Lift or Thrust?

B767Driver

New Member
Here's an interesting topic I'll start. Anytime I have this conversation most people disagree with me, so maybe I'm wrong. I'm not an aero engineer but have a average grasp on aerodynamics. I'm sure to get some insight here.

So, does an aircraft climb because of excess lift or thrust?

I always say an aircraft climbs do to excess thrust(power)...how about you?
 

mtsu_av8er

Well-Known Member
How dared you attempt to make me think this hard in the morning....


On a more serious note, I would say that it depends a bit on how you look at it. Something tells me that this is going to be alot like an "airspeed vs. power" discussion....

So, what would you consider "excess thrust"? Technically speaking, excess thrust would be any thrust in excess of that needed to sustain level flight. If this is your definition of excess thrust, then yes, you do need this in order to climb.

That being said, you do need lift in order to climb. In order for an aircraft to climb, you're going to have to produce more lift than that which is required for sustained flight. The only way to do this is to alter something in the lift equation (we all remember the lift equation...right???). So, in this regard, one could say that lift is required to make the aircraft climb.

Any other bites??
 

RiddlePilot

New Member
I'd venture to say that "excess thrust" has most to do with climb capability. More specifically, angle of climb. "Excess power" relates to rate of climb.

I'd go more in depth, but I just woke up. *rubs eyes*
 

EatSleepFly

Well-Known Member
[ QUOTE ]
I always say an aircraft climbs do to excess thrust(power)...how about you?

[/ QUOTE ]

I agree.

You need excess thrust before you can produce the lift required for a sustained climb. I don't even know if there is a such thing as "excess lift" in this context.

For example:

You are cruising along in level flight with less than full power. You want to climb an additional 2000 feet higher, so without adjusting power, you simply increase pitch/AOA. Sure, you'll increase lift and get some climb, but not for too long. Eventually the wing is going to stall and your weight/drag is going to be greater than your lift/thrust...


Same scenario, only now you set climb power as you increase the pitch. You're using "excess thrust" to enable a sustained climb. Eventually the same thing will happen- you will no longer be able to sustain a climb. But this will happen a lot later in this scenario than it did in the first one.

In a steady-state climb, the sum of the upward forces (lift/thrust) is greater than the downward forces (weight/drag). You can't acheive that without excess thrust.
 

SteveC

Really?
Staff member
Excess thrust.

Wolfgang Langweische offers just about the best explanation I've seen in his book Stick and Rudder. Don't have it handy, and I'd probably butcher it if I tried to paraphrase....
 

carlos

Well-Known Member
From the FAA's Pilot's Handbook of Aeronautical Knowledge, Chapter 1, comes the following (the bolding is mine):[ QUOTE ]
As speed increases, drag increases, until a point is reached where drag again equals thrust, and the airplane will continue in steady flight at a higher speed. As another example, if power is applied while in level flight, and a climb attitude is established, the force of lift would increase during the time back elevator pressure is applied; but after a steady-state climb is established, the force of lift would be approximately equal to the force of weight. The airplane does not climb because lift is greater than in level flight, but because thrust is greater than drag, and because a component of thrust is developed which acts upward, perpendicular to the flightpath.

[/ QUOTE ] If that thrust component were kept from acting upward, by holding or trimming the nose down, you would get additional speed rather than altitude. Or, you can get additional altitude by exchanging airspeed for altitude; that is, hold or trim the nose up to establish a climb at a slower airspeed. It's your choice whether to use your current or additional thrust to climb or to go faster.
 

mtsu_av8er

Well-Known Member
Man, just push the black thingy in some, and pull the wheel thingy back some, and don't let the horn thingy come on.....
 

B767Driver

New Member
[ QUOTE ]

That being said, you do need lift in order to climb. In order for an aircraft to climb, you're going to have to produce more lift than that which is required for sustained flight. The only way to do this is to alter something in the lift equation (we all remember the lift equation...right???). So, in this regard, one could say that lift is required to make the aircraft climb.

Any other bites??

[/ QUOTE ]


I disagree. In a steady state wings level climb ( a 1g maneuver) you need the same amount of effective lift to keep the aircraft bouyant as you did in level flight (constant altitude). In a climb, the lift vector was reoriented (deflected rearward ) adding drag (induced) and total lift (perpendicular to the relative wind) was increased, but effective lift (vector opposite to weight) remains the same as in constant altitude flight.

My contention is that, to climb, you need only reorient the lift vector using the elevators...not necessarily increase lift.

However to climb, you do need extra thrust to overcome the increased drag of the deflected lift vector plus drag.

A look at the basic angle of climb formula states that Angle of Climb = thrust - drag/weight. Rate of climb = Pavailable - Prequired/Weight X 33,000.

When I have a conversation with another pilot concerning what makes an airplane climb, 90% will tell me that an airplane climbs because of lift. I like to think that an airplane is "bouyant" because lift overcomes weight due to gravity but climbs because thrust is greater than drag.

