The best 2-engined bomber in 1944-45?

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Still doesn't explain what the swedes would have better spark plugs. Did they make their own? I doubt a western plug is going to fit into German engine...
 
A-26 Invader, Mosquito and Ar-234B to me.
No pure bombers, multipurposes a/c, love them.
 
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Personally my choice for a bomber would always be the Do217 but an outside option would be the Ki67. The Ki67 is fast, well protected, agile and with a strong defence. Its main problem would be a limited payload, but it ticks all the other boxes.
 
As usual, this question is difficult to answer in general. I picked up seven contenders (in alphabetical order) for the comparison below , which were in general operational service during the 1944 to 1945 timeframe, I require them to be deployed operationally by dec. 1944 at the very least to get rid of some pre production or last resort types. Note that I do accept the Ar-234B (which sortied as early as during the Invasion of France, in PR mission and was employed in bombing missions by the turn of 44/45).

PLANES
A-26, US, twin radial air cooled engined
Ar-234B, german, twin axial jet engined
B-18, swedish, twin inverted V-liquid cooled engined
Ki-67, japanese, twin radial air cooled engined
Me-410A, german, twin inverted V-liquid cooled engined
Mosquito B. Mk. XVI, british, twin V-liquid cooled engined
Tu-2S, soviet, twin radial air cooled engined

METHODS
In order to get meaningful results, I herewith follow z-normalization practices, which are applied successfully in descriptive statistics. Normalization is important if You want to get comparative values. My choosen approach is z-normalization, a value between 1.0 (max. possible) and 0.0 (min possible). The extracted figures can be directly compared with each other, they represent relational units.
Note: Imagine You want to compare ceiling (varying between 30000ft and 48000ft) with length (varying between 75ft and 90 ft). The first category not only varies much more than the second but also has much higher absolute figures and would- if You don´t apply any normalization, skew the results in a comparison between both by inertia effects if You enter the field of explorative statistics.

The comparison is split up in successive parts. One count for offensive and another onw for defensive and general aspects. Normalised Counts can be positive (the more speed, the better) or negative (the larger the size the worse it is for survivability).

I. OFFENSIVE COUNT.
For offensive counts, I selected -owing to limited database aviable- only two categories, bombload and range. Both counts are positive (the higher the bombload and the larger the range, the better it is) and direct, that is any payload between 0 and max is possible to be flown by th aircraft (thy don´t require a min. bombload to lift off in simple words). I am aware that fuselage mounted offensive gunnery is not mentioned here but it´s inclusion -albeit possible- would require a different explorative approach to be statistically valid. Please keep this in mind, some planes benefit by the exclusion of f.e. fuselage mounted fwd directed guns (Mossie and Ar-234), some are not having received full credit for extensive fwd guns (A-26 and Me-410A).
The first data is for payload in lbs, the following table is sorted by rank with the normalised values beeing printed on top of each column. These figures are relational, which is correct, as You have probably noticed that the normalized figure (=0.25) for payload of the Me-410A (=2,204lbs) is exactly one quarter as large as the max. figure in this comparison (1.0 for the Tu-2s´s 8,816 lbs max bombload).




Appearently, the Tu-2´s bombload is heavy enough to form a distinct unit in this comparison. The A-26´s ordenance is also very large and seperates the A-26 clearly from other A/C in this category. Differences in bombload between Ki-67, Mossie, B-18 and Ar-234B are negliable with only the Me-410A beeing distinctly weaker in this category.

The next count is range. Bombload and range are varyable, still, one might assume that specifically short legged A/C like the jet powered Ar-234B may also proportionally suffer here.



Unsurprisingly, the Ki-67, owing to it´s superior range (more than twice the range of a jet powered Ar-234B) comes out best with most of the other planes forming a comparable cluster, except for the notorious jet powered A/C which comes out clearly worst.

Now we enter the ormalised figures in a table and compare the results (figure for bombload times figure for range). The resultant value can never exceed 1.0 and usually falls clear short of this figure. Indeed, the best offensive count goes to the soviet Tu-2S with 0.53. This is the reference for 1.0, and the normalized figures from this reference show a very close 2nd place shared between A-26 and Ki-67, respectively. Also the third place is shared between Mossie and B-18. The last place finally, is shared by the two german entries, the Me-410A and Ar-234B, respectively. The principal result of low payload (Me-410A) and short range (Ar-234B), respectively.




