Old school design methods
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probably not true, but i used to have a stress engineer colleague who claimed to have been on the original comet stress team, and he always told us how some of the numbers they were getting from certain areas, were far above expected, so they disregarded them as spurious.
so here endeth the lesson, don't disregard, disprove.
edit, just been in the loft ( attic ) and found my old slide rule, and a mechanical calculator with instructions, with a certain 2 letter logo embossed in the hammerite painted case, she's in fine fettle, must be worth a few bob on ebay.
so here endeth the lesson, don't disregard, disprove.
edit, just been in the loft ( attic ) and found my old slide rule, and a mechanical calculator with instructions, with a certain 2 letter logo embossed in the hammerite painted case, she's in fine fettle, must be worth a few bob on ebay.
Last edited by Bye; 7th Jun 2013 at 14:27.
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Slide rules wouldn't be any use today - you have to be able to add and subtract using pen and paper.....
My old boss once remarked that when he was a very junior stressman and his mistakes cost the company a few hundred, he was given a large circular slide rule, but now he was TD and his mistakes might cost millions he only had a six inch rule.
My old boss once remarked that when he was a very junior stressman and his mistakes cost the company a few hundred, he was given a large circular slide rule, but now he was TD and his mistakes might cost millions he only had a six inch rule.
Last edited by Owain Glyndwr; 7th Jun 2013 at 16:24. Reason: change of emphasis
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I went to McDonnell Aircraft to pick up a new aircraft for my squadron. A good friend who was working in engineering showed me his work area.
It was in a large room the size of two basketball courts chockablock with narrow aisles and desks shoulder to shoulder in rows.
The theory was to put the engineers close enough together that they could take a few steps and communicate with the all the other engineers in their work group, or take a few more steps and communicate with adjacent work groups as necessary.
This was how the F-4 and F-15 were designed in the days before CAD.
It was in a large room the size of two basketball courts chockablock with narrow aisles and desks shoulder to shoulder in rows.
The theory was to put the engineers close enough together that they could take a few steps and communicate with the all the other engineers in their work group, or take a few more steps and communicate with adjacent work groups as necessary.
This was how the F-4 and F-15 were designed in the days before CAD.
I can't recall a single occasion where my slide rule stopped working because of battery problems
One thing I have noticed recently is how much the price of wide carriage printers has dropped.
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god the time i spent washing out ink pens in the sinks was horrendous, i even resorted to taking the pens on holiday for 2 weeks once to avoid the dreaded monday morning dried out pen.
we used to draw on vellum after the linen was replaced, and my old section leader would come around with his pipe alight, take a look at the scheme and blow down the pipe, the following shower of sparks would ignite lots of little holes in the vellum which then had to be designed around, which is why the core fairings on the E4 are the shape they are
we used to draw on vellum after the linen was replaced, and my old section leader would come around with his pipe alight, take a look at the scheme and blow down the pipe, the following shower of sparks would ignite lots of little holes in the vellum which then had to be designed around, which is why the core fairings on the E4 are the shape they are
which then had to be designed around
Love it. Only slightly of the thread, but reminds me of being handed up sudden major heading changes in the middle of the night, in the middle of the Indian Ocean. Seems an unthinking F/E had put his teacup on the N/Os chart.
The heading changes were to navigate around the teacup!!
I went to McDonnell Aircraft to pick up a new aircraft for my squadron. A good friend who was working in engineering showed me his work area.
It was in a large room the size of two basketball courts chockablock with narrow aisles and desks shoulder to shoulder in rows.
The theory was to put the engineers close enough together that they could take a few steps and communicate with the all the other engineers in their work group, or take a few more steps and communicate with adjacent work groups as necessary.
This was how the F-4 and F-15 were designed in the days before CAD.
It was in a large room the size of two basketball courts chockablock with narrow aisles and desks shoulder to shoulder in rows.
