Metal Mosquito built massively in the US

[Elmas]

Exam of one of the most dreaded subjects of the first year of University, Structural Engineering: Physics 1.
One of my Colleagues is standing in front of the blackboard.
Professor: "There is a car that starts with zero speed and an acceleration of xxx meters per second squared, find me the distance the car traveled after yyy s."
The student writes on the blackboard, after a short calculation: "zzz m."
Professor: "I'm afraid you have to come again to repeat the exam, Sir. m is a symbol, not an abbreviation, and must be written without period. Next one, please."
Needless to say, that Professor was not very well regarded by the University students, even if he was right.

 

[pbehn]

Exam of one of the most dreaded subjects of the first year of University, Structural Engineering: Physics 1.
One of my Colleagues is standing in front of the blackboard.
Professor: "There is a car that starts with zero speed and an acceleration of xxx meters per second squared, find me the distance the car traveled after yyy s."
The student writes on the blackboard, after a short calculation: "zzz m."
Professor: "I'm afraid you have to come again to repeat the exam, Sir. m is a symbol, not an abbreviation, and must be written without period. Next one, please."
Needless to say, that Professor was not very well regarded by the University students, even if he was right.

The team that lost a space probe by confusing imperial and metric units were missing at least one pedant like the professor.

 

[Elmas]

More simply, I always said my students that between a wall built with "bricks and stones" and a wall built with "brick or stones" there could be a difference of several thousands of euro, possibly to be paid out of their own pockets, so to be careful to what they were writing on their drawings...

 

[pbehn]

Out of interest, here is the abridged text from the letter that Geoffrey de Havilland wrote to Wilfrid Freeman proposing the concept that became the Mosquito, dated 20th September 1939.

"Dear Freeman, We have stopped all civil design and want to put our whole design staff on to war work. From former conversation with you and using the experience we have gained in very quickly producing types which have to compete with others from all over the world, we believe we could produce a twin engine bomber, which would have a performance so outstanding that little defensive equipment would be needed. This would employ the well tried out methods of design and construction used in the Comet and Albatross and, being of wood or composite construction, would not encroach on the labour and material used in expanding the RAF. It is specially suited to really high speeds because all surfaces are smooth, free from rivets, overlapped plates or undulations. It also lends itself to very rapid initial and subsequent production."

"The principal objects which would be achieved by this are shortly as follows:- 1. Its production would absorb a class of labour and material which is outside and additional to that used in the main aircraft production. 2. The smallest possible call would be made on 'Embodiment Loan' stuff etc., owing to its simplicity and to the fact that it relies mainly on performance for its defences. 3. it makes use of a design staff which has had much experience in very quickly producing aircraft types to meet specific and competitive needs. 4. The wood or composite construction allows of the minimum time and man-hours being spent on making jigs etc..."

It is a pity they didn't mention its use as a night fighter, photo recon, heavy long rage fighter and include its future role using the curvature of the earth and high altitude performance to extend the range of navigation beams, all of which were obvious strengths in 1938 when all has 20/20 vision about the future.

 

[pbehn]

Hey pbehn,

I am not trying to be obtuse, but I still do not see the problem with using the term stronger as I have done so above.

If you have two I-beams, one made of structural steel and the other made of structural aluminum, both having the same dimensions in all respects, which will support more weight? Which is 'stronger'? Assume the intent is to have the I-beam support as large a load as possible, without failure, at a relative short span.

).

You say you are not being obtuse but you just made a persuasive argument for aircraft wings to be made from steel, why weren't they? You may have all sorts of letters behind your name but I worked with engineers up to the top engineering head honchos with companies like Exxon Mobil, everyone was an engineer with letters of some sort, I was one of the few that wasn't. Make your case, you havnt so far.

 

[pbehn]

..If anyone tries to tell you something about an aeroplane which is so damn complicated you can't understand it, you can take it from me it's all balls.
R. J. Mitchell, advice given about his engineering staff to test pilot Jeffrey Quill during Spitfire prototype trials.

Gentlemen, please, don't be more Catholic than the Pope himself.
And, being born and raised in a Catholic Country, I know what I mean.

There have been some very complicated explanations here of the "ins and outs" of aerodynamics and fluid dynamics of aircraft structures and supercharged and turbocharged engines which when clearly laid out were perfectly understandable to me, and while I liked maths and physics I left school at 16. That doesn't mean I can design an engine or an aeroplane but I can follow the ideas and principles of those who did without thinking they were gods dabbling in hocus pocus and witchcraft.

