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DeHavilland Comet 1 Design

DeHavilland Comet 1 Design

DeHavilland Comet 1 Design

(OP)
thread2-491869: de Havilland Comet Design changes
Hello, new to this forum. The above discussion was Closed, so I'm starting a new discussion.

I think there were some misstatements in the other discussion. The Comet 1 had a fuselage diameter of 10' 3", and the general skin thickness was 0.040". I forget what alloy was used, but it was of a more-brittle nature.

DeHavilland had several punch-riveting processes, but attached is a photo of an Erco punch-riveting machine used by DeHavilland for the Comet 1. In this photo, three 22' 0" x 2' 6" panels are being double-row-riveted to form a lap joint. The Erco machine had manual and automatic pitch movement controls, enabling the operator to move the pitch to the next riveting location. I believe it punched the holes, dimpled them, and then riveted them.


RE: DeHavilland Comet 1 Design

(OP)
Attached is a closeup photo of Comet 1 F-BGNX at the DeHavilland Aircraft Museum in England. It shows the finished rivets (double-row lap joint) that were punched/dimpled/riveted.

RE: DeHavilland Comet 1 Design

(OP)
Another photo of the rivet lines.

RE: DeHavilland Comet 1 Design

(OP)
You can see my video footage of the only remaining Comet 1 fuselage at https://www.youtube.com/watch?v=XvNGL8sqxyw&t=665s starting at 5:49.

I am building a full-scale Comet 1 nose replica from riveted sheet metal. Photos of the production jig are attached.

RE: DeHavilland Comet 1 Design

well you`ve set yourself a task ! Good Luck with it. Let us know when it`s done and I`ll come visit ! (my grandfather worked at Hatfield (design Engineer) on Dove/Heron and I`ve got a book of Trident calcs !)

I thought the Comet skin was thinner, 0.028" thk ? Whatever the Limies call 2024t3 ... L62? maybe 24-ST ??

I assume you have the RAE reports ? I found their conclusion (of 10" frame spacing) "amusing" = impractical = theoretical.

I think this punch riveting was the cause of a lot of Comet's problems, that and a high hoop stress (I calc'd it at close on 20ksi). And their testing methodology (assumed to be conservative, but unfortunately not).

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

Good Day.

The Comet I fuselage skin was mainly from D.T.D.546B Aluminum alloy with thickness along the sides 0,036" and top and bottom 0,028".
Frame spacing was 21" and stringer spacing 5,5"(average).
Source: Aeronautical Research Council R & M No 3248: Behaviour of Skin Fatigue Cracks at the Corners of Windows in a Comet I Fuselage.

Regards,

Andries

RE: DeHavilland Comet 1 Design

Looks like a fun project, but I can't help but ask - what's the utility of a replica of the nose cone of a Comet 1?

RE: DeHavilland Comet 1 Design

A neat home for a flight simulator ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

That's one reasonable answer I suppose

If it's Comet 1 accurate though, does it have room for all 3 of the friends you need to properly simulate a flight? upsidedown

RE: DeHavilland Comet 1 Design

(OP)
SwinnyGG, you asked what's the utility of a replica of the Comet 1.
  1. To impress the ladies. : )
  2. To bring back something that is nearly extinct (the only Comet 1 fuselage is at DeHavilland Aircraft Museum in England.
  3. The various museums have (sadly) rejected my offers to buy one of their Comet noses.
  4. This is a full-scale replica, so it will have room for all FOUR friends that occupied a Comet 1 cockpit.
  5. The Comet has a special place in my memory -- see my 6-minute YouTube documentary: https://www.youtube.com/watch?v=NjkO-8OUMYQ&t=21s
  6. This isn't my first rodeo: check out my full-scale, fully-functioning AVRO Vulcan simulator at http://www.avtutorials.com/vulcan_simulator .


RE: DeHavilland Comet 1 Design

(OP)
rb1947 and Andries, thanks for the input on the Comet 1 construction. That's insane that the top/bottom skins were 0.028" That's what I'm building my entire replica of (0.030"), and it's way too thin for a pressurized structure.

Attached is an image I made, comparing the dimensions of the B707/727/737 passenger window size compared to the Comet 1. It drives me nuts when people call them "the square windows." They weren't square at all, and the corner radius and height were identical to the B707/727/737. I've often wondered if Boeing copied these measurements from the Comet 1, but made the windows more narrow due to the closer frame spacing of the Boeing jets.

And, rb1947, that's fascinating that your Grandfather was an engineer at DH. Thank you for sharing that!

RE: DeHavilland Comet 1 Design

Thanks for those photos, they shed a bit of light.
Short pitches aplenty in that design.
It must have been a Friday afternoon too... lots of positional variation.

RE: DeHavilland Comet 1 Design

compare a Learjet cabin entry door with a HS125 door ... which company was traumatized by a fatigue failure ?

shows you that square cut-outs are acceptable ... if you use enough Aluminium.

I hadn't realised that the Comet windows were so wide.

Have you done a Black Buck raid in your Vulcan ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

Ever thought of building a 1/3-scale Comet 1, 2 or 3?

B-29 Replica Takes Shape [35% scale]
https://www.eng-tips.com/viewthread.cfm?qid=497673

BTW... thin pressurized skins were possible in the 1950s... if NOT riveted. Boeing KC-135, 707-100 and 720 fuselage skin panels were made from thin sheet, with internal doublers and stiffeners... all 'bare aluminum'. These parts were placed on curved-contoured tools, 'stacked/clamped-in-place' and spot weld-thru. VERY large panels could be made from 2 or 4 large panels... also spot welded together along edges. After the bare panel was assembled, then it had rudimentary corrosion protective finishes and edge sealing applied. This construction was generally durable enough for 25-to-35-years.

