Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Kurfürst on May 11, 2005, 05:59:12 AM
-
'Climb is not dependant on lift.'
I have just read that. First I thought I misread it.
Is it true ?
-
Think of it otherwise , how do you climb without power ?
-
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.
-
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.
-
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.
-
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)
-
lift is a factor
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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 ;)
-
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.
-
Originally posted by Nashwan
If a plane climbs better at a particular speed, it will also accelerate better at that speed..
Unproven claim, no more.
I ignore them because I am not going by theoretical models, but test results.
No, you are doing the exact opposite. You came up with a questionable, and very much simplified theoretical model of your own, and want to enforce it over real life flight test, which are the things you cannot show to back up your theoretical model.
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..
Basically you just connect two lines (climbmax, climb0), which will give a linear curve. It immidiately shows how flawed your idea is, as the factors effecting accelerations, namely, drag and propellor effiency, are NOT linear function, therefore neither could be the acceleration curve.
Stripped of the rhetorics, you basically make the point that climb = acceleration. That`s simply silly.
No, climb is no more dependant on lift than level flight is, that's why acceleration and climb are directly proportional..
Quite a few people pointed out for you the connection between lift, wing area and excess power. You ignore those, and repeat your own theory. Repeating things don`t make things true, it`s just a Goebbelsian method.
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.
Most if not all dynamic functions of an aeroplane are related to excess thrust, however excess thrust is different for climbs, dives, level flights and accelerations. One of the core mistakes you make is hypothesizing that excess thrust is always the same, wheter it`s level flight or climb.
(The 262 had another problem, of course, in that you couldn't throttle up as quickly as a piston fighter).
Not to kidnap the thread, but that`s why 262s run at constant, near max throttle - jets fuel economy is different from piston engines, giving about the same range. It was a problem during takeoff, but quite irrevelant except that longer runways were needed.
No, AoA does not increase in climb (it does when pitching up into the climb, but not when settled in to the climb)
AoA constantly changes with climb. The air gets thinner, Nashwan.
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.
Now that you have repeated that claim for the 100th time, you should move on proving it, too. How about flight tests that show this supposed working mechanism ?
Good climbers are NOT neccesary good accelerators, or speedy, Nashwan. Or why is that I have British instructions to pilots that tels about the poor acceleration of the Spitfire V at +16lbs at low speeds? It says exactly the opposite what you claim. Show us something that tells the Spit had exceptional acceleration, Nashwan - after all it all revolves around your claim that it was better than the FW because of it`s higher ROC. I can find dozens of such sources for the 190, but none for the Spit. Even GWShaws calculations showed the opposite of what you claim.
-
I belive HoHun stated that there is an absolute link between ROC and acceleration, just like Nashwan said.
I was never quite sure about it myself, because parasite drag will eventually influence acceleration at higher speed bands more than the induced drag, but alas, I could be wrong there.
But seriously, if you increase wingloading of the same airframe and have the same power, acceleration will be less, and same with ROC. That is absolutely safe, and you can call me SUSAN if I'm wrong there.
Or Charlotte maybe
:D
-
Hi guys,
I haven't read through all of this, but I think the contradiction you perceive is only apparent and you're not that far apart after all :-)
The thing to remember is that acceleration and climb rate are proportional only as long as you keep the comparison speed constant. That means if you compare published climb figures, they only tell you about acceleration at that speed.
For propeller fighters, best climb speed is usually fairly low, so "low-speed" acceleration can be deducted pretty reliably from climb rate. For a jet fighter like the Me 262, the best climb speed is fairly high, so low-speed acceleration is only losely related to climb rate.
The thing about the Spitfire V (+16 lbs/sqin) vs. Fw 190A-5 comparison is that in real life, acceleration doesn't happen at a constant speed ;-)
Without looking it up, the Spitfire V, a fairly powerful, reasonably light aircraft, might well outaccelerate the Fw 190A-5 at a certain (low) altitude.
However, the result of course is that both aircraft get faster, and at increasing speed the acceleration drops off - and for the Spitfire V with its slower top speed, it falls off more quickly. At some point, both become equal, and then the Fw 190 outraces the Sptifire from there up to its top speed.
