A couple more B-17 questions...

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Hmmm - the last time I looked large structural components (like wings) are built on large wing jigs, usually made from some form of mild steel (4130 the most common). Now I've been to Seattle and worked at both the Lockheed Burbank and Douglas (McDonnell Douglas) plants located in Burbank and Long Beach respectively and never heard of large components not fitting together due to "assembly occurring in a higher temperature environment." Wood expands, I wonder how much thermal expansion occurs in tool steel

This is what the B-17 wing assembly jigs looked like at Douglas' Long Beach facility.



Production. B-17F heavy bombers. Three-story jigs are used for the assembly of the inner wings of B-17F heavy bombers at the Long Beach, California plant of Douglas Aircraft Company. Better known as the "Flying Fortress," the B-17F is a later model of the B-17, which distinguished itself in action in the South Pacific, over Germany and elsewhere. It is a long range, high altitude heavy bomber, with a crew of seven to nine men and with armament sufficient to defend itself on daylight missions. Douglas Aircraft Company

I'm sorry, this is laughable.

When I worked on the P-3 assembly line I could tell you that the wings and stub wing were built in Canada (Montreal), fuselage barrels were built in California. They went together just fine.
 
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Can you email me the answer (at AFROBINSON808@gmail.com) when you find it?
 
Flyboy, is there a wt and balance section of the wartime POH? If the basic empty was compared (serial numbers Boeing vs Vega) might reveal a somewhat consistent weight number. Ceteris Paribus wouldn't that reveal (or hint at) different production weight?
 
There are weight and balance charts in the B-17 -1 (POH). The empty weights out of the factory (and we're talking empty weight used for flight planning purposes) will not vary between production serial numbers in the POH and as earlier stated, when each aircraft rolled out of the factory their weight had to be within a certain percentage of each other, and it didn't matter if what production line you're talking about. Here's a link for a B-17F flight performance charts. Note the charts say "B-17F." They don't say anything about pertaining to certain lot numbers.

http://www.wwiiaircraftperformance.org/B-17/B-17F_Flight_Operation_Data.pdf

Here's an original 1942 performance report.

http://www.wwiiaircraftperformance.org/B-17/B-17F_41-24340_FS-M-19-1470-A.pdf

Once again Mike Williams' site shows it's value.
 
I see. So it's not tail specific, it's more model specific- military standard- one size fits all.
 
What do you mean, "within a certain percentage of each other"?
 
Roger Freeman may not have been 100% wrong on this. Certainly some of what he says about the wings can be said to be basically correct.

It is possible he had access to Technical Order 00-45S-1 and either did not fully understood what he was reading and/or took advice from someone who mislead him with some urban legend of the time.

As you can see from the pages below there are most definitely interchangeability issues between BO, DO and VE B-17F wings and some/all of the issues are highlighted in the remarks section at the bottom of img3. E wings are not useable on any F but late F wings are interchangeable with G wings and vice versa.

(PS I only uploaded img3 once so have no idea why is shows twice - I would hope that a moderator can delete the second copy)



 
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What date was that technical order published?

BTW, I think I read somewhere that the later B-17Gs built at the three "BVD" factories had full interchangeability of components. Can someone try to confirm whether or not this is correct?
 
Hoggardhigh said:
What do you mean, "within a certain percentage of each other"?
Click to expand...

When each aircraft rolls off the assembly line, they are expected to be just about identical in dimension, weight and configuration. There is consideration for "build up of tolerances" added weight because of repairs made due to production errors and variances because of application of paints, sealants and other organic materials. I recall 2%, SR mentioned 3%.
 
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No worries about the second copy (its easier if I just leave it) and EXCELLENT post - this is the "smoking gun." I heard of this type of document but never seen it for the B-17. If one understood it and explained it in proper context it would make better sense then insinuating that each B-17 subcontractor (Vega, Douglas) arbitrarily deviated from the original design. Don't put something to press unless you have a verified source and fully understand what you're writing about!

I could say then and now, once a US military design was/is frozen and placed into production the contractor, despite designing the item DOES NOT have the authority to undertake a major design deviation without approval from the government, and even more so when you subcontracted part or all of the end item.

Unless I'm reading this document wrong, I see many wing components produced by all 3 factories that are shown as interchangeable.

