David I with you agree 100%

I take it all back clearly not having been involved in the restoration and not having seen the Hinds recovered from Afghanistan you are clearly a genius! As Churchill once said or was Sir Sidney Camm?

“Never in the field of aircraft restoration has so much been deduced from so little, from an armchair”

I take my hat off too you sir. Maybe you should nip out to Myanmar and get your deductive juices flowing they clearly need your amazing abilities.

All I ever hear is Spitfire, Spitfire, Spitfire! I’m bored with your pseudo expertise. At least you have finally admitted that it is what you think. What do you know about the condition of the Afghan Hinds please enlighten me? Half of the existing Hinds are New Zealand by the way! People can make their own minds up about what fires their imagination or are you an expert on that too? For some of us it is not just Spitfires!

Right so I know someone who has rebuilt Hawker biplanes and he for one has told me some of the costs involved therefore that is the first hand telling it to the second hand. Its not Chinese whispers – if someone tells you the labour rate is ‘x’ and it has taken ‘y’ hours its pretty simple maths.
In terms of rebuild costs all materials and parts need to be certified . That is expensive then add to that labour if your paying someone to build it and its becomes very expensive . In terms of the American Hurricane -he is clearly in a position where he can do a lot of the work himself and is in a country where raw material costs are better than the U.K. As for the CAA -they have a cost as per any other regulatory body .

I know all of the people building Hawker Biplanes and it still does not mean I KNOW. It means that is what I have been told. Not everything needs to be produced commercially, or did you completely miss the point about John? Aerospace materials are a global market so there is very little difference in the price between the US and UK and as you have just pointed out its the commercial labour costs that push up the costs. Anything is possible, you just have to try! Despite evidence to the contrary i.e. johns hurricane, multiple mosquitoes in NZ, Hornet project, Whitley project etc etc. People like you are always say what can’t be done.instead of what can. I anticipate yet another response explaining to me how you are right, but frankly I am bored and have better things to do. I actually responded to your negativity for others who might be put off by your arm chair polishing negativity!

My point is how do you know if you haven’t been involved? That’s not fact it’s your opinion and i think it’s a defeatist attitude. It’s easy to repeat what you have been told that doesn’t make it a fact. Otherwise we would be knee deep in Burmese spitfires which is all anybody seems to be interested in! You obviously haven’t taken my advice and looked at Johns website. For anyone else who may wish to be inspired have a look!

http://www.jneaircraftrestoration.com

All power to your elbow! More attention should be placed on worthy projects like this. It is a shame that all the money that has been spent digging up empty crates in the endless pursuit of non existent spitfires hasn’t been spent on some of the lost types that are being recreated like this one!

how many have you rebuilt?

My interest is 1930’s steel framed aircraft using tubular steel construction with steel plate gussets/fish plates, eg Hawker Hind – Hurricane. CAD drafting, 3D laser scanning and laser cutting are wonderful productivity tools that allow the recreation of small runs of antique steel fuselage members. This would have been cost prohibitive or impossible to imagine ten years ago. These tools allow the recreation of wonderful aircraft. Anecdotally , I have acquired an impression that laser cut parts are not accepted in aviation circles. At core, I surmise that heat affected zones at laser cut boundaries are considered to render such parts unacceptable.

I don’t think unacceptable would be the correct way to describe the attitude towards laser cutting for primary structures in aircraft. Simply there are other methods available that do not create the type of issues you describe. So why use it?

In the course of other engineering work I conduct business with laser cutters producing work for racing teams using 4130 tubes. I would accept that the forces that racing car bodies are subjected to may be equal or in excess to those that aircraft are subjected to. Laser cutters report no issue with the supply of laser cut 4130 components into the car racing industry.

These tubes are probably welded at the joints so the heat stresses imparted into the component would not be an issue. Chances are that they would not be an issue if they were not welded but how would you know? There are two methods, press on regardless and court disaster or test the material at great expense. Hawker biplanes and hurricanes are not made of 4130 they are t45 and t50. Nothing wrong with the material but it is different and should be treated as such.

I can understand that new technologies can be too complex for some to assimilate, and that a defensive response is to ride on the wings of hard earned credibility to dismiss an approach that requires you to launch a boat on unknown seas. This is OK, as long as it does not disadvantage or discourage progress. I can understand that the laser cutting technology of 2000 may have been cumbersome, and may have adversely affected materials, but I see the laser cutting technology of 2013 as entirely different.

It Is not ‘credibility’ it is reliability and predictability that are the watch word for aircraft. i.e. If in doubt test it properly or don’t do it. whilst on the face of it laser cutting seems cost effective if you use the method carry out all you stress testing and find it is all scrap it won’t work out cheaper. People do not cling onto old methods because they are prejudiced they do it because it works reliably and has done for decades. Other methods may well work but if they are not proven then why use them?