I'd say this shows that comparisons have to be done for the entire envelope, not just for a single point, to allow tactically useful conclusions. Flying an aircraft in the part of its envelope where it excels is part of the game, and I think the aces of both sides did just that, leaving us with contradictory reports on what aircraft outperformed which :-)
Kurfürst, it would be interesting to have a look at the statement regarding the Spitfire V's poor acceleration. Maybe this was caused by engineering issues or control concerns - it's stuff like that makes aircraft discussions so complex at times :-)
(Is it the Air Ministry memorandum on the use of +16 lbs/sqin perhaps? I think they mentioned the topic of acceleration, too.)
Generally, I'd tend to agree with Nashwan that the Spitfire V (+16 lbs/sqin) should accelerate well at low altitude - at least as long as we keep it near its climb speed.
An experienced Fw 190 pilot of course would strive to keep his fighter fast, and not accelerate on engine power alone but always put down the nose a bit initially. That might leave everyone with the impression that the Fw 190 acceleration is superior simply by refusing to play in the Spitfire's area of superiority :-)
Regards,
Henning (HoHun)
-
I haven't read through all of this, but I think the contradiction you perceive is only apparent and you're not that far apart after all :-)
I don't know about that ;)
The reason for this argument is some acceleration tests carried out by others in IL2.
They found the Spitfire VIII to accelerate better up to 450 km/h (iirc), the 190 A5 better abouve that speed (tests at sea level).
I said that sounds about right, as the Spit VIII had a better climb rate than the A5, and therefore should have better low speed acceleration, but the A5 had a higher speed, and therefore better high speed acceleration.
Isegrim challenged that, saying the Spit had a higher climb rate by virtue of it's low wingloading, and that you couldn't equate climb rate and acceleration.
My argument is that at any particular speed and altitude, climb rate and acceleration are proportionate, and that the better climbing plane at a particular speed and altitude will also accelerate better at that speed and altitude.
The whole thing is getting sidetracked now into theoretical discussions on wingloading etc, but my point is that the theory is already incorporated into the test results, and that if one plane outclimbs another, both at the same speed and altitude, then that plane will also out accelerate the other at that speed and altitude.
ie it's safe to assume that the Spit VIII, 4600ft/min at about 175 mph at sea level, is going to out accelerate the 190, about 3800 ft/min at 175 mph at sea level, when both are doing 175 mph at sea level. (And equally, the A5, 350 mph at sea level, is going to out accelerate the Spit VIII, 330 mph at sea level, at higher speeds at sea level)
-
Originally posted by straffo
Think of it otherwise , how do you climb without power ?
(http://soaring.aerobatics.ws/SOARING/images/ls6_soaring_388x343.gif)
-
Hmm, in the Il-2 sim, the Spit IX/VIII manage to outdive/dive with the whole 109G series, which I think even good old Nashwan would agree that to be wrong. So how much it means that the theory is incorporated into the sim flight test, well...
To accelerate better, the Spit needs more excess thrust to than the FW.
It do it by having more total thrust, brute force approach. But it doesnt, 1680 HP vs. 1800PS, even w/o the ENotleistung, which is listed as 2100 PS..
So if doesnt have more total thrust, it should have less total drag, the other factor. trouble is that the Spit is also slower at SL, and in fact almost any low-medium altitude.
One can say that the Spit had low drag at low speeds, but it quickly increased at high speeds. But Nashwan theory is also that those .89 MAch numbers are due to the Spits thin, low-drag high speed wings, at least if I recall correctly... hmm.
So in brief I cannot see what makes the Spit accelerate better. It doesn`t have more total thrust, it doesn`t have lower drag, thus it cannot have more excess thrust. Moreover, the Spit develops it`s best climb at lower speeds than the FW 190, thus the greater ROC is achieved where the drag factor is lower. One cannot ignore the fact it`s peak climb is achieved at lower speeds.
And note that we are talking about 170mph-odd speeds here. NOT 300mph area, which the sim tests showed as the crossline...
Let me just add that in Il-2 the LF Mk IX is way much faster than it should be, easily doing 680-690 above it`s rated altitude. Which might as well tell the whole story : it has too little drag modelled.
HoHun,
Is it the Air Ministry memorandum on the use of +16 lbs/sqin perhaps? I think they mentioned the topic of acceleration, too.)
Yep, the Aug 1942 one. They mention at one paragraph for Spit V pilots (+16) to avoid lower cruise speeds specifically because of the poor acceleration of the Spitfire at low airspeeds. I dont have it with me at the moment, but I think many of you already have it. Nashwan could post it for us, for example. :D :p
That`s the major concern with NashwanHops theory. It`s exactly contrary to all factual sources like flight tests, instructions etc.
