XP72 "superthunderbolt" vs TA152 How would they stack up?

[Kryten]

one thing that always has me frowning when reading aircraft performance stats is there is no mention of how long it takes to reach these max speeds, an aircraft with a lower max may reach its limit faster than an aircraft with a higher max, in fact the only quote of acceleration I have seen is for the Mossie, which stated the mkVI went from a fast cruise to its max in 90 seconds, unfortunatly it did not define "fast cruise" or give any weight reference?
prop efficiency, weight and drag must be critical in this manner, but logically speaking would'nt a twin engined aircraft have ing two props to trasmit the thrust be more efficient than a single prop?
rambling a bit there but you get my drift, top speed figures dont really tell the whole story?

 

[Siegfried]

one thing that always has me frowning when reading aircraft performance stats is there is no mention of how long it takes to reach these max speeds, an aircraft with a lower max may reach its limit faster than an aircraft with a higher max, in fact the only quote of acceleration I have seen is for the Mossie, which stated the mkVI went from a fast cruise to its max in 90 seconds, unfortunatly it did not define "fast cruise" or give any weight reference?
prop efficiency, weight and drag must be critical in this manner, but logically speaking would'nt a twin engined aircraft have ing two props to trasmit the thrust be more efficient than a single prop?
rambling a bit there but you get my drift, top speed figures dont really tell the whole story?

I'll answer you and GregP response to my post in one respone. The FW 190D-9 was fully opperational in November 1944 though some were in use with squadrons around Spetember by november all should have with erhoete leistung ( increased power) obtained by injecting fuel into the eye of the supercharger. These variants also should all have had their supercharger improved for another 100hp at altitude. At the same time by the time they were entering service MW-50 systems were being retrofitted in the field; there was no time to factory fit them. We may not know the numbers but they were virtually all equiped with one of the two systems by start of december and certainly by Han 1945. This means a FW 190D-9 was a 428mph to 432mph aircraft when encountered in combat. It just wouldn't be worh bothering with a D-9 if it were no better than an A-8.

The FW 190D-9 speed at sea level with B4 + MW50 seems equal to that of the P-51 on 100/130 though it lagged slightly against the P-51 on 100/150. A FW 190D-9 with C3 +MW50 seems almost equal. At high altitude the FW 190D9 couldn't compete with the two stage supercharger of the Merlin.

However at between 10000 to 20000ft its seems highly competitive.

Noteworthy is the power to weight ratio, all data wiki.
P-51D 100/130 Empty weight: 7,635 lb (3,465 kg) over 1720hp ie 4.438 lbs per hp.

FW-190D9 B4 + MW50 Empty weight: 3,490 kg (7,694 lb) over 2100hp ie 3.664 lbs per hp

Even the use of 100/150 (which provides 1850 hp?) won't close this weight to power ratio gap.

I am assuming that by the time they meet fuel burn off, ammunition and radio equipment would keep these relative ratios equal.

The FW 190D9 thus would have had a very potent acceleration and climb, especially around 360mph and 10,000-20,000ft.

 

[Shortround6]

Shortround, there is an EASY way to measure combat speed ... read combat reports. The speeds (in IAS) are reported.

I won't get into a research project for someone else at this time (I have one myself that has been running for more than 15 years), but there are plenty of combat reports available to the person who looks for them. Reading about 10 - 15 combat reports for any single type will give the reader a good feel for the combat speed of a particular mount.

I have read the first 2` combat reports for the P-51 at Spitfire performance. Only three reported the speed with a numerical value. This could very well change in the next 20 reports however.

You still are not "measuring" anything. you are collecting reports of speeds used, but it only gives a partial picture of the capabilities of the aircraft as does just quoting a "single" top speed of an aircraft or a single climb speed.
If I read that a pilot was flying at 360mph (indicated) that does not tell me much unless I know the altitude at which he was flying. And I still don't know if he was in a gentile descent or a gentile ascent or banked or both.
Flight test reports are often corrected for pitot head location correction, and further adjusted to reflect standard atmospheric conditions (59 degrees Fahrenheit/15 degrees Celsius and standard pressure) while combat reports are not.

