hole or time warp lol. The engine shakes like crazy. I don't know how they can make engine mounts that can handle this kind of power. Watch at 2:20, it's pretty cool they reduce power then push it back up to what seems like very high thrust settings and you just get a real sense of the amount of power.

https://youtu.be/waDeveWle54

Bad ass video!!!!!

mcdu wrote:

spudsmac wrote:

Didn't they also increase the approach speed so that if there is a rudder hardover the pilots will have enough control authority to keep the plane from continuing the roll?

No the speeds were not increased for rudder hard over The speeds were increased because the airplane has geometric limits with flare and to reduce the risk of tail strikes.

Correct me if I am wrong but I believe Spudsmac is referring to the Approach flap setting of 1-10 on the B737 due to the rudder hardover incident on USAir flt 427. In that case they did increase the block speeds for flaps 1-10 in March of 1999.

However I believe MCDU you are referencing (Vref) which is the speed in which you would cross the threshold at on approach....That's the only speed that makes sense with your point. I don't believe that is the speed that Spudsmac was referring to.

CorpCareer wrote:

mcdu wrote:

spudsmac wrote:

Didn't they also increase the approach speed so that if there is a rudder hardover the pilots will have enough control authority to keep the plane from continuing the roll?

No the speeds were not increased for rudder hard over The speeds were increased because the airplane has geometric limits with flare and to reduce the risk of tail strikes.

Correct me if I am wrong but I believe Spudsmac is referring to the Approach flap setting of 1-10 on the B737 due to the rudder hardover incident on USAir flt 427. In that case they did increase the block speeds for flaps 1-10 in March of 1999.

However I believe MCDU you are referencing (Vref) which is the speed in which you would cross the threshold at on approach....That's the only speed that makes sense with your point. I don't believe that is the speed that Spudsmac was referring to.

He said approach speeds, which is Vref. Maneuvering speeds are what you are talking with anything less than landing flaps. And in that case the answer is no. In the classics they manipulated the maneuvering speeds. In the NG they didn't, new wing and new rudder PCU.

yes that's true MCDU, but sometimes people don't always say what they mean....Given the nature of the crash and the configuration of the aircraft at the time of the crash which wasn't in the landing configuration I assumed he meant the flap block speeds for 1-10 and wasn't referring to Vref..My fault if that's what he was referring to

If you YouTube KPAE you will see just how much movement the vertical and horizontal tail moves when takeoff power is applied especially on the 777's! Every plane nut must watch these videos they are amazing!:-)

Thanks for all the responses

DFWflightpath wrote:

question related to the high power test runs in the videos: how are brakes and chocks able to keep aircraft from moving when the engines are at TOGA thrust levels?

For high power engine runs, the aircraft is loaded with A LOT of fuel, and if one engine is taken to Takeoff Power, the other engine engine is usually brought up with power, to flight idle, 70 % N1 or what ever the manufacturer states, to balance out the loads on the airplane.

Usually just brakes, no chocks, as the aircraft had to taxi to the approved engine run area.

At Denver Stapleton, running engines at high power in Fort Apache, was fun in the winter when ice and snow covered the ground...........

The shaking is scary for some the first time..........

http://www.youtube.com/watch?v=Du_TUbdWWcY