Skipjack 1/72

[greenman407]

By the way, shes running right in the ballpark where the Albacore runs. However Im taking the Albacore up a notch or two by changing to 550 motors instead of the 400s shes using now. If I wanted more reliable speed from the Scamper I would need to put more weight in her keel, as you can see her healing over on her side as you add throttle. But weight brings its own penaltys, so ill probably leave her as is. The Albacore on the other hand has counter-rotating props, which nullify the torque roll.
However, there is much to be said about reliability and control-ability. I dont always go crazy fast. The one thing that can be said about submarines. A fast submarine can go slow if you want it to, but a slow submarine cannot go fast. Id rather have an over-powered submarine that gives me more options as to how to run her that day, than to have a submarine that cant get out of its own way. For what its worth.

[He Who Shall Not Be Named]

Hello, 'snap-roll'.

A combination of turbulent water sheering off the hull and slamming into the outboard face of the sail and foil-roll. Foil-roll is the lateral force (lift) produced by the sail that acts to rotate the hull inboard of the turn owing to the positive angle of attack the sail takes to the relative water flow.

The faster you go the more progressive the foil roll, and you can anticipate it, which makes it easier to counter with rudder.

However, with flow separation off the hull which then hits the outboard side of the sail, that is something that will take you off guard. It's sudden and nasty.

In either case, the boat rolls into the turn, and the hard-over rudder now works as a stern plane to point the bow down. And down you go ... and it's hang onto your ass time. The only recovery is to go back-emergency, shift your rudder, full rise on the planes, hit the chicken-switch, and rattle your beads.

The real SKIPJACK's and the LA's had the performance to get into this particular bind. The other classes, not so much: the THRESHER and STURGEON class boats were slower, and the SEAWOLF and VIRGINIA class boats, though fast, are fly-by-wire and the computers won't let you get stupid at the dive-stand.

Know your speed-turn envelop! And that's what Mark is doing -- he's coming to terms with what he can, and can not do with his gray SKIPJACK. Thank God for transmitters that permit end-point adjustments.

And, Mark: you want to do stupid fast underwater turns, consider putting an angle-keeper -- sensing roll -- in the loop between stern planes and ADF2. You'll probably need a v-mixer to integrate the two sensors. Add a servo. One servo per plane so they can work as elevons. The German's have been doing this with their fast stuff for decades.

M

[roedj]

Hello, 'snap-roll'.
And, Mark: you want to do stupid fast underwater turns, consider putting an angle-keeper -- sensing roll -- in the loop between stern planes and ADF2. You'll probably need a v-mixer to integrate the two sensors. Add a servo. One servo per plane so they can work as elevons. The German's have been doing this with their fast stuff for decades.

M

DM,

How exactly would that work?

To me, when the boat rolls over in a tight turn at speed you have transitioned from a cruciform type stern to an "X" tail stern. Are you saying that an ADF, if properly placed would sense this and "correct" the horizontal stabilizers to prevent the unwanted dive?

More explanation, please.

Dan

[Subculture]

Two levellers mounted at 30 degrees to the keel centreline. You need independent control of the vanes naturally, and mixing can be done in the TX or onboard. Norbert Bruggen does this on his Deepflight Aviator and Delphin models. If you have a look at page 12 of his downloadable build instructions for the Delphin you can see how the levellers are mounted.

http://modelluboot.de/Anleitungen/Anleitung_Delphin_4_10.pdf

[roedj]

Two levellers mounted at 30 degrees to the keel centreline. You need independent control of the vanes naturally, and mixing can be done in the TX or onboard. Norbert Bruggen does this on his Deepflight Aviator and Delphin models. If you have a look at page 12 of his downloadable build instructions for the Delphin you can see how the levellers are mounted.

http://modelluboot.de/Anleitungen/An...lphin_4_10.pdf

Very clever. I understand - must file that idea away for future use.

Thanks for the info.

Dan

[roedj]

Very clever. I understand - must file that idea away for future use.

Thanks for the info.

Dan

Wait a minute - I don't understand. I've studied his Delfin instructions - muddled through the German - and what I see is he has independent control of the two horizontal stabilizers, i.e., one servo for each stabilizer and one servo for the rudder.

As I said before, I would think that a cruciform tailed boat, when laying on its side in a snap roll turn would, in effect, be an "X" tail boat. Wouldn't one want total independent cobtrol of all four control surfaces - one servo per surface?

I have absolutely no lnowledge of how the prototype "X" tail boats work but I would guess that they have total independent control of all four surfaces with a computer keeping track of desired course, depth, and roll and making the appropriate adjustments as needed.

Or am I wildly over thinking this?

Dan

[He Who Shall Not Be Named]

Most X-tails don't have a ram for each control surface. Typically the control linkages are just like those of the cruciform arrangement, only rotated 45-degrees. The two pair of control surfaces, each pair worked by one ram, work collectively to produce pitch and yaw forces. The Newer X-tails do go for individual control of the planes, each control surface pushed by its own ram, affording rolling forces in addition to the yaw and pitch.

The American navy -- in no small part to the conservative engineering practices imposed by Rickover (and today that thinking as dead as the man himself) -- was keen to keep computers out of the engineering and ship-control loop. So, back in the day, the simplified X-tail actuation scheme was front and center for the ALBACORE when it came time to play with that arrangement.

For the record: I'm with Rickover's philosophy here; if the steering-diving system aboard the boat can't be operated remotely with two phone-talkers and a pair of Snipe's pushing servo-control valves back in the engineering spaces, I don't want the steering-diving system on my boat! If a knuckle-dragger can't operate a system by hand, on site, then its a system that can kill the boat!

I wouldn't crew on a post LA class boat to save my ass!

M

[greenman407]

You are right Dan. My X-tail uses two servos with an electronic mixer. Therefore, all four surfaces are the rudder and all four surfaces are also the stern planes. There functions blend together. When the Scamper turns the sail lays all the way over past 45 degrees over to a full 90 and beyond. The rudder now becomes a stern plane that set for dive. To stop this, first you would have to know that its actually going down as it doesnt always do that, so visibility is the key. At that point you could swing the rudder over hard to port which would actually be full rise on the stern planes, in this condition but just for a moment.
With the X-tail, you will still have the same problem. I love to see a submarine banking into a turn.

[greenman407]

As for the painting of this fellow, Im just now started hitting the seams with filler and giving the whole thing a rub down with sandpaper. What are these round dimples in the hull? Should I drill them out or fill them in? Your comments please.

[He Who Shall Not Be Named]

Auxiliary and AC suction-discharges. Open 'em up, Mark.

M

[greenman407]

Thanks Dave.

[greenman407]

Anybody recognize it? I hit the whole thing with 220 sand paper, ill go back over it with 320 before painting. Evercoat Easysand and some off brand red spot putty.

[He Who Shall Not Be Named]

Could you possibly get any sloppier with the putty and filler applications??

Looks like you applied it all with fire-crackers!!!!

Next time first mask off the areas you don't want the putty/filler, then apply the putty/filler with a spatulla with some frig'n care!

You people!!!!!!!

M

[greenman407]

Now thats a good idea. Ill do that.................next time. My only excuse is that this stuff becomes unusable pretty quick, so Im trying to get it on. Ya Know. If I had more time id smooth it out more.

[alad61]

Mark try some thinners (not a lot)in your fillers to keep your wet edge a little longer or just cut back on the hardner. But I will admit that I don't use the evercoat brand down under, but I'd assume cutting back the catalyst a bit should still work with the evercoat range. I also found with the stuff I use cutting back on the catalyst takes longer to harden but it gives me extra sanding an shaping time when I get heavy handed