The theory was to put the engineers close enough together that they could take a few steps and communicate with the all the other engineers in their work group, or take a few more steps and communicate with adjacent work groups as necessary.
This was how the F-4 and F-15 were designed in the days before CAD.
My current employer places people in different locations - the CAD design draftsmen are in a different building to the senior engineers managing the design, and the junior engineering was outsourced to another country. To say that communications and teamwork have suffered would be an understatement.
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sorry, even further off thread, Leadsled, a very good mate of mine known as "the model citizen" in OZ was ATC for many years down there and has told me some stories that make your tea cup avoidance procedure very very real, in fact mild by all accounts.
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Hursley park
Hi jxk
I have just found your post from a few years ago about Supermarine at Hursley ...
I am the (volunteer) historian at Hursley Park and would very much like to chat about your time there with Supermarine if that is possible?
I have just found your post from a few years ago about Supermarine at Hursley ...
I was around in the days of the Attacker, Swift and Scimitar and remember that a full size wooden mock-up of the later was in the 'sheds' at Hursley (near Winchester). To reach this mock-up, draftsman had to negotiate a lengthy walk across a field of nettles armed with a ruler to take measurements and then go back to their drawing-boards and create the 3 view drawing.
When Computers Were Human...excellent read
https://www.google.com/search?q=when+computers+were+human&client=ms-android-metropcs-us&source=android-browser&prmd=ivsn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjhhp-UxfDSAhWpKsAKHRiFD2UQ_AUICCgB&biw=320&bih=486#imgrc=gYt8vEND 5idZUM:
https://www.google.com/search?q=when+computers+were+human&client=ms-android-metropcs-us&source=android-browser&prmd=ivsn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjhhp-UxfDSAhWpKsAKHRiFD2UQ_AUICCgB&biw=320&bih=486#imgrc=gYt8vEND 5idZUM:
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Perhaps some of you old timers can tell me if my thinking is correct in this regard. I have a picture in my mind of the old time design and manufacturing process. It had its limitations and one of these in the matter of stress and strain was estimates.
The old boys built em good! There was always a little bit more than required in each part and collectively those additions made for a very strong airframe. My company operated the BAC-111 until the 90's. We had DC-9's until 2002 and they were all designed "hell for stout" and stood up very well but they were very heavy airframes. The old joke was if you drove an tug into a parked BAC-111, you broke the tug. The old Douglas Direct Cable and Airplane Company came in a close second.
By way of an example, TWA Flight 841,On April 4, 1979, at or around 9:48 p.m. Eastern Standard Time (01:48 UTC), while flying over Saginaw, Michigan, the Boeing 727-31 airliner began a sharp, uncommanded roll to the right, and subsequently went into a spiral dive. Pilots were able to regain control of the aircraft and made a successful emergency landing at Detroit Metropolitan Airpor Despite the best efforts of the flight crew, the aircraft spiraled out of control, diving about 34,000 feet (10,000 m) in just 63 seconds.[1]:2 During the course of the dive, the plane rolled through 360 degrees twice and crossed the Mach limit for the 727 airframe. Control was regained at about 5,000 feet (1,500 m) after the pilots extended the landing gear in an attempt to slow the aircraft[3][4] The plane suffered substantial structural damage, but made an emergency landing at Detroit Metropolitan Airport in Michigan at 10:31 p. m. EST without further trouble. No fatalities occurred among the 82 passengers and seven crew members. Eight passengers reported minor injuries related to high G forces. https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)
Considering that CAD/CAM now makes airframes much lighter and that computer aided design makes limits a better known quantity, would an A320 hold up as well in the above scenario? Is there as much buffer in the newer airframes.
The old boys built em good! There was always a little bit more than required in each part and collectively those additions made for a very strong airframe. My company operated the BAC-111 until the 90's. We had DC-9's until 2002 and they were all designed "hell for stout" and stood up very well but they were very heavy airframes. The old joke was if you drove an tug into a parked BAC-111, you broke the tug. The old Douglas Direct Cable and Airplane Company came in a close second.
