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B757-300 Problems?  
User currently offlineUdo From , joined Dec 1969, posts, RR:
Posted (15 years 3 weeks 6 days 13 hours ago) and read 1269 times:

Just some days ago I talked to an aviation engineer and we discussed several topics. He told me Boeing's B753 still suffers from strange vibration in the aft/tail section whíle flying, and they haven't found a solution yet.
I tried to get more about that but couldn't find anything. Who knows more about that? Is it true or is nothing behind it?

Regards
Udo

5 replies: All unread, jump to last
 
User currently offlineMAC_Veteran From Taiwan, joined Jun 1999, 726 posts, RR: 7
Reply 1, posted (15 years 3 weeks 6 days 7 hours ago) and read 1269 times:

Udo

It would not surprise me given the "arm" from the wing to the tail, that this airplane has, another important point is it uses the same rudder as the 757-200. The same sort of complaint used to be reported on the Douglas DC-8-Super 60 series jets, -61 and -63 models. They would shimmy back and forth in the rear fuselage areas also.

The primary reason I believe this is occurring on the 757-300 is the original tail is being used, and it might not be enough to compensate for yawing tendencies. It may boil down to a modified fin and rudder assembly adding more area to eliminate the yawing, like those seen on the A330-200, same concept being used there. The Airbus widebodies also have this tendency -except- the A330-200 from what I've been told, so it appears that a bigger tail fin and rudder does make a difference here and possibly why they have elected to use it on the A340-500/600 as well.

The earlier the better on this path of rectification, if not and especially if it was not part of the design in it's capability, (they do figure these things into airplane design of course-but if its becoming a problem then its something to investigate before it becomes a bigger one) it could lead to problems with structural fatigue. But that's in a worst case scenario.

Regards
MAC_Vet


User currently offlineDash8 From New Zealand, joined Aug 2005, 2 posts, RR: 0
Reply 2, posted (15 years 3 weeks 5 days 20 hours ago) and read 1269 times:

Remember though that vibration is a completely different thing than yawing oscilations. What MAC said is correct but if it's vibration then something else is at play. I have no clue though if this is true or just a rumor. What i do know is that the 753's are enjoying the highest dispatch rates ever for any Boeing jetliner.

User currently offlineNavion From United States of America, joined May 1999, 1010 posts, RR: 1
Reply 3, posted (15 years 3 weeks 5 days ago) and read 1269 times:

I have to say this is the first time in my aviation career I've ever heard it suggested to increase rudder and vertical stabilizer area for a longer fuselage. Typically, you increase the area the shorter the fuselage as you get greater moment force for a given area if the arm is longer. Longer fuselage, usually same or smaller fin (if all other aspects remain the same). If a lot more power were installed, then you may need more rudder movement or a larger stabilizer, but not usually. A good example of this is the larger fin on a 747SP compared to the longer fusealage 747-100/200/300/400.

User currently offlineMAC_Veteran From Taiwan, joined Jun 1999, 726 posts, RR: 7
Reply 4, posted (15 years 3 weeks 4 days 14 hours ago) and read 1272 times:

Navion

The smaller rudder/fin versus bigger rudder/fin is something worth looking into on the 757-300. What is the engine duo fitted to this? I believe it's an uprated version of the RB211-535E4 as well as an uprated version of the PW2040.

The SP required the rudder increase for many reasons like those you mentioned, aerodynamically it fit perfectly because of the reduced fuselage length and the engine power was somewhat different on these models from standard -100/-200 models, generally in the 47000-to-51000 lb range, whereas most -100/200 models at that time (1976) were in the 43-45000 lb class. Later on the higher engine thrust were retrofitted or built onto new-build -100/-200s.

Another example is the new rudder/fin on the 737NG, same airplane in size compared to the 737-500 and 300, slightly longer than the -400, yet they opted for a bigger rudder/fin assembly. Better control? Wonder why.

Same holds true for the A340-500 and -600. It's going to be a more powerful and heavier airplane of course. But..the airplanes are longer than the A340-300. They will incorporate the A330-200's fin/rudder. By comparison, The A330-200 is less than a foot smaller in length compared to the A340-200, but it's power package of two CF680, PW4000 or RR Trent outstrips the 4 CFM engines on the A340 , and quite possibly something must have borne out in the design showing the benefits of a larger tail fin/rudder assembly on these types of airplanes.

I've wondered if there is a problem like this on Boeing's 777-300. What must compensate is it's fuselage structure being wider and 'beefier' therefore it may not "wobble", but the narrower a fuselage the twisting movement get's amplified. That's the "flip side to the coin"; fuselage width. The wider the fuselage, generally the twisting movement gets reduced.


Regards
MAC_Vet


User currently offlineNavion From United States of America, joined May 1999, 1010 posts, RR: 1
Reply 5, posted (15 years 3 weeks 3 days 3 hours ago) and read 1269 times:

You bring up some important points which I think need clarification. First of all, any engine installed at any thrust on the 757-300 is certified on the -200 up to 43,000 lbs. The rudder on the 753 will be more than adequate given the same wing, engines and layout but with the advantage of greater length. If you notice, when the A340-200 was lengthened to the -300, the original rudder sufficed. Same goes for the DC-8 stretches. Look however at the A330-200 which needed a larger vertical stabilizer to offset the lesser arm due to decreased length. The fact the new A340-500/600's need a larger rudder is due to the fact they have a larger wing with a great increase in installed power. Same goes for the new 747 growth derivatives being examined. With a substantial increase in thrust comes a greater need for rudder authority. When the 767 is stretched each time, the rudder is adequate as the installed thrust is not much greater. I think the differences you refer to on the A340-500/600 are mainly due to the fact those aircraft really are different beasts with greatly increased power and weights. (Note the MTOW is approx 365,000 kg compared to the heavy A340-300 MTOW 275,000). If you have other thoughts or think something I've said is wrong or inaccurate, let me know and I'll try to correct it. Talk to you later.

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