Help + Info wanted. Buying a fire exposed air frame.
Hi dear Aviation pro´s,
Today I made a pre-buy inspection of a 1944 L4. The aircraft is in a dismantled state. The airframe looks good besides a welding of the frame. I just found out however that it was originally destroyed in a hangar fire. The only remains were the metal frame and some other tubings. All other parts used to belong to other cubs. The idea is to restore the aircarft to flying condition. My question; if this airframe was subjected to an enormous heat,... the danger would be that the strength is compromised. Would you buy such an aircraft? How can I found out the structural integrity? I am aware of destructive testing where a force is used to penetrate the metal. The depth of the point tells you something of the strength. Can I use this method to asses?
I would be really grateful if somebody could shed some light. The project promises to be a real interesting one besides the fire issue.
I'd be cautious, but not regard it as a show stopper.
Having an aeroplane that old which is, in effect, a "new" aircraft built from bits from numerous sources is really not that unusual - the frame has been re-used to carry the serial number and give it an original identity.
So, the issue is the condition of that frame, which may in reality have been a new-build item by a competent fabricator. So, there's a a possibility that it's good as new.
And there's a possibility that it's extremely dangerous and fire damaged.
If the second, the rest is fine, it needed re-covering anyhow, and you can get hold of a new frame to transfer the data plate onto, then this might yet be a bargain.
If you can find a good licenced engineer, who knows welded steel spaceframe structures (and in an ideal world who is also a qualified welder) they should be able to look over it and give you a useful opinion - they can probably also tell you how much work the rebuild will take you!
thanks for your reply. Indeed, it might be possible that it is not "THE" airframe but in this case I am pretty convinced that it is the same airframe. I have seen pictures (before and after the fire) and did a lot of research. I even have parts that are fire damaged. The frame itself is painted in a primer. As far as I know there is an airframe S/N, left and right wing spar number, aircraft S/N ad engine S/N. I have the registration documents and it all matches.
So my question, how can I be sure that this frame can be brought into the air? Any form of Non destructive testing I can use to asses a fire exposed airframe?
Yes there is, although a thorough visual inspection by a really experienced ground engineer is probably the most valuable thing you can have.
Also checking geometry against a known good frame.
You could get really clever and use a hardness tester and compare the results to the correct material in the correct temper to see if the steel has been de-natured. The risk with that is of the indentations that are used to tell the hardness causing a later fatigue issues.
Not having much of an NDT background am no pro but I am pretty sure a rockwell hardness tester or something of the like may tell the hardness of the steel (brittle if exposed to extreme heat). I would also think that rust would become a larger problem if the heat was excessive as the metal would have a higher carbon content.
The harness test is something I will definitely proceed with.
The more I am spitting around, I tend to believe that it is not the same airframe although the same S/N. I compared pictures of both airframes (one after the fire and the other one I saw today) Due to metal bending, there should have been a large part replaced. Not on the one I have seen today. No welding marks on that portion.
It is slowly coming together. Is it possible for the UK CAA to register an aircraft with a same serial number although with a different airframe number? As you mentioned, I take a serial number plate and put it on a new old airframe.
Last edited by el caballero rojo; 28th Sep 2011 at 08:49.
it may be worth removing a small section of the frame (and welding in a replacement bit of course) to subject it to stress/strain testing, and vickers hardness testing, in something such as a materials lab. this will quickly tell you if the rest of the airframe is still suitable
Regarding the legal aspects; is there anybody who can comment on the way to take a restoration project started. My aircraft is presently in a raw state. It has the registration paperwork from the CAA. Can I proceed myself (former aircraft mechanic) with an oversight by a JAR approved Inspector. As the new EASA rules will be implemented, I presume there will be some changes.
In your shoes, I would speak to somebody from the CAA before you start. It would be heartbreaking to spend time and money on a project to have a CAA surveyor reject it at the end. A phone call costs nothing (in real terms)
They have been quite hot with us on data plates and serial numbers (I work with historic aircraft) and if there are any doubts about the aircraft's true identity then the CAA will require that you absolutely prove the history beyond all doubt. That will of course mean log books and photos but also permanent markings on the structure.
Find out who your local CAA surveyor is, and get some advice from him. If he is happy with your plans at the beginning, you stand a much better chance of getting a succesful outcome.
the aircraft has already the registration document of the CAA but I am not living in the UK. I am presently starting to organize the restoration in Germany. So it will be difficult keeping everything going via the UK CAA. I am thinking however to continue via the UK way but need to find out how far local JAR approved technicians and inspectors can overview the restoration. The aircraft will not be EASA certified ( does it matter???). I got another tip to proceed via the LAA (light aircraft association) in the UK. Same problem; they only have UK based approved technicians and inspectors.
Your tip to call the CAA will definitely be the next step. NO way I want to spend all the money and effort to start all over again.
There are two possibilities...........the frame just burned out and was salvaged, or the frame was burned and then quenched during firefighting procedures. If it was the second, I would proceed with extreme caution. I once lost some WW11 truck wheels and tyres during an arson attack, and due to known quenching issues, was told that no way should I re-use the wheels, due to compromising of the metal's strength.