By way of an example, TWA Flight 841,On April 4, 1979, at or around 9:48 p.m. Eastern Standard Time (01:48 UTC), while flying over Saginaw, Michigan, the Boeing 727-31 airliner began a sharp, uncommanded roll to the right, and subsequently went into a spiral dive. Pilots were able to regain control of the aircraft and made a successful emergency landing at Detroit Metropolitan Airpor Despite the best efforts of the flight crew, the aircraft spiraled out of control, diving about 34,000 feet (10,000 m) in just 63 seconds.[1]:2 During the course of the dive, the plane rolled through 360 degrees twice and crossed the Mach limit for the 727 airframe. Control was regained at about 5,000 feet (1,500 m) after the pilots extended the landing gear in an attempt to slow the aircraft[3][4] The plane suffered substantial structural damage, but made an emergency landing at Detroit Metropolitan Airport in Michigan at 10:31 p. m. EST without further trouble. No fatalities occurred among the 82 passengers and seven crew members. Eight passengers reported minor injuries related to high G forces. https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)
Considering that CAD/CAM now makes airframes much lighter and that computer aided design makes limits a better known quantity, would an A320 hold up as well in the above scenario? Is there as much buffer in the newer airframes.
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This might be of interest:
https://en.wikipedia.org/wiki/Slide_...of_an_Engineer
Cheap new & s/h copies available (re-search with your location & currency).
https://www.bookfinder.com/search/?a...slide%2520rule
https://en.wikipedia.org/wiki/Slide_...of_an_Engineer
Cheap new & s/h copies available (re-search with your location & currency).
https://www.bookfinder.com/search/?a...slide%2520rule
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It had its limitations and one of these in the matter of stress and strain was estimates.
Not really .. the numbers come out of equations although some of the set up conditions may require a bit of artistic licence at times. The bigger problem was the time and labour resource limitation. Hence one needed to be a tad more conservative to make up for not being able to look at a widget in sufficient detail.
With the advent of electonic computers which are great at doing LOTS of sums very quickly, the stressman can drill down a lot further into smaller and smaller parts of the structure. At the end of the process you can realise some weight savings.
Another consideration, if I recall correctly, is that some of the Airbus Types negotiated a reduction in the proof to ultimate factor which really gave a weight benefit.
Not really .. the numbers come out of equations although some of the set up conditions may require a bit of artistic licence at times. The bigger problem was the time and labour resource limitation. Hence one needed to be a tad more conservative to make up for not being able to look at a widget in sufficient detail.
With the advent of electonic computers which are great at doing LOTS of sums very quickly, the stressman can drill down a lot further into smaller and smaller parts of the structure. At the end of the process you can realise some weight savings.
Another consideration, if I recall correctly, is that some of the Airbus Types negotiated a reduction in the proof to ultimate factor which really gave a weight benefit.
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John,
I had a lot to do with Airbus loads and stressing,and I have never heard of any such negotiated reduction.
The big difference between now and then is that where in the old days resources limited one to studying say half a dozen cases on whatever depth ones budget and skill allowed, nowadays it is common to calculate the detailed loads for many more cases and many more locations and then to scan the total data set to get the worst case at each critical location. It is a different world from adding a bit of strength in case.
As a matter of fact, quite a lot of the airframe these days (or at least in the last days of metallic construction) is/was designed not by static strength but by damage tolerance, so there is a margin over the static strength requirements which I think was not there at the time of Zaphod's 727 incident.
Zaphod
Difficult to say how an A320 would have come out of that because the "Gs" are not known. A spiral dive of itself doesn't generate much g so it would depend on the severity of the pull up. All aircraft are designed to withstand 3.75g ultimate load at MTOW, so at lower weights they can stand much more. That 727 I think was at the end of the flight so it might well be capable of (say) 5g. In similar circumstances I would think that about right for an A320 also.
