Moebius Skipjack with R&R WTC question

[g2tiger]

Hello,

This information may be elsewhere but Im a bit frustrated so I'm posting here, please dont recommend I search the fourms, I'v e done that but not found anything.

I am having trouble getting the Moebius Skipjack balanced with the R&R WTC. I had it mostly level for surface running but I want her to dive. Ron at R&R said not much foam at the top and weight at the bottom. Fill the tank and ballast to desired level for submerged operation. So I followed the recomendations. My trouble is it wont level out submerged no matter what I do! I have rubber bands around the otuside and have added foam or weight and it still is giving me trouble. Now the WTC is leaking. I think its the ballast tank seal.

My question is what is the ammount of weight those who have built one of these have for the lower hull without the WTC? I ask so that perhaps I can duplicate your set up. I am using 1/2 Oz automotive tire weights. If you have pictures that would be great. I would have some pictures but I think that trying to take a picturs right now would end up with lots of broken equipment :)

In short, looking for some detailed ballast ammounts, the hull location, and possibly foam ammounts and locations. I was hopping to get her running for SubFest.

Thanks in advance,

Charlie

[Subculture]

Centre of gravity is out of alignment with the centre of buoyancy. In free air your boat should balance at the centre point of the ballast tank. Ballast amounts won't help you at all, this is about weight distribution.

[g2tiger]

Subculture,

I think I understand that concept. The weight is like a see saw. Same weight closer has different result than the same weight farther away for center. Should I set my model up to balance the wieght from the center of the ballast tank then? sort of like balancing a propellor for a model airplane? That sounds right. Next question is how much weight should I have in the lower hull to get the to a general area of operations?

My first issue if the Ballast tank leak. I think I need to reseal the rear cap on the tank. It is located inside of the WTC and is leaking into the motor compartment and then the forward copmartment. More work for me I guess. Thanks for the quick response. Ill take a few shots and give some weight measurements later if I am not locked in a straight jacket.

[Subculture]

I can't give you figure for the amount of weight required, it'll differ from boat to boat, but you want to add enough to get the boat to a scale surfaced waterline, then with the tank flooded just the top part of the fin/sail afloat, you will only need a whiff of throttle to submerge then.

Correct that you balance the boat from the location of the ballast tank centre point, the aeroplane prop analogy is apt- you should aim to get any ballast weight as low in the boat as possible to help with stability.

With a Skipjack depending on how far aft the c.g is then you may need a small bit of foam in the stern to counter the displacement of the forward mounted fin/sail, but you shouldn't need very much. You should get the C.G right first however.

Everyone has slightly different