John Cobb’s Crusader

[ashley needhamParticipant @ashleyneedham69188]

Carbon fibre struts covered in balsa,a relatively easy operation, sanded and sealed.

Have had a quick dust of spray primer revealing loads of small dings, dents and grain to be filled.

Have had a thought and MAY paint the boat with some Rustins external grade silver paint as used on the saucer. This is relatively thick and may do a better job of hiding tiny imperfections rather than spray, which shows ALL imperfections.

Law of diminishing returns filling and sanding horribly curved foam bits.

Ashley 🚣🏿‍♂️

[Bob Abell 2Participant @bobabell2]

Hi Aashley

What power unit are you going to use?

How about a Ducted Fan?

Or……..A sneaky prop motor and some sort of smoking device in the engine tube?

Food fo thought eh?

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. I perhaps have not mentioned it, but it will be ducted fan powered. I have a feisty 64mm unit (minus 3500Kv motor at the moment) to install. Would not want to use a water prop… has to be a "jet"…?

Its a bit silly really, as I will have finished this one before I have tested it, and I have not even tested the Bluebird yet, also powered by same size/make of edf!!

Spent half the day filling (with Ronson`s wood filler) dents and grain, and have only just applied a brush coat of Ruston's Grey Acrylic primer. I have painted a bit of MDF with it to act as a test piece to see if the Halfords acrylic silver spray paint will react to it.

If it IS ok, then that's handy, if not, I can always just paint it with ezecote and then spray.

I was pleasantly surprised after painting it (although not quite dry at the time) as it looked much better than I thought it might.

[Paul TParticipant @pault84577]

Ashley

Another problem that I encountered was insufficient airflow through the small intakes, I ended up having hidden intakes around the motor housing and through the cockpit.

You wont have the worry about exhaust heat setting fire to the model but you might have some trouble with the centre of gravity.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Paul. Anticipating this, the elephant ear intakes will be overscale, and the pilots cockpit will also be used to let air in, and his headrest will also be an unfeasibly large air-scoop.

I am hoping this will be enough???

Had a quick test float in the bath, with the battery fully back and 150gm of lead stimulating the brushless motor. The nose was well up, and the stern down….however the front of the sponsons were not that far above the water despite being in approx. the right place. I am hoping this will not matter as the boat SHOULD rise as soon as it starts to move (???). There is scope to widen the front lifting wedge…this will give a bit more lift and buoyancy to the front and lift the back up as the battery could be shifted forward a bit, however all this needs a proper pond test.

My Rustin's Acrylic grey primer appears to be Halfords spray compatible, which is handy, and I have painted the hull and done ABSOLUTELY the last lot of filling barring the nose section.

I have been smoothing off the "lid" and may get around to trimming it tomorrow to fit the hull. Only when this has been settled can I sort out the intakes and final sanding of the nose.

I have a feeling the sponsons will make the boat very wet until it starts to get up to speed.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

The top which I made from fibreglass is no good…

The fan unit I had hoped to fit just aft of the parallel centre section after careful measurement sticks up too much and needs to be shifted further forward. It looks like plan B will come into play now: The rear half of the hull top will be planked with 2mm lite ply, and the reducer funnel (carrying the edf jet exhaust out diminishing in size from 64mm to 50mm in a smooth manner) will have to be permanently built in. It means I can still take the fan unit out, and there is nothing aft of the fan to have to get at (the rudder stuff being forward).

The fan cowl mount will have to be repositioned, not a difficult job.

It means I will make a laminated barrel `hood` for the front section into which I will have the intake ducts and headrest duct.

Ashley

[Ray Wood 3Participant @raywood3]

Hi Ashley,

Have you tried Depron, it really is good stuff & Super lightweight ??

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

Ray. Not tried depron I must say, but the bit I need to ‘plank’ is not very big, so probably wouldn’t make too much difference? About 140mm long by 100mm wide down to about 60mm in a barrel sort of shape.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Have moved the motor mount forward and laminated a hoop to go over the fan housing to support the rear section. It may be that I can use the original this fibreglass rear tunnel section? Once I have glued the hoop in place we will see.

I have to make a funnel to take the edf jet efflux cleanly out the rear `ole, and then once fixed in place I can deal with the cover.

Prog so far…

Ashley

[Ray Wood 3Participant @raywood3]

Hi Ashley,

The current thought with the edf fly boys is a rolled acetate tube with the joint taped, and hot glued into the fan shroud. Mainly a Tony Nijhuis idea on his series of mini jets in RCM&E worth looking at on the Model flying forum.

Regards Ray

Edited By Ray Wood 2 on 18/04/2020 19:24:09

[ashley needhamParticipant @ashleyneedham69188]

Ray. I have some acetate (I think that’s what it is) but I would like to b3 able to remove the fan, and as the back will be fixed, the funnel will just have to be held in place without being glued to the fan cowl.

Will have to arrange that before doing the top.