-
I wonder why these discussions allways turn to an another plane x vs plane y stuff?
gripen
-
I know I was a glider pilot sometime ago ... before the kids :( :(
Originally posted by Holden McGroin
(http://soaring.aerobatics.ws/SOARING/images/ls6_soaring_388x343.gif)
-
Hi again,
Thanks for the additional explantion, I think I understand the topic a bit better now :-)
With regard to Il-2:
I'm with Nashwan on the validity of the conclusion climb rate->acceleration at a fixed speed, provided the simulation physics are consistent :-)
(If the individual aircraft models are inaccurate as suggested by Kurfürst, that wouldn't affect the conclusion as long as we consider only the game, not historic reality.)
Nashwan's comment on the relative speeds seem reasonable - if you're interested, I could try and graph relative acceleration for a set of assumptions about both planes' performance.
I think I can solve the excess power issue: It's not total excess thrust that counts, it's specific excess thrust. In other words, it's excess thrust divided by aircraft mass - I'm sure the Spitfire variant in question is some 500 kg lighter than the Fw 190, so it gets comparable low-speed performance out of lower total thrust.
(As Hitech pointed out, lift is not an issue in a climb. Weight certainly is, thus the use of specific excess thrust.)
And as Kurfürst pointed out, at higher speeds total power becomes the decisive factor - that's the region where the Fw 190 gains the advantage. As the Fw 190 has higher total thrust at similar drag, there's a point where the excess thrust is so much greater that it gains the lead in spite of the mass disadvantage.
>They mention at one paragraph for Spit V pilots (+16) to avoid lower cruise speeds specifically because of the poor acceleration of the Spitfire at low airspeeds.
Ah, yes, that's the one. I'd say it's meant more to emphasize to lack of total energy when intercepted by an enemy who is already at full combat speed. A similar warning probably would have been appropriate for any WW2 fighter cruising at maximum endurance settings, so in my opinion this memorandum wasn't really written with a head-to-head comparison in mind.
(By the way, I believe the Spitfire's famous high-speed dive capability was not due to low drag, but due to good controllability. Exceeding the speed at which the aircraft was controllable was the usual reason for "graveyard dives" in WW2 era aircraft, including the early jets - even the clean Me 262 with its swept wing. In fact, low drag augmented the danger as it became easier to exceed the critical speed!)
Regards,
Henning (HoHun)
-
Originally posted by gripen
I wonder why these discussions allways turn to an another plane x vs plane y stuff?
gripen
The participants I think :)
If I never saw another thread comparing Spits and 109s, it would be too soon.
Dan/CorkyJr
-
I would like to point out that Hitech has already posted a perfectly correct response… Aircraft climb with their engines not their wings! Climb angle depends on specific excess thrust and climb rate on specific excess power. The lift only influences the speed at which it all happens. Hitech’s car climbing a hill analogy is good. Also, gliders don’t climb in the same sense, they soar. Soaring is usually achieved by flying through a mass of air that is ascending faster than the glider is descending, that’s why it gains altitude.
Hope that helps…
Badboy
-
Imagine a race between a Spit IX and a 190, starting on the runway. I'll pretty much bet that the Spitfire will be airborne before, and then some distance ahead. (it needs a shorter runway). A little later the 190 starts to gain, and will eventually overtake.
In a test with Faber's aircraft, and that was not the fastest 190, A Spitfire w. Griffon, the 190, and a Typhoon, all opened up from cruising speed.
From the text alone (it was Quill who flew the Spit) the 190 actually seems to have either taken the lead, or maybe it was at the front. The Spitfire actually outran both, - but it was the Griffon one, - a mk XII or something.
Anyway, HoHun, as I suspected sorted this pretty well out.
One thing to add to this sentence:
"And as Kurfürst pointed out, at higher speeds total power becomes the decisive factor - that's the region where the Fw 190 gains the advantage. As the Fw 190 has higher total thrust at similar drag, there's a point where the excess thrust is so much greater that it gains the lead in spite of the mass disadvantage."
Yes, yes, because at high speeds, induced drag is no longer a big factor. Induced drag = LIFT induced drag.
-
Originally posted by Angus
Imagine a race between a Spit IX and a 190, starting on the runway. I'll pretty much bet that the Spitfire will be airborne before, and then some distance ahead.
OTOH, Eric Brown, the RAE tried this 'runway race', and all found the Spit and 190 need equally long distance for the takeoff run. No imagination stuff, it just happened that way.
-
Really??