 

[nuuumannn]

It is a pity they didn't mention its use as a night fighter, photo recon, heavy long rage fighter and include its future role using the curvature of the earth and high altitude performance to extend the range of navigation beams, all of which were obvious strengths in 1938 when all has 20/20 vision about the future.

Y'know, it's interesting that you say that, because even without hindsight, that could have been done and would have been a smart thing for de Havilland to do. Before the war, the concept of a high speed bomber tickled the Air Ministry and the C-in-C Bomber Command, Ludlow-Hewitt and head of the Technical Department, R.N. Liptrot were enthusiastic about it, but it was Assistant Chief of Air Staff William Sholto Douglas who was not. Simultaneous to the issuing of a requirement for the DH.98, Blackburn was also given the opportunity to develop its B.28 unarmed bomber, but it was also stipulated that it could be used for high speed reconnaissance and armed with cannon as a heavy fighter, yet it did not receive anything like the derogatory comments the DH.98 did.

When de Havilland published its figures for the DH.98, few believed them and this is what caused the negative reviews of the project - no one could believe that a bomber could do the speeds de Havilland promised, yet the B.28 was promising similar performance, but right from the bat it was touted as a multi-role aircraft. An order for a night fighter DH.98 basically saved the unarmed bomber's bacon and enabled the unarmed prototype to go ahead. Sholto Douglas wanted to fit the bomber with a tail turret though and requested that DH build two prototypes, one with a tail turret and one without, but Freeman gambled the performance of the unarmed prototype on that, stating that if it didn't meet performance, then DH would build the Mossie with a turret!

 

[ThomasP]

Hey pbehn,

Sorry, I misunderstood at first where you were coming from. Please grow up.

 

[Elmas]

Hey pbehn,

Sorry, I misunderstand at first where you were coming from. Please grow up.

So did I.
Dear ThomasP, I hope we will be able to continue discussion about Euler's critical load ( and also Johnson's parabolic formula, of course), Bredt's Formula and Mohr's circle and their application to airplane design in other places.
Ciao
Antonello

 

[ThomasP]

 

[pbehn]

So did I.
Dear ThomasP, I hope we will be able to continue discussion about Euler's critical load ( and also Johnson's parabolic formula, of course), Bredt's Formula and Mohr's circle and their application to airplane design in other places.
Ciao
Antonello

Just a simple explanation of the various methods of determining yield strength and factors affecting it would do, especially the Bauschinger effect.
I worked in testing for 30 years and its the first time Ive seen a so called engineer sound like an utter prat.

 

[Dana Bell]

When I studied engineering at RPI in the late 1960s, there were no freshman English classes - they figured if you knew enough of the language to get into the school, you didn't need any more. I always remember that when I find engineers who have trouble communicating complex topics in simple terms. Fortunately, in the last 50 years the emphasis has changed somewhat, and I find far more engineers who are great at explaining things...

Cheers,


Dana

 

[SaparotRob]

When I studied engineering at RPI in the late 1960s, there were no freshman English classes - they figured if you knew enough of the language to get into the school, you didn't need any more. I always remember that when I find engineers who have trouble communicating complex topics in simple terms. Fortunately, in the last 50 years the emphasis has changed somewhat, and I find far more engineers who are great at explaining things...

Cheers,


Dana

E to the X Dx Dy
E to the X Dy
Cosine tangent log of pi
Three point one four one five nine
Dis-integrate them, RPI!

 

[Dana Bell]

Hi Rob,

We learned "Tute Sucks" back then. we learned your fight cheer (designed to strike fear in the heats of of all Engineer sports fans everywhere) as an MIT call:

E to the X, d u, d x
E to the X, d x
cosine, secant, tangent, sin
3.14159
square root, integer, u d v
slip-stick, slide rule
MIT

Thanks for the reminder - I haven't thought of that in years!

(BTW, that's all one of the reasons I moved from engineering to history. Now I write books for a living. And my first research topic was the history of the Mosquito in US hands...)

Cheers,


Dana

 

[SaparotRob]

I didn't go to RPI but a good friend did. I did, however, conduct independent research into psychoactive substances there.
I was leery of writing "tute sucks". I went with the cheer as best I remembered.
Rob

 

[swampyankee]

E to the X Dx Dy
E to the X Dy
Cosine tangent log of pi
Three point one four one five nine
Dis-integrate them, RPI!

