Crusader.

[bob horowitz]

That is fabulous. You are a master!
Bob

[fweasel]

What a monster of a boat.

[golfito]

Awesome!

[785boats]

Thanks for the compliments guys. I'm happy with the way this one turned out.
Here are some stats.

Scale...1/8
Length... 1170mm ( 46" )
Finished hull weight c/w servo & rudder...2660g ( 5lb 14oz )
9s 6000mah ( 3 x 3s )...1394g
ESC & UBEC ...280g
90mm EDF...600g
Rx...6g
Pilot...25g

Total...4965g ( 10lb 15oz )

Pretty light for this Whale of a boat. I hope she gets up on the plane as easily as the Spirit of Australia did.

[Beaux]

That is one cool boat, good luck.

[785boats]

Thanks for that Beaux.

[golfito]

I wait to see it in operation!
Regards!
Hernán.

[785boats]

Well she had her first test run today.
A dismal failure I'm afraid. It just wouldn't get up onto the plane. Just ploughed through the water. Those front struts pushing a wave of water in front of them.
After discussions with fellow club members, it was decided that the reason is that the drive line of the thrust is a bit too negative & just wants to push the nose down. Added to that, the CoG is too far forward for a canard set up. I knew it probably was, but I can't move the packs any further back. I'll sort something out .
Either by raising the rear of the thrust tube or adding a horizontal stabiliser into the rear of the tube to deflect the thrust upwards & push the rear of the boat down a bit. Or both.
The GoG is my main concern though.
Might even need a bigger fan .

[785boats]

I've had no time to work on this boat until last Sunday
So, I hacked into it & ripped out the fan & mounts so I could move the fan further back in the boat 8 inches to the rear bulkhead.
I also dropped it down to reduce the negative angle of the thrust line. It's now a tad positive which should push the rear down & help raise the nose instead of pushing it down into the water.
That only moved the COG back 1-1/2 inches from the original position. I don't think that will be enough. I might need to add weight to the rear. We will see at the next test. It all depends on what effect the change in the thrust line has.
The rudder may still be a problem, as it had no turning effect at slow speed.

Original position.

003.jpg

New position. 8" further back & lower down to change the thrust line from negative to positive.

001.jpg

[golfito]

What a beautiful challenge !.

[785boats]

Yes golfito. A beautiful old boat. And certainly a challenge.

[785boats]

Well the challenge beat me I'm sorry to say.
The last lot of changes didn't help at all. After a few attempts I just couldn't get it up on the plane. The front struts just plowed through the water & the poor thing wouldn't get up above a fast walking pace.
I finally bit the bullet & decided to take out the fan & put in a normal motor & drive system.

I got started on it a couple of days ago. Finally.
So, out came the fan, ESC, servo & front rudder. And the thrust tube.
The only strut I had that was long enough to reach the bottom of the sponsons from the transom was an old 1/4" one that was 100mm long. I only wanted to run a 3/16 drive line so I put a sleeve in it & a 3/16" floating bush.
The stuffing tube then needed a couple of pieces of tube added to the end of it to fit snugly into the front of the strut.
I knocked up a motor mount from some aluminium angle & that was epoxied & glassed into the hull along with the stuffing tube.

I had a 160mm long rudder but no bracket for it. So, one had to be made.
There should be enough rudder in the water for straight line runs.
So then a 1/8" aluminium transom doubler was cut & epoxied to the inside of the transom.
The strut & rudder bracket were drilled & tapped on to the transom.
A servo rod was fashioned up & installed through to the engine bay. A servo bracket was made up & fitted beside the motor.

The cog is a lot further back, now that I can fit the packs all the way to the back of the boat.
Hopefully it is enough.

The ESC I use for the EDF is a Flycolor HV 150A. It has no water cooling which is fine when it is in the airway of the fan.
But I needed to add a couple of cooling tubes to the finned cooling plate, now that it will need to be water cooled. I had to bend the fins first to allow the brass tube to fit in between them, & then with a liberal application of thermal adhesive the tubes were pressed into place. It should be fine for the short straightline runs the boat will be doing.

I've just got to block up all the air intakes & the exhaust now, & she will be ready for another test.

The strut setup.
002.jpg

Rudder & strut.
006.jpg

Motor & servo mounts installed. Also Epoxy putty around the stuffing tube for added strength.
005.jpg

The 2 x 4s packs easily fit right to the back of the boat now.
006.jpg

The cooling tubes added to the Flycolor HV 150A ESC.
004.jpg

[fweasel]

Knowing what you know now, if you could go back, would you just have left it as it was after the first few test runs on the fan? Or, was that just never good enough and this major revision was inevitable?

