John Cobb’s Crusader

[carl brothertonParticipant @carlbrotherton75833]

This is the first time I have been informed of the correspondence on this thread.

I must thank Paul for his responses, which I was unaware of,

Ben I found a drawing on the web, printed it of. Then scaled it up, again using information with respect to the overall dimensions, posted photographs again printed out, using proportional dividers and a calculator.

I still have not put a power train in, with Paul's confirmation of what I suspected I will start considering the issues again. The indicated CG indicates that as much weight as possible has to go to the rear, particularly the lipo, as probably both the bulkiest and heaviest item.

[HowardParticipant @howard79726]

Paul

I'm sure that by now you have plenty of information on this craft, but the 7 November 1952 ( less than 6 weeks after Cobb's death) issue of 'Eagle' comic published quite a decent centre spread colour cutaway drawing by L Ashwell Wood showing the main general arrangement illustration with smaller side and front elevations. This reappeared in 'The Eagle Book of Cutaways' published in 1988 by Webb & Bower which you may be able to get a copy of – ISBN 0-86350-285-7. I found mine in a charity shop!

Howard

[ashley needhamParticipant @ashleyneedham69188]

Shame there did not seem to have been a follow up to this,…ie..did these get built and if so how did they run.

BUT I am in a position of perhaps trying to have a go myself and wondered in the interim if anyone indeed did get a plan together??

PT has the Jetex powered mini plan (hopefully) somewhere and that would be a great start but having had a quick sketch-up in the shed realise I need a bit more info.

Ashley

[John DickinsParticipant @johndickins22212]

Perhaps I'm showing my age, but I remember the day hearing the news of John Cobb's death. And seeing the newsreel film of his last tragic run on Loch Ness. I had a Keil Craft model of Crusader, it was built in the same way as a model aircraft and powered by a Jetex solid fuel jet engine. Anyone else remember them?

[Ray Wood 3Participant @raywood3]

Hi All,

As most things are On YouTube these days, and sure enough film of the crash !! hits 240mph looks like it hits a wave and sticks it's nose in a wallop 😢,

I suppose with the sponsors at the back the extra thrust pushed the nose under the water ??

It didn't take off like Bluebird which was doing 400mph +

Regards Ray

Edited By Ray Wood 2 on 01/04/2020 21:36:50

[ashley needhamParticipant @ashleyneedham69188]

Not that I have done much research but it looks like Cobb`s boat exploded rather than hit something. Not sure there is a consensus of agreement on exactly what happened?

Not seen the keil craft model, although there is a plan for a jetex one lurking out there somewhere.

Sometimes I can be so stupid. After faffing about trying to make sense of low resolution images off T'internet, it struck me that in the very same MB issue that the London was in, there was a Bluebird/Cobb article (using proper jet engines), accompanied by some very nice artwork, which is sharp and uncluttered and is exactly what I need!

Having just built (but not tested!!!) the Bluebird, I appear to be drawing much the same thing other than having sponsons at the rear.

The issue is what modifications to make?? Non scale water being thick and clingy it seems to me I need more buoyancy at the rear to try and keep the stern off the water a bit, so fatter sponsons. Then there is the rudder arrangement. Cant see one externally so the rudder must be underneath as per usual boat practice…BUT…in theory the rear hull lifts off the water….does this mean I need a little skeg or just a long deep rudder???

Ashley

[Paul TParticipant @pault84577]

Ashley

I didn't do a follow up simply because I was producing the drawings for someone else and my involvement ended when I sent him the drawings and specifications, as this was a commissioned project I didn't keep any copies of the drawings.

I do remember having a big problem with the centre of gravity and a slight problem with torque steer from the Jetex unit. To help overcome the C of G the sponsons became fuel tanks, the calculations indicated that the model would run fine until 50% of the fuel was expended after which it became unstable.

The torque steer became progressively worse as the motor reached it maximum revs but this was overcome by linking a small trim tab to the throttle servo.

Sadly I never saw it built or sailed but I did hear that the final version did run successfully on a Scottish loch.

Paul

[redpmgParticipant @redpmg]

This might be of interest to the modellers building various Bluebirds, Crusader & other Record Breakers

There is an in depth article by Ernie Lazenby and Eddy Mathews on building a working model Crusader from the now defunct MMI in June 2003 using prop drive and a 900 size rare earth magnet motor . Send me a pm if you are interested.. The article sets some background to John Cobb .

Vol 49 No 582 MB Hydro Topics article by Peter Hill on Crusader from which has a copy of the old plan

Jan 04 MMI Gas Turbines – The Future – again by Ernie L

Aug 04 MMI .The Spirit of Australia by El & EM (which I believe is the current record holder?)