The overload due to high speed gear extension is another matter which would depend not only on the overspeed but also the detailed design of the gear.
I had a lot to do with Airbus loads and stressing,and I have never heard of any such negotiated reduction.
The big difference between now and then is that where in the old days resources limited one to studying say half a dozen cases on whatever depth ones budget and skill allowed, nowadays it is common to calculate the detailed loads for many more cases and many more locations and then to scan the total data set to get the worst case at each critical location. It is a different world from adding a bit of strength in case.
As a matter of fact, quite a lot of the airframe these days (or at least in the last days of metallic construction) is/was designed not by static strength but by damage tolerance, so there is a margin over the static strength requirements which I think was not there at the time of Zaphod's 727 incident.
Zaphod
Difficult to say how an A320 would have come out of that because the "Gs" are not known. A spiral dive of itself doesn't generate much g so it would depend on the severity of the pull up. All aircraft are designed to withstand 3.75g ultimate load at MTOW, so at lower weights they can stand much more. That 727 I think was at the end of the flight so it might well be capable of (say) 5g. In similar circumstances I would think that about right for an A320 also.
The overload due to high speed gear extension is another matter which would depend not only on the overspeed but also the detailed design of the gear.
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OG,
The advent of computers for everyone certainly has meant that one can spend the effort drilling down to that which is, rather than using that which appears to be, critically limiting.
Re factors, perhaps I dreamed it all.
When the A320 first was introduced into Oz by AN in the 80s, I had a number of discussions regarding the aircraft with whatever name CASA was that week (particularly in respect of flight test matters - which would have been with one of our PPRuNe posters who was the then local regulatory test pilot). My quite distinct recollection was that Airbus had negotiated a reduction from the usual 1.5 factor on the basis of all the electronic gee-whizz protection capability.
My recollection may well be flawed, of course, .. or the brain, as the seconds tick, slowly is following the body into decreptitude.
The poster to whom I referred probably will see this thread and correct my thoughts in due course ?
The advent of computers for everyone certainly has meant that one can spend the effort drilling down to that which is, rather than using that which appears to be, critically limiting.
Re factors, perhaps I dreamed it all.
When the A320 first was introduced into Oz by AN in the 80s, I had a number of discussions regarding the aircraft with whatever name CASA was that week (particularly in respect of flight test matters - which would have been with one of our PPRuNe posters who was the then local regulatory test pilot). My quite distinct recollection was that Airbus had negotiated a reduction from the usual 1.5 factor on the basis of all the electronic gee-whizz protection capability.
My recollection may well be flawed, of course, .. or the brain, as the seconds tick, slowly is following the body into decreptitude.
The poster to whom I referred probably will see this thread and correct my thoughts in due course ?
Moderator
When I worked for deHavilland in the early '80's, during the infancy of the Dash 8, it was designed with the aid of rather basic computer assistance. I think that even though computers were involved, there was a lot of old school slide rule calculations which really made the plane.
Following the fatigue test program of the "iron bird" airframe, the wing was to be pulled to failure. I recall that they installed the longest stroke hydraulic pull cylinder they could find - 8 feet of stroke. They pulled up on the wingtip with it (with the wing root very firmly held in the frame). The cylinder used up all 8 feet of stroke, yet the wing did not break. I don't recall if it "yielded", but had that been done in flight, the aircraft would still have been whole. Imagine a Dash 8 wingtip displaced 8 feet up, and not broken!
Following the fatigue test program of the "iron bird" airframe, the wing was to be pulled to failure. I recall that they installed the longest stroke hydraulic pull cylinder they could find - 8 feet of stroke. They pulled up on the wingtip with it (with the wing root very firmly held in the frame). The cylinder used up all 8 feet of stroke, yet the wing did not break. I don't recall if it "yielded", but had that been done in flight, the aircraft would still have been whole. Imagine a Dash 8 wingtip displaced 8 feet up, and not broken!
