Moebius Skipjack with R&R WTC question

[trout]

You are close. Putting weight in the middle of the sub is a good start. Move it a little aft may help on the surface. Once submerged, use a small amount in the bow. You may have noticed this already. I can put a lot of weight in the middle and little change happens (yet this is a good spot for stability and maneuvering), how ever a small weight will have a big impact if put on the extreme ends of a sub while submerged. Using a small weight will have a smaller impact on the surface trim. Did this make sense? Make sure you move foam in the bow to be below waterline (I see that you did). The only foam you add above waterline is for submerged trim. Moving the main weight back may lift your bow up enough too.

Just recently I was doing a final trim on an Alfa. The weight started a bit aft of mid going all the way to below the rudders. Each time I had to let the sub settle and see if it was enough. I could have thrown in a larger weight, but then I may have needed more foam to counter. I think you are at the small step stage. You may still do this 2-4 more times, but be patient.

[He Who Shall Not Be Named]

OK Team,

The model is a 1/72 scale Moebius Skipjack with R&R Engineering WTC, I have a 2.4 Ghz radio in it right now.
I'm still not able to trim the model. I have tried both starting trim set for surface and trim set for submerged. I must be missing something. Here is what I have done and would like input/advice. I put the model in the tank with no foam and with lead in the lower section and filled the ballast tank, it sink's OK. 1/2 the job is good. I next add foam to get the sail about to the quarter mark above the water, I next empty the ballast tank and she comes up, but is nose heavy. I tried several times adding foam or lead to no avail.
My next attempt is to trim for surface level then sink her and trim her. Neither method works, same result. Always either too heavy or light at the bow, sometimes at the stern. I think working the submerged trim method first is better. I just can't get her to surface trim once it is trimmed for surface or submerged trim. Adding foam and weight is a no-go as they both end up balancing each other out and there is no trim change.
What am I missing? I have read and re-read Merriman's article to the Cabal on The joys the trimming of a wet-hull type R/C submarine and also Bob 's article on how he trimmed a sub from you tube as well as his tips for trimming a sub from the Forum. I also watched Bob's video on the R&R Engineering Skipjack that he reworked for a customer that is posted here earlier in the chat. I froze the video and studied the weight layout, type and amount of weight and think I am close to that. Nothing I do works and its fairly frustrating to be so close.

The R&R WTC, what's its diameter? Further advice will be predicated on how much annular space exists between the WTC and hull.

David
The Horrible

[g2tiger]

Trout, thank you. I agree that I am close. I may move the weight to be more centralized. So, I'll re-evaluate the weight distribution, and re-locate
He Who Shall Not Be Named, the WTC is about 2.5 inches diameter. I will need to take some measurements later tonight to be exact. I did not see the specific information listed on the R&R engineering site. Here is a quick photo from the site as reference that may be helpful and the web site link: http://www.rcsubs.co.uk/revellskipjack which I think you are probably already ware of.
Now that I am looking at the photo of the model from the R&R site I see they have their weight much more central than I do right now. This may also be an earlier WTC as the one I have it longer, or is located further aft based on the instructions. the instructions photo are more how my WTC is located.

[Subculture]

Does the boat balance at the longitudinal centre of the ballast tank?

If not sort that first.

[g2tiger]

Subculture,

Yes. I can get it level balanced either surfaced or submerged. but then when I move from the balanced state to the other state I loose balance.

[Subculture]

Not in the water, out of the water in the dry. Balance the boat on a sling, does it balance in the middle of the tank with no tilt fore or aft?

[g2tiger]

Subculture. OH, I can try that. Sort of like balancing a propellor for an RC airplane. I guess your thinking about a wide single sling under the center of the ballast tank. Perhaps I can set her on the desk with a bar under her so I don't have to lift her up and down so much. I have some time this weekend so I will give that a try.

He Who Shall Not Be Named, I did measure the WTC, 5.25 inches for the interior ballast tank, it is 1/4 inch smaller that the I.D of the main WTC. 3 inches diameter, 21 3/4 long total. looks like it gives about 1/2 to 3/4 inches between the hull and the cylinder.

One additional question. How much weight should I begin with? Just enough to sink her or go heavy?

[He Who Shall Not Be Named]

Subculture. OH, I can try that. Sort of like balancing a propellor for an RC airplane. I guess your thinking about a wide single sling under the center of the ballast tank. Perhaps I can set her on the desk with a bar under her so I don't have to lift her up and down so much. I have some time this weekend so I will give that a try.

