A couple more B-17 questions... (1 Viewer)

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Iron and steels have a big variance in thermal expansion...............
I am sure if i was an issue in USA aviation there would be conventions to cope.

As you say, it was well known since blacksmith days, and yet people believe that the makers of large, complicated aircraft hadn't figured it out by the 1940s.
The coefficients of expansion were known and would be allowed for. The planes were not assembled out doors and while the California plants were not air conditioned in the early 1940s the Seattle plant was not unheated in the winter. We are talking about a difference of around 40 degrees at most?

Differences between aluminium and steel were also well known, the engine makers went through a lot of different alloys of both to get steel cylinder liners to stay in aluminium cylinder barrels, not to mention getting a good fit for aluminium cylinder head structures to stay fitted to closed steel cylinder barrels ( cylinder liner was not open ended but a closed tube on the cylinder head end, holes for valves and spark plugs excluded) in the 1920s.
BTW, normal assembly for the big air cooled radials in WW II was to screw the cylinder head onto the cylinder when the head was hot an allow the head to shrink onto the barrel. Of course the temperature difference was a lot more than 30-50 degrees.

The coefficient of plain steel is 0.0000072in per inch per degree Fahrenheit. or about 0.345in for a 100 ft span and a 40 degree shift.
Aluminium expands somewhat more (at least most alloys). The B-17 wing was built in four sections and attached to the fuselage.
Again this expansion was well known and charts/formulas were published in training manuals and handbooks for machinists and engineers. Such as Machinery's Handbook. 1st published in 1914 and updated ever few years.
see: Machinery's Handbook - Wikipedia


Also please see the erection and maintenance manual available on this site. The tools section shows a selection of tapered reamers for working on attachment holes to fit the tapered bolts/pins. You could enlarge a hole to fit but very little 'slop' was going to be allowed ( repeated reaming of holes as large components were swapped between aircraft). I don't know if oversized pins/bolts were available.
 
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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).

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


Thermal expansion affects everything, the biggest problems it caused historically were to makers of clocks/chronometers. At one time there was a prize worth millions in todays money just to produce a time piece that kept accurate time at sea. The expansion of a pendulum or spring is so small it is almost impossible to measure but it affects accuracy, bimetallic strips were used to counter this effect as early as 1730. I have no doubt that what you saw and worked on was done just fine but I am also certain that thermal expansion was considered at the design stage.

I was careful with my posts to mention Iron and steels, steel is just an alloy of Iron but has many different structures, The attached table quotes 4 types however there are many more. It only has one value for aluminium, but aircraft were not always made from aluminium itself but alloys of it.
Coefficients of Linear Thermal Expansion
It is possible that some wings some where didnt fit. My money would be on someone not doing things to procedure rather than there being no procedure to account for temperature differentials. It is basic engineering.
 
Main problem with not fitting would be the bolt holes not lining up when attaching the inner wing to the fuselage and the outer wing to the the inner wing.
B17_Av_4402_sk_spar_p137_W.png

Distance between bolt holes is measured in single digit feet. And as mentioned before, it was allowable and tools provided to ream out the bolt holes to correct minor problems.

See the erection and maintenance manual available here: B-17 Manuals

go to post #14

Part I, starting on page 58.

No mention I have found yet of differences in wings between manufactures, although they did use different landing gear retracting motors and the manual landing gear cranks turned in opposite directions between Vega aircraft and Boeing/Douglas aircraft.
I am sure there were other differences :)
 
Thermal expansion affects everything, the biggest problems it caused historically were to makers of clocks/chronometers. At one time there was a prize worth millions in todays money just to produce a time piece that kept accurate time at sea. The expansion of a pendulum or spring is so small it is almost impossible to measure but it affects accuracy, bimetallic strips were used to counter this effect as early as 1730. I have no doubt that what you saw and worked on was done just fine but I am also certain that thermal expansion was considered at the design stage.