Which Spit? Griffon maybe?
I've seen some dozens of RL takeoffs, and they go up phenominally fast. 190 I have only seen on video though.
Bear in mind that the MkV with a belly full of fuel could hop off in some 150 metres.
-
Originally posted by Kurfürst
OTOH, Eric Brown, the RAE tried this 'runway race', and all found the Spit and 190 need equally long distance for the takeoff run. No imagination stuff, it just happened that way.
Lets see some data for the distance required to clear the 50' altitude. Please say which model of the a/c.
-
not sure, but i dont think induced drag exists in ground effect
-
Spitfire Mk.IX-400ER - the one with winglets - was kick bellybutton in dog fights
-
Both accel and climb are purely about PsubS, excess power. The only influence lift has on either is the induced drag, and the change in induced drag as the aircraft accelerates.
The equations are even similar:
Accel(fps) = xThrust(lbs) / Slugs (weight(lbs)/32.2)
Climb(fpm) = 33000/weight(lbs) * xHP
(By definition 1 HP lifts one lb 33,000 ft in one minute. That is where the 33,000 comes from)
Note that one equation is in xHp and the other in xThrust, so you will have to convert between units to solve them. But the end result is that climb and accel are both purely PsubS. Whoever has the best climb rate at any fixed speed will have the best accel at the same fixed speed, and vice versa.
But as HoHun has pointed out the situation is dynamic, not static. As the aircraft accelerates the induced drag decreases, pressure drag increases and P% changes. All of those factors are to the Fw 190A's advantage in a drag race from say 150 mph IAS vs a Spitfire V. The Spitfire's drag curves will cross about 160 mph, the Fw's about 180 mph or so. So while the Spitfire's total drag will start to increase about 160 mph, the Fw's will continue decreasing to about 180 mph. The Fw will retain the advantage of lower total drag all the way to vMax.
Even more important is P%, the Fw 190A appears to have had mediocre P% at climb speeds. When I have calculated it previously it tends to come out around 73-75%, compared to 80-82% for Spitfires, while both probably max at about 85% at high speeds. So as the Fw 190 accelerates its P% goes up, which translates into more excess power and better acceleration.
There is really no contradiction between a Spitfire V being able to outclimb a Fw 190A at climb speeds, and the Fw 190A being able to out accelerate the Spitfire V over time. The Spitfire V would have an initial advantage, but that would swing further and further in the Fw 190's favor as speed increased.
Greg Shaw
-
Originally posted by HoHun
Nashwan's comment on the relative speeds seem reasonable - if you're interested, I could try and graph relative acceleration for a set of assumptions about both planes' performance.
If the offer's still open, I'd like to see the graph.
Isegrim/Kurfurst still doesn't accept that climb and acceleration are proportional at any particular speed/altitude, and I think the graph would help clarify.
(It was a rather inaccurate graph of mine along the same lines, with hypothetical data, and the comment "The left colum shows climb rate, but could equally show acceleration, because climb rate and acceleration at any particular speed are directly proportional." that sparked the discussion in the first place)
-
Nashwan, don't waste your time, this guy has absolutely no idea what he is talking about. Page after page of gobbledygook.
-
.....And a special appearance by the friendly neighborhood forum four eyes :aok
-
climb is dependent on "excess power"
excess power is the difference between available power and the power required to keep the airplane flying level.
that varies with airspeed, because drag also varies with airspeed.
there's an airspeed where you get the lowest drag, and that means you spend the least amount of power from your engine to maintain level flight, which means you have the most power to climb. you get best rate of climb at that airspeed.
(http://www.aeromuseum.org/Articles/Dec04/AeroDynamicsImages/TotalDragVsJet&Piston.gif)
now what happens at different airspeeds?
as you increase airspeed, parasite drag increases(simply put more friction between air and the airplane because more air molecules get in the way at high speeds) . At the same time, induced drag (the drag that accompanies any wing that produces lift), decreases with airspeed.
As you lower the airpseed, the exact opposite happens. More power is needed just to keep the airplane flying, because you are now flying slow, the wing has to develop more lift (hence you have to increase the AOA), and induced drag increases.(hey, your lift vector is now pointing sort of up AND backwards!). Also, induced drag is not entirely dependednt on AOA. A wing designed to produde a lot of lift will also produce a high downwash, effectively simulating a wing at high AOA.
see here for explanations
http://www.grc.nasa.gov/WWW/K-12/airplane/induced.html
-
Originally posted by Nashwan
Isegrim/Kurfurst still doesn't accept that climb and acceleration are proportional at any particular speed/altitude, and I think the graph would help clarify.