He Who Shall Not Be Named, I did measure the WTC, 5.25 inches for the interior ballast tank, it is 1/4 inch smaller that the I.D of the main WTC. 3 inches diameter, 21 3/4 long total. looks like it gives about 1/2 to 3/4 inches between the hull and the cylinder.

One additional question. How much weight should I begin with? Just enough to sink her or go heavy?

Two pounds.

[g2tiger]

He Who Shall Not Be Named, OK, two pounds it shall be for my starting point. Thank you.

[g2tiger]

Update, I did some work on her and have moved to one large long section of foam that runs between the two WTC mounting brackets. the goal is the go with the 2 pounds of weight recommended. I also am moving the ballast closer to the middle of the boat. I have not been able to balance the mode as recommended earlier in the post. I did get a sling but balancing it on a 1-inch-wide strap is something else. I think I am close now and my thought with the single large section of foam is ease of getting her balanced. Using the many smaller sections of foam was driving me nuts! The mode is now fairly balanced so much more that I am almost happy. The photo is from Saturday evening. I stopped shortly after this as I was running out of blood due to the skeeters thinking I was dinner. Anyway, I plugged in the lights and tested her, looks good. I also have found that the pump is one leaky thing. After bout four cycles she gets enough water in her that I think balance becomes disturbed. So I am getting a new pump. I have a shot of the old pump which is leaking. The new pump is a diaphragm type so it should not leak as readily.

[neitosub]

Diaphragm pumps are not reversible. I would recommend getting a replacement of the existing red pump, it could be that you got a defective one. Usually these red pumps are pretty robust.

[RCSubGuy]

You can use a windshield washer pump. They're cheap off of Amazon.

[Subculture]

https://www.ebay.co.uk/itm/395294539308?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D275820%26meid%3Df0e63c87ebf7419d812a4dc23d167ef3%26pid%3D101875%26rk%3D2%26rkt%3D4%26sd%3D335519917838%26itm%3D395294539308%26pmt%3D1%26noa%3D0%26pg%3D2332490%26algv%3DSimVIDwebV3WithCPCExpansionEmbeddingSearchQueryRecall%26brand%3DUnbranded&_trksid=p2332490.c101875.m1851&itmprp=cksum%3A395294539308f0e63c87ebf7419d812a4dc23d167ef3%7Cenc%3AAQAJAAABIEK7FTfzsGw0VauxYyX1IOHjsuXJ1NPjVWebvOca%252BJbVzh3VqcrGnLFKHjKk2M42BtfNs8bK1jFneKBZqmubi3Iga13eADl2itCca9HAURkDLvdXmm5qgw4JRCP8VPESZY7ihfZ9mAVAHdacbckBk%252F9ee3QkX%252Fkf%252FOF9udb%252FMwVjTY5E6bG3sG3EEd6kwvReD7%252BNYjBKEs7iTuPBeYsuIMGzjzFKlh0Zf1gxmXHRB6HYjujqd7dvEWJL%252FdGRQOyaK30jkb0BLiLb29ejwEllnnydCVtvh8Y7CaX5c5JbF1z8qbcj96RgP1SD5jc5VsgMLP53ZIpxtG9s18erMhKMyejjuDhTaMA43Jjfk1K%252BxVIXNZeeQL1x%252BXYcjrrWjeUg2A%253D%253D%7Campid%3APL_CLK%7Cclp%3A2332490&itmmeta=01JBKSR6B0Z68E34D81166G0VM

[Subculture]

These pumps used to be made in France, and they had metal gears. Production moved to China, and they have plastic gears so avoid running the pump dry. if your pump is leaking, the it sounds more like a failed shaft seal. Kavan make a very good quality geared pump, with lapped brass gears. They’re on the larger size however, and would need a motor swap to fit in smaller cylinders

[g2tiger]

Subculture, Thanks for the advice. I did purchase a second pump and it is leaking as well. I tried putting some silicone on the O-ring which is around the gears would stop the leak but It did not. I tried silicone on both. I looked the pumps over to see about taking them apart but it looks like it will break where the tan section meets the orange body housing. I'll give it a closer look and give it a try. I have two to mess with so what's the big deal if I break one. It would be nice to use the original pump type as the frame is designed for it.
I was not aware diaphragm pumps are not reversable. I did get a diaphragm pump in the mail already so I will check it out for reversing. When I ordered it I did not see anything noting it was not reversable.
Any specific pumps you guys can recommend that you have experience with?
I will get back to work on her this weekend if all goes well. I think I have the weight and foam about figured out.