E to the x dy dx
E^ x dx
cosine secant cosine sine 3.14159
Go Tech!

I went to IIT, in Chicago.

-----------------

 

[swampyankee]

When I studied engineering at RPI in the late 1960s, there were no freshman English classes - they figured if you knew enough of the language to get into the school, you didn't need any more. I always remember that when I find engineers who have trouble communicating complex topics in simple terms. Fortunately, in the last 50 years the emphasis has changed somewhat, and I find far more engineers who are great at explaining things...

Cheers,


Dana

When I started in college (after some wandering around, I ended up a mechanical engineering major at a different school), one of the other freshman said he wanted to be an engineer because they didn't have to write, and he hated writing.

My first engineering job was as a test engineer. I spent about 75% of my time writing. Project engineers did even more (I managed to avoid that trap ). When I moved to more analytical positions, it dropped to about 50%. Overall, Strunk and White has been more useful than Abramowitz & Stegun or TImoshenko.

 

[ThomasP]

Hey pbehn,

First, re: "You say you are not being obtuse but you just made a persuasive argument for aircraft wings to be made from steel, why weren't they?"

Learn to read, or possibly learn to think about what you read relative to what your have read in the previous posts. My example of the I-beam in no way, either directly or indirectly, implies that the airframe of the Mosquito should be made of steel.

Two, re: "Exactly my point, it isn't complicated."

If it was not "complicated", there would be no need reason for this discussion. Nor would there be any need for engineering classes, or physics classes, or fabricating classes (including how to test materials), nor would there be any need to learn higher mathematics, or concepts/methods such as finite element analysis.

If it were not "complicated" you would realize that between what I have posted, and what Elmas has posted, you already have pretty much what you need to know (along with figuring out what to look up) to solve the relative 'strength' question of a cylinder made of Duramold vs typical aircraft grade aluminum of the earl 1940s. The only difficult part is setting up the problem (ie determining what all the factors are that matter relative to a complete and accurate answer to the question).

If you want a formal engineering description and analysis of the merits of a Mosquito airframe made of Duramold vs typical aircraft quality aluminum of the time, go ahead and try it. Once you learn all the engineering terminology, analytical methods and mathematics used, plus get ahold of a complete set of blueprints for the Mosquito airframe, sort out how the aeronautical engineers of the time would have gone about using aluminum to build a comparable airframe (ie learn what is needed to become an early-1940s aeronautical engineer), then actually perform the finite element analysis needed to determine what bits support what structure to resist what stress and how 'strong' the bits have to be to support the loads put on the structure, all having to work in concert to achieve the goal of not failing from one cause or another, you just get back to me. After you have done all this, even if you use modern day methods, such as computer programs for the math and finite element analysis, it will take you about a year to do the analysis.

Also, I do not understand why you think that I should have to explain something like the cylinder example - or the implications that it has for an airframe made of the same material (either material) - in terms of your liking. I can not see that I am under any obligation to do so - I am not being paid to teach you engineering methods or mathematics, nor have I been asked to do so as a favor.

The above may sound a bit snarky, but it really is not meant that way (well, except for the "you just get back to me" part, I must admit that is intended to be snarky).

 

[Elmas]

Physics I exams ( General Static, General Dynamic (including harmonic motion), General Thermodynamics) and same Professor of the previous post. A Student goes to the blackboard for his exam. The Professor is confabulating in a low voice with his Assistant and, without even looking at the blackboard, says in a dry tone: "Draw a Carnot cycle". ( don't you know what a Carnot cicle is? a thing that must be known before speaking about engines and compressors)... While the Professor resumes is confabulating with the Assistant, the Student seems to think about it a little and, taking the chalk in his hand and demonstrating remarkable drawing skills, much less Physics, draws an almost perfect circle. The Professor continues intensely to talk with the Assistant, then he looks up at the blackboard.

He suddenly becomes purple and the veins in his neck swell, but fortunately he avoids a stroke. "Draw me another one" he says in a strangled voice, resuming his conversation. Another equally perfect circle appears on the blackboard next to the first one. The Professor looks up. Almost climbing over the desk to make to the blackboard faster, he takes the chalk in his hand: between the two circles appears a frame, a handlebar, a saddle, a chain and two cranks: "Take this cycle and go!" he screams with all his breath "this is, as far as I'm concerned, the only cycle you will see in your life !!!!!"

Moral
......

 

[ThomasP]

?
Had to look that one up. Maybe so, but I do not like to think so.