B-17 vs Avro Lancaster

[PR19_Kit]

Perhaps a telling case of the aeronautical folks having a better grasp of the realities of the contemporary technology than their customers.

Now why does that sound familiar? 

[KJ_Lesnick]

Captain Canada

Orenda tested their early turbos on borrowed RCAF Lancs.

Yeah, but I didn't know they used them operationally in that role...

As for the story, they saw the B-17 coming, so throttled back to let him catch up, then poured on the coals and passed him. No idea if the Fort was going full bore or just cruising, but it's still a good story !

Hmmm, that actually leaves me with more questions than answers


Wuzak

The Lancaster had more power at take-off than the B-17 (~1600hp for later versiosn vs ~1200-1350hp). However, the Lancaster used single stage Merlins (mostly), so their altitude performance was lower than the take-off performance.

For some reason, when I hear merlin I tend to automatically think of the twin-stage twin-speed supercharger.  I suppose it's a good point to remember that they generally did not have these except for a small number.  Admittedly it is interesting that even the variants that used twin-speed, twin stage superchargers, more horsepower (and the design could hold max HP up to similar altitudes to our turbochargers), and lower drag (cooling drag, nacelle shape) and it's top speed was about the same as the radial B-17E's (admittedly the -F's were slower due to being able to carry more bombs, landing-gear and possible structural mods).

Cruising altitude for the B-17's were typically around 22,500 to 26,500, though the service ceiling was around 34,000 to 35,000 feet(?); the Lancasters flew at around 19,000 feet in combat if I recall, though their service ceiling was higher.

I'm curious as to which plane had a cleaner fuselage

• The B-17E had more of a teardrop shape which tends to be a naturally aerodynamic shape
  
• The V-hull shape of the Lancaster can be more advantageous when you don't have the luxury of CFD
  
• The B-17E's gunner station seemed less aerodynamic, but the turret seemed much more aerodynamic than the Lancaster's which seemed quite draggy
  
• The birdcage on the Lancaster appeared streamlined, but it might very well have added more frontal area to the plane than the B-17 cockpit area
  
• The turret on the B-17 was on top of the cockpit, not behind it and would not effectively be a draggy surface behind another draggy surface
  
• While a twin-tail set-up does increase the effectiveness of the tail surfaces by acting as an endplate, and does technically allow the two tail surfaces to actually be even smaller than one big tail-surface (the tail by being mounted out to the side exerts more lever arm), each tail surface can potentially produce more vortex drag particularly when a pressure differential exists (and rudder deflection is necessary for most props) as you have four sets of vortices instead of 1.
  

Please correct me if I am wrong in anyway.

Bomb creep was often caused by the smoke from the bombs obscuring the target, following bomb aimers losing the target and dropping their bombs early.

That was the sole cause?

The RAF developed a master bomber system whereby the master bomber would observe the bombing and apply corrections to the aim, would advise crews as to which of several markers are positioned well and should be used and which are poorly located and should be ignore and would call for additional marking if the original markers had gone out or had become obscured.

Ironically, accuracy with the pathfinder force sometimes got within a 400 foot CEP.  Same as us on average.

This was easier for the RAF to do since bombers still aimed individually, unlike the USAAF.

With the bombardier/toggleer system, did they have just one bombardier or a few spaced throughout the formation?

Some Lancs had their rear turrets modified with twin 0.50" mgs instead of the 4 x 0.303"s.

That's good to know

I would say that the Dams raids were precision bombing raids, and some of the bomb aimers used nothing more than a piece of string and the window frame....

Well they used a pair of lights to determine exact altitude, they timed the turns so they'd follow the contours of the rivers, and the string and window frame was a good aiming system for that purpose.  They knew the towers would appear to be the distance apart when they got in the right range.  So once they reached the point where the towers overlapped the frame they hit the bomb-release button.

The Norden has a spectacular reputation, but it did have its downsides - one of which was the requirement to maintain a straight and level course for some time - not sure how long exactly, but it may have been a minute or more.

I thought it was around 30 seconds.

The regular British Mk XIV bomb sight needed only 10s of level flight prior to the drop, allowing the crew much more flexibility in manoeuvring.

It also was better able to factor in for climbs and descents.  Regardless, from 14,000 feet to around 16,000 feet (at least) it was similar to the Norden.  The USAAF interestingly did purchase some of these, though I don't know what they used them for; they'd have been good on some B-25 missions.

It appears that only 617 Squadron used the SABS - 9 Squadron, who also dropped Tallboys, used the Mk XIV.

How good were they for calculating the ballistics of a supersonic bomb?  I know our Nordens had difficulty...


joncarrfarrelly

It had a pretty good cowling design, you can't see it from most angles but it's got a decent bell-mouth to it from this position

[PR19_Kit]

• The V-hull shape of the Lancaster can be more advantageous when you don't have the luxury of CFD
  

V-hull shape? What's V shaped about it? The Lancaster fuselage cross section is a box with the corners rounded off.