Later-on adhesive bonding and chem-milling and now precision milling can do the same... for long/wide, thick, contoured sheet-panels... did the same 'job' with much lower weight, greater durability and low human 'touch-labor'.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

RE: DeHavilland Comet 1 Design

(OP)
rb1957, yes, a Black Buck raid would be cool! A little bit lengthy, though... You know your history! And, yes, that HS.125 door had a big, round top, with radius corners at the bottom.

WKTaylor, with respect to model builders, I never had interest in scale models. A 35% scale B-29 is very cool, but my interest lies in the real airplane. Of course, one cannot buy a B-29, or a Comet 1. The only solution is to build one.

Ng2020, you mention the short rivet pitch and positional variation. I noticed that, too... I always wondered if the short pitch was too short. The positional variation? That's tough to get right if a machine/robot isn't doing the riveting or a drilling template isn't used. I'm guessing that neither was available for those complex curves near the fuselage nose, so it was all hand-drilled, dimpled, and riveted.

RE: DeHavilland Comet 1 Design

I guess all the old Nimrods have gone to the great hangar in sky ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

(OP)
rb1957, yes, the last iteration was the Nimrod MRA4. The program was cancelled in 2010, and the completed airframes (and of which some flew) were torn down in complete secrecy. Only covert photos exist showing the teardown.

The Nimrod MRA4 was not much like the Comet, or the other Nimrods, though. It was really like the 737MAX compared to the 737NG and Classic series. Not the same plane by a long shot.

RE: DeHavilland Comet 1 Design

would've thought the nose was similar ... even with the bomb bay fairing

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

(OP)
rb1957, no, all that Nimrod structure was rebuilt in the nose, especially the windshield section. When Boeing closed the 737-100/-200/-300/-400/-500 line and built the 737NG (-600/-700/-800/-900), they designed and built completely new wings, landing gear, vert/horiz stab, flaps, landing gear, cockpit arrangement, and also made major modifications to the fuselage structure design. That's what one calls a completely new airplane... not a 737. The 737MAX is, to an even greater degree, a completely new airplane. The 737 Classic, 737NG, and 737MAX really have nothing to do with each other, other than they share the same pilot Type Rating -- this means costs savings to airlines, and nothing more. It's about the pilot Type Rating.

In the case of the Comet > Nimrod Classic > Nimrod MRA4 progression, each iteration was a completely new airplane.

But, it was sad to see the Nimrod MRA4 project destroyed.

Now, there's nothing left except a few museum pieces, which will never go into private hands. That time has passed. If this was the 1990s, one could still get a Comet 4C nose or something, but no more. So, let's go back to 1949 and build a replica of the Comet 1. That's the idea.

RE: DeHavilland Comet 1 Design

As I recall the RAF Nimrod MRA4 was intended to be electronic surveillance/countermeasures. However the design had many/unresolved safety issues with environmental and electrical/electronic systems... which eventually lead to the loss of an aircraft during an airshow.

I think the RAF acquired a few EC-135R... and may be acquiring a few E-7 AEW&C 'Wedgetails', also.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

RE: DeHavilland Comet 1 Design

not my memory ... Nimrod just became too expensive. Yes, there was an airshow accident. Yes, there could be an issue with the systems (not if they were new builds)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

RB.. I think that the RAF mishap investigation opened the can-o-worms and identified several serious/complex/expensive systems problems. Scared them and decision was made... The jets were removed from service ~2011. I saw a 'briefing on the Nimrod issues'... just can't remember 'where/when'. Here is some google results.

The crash near Toronto [into lake Ontario] during a demonstration flight...

1995 Royal Air Force Nimrod MR2 crash
https://en.wikipedia.org/wiki/1995_Royal_Air_Force...

Royal Air Force Jet Crashes in Toronto During an Airshow
https://www.youtube.com/watch?v=-ftXLyBqNKU

And wartime accident 2006...

2006 Royal Air Force Nimrod crash
https://en.wikipedia.org/wiki/2006_Royal_Air_Force...

RAF Nimrod air crash investigation delivers devastating verdict
https://www.theguardian.com/uk/2009/oct/28/nimrod-...

The Tragic Story Of Nimrod XV230
https://www.youtube.com/watch?v=QXEFgJKZZ4g


Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

RE: DeHavilland Comet 1 Design

true, accidents have many fathers. I think the way the plane was operated, without a strong safety culture, (much like many other spectacular accidents) had a lot to do with it. Working with an old airframe and sys architecture also. Yes, much had been spent, and much more needed. I think ultimately it came down to money.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: DeHavilland Comet 1 Design

At the end of the Nimrod MRA4 saga, Boeing suddenly announce that they were closing the AWACs Sentry production line and would be taking final orders.

Message to UK 'buy AWACs or you will have nothing’. So UK bought seven E3D Sentry, to be based at RAF Waddington, NIMROD was cancelled.

RE: DeHavilland Comet 1 Design

E3 sentry is not a maritime patrol aircraft. Is it comparable?

RE: DeHavilland Comet 1 Design

RAF is acquiring/operating Boeing P-8 Poseidon's for maritime patrol...

https://www.raf.mod.uk/aircraft/poseidon-mra1/

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

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