Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Posted (10 years 1 month 3 weeks 5 days 6 hours ago) and read 4411 times:
There have been several posts in this forum which mention that jet aircraft normally fly with a few degrees of Nose Up angle of attack (AOA), in order to maintain level flight.
Recently a member asked about why some airliner's engines are angled downward a few degrees in comparison to the airliner's fuselage centerline (longitudinal axis). It was explained to him that the reason for this was because most jet aircraft fly with a few degrees of "positive deck angle" (nose up pitch), while in level flight, so the downward angled engines are better aligned with the relative airflow while cruising enroute.
My question is ......
Is this photo of a 737-7 a good representation of the nose up pitch angle that jet airliners use (a least the 737), while cruising in level flight? Or is this 737 actually climbing?
I suspect that this 737 is in a slow rate of climb with that angle of attack, however, I also suspect that an airliner's AOA probably increases with higher altitudes in order to maintain level flight because of the thinner air creating less lift. So, I'm not sure if she's climbing or not.
Mb339 From Italy, joined Jun 2001, 238 posts, RR: 3 Reply 1, posted (10 years 1 month 3 weeks 5 days 5 hours ago) and read 4379 times:
I think that the aircraft is in level flight. The "high" angle of attack is caused probably by the low speed of the aircraft.
I assume that plane was flying at minimum clean speed, when the photo was taken.
Normally when these kind of photo are taken both aircraft flies not more than 220/230 knots, so at such speed with no flaps, in order to maintain altitude the plane is forced to increase AOA.
Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Reply 2, posted (10 years 1 month 3 weeks 5 days 3 hours ago) and read 4288 times:
Thanks for your thoughts about this.
I understand what you mean by the need to fly with an increased AOA if you're flying slower than normal cruise speed with no flaps.
One thing that had me thinking that this 737 was still climbing is the fact that it doesn't seem to be that high up with regards to a typical cruise flight level for a medium to long range flight. Based on the type of clouds it's above, which I think are Altocumulus clouds (Mid-Level Clouds - with bases between 6,500 & 20,000 ft), I would say she's only around 26,000 feet (it's hard to tell though).
Then again, if this 737 is only airborne for a photo shoot, or is on an actual flight of a short distance, there wouldn't be a need to climb any higher ...... such as up to FL 390 (39,000 feet) for example.
Mr Spaceman From Canada, joined Mar 2001, 2780 posts, RR: 15 Reply 4, posted (10 years 1 month 3 weeks 3 days 4 hours ago) and read 3989 times:
Thanks for the info about how many degrees of nose up is typical for a 737-800, like the type that you fly.
The 737-700 in the photo above looks to me like it's flying with a nose up deck angle of around 4 degrees, so I guess it is in level flight.
PS, have you flown the Los Angeles (LAX) to Toronto (YYZ) route lately? If I remember correctly, I believe the Flight Number was American Airline's AA 1586 scheduled to arrive at YYZ around 5:00 pm (17:00 hrs).
Positive rate From Australia, joined Sep 2001, 2143 posts, RR: 1 Reply 6, posted (10 years 1 month 3 weeks 2 days 17 hours ago) and read 3864 times:
Yep i'd say that 737 is in level flight. Looks like the altitude is only in the 20,000's though i think you're right, there appears to be some Cirrostratus cloud above the plane which implies it's relatively low.
Musang From United Kingdom, joined Apr 2001, 754 posts, RR: 7 Reply 7, posted (10 years 1 month 3 weeks 9 hours ago) and read 3691 times:
Just a couple of thoughts ref. engine mount angle, another reason is to position the intake ideally for the airflow coming off the wing. 727s (1 and 3) and DC-9 series engines are aimed a few degrees tail down to align them with the down-flowing air.
It would also provide a small amount of nose-down pitching moment to reduce the amount of negative lift the tailplane (horizontal stab.) is required to produce. This is true on the No 2 on the DC-10 and L1011. Indeed a Delta L1011 with a stuck elevator (somewhere in California I recall) once used differential No 2 thrust to aid in pitch control.
I can't explain why the BAC 1-11 engines appear perfectly horizontal, though!
Note also the DC-8-62 and 63 pods which point nose up.
You'd expect a nose-down position if it was simply to compensate for the aircraft's nose up cruise pitch angle, so theres more to it than that!
Regardless of the mounting angle of the pod, the leading edge of the intake is often angled so that when viewed from the side it is vertical or "faces" slightly downwards. This gives the fan a better gulp of air when the aircraft is flying at higher angles of attack, and the feature is taken to the extreme with military fast jets.
Positive rate From Australia, joined Sep 2001, 2143 posts, RR: 1 Reply 8, posted (10 years 1 month 3 weeks ago) and read 3626 times:
How about when the engines are pointing in towards the fuelage(wing mounted engines)?? I have a picture in a book of an Airbus A300 with the engines pointing slightly inwards towards the fuselage. Any idea what that helps with???
Ual747 From , joined Dec 1969, posts, RR: Reply 9, posted (10 years 1 month 2 weeks 4 days 21 hours ago) and read 3491 times:
It helps with the inward flow of air into the intakes. Imagine the fuselage flowing through water. The front of that fuselage will cause the water to flow out and around the fuselage. The toed-in stance of the engines accounts for this and supplies the engine with better airflow.
Eg777er From United Kingdom, joined Feb 2000, 1829 posts, RR: 13 Reply 11, posted (10 years 1 month 2 weeks 4 days 12 hours ago) and read 3422 times:
As a little bit of trivia, when you turn the British Airways First Class seat into a 6' 6" flat bed, it is also a 'level' bed, as it is at a 3 degree slope to compensate for the 3 degree pitch up attitude of the aircraft in flight.
JBirdAV8r From United States of America, joined Jun 2001, 4459 posts, RR: 22 Reply 14, posted (10 years 1 month 1 week 5 days 19 hours ago) and read 3101 times:
Oh, you can get close enough not to use a super-zoom
Most photo chase planes are relatively slow (B-25's seem to be the airplane of choice for most pro photogs, actually). That 73G doesn't seem to have flaps/slats out, either, which would probably be a reason why the AOA is so great. Drop about flaps 5 in there and the deck angle would change considerably, in my opinion