We also don't have a good definition of what "combat speed" even is. Granted it is the speed used in combat but on various aircraft if could depend on power settings ( many pilots did not go to WEP or emergency settings on sighting the enemy, depending on position (height difference-distance) and enemy aircraft type ). It could depend on control response, flying 30-60mph below max level speed could give better aileron response or need less rudder trim?

Please note that I am not trying to say that pilots engaged at max level speeds most of the time. I would be surprised if they did (especially those on the receiving end of a bounce). many aircraft types could vary around 3% from aircraft to aircraft even in the same production run so absolute top speed differences of just a few mph don't mean much but a difference of 10% or more does mean something even if the speed in "combat" is 15-20% lower than max level speed.

out of the extremely small sample that I read the pilot that used 350mph indicated was chasing a 109 up a shallow valley. Actual altitude unknown but probably under 2000ft. 350mph indicated isn't that far off the max speed of of P-51 at that altitude is it?

one of the other reports simply says that it took 10 minutes of "balls out flying" to catch the enemy targets after which he throttle back to a small closing speed. Which is his combat speed? the " balls out flying" it took to get into firing position or the slower speed he used to get better accuracy and not over run the target as he fired?

Another report gives a 5 minute pursuit of the enemy before getting into firing range as the enemy tried to get away by out running them. I may be wrong but I would think that in a 5 minute stern chase (even throwing in a few gentile curves) the P-51s worked up to whatever their max level speed was at that altitude or darn close to it.

One report gives 450mph+ at 2700ft in a downward spiral or just leveling out from the downward spiral. this could very well be an exception. But it does point to the difficulty of using combat reports to "measure" speed. There are too many unknowns or variables.

The max level speed does give a good indication (even if it is not a guarantee) of planes ability to engage or disengage in the horizontal plane or to get into or out of firing position even if it does not accurately describe the speed the plane is doing while in a deflection situation.

 

[GregP]

Siegfried,

The Fw 190D-9 could make 428 to 432 mph at one and only one altitude, if factory fresh and clean witn internal ammunition, just like a P-51D could make 437 mph if factory fresh and clean with internal ammunition. These numbers are, of course, ±4 - 5 mph since no two aircraft were exactly identical. In combat, neither one was likely to get the chance to accelerate from whatever speed they aere flying to maximum and the chances of being at just the correct altitude were almost nil.

You seem to be counting on the maximum specs for combat performance and that almost never happened. If they entered the fight at cruise speed, then the fight happened at about cruise speed ±30-45 mph depending on whether the fight went up, went down, or stayed about level. There weren't many fights where the two protagonists (or more) stayed straight and level and allowed each other to accelerate to max speed before engaging.

You are perfectly free to believe whatever you want, but most combat reports I have read happened well below maximum speeds for the mounts involved.

Putting it another way, say YOU were the fighter pilot and you were over enemy territory. After an aerial encounter with an enemy formation, you find yourself alone and half a mile behind the enemy. Would you go to war emergency pwoer (or whatever the German equivalent was) and give chase while the enemy is descending toward his home airfield that is ringed with flak batteries ... or would you perchance take care of the engine, realize the fight is mostly over, and start looking for your friends to fly home with?

Shortround, some combat reports show a tail chase that goes on for some time ... not many. I'd say the these tail chases I have read happened at low altitude about 50% of the time because WWII aircraft combat was generally a deascending affiar ... until they got to ground level. After that, there's nowhere to go except at ground level. The first one who climbs will likely get shot down when he slows down in the climb. Sure, these things happened, but that type of combat was, by far, the exception rather than the norm.

Most aerial combat reports I have read were over in 30 seconds or less, and once the ambush was over, they broke off or got maybe one more victim before everyone was scattered. That wasn't true all the time, but was a large percentage of the time.

If you look at the top speed curves, all single-stage, single-speed fighters got faster up to the critical altitude and got slower if they went any higher. If the aircraft had a two-speed supercharger or a 2-stage supercharger, therre were two altitudes at which there was a relative maximum speed. The speed went up until the first critical altitude, then dropped until they shifted speeds or went to the next blower stage, and then the speed went up until reaching critical altitude, after which it drops off if going higher.