I believe this is accurate, but I have so many pilots tell me that lift makes an aircraft climb that I'm beginning to wonder.
 

SteveC

Really?
Staff member
[ QUOTE ]
Man, just push the black thingy in some....

[/ QUOTE ]
Is that the engine volume control? Push in, engine gets louder?
 

JAM

New Member
Everyone knows that lift makes an airplane fly. And sunshine creates lift. That's why so few planes are flying when the weather is crappy. Sheesh! This is pvt pilot stuff guys!
 

mtsu_av8er

Well-Known Member
[ QUOTE ]

I believe this is accurate, but I have so many pilots tell me that lift makes an aircraft climb that I'm beginning to wonder.

[/ QUOTE ]

Thank you for the correction regarding thrust required in a climb. I'll cross-check some references, but that does sound familiar.

I don't think that anybody is really wrong...yet. Pilot602 kind of said it right when he said both.

My challenge to your argument is that when the pilot reorients the lift vector, he does so by changing the angle of attack. When the angle of attack is changed (in this case, increased), the coefficient of lift is also increased (provided that the critical angle of attack is not exceeded). Once again, our lift equation will prove that anytime you increase the angle of attack with ALL OTHER THINGS being equal, we will have an increase in lift.

Now, of course, we will also have an increase in drag....but that's a seperate discussion....
 

B767Driver

New Member
My challenge to your argument is that when the pilot reorients the lift vector, he does so by changing the angle of attack. When the angle of attack is changed (in this case, increased), the coefficient of lift is also increased (provided that the critical angle of attack is not exceeded). Once again, our lift equation will prove that anytime you increase the angle of attack with ALL OTHER THINGS being equal, we will have an increase in lift.

Now, of course, we will also have an increase in drag....but that's a seperate discussion....

[/ QUOTE ]


This gets a little over my pay grade, however, I believe you increase total lift but effective lift remains the same. Someone else may be able to comment for you regarding this.
 

Minuteman

“Dongola”
Excess Thrust causes an airmobile to climb? OMG OMG!!1! Gliders can't climb!

I'm sure you know that's not true ... any lift in excess of what's needed to maintain an altitude will cause the plane to climb. Whether its thrust or thermals, energy is being added to "the system." Most of that energy is either going towards potential (altitude) or kinetic (speed). Wings just happen to help the airplane convert kinetic energy into potential energy.

How about hot air balloons? There's no thrust, but there's certainly an excess of lift that causes the craft to climb.
 

EatSleepFly

Well-Known Member
[ QUOTE ]
How about hot air balloons? There's no thrust, but there's certainly an excess of lift that causes the craft to climb.


[/ QUOTE ]

Uh, thats not exactly the same kind of lift. Thats hot air rising, simple as that. No airfoil involved.
 

Minuteman

“Dongola”
[ QUOTE ]
Uh, thats not exactly the same kind of lift. Thats hot air rising, simple as that. No airfoil involved

[/ QUOTE ]

OK, true, true
... but its still excess lift that results from a pressure differential.
 

EatSleepFly

Well-Known Member
I suppose.


Thats comparing apples to oranges though. The intent of the discussion was toward powered aircraft. Though I could be mistaken...
 

E_Dawg

Moderator
I thought gliders climb because they enter air that is rising faster then the gliders are sinking; no excess lift involved.

Anyway everyone knows the real reason airplanes climb is $$$
 

B767Driver

New Member
[ QUOTE ]
Excess Thrust causes an airmobile to climb? OMG OMG!!1! Gliders can't climb!

I'm sure you know that's not true ... any lift in excess of what's needed to maintain an altitude will cause the plane to climb. Whether its thrust or thermals, energy is being added to "the system." Most of that energy is either going towards potential (altitude) or kinetic (speed). Wings just happen to help the airplane convert kinetic energy into potential energy.

How about hot air balloons? There's no thrust, but there's certainly an excess of lift that causes the craft to climb.

[/ QUOTE ]


Definitely, increasing lift will cause an aircraft to climb. This statement reinforces the assertion that a sustained power climb is due to excess thrust/power.

Load Factor = Lift/Weight. In a sustained climb the load factor is 1.0 (or very close to it considering other effects negligible). This means that lift equals weight and there is not extra lift to "climb" the airplane. If lift was greater than weight throughout the climb then we would feel and uncomfortable sensation throughout the climb similar to steep turns when alot of extra lift is being produced.

Obviously, the impulse required to reorient the lift vector and change the angle of attack requires a brief introduction of lift and stabilizes to a point where lift again equals weight. So, to enable a climb, thrust must overcome the force of drag.
 

Eagle

New Member
[ QUOTE ]
Everyone knows that lift makes an airplane fly. And sunshine creates lift.

[/ QUOTE ]

No,
Money makes airplanes fly.
 
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