Putting on my Spock ears, the only way I can pecieve that laser cutting may affect a material is via heat. In the case of a high tensile steel, this may soften the material in the heat affected zone. So what ? ( I am not a metallurgist, so this is where a metallurgist can sit me on my behind and put me right ).

It puts heat stresses into the material that create a range of hardness and changes the tensile strength at the margins. Aerospace material manufacturers spend a great deal of time making sure that the materials are consistent so that loading’s are spread equally through the structure. If they are not your structure is now as strong as the weakest point. Welding can do this if it is not done properly that is why anyone welding up an aircraft structure should be approved.

In order to understand where a thought has come from, I try to go to the source. I figure most aeronautical engineers are afraid of things cracking up. Steve Austin, astronaut, a man barely alive. Challenger. Sally Ride. De Havilland Comet, lots of things falling after fluttering wings. I figure that cracks are what keep the engineer awake at night.

exactly and anyone carrying out this work should think about it very carefully. Don’t make assumptions it gets people killed!

I figure stress cracking, or more realistically corrosion/stress cracking is the issue. The segue to laser cutting is the creation of weakened boundary zones on laser cut parts that allow stress cracking to originate. My gut feel is that a soft boundary zone may actually mitigate against the birthing of cracks in fishplates.

Refer to my previous comment i.e. don’t make assumptions it gets people killed!

I have before me “Ferrous Metallurgy in Aeronautics – A complete survey of the qualities and characteristics of modern steels for Aero Work” by WH Hatfield, Aircraft Engineering May 1935. Relax, I also have a beer. Hatfield was the dude from England’s Vicker’s steel that I guess most influenced ferrous material selection for things like the Hawker Hurricane, which had high tensile stainless fish plates rivetted to a high tensile steel tube construction. I figure that this stuff was absolutely cutting edge in the 1930’s, requiring imaginative and open minded engineers exploring all the possibilities of fascinating new materials and processes. But their virgin, firework thoughts have now become the ossified dogma of the staus quo. I think Hatfield would have been driven to poetry by laser cutting and its possibilities.

Don’t underestimate 1930’s and 40’s technology and engineering some of it is still cutting edge.

I figure the fear of cracking really started with the move from timber based aircraft to metal based aircraft. In the opera citare Hatfield writes about the stresses created by punching and shearing metal parts. The staus quo accepts punched and sheared parts as being OK. The staus quo is comfortable with the creation of expensive punching and shearing tooling by vanishing artists, which, by its cost, holds back aircraft restoration. But the author of the staus quo warns : “there are a number of processes employed in fabrication, particularly with sheet materials, which are liable to leave the parts concerned in a state of internal stress. Any cold pressing or cold forming operation is liable to do so….it should be remembered that stresses of this kind are additional to the service stress, and they are apt to be ignored in calculations when designing.”

Exactly do not ignore the stresses imparted by the process that is as relevant now as it was then. If you look at Hawker fish plates they are polished on all side this to minimise the creation of stress points and spread the load equally through the structure. The holes for the ferrules are reamed for the same reason. They were not punched and were hand finished.

Put with colour, hidden microscopic stress zones created on material boundaries by punching or shearing operations affected by corrosion develop into microscopic cracks that open up on a sunny day and cause your wings to fall off above a preschool. So perhaps laser cutting may prevent this? Hatfield writes about how they tested for this in 1935 : ” Two pieces of 2.5 inch square were cut from high tensile stainless steel strip of two different qualities. Erichsen impressions (The depth of impression in millimeters required to fracture a cupped sheet metal supported on a ring and deformed at the center by a spherically shaped tool) were put on these four samples and, recognising that this left the samples in a state of internal stress, they were placed in a solution designed to cause accelerated corrosion. The solution was 50% HCl cold, and the pieces were left overnight. Numerous small cracks developed in two of the samples.”

So perhaps the thing to do is to crop some samples of high tensile steel in a sharp guillotine, a blunt guillotine and via laser cutter, and test them for corrosion cracking on their boundaries as described above. I will bet a six pack of Coopers stout that there will be more stress cracking in the guillotined samples. I would be interested in what anyone knows or thinks.

The operative word here is testing. I don’t know of any primary structure on a hawker biplane that would be sheared and left unfinished so i am not sure of the relevance? All the fish plates and fueselage tubes were cut and finished. the ferrules were ground and polished and are very high precision, the spacers and rivets just hold the joints together. To make fuselage tubes out of 4130 you may need to heat treat it. You might be able to laser cut the tubes and then hand finish them but i am not sure why you would want to? The watch words are tried and tested and that equals safe. There are plenty of methods of cutting tubes without creating a whole hot of potential issues for yourself. All food for thought though!