I was careful with my posts to mention Iron and steels, steel is just an alloy of Iron but has many different structures, The attached table quotes 4 types however there are many more. It only has one value for aluminium, but aircraft were not always made from aluminium itself but alloys of it.
Coefficients of Linear Thermal Expansion
It is possible that some wings some where didnt fit. My money would be on someone not doing things to procedure rather than there being no procedure to account for temperature differentials. It is basic engineering.

Appreciate the link but this is something I'm fully aware of - spent many years at heat treating facilities. I think your last sentence sums it up. If thermal expansion was an issue in aircraft tooling (especially during WW2) this would have been well documented. The biggest issue I ever heard of with regards to large production tooling was the tooling being moved and not properly leveled.
 
Appreciate the link but this is something I'm fully aware of - spent many years at heat treating facilities. I think your last sentence sums it up. If thermal expansion was an issue in aircraft tooling (especially during WW2) this would have been well documented. The biggest issue I ever heard of with regards to large production tooling was the tooling being moved and not properly leveled.
It is difficult to discuss two different topics without some misunderstanding and I think we have had a misunderstanding. The effects of thermal expansion and even some quite complex metallurgy was known to ancient cultures, even if they didnt know why the things they did worked. Discussion of metallurgical effects can be interesting and informative especially to those who have never studied it. My points in this discussion is that:

1 All metals in aircraft experience thermal expansion to some extent.
2 By WW2 thermal expansion was so well known it was built in to engineering custom and practice. In terms of this discussion (as previously stated) it may have been the case that some assemblies did not fit but I cannot believe that thermal expansion was the cause, and lack of knowledge of thermal expansion was certainly not the cause.

Maybe I am just a bit "irked" that great engineers many of whom are not named or living are portrayed as buffoons simply from a story about wings not fitting because they didnt realise a temperature differential was important. It bears as much weight in fact as eating carrots improving night vision.
 
It is difficult to discuss two different topics without some misunderstanding and I think we have had a misunderstanding. The effects of thermal expansion and even some quite complex metallurgy was known to ancient cultures, even if they didnt know why the things they did worked. Discussion of metallurgical effects can be interesting and informative especially to those who have never studied it. My points in this discussion is that:

1 All metals in aircraft experience thermal expansion to some extent.
2 By WW2 thermal expansion was so well known it was built in to engineering custom and practice. In terms of this discussion (as previously stated) it may have been the case that some assemblies did not fit but I cannot believe that thermal expansion was the cause, and lack of knowledge of thermal expansion was certainly not the cause.

Maybe I am just a bit "irked" that great engineers many of whom are not named or living are portrayed as buffoons simply from a story about wings not fitting because they didnt realise a temperature differential was important. It bears as much weight in fact as eating carrots improving night vision.
Agree on all points. I've seen issues on structural components where thermal expansion was deemed the culprit, but I'll remain, you're not going to see this on a huge assembly tool (as shown on post 42)
 
Agree on all points. I've seen issues on structural components where thermal expansion was deemed the culprit, but I'll remain, you're not going to see this on a huge assembly tool (as shown on post 42)
Joe, every night of the week a girl get pregnant and a drunk crashes a car. That does not invalidate all the research on contraception and drink driving, In some cases people may forget the possibility of the effects of thermal expansion, just like they forget the effects of driving on ice, I cannot believe that ever happened on major assemblies on the USAs front line bomber force.
 
Joe, every night of the week a girl get pregnant and a drunk crashes a car. That does not invalidate all the research on contraception and drink driving, In some cases people may forget the possibility of the effects of thermal expansion, just like they forget the effects of driving on ice, I cannot believe that ever happened on major assemblies on the USAs front line bomber force.
On an assembled piece of structure in post assembly - absolutely, I've actually seen it; On a huge assembly jig - no way! I've probably seen 500 large components built on similar jigs shown in post 42, there was never a peep about thermal expansion on the fixtures by tool and die makers, tooling inspectors or tooling engineers.
 