[KJ_Lesnick]

PR19_Kit

V-hull shape? What's V shaped about it? The Lancaster fuselage cross section is a box with the corners rounded off.

From the side it reminds me of the hull of a ship.  Regardless a flat-sided hull is easier to design than a circular one. 

This is why spatular nosed hypersonic waveriders did better than their purely triangular counterparts (Pike, 1966)

[wuzak]

joncarrfarrelly

It had a pretty good cowling design, you can't see it from most angles but it's got a decent bell-mouth to it from this position

It's a standard NACA cowling of the mid to late 1930s.

http://upload.wikimedia.org/wikipedia/commons/8/8e/Curtiss_P-36A_38-33_16th_Pursuit_Group_1940.jpg

[wuzak]

The RAF developed a master bomber system whereby the master bomber would observe the bombing and apply corrections to the aim, would advise crews as to which of several markers are positioned well and should be used and which are poorly located and should be ignore and would call for additional marking if the original markers had gone out or had become obscured.

Ironically, accuracy with the pathfinder force sometimes got within a 400 foot CEP.  Same as us on average.

This was easier for the RAF to do since bombers still aimed individually, unlike the USAAF.

With the bombardier/toggleer system, did they have just one bombardier or a few spaced throughout the formation?

RAF crews all bombed with the bomb sight and/or their navigation aids (H2S, Oboe, Gee-H). They didn't toggle bomb switches in response to a lead bomber. They did drop their bombs on a signal from their navigation aids (Oboe and Gee-H) where so equipped.

I should think that the pathfinder force were able to get much better accuracy than the US 8th AF. They used the aids, and would often mark visually. In the case of 5 Group (which included 617) target marking would be done at low level and sometimes in a dive.

The regular British Mk XIV bomb sight needed only 10s of level flight prior to the drop, allowing the crew much more flexibility in manoeuvring.

It also was better able to factor in for climbs and descents.  Regardless, from 14,000 feet to around 16,000 feet (at least) it was similar to the Norden.  The USAAF interestingly did purchase some of these, though I don't know what they used them for; they'd have been good on some B-25 missions.

Sperry made the Mk XIV under licence.

[wuzak]

Bomb creep was often caused by the smoke from the bombs obscuring the target, following bomb aimers losing the target and dropping their bombs early.

That was the sole cause?

No, not the sole cause.

Another would be panic, I guess. Flying along, getting pummelled by flak the 30s-1m (whatever it was) required by the Norden would have seemed like aeons. I'm sure some crews would have said, "that's close enough"!

The RAF developed a master bomber system whereby the master bomber would observe the bombing and apply corrections to the aim, would advise crews as to which of several markers are positioned well and should be used and which are poorly located and should be ignore and would call for additional marking if the original markers had gone out or had become obscured.

Ironically, accuracy with the pathfinder force sometimes got within a 400 foot CEP.  Same as us on average.

I misunderstood you in your last post. I think you are saying that RAF Bomber Command achieved similar accuracy to the 8th AF when assisted by the Pathfinder force?

That is a reasonable observation, and I've seen it said (Stephen Bungay IIRC) that the USAAF area bombed precision targets, and the RAF precision bombed area targets.

[KJ_Lesnick]

Wuzak

RAF crews all bombed with the bomb sight and/or their navigation aids (H2S, Oboe, Gee-H). They didn't toggle bomb switches in response to a lead bomber.

I know that... I was talking about the USAAF

They did drop their bombs on a signal from their navigation aids (Oboe and Gee-H) where so equipped.

How did the Oboe and Gee work?

Sperry made the Mk XIV under licence.

Did anybody in the US use it?

I misunderstood you in your last post. I think you are saying that RAF Bomber Command achieved similar accuracy to the 8th AF when assisted by the Pathfinder force?

That is correct.

[wuzak]

They did drop their bombs on a signal from their navigation aids (Oboe and Gee-H) where so equipped.

How did the Oboe and Gee work?

From Oboe (Wiki):

]Oboe used two stations at different and well-separated locations in England to transmit a signal to a Mosquito Pathfinder bomber carrying a radio transponder. The transponder re-transmitted the signals, which were then received by the two stations. The round-trip time of each signal gave the distance to the bomber.
Each Oboe station used the radio ranging to define a circle of specific radius, with the intersection of the two circles pinpointing the target. The Mosquito flew along the circumference of the circle defined by one station, known as the "Cat", and dropped its load (either bombs, or marking flares, depending on the mission) when it reached the intersection with the circle defined by another station, known as "Mouse". There was a network of Oboe stations over southern England, and any of the stations could be operated as a Cat or a Mouse as the need demanded.

From Gee-H (Wiki)

Gee-H was used to supplant the Oboe bombing system, both of which worked along similar lines. By measuring the distance to a radio station, the bomber was able to navigate along an arc in the sky, dropping their bombs when they reached a set distance from another station. The main difference between Oboe and Gee-H was the location of the equipment; Oboe used very large displays in ground stations to take very accurate measurements but could only direct one aircraft at a time. Gee-H used much smaller gear on board the aircraft and was somewhat less accurate but could direct as many as 80 aircraft at a time and was passive.

