Aerodynamics: B-17 vs Avro Lancaster

Discussion in 'Flight Test Data' started by Zipper730, Sep 9, 2016.

  1. Zipper730

    Zipper730 Member

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    I'm curious which aircraft is cleaner aerodynamically.

    The B-17E seems to have higher maximum speed (and possibly a higher cruising speed) than the Lancaster Mk.I. This however is misleading as the Lancaster Mk.VI has a similar top-speed owing to it's twin-stage supercharger and higher critical altitude than the earlier Mk.I.

    I'm curious which aircraft is cleaner in the following respects

    Fuselage

    B-17E Flying Fortress
    1. The basic fuselage is essentially circular in cross section
    2. Basic areas of exception would include: The cockpit area which forms a rectangular hump atop the rest of the fuselage (this rounds out and blends into the fuselage at around 40-50% of the aircraft's overall length and also mounts the upper turret, as well as another 0.50 calibur gun); the areas where the wings and tails join the fuselage; the tail-gunner's station which extends off the back of the tailfin, and is rectangular in shape, as well as the tailcone itself, which is of flattened oval cross-section
    Avro Lancaster (General)
    1. The basic fuselage is that of a rounded rectangular cross-section, of a greater height than width, with the rounded sections being the top and bottom sides.
    2. Basic areas of exception would be the nose-cone which seems fairly circular or flattened oval, as well as the nose-turret which seems a narrowed oval from the front perspective.
    Looking at the two aircraft, it would be easy for a person to conclude the B-17's basic fuselage was cleaner: I'd like to point out that a rectangular cross-section is not intrinsically a bad shape, boats use this configuration a lot (the v-hull) as did the B-24 with substantial success.

    If I was to look at areas of drag on B-17 that would stand out in comparison to the Avro Lancaster, it'd be the ventral guns, though the Lancaster had the provision for such an armament, though they rarely carried it (Evidently, it was difficult to sight the guns, though I'm surprised the B-17 wouldn't have the same problem. Later on, though the H2S took up it's spot); airflow over the open doors for the waist-gunners might produce some turbulence when opened (I can't say for sure).

    Looking at the Lancaster for notable sources of drag: I'd say the tail-gun looks substantial (though I cannot say for sure how the boxy 'cockpit' for the B-17E's tail-gunner would compare), especially when some crews actually took out the glass pane to increase visibility; the non-retractable tail-gear seems something that would produce some drag (the B-17 doesn't have a non-retractile tail-gear); looking at the mid-upper turret, it seems larger than those used on the B-17 despite using a smaller caliber (admittedly, it has fairings to help blend it in with the fuselage); despite actually liking the good visibility of the canopy, it might actually be a greater source of drag, though I can't say for sure (as it's narrower than the B-17).

    Aerodynamic Surfaces

    B-17E Flying Fortress
    1. The B-17's wing is larger, though more tapered
    2. The B-17's all have a single vertical-fin, which the B-17E's is larger than the previous designs, and the same as the later models that would see service (far as I know): I'm not entirely sure the advantages of one tail over two except that if they were mounted on the tail, they would act as endplates.
    3. I know little about the tail-surfaces of the two aircraft except that the B-17's were heavier in dives.
    Avro Lancaster (General)
    1. The Lancaster's wing has a smaller wing-area and a higher aspect-ratio: This could increase aerodynamic efficiency. I'm not sure how thick the two wings compare, but the Lancaster (provided it could get high enough) was able to reach 350 mph TAS which at 25,000 feet is Mach 0.72
    2. The Lancaster's tailfins were mounted on the ends of the tailplane which might have increased the aerodynamic efficiency of the tailplane (acting as an endplate), though I'm not sure if the extra drag from two tail-surfaces was worth it.
    The B-17's tail-surface looks more aerodynamically efficient, but looks can be deceiving: The highly swept-dorsal root extension does look like a way to avoid fin-stalls, though it's highly swept configuration might (if my knowledge of swept wings is correct) yield a lower T/C ratio. There was interestingly, a plan to put twin-tails on the B-17E, though I think this was to make it easier to put the tail-gunner in the plane.

    The Lancaster's twin-tails seem on instinct, to be a greater source of drag because you would have more surfaces in the wind, and side-slip would produce a vortex off both tails, though to some degree this would be countered by the fact that they aren't attached to the fuselage and might reduce interference effects. They could potentially increase the effectiveness of the tailplane, acting as end-plates.

