Climb is not dependant on lift.

[Kurfürst]

'Climb is not dependant on lift.'

I have just read that. First I thought I misread it.

Is it true ?

[straffo]

Think of it otherwise , how do you climb without power ?

[MANDO]

Originally posted by Kurfürst
'Climb is not dependant on lift.'
 

Well, I would say that the less the lift, the more the needed power from engine to keep the same climb rate.

Lets consider the 0 fpm climb rate (level flifght), two different versions of the same plane, version B with larger wings and less fuel than version A to keep the very same weight and power/weight ratio. Which one will need to apply more power to keep just 0 fpm without losing alt? Well, for the same AOA, pane A will need more power, if plane A increases the AOA things may change. This increase of AOA will increase the lift, but also the drag, but the B version with larger wings has also more drag and bigger flat area. If the excess of drag due larger wings of the B version is equivalent to the excess of drag due higher AOA of the A version, then both planes would require the same power to keep the level flight at minimum possible speed, one due its larger wings and the other due a higher AOA.

[Angus]

With enough thrust one does not need lift, - look at a rocket!

But if you have a surface that creates lift, given an A.o.A., then the power needed to create the lift is less.

The penalty is induced drag of course.

[Tails]

A Bf-109G10 (or atleast AH2's) is a good example of climb more from engine power than lift.

A C-130 is a good example of climb more from lift than engine power (just watch one take off to see what I mean).

So it goes both ways.

[Nashwan]

This is an argument Kurfurst and I are having on the Ubi boards.

My position is that climb and acceleration are directly related at any speed, and that the better climbing plane at a particular speed will also accelerate better at that speed.

Again my position is that that's because climb and acceleration are both functions of excess thrust.

Kurfurst's position is that climb is dependant on lift, so has no direct correlation to acceleration.

I've tried to point out to him that lift is virtually the same in a normal climb as it is in level flight, therefore lift is as important to acceleration as it is to climb, but Kurfurst believes lift is much higher during the climb.

What he's just posted on the Ubi boards:

You think 'excess thrust' is exactly the same value in both climbs and level flights at the same speeds, but it isn`t.

Excess thrust is the total thrust, minus the drag of the airplane at a given angle of attack and airspeed.

And the angle of attack is totally different in level flight and in climb, so is the drag of the airplane : drag is much higher higher in climbs, therefore the excess thrust is much lower than in level flight.

Here`s where higher lift/lower wingloading aircraft has the advantage. The larger wing can generate the same lift at much lower angle of attack than the aircraft with the smaller wing -> less drag in climbs -> higher excess thrust available.

IMO that's wrong, angle of attack is relative to path, and is the same in climb and level flight (under normal conditions), therefore lift is the same, and drag is the same (within reason, it's my understanding that lift and AoA decrease the steeper the climb, but not significantly at normal WW2 prop fighter climb angles)

[BUG_EAF322]

lift is a factor

[hitech]

Lift does not effect climb rate, only power. Basicly in any normal climb  the lift generated = the weight of the air plane (btw is only close the amout of lift goes down the steaper you climb).

Adding more lift makes the plane loop.

It is the power that is pulling you up the hill. Think of lift like the tires of your car. They holds the car up just like lift does. But it is the engine that pulles it up the hill.


HiTech

[Kurfürst]

Originally posted by Angus
With enough thrust one does not need lift, - look at a rocket!

But if you have a surface that creates lift, given an A.o.A., then the power needed to create the lift is less.

The penalty is induced drag of course.

Exactly my point. More lift generated by the wings -> more excess thrust available to climb.

It`s easy to see in practice, planes with lower wingloading are generally good climbers, but at the same time slower and more sluggish to accelerate. There is no way to have both.

[Nashwan]

But if you have a surface that creates lift, given an A.o.A., then the power needed to create the lift is less.

The penalty is induced drag of course.

That's true, but it's equally true for acceleration in level flight.

You need enough lift to counteract the weight of the plane, whether in climb or level flight.