My point is that there is only one or two altitudes at which any WWII piston fighter went at top speed, and it was un;ikely that a fight would happen exactly there.

My databse shows the P-51D at 437 mph at 25,000 feet. That's one entry. So it was slower at 30,000 feet and definitely slower on the deck. From an actual test flight chart, at sea level, the P-51D was about a 340 - 350 mph. The chart I looked at said 344 mph. The first supercharger stage was maxed out at about 16,400 feet where it could hit about 425 mph. The speed dropped of to about 410 mph at 22,500 feet and built back up to about 437 mph at about 30,000 feet.

Let's say the bomber stream was at 28,000 feet. The P-51D could make about 430 mph at that altitude, but the B-17's were cruising at about 180 - 200 mph and the P-51D escort was cruising at about 250 mph. If they encountered climbing Germans, the fight would be at about 250 - 300 mph. If they encountered German already at the same altitude, the fight would be at 280 - 330 mph. If they encountered Germans who had climbed abd were attacking from an altitude advantage, the fight would be at anywhere from 230 - 420 mph depending on the tactics employed by the attacking Germans.

If the Germans used a dive and zoom tactic, the Mustangs would be trying to climb and would be slow. Usually the Germans would ignore the escort and attack the bombers. That's why some portion of the escorts weer flown 4,000 - 6,000 feet above the bomber stream ... to take on the boom-and-zoom attackers. If the Germans used a dive and continue diving tactic to take a shot and get home, then the Mustangs would go tio high power and dive after the Germans, turning into a high-speed fight, at least on the way down. If the combat got down to ground level, the fight would be back to 300 - 330 mph after the extra energy gained from the dive was used up. I think that because no WWII aircraft could susting maximum speed while pulling 2 - 4 g's in a turn. ALL of them would slow down while maneuvering. There were very few German fighter units who would elect to stay at the Mustang's best altitude and fight in a more or less level planem, expecially if the Mustang escort was more numerous than the German attackers.

My fictional account above comes from listening to WWII fighter pilots ho give talks at the Planes of Fame Museum on a regular basis. Earlier this month we had a talk from two German pilots who flew the Me-262 and the He162. Our featured aircraft was the Heinkel He-162 Volksjagger. We repainted ours and it was looking quite spiffy in its new paint. They described their experiences, the tactics used, and the performance of their aircraft, and were very nice people to talk with.

So while not every encounter would be as described above, I believe a lot of then would be that way becasue the guys who were there and did it back in WWII say it was usually that way. Almost all have respect for their opponents and, in some cases, are friends with them today. Occasionally we get a guy who still hates the enemy, whether it be German or Japanese. We don't usually get any Germans or Japanese who still hate Americans or they would not agree to come give a talk at an American Museum.

 

[davparlr]

Noteworthy is the power to weight ratio, all data wiki.
P-51D 100/130 Empty weight: 7,635 lb (3,465 kg) over 1720hp ie 4.438 lbs per hp.

FW-190D9 B4 + MW50 Empty weight: 3,490 kg (7,694 lb) over 2100hp ie 3.664 lbs per hp

Even the use of 100/150 (which provides 1850 hp?) won't close this weight to power ratio gap.

I am assuming that by the time they meet fuel burn off, ammunition and radio equipment would keep these relative ratios equal.

The FW 190D9 thus would have had a very potent acceleration and climb, especially around 360mph and 10,000-20,000ft.

Although I have used this type of comparison, this is misleading. Aircraft are not like automobiles accelerating from 0-60 mph. They are typically accelerating from a relatively high speed, which in itself absorbs a significant amount of engine hp. The absolute power is not what drives acceleration, rather it is the excess power available. If we take the data you provide, and a sample we can see the difference. Both the P-51D and the Fw-190D-9 is at SL and max equal speed of, say 380 mph. Both planes use all available power to maintain this airspeed, the Mustang using 1720 hp and the D-9 using 2100 hp. There is no excess power available and neither aircraft is capable of accelerating in level flight. Now lets lower the airspeed to 350 mph, now there is excess airspeed. With some calculations, which I hope are close, the Mustang is going to use 1343 hp to maintain airspeed, the D-9 will require 1640 mph. Subtracting this from the power available and comparing the two, the D-9 has 83 hp excess at 350 mph. At 300 mph, this excess increases to 193 hp. accelerating an 8000 lb vehicle with 193 hp is not providing what I would call potent acceleration. Performance of the D-9 does improve with slower airspeed.