    I'm not sure totally about the details as there were some aircraft in the development stage (B-36) that switched from two tailfins to one, as well as designs that were modified (B-24 to the PB4Y) into single tailed aircraft.

    Engine Mounting & Installation

    B-17 Flying Fortress (General)
    1. The B-17's engines are radial in design, which yields a lighter engine that's more damage resistant, but also is an engine with a greater frontal area, less overall length (could affect fineness ratio), the only "radiator" is the cowl (whereas on an inline you can put the radials in an annular layout, you can hang them on the front of the nacelle, the middle of the nacelle, on either side, under the wings, under the fuselage, etc), and most NACA cowls, while efficient at providing cooling, were often not ideally suited for exploiting the Meredith effect.
    2. The nacelles, regardless, did seem to blend into the wings fairly well despite the larger diameter, which overall seems to have worked out pretty good. I'm not sure how the depth of the nacelles compared to the Lancaster.
    3. The turbocharger turned out to be a big secret in the B-17's performance, and allowed it to keep critical altitudes up to at least 25,000 feet. Admittedly, the use of the turbocharger did mean there was little thrust compared to a twin-stage supercharger, but I'm not sure how much use it would have been considering the speeds the plane flew at. It would have been useful for pumping the cowling if it was available.
    4. The fact that the landing-gears were partially exposed instead of totally retracted might have added a slight bit of drag over the Lancaster, which retracted them fully.
    Avro Lancaster (General)
    1. The Merlins were longer and smaller in diameter than the R-1820's used on the B-17, and might have permitted a superior fineness ratio (thus less drag): I'm not sure how efficient the radiator was, and the depth of the nacelle compared to the R-1820's
    2. The nacelles seemed to blend into the wing less and while their mounting below the wing seemed better, at least based on my knowledge of jet-engine pylons, I'm not sure the integration with the wing in this case as the aircraft was slower. Even the Mk.VI with twin-stage superchargers and jet-stacks managed at the same altitude, just about the same speed as the B-17E, except without the benefit of the greater armor, the waist-guns, a lower-turret installed, and 0.50 calibur armament.
    Overall

    Clearly, the Lancaster could fly further than the B-17 for the same bomb-load. It also had the ability to carry heavier internal loads from the start to the finish, as well as the ability to carry fundamentally bigger loads than the B-17 was ever able to carry internally. It's overload capability was overall superior as well.

    The B-17E was capable of taking a better beating and had heavier firepower, it also routinely carried defensive armament in the waist position, which the Lancaster could only in a limited extent (the top gunner could technically fire sideways), and the ventral was rarely carried.

    The performance figures are difficult to quantify based on the fact that the designs were very different in many ways, and performance is often based on the aircraft weighing a specific amount under a specific set of conditions which I'm uncertain of.

    I'm hoping I can get an answer
     
  2. pbehn

    pbehn Well-Known Member

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    Two completely different aircraft with different philosophies, the Lanc was originally designed as a medium bomber, it had no co pilot. When first introduced it was described as a flying bomb bay however inside there was little room, passing the wing spar was/is difficult,

    As far as aerodynamics goes I believe the wing position of the lanc, being at 90 deg to the fuselage as opposed to the low wing of the B17 is theoretically advantageous however with so many rivets, guns holes and ariels on both I would say they were both pretty bad in the drag department.
     
  3. Zipper730

    Zipper730 Member

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    The Manchster was designed as a medium, the Lancaster was designed as a bigger more powerful heavy...

    I didn't know the Manchester had no co-pilot, though I was aware the Lancaster lacked one.

    That sounds about right, why did they build it so big?

    True, I was just kind of curious which was better.

    Honestly I'm starting to think the B-17E was equal or better than the Lancaster Mk.VI because of it's ability to fly faster with a ventral turret, though the Lancaster might have been heavier empty and loaded.

    Admittedly I'm not sure what conditions the cruise and top speeds were specified for: A lightly loaded plane flies faster than a heavy one...
     
  4. wuzak

    wuzak Well-Known Member

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    #4 wuzak, Sep 11, 2016
    Last edited: Sep 11, 2016
    The Lancaster was not really designed - it was adapted from the Manchester with longer wing span and 4 Merlins. The fuselage remained the same, as did the bomb bay.


