What the heck is Muck tuck?
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pencilneck
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What the heck is Muck tuck?
At the risk of sounding like a real pencilneck I was wondering what muck tuck is.
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monkeyspankmasterflex
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Mach Tuck
If you fly too fast on a sub-sonic Jet you will reach Mach Crit. The center of pressure moves aft causing the nose to drop. The aircraft continues to accellerate... bad news.
If you get too high for your weight you can put yourself at risk of exceding the High speed Mach limit and find yourself in this predicament.
Been awhile... If I recall ... You do not pull back on the control yoke if you face this for real. Rather you bring the thrust to idle and raise the speed brakes... once you have decellerated away from Mach Tuck you can pull out of the resultant dive.
Any ex snow birds out there that can confirm this?
If you fly too fast on a sub-sonic Jet you will reach Mach Crit. The center of pressure moves aft causing the nose to drop. The aircraft continues to accellerate... bad news.
If you get too high for your weight you can put yourself at risk of exceding the High speed Mach limit and find yourself in this predicament.
Been awhile... If I recall ... You do not pull back on the control yoke if you face this for real. Rather you bring the thrust to idle and raise the speed brakes... once you have decellerated away from Mach Tuck you can pull out of the resultant dive.
Any ex snow birds out there that can confirm this?
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sky's the limit
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"Hey pilots I only got two buckets a grease dis trip."
Indian Ice Cream: Oolichan grease stirred with handfuls of blueberries - yum!
Had a sea lion stew once that memories are made of. Could still taste it three days and a thousand miles later.
Indian Ice Cream: Oolichan grease stirred with handfuls of blueberries - yum!
Had a sea lion stew once that memories are made of. Could still taste it three days and a thousand miles later.
"What's it doing now?"
"Fly low and slow and throttle back in the turns."
"Fly low and slow and throttle back in the turns."
wsguy wrote:Mach Tuck
If you fly too fast on a sub-sonic Jet you will reach Mach Crit. The center of pressure moves aft causing the nose to drop. The aircraft continues to accellerate... bad news.
Been awhile... If I recall ... You do not pull back on the control yoke if you face this for real. Rather you bring the thrust to idle and raise the speed brakes... once you have decellerated away from Mach Tuck you can pull out of the resultant dive.
Any ex snow birds out there that can confirm this?
Just want to mention DON'T use speedbrakes / spoilers as they will cause a pitch-down motion and worsen the situation. My understanding is they lost a few early Lears this way. Instead extend the gear
and esae out of the dive ( throttles idle of course )Just callin it like it is.
Muck Tuck:
The act of removing one's underpants and using them to sop-up butt leakage.
"I had to do the Muck Tuck after the whiskey and Taco Bell last night"
The act of removing one's underpants and using them to sop-up butt leakage.
"I had to do the Muck Tuck after the whiskey and Taco Bell last night"
"FLY THE AIRPLANE"!
http://www.youtube.com/hazatude
http://www.youtube.com/hazatude
Mach Trim..... puts aft trim pressure usually at around Mach .70
Mach Tuck comes later!
Interestingly enough not all Modern Jet Aero planes have a Mach Trim System....
Here is a link that compares the B757 with the B767
http://www.aerospaceweb.org/question/dy ... 0137.shtml
Mach Trim and Boeing 757 / 767
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I'm set for an airline interview and hope to have this question answered by an authoritative guide. Is the Boeing 757 wing a supercritical wing? Why does it have a mach speed trim whereas the Boeing 767 aircraft does not? Does the answer have to do with the movement forward of the 767 wing, reducing the longitudinal instability, whereas the 757 wing was not moved forward? Your help is appreciated.
- DKM
Your first question is quite simple. Yes, the Boeing 757 uses a supercritical airfoil, the Boeing TR-51 series to be exact. More information on these airfoils can be found in previous questions we've answered on the 757 airfoil and aft-loaded wings.
The second question is a bit tougher. First of all, I am a little surprised that the 757 would be equipped with a mach speed trim control and the Boeing 767 would not. I'd suspect that the two are similar enough that both would either need or not need such a device. But assuming that you are correct, I can think of a few factors that might play a role.
The reason an aircraft would need a mach speed trim control in the first place relates to the behavior of its wing center of pressure as speed changes. The center of pressure (Cp) is the point on a wing where the lift force acts. In low subsonic flight, the center of pressure is usually pretty stable for a conventional airfoil shape and is located about one-quarter of the way back from the wing leading edge. But as speed increases, the center of pressure begins moving aft, particularly at transonic speeds starting at about Mach 0.7. As the Cp moves aft, the moment arm between it and the elevator decreases. This movement makes the elevator less effective in providing pitch control. The difference in location between the Cp and the center of gravity (located in front of the Cp) causes the aircraft nose to pitch down, so more elevator trim is required to keep the aircraft level.
Comparison of the Boeing 757 and 767
Now that we know what mach speed trim is, the question becomes why would one aircraft need it and the other not. What this question suggests is that there is no movement of the Cp on the 767, or at least much less than there is on the 757. Cp travel is usually associated with the wing airfoil section, but I believe that both aircraft use the same airfoils, or ones similar enough that their Cp movement should be similar. Another method of reducing Cp movement is to use wing sweepback. This is indeed one major difference between the wings of the two aircraft. The 757 wing is swept 25° while the 767 wing is swept 31.5°. That 6.5° difference seems pretty small, but I think it likely plays a major role.
Your theory on the wing's location might also have some effect, but I don't think it would be very significant. The 767 also has a thicker wing, greater wing chord, and a larger horizontal tail than the 757. A combination of some or all of these variables may have the effect of making the aircraft less sensitive to any Cp movement.