PS - I see nothing in there about "components not fitting together due to assembly occurring in a higher temperature environment."
 
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What does "build up of tolerances" mean?
 
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It means not every part was produced to a tolerance of plus or minus a fraction of an ounce. When you get an assembly of a dozen of parts (or a few hundred) that assembly could be several pounds over or under (much rarer) the "design weight". A complete airplane made of thousands of parts (or 4 engine bombers 10s of thousands of parts) could weigh several hundred pounds over the design weight. In some cases some lighter parts tended to counter act heavier parts, some planes came out a bit light and some a bit heavy. As long as the total weight variation was not over the 2-3% margin (or whatever the contract called for) the plane, subject to flight test, would be accepted and paid for. If it was too far over weight it wasn't even test flown. It was rejected for rework.

I don't know how they did it but I would guess that major components/sub assemblies were weighed as they were built and inspected and particularly heavy or light ones set aside/reserved for assembly to correct problems. Each airframe probably had paper work attached to it with a running tally of weight/s of components added at each stage or particular stages of assembly.
 
Many fabricated components will fall into a designed weight tolerance if they are "built to print." Engineers can almost predict what the weight of a casting or forging will be after it is machined down to BP tolerances. Again I'll repeat, what many people miss or ignore is the fact that aircraft are built on assembly jigs and fixtures as with many smaller sub assemblies. This will take the guess work out of hand lay outs and ensure that you get a "cookie cutter" production line. Blue prints show the design intent and provide inspection criteria, the goal is to have your tooling to be able to produce exactly what's on the drawing.

I mainly worked on "mature" production lines and don't remember issues with aircraft being over or under weight.
 
Most of an aircraft surface is made up of rolled metal, when rolling metal you have a tolerance =/-. If you make the aircraft with all metal on the maximum it will be heavier than one made from metal made on the minimum tolerance. If this is a problem then obviously the tolerances need to be tightened and the rolled metal becomes more expensive simply because the manufacturer rejects more strip at the rolling stage. When the soviets reverse engineered the B29 to the Tu4 it turned out 345kg heavier, while less than 1% it is still one third of a ton added which no one can see.
 

Iron and steels have a big variance in thermal expansion. Between room temperature and melting it can have several physical states, the change from face centre cubic to body centre cubic structure has a measurable change in volume which is the basis of dilatometry tests to establish heat treatment temperatures and weldability. There is a pin somewhere in a Spitfires wing assembly which is an interference fit, during assembly the pin must be cooled (or cooler than the hole it is put through), once assembled the thermal expansion ensures a tight fit since they are permanently at the same temperature.

Thermal expansion of Iron/steel is well known and widely used since the days of shrinking a wagon wheel rim onto a wooden framework. I have seen a pipeline structure mounted on rails grow as the sun started to shine on it and warm it, I have also seen steel pipes tested with aluminium "go/no go" gauges pass on a morning then fail at lunchtime when cross checked. In my experience it is something that occasionally had to be taken account of. It is for this reason, when taken to the limit all goods are quoted at 20 Celsius today, I am sure if i was an issue in USA aviation there would be conventions to cope.
 
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pbehn said:
Iron and steels have a big variance in thermal expansion.
Click to expand...

I was being cynical in my response...

You're getting very confused here with regards to single linear structure items and large aircraft assembly tooling that rival the primary structure of a battleship.

There is no substancial thermal expansion when you're talking about an aircraft assembly jig the size of a house and with dozens of gussets and fillets that allows no movement and in some cases are held to .0000 tolerances (look at the photo I posted in post 42). I've inspected tooling that were located on two continents with different weather conditions, these tools assembled items a lot more complicated than a B-17 wing and their dimensions and tolerances were identical and achieved perfect interchangeability.

Aside from this - the original comment was made about Boeing wings not being interchangeable with Vega or Douglas wings due to temperature conditions - I think we seen that this statement was extremely wrong if not utterly ridiculous. If weather conditions would have dictated a degree of interchangeability on aircraft structures, then think of the aircraft produced in Buffalo and on Long Island (Bell, Curtiss and Grumman), how about B-24s built at Willow Grove compared to those at Fort Worth, San Diego and Tulsa????

Maybe the B-24 didn't expand that much because some considered it ugly!
 
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