I think it can be comfortably said of two aircraft, at the same weight and engine power but with one aerodynamically cleaner than the other, that the cleaner one will use less hp at any given speed and therefore have more excess power and thus faster acceleration. Other variations such as engine performance, weight, and descent rate obviously affect this value.

 

[davparlr]

"Combat speed" is going to lower but there is no real way to measure "combat speed". Any deviation from straight and level flight is going to slow the plane down, even a bank of 5-10 degrees is going to try to cause a gentile turn, the combination of the loss of lift and the drag will slow the plane down.

This comment is not for you Shortround6, but for young future pilots and aerodynamicist gamers and other participants. Lift does not change with angle of bank. It operates perpendicular to the wing. When a pilot banks, the vertical component of lift, the part that fights gravity, decreases. In order to maintain altitude, the pilot must raise the nose, increasing the angle of the wing to the wind. This is called angle of attack or alpha. Increasing angle of attack increases lift which also increases the vertical component and level flight is maintained. This increase of lift produces more drag, called induced drag.

 

[GregP]

Lift does not change with angle of attack?

All my aerodynamics professors go it wrong? Damn ...

 

[Siegfried]

Although I have used this type of comparison, this is misleading. Aircraft are not like automobiles accelerating from 0-60 mph. They are typically accelerating from a relatively high speed, which in itself absorbs a significant amount of engine hp. The absolute power is not what drives acceleration, rather it is the excess power available. If we take the data you provide, and a sample we can see the difference. Both the P-51D and the Fw-190D-9 is at SL and max equal speed of, say 380 mph. Both planes use all available power to maintain this airspeed, the Mustang using 1720 hp and the D-9 using 2100 hp. There is no excess power available and neither aircraft is capable of accelerating in level flight. Now lets lower the airspeed to 350 mph, now there is excess airspeed. With some calculations, which I hope are close, the Mustang is going to use 1343 hp to maintain airspeed, the D-9 will require 1640 mph. Subtracting this from the power available and comparing the two, the D-9 has 83 hp excess at 350 mph. At 300 mph, this excess increases to 193 hp. accelerating an 8000 lb vehicle with 193 hp is not providing what I would call potent acceleration. Performance of the D-9 does improve with slower airspeed.

I think it can be comfortably said of two aircraft, at the same weight and engine power but with one aerodynamically cleaner than the other, that the cleaner one will use less hp at any given speed and therefore have more excess power and thus faster acceleration. Other variations such as engine performance, weight, and descent rate obviously affect this value.

While I agree with your arguments over the relative effects, the point I wanted to get to was that at speeds lower than maxium the aerodynamic advantage of the P-51 in having lower parasitic drag rapidly reduces, with the cube of velocity, if you look at it in terms of excess power. This excess pwer then becomes available for acceleration or sustained high g turning flight.

Furthermore, in turning flight as the aircraft might be pulling as much as a sustained 6g, induced drag rapidly becomes the dominant form of drag. I doubt the P-51 had much advantage if any in having lower induced drag.

Ultimatly if an aircraft has more power it simply overcomes its disadvantage in terms of parasitic drag.

Having said that: it would seem MW-50 systems didn't become all that common till the end of Jan 1945 so most encounters with 100/150 Mustangs wouldn't have gone to the FW 190's advantage in terms of power to weight ratio. It's worth noting that C3 fuel alone (likely rarely if ever used opperationally, though there is the possibillity of it being used on the eastern front) produced the highest speed of 437mph in the FW 190D-9, somewhat more than B4 + MW50.

The limits on overall availabillity of high octane fuels certainly hampered German engine power. A series of alkylation plants to substantialy increase the quality and quantity of C3 fuel had started to come on line in 1943 (the plants design or construction had started in 1940) however the oil bombing campaign of early 1944 disrupted this. It made the Germans change tack and re-engineer their engines to opperate on the lower grade B4 (87 octane) fuel after plans had been made to convert to C3 (96/130). It foced them to reschedule production.

