Retry: Could the Spitfire turn with the Zero?

[NightFighter]

WW2 Aircraft Performance (wwiiaircraftperformance.com) - Has primary source data in droves for the Spitfire Mk.V and a good bit on the A6M2 and A6M5.

Spitfire Va:

Flaps Up - Gear Up around 76 mph (Indicated Air Speed)

Flaps Down Gear Down around 69 mph (Indicated)

Wing Loading : 25.3 lbs/ft^2

A6M2:

Kinda all over the place with regards to in air testing - Navy says 74mph clean, 61 mph dirty (Indicated) but Air Force has 65mph clean and 59ph dirty (Indicated). Most wartime testing is pretty inaccurate so take these with a grain of salt.

Wing Loading : 22.77 lbs/ft^2 [5500 Gross Weight (Average between several tests and MGW) / 241.5 ft^2 (Wing Area)

 

Wing loading is definetly lower for the A6M2 so instantaneous turn is well in its favor.

 

 

I think the A6M2 definetely has the edge in terms of low speed and aerodynamic turning, however its low weight and engine power did reduce its ability to retain energy. A Spitfire on the tail of an A6M2, IMO, will not be able to stay on its tail, and if the Spitfire is caught at a low enough speed I think it is in a decisively dangeous position. However, medium to high speeds is obviously where the two switch.

Edited October 10, 2023 by NightFighter

[ZachariasX]

9 hours ago, GrungyMonkey said:

But the A6M5 had smaller wings and was over 500 pounds heavier.

True that. But it is also about the amout of lift the wing profile can generate. Without going into XFOIL, the wing of the Spit and the Zero differ quiet a lot. The Zero has as in apporximation a ClarkY profile that gives you a max lift coefficient of slightly more than ~1.5. The Spit has a very thin wing that has isome 20% less max lift.

 

TL, DR: Even in a SpitV accepting a Zero's fight is still really asking for it. For the early Hurricane, the slow speed contest its almost the only hope it has, and worse, it is only very marginally an even fight given the poor power to weight ratio. With a Merlin XX high up where the Zero runs out of breath, tables turn. Numbers don't lie.

 

Let's have a look at documented stall speeds (note, from here I take over the thumb values, as all aircraft differ some kg in weight anyway):

SpitV: wing area 22.5 m2, weight 3000 kg. Stall speed 120 km/h, -> Clmax 1.92 (as Gav mentiond in your quote)

Zero5: wing area 22.44 m2, weight 2800 kg, Stall speed 105 km/h, -> Clmax 2.27

With the book values, both lift values are idiotic for given profiles, and Gav is quite right that these figures are fantastic as they are fishy. Point is that it is tremendously difficult measuring accurate stall speeds for various reasons and those figures are usually way lower than what they actually are or they reflect in aircraft speedometers.

As mentioned in theory, the ClarkY can reach a Clmax of about 1.5. the Spitfire wing has in theory about a Clmax of ~1.3. In reality, as the profiles are never perfect and the wing of finite span, so it is even less.

For an all up configuration, taking the mentioned lift coefficients, simple physics tell us the following:

SpitV: wing area 22.5 m2, weight 3000 kg. Clmax 1.3 -> Stall speed 146 km/h (91 mph)

Zero5: wing area 22.44 m2, weight 2800 kg, Clmax 1.5 -> Stall speed 131 km/h (82 mph)

All down configuration surely lowers the speeds, but they are not a configuration you'd have in regular combat. That the Spitfire gets iffy below 90 mph in clean configuration, that I know because I've flown it. Actually, you pop the flaps at 110 mph and take her from there.

In case of the Mustang, (25.3 m2, 3950 kg, assumed Clmax 1.4) we get a clean stall at Flying the Mustang shows a clean stall of 152 km/h / 95 mph or 82 knots.

Here, you can see how exact you you can predict those speeds:

In the video, they have the stall just above 80 kt. (Keep in mind that the TF-51 flown is probably a bit lighter then those 3950 kg, hence the wing has even less lift than the Clmax of 1.4!) It is of note that for instance this speed difference reflects very well in the approach speeds that in the Mustang are about 20 mph higher then even in the Spit9.

Long story short, please take those stated stall speeds in the manuals with a grain of salt, they have more contex than what meets the eye.

Looking at the Hurricane, with an assumed same ClarkY wing  and Clmax of 1.5 (for consistencys sake), wing area of 23.92 m2 and a weight of 3000 kg you get a stall speed of 132 km/h (82 mph / 71 kt)

Hence the Hurrcicane very much matches the Zero. But is it equal in a fight?

The Zero can, according to @NightFighter's posted reports loop from 160 mph level. This is almost outrageous for such kind of aircraft and makes the Zero a VERY special proposition. I vehemently doubt that such is possible with aslug as the Hurricane. You wouldn't even try that in a Spitfire if you didn't have to. The aerobatic capabilities certainly outclass the Hurricane significantly. The advantage of power to weight ratio of the A6m5 over the Hurricane is significant, (all best cases: ~2.35 kg/hp vs 2.8 kg/hp). The Spitfire V gets near 2.14 kg/hp and is indeed a hard match, even though slow speed agency is below that of the Zero.