Sperry made the Mk XIV under licence.

Did anybody in the US use it?

Looks like they were only for British use.

[KJ_Lesnick]

Wuzak

Oboe used two stations at different and well-separated locations in England to transmit a signal to a Mosquito Pathfinder bomber carrying a radio transponder. The transponder re-transmitted the signals, which were then received by the two stations. The round-trip time of each signal gave the distance to the bomber.

So each had the same data?

Each Oboe station used the radio ranging to define a circle of specific radius, with the intersection of the two circles pinpointing the target.

When you talk about the circles, do you mean the intersection of several radio wave intersections or coordinates?

Gee-H was used to supplant the Oboe bombing system, both of which worked along similar lines. By measuring the distance to a radio station, the bomber was able to navigate along an arc in the sky, dropping their bombs when they reached a set distance from another station. The main difference between Oboe and Gee-H was the location of the equipment; Oboe used very large displays in ground stations to take very accurate measurements but could only direct one aircraft at a time.

So this was used for either the master-bomber, or nuisance raids...

Gee-H used much smaller gear on board the aircraft and was somewhat less accurate but could direct as many as 80 aircraft at a time and was passive.

This was probably used for the area bombing raids....

Looks like they were only for British use.

Understood...

[wuzak]

Each Oboe station used the radio ranging to define a circle of specific radius, with the intersection of the two circles pinpointing the target.

When you talk about the circles, do you mean the intersection of several radio wave intersections or coordinates?

The circle is around one of the radio transmitters.

The range to that transmitter (radius of the circle) was determined by the length of time the signals would take to be sent to the aircraft and retransmitted back to the transmitter station.

[wuzak]

Gee-H was used to supplant the Oboe bombing system, both of which worked along similar lines. By measuring the distance to a radio station, the bomber was able to navigate along an arc in the sky, dropping their bombs when they reached a set distance from another station. The main difference between Oboe and Gee-H was the location of the equipment; Oboe used very large displays in ground stations to take very accurate measurements but could only direct one aircraft at a time.

So this was used for either the master-bomber, or nuisance raids...

Gee-H used much smaller gear on board the aircraft and was somewhat less accurate but could direct as many as 80 aircraft at a time and was passive.

This was probably used for the area bombing raids....

Oboe would have been primarily used by pathfinders, since there were limited numbers of aircraft that could use it. Note that one aircraft could use Oboe per transmitting station pair (Cat & Mouse), but there were several transmitting station pairs that could be used and that any two stations could be paired as Cat & Mouse.

Gee-H would enable the main bombing force to use the navigation aids, since many aircraft could be directed using the one transmitting station pair.

I'm not certain, but I think that the master bomber in RAF raids would often be a pathfinder, equipped with Oboe and target indicators TIs.

I remind you that the RAF Master Bomber role differed from that of the USAAF. The RAF's MB's role was to direct the bombing, call for corrections, remarking, etc.

[KJ_Lesnick]

The circle is around one of the radio transmitters.

So it marks the distance...

Oboe would have been primarily used by pathfinders, since there were limited numbers of aircraft that could use it.

Okay, I gotcha

Oboe would have been primarily used by pathfinders, since there were limited numbers of aircraft that could use it. Note that one aircraft could use Oboe per transmitting station pair (Cat & Mouse), but there were several transmitting station pairs that could be used and that any two stations could be paired as Cat & Mouse.

So there were enough pairs to guide in a couple of path finding aircraft...

I remind you that the RAF Master Bomber role differed from that of the USAAF. The RAF's MB's role was to direct the bombing, call for corrections, remarking, etc.

I didn't know the USAAF had a master bomber...

[wuzak]

The circle is around one of the radio transmitters.

So it marks the distance...

The Cat station sends out a signal. The aircraft's transponder returns it. The Cat station calculates the distance.

The signal is sent in morse code - dots or dashes. If the aircraft is too close then it is all dots, if it is too far the signal is all dashes.

Oboe would have been primarily used by pathfinders, since there were limited numbers of aircraft that could use it. Note that one aircraft could use Oboe per transmitting station pair (Cat & Mouse), but there were several transmitting station pairs that could be used and that any two stations could be paired as Cat & Mouse.

So there were enough pairs to guide in a couple of path finding aircraft...

Yes, several pathfinder aircraft could be controlled.

I remind you that the RAF Master Bomber role differed from that of the USAAF. The RAF's MB's role was to direct the bombing, call for corrections, remarking, etc.

I didn't know the USAAF had a master bomber...

In the USAAF the master bomber is the lead bomber which has the Nordon bomb sight and actually aims at the target. The "toggleers", as you describe them, follow his lead.

[KJ_Lesnick]

wuzak

The signal is sent in morse code - dots or dashes. If the aircraft is too close then it is all dots, if it is too far the signal is all dashes.

Primitive electronics eh?

Yes, several pathfinder aircraft could be controlled.

Okay