The logistically oriented readers will be surprised to see that a squadron of Tu-2S is a very deadly offensive instrument. You can send in thirty-six Mosquite B Mk XVI or a squadron of only twelve Tu-2 provided that the pilots are capable to do the same and operate under an escort fighter umbrella in low thread areas with little AAA. We will see if that holds true when confronted with real data. The next comparison will be general and defensive counts. The methods stay the same.
(...to be continued)
 
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II. GENERAL AND DEFENSIVE COUNT

At the end of ww2, surface directed air defense efforts prooved to be a very serious thread for all involved airforces with losses inflicted by fighters usually rank 2nd. Then again, A/C have been improved in their capability to take damage. Self Sealing fuel tanks and pilot armour plating was a general standart in this period. Air cooled radials reduce the risk of coolant damage but then again, air cooled radials represent larger targets and increase the exposed area. Jet engines may be unreliable but then again, jet engines prooved to be much less complicated in operation and jet propelled A/C prooved to be more difficult to take down for this reason (The USAAF invented a specific jet-killer bullet to adress this problem). An as small as possible target area is a generally good asset in high thread environments. But typically, reduced wing area corresponds with reduced low speed handling and load taking capbilities. The comparison consist of four independent categories here. Generally spoken, we are confronted with both, positive and negative categories.


[A]-max Speed. This is a distinct defensive asset. A high top speed allows short exposure times on target and may even extract the plane from enemy pursuit fighters as demonstrated by the Mosquito and Ar-234 multiple times. This is a positive relationship.

-cruise Speed. This is a general asset. While top speed may be boosted, the cruise speed ultimately allows to enter and exit target airspace at the max. permissable (for range) speed the airframe and engines can tolerate. This is a positive category.
My personal ideal would be to know the landing speed for each plane. Unfortunately, these data do not exist for all planes and I have to resort to other criteria. Landing speed would be greatly welcome as it allows to study and compare the whole flight envelope and not parts of that.
Take notice that neither plane can operate adeaquately at only 200mph with gears and flaps fully retracted (actually the Ki-67 can but only at much reduced capacities). Thus, 200 mp/h is considered to be the bottomline for comparison. Any speed in excess of 200mp/h counts compared to the max speed of all contenders. Note that this may slightly but linearely over-emphasize speed differences shown by these planes. The increase of speed is not linearely with power but more a cube fit function, with this in mind it becomes very difficult to increase the speed of an already fast A/C. Fighter A/C had a speed envelope of 400 to 450mp/h, so any speed coming close to this line is worth all the effort.


As You may see, the best places for cruise and top speed go to the jet-propelled Ar-234B, the second beeing the Mossie closely followed by the Me-410A. These three planes were generally on the low ranks in the previous comparison, reflecting the effort put in designing a bomber to operate under more hostile environments, which dominated particularely the german airplane design at the close of ww2.
B-18 and A-26 don´t differ much in their relative speed with the two candidates Ki-67 and Tu-2S beeing the slowest and most exposed in comparison.

The next criterium is wing area. A large Wing area is considered to be a negative aspect for defensive questions, as it ultimately leads to a larger aircraft, which is easier to hit. Thus the numeric relationship of the normalised values is negative, the larger the wing area, the more the likelyhood f beeing hit by cannon or Flak fire. A large wingload helps in load taking abaility, but the general advent of high lift flaps in the second part of ww2 made this benefit also aviable to small wing aread designs.


It can be seen that both, the Mossie and the Ar-234B are extremely small aircraft, the Mossie beeing basically half the size of the japanese Ki-67, the Tu-2 and A-26 are also relatively large aircraft.

The final criterium is the relationship between maximum take off weight an power aviable. This again is a negative relationship, the less weight is related to a single hp engine power the shorter the take-off-run, the better the acceleration and the powered handling capacity of the airplane. Jet´s generate thrust, not hp. The relationship of thrust to speed is a square one instead of a cube fit, making jet propelled A/C the clearely preferable choice for high speed aircraft.