[785boats]

After running a few canards I knew that the cog was too far forward. I expressed my concerns in Post #1 & had already accepted that it may need to be converted to a surface drive. I was hopeful that the previous relocation of the fan might be enough. But it was not to be. The cog was still too far forward.
I did contemplate adding about 1/2" of balsa on the front ski to raise the angle of attack. But I didn't think it would raise those front struts out of the water to allow it to pick up speed.
Adding weight at the very rear might have helped.
A larger fan was considered, but would have been inefficient because the exhaust opening of the thrust tube can't be made any bigger. It was only just big enough for a 90mm fan.
So I bit the bullet & changed the fan for the surface drive.

But trust me. The next one I build will be the Hustler, and that one will work with an EDF as it is similar to the Spirit of Australia but with no air intake restrictions.

[golfito]

Following your work, you are a great builder.
I like the idea of the EDF!

[Beaux]

looks like that ought to work. Good job.

[785boats]

Thanks golfito, Beaux.

I just dug theses two pic out of my files.
The first one at rest, shows that the struts don't actually touch the water. Not even out where they attach to the sponsons. That's how my boat sat in the water.
The second pic shows the boat moving off at slow speed. See how the water is being pushed by the struts & how it flows over the struts & on the sponsons. That's exactly what happened with my model. The EDF just couldn't push the boat through it, & allow the front ski to lift up onto the plane with more speed.
Curious how both the full size boat & the model have that problem with the struts, when they aren't touching the water at rest. I can't understand it.

John-Cobb.jpg


crusader-jet-thrust-loch-ness-john-cobb-k6-wsr.JPG

How it should have been running.
04.jpg

[Jesse J]

I think there are two compounding effects.
The first is shared with the full scale: the bow wake lines up with the front strut and only hits it when underway at a specific early speed.
The second is that the edf doesn't have the thrust until it can have a sufficient amount of air moving through it.
The combination at that early speed is maximum drag and minimum thrust...
Solution, maybe a solid rocket booster?

[ray schrauwen]

I think there are two compounding effects.
The first is shared with the full scale: the bow wake lines up with the front strut and only hits it when underway at a specific early speed.
The second is that the edf doesn't have the thrust until it can have a sufficient amount of air moving through it.
The combination at that early speed is maximum drag and minimum thrust...
Solution, maybe a solid rocket booster?

Yeah BABY!!

[785boats]

Totally correct on both counts Jesse.
But another thing I have realised too, is that, at the slow speed the water also rides up the sides of the sponsons & over the top of them, completely burying them with a fair weight of water. This would also contribute to the hull not being able to lift up on to the plane.

[Jesse J]

Spray rails?

[785boats]

Yes. I thought of that as I typed the last post. Pity I didn't notice it in that photo before I took the fan out. I would have tried it. I didn't really recognise it on the model until I saw it in the photo & realised what it was doing. But the cog would still have been too far forward, I feel.
Should get a few test runs in tomorrow, I hope.
The spray rails might still be needed. We shall see.

[785boats]

I had a few successful runs with the Crusader today.
It was only at our smaller track at Boondal, not at our full race track, so I couldn't get it up to full speed. But it looks promising.
The first runs (not in either of the videos) were a bit bouncy when it was at high speed, so I added a tad of negative angle to the strut. Still couldn't use full throttle but it was much better at higher speed.
Prop was an x447/3 motor is an HET 4083 1080kv on 8s. I might drop it back to 6s, because I think it will be too far above scale speed when I open it right up.
Here's a couple of short videos posted on my channel. I'm happy with the way it performed. Even though it wasn't with an EDF.

https://www.youtube.com/channel/UCmc...Hpw83p9Hn-l1hg

[zooma]

Way better than the leaf blower power.

[785boats]

Unfortunately, yes.

[golfito]

I loved it. Beautiful model
I found a model recently that left me impressed:article-1341140-0C924F02000005DC-106_634x630.jpg

[785boats]

Thanks man.
Yes. I've really got to put some effort in, & finish mine off.

https://forums.offshoreelectrics.com...light=bluebird

[golfito]

Subscribed to the thread!

[Jesse J]

I had a few successful runs with the Crusader today.
It was only at our smaller track at Boondal, not at our full race track, so I couldn't get it up to full speed. But it looks promising.
The first runs (not in either of the videos) were a bit bouncy when it was at high speed, so I added a tad of negative angle to the strut. Still couldn't use full throttle but it was much better at higher speed.
Prop was an x447/3 motor is an HET 4083 1080kv on 8s. I might drop it back to 6s, because I think it will be too far above scale speed when I open it right up.
Here's a couple of short videos posted on my channel. I'm happy with the way it performed. Even though it wasn't with an EDF.

https://www.youtube.com/channel/UCmc...Hpw83p9Hn-l1hg

Looks real nice, even navigating the Lilly pads!

[785boats]

Thanks.
I got caught in the lilies a couple of times, & had to go out & get it.