    The original specification required the aircraft to be able to carry two 18" torpedoes (the Halifax was built to the same specification), which required long bomb bays.

    Note that while the Manchester was nominally a "medium" bomber its bomb load was specified to be 8,000lb.


    The Lancaster B.VI was measured at 313mph @ 18,300ft loaded to 62,000lb (95% of take-off weight of 65,000lb). Which means a bomb load likely of 12,000lb and possibly 14,000lb.

    http://www.wwiiaircraftperformance.org/Lancaster/Lancaster_VI_JB675_Performance.pdf

    The B-17E was tested at 317mph at a load of 40,260lb. That was the nominal gross weight - but it wouldn't be a particularly large bomb load.

    http://www.wwiiaircraftperformance.org/B-17/B-17E_41-2399_PHQ-M-19-1315-A.pdf

    So the Lancaster wins.

    Though, to be fair, when the B.VI came out the B-17E was gone from the production schedule, replaced by the F and then the G, which is the VI's true contemporary.
     
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  5. wuzak

    wuzak Well-Known Member

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    The Manchester regularly went to war with bigger bomb loads than the B-17 did, though it was quite limited in the altitude it could reach (ie ~ 10,000ft).

    The superiority of the Lancaster wasn't just about the maximum loads - it was also about the size and variety of the bombs the Lancaster could carry.

    The 4,000lb HC "cookie" for instance, could not fit inside a B-17's bomb bay without reworking both the bomb and the bomb bay. Forget about the 8,000lb and 12,000lb variants (bigger diameter and longer).

    In terms of the overload capacity, I think the Lancaster was quite limited as well. That is, to be able to carry the Grand Slam any useful range required deletion of the upper and front turrets.


    I'd argue that the waist gun positions in US bombers were largely a waste of crew. I seriously question the effectiveness of those positions.

    The Lancaster;s top gunner could fire sideways, as could the front and rear gunners. As could the similar positions in the B-17 (although only from the G did it have a nose turret).


    I think the B-17 was aerodynamically superior than the Lancaster, but became less so as each new variant spouted more guns. The earlier B-17s were able to fly faster on less power, but they also couldn't carry as big a bomb load.

    By the time of teh G teh Lancaster and teh B-17 had similar performance - empty weights around 35-36,000lb, normal maximum loaded weight around 65,000lb and a maximum speed of around 285-290mph.
     
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  6. pbehn

    pbehn Well-Known Member

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    The Lanc and B17 were completely different beasts, the Lanc needed complete air superiority for daylight raids it had insufficient defensive armament. The bomb bay of the Lanc gave it great utility in terms of bombs cookies incendiaries that could be carried.

    Maximum speed for daylight heavy bombers is a bit of a distraction, since they traveled in formation it is the highest cruising speed of the slowest plane in the formation that matters.

    Aerodynamic efficiency of a bomber most affects the bomb load v fuel calculation on long range missions. This throws up some query stats like a Mosquito dropping as much weight as a Stirling at long ranges.
     
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  7. Zipper730

    Zipper730 Member

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    Actually the fuselage was a little shorter and reshaped in a few areas, but I see your point.

    Judging by the length of the torpedoes, were they carrying them in tandem?

    What could it have done with the normal loads they carried in combat?

    The B-17E was tested at 317mph at a load of 40,260lb. That was the nominal gross weight - but it wouldn't be a particularly large bomb load.[/quote]I assume this was at 25,000 feet or greater correct? How did the B-17E perform with the 4,000 or 4,800 pound load it was supposed to carry practically?

    I just put it in because of the fact that it was a high altitude variant, though for some reason I thought it could operate at 25,000 instead of 18,300.

    That I'm aware of: I mentioned that in the OP on the bottom of the post. When I said fundamentally bigger, that's what I was referring to, not just mass but volume.

    True, but the B-17 couldn't carry them at all

    I suppose that could be argued multiple ways
    1. The side-turrets could technically hit aircraft coming along the sides unless possibly up close (depression angle and no bullet drop)
    2. The waist-gunners could engage targets approaching the sides even as the top gunners engage aircraft from above
     
  8. pbehn

    pbehn Well-Known Member

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    Wuzak wasnt making a "point" he was pointing out the same historical fact that I mentioned. The Lancaster was produced when the Manchesters Vulture engine was discontinued. I am coming to think you are twisting the forums tail, firing questions around to provoke then looking up details to give answers to appear "informed" You cannot possibly know that the Lancaster was 6 inches shorter than the Manchester without knowing that the Lancaster was the 4x Merlin replacement for the 2x Vulture powered Manchester.
     