The A-26 this time appears to be less well provided with power for the max weight of the plane, Tu-2, B-18, Me-410A and Mossie are remarkably similarely powered in relative terms. The Ar-234B has excellent acceleration, albeit not at take off or landing, of course.

The result is quite clearly cut.



The Ar-234B, Mosquito B Mk-XVI and Me-410A are the winner of the defensive general Counts with the Ki-67 claiming the last place for itselfe.
 
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The concluding comparative figures for offensive and defensive may be valued according to the desired thread scenarios. I didn´t attempt a valuing as these undertakings are highly subjective in nature and varyable, too.
But one may prefer higher offensive values when operating in dominated or friendly airspace while engaging missions under hostile or contested airspaces one may prefer to overvalue the defensive figures.



The concluding count shows my personal selection of the best 44/45 2-engined bomber A/C. I hope, I succeeded in outlining the reasons for this selection in the two rather long memos above. Please note that this still remains to be my subjective perspective. Other readers will perhaps discuss different criteria or use different methods to explore on their own initiative. I need to outline that I was surprised to see the Tu-2S staying relatively comfortable as a third choice. To be honest, I didn´t expected this. These bombers are slow but compact and well powered with a comparably large payload, making them very competetive. The Ar-234B´s primary asset is the new jet propelled propulsion technology, which paved way for the more general advent of the jet bomber following the years after the end of ww2. The speed alone and the small target size of the airplane allowed it to operate where needed, despite beeing under enemy controlled and thus hostile airspace from anywhere after take off. This is a remarkable achievement.
The Mosquito ended up at a well respected second place, beeing basically the best piston engined bomber A/C of this comparison, with both, Me-410 and B-18 challanging each other for No. 4 5. These two planes show very similar approaches, the B-18 beeing a bit better in the offensive with the Me-410A beeing more survivable, so I take it that every airforce got precisely what they required. The US A-26 INVADER ended only beeing sixth, something I didn´t expected. It´s a large airplane, comparably slow and less well powered than most of the others. The Tu-2S shows what improvement could have been possible for a bomber with good payload. Then the final place goes to the japanese Ki-67, an airplane with possibly to arrow an prupose envelope to be reflected correctly in this kind of comparison. Long range was an existential requirement for the Pacific theatre and not nearly as important in europe. The Ki-67 stays out as a medium bomber with long legs but a poor tune of speed, relatively underpowered and an easy to hit, large target. It would not be as competitive in Europe as it was in the Pacific.
 
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Delcryos, I certainly can't and won't take issue with your exhaustive analysis, and I am certainly glad it included the Tu-2, since Soviet types are often forgotten in these discussions. The only comment I would make regarding the Ar 234's placement at the top is that these rankings do not take into account the unreliabililty and short service life of its turbojet engines. If I was forced to chose one of these planes around which to build a late war twin-engined bomber force, it would not be the Blitz. I would go with the Tu-2, followed by the Mossie and A-26.
 
Hmmm....in what universe does a Me 410 have a higher top speed than a Mosquito B.XVI?

Also, Wiki says that the internal bomb load for a Tu 2 was 3300lb, and if it wanted to carry more then it carried the extra externally. That is less desirable, as it slows the aircraft down and reduces range. Similarly for the A-26, only 4000lb could be carried internally.
 
A Spitfire pilot might beg to differ that "a large wing area is considered to be a negative aspect for defensive questions" as he turned inside a Bf 109.

Steve
 
While the Tu-2s was a very remarkable plane many of the published figures are a bit too remarkable as little note is taken of the difference in bombload between inside and outside. Or war time aircraft and post war aircraft. Perhaps the post war aircraft used better runways?

See: Tu-2S, ANT-61 by A.N.Tupolev

Little seems to be availalbe as to what the range of the TU-2 was when carrying heavy loads as 3000kg can suck up a very large amount of it's allowable payload without going over most commonly quoted Max Gross weights ( B-26 weights are a bit strange themselves. Max Gross can be 8,000lb higher or more than normal gross weight.)
 

