Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 8 Posted (14 years 3 months 1 week 6 days 11 hours ago) and read 12620 times:
I've read that pilots who fly business jets in the upper flight levels can experience a high altitude aerodynamic force called Mach Tuck. However I don't know what this term means. It sounds like it might have something to do with transonic flight and the formation of shock waves, but I'm not sure, and I don't know if this force is an advantage or disadvantage to the pilots.
Ivo21 From Netherlands, joined Jan 2002, 25 posts, RR: 0
Reply 1, posted (14 years 3 months 1 week 6 days 11 hours ago) and read 12569 times:
I don`t know for sure, but I think it has indeed something to do with transsonic flight. When a relatively small business jet reaches transsonic speed, the lift and thrust decreases. Therefor the aircraft will react by the bpilot in a nose up pitch. That`s your Mach Tuck, I think.
But of course I cannot say that for sure.
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 8
Reply 2, posted (14 years 3 months 1 week 6 days 11 hours ago) and read 12546 times:
Thanks for your reply.
Well, just the word Tuck itself makes me think of something going down. In this case I believe it would be the pitch of the Biz Jet's nose. If a small jet's lift and thrust starts to decrease as it approaches Mach 1, the angle of attack will also decrease causing the pilots to react by raising the nose...as you mentioned.
I wonder if the concorde and fighter jets experience this at all? Or if they just punch right through Mach 1 without experiencing Mach Tuck?
MD11nut From , joined Dec 1969, posts, RR:
Reply 4, posted (14 years 3 months 1 week 6 days 10 hours ago) and read 12527 times:
You probably are talking about the TuckUnder effect. There are several factors causing it. The main one is that as airflow separation takes place, the downwash behind the wing is decreased. Prior to this, the horizontal stabilizer is trimmed to keep the airplane level. With this decrease in downwash, the stabilizer AOA, in effect, is increased thus pushing the tail up hence the pitch down.
There are two other factors. One is that as the shock waves move rearward, so is the center of pressure, adding to the tuckunder. The second is that, as Seagull said, is the aerodynamic center shifts rearward, adding to the Tuckunder effect. One interesting about the aerodynamic center shift is that in some aircraft, the aero center shift forward first (causing momentary pitch up) before eventually shifts rearward (pitch down). this was probably what CULBER was thinking about.
All aircraft flying supersonically suffer a nose down pitching moment.
411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 8, posted (14 years 3 months 1 week 6 days 5 hours ago) and read 12473 times:
All airfoils have the tuck-under or turning moment effect, whether straight wing or swept, and this was discovered in the 1922-23 experiments by the NACA. It is however more pronounced on high speed sweep wing jets. The mach trim system on jets is certainly there for a purpose. If the system becomes inoperative enroute, many types require a speed reduction and/or manditory autopilot use.
Skyguy11 From , joined Dec 1969, posts, RR:
Reply 9, posted (14 years 3 months 1 week 6 days 5 hours ago) and read 12468 times:
I don't understand this so I'm not going to try to answer, but I do have 1 tidbit of cool info:
During WWII, when some of the planes during combat and flight testing exceeded Mach 1 (yes it did happen, but not officially), the nosed picthed down uncontrollably. This unexplained phenomenon was later found to be the center of lift shifting backwards during the approach and breach of Mach 1.
TimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 10, posted (14 years 3 months 1 week 1 hour ago) and read 12401 times:
The venerable DC-9 has a tendency toward 'mach-tuck" also. On the inboard side of the F/O's control column, there is an indicator that protrudes from it's housing when mach speeds are approched. As it does the column is pulled back to a nose up position. This prevents overspeeding the aircraft. As I see it, (and I'm not an engineer) the center of lift moves aft at higher speeds and could travel right off the trailing edge of the wing.
The DC-10 has an overspeed indicator too. It starts ticking at you. (Clicking sound from the master warning and annunciator)