May 97 MMI  Second build of a K7  Bluebird by EL & EM

July 94 MB Plan feature on K7 by Andrew Mccoy

Feb 05 MMI EL builds a working version of Speedlines K7

Apr 06 MB review of Speedlines K7 by Dave Abbott

Nov 98 MMI review of Don Walkinshaws Gas Turbine K7

Feb 03 MMI second review of D W's Gas Turbine K7 by Ian Williams

(saw this in action at Beale Park that year – water too short for it to get up to speed – incredible boat)

Oct 95 MMI Ernie L builds a K4 fast electric

Aug 94 MB Alan Miller reviews Touchwood Models K4

Mar 97 MMI Ernie L builds K3

May 03 MB Hydro Topics by Peter Hill has plan of Bluebird II

May 06 MMI Ernie L writes an article on the History of World Water Speed Records

Oct 04 MMI Ernie builds Miss England II – (Henry Seagraves)

Jan 00 MMI Graham Charles with free plans Miss Britain II

Sep 00 MB Model of Miss Britain III restoration in the US by Kevin Desmond

Jul 06 MB An Stradag Electric power by Kevin Desmond

then some on Miss America, Miss Canada III, and 6 articles on Slo Mo Shun

All in my collection .

 

Edited By redpmg on 02/04/2020 13:21:32

Edited By redpmg on 02/04/2020 13:28:07

[ashley needhamParticipant @ashleyneedham69188]

Pm sent!

cheers Ashley

[redpmgParticipant @redpmg]

Further I did hear at one time that it was thought that one of the sponsons took on water causing Crusader to virtually explode on her fateful run.

[Paul TParticipant @pault84577]

I've emailed the owner to ask him how he got on with it.

[carl brothertonParticipant @carlbrotherton75833]

I have over the years bought stuff to power the model, although I have made no progress.

I bought some bits and pieces to make a flexi shaft drive. The problem it does not seem to fit together. The Prop skeg? has a cantilevered rudder, which although a bit of an eye sore, I thought was a practical solution to steering.

My intention has been to drive it with a high KV inrunner, that would provide more power than a 480 brushed motor. This motor I was thinking of stuffing up at the front end, with a Lipo inbetween the rear sponsons, being the heaviest bit of kit.

All I wanted to do was run the model in a straight line, over a shortish distance, on the plane. Even this perhaps limited ambition, seems beyond my capabilities.

[ashley needhamParticipant @ashleyneedham69188]

I believe they found some wreckage, but I don’t suppose that they would be able to tell much, especially as the boat was doing 200+ mph?

Paul. Yes, be interesting.

one of the chaps at the pond did build a prop powered model, and this went quite well, however it was really “wet” until going fast. Always going to be an issue with this sort of thing, however it is something t.o be avoided on an edf model as it would just fill the hull with water.

I was worried about the Bluebird, however the very light weight means it draws very little depth of water, and (albeit at not very fast speeds) seems to be very dry. This should be good at speed, as the boat will lift further reducing big water ingress.

Ashley

[Paul TParticipant @pault84577]

A quick reply to my email

The first prototype build was done in ply and performed quite well but suffered from instability at higher speeds, it turned out that this model was out of balance and slightly heavier on the left side.

The final version was built out of carbon fibre and sailed very well, an official speed run was clocked at 53m/s (120mph) not fast enough for a record but the chap did admit to running out of nerve on the return run.

The boat is now in the USA.

[ashley needhamParticipant @ashleyneedham69188]

Carl. Procrastination and dithering are the enemy of the ‘specials’ builder.

i have personally seen one prop drive Crusader, and there are several on you tube.

Now is the time to resurrect your Cobb! Why don’t you post snaps of your bits on the forum and we can see what you have. With a flex I drive the motor would have to be forward, so that’s not a “choice” you have to make. The prop centre needs to be just above the bottom of the sponson floor, assuming you fit a surface piercing prop. See, it all just falls into place!

Paul. My bottle would go trying to control a boat doing 120 mph….

Scan of plan (Jetex) from redpmg received and very useful, thanks very much. Although as a plan per-se it it not of use, it has cleared up one or two issues for me and shown me the way regarding construction with useful bulkhead cross section shapes. It has also confirmed the overall proportions of the thing.

This will be a “representation of” model, like the Bluebird, but the challenge is the rather more difficult shape, and there is more to go wrong regarding depth of immersion and angles of the skids.

But. I have sufficient lite-ply and glue, so will get cutting tomorrow..Ashley

Ashley

[Dave MilbournParticipant @davemilbourn48782]

I may have got this horribly wrong, but my recollection of Jetex was a tiny, solid-fuelled motor which would run for about six or seven seconds – during which it wouldn't produce enough thrust to worry the skin on a rice-pudding. Did someone latterly nick the name?