 

[Siegfried]

Increasing angle of attack increases lift which also increases the vertical component and level flight is maintained. This increase of lift produces more drag, called induced drag.

It's worth noting a little appreciated fact. While lift increases approximatly linearly with increase angle of attack drag tends to increase with the square of angle of attack. Hence while a bigger wing has a disadvantage in terms of parasitic drag it will tend to gain in turning flight as induced drag become significant.

Afficianados of the Me 109 often point out that its slats would have added 40% extra lift under turning flight and this would have allowed it to out turn a Spitfire.

When slats open they do not increase the lift or coefficient of lift (hence no snatching when they deploy ) however they do allow an substantially increased angle of attack before stall occurs and it is this where the higher lift comes from. However the lift comes at a disproportionate (square) increase in drag which at some point will overwhelm the drag advantage in weight and parasitic drag of the smaller wing. The aircraft will slow down, loose lift and height etc.

The use of high aspect ratio wings (eg Ta 152H) or possibly elliptical planforms (Spitfire) also increases L/D ratio under high lift conditions. This is the reason the 'high altitude' Ta 152H actually did quite well at low altitude turning flight.

Heinrich Beauvais, a Rechlin test pilot (I believe a Cheif there), claimed that the Me 109 could turn inside a Spitifre, he wanted to meet Eric Brown to argue his point but Brown apparently didn't want to. I suspect Beauvais's technique was to turn in an elliptical path. This to me it would seem would convert the Me 109's kinetic energy into lift thus tempoarily overcomming the the higher induced drag. So long as there was power available to accelerate or climb the aircraft could recover its lost speed. So to me, it believable that an expert pilot might have managed to turn inside a spitfire for a single turn at least though not in a sustained turn.

Erwin Leykauf, LW fighter pilot, 33 victories:
"It was a matter of feel. When one noticed the speed becoming critical - the aircraft vibrated - one had to ease up a bit, then pull back again, so that in plan the best turn would have looked like an egg or a horizontal ellipse rather than a circle. In this way one could out-turn the Spitfire - and I shot down six of them doing it."

 

[GregP]

I wish I had BOTH planes today so I could compare them! Now THAT would be fun, whichever one wins, the other one isn't far behind and is just as big a kick to fly.

 

[davparlr]

Lift does not change with angle of attack?

All my aerodynamics professors go it wrong? Damn ...

I said lift does not change with angle of bank.

 

[davparlr]

While I agree with your arguments over the relative effects, the point I wanted to get to was that at speeds lower than maxium the aerodynamic advantage of the P-51 in having lower parasitic drag rapidly reduces, with the cube of velocity, if you look at it in terms of excess power. This excess pwer then becomes available for acceleration or sustained high g turning flight.

Furthermore, in turning flight as the aircraft might be pulling as much as a sustained 6g, induced drag rapidly becomes the dominant form of drag. I doubt the P-51 had much advantage if any in having lower induced

I have no disagreement with what you have said. However, when aircraft pull three to six "g"s, the induced drag becomes so great that deceleration is fast and engine power, for ww2 aircraft, becomes comparatively small along with their differences. Wing efficiencies are indeed magnified and it would be best if the P-51 avoid this type of combat with high lift aircraft. The Fw-190D-9 and P-51D were voracious opponents and at low to med alt neither type offered significant advantage to the other and engagement circumstance and pilot proficiency were the important factor in victory, as usual.

Ultimatly if an aircraft has more power it simply overcomes its disadvantage in terms of parasitic drag.

Yes

One advantage both the P-51 and P-47 had that is often overlooked is the command of combat energy, certainly in initial engagement. Both aircraft had great speed and high altitude performance, both factors of energy, which allowed the pilot to engage with superior energy. When expertly used, this controls the combat. The P-47 probably exceeds here but had the initial problem of mediocre low altitude performance the P-51 did not have. The only German aircraft I have seen that seemed to have advantage in speed and climb over the P-51 at all altitudes is the Bf-109G-10, I think, and certainly the Bf-109K. These, I believe, were pretty limited hot-rods.

