Would a plane climb better if its engines stayed level?

[bozon]

Planes generally have a lift to drag ratio greater that 1. As long as that is the case, the engine is better used to offset drag than contributing directly to lifting the plane by pointing the jet downwards. This is why planes with anvery low thrust / weight ratio can fly at all.

If you incease engine power, speed will increase till the drag is againt equal to thrust and the climb rate incease too ( lets say we fly at maximal angle of attack to keep it a constat). But as speed increase, total drag increase till L/D ratio is smaller that one. At that point, diverting the engine thrust so part of it directly contribute to lifting the plane may start to pay off. Planes normally do not fly at that regime, so it is better to align the engine with the airflow.

[NatCigg]

I climb/descent calculations, thrust angle is calculated and thrust angle against gravity actually helps the efficiency side of the calculation when doing a minimum-fuel climb/cruise/descent profile.  Not much, but its there.  No I can't regurgitate the formula since it was 25 years ago, but we spent a week or two in aero engineering back at USAFA on the calculations involved in climb/cruise/descent and various other efficiency factors in aircraft design.  Bottom line, a climbing aircraft with the engines angled along the wing chord (or very close to it) is more efficient in small part due to some of the thrust angled down against gravity.

so if i may.  the md80 is angled upward to be in better position because of airflow over the wing (wing chord?) and it is noted a additional "upwards boost" is achieved from downward vector thrust? 

Or does wing chord have a angle with respect to the "angle" the wing is mounted?

[icepac]

Engine alignment is a trade-off between cruise efficiency and pitch changes encountered by changes in thrust.

[BuckShot]

Pivoting engines AND a conveyor belt takeoff, now we're talking.

[eagl]

Phew, for a second you had me worried they were going to expect me to do that kinda math in the near future!

USAF UPT students get to see/work the equations, but in a session lasting an hour or two.  Just familiarization to "prove" that a min-fuel profile in a jet involves a full power climb to a pre-calculated optimum cruise altitude, a max range cruise, followed by an idle descent.

In the T-6 the min-fuel profile is a bit different due to differences between props and jets, partly because an idle descent results in a ton of prop drag.

[eagl]

so if i may.  the md80 is angled upward to be in better position because of airflow over the wing (wing chord?) and it is noted a additional "upwards boost" is achieved from downward vector thrust? 

Or does wing chord have a angle with respect to the "angle" the wing is mounted?

If the engines are angled up, it could be to zero out the thrust angle in cruise.  Or it could be to reduce the horizontal stab / elevator load during cruise which would decrease induced drag from the horiz stab and elevator.

And yes wing chord determines wing angle of incidence.  Wing and tail incidence must balance out nose-down pitching moment from the wing, and it may be adjusted one way or another relative to fuselage, tail, or engines, to optimize climb, cruise, or takeoff/landing performance.  Tradeoffs everywhere.

[Bizman]

I don't know anything, and I mean anything, about aerodynamics. But I do know something about being snappy, or drawing attention to details...

So: What kind of a climb are we discussing? VTOL planes that can climb relatively fast by turning their engines' thrust towards the ground.

The title makes me think of F1 cars where they use wing type surfaces to keep the tyres, i.e. the parts that create movement, on the track at an optimal grip. In planes there's no need for a ground connection, on the contrary, but it makes sense to try to push the plane to the direction where you want to go.

Another thing that comes to mind is the water jets where there's no flying surfaces whatsoever. All directions are created by adjusting the thrust angle.

[Serenity]

USAF UPT students get to see/work the equations, but in a session lasting an hour or two.  Just familiarization to "prove" that a min-fuel profile in a jet involves a full power climb to a pre-calculated optimum cruise altitude, a max range cruise, followed by an idle descent.

In the T-6 the min-fuel profile is a bit different due to differences between props and jets, partly because an idle descent results in a ton of prop drag.

The differences between the Air Force and Navy still astound me lol. When they told us the bingo profile (full power climb, idle descent as you say) they literally said "just press the 'i believe' button" and that was all there was to it, no one ever hesitated or questioned it lol.

[DaveBB]

Interesting responses.  So the consensus is that an aircraft will climb better with the engines aligned with the airstream, even though the thrust is diminished in the X-axis and slightly increased in the Y-axis.

[Serenity]

Interesting responses.  So the consensus is that an aircraft will climb better with the engines aligned with the airstream, even though the thrust is diminished in the X-axis and slightly increased in the Y-axis.

The thing is, you're thinking of the X and Y axes as being in relation to the horizon, but (if I understand aero) they should be relative to the airflow.

[Vulcan]

What about if...



...it was on a conveyor belt?

[Zimme83]

It depends on what color the plane has.

[FLS]

Interesting responses.  So the consensus is that an aircraft will climb better with the engines aligned with the airstream, even though the thrust is diminished in the X-axis and slightly increased in the Y-axis.

You want to maximize climb rate. Thrust is fixed. Your option is minimize drag. The thrust to drag ratio determines the optimal climb angle.

[rabbidrabbit]

What about if...



...it was on a conveyor belt?

I think you are on to something here.  The two factors combined would help take off immensely.

[cav58d]

I wouldn't want to do V1 cuts or any single engine work for that matter withthe proposed design.