Ashley

[Chris FellowsParticipant @chrisfellows72943]

I admire your perseverance Ashley. Now that you've sorted the sponsons it's coming along nicely. No doubt other challenges to come.

Chris

[ashley needhamParticipant @ashleyneedham69188]

Chris. The main challenge will be when I finally get to put it on the water!

Ashley

[ashley needhamParticipant @ashleyneedham69188]

No, the challenges continue…

i took the edf out theBluebird to test fit on Crusader and it doesn’t……at least, it is too difficult. I COULD fit it, but it would be a fiddle to setup, and, well >>

I have ordered a 50mm edf!

Although slightly less powerful, it is half the weight and can be fitted well to the rear, giving much superior room for wires and wotnot. Waiting game for the fan to arrive now (not from China I hasten to add).

Ashley

Edited By ashley needham on 19/04/2020 13:29:20

[ashley needhamParticipant @ashleyneedham69188]

Nothing is simple. GOEORGE says that he has sold the last 50mm of the type wot I desired, so I have purchased another type which is a bit more powerful, and has a 5400Kv motor !!!!!!!

64000 rpm !!! wowsy wowsy. At least it should SOUND good even if it goes rubbish!

I have also had a moments inspiration as to mounting the unit, which is flangeless, and the switch to a smaller edf is not all bad, as besides saving space, it weighs slightly less than half the 64mm unit, and I reckon it MAY deliver the goods on a 2s Lipo ( 43000 rpm!!! oh yes) what with the attendant weight loss of using a 2s. The thrust may be down but there is a good weight saving.

Its all rubbish really, I have not even tested the edf Bluebird so may be utterly wasting my time.

Trevor is building something with TWO of these 50mm units…ooo er. He may eclipse the saucer by some margin!

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Have been fiddling with the hull cover which I made in fibreglass and had another flash of inspiration.

Along with the edf mount brainwave, it occurred to me that if the edf could be slid forward to take it out for replacement or whatever, then the rear cover COULD be glued in place as it needn’t be detachable to get at the motor. There is nothing else under the cover…the servo and receiver are Both in the front section, and the esc and battery are “loose” as it were pending trials.

I could then fill around the cover and get a nice smooth finish, leaving only the cabin area cover to worry about. As this is on the parallel sides bit, much easier to sort.

Although having cut the cover appropriately and got it to fit, I am resisting the temptation to glue it on until such time as I get my grubby hands on the new fan and fit it.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

I now have the 50mm edf from George. Wow! Work of art….tiny…..64000 rpm!!!

0.8mm ply has been hot-watered and is currently rolled around a Humbrol spray can (as its the right size) and tomorrow when dry I can sort out how to mount the bits.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Ply ring made and fitted to a “sled” for want of a better word. Rails underneath the sled allow the mounted fan to side from the cabin rearwards on the battery guide strips, and two thin ally long brackets epoxied in place hold the sled on to the track. A tab at the front of the sled is drilled for a small screw to screw into a purpose fitted wooden block to stop any movement and contain the AWESOME THRUST of me Goblin (or was a ghost?) edf substitute.

it means I can now glue the rear tapered cover in place and fill it for a decent fit/finish. All I have to do is make the jet tube to fit permanently inside the rear cover to duct the supersonic air smoothly rearwards (from the 43000 rpm fan).

Its all of a sudden brightened up here so hopefully the temp will rise and the PVA holding the bottom of the duct will go off quickly.

Ashley

[Paul TParticipant @pault84577]

Ashley

The words 'small screw containing the AWESOME THRUST' don't inspire confidence especially for the wildfowl but, on the other hand, shredded duck does make a very nice meal.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Ok, ok, its a MASSIVE screw to contain the AWESOME THRUST…..

Actually the motor mount is a stiff fit in the runner so that should be enough on its own!

At almost 65000 rpm, the duck would be a bit more than shredded.

Ashley

[Ray Wood 3Participant @raywood3]

Hi Guys,

Joking aside, most clubs I've belonged to won't allow air screw driven boats to be run because of the risk to wild life.

Ashley you'll be as you guys are not a club, do you have public liability insurance as individuals ??

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

No p l insurance. We take a bit of care and so on.

Thank god we are not a club! Other than no I/c, anything goes…although we are careful regarding the wildlife.

Ashley

[Ray Wood 3Participant @raywood3]

Hi Ashley,

Sounds great with your crew over there, I hate rules! But like common sense 😃

I do have insurance for rc flying with the BMFA but that's different.

Regards Ray

[Trevor HollowayParticipant @trevorholloway99134]

The only rule I am aware of is no ic, if there is a fast boat on the water we just potter around the landing stage until the batteries run out !

I think the most boats we have had at once is ten or twelve, usually half that on a Sunday morning.

[ashley needhamParticipant @ashleyneedham69188]

Yes, we go for quality, not quantity 🛥🚤⛵️🛶

Ashley

(we do have an unwritten rule…no underpowered boats allowed!)

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