 

[davparlr]

Erwin Leykauf, LW fighter pilot, 33 victories:
"It was a matter of feel. When one noticed the speed becoming critical - the aircraft vibrated - one had to ease up a bit, then pull back again, so that in plan the best turn would have looked like an egg or a horizontal ellipse rather than a circle. In this way one could out-turn the Spitfire - and I shot down six of them doing it."

This one of the many things combat simulators lack. Aircraft communicates to the pilot in many ways including feel and sound. Vibrations, stick forces, g forces, response speeds, sounds, etc. all tell the pilot how things are going and the pilot becomes part of the aircraft, something I have never felt in a simulator.

 

[davparlr]

duplicate post

 

[GregP]

Sorry davparlr. I made an assumption of "anlge of attack" instead of READING the post. I stand corrected.

I hope to not DO that in the future. When I read it I thought, "Where did THAT come from?" and probably read what I was thinking you wrote instead of what you actually wrote.

Mea Culpa.

 

[davparlr]

Sorry davparlr. I made an assumption of "anlge of attack" instead of READING the post. I stand corrected.

I hope to not DO that in the future. When I read it I thought, "Where did THAT come from?" and probably read what I was thinking you wrote instead of what you actually wrote.

Mea Culpa.

no sweat. I often bang on my keyboard before my mind is engaged!

 

[GregP]

By the way davparlr, your location says "Southern California." Where are you located? I'm in Rancho Cucamonga.

Any chance of you making out to Chino some Saturday to see the Planes of Fame Museum? Like to meet you.

 

[Siegfried]

I wish I had BOTH planes today so I could compare them! Now THAT would be fun, whichever one wins, the other one isn't far behind and is just as big a kick to fly.

Despite my high respect for the Me 109 I am inclined to accept that the Spitfire was the bette raircraft. It seems from mid 1942 to early 1945 the Me 109 lagged in power. If the Me 109 had of had the same power as the Spitfire I might have been the better aircraft. However, if you are going to be short of power it is more easily accomodated by an aircraft such as the Spitfire.

 

[jim]

Despite my high respect for the Me 109 I am inclined to accept that the Spitfire was the bette raircraft. It seems from mid 1942 to early 1945 the Me 109 lagged in power. If the Me 109 had of had the same power as the Spitfire I might have been the better aircraft. However, if you are going to be short of power it is more easily accomodated by an aircraft such as the Spitfire.

Mid war 109s suffered from aerodynamic point of view as well. Simply from middle 42 to early 44, 109 received not one significant improvement in any way, engine or airframe or controls.
In WW1 germany also lacked competitive high power engines but still ,by excellent work in airframes and wings , created aircrafts fully equal (if not superior ) to the alleid fighters and pilot friendly (Fokker DVII , DVIII, Siemens DIV) .But in DVII case, it was MvR who had the final word how should be build. In WW2 aircraft programs was a chaos between Udet, Milch, RLM , Goring, aircraft companies, Hitler, political friends etc...Somewhre among them was the General der Jagdflieger but without any important impact.
I dont know if the Spitfire was overall better but certainly had a more orthodox and logical evolution

 

[riacrato]

However, if you are going to be short of power it is more easily accomodated by an aircraft such as the Spitfire.

I don't know how you came to that conclusion: The Spitfire is a larger and (on average) heavier aircraft that, from what I gather, overall produces more drag (mainly lift-induced). With the same power, the Me 109 should always have a higher top speed and better acceleration. Climb can be debated. So unless you change your whole air combat doctrine from what it was historically to a "Japanese" one (probably not a good idea) you end up with an aircraft performing worse under most circumstances.

The reason the Me 109 suffered form late '42 on are many:
- problems of the DB605 not being solved early enough (though I think that point is much overstated)
- an ever increasing focus on production simplification in lieu of performance improvement
- the need to make a high performance "race horse" fighter capable of operating on the rough fields of the eastern front
- the need to combat heavy bombers, thus a task the airframe simply wasn't very suited for

So imo besides the engine problems the airframe simply had no margin for getting heavier or bulkier equipment.