  9. wuzak

    wuzak Well-Known Member

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    Reshaped where?

    I wouldn't take much heed in the Wiki figures which state the Lancaster was 8" shorter.


    You have dimensions of the torpedoes?

    I should imagine they would have been carried side by side.


    12-14,000lb WAS a normal combat load for a Lancaster.


    I don't know if the tested weight included 4,000lb of bombs. Or not.


    It could operate at 25,000ft. But why would you want to? Bombing accuracy would be less, conditions inside an unpressurised aircraft were worse.

    The service ceiling at 65,000lb was 27,000ft. 18,300ft was the full throttle height of the engines, and thus the point of maximum power.


    I seriously question the effectiveness of waist gunners.
     
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  10. nuuumannn

    nuuumannn Well-Known Member

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    Essentially the B-17 did too. The B-17 had no real advantage over the Lancaster apart from that it had more guns in heavily defended airspace; during the day without fighter escort both were targets for interceptors or were flak bait, one not more so than the other.

    I'm struggling to find the point behind this; are we comparing the two or establishing which was aerodynamically more efficient? And then to what end?
     
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  11. buffnut453

    buffnut453 Well-Known Member

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    Frankly, I'm with Nuuumannn here. I'm struggling to understand the point of the question. The early B-17s were certainly the cleaner of the 2 designs but operations quickly demonstrated the need to mess with the aerodynamics to add guns, guns and more guns. Even if we could determine which was the more aerodynamic, what does that prove? Range, payload, ability to hit the target, survivability are all (IMHO) more important than purity of aerodynamic design.

    I also agree with Nuuumannn's point about both the B-17 and the Lanc requiring air superiority to operate in daylight. The USAAF daylight bombing offensive encountered considerable losses until the advent of long-range fighter escort which offered the promise of localized air superiority.
     
  12. Zipper730

    Zipper730 Member

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    pbehn

    Post #6: 9/10/16

    I assume this is mostly due to caliber?


    Post #8: 9/10/16

    I suppose it makes sense that they'd discontinue the engines if they were suitably unreliable, but I honestly didn't think it that far. I just figured the engines were unreliable, and the plane needed more power, so they replaced the two Vultures with four Merlins.

    I'm not trolling if that's what you're getting at, and on that note: I'm not sure if I ever thought I appeared that "informed" to be honest. I'm not really all that knowledgeable about World War II aircraft in general, and have just started to take an interest in early aviation over the past year.

    Actually, from what I read, the Lancaster was a development of the Manchester, and I heard that the Vultures were unreliable and yielded an underpowered aircraft compared to the Lancaster.

    When I looked at the Manchester, it appeared to have a few subtle differences in shape (the most obvious is the mid-upper turret), and it wasn't after I did a search (which was started because of my conversation with wuzak) that I found the differences in length: I was very surprised to find the Lancaster was shorter.


    wuzak

    Post #9: 9/10/16


    The most obvious difference I can find is the mid-upper turret (the Manchester's turret seems flat up front), but the nose-gun is either moved closer to the nose-cone, or is flatter, and the tail-gun is slightly different.

    Unfortunately there doesn't seem to be a Joe Baugher equivalent of British Aircraft (at least I haven't found it)

    I'm not sure exactly what model they were building the aircraft around, but the two torpedoes that were in the era that I can find data for length on seemed to be the XII which was 16'3" in length and 17.72" diameter.

    Since the Lancaster and Manchester both had a bomb-bay around 33' in length, I made a guess.

    Really? Wow... I thought the normal load was like 6500 to 7500 pounds with 14000 being the maximum normal :shock:

    I just want to make sure we're on the same page: I was under the faulty impression that it could reach a critical altitude of 25,000 feet :eek:, and because of that I assumed higher would equate to faster speeds, and both would require more effort to intercept. I didn't really consider crew conditions based on the fact my question was mostly aerodynamics related (and the USAAF operated in this environment all the time).

