John Cobb,

[carl brothertonParticipant @carlbrotherton75833]

John Cobb the ill fated quest for speed.

[carl brothertonParticipant @carlbrotherton75833]

I have bought the book and read it! Quite an accomplishment for a state educated numpty.

Enough about me, it is time to say any boat modeler this is a must read.

For me it is a great read, about technicalities, what could have been and should have been, if those traditionalists, would only have recognised and appreciated that there is benefit from listening and adhering to contracts, the wishes of the bill payers, and professional engineers.. A bit boring for some, yet a good read.

The fact that jet X motors, were used in testing models, gives me hope that I can complete my own similar sized model.

The book is available for £20, delivered, from Thrift books, quite a discount from many sites.

[Richard SimpsonModerator @richardsimpson88330]

I did once read an article about John Cobb and was surprised at how accomplished he was while having nothing of the fame of the likes of Campbell. A very quiet and unassuming chap from what I remember.

Edited By Richard Simpson on 05/07/2021 22:45:27

[redpmgParticipant @redpmg]

Sad that John Cobb died in much the same way as Campbell – remember seeing a film clip of the crash as a child – had a far bigger impact on me than the K7 one – read somewhere John Cobb was indeed a very quiet & unassuming man – believe that holds true for the majority of great people.

Believe that Donald Campbell owed his fame to the fact that he was the heir to a speed dynasty – but also  think he was a much more unassuming and quiet person than his father. .

There are still wheel tracks visible in the salt from Malcolm Campbell's unsuccessful 1929 run at Verneuk (deceitful) Pan here in SA

Edited By redpmg on 06/07/2021 10:34:53

[carl brothertonParticipant @carlbrotherton75833]

It is a very interesting story, supported by actual correspondence. I was very surprised at the inter relationships of a large number of personalities, some well know, plus a lot of inputs from various institutions and their facilities.

It is tragic that it seems that the accident probably should not have occurred, also if it had, the boat probably would not have broken up, as it did, although this may not have saved Cobbs live.

It is an excellent book, clarifying what did happen and probably why. It seems that the boat was capable of +200 mph reasonably safely.

[PhilbyParticipant @philby]

Hi Carl

Thanks for the information, copy on order

Looking forward too reading this

Phil

[ashley needhamParticipant @ashleyneedham69188]

+200 mph….but not with a Jetex! There is a scale jetex Crusader plan out there somewhere for balsa construction, see Jetex.org,  but good luck with that!

Bluebirds success partly due due to analysis of the Cobb issues, and of course by carrying out several trials and lots of mods on the craft.  Also bb Jetex plan at jetex.org (more luck required)

And…. Swordfish plan, no luck required, works a treat 🤓

Ashley

Edited By ashley needham on 08/07/2021 12:49:06

[Paul TParticipant @pault84577]

The Jetex plan is here LINK but this particular plan is copyrighted by Jetex

[Ray Wood 3Participant @raywood3]

Hi All,

That is a Model Maker plan, I doubt if it's still 2/6d but it could still be on the SARIK X-plans list ??

Regards Ray

[carl brothertonParticipant @carlbrotherton75833]

I drew up my own plan, based on a drawing on the Internet, studying photos on the internet. Then the project stalled, partly not being clear where the CG should be. Then I had and have drive line issues, wanting to use a flexi drive shaft.

More recently I decided that the CG needs to be pretty far back.

The initial thoughts were using a (I think) 7 cell Sanyo Nicad, using a 480 motor.

My present thoughts are a Inrunner using a Lipo. I probably now would now use a solid shaft, at a shallow angle. With the passage of time I am thinking of about, 150-200 watt motor. I now need to identify the most useful KV.

Finishing is the most problematical set of issues now.

In a way the book did help in understanding a little of what was intended.

With respect to Bluebird, it is evident that the forward 3 pointer is not the only concept. As the Spirit of Australia is not apparently a 3 pointer of the Bluebird or Crusader type.

As for scaling speed, dimensionless analysis is often used to provide a pointer. I have no idea as to what is an appropriate set. What is certain is that the Froude relationship is not the one. As it really tells you a long hull narrow beam provides the highest speed for a set power input, for a displacement hull. |Mentioned in the book, much to the disappear of Railton.

[ashley needhamParticipant @ashleyneedham69188]

The cobb needs to have the c of g really rearwards, reports of model builders all say the weight needs to be as far back as poss, as the nose digs in.

One of our chaps has a prop powered model and it is really wet until going very fast, and this has been borne out by the one and only test run of mine.

As mine is edf powered then this is even more of an issue. The other issue is the forward rudder which is….interesting.

Ashley

[Paul TParticipant @pault84577]

This thread might be helpful LINK

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