In other words, the effects of wingloading are the same in acceleration and level flight.

Exactly my point. More lift generated by the wings -> more excess thrust available to climb.

Or accelerate.

Your point only works if more lift is required in the climb than level flight at the same speed, and it isn't.

Basically the amount of lift is the same for level flight and climb, therefore doesn't change the relationship between climb and acceleration.

[Angus]

Emm, from Straffo
"Think of it otherwise , how do you climb without power ?"

In a glider

And from Kurfurst:

"It`s easy to see in practice, planes with lower wingloading are generally good climbers, but at the same time slower and more sluggish to accelerate. There is no way to have both"

I belive HoHun was analysing this, and his claim was, as far as I remember, that lift was parallel to acceleration.

What I know, is that a higher wingloading gives you a higher A.o.A. to maintain flight at low speed.
So, the higher wingloaded aircraft will accelerate slower from stall speed due to more induced drag.
But as induced drag falls with more speed, parasite drag comes instead, and there the smaller wing creates less.
It's two curves, - V- shaped basically. So they cross one time or another.

[Kurfürst]

In climb higher power is required to generate the same lift, as the drag of airplane is also higher in climb. This favours the plane with the lower wingloading in climb, as it can create the same lift with less AoA and less drag. You can argue that until eternity, but if you look at actual drag coefficient tables for plane types, you can see its always higher for climb than level flight.

Just for those who dont understand what is behind this... Nashwan came up with another Magic Theory why Spitfire does X better than Y other plane. As usual.

In this case, his claim is that the Spit accelerates better in level flight than the FW 190A, because it climbs better, as, at least according to him ROC has 'direct correlation to acceleration'. I wonder what Crumpp has to add on this, but me myself haven`t seen any flight test that would indicate it. Eric Brown said the takeoff rolls of the 190/Spit was similiar, but the 190s take off speed is much higher, which means it accelerated faster on the ground, arriving at greater speed on the same distance.

Naswhan ignores drag factors between airframes that effect excess thrust, he ignores how wing- and liftloading effects the neccesary angle of attack and drag during climbs.. The whole arguement is about repeating that 'rate of climb direct correlation to acceleration', and that 'Climb is not dependant on lift.' Both are very questionable, if not outright silly. Dozens of planes can be cited that climbed well but had only avarage acceleration, having large wings, fuselages that created a lot more drag than smaller airframes.

Take, for example, the Me 262. It climbed at around 21 m/sec, but it`s low speed acceleration was notoriously poor... It`s supposed to be a magnificent, if we follow Nashwan`s ideas.

The facts are quite simple. A heavier plane with a smaller wing needs to generate more lift, and needs to maintain higher AoA. Lift (CL) increases more or less linerarly with AoA, but drag increase is non linear. Thus the heavier, small winged plane`s drag increased more greatly when it climbs, which explains why it has less excess thrust to climb and lower climb rate.

If a plane has a lighter body, it needs to generate less lift, and also with large wings, lower AoA is enough. It`s easy to see why it has more excess thrust and higher rate of climb. Unfortunately the same phenomenon does not stand true for level flights, as drag coefficients for level flight and climb are DIFFERENT. So is excess thrust and the ability to accelerate.

Besides Nashwan was unable to back up his theory which he applied for practical purposes with anything... he just wishes to be that way. But you cant have everything in a single design. All fighters were compromises between flight qualities. Tell that to a fan.

[Angus]

Basically you are both right

This:
"In this case, his claim is that the Spit accelerates better in level flight than the FW 190A"

It probably does from takeoff to some certain speed where the lines cross. Wouldn't bet on it though, for the 190A has a ton of power.
Given the same power, the Spitfire would almost definately accelerate better untill the lines cross.
Bear in mind that it already shows, for the Spitfire needs a much shorter runway to take off!