I understand this concern. Short overhaul times were a general problem in this period (The J-47 required 25 hours in 1948). It´s particularely a problem for the Jumo-004B driven Ar-234´s but less by those which were driven by a BMW-003. The BMW-003´s lifetime of the combustion chamber was 200 hours, significantly longer than the Jumo-004 (acc. to Anselm Franz 60 hours for the final -004D and much less -about 30 in the regular -004B) or most period german high performance piston engines. The disadvantage of the Jumo´s in general, beside of the average lifetime was its prone to flameouts under 6.000 rpm. This is mostly because of the fuel regulation system at lower rpm (easy to burn out the turbine blades if too much fuel is injected at low rpm):
A gear driven pump that produced a linear amount of fuel proportion to the engines rpm, the pilots throttle was directly connected to a bypass valve that would recirculate unwanted fuel. Fuel then passed to a centrifugal speed governer that operated another bypass valve. However, if the engines rpm was under 6.000 rpm (set to idle), the speed governer did not take into effect and the throttle bypass was the only fuel flow regulation. The pilots throttle also was connected to a governor by a pressure spring and would regulate the governers rpm setpoint this way. At full throttle, for example, the rpm of a Jumo-004 B4 was at 8875 rpm. Under 6.000 rpm the pilot had to be very careful, because without the governeor it was easy to allow to much fuel entering the combustion chambers and thereby burn them out.
So there can be a dissimilarity between engines rpm and air flow. The BMW-003 had a similar layout but in addition a device that consisted of an aneorid capsule across the compressor stages. This "accelerator valve" regulated the fuel flow in correspondence to the air flow (by pressure) and the governeor had less importance. In the end the actual air flow and spool up time was taken into account, so that the BMW-003 throttle could be handled less gingerly. The Jumo-004 on the other hand had a more sophisticated system to regulate the exhaust nozzle, while the BMW-003 exhaust nozzle was manually controlled. In the end, the BMW-003 is much easier to operate, more reliable and durable and less prone to flameouts in direct comparison to the JUMO-004. The latter´s principal advantage over the BMW-jet engine was it´s earlier aviability as a functional prototype (roughly 1942/3 compared to 1943/4) and mass produced engine (mid 1944 vs late 1944 to 1945) plus it´s larger production quantity.
 
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Thanks for the replies Wuzak, In the above comparison, I don´t care if a bombload is carried internally or externally as long as the bomber A/C is able to drop the bombs in case of an emergancy and can restore it´s max. top speed. As mentioned previously, top speed is considered by myselfe as a distinct defensive asset for an bomber A/C. A bulged bombbay (say Ju-388K2 f.e. or some specially modified Mossies to carry extra large bombs) is something else as it doesn´t allow to restore the planes max. speed after emergancy drop. That´s how I see it, Your perspective doesn´t necessarely need to match mine.
 
stona said:
A Spitfire pilot might beg to differ that "a large wing area is considered to be a negative aspect for defensive questions" as he turned inside a Bf 109.

Steve
Click to expand...
Wingarea doesn´t help in turning per se, only in combination with a high lift generation per ft^2 (caused by a high lift airfoil/devices/planform) and a low weight. Thus what You are talking is basically a very low wingload caused -in part- by a larger wingarea (in part by a high Cl-max, too).
Generally, low wingload may be an asset for a fighter bt not for a bomber. Any Ju-87 can outturn any late ww2 fighter A/C but that doesn´t make the Ju-87 competetive or less vulnerable to a fighter. Any biplane can outturn a late ww2 fighter, so what?
I am referring to wing area as an indicator of target size and that´s true not only against fighters but also against AAA.
 

delcyros, the Mosquito B.XVI is rated as having a top speed of 408mph. That is some 20mph from the quoted speed of the Me 410. Other sources give 408mph as the speed with a 4000lb bomb, 416mph as the speed after dropping the bomb.

A B.IX with a bomb under each wing and a full load of bombs (2000lb) and fuel was measured at the same speed as a Me 410 (388mph), albeit with +21psi boost.
http://www.wwiiaircraftperformance.org/mosquito/lr495-b.pdf

It was still recorded at 383mph with the normal +18psi, and the conclusion was that the wing bombs cost between 15-18mph in top speed.

The Mosquito B.XVI Data Sheet gives a maximum speed of 408mph after dropping the wing bombs.

External stores not only affect top speed, but also cruising speed, height for best performance, ceiling and, more importantly, range.
 