    Just out of pure curiosity, why didn't they use something like the Merlin 60's which produced more power at higher altitudes? Was this similar to the B-29 (poor climb rate meant excessive fuel was burned getting to altitude that it offset the benefit of cursing higher)?


    Nuuumannn

    Post #10: 9/10/16

    [QUOTEI'm struggling to find the point behind this; are we comparing the two or establishing which was aerodynamically more efficient?[/quote]Aerodynamically more efficient at a given altitude

    Honestly, part of me was curious as to how much of the B-17's performance edge lied in the turbocharger, and how much lied in the overall aerodynamic cleanliness.
     
  13. wuzak

    wuzak Well-Known Member

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    Since they could fit side by side that's how they would be. It would be better for CoG as well.


    Yes, really. It depended on target and bomb mix - more incendiaries the lower the bomb weight.

    6500-7500lb is around what a Manchester would carry. Although it could carry over 10,000lb.


    The Merlin 85 was a 2 stage engine, a development of the 60-series.

    18,300ft was the FTH at +18psi boost. At +15psi boost the FTH would be higher.

    The fact that the Lancaster didn't have a very high ceiling, despite having similar or more power at the altitudes we are talking about, should give you the answer to your original question.
     
  14. wuzak

    wuzak Well-Known Member

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    Francis K Mason, The Avro Lancaster, gives the length of the Lancaster as 69ft 6in tail up and 68ft 10in tail down.

    No mention of fuselage changes between the Manchester and Lancaster prototype. Except for the eventual deletion of the centre fin (which happened on poduction Manchesters anyway).
     
  15. pbehn

    pbehn Well-Known Member

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    It is a bit lost on me too weight causes drag as do defensive guns what is the point of establishing the cleanest plane when tht cleanliness renders it useless. From what I read both the B17 and the Lanc were wonderful planes to fly with minimal crew no defensive armament or bomb load.
     
  16. wuzak

    wuzak Well-Known Member

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    Can I ask, what was funny about this post?
     
  17. pbehn

    pbehn Well-Known Member

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    probably just a guy viewing on a kindle, i have cast a few unintentional votes like this.
     
  18. Shortround6

    Shortround6 Well-Known Member

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    As far as aerodynamic "cleanliness" goes and B-17F might very close but just a bit worse than a Lancaster I.
    Based off of speeds at 15,000ft and power used. Max cruise on the B-17 engines was 2300rpm and 38In at which point they gave 1000hp (or very close).
    The Two speed Merlins in the Lancaster were good for about 1015hp at 14500ft in high gear using 2650rpm and 7lbs of boost.
    I, for one, am not going to worry about 60hp out of 4000hp.
    Pilots manual for a B-17F says in can do 192mph IAS at 15,000ft with the engine settings above at 60-65,000lbs. Loosing 5,000lbs gains about 2mph IAS and loosing another 5,000lbs (flying weight 50-55,000lbs) gets the plane to 200mph IAS at 15,000ft. According to one online IAS to true airspeed calculator (others may differ?) the 192mph IAS is equal to 249.6mph True.
    A Lancaster MK I was supposed to do about 253-254mph at 15,000ft using the engine settings given above at 62,000lbs.
    From a drag standpoint the planes are almost identical with the Lancaster having perhaps a 1.7% edge (please note that even planes of the same type and only few serial numbers apart could have a 2-3% difference in speed).
    What the designers were able to do with weights as far as payload and such (size of bombay?) is a different story.
     
  19. XBe02Drvr

    XBe02Drvr Active Member

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    MEA CULPA! Pbehn is correct. Fat fingers trying to scroll a tiny Samsung smart?phone screen. I have retracted my accidental comment. Apologies to all. I agree with him also on "What's the point?". Reminds me of dark ages theologians arguing how smany angels could dance on the head of a pin. Zipper, go read some history, gain some perspective, and come back with some meaningful questions.
     
  20. RCAFson

    RCAFson Well-Known Member

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    #20 RCAFson, Sep 14, 2016
    Last edited: Sep 14, 2016
    Most bombers had lowered ceilings when loaded to max TO weight:

    B29 @ Max TO (140000lb)= 23950ft
    B17G @ Max TO (67860lb) = 28250ft
    Lanc I @ Max TO (65000lb) = 22000ft
    Lanc I at Overload TO (70000lb) = 20000ft
    Lanc VI @ Max TO (65000lb) = 28500ft
     
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