That`s like saying Nashwan still doesn`t accept the Holocaust did happened. It`s a strawman arguement from Nashwan, the like we got used to from him. Strawman arguements and manipulating others comments is the thing you know it is a Nashwan Post.
Personally, I do not need Nashwan to put words into my mouth. Yet, he does that on both forums.
Ie. his claims there about my position :
"Isegrim posted a thread on the AH board questioning whether climb and accelerated are proportional, as I claimed."
He is lying there, as I asked in my first post :
" 'Climb is not dependant on lift.'
I have just read that. First I thought I misread it.
Is it true ? "
That`s something completely different. I am getting bored with the tricks Nashwan uses in every discussion.
What Nashwan is playing on both boards in selectively qouting peole and switching his and distorts his opponents position.
Originally Nashwan claimed two things :
a, that climb is not dependant on lift.
This was proven wrong as we all agreed that lift DOES depend on lift, as lift effects the excess power. So Nashwan was wrong.
b, Nashwan claimed the Spitfire should outaccelerate the FW 190.
This was again proven wrong by GWshaw.
(Nashwan qouted Shaw at ubi, but he did it selectively. He cut off the part in which gwshaw made it clear that the 190 will outaccelerate the Spit at most airpseeds except near-climbing speeds. Nashwan cut off that part of that qoute, as it proved his claim wrong, and represented it in it`s incomplete form).
"...But as HoHun has pointed out the situation is dynamic, not static. As the aircraft accelerates the induced drag decreases, pressure drag increases and P% changes. All of those factors are to the Fw 190A's advantage in a drag race from say 150 mph IAS vs a Spitfire V. The Spitfire's drag curves will cross about 160 mph, the Fw's about 180 mph or so. So while the Spitfire's total drag will start to increase about 160 mph, the Fw's will continue decreasing to about 180 mph. The Fw will retain the advantage of lower total drag all the way to vMax.
Even more important is P%, the Fw 190A appears to have had mediocre P% at climb speeds. When I have calculated it previously it tends to come out around 73-75%, compared to 80-82% for Spitfires, while both probably max at about 85% at high speeds. So as the Fw 190 accelerates its P% goes up, which translates into more excess power and better acceleration.
There is really no contradiction between a Spitfire V being able to outclimb a Fw 190A at climb speeds, and the Fw 190A being able to out accelerate the Spitfire V over time. The Spitfire V would have an initial advantage, but that would swing further and further in the Fw 190's favor as speed increased.
So in the end Nashwan was wrong in both of his claims. Now he puts up an partisanfight, and puts words into my mouth I did not say.
Because he does that repeatedly, let me clarify my position :
a, Climb is also dependant on lift, lift being a factor that determines remaining excess power on different aircrafts.
b, Nashwan was wrong and unable to support his claim that the Spit would be able to outaccelerate the FW 190 to as high airspeed as 300mph.
I have to ask Nashwan this : You still don`t accept that climb is also dependant on lift ?
-
Funked, I've had quite a bit of prior experience of Isegrim/Kurfurst on quite a few boards, so I know what to expect. (Physics isn't his strong point, which is obvious not just from this topic but his previous claim that when net thrust (inc acceleration due to gravity) and drag are equal, a plane will be stationary, rather than maintaining whatever speed it is at)
He is lying there, as I asked in my first post :
" 'Climb is not dependant on lift.'
I have just read that. First I thought I misread it.
Is it true ? "
That`s something completely different. I am getting bored with the tricks Nashwan uses in every discussion.
What Nashwan is playing on both boards in selectively qouting peole and switching his and distorts his opponents position.
No Isegrim that's what you first asked here, which isn't the gist of the argument on the UBI boards.
You're first post there was:
Originally posted by hop2002:
The left colum shows climb rate, but could equally show acceleration, because climb rate and acceleration at any particular speed are directly proportional.
Simply, the better climbing plane accelerates faster at climb speed, the faster plane accelerates faster at high speed.
---------------------------------------------------
That`s absolute nonsense, made up by Hop who`s newest aganda seems to be to propagate that his beloved Spitfire does everything, in this case, acceleration than any other plane... a claim completely unsupported by any factual data.