When CAD started to appear in drawing offices some of our older friends caused a drawing sticker to be produced with a DBH logo - "Drawn By Hand".
If we Future Projects numbers men defined an aeroplane, one of those DBH drawings of a three-view GA could be ready by lunchtime, whereas coding it for CAD could take a week. The latter was better if you were going to try a multitude of small variations, but as we rarely did that DBH won.
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DBH.
For sure.
A good mate of mine was (is) a superb on-the-board designer and draughtsman.
Utterly refused to be seduced by the new computer God .. and, likewise, could run off an original drawing far quicker than CAD output .. not to mention they were far more pleasing to the eye.
CAD, like WP .. great if you can develop and exploit a library of drawing elements and use previous drawings as the basis for new.
For sure.
A good mate of mine was (is) a superb on-the-board designer and draughtsman.
Utterly refused to be seduced by the new computer God .. and, likewise, could run off an original drawing far quicker than CAD output .. not to mention they were far more pleasing to the eye.
CAD, like WP .. great if you can develop and exploit a library of drawing elements and use previous drawings as the basis for new.
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Allthough modern CAD software seems to do magic, the geometry formulae behind are quite simple and can typically be solved geometrically. One of the first lessons engineers took in the past was how to dertime the intersection of two cylinders just be use of a ruler, pen and sheet of paper. It really is not black magic.
Or out of diagrams or Nomograms some clever scientist were coming up with.
In old style manufacturing you anyway required simple 2D drawings, for example to do a sheet metal cutout. You needed some simple basic geometry data to build your rigs, jigs and templates. So were used to already design that way, you defined your geometry in a way that you can determine the intersections and shapes you needed.
Today you design however you like (and however Nastran gives you some nice results) and then you hae to mill the part from a huge block of metal or (in the very near future) 3D print it. Old school engineers always designed with production and strength calculation in mind. They designed shapes for which reliable stress/strain/stiffness/buckling formula were existing and which were easy (and precise) to manufacturer. Many Details on the drawings were actually just "artists impression", as they did not define actual dimensions. Especially rounded sahpes (e.g. of a fuselage nose) were somehow accidental and high tolerance between frames / stringers, as the exact shape simply does not matter. Today in CAD you have to define all shapes exactly, as the computer can not deal with "some arc between these two points", it needs to know everything exactly. Much more exactly than it can finally be manufactured...
There are great benefits of modern technology CAD/CAM/FEM tools, but when it comes to initial design, to get quick estimates, to decide whether something can be realistically done or is practically impossible, old style scratch and simple formula technique work still great. If you want to optimize the last kg of dead weight out of an aircraft, modern tools are perfect. If you want to have a quick estimate, they fail.
the numbers come out of equations although
In old style manufacturing you anyway required simple 2D drawings, for example to do a sheet metal cutout. You needed some simple basic geometry data to build your rigs, jigs and templates. So were used to already design that way, you defined your geometry in a way that you can determine the intersections and shapes you needed.
Today you design however you like (and however Nastran gives you some nice results) and then you hae to mill the part from a huge block of metal or (in the very near future) 3D print it. Old school engineers always designed with production and strength calculation in mind. They designed shapes for which reliable stress/strain/stiffness/buckling formula were existing and which were easy (and precise) to manufacturer. Many Details on the drawings were actually just "artists impression", as they did not define actual dimensions. Especially rounded sahpes (e.g. of a fuselage nose) were somehow accidental and high tolerance between frames / stringers, as the exact shape simply does not matter. Today in CAD you have to define all shapes exactly, as the computer can not deal with "some arc between these two points", it needs to know everything exactly. Much more exactly than it can finally be manufactured...
There are great benefits of modern technology CAD/CAM/FEM tools, but when it comes to initial design, to get quick estimates, to decide whether something can be realistically done or is practically impossible, old style scratch and simple formula technique work still great. If you want to optimize the last kg of dead weight out of an aircraft, modern tools are perfect. If you want to have a quick estimate, they fail.