707 Questions

[avialuver33]

I just finished reading #6 in the "Legends of the Air" series by Stewart Wilson. The volume looked at the 707, DC-8, and VC10. There was an interesting chapter regarding QANTAS and their early days with the 707. The chapter mentions a Captain A A E (Bert) Yates, and some proving flights.

I quote, "On a flight from Hong Kong to Tokyo, it was decided to leave the power up in cruise with the altitude lock in, and ignore the Mach number increase. One eventually got used to the Mach warning bell ringing. This was continued until Mach tuck started to become too evident for comfort."

My questions: (I'm not a pilot)

I'm assuming altitude lock keeps the airliner at a certain speed at a certain altitude? If the altitude lock was not engaged, as the Mach number increased, would the airliner climb?

Does Mach tuck mean the airliner's nose pitches down? If so, is Mach tuck predictable, or does it happen suddenly & violently?

[411A]

Ah, the 707, what a nice machine.

On the older models, mach tuck started at about .84 and if the height lock (altitude hold) was engaged, as the speed increased, you could clearly notice the stab trimming nose up. This was expecially noticable on the -138's that Qantas operated.

[Engineer]

Mach Tuck (http://142.26.194.131/aerodynamics1/High-Speed/Page6.html)

Hope it help

[mustafagander]

avialuver33,
Did you like the picture on page 21? :D

[avialuver33]

411A, Engineer, & Mustafagander,

Thanks for the replies. You must get bombarded with questions from us non-pilot types, yet you still take the time to politely answer. You PPRuNe guys are the best.

411A: Thanks---the info helped my understanding of what the text was saying.

Engineer: I put the page on my favorites---thanks

Mustafagander: Yes, I did like the picture of the inverted starboard wing. Would the sophisticated computers on Airbus & newer Boeings allow this type of maneuver?

[Tinstaafl]

I'm assuming altitude lock keeps the airliner at a certain speed at a certain altitude

avialuver

There's an error in your assumption. Altitude lock only maintains the designated altitude, not speed.

When engaged & without any additional automatic speed control devices speed becomes a function of thrust output from the engines.

The speed control is done manually by the pilot setting an appropriate thrust setting with the thrust levers/throttles.