Mach Tuck comes later!
Interestingly enough not all Modern Jet Aero planes have a Mach Trim System....
Here is a link that compares the B757 with the B767
http://www.aerospaceweb.org/question/dy ... 0137.shtml
Mach Trim and Boeing 757 / 767
--------------------------------------------------------------------------------
I'm set for an airline interview and hope to have this question answered by an authoritative guide. Is the Boeing 757 wing a supercritical wing? Why does it have a mach speed trim whereas the Boeing 767 aircraft does not? Does the answer have to do with the movement forward of the 767 wing, reducing the longitudinal instability, whereas the 757 wing was not moved forward? Your help is appreciated.
- DKM
Your first question is quite simple. Yes, the Boeing 757 uses a supercritical airfoil, the Boeing TR-51 series to be exact. More information on these airfoils can be found in previous questions we've answered on the 757 airfoil and aft-loaded wings.
The second question is a bit tougher. First of all, I am a little surprised that the 757 would be equipped with a mach speed trim control and the Boeing 767 would not. I'd suspect that the two are similar enough that both would either need or not need such a device. But assuming that you are correct, I can think of a few factors that might play a role.
The reason an aircraft would need a mach speed trim control in the first place relates to the behavior of its wing center of pressure as speed changes. The center of pressure (Cp) is the point on a wing where the lift force acts. In low subsonic flight, the center of pressure is usually pretty stable for a conventional airfoil shape and is located about one-quarter of the way back from the wing leading edge. But as speed increases, the center of pressure begins moving aft, particularly at transonic speeds starting at about Mach 0.7. As the Cp moves aft, the moment arm between it and the elevator decreases. This movement makes the elevator less effective in providing pitch control. The difference in location between the Cp and the center of gravity (located in front of the Cp) causes the aircraft nose to pitch down, so more elevator trim is required to keep the aircraft level.
Comparison of the Boeing 757 and 767
Now that we know what mach speed trim is, the question becomes why would one aircraft need it and the other not. What this question suggests is that there is no movement of the Cp on the 767, or at least much less than there is on the 757. Cp travel is usually associated with the wing airfoil section, but I believe that both aircraft use the same airfoils, or ones similar enough that their Cp movement should be similar. Another method of reducing Cp movement is to use wing sweepback. This is indeed one major difference between the wings of the two aircraft. The 757 wing is swept 25° while the 767 wing is swept 31.5°. That 6.5° difference seems pretty small, but I think it likely plays a major role.
Your theory on the wing's location might also have some effect, but I don't think it would be very significant. The 767 also has a thicker wing, greater wing chord, and a larger horizontal tail than the 757. A combination of some or all of these variables may have the effect of making the aircraft less sensitive to any Cp movement.
Bede wrote:
I don't think anyone on this forum has ever been in a mach tuck situation.
Most military trained pilots (the ones that flew the Tutor Jet) have experienced Mach Tuck as it was demonstrated and practiced during pre-wings training. The standard recovery was idle and speedbrakes, but don’t pull back too hard during the recovery or you would go for a wild ride as the aircraft re-tucked.
I don't think anyone on this forum has ever been in a mach tuck situation.
Most military trained pilots (the ones that flew the Tutor Jet) have experienced Mach Tuck as it was demonstrated and practiced during pre-wings training. The standard recovery was idle and speedbrakes, but don’t pull back too hard during the recovery or you would go for a wild ride as the aircraft re-tucked.
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Clodhopper
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Just like to toss in a few observations, feel free to correct me if I'm wrong:
Mach Tuck, as described above is when the center of pressure shifts as the aircraft accelerates beyond Mcrit, the shift causes a nose-down tendency.
Now, on a T-tail aircraft, isn't this super-critical because at the point of Mach Tuck, the trans/super-sonic flow coming off the wings can blanket or disrupt the flow over the tail, further aggravating the nose-down tendency?
I recall an issue a while ago about a certain LCC in Canada that operated T-tails. The flight crew, in an attempt to more or less "race" either another aircraft, or one of their previous times for a certain leg, reprogrammed the FMS to make the aircraft think it was lighter than it actually was. This altered the auto-pilot's throttle control, over-accelerated the aircraft, and resulted in a Mach Tuck with a rapid loss of altitude.
It was one of a few factors that resulted in said carrier losing its RVSM certification.
Just a story that I heard...repeating for your enjoyment.
Mach Tuck, as described above is when the center of pressure shifts as the aircraft accelerates beyond Mcrit, the shift causes a nose-down tendency.
Now, on a T-tail aircraft, isn't this super-critical because at the point of Mach Tuck, the trans/super-sonic flow coming off the wings can blanket or disrupt the flow over the tail, further aggravating the nose-down tendency?
I recall an issue a while ago about a certain LCC in Canada that operated T-tails. The flight crew, in an attempt to more or less "race" either another aircraft, or one of their previous times for a certain leg, reprogrammed the FMS to make the aircraft think it was lighter than it actually was. This altered the auto-pilot's throttle control, over-accelerated the aircraft, and resulted in a Mach Tuck with a rapid loss of altitude.
It was one of a few factors that resulted in said carrier losing its RVSM certification.
Just a story that I heard...repeating for your enjoyment.
a.k.a. "Big Foot"
This article is only partly true.Interestingly enough not all Modern Jet Aero planes have a Mach Trim System....
Here is a link that compares the B757 with the B767
The 767-200 has no mach trim system, as is evedent by the split between the inbord and outbord elevators. The 767-300 has aligned elevator sections and therefore has a mach trim system installed.
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ScudRunner
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Over the Horn
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