Thanks, Wuzak, that´s definitive enough for me. I update the Mossie entries above (top speed: 408mph, cruise speed 321mph (max. weak mixture), bombload 4000lbs, range 850 (at cruise speed -but I keep the old range as I suspect other planes are reported with a range not fitting to optimum bombload)). There are different configurations possible, unfortunately that great deal of information isn´t aviable for other planes, too. The total doesn´t change much, the lower cruise speed is offsetting what it gained in top speed in the first place (0.89 top speed*0.51 cruise speed =0.454 compared to previously 0.71*0.71 =0.504).
In reflective terms the new speed data compared to the Ar-234B´s 1.0 rating is:
Nr²= topspeed*cruisespeed that results to
Nr= sqrt(topspeed rating * cruise speed rating)

1st) Ar-234B = 1.0
2nd shared) Me-410A = 0.68 (due to higher cruise speed, top speed inferior to Mossie)
2nd shared) Mosquito BMk XVI = 0.67 (better top speed but worse cruise speed)
3rd) B-18 = 0.57
4th) A-26 = 0.55
5th) Ki-67 = 0.47
6th) Tu-2S= 0.44
 
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Production Saab B-18s don't get the DB 605 engines until after the war.

TU-2 bombers used normal bomb loads of under 1500kg for most missions during the war.

No mention is made of defensive guns. While the A-26 had 4 compared to the TU-2's 3 the A-26 guns were in remote aimed turrets/barbettes (very similar to B-29) with much wider fields of fire and better ammo supply.
 
Shortround6 said:
Production Saab B-18s don't get the DB 605 engines until after the war.
Click to expand...

Almost correct. Saab took delivery of some 70 german built DB605A complete with props and reduction gears already in 1943. They were initially used in the B18B from june 1944 in testing. During testing the german built engines were found to be of questionable quality so a decision was made to wait for the swedish license built DB605. The first production built B18B with the swedish license built DB605 were delivered to the swedish air force in october 1945.

The B18A had swedish license built TWC-3 engines and the first production built B18A were delivered to and in service in the swedish air force in march 1944.
 

How able was the A-26 to simultaneously defend vs. 2 fighters?
 

The comparison reflect capabilities of the bomber A/C not how they were employed or what was the normal bombload at the most common mission profile. The normal bombload of the Tu-2 in missions flown 1944 was 1000kg though at several occassions, entering low thread areas, 3 ts of bombs were delivered and in few cases on short range trips engaging the remains of the KM in the Baltic 4 ts were delivered in spring 1945.

Also, You will notice that defensive guns are indeed mentioned and listed in these posts. The A-26 is there credited with four 0.50cal M2 BMG in RC (=remote controlled) barbettes. The Tu-2s has three seperated gun stations with one LMG (replaced with BMG later) each. Defensive gun positions are not part of the statistic analysis because they have a different scale level (0.50cal BMG is not a measurable metric but can be counted, thus beeing in principle a nominal scale level) and shouldn´t be mixed with metric scale levels, which form the base of the analysis.
In principle, it is possible to code nominal scale levels along a metric axis, though this is not justified here as it would involve very many questions, which would easily end up in a study of it´s own.

How able was the A-26 to simultaneously defend vs. 2 fighters?
Click to expand...

In principle one target can be engaged at any time. The system works, remote controlled barbette with BMG guns were also placed in the Me-410A fuselage as defensive armement and we know some fighters were downed by that. However, it helped little to nothing to make these A/C more survivable against fighter opposition, though it drastically increased claim rates. That the Me-410A was not able to operate at daylight despite it´s high defensive ratings lends us an idea just how inferior twins were against single engined fighter A/C opposition.
 
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While statistical analyses are always fun, they are always limited by the factors chosen and the data available. Nice effort nontheless.

But what immediatly came to mind after reading your posts is the fact that accuracy seems to me to be a more decisive offensive factor especially for the light-to-medium bombers that we are talking about here.

How does an Ar 234, with its one-man-crew stack up against the ones with a dedicated bombardier (autopilot, I know but still)? Or a bomber capable of dive bombing?

And on a small note: I don't think any Ar 234s were ever fitted with the two MG151 operationally.
 
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