Now, take a mind trip. Clip the Spitfires wings. It will give you a higher wingloading with less frontal area, - less parasite drag. It will be faster as a total (which was the case), but more draggy at lower speeds (which was the case)
Now, take another thought. Put a heavy load  into it, - say 500 lbs. Wingloading has gone up, but you'll need a higher A.o.A. to maintain flight.

I don't know if you guys fly, but this is very easy to see in a small aircraft. Increase airspeed, and the nose starts coming down.

[Angus]

ooops, pressed reply too quickly.
Anyway, just think this:
Induced drag decreases with airspeed
Parasite drag icreases with airspeed
Total drag is basically the sum of both.

So, at lower speed bands, induced drag has a big effect on airspeed, while at high speed bands it's all about parasite drag.

increasing the weight increases the wingloading, - if you're comparing various weights on the same aircraft, increasing the loading will reduce both total max speed and acceleration. The only benefit from more mass is a quicker return to terra firma

[Nashwan]

In this case, his claim is that the Spit accelerates better in level flight than the FW 190A, because it climbs better, as, at least according to him ROC has 'direct correlation to acceleration'.

At a particular speed.

If a plane climbs better at a particular speed, it will also accelerate better at that speed.

(And the 190 being faster than the Spit at some alts will naturally accelerate better at high speed where it has more excess thrust available)

Naswhan ignores drag factors between airframes that effect excess thrust,

I ignore them because I am not going by theoretical models, but test results.

Basically we know climb rate of a plane at two speeds, best climb rate (typically around 160 - 180 mph) and maximum speed (when climb rate is 0)

If you've got 2 data points from tests, you don't need to work out the drag, lift etc, because it is already part of the results.

It's quite simple, if lift is practically the same in climb and level flight (at a particular speed) then there's no need to work out the theoretical stuff, because we have actual test results (climb rates) to use.

The whole arguement is about repeating that 'rate of climb direct correlation to acceleration', and that 'Climb is not dependant on lift.' Both are very questionable, if not outright silly.

No, climb is no more dependant on lift than level flight is, that's why acceleration and climb are directly proportional.

Both are very questionable, if not outright silly. Dozens of planes can be cited that climbed well but had only avarage acceleration, having large wings, fuselages that created a lot more drag than smaller airframes.

I'm not arguing that wing area has no effect, I'm arguing it has the same effect on climb and level flight, and that climb and accelerations are both functions of excess thrust, and are proportional.

Take, for example, the Me 262. It climbed at around 21 m/sec, but it`s low speed acceleration was notoriously poor... It`s supposed to be a magnificent, if we follow Nashwan`s ideas.

The 262 had a speed of about 280 mph for best climb rate, I think, and yes, at those speeds and higher it would accelerate well.

(The 262 had another problem, of course, in that you couldn't throttle up as quickly as a piston fighter)

The facts are quite simple. A heavier plane with a smaller wing needs to generate more lift, and needs to maintain higher AoA.

Of course it does, but it does so in level flight just as much as in climb.

Lift (CL) increases more or less linerarly with AoA, but drag increase is non linear. Thus the heavier, small winged plane`s drag increased more greatly when it climbs, which explains why it has less excess thrust to climb and lower climb rate.

No, AoA does not increase in climb (it does when pitching up into the climb, but not when settled in to the climb)

Lift does not increase when climbing.

If a plane has a lighter body, it needs to generate less lift, and also with large wings, lower AoA is enough.

Again, true in level flight or climb.

It`s easy to see why it has more excess thrust and higher rate of climb. Unfortunately the same phenomenon does not stand true for level flights, as drag coefficients for level flight and climb are DIFFERENT. So is excess thrust and the ability to accelerate.

No, they're not, not at the same speed.

A plane does not climb by generating excess lift, it climbs by flying up an incline. It's AoA relative to that incline is the same as it is to it's path in level flight, providing the speeds are the same.


Just to reiterate the point, because Iegrim seems to be confusing the issue:

Climb rate and acceleration are directly proportional at any particular speed. The better climbing plane at a particular speed will also accelerate faster at that speed.