DM

[ashley needhamParticipant @ashleyneedham69188]

DM. Tricky. The internet muttering go on about a Jetex plan, but The accompanying article goes on about RAE Farnborough producing a rocket motor producing 30Lbs of thrust for 20 seconds. That would be one impressive Jetex unit!! I think that the article is concerning the development of test bed type craft, and it may be that the plan was provided for home use. A model of about 11 or so inches would be built from the plan which may have been suitable for the larger of the Jetex units??

 

Edited By ashley needham on 03/04/2020 09:05:42

Edited By ashley needham on 03/04/2020 09:20:35

[ashley needhamParticipant @ashleyneedham69188]

sorry…been looking T`internet whilst typing. Found this, with THRUST AUGMENTATION TUBE, as per the plan.

[Dave MilbournParticipant @davemilbourn48782]

Yep – that's the way I remember it. The "standard" motor was a Jetex 50, while they made a smaller one called an Atom 35. I fitted one of those to a Ray Malmstrom-designed sheet-balsa Vulcan and it flew away on its one and only flight. The Jetmaster 100 was by far the largest and most powerful. My mate Dave had one but he could never afford the pellets!

I also remember D E Sebell and Co produced a series of scale aircraft kits for the 50 with its augmenter tube. These had very clever moulded balsa fuselages – like GRP mouldings but made from 1/16" balsa.They looked beautiful but cost a packet and I never got one to fly properly. I think I had a Hunter and a Gnat.

DM

Edited By Dave Milbourn on 03/04/2020 11:25:54

[redpmgParticipant @redpmg]

Was there not a Jetex 100 originally – about twice the size of a 50 – seem to have seen a few aircraft plans for it . Would have been much more powerful . never owned one – only the 50 model – and must admit all attempts in the air or on water ended in disaster.

Revamp of the original was called Jet-X ans seem to have only produced a 50 size motor . Have one here with a kit of Hawker Hunter produced by Keil Kraft in the late eighties as far as memory serves.

There's quite a few videos on you Tube of Jetex flying models revived powered by what looks like the head of a small fireworks rocket – some flights are really impressive – however cant for the life of me recall what they are called…………

[carl brothertonParticipant @carlbrotherton75833]

From my limited experience, I would not expect much from a Jetex 50.

In my case I put my unit in a Fairy Delta and a Starfighter, from memory they used moulded layered Balsa shells for the Fuselage. Both with Augmentor tubes. There was a problem of lighting them from memory.

I also mounted the unit on the flat bit of a Airfix Bentley (the so called fast truck)

The point is the flight of the aircraft owed more to how far you could throw it than the Jetex. In the case of the Bentley, barely moved, on a dead smooth surface. The thrust was for a few seconds only. I did try all the so called fuel mods of the time, filing groves down the pellets and some other things I have forgotten, probably related to ejecting the fuse as the thrust built. I remember that you had to clean the residue out, after each run, I think in soppy water to clean them out properly.

I know that some have in the past got them to fly light weight gliders, well, so the mags reported.

There were more powerful units available I think, 100, 150, and 200, as well as a unit called a rapier. I never saw any.

Personally, I had more success with a Guy Fawkes rocket strapped onto a KK Marlin boat. The thrust line was critical, either nose diving, taking off, or planing. The thrust from these items was comparatively immense, for just a few seconds. I tried two mounted on top of each other, staged, which ended with the model spinning and tumbling, without direction. I used the local canal for this.

[John DickinsParticipant @johndickins22212]

If I remember correctly there were several Jetex" motors sold by Wilmot Mansaur from "50" to "250". There were gauze and fuse included in the packet of solid fuels. I think that I built a "DH Vampire" and a "Mig 15", both were Keil Kraft kits and flew reasonably well. But like most of my model aircraft they came home in a paper bag!

[carl brothertonParticipant @carlbrotherton75833]

Ah, they are using Rapier powered Jets, a throw away motor. I do not think they are imported anymore, from the Czech republic. It was EU regulations that kibosh them. Perhaps things have changed.

Have a look a Mikes Flying Models, relevant section.

[Paul TParticipant @pault84577]

Dear All

I have caused some confusion in calling these things 'Jetex' its a hangover to my youth when I used to mess about with the real Jetex motors, which were actually solid fuel rocket motors.

The power unit that I designed this Crusader around is in fact a fully working miniature jet turbine engine built by Graupner link

As you can see from the video these engines are completely different to the little rocket motors.

Not for the faint hearted, a single engine can push a 1/6 scale model jet up to 250mph

Paul

[Paul TParticipant @pault84577]

To show how powerful these engines are take a look at this amazing model Blackbird link

Sorry about the idiot advert at the beginning but you can skip it after 5 seconds.

Edited By Paul T on 03/04/2020 13:32:13

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