 

Getting slow comes with issues of several kinds, one is that drag increases to unhealthy levels. To picture this I can refer you to one of Gregs videos, as I think he does a great job in walking the audience through a non-trivial matters:

It is of note though that also he at times gets things wrong, same as everyone. But on average he can read his source material (unlike many others) and it shows in his videos. Long story short in the video, we see that on both ends of the speed range, drag rises exponentially. This is why there is such a thing as "coffin corner" for heavy aircraft, like the Thunderbolt: a speed below where even full emergency power will not be enough to accellerate you again and downwards it goes.

Now, how much the drag rises on the slow side is mostly determined by the span loading when comparing similarish aircraft. This means, that when you turn and you pull, the threshold speed from where you will see the airspeed drop varies as well as how much it drops by g pulled. The more pull, the pore power you need to offset this added drag. Flying the Mustang, this is very much felt vs when flying the Spit. In the Mustang, you have to be faster then 200 mph indicated for not starting to bleed too much speed during light aerobatic maneuvers. The Spit9 on the other hand will not let you feel that down to some 150 mph, it just pulls on the turn. I have no doubts that the Zero would EASILY pull away from the Spit in a slow speed turn, same as the Spit pulls away from the Mustang in such a situation.

This means that just minute differences in span loading will have a significant effect on how much you can maneuver at slower speeds. One aircraft will easily maintain the speed while the other, with a similar engine, will just hit the brakes and fall out of the sky. THIS is for instance the reason why the Sopwith Camel is considerably superior to the Dr.I, because three wings srews up your span loading. You can even go forther and make a narrower wing like in the Simens Schuckert D.IV to decrease your span loading and you get an aircraft that in terms of performance is head and shoulders over the competition, even with a similar engine and similarish weight. Span loading makes the difference, much more so than mere wing loading when comparing similarish aircraft.

The less energy you bleed in flying slow, the better your cards are in a one circle turn fight.

 

Now, the issue of turning circe and instantaneous maneuverability.

11 hours ago, GrungyMonkey said:

There's no way this is true, right? Speed lets you rate better, but it shouldn't improve turning circle significantly. Unless you meant that the faster aircraft turns worse than the slower one?

As you point out, this does not affect diameter of the minimum turn your aircraft can fly theoretically, but this is largely irrelevant in the real world, as all that matters to you is the state of the enemy aircraft and what he can do from there.

The turning circle is determined by your flight speed and the accelleration you give inside your turn. For all aircraft, this works the same and the structural limits of the aircraft decide the higher end of the speed, meaning the amount of g's you're capable of pulling without losing the wing define your tightest circle. Your turn is just defined by F=m*v2/r. As we have learned, flying in circles works as an airbrake and you lose speed doing so, some aircraft faster than others.

At some point the airspeed will fall below the speed required to pull max. g and then your max lift coefficient along with the wing area will decide how tight you can pull. So, it is not just your wing loading. Span loading will decide how much you slam the brakes. The aircraft with the lower span loading will leave the other aircraft in the dust during just that maneuver and pull away from it. Conversely, if slowing down is what you want to do (in the one circle fight to force the overshoot), the lower span loading will make it easier for picking up speed again, once you reached a favorabale position, given equal engien power.

Weight does in no way really impact your ability to control your aircraft. What determines how "lively" your aircraft reacts (and encourages you to go close quarters in a real aircraft) to control is deretmined by CoG and thus how aerodynamically stable the aircraft is. The Spit is very nippy on the elevators due to being a tail heavy design. The Mustang requires more force to pull the nose up. However if you fill its rear tank, things change and it becomes very delicate on the elevator, but not in a way you want to take it into a fight. Weight does not matter here if you have the power for it, see an F-22.

Theoretical minima and maxima don't matter if you can't reach that state. Like a game of poker, the better cards help for sure, but since the players are not all showing their cards right after receiveing them, the better card sometimes don't win. In air combat, it is the same. You want to force your opponent in a fight where your cards are better, you NEVER accept a fight on his terms. If he has in principle the smaller circle, you rate him if that is what you are good at. If you have the smaller circle, you force the one circle fight. He plays along in either case, he's dead. Any plane is better then the other when flown to its strengt, where you have the better cards.

[ZachariasX]

Just to add some more deatil, I looked up Eric Browns account of the Zero and he states the landing speed to be 81 mph on an US-fitted ASI.

Given above I calculated 82 mph for clean stall, having that speed for landing all down makes sense. Even tough the math is done somewhat over the thumb, it works out.

[GrungyMonkey]

15 hours ago, Jason_Williams said:

Guys,

Please be careful with the political talk even if discussing history. Gets people worked up.

Jason

Noted.