Tuffty From United Kingdom, joined Mar 2001, 92 posts, RR: 0
Reply 1, posted (12 years 10 months 3 weeks 2 days 4 hours ago) and read 2209 times:
Though im not a pilot ive been told by some flight engeneers who served on the 200's that they would stager the throttles to get all of the engines to have te same power out put. however i dont think that this was what you were asking and i to am interested to know if they were awkward to fly with the throttle stagger taken out, say at a change of throttle possition on approach.
Panman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 4, posted (12 years 10 months 3 weeks 1 day 12 hours ago) and read 2122 times:
Mandala think about it.
Q: Why do they stagger the throttles?
A: To have the engines producing the same output more or less.
Q: What would happen if they didn't stagger the throttles?
A: Each engine would produce a different amount of thrust.
Q: What side effects if any would arise?
A: Each engine producing a different amount of thrust, each engine having a different fuel consumption.
Q: What are the benefits of staggering the throttles?
A: Like mentioned previously engines producing same amoung of thrust more or less, all gauges on the panel reading the same more or less, thus making it easier to see if there is a problem with one engine as it's corresponding gauge would be out of line with the others.
BR715-A1-30 From , joined Dec 1969, posts, RR:
Reply 6, posted (12 years 10 months 3 weeks 1 day 8 hours ago) and read 2094 times:
Why do they have to stagger the throttles. What I mean is why do the engines produce different amounts of thrust if you dont stagger them. Why aren't they like the 717 where both throttles in the same place equals both engines at the same thrust.
Barney captain From United States of America, joined Nov 2001, 1089 posts, RR: 12
Reply 7, posted (12 years 10 months 3 weeks 1 day 5 hours ago) and read 2079 times:
In a perfect world, they would all be in alignment. From time to time, it's not at all surprising to find a little out-of-rig situation. Typically, you just match the N1 to produce symmetrical thrust. When hand flying during an approach, I usually match fuel flow and yes, some times there is a little throttle split but it is usually easily managed.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 9, posted (12 years 10 months 3 weeks 20 hours ago) and read 2031 times:
The limits we use in our MM are:
Up to 1 knob from difference, no action required
1 to 1.5 knobs defered for 5 days for trim run and correction
Over 1.5 knobs must be fixed before further flight
A throttle on a classic can be out of rig for several reasons, but the miost common we come across is a slowly wearing jet fuel control. This normally requires trimming the fuel control under controlled circumstances until the throttles match or the fuel control is replaced because the trim screw is bottomed out.
Expratt From United States of America, joined Mar 2000, 311 posts, RR: 0
Reply 12, posted (12 years 10 months 3 weeks 4 hours ago) and read 1976 times:
No two engines will ever have the same performance. Not even two new production engines in serial number sequence will have the same performance. Most of the time, the differences in performance between engines is fairly slight so there is not much if any change in throttle position. The bigger the engine like a JT9D, the more likely it will show throttle stagger than it will on a small engine like the BR715. In addition to the items previously listed, another cause for throttle stagger is engine deterioration. As the engines age, the throttles have to pushed higher to attain a given amount of thrust. With engines of similar vintage installed, the added throttle push is not noticeable because the engines will most likely age the same and the throttles will be pushed forward similar amounts. If one of the older engines is replaced, the throttle for the newer engine will not have to be pushed as high as that on the older engine to attain the given amount of thrust, hence the throttles become staggered and difference becomes obvious. Engine deterioration can be many things: worn compressor and turbine outer air seals, bowed or burned turbine nozzles, dirty compressors. As was previously stated, there are limits on how far the throttles can be staggered. Most allow up ot one knob width before maintenance has to adjust the throttle rigging or engine trim.
Bio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7
Reply 13, posted (12 years 10 months 3 weeks 1 hour ago) and read 1969 times:
The reason for 747-400 and more modern aircraft not having the need of staggered their throttles, is that they have FADEC (Full Authority Digital Engine Control) which is the fly-by-wire of engines. Depending on throttle position, the system controls the adequate fuel flow electronically. No direct mechanical links from the throttle levers. This is more reliable as to precission, and that's how the same thrust (more or less) can be generated on all four engines without the staggering.
Tuffty From United Kingdom, joined Mar 2001, 92 posts, RR: 0
Reply 14, posted (12 years 10 months 2 weeks 6 days 23 hours ago) and read 1957 times:
yeah thats right on the 400's yove got a trim plug on the fadec that denotes the max thrust rating making it an "h" or "g" rated engine. this will also allow the engines performance to be flat rated so that at ISA conditions you are given an exact thrust rating which is acurate. this alllows any differences in the engines from manufacture to be alleviated.
B747skipper From , joined Dec 1969, posts, RR:
Reply 15, posted (12 years 10 months 2 weeks 21 hours ago) and read 1828 times:
Flying a 747 (or any other 4 engine aircraft - I flew the 707s and DC8s as well) is never a problem, power adjustments are done by "feel" and, if necessary, by asking the flight engineer to adjust EPR (on the JT9s) or N1 (on the CF6s)...
As a matter of fact, I would sometimes "stagger the power" in cross-wind landings... And flying an "ILS" in real life (or in a simulator) requiring a very slight power adjustment, I would do it, using the "inboard" engines only, such as pushing "half a knob" on both "inboards" to gain an extra 2 or 3 knots on the approach (Vref) speed... never a problem... hell, we practice with outboard engines "out", even with "two engines out" on the same side... the 747 is a very easy and stable aircraft to fly...