Climb is not dependant on lift.

[Kurfürst]

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.

[Angus]

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

[HoHun]

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)

[Nashwan]

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)

[Holden McGroin]

Originally posted by straffo
Think of it otherwise , how do you climb without power ?

[Kurfürst]

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.

That`s the major concern with NashwanHops theory. It`s exactly contrary to all factual sources like flight tests, instructions etc.

[gripen]

I wonder why these discussions allways turn to an another plane x vs plane y stuff?

gripen

[straffo]

I know I was a glider pilot sometime ago ... before the kids  

Originally posted by Holden McGroin

[HoHun]

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)

[Guppy35]

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

[Badboy]

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

[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. (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.

[Kurfürst]

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.

[Angus]

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.

[MiloMorai]

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.