Now the claimed proportional relation between climb speed and acceleration... completely silly. It seems Hop just doesn`t get climb is dependent on LIFT by a large margin. A simply example, make the Spitfire a biplane. It has now twice the wing area with massively higher rate of climb because of the lift area that doubled... would acceleration also double? Of course not, why would it, there is only extra drag and weight on the plane...
Look at actual examples, the Fiat Cr 42s were not known to be particularly fast, but with their biplane design, they easily matched the climb rate of the early Spits/109s even with much weaker engines.
That was on the 10th May. Today you went back and edited it to remove the first paragraph (the straw man attack)
You started this argument by claiming that increasing the lift would increase climb rate and reduce acceleration, and all the comments on this thread have said the opposite.
Originally Nashwan claimed two things :
a, that climb is not dependant on lift.
No, that's not what I claimed originally.
Here was my first post, that drew the response from you above:
Pingu, Oldman, and myself tested the Bf-109G-6 Late, FW190A-8 and Spitfire VIII today. More will come from those tests but we did some acceleration (right from standstill) and found the 109 accelerated best from the start, with the FW190 in close second, then the VIII gains and overtakes...with the 109 close behind and the FW190 in the dust. Eventually the 190 passed us in a level speed run....so it does appear that its acceleration is behind that of the Spitfire and 109...more testing required.
--------------------------------------------------
I don't see much wrong with that, apart from the Fw190 doing well from standstill (although even that's possible. You were on the ground to begin with? If so, it eliminates induced drag, which would be worst of all on the 190)
Around climb speed (150 - 200 mph) the 109 and Spit should be doing much better than the 190, the 190 should begin to gain an advantage as the speed gets higher.
Here's a simple graph to illustrate the point:
(http://www.onpoi.net/ah/pics/users/282_1093216393_rocspeedspit190.gif)
(It's not supposed to be accurate, just illustrate the general principle. The drop in climb/acceleration with speed is not linear, but not that far off either)
The left colum shows climb rate, but could equally show acceleration, because climb rate and acceleration at any particular speed are directly proportional.
Simply, the better climbing plane accelerates faster at climb speed, the faster plane accelerates faster at high speed. Somewhere the points cross, and that depends on both the climb rate advantage and the speed advantage (of course, if the better climbing plane is also faster, the points don't cross, and it accelerates faster at all speeds (above climb speed anyway).
Note that all this is altitude dependant, as both climb rate and speed vary with altitude, so will acceleration. For example, the Spitfire IX climbs better than the 190 at almost (all?) altitudes, but is slower at most. However, at some alts the Spit is both faster and better climbing, so you need to work out figures for any particular altitude.
That was my original claim.
The comment about climb not being dependant on lift was later on, in the following context:
Originally posted by Kurfurst:
It seems Hop just doesn`t get climb is dependent on LIFT by a large margin.
-----------------------------------------------------
Climb is not dependant on lift.
Well, no more than level flight is.
Lift causes induced drag, and that has an effect on excess thrust, but the effect is exactly the same in climb or level flight.
In a normal climb, lift = weight, exactly the same as in level flight.
Planes climb because they increase their attitude (point the nose up), not because lift is pushing them up.
That's my actual position, not what you are trying to present.
This was proven wrong as we all agreed that lift DOES depend on lift, as lift effects the excess power. So Nashwan was wrong.
That's exactly what I said in the first place, although it seems your grasp of physics doesn't allow you to understand the argument.
b, Nashwan claimed the Spitfire should outaccelerate the FW 190.
b, Nashwan claimed the Spitfire should outaccelerate the FW 190.
This was again proven wrong by GWshaw.
I was talking about the Spitfire LF IX, gwshaw about the Spit V, but we both agreeded on the principle that the Spitfire should accelerate better at low speed, the 190 better at high speed.
It should be obvious even to you that the Spitfire LF IX will do better against the 190, and shift the speed at which the 190 wins higher.
Originally posted by Kurfurst:
Because he does that repeatedly, let me clarify my position :
a, Climb is also dependant on lift, lift being a factor that determines remaining excess power on different aircrafts.
Only that was not your initial claim, and was mine.
Your initial claim:
Originally posted by Kurfurst:
It seems Hop just doesn`t get climb is dependent on LIFT by a large margin. A simply example, make the Spitfire a biplane. It has now twice the wing area with massively higher rate of climb because of the lift area that doubled... would acceleration also double? Of course not, why would it, there is only extra drag and weight on the plane...
My initial claim:
The left colum shows climb rate, but could equally show acceleration, because climb rate and acceleration at any particular speed are directly proportional.
My second claim in clarification:
Climb is not dependant on lift.
Well, no more than level flight is.
Lift causes induced drag, and that has an effect on excess thrust, but the effect is exactly the same in climb or level flight.
For anyone who wants to see the original argument:
http://forums.ubi.com/eve/ubb.x/a/tpc/f/63110913/m/7701003813/p/2
Isegrim's first response is at the bottom of page 3, my response to that p 4.
-
uHUMMM, Izzy/Barbi/Curfew....:
"That`s like saying Nashwan still doesn`t accept the Holocaust did happened. It`s a strawman arguement from Nashwan, the like we got used to from him. Strawman arguements and manipulating others comments is the thing you know it is a Nashwan Post. "
I know this from yourself, in the form of selective data and clipped quotes. Anyway, enough on that.
Ok, here is a straw for the both of you:
a) Climb does depend on lift as well as power
b) With enough power (thrust) no lift other is needed. Like a rocket!
c) Acceleration at a given speed holds hands with climb at the same speed, exactly like HoHun put it.
So what's all the squabble!
-
Angus:
a) Climb does depend on lift as well as power
Would normaly be considered false.
There have been discusion that climb is dependent on drag, And discussions that changing wing sizes can change a planes drag profile. But for any given wieght that a plane flys. The lift is always the same in steady state flight. Making the wing larger or smaller does not change the fact that in level or steady state climb the wing on any plane of the same weight is producing exactly the same amout of lift (no mater how that wing is shaped).
Therefore you can not increase LIFT and make a plane climb better. You can only decrease drag or increase thrust to make a plane climb better.
HiTech
-
Well, maybe it should be noted that required lift (of the wing) reduce when the steady climb angle increase. The extreme case is a straight steady climb vertically when wing does produce no lift at all. That of course means that there is more thrust available than the weight of the plane.
gripen
-
Oh, HiTech:
"Therefore you can not increase LIFT and make a plane climb better. You can only decrease drag or increase thrust to make a plane climb better. "
Ehmm, I'm not getting this, for certainly, you can decrease lift for the same given power, same airframe, by i.e. clipping the wings if you see what I mean.
So, power + wings = climb rate right?
Wings do not lift alone of course, you always need thrust, and with enough thrust, you do not need another source to create lift.
Or am I lost here?
-
Angus,
The required lift (of the wing) in the steady climb depends on the weight of the plane and the angle of the climb. Decreasing the wing area means just that same lift must be produced with less area (assuming that the weight of the plane stays constant).
And yes, you are lost here :)
gripen
-
in 1986, Robert R. Harris climbed to an absolute altitude record of 14,938 m using no power at all after a low altitude tow plane release.
The motion of an aircraft is based upon the imbalance of four vectors. Lift, weight, thrust and drag. Change one and the other three seek equalibrium. The only one we have direct control over is thrust, but Robert Harris climed to over nine miles high with no engine power at all. So the requirement for thrust is somewhat negotiable.
-
Holden McGroin,
Read Badboy's post above; basicly a sailplane is sinking all the time (relative to the air around the plane) but the air around the plane might be rising (due to thermal or some other reason) faster than the sink rate of the plane ie the plane gains altitude.
gripen
-
There are times in a sailpanes flight where it is not sinking. It is climbing when pulling up in a loop for instance. It expended potential energy of altitude in order to gain the kinetic energy for the pull up, and the net after the manuver is a sink, however it climbs during the pull up.
I realise it is somewhat a semantic argument, but if one defines lift as the force necesary to overcome the pull of gravity, and my back feels that when I lift the couch, then all flying vehicles climb solely dependant on lift, whether that lift is aerodynamic lift given by forward speed and differential pressure on an airfoil or the chemical thrust of Jupiter engines on a Saturn V.
-
More importantly, what about induced drag in ground effect?
-
Holden McGroin,
Well, making a loop with a sailplane is not a steady climbing condition as discussed in this thread.
The lift discussed in this thread means lift generated by the airframe (wing etc.).
gripen
-
I'd bet Mr. Harris could add on a mile or two more, given just the right unstable tropical airmass
-
Originally posted by Holden McGroin
There are times in a sailpanes flight where it is not sinking. It is climbing when pulling up in a loop for instance. It expended potential energy of altitude in order to gain the kinetic energy for the pull up, and the net after the manuver is a sink, however it climbs during the pull up.
There is an important distinction to be made though, when you pull the nose up above the aircraft's maximum climb angle, it is referred to as a zoom climb. That's when you gain altitude at the expense of speed, it is not sustainable, and there is a net loss in energy in contrast to a steady state climb in which energy is being gained.
Hope that helps...
Badboy
-
Originally posted by Angus
Or am I lost here?
Yep, but keep reading and asking the right questions, HiTech HoHun and Gripen are posting good information.
Badboy
-
Aha.
From Gripen:
"Angus,
The required lift (of the wing) in the steady climb depends on the weight of the plane and the angle of the climb. Decreasing the wing area means just that same lift must be produced with less area (assuming that the weight of the plane stays constant). "
So, to produce enough lift to keep that smaller winged aircraft airborne with the same given power, you need a higher A.o.A., which gives you a higher induced drag, while the parasite drag from a smaller wing is less, right.
So it should also work the other way, increase the span or area a little, you have a lower wingloading and can therefor fly at lower A.o.A. with therefor less induced drag, but more parasite drag.
So, am I then wrong to say that by altering the wing you DO affect the lift outcome at the same power at a given speed?
-
So, am I then wrong to say that by altering the wing you DO affect the lift outcome at the same power at a given speed?
Yes you are wrong,if you are refering to steady state flight.
(i.e. level or steady state climb)
The lift will not be change at all. The AOA required to generate the lift will change. Also the max. amout of lift availible at any given speed will also change. And the amount of drag will also change hence changing climb rate. But the key point is, it is the drag that is changing the climb rate, not the lift.
But now life gets a little more complicated decreasing wing area will typicly reduce drag at higher speeds and increase it at slower speeds. So now at slower speeds the plane will climb worse, and at higher speeds the plane will climb better. But the total amout of lift for steady state flight at any speeds will not have changed at all.
HiTech
-
Aha!
"Also the max. amout of lift availible at any given speed will also change."
It's me putting the wrong words up I guess, this is actually what I was trying to promote. Availability of lift it is.
So...
Thanks ;)
-
Originally posted by Badboy
There is an important distinction to be made though, when you pull the nose up above the aircraft's maximum climb angle, it is referred to as a zoom climb. That's when you gain altitude at the expense of speed, it is not sustainable, and there is a net loss in energy in contrast to a steady state climb in which energy is being gained.
Hope that helps...
Badboy
Slight edit... when you gain altitude at the expense of fuel, it is not sustainable, and there is a net loss in energy in contrast to a steady state climb in which energy is being gained.
Same same...
Kinetic energy from potential or from chemical causes lift. Lift allows climb.
It's just how you look at it, I look at it from a lift POV.
-
Well, imagine completely still air. You haul a glider up high and release it. It just depends on wings and weigh how far it will go right?
-
Originally posted by Holden McGroin
Slight edit... when you gain altitude at the expense of fuel, it is not sustainable, and there is a net loss in energy in contrast to a steady state climb in which energy is being gained.
A zoom climb can only be sustained for a very short time and a relatively small altitude increase before the speed bleeds off. However, a steady state climb can be sustained until the aircraft reaches its ceiling, and that can be repeated until the fuel runs out... That's as sustainable as it gets in aviation.
Badboy
-
Okay, I understand completely the forces required to fly. Not a problem...
Like I say this is largely a semantic argument, but to say that lift is not a factor in climb is erroneous.
An airplane that has no lift does not fly. Without flight, an airplane will not climb.
Therefore climb is dependant on lift, as opposed to the title of this thread.
And Badboy, the only difference is the amont of energy you have in reserve for climbing.
-
Getting to the thread headline, "Climb is not dependant on lift", one can play the words a wee bit.
This refers to WW2. Now, no WW2 aircraft flown by a pilot could climb without lift, if you see what I mean :D
Cut them wings off and the kite won't fly.
But HiTech got my head spinning a bit, but it was all about the availabiliy of lift. So, I must say thanks again for clearing up some definitions HiTech :aok , but basically I wasn't that lost at all in the base theory.
(I think :confused: )
-
Getting to the thread headline, "Climb is not dependant on lift", one can play the words a wee bit.
This refers to WW2. Now, no WW2 aircraft flown by a pilot could climb without lift, if you see what I mean :D
Cut them wings off and the kite won't fly.
But HiTech got my head spinning a bit, but it was all about the availabiliy of lift. So, I must say thanks again for clearing up some definitions HiTech :aok , but basically I wasn't that lost at all in the base theory.
(I think :confused: )