About the remarks at the bottom of page 3 - did they apply to ALL B-17F/G aircraft or just the F models?

Yes and no.

If you look at the first note, the asterix (*) signifies that it applies to all Panels in Section 11 which runs from line 1 (Wing assembly - Inboard) to line 15
img6.jpg


img7.jpg



If you look at the various other notes they have a red number (in brackets) beside them that refers to the line number to the left of the left column of the table.

Using the sample below we find that note (A) relates to lines 4 and 11.
img4.jpg


img4.jpg


In line 4 that means that the A above the X identifies this part number wing assembly was fitted to B-17E-BO aircraft serials AAF42-2493 and subsequent E-BO series aircraft. For the part numbers above this in lines 2 & 3 the A indicates the serials of the B-17E-BO aircraft the wings were fitted to. All three wings are interchangeable.

When we get to lines 5 & 6 it gets a little more complex
img11.jpg


Line 5 wings are completely interchangeable with line 6 wings from the same manufacture. The serials are to identify when the wing change was incorporated. Interestingly the 15-7975 wing was carried as spares but the -79 is marked NP meaning not carried as a spare.

Taking line 5 on its own the wings all have the same part number but are the only completely interchangeable within their own serial group - that is BO wings are not completely interchangeable with DO or VE wings, DO wings do not completely fit BO and VE aircraft, etc. The reasons are covered in the big note (*) at the bottom of the page but that also indicates that in a worst case scenario you can fit it to any F model - that is a Boeing wing will fit a Vega with some rework like to the fire system and pressure transmitter system. I am not sure what that would involve but given that the PTM for the B-17 I would expect deleting the cockpit firex controls would be the first priority and given the USAAC/F's love of manuals there was probably even a TO detailing the work required.
img10.jpg


When we get to lines 7 & 8 it gets even more complex
img9.jpg

The -81 wing and the -122 wing are completely interchangeable with each other but are only fitted to the identified F model aircraft.
The wings of those F models and all G models are completely interchangeable regardless of manufacturer and dash number so there was full standardisation starting with the late F model wings. These two wings can be fitted to the earlier aircraft but with the fire extinguisher etc issues of the earlier wings still being a consideration.

Easy if you are used to deciphering this data but very confusing otherwise.
 

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DO wings do not completely fit BO and VE aircraft, etc. The reasons are covered in the big note (*) at the bottom of the page but that also indicates that in a worst case scenario you can fit it to any F model - that is a Boeing wing will fit a Vega with some rework like to the fire system and pressure transmitter system. I am not sure what that would involve but given that the PTM for the B-17 I would expect deleting the cockpit firex controls would be the first priority and given the USAAC/F's love of manuals there was probably even a TO detailing the work required.

Great info and agree with your last statement - Unless structure was built around the fire system and pressure transmitter system, I would guess this would not be that difficult to do, especially if a TO exists for detailed instructions.

Easy if you are used to deciphering this data but very confusing otherwise.
Agree - In some respects this is a lot less confusing than some other manuals I've seen. Thanks for breaking this down! I was going to attempt to this this but a little inconvenience called "a job" got in the way! ;)
 
What do you suppose may have inspired Freeman's "information" about the reinforced fuselage of Vega-built B-17Fs?
 
I suspect he meant that Freeman certainly interviewed folks that worked on assembly or field maintenance of B-17's while in service. While they could be considered a primary source the fact is that any author or police detective will tell you is that memory is terrible and very subject to change, hence unreliable.
 
I suspect he meant that Freeman certainly interviewed folks that worked on assembly or field maintenance of B-17's while in service. While they could be considered a primary source the fact is that any author or police detective will tell you is that memory is terrible and very subject to change, hence unreliable.

And every companies staff likes to think their products are superior to every other companies equivalent products so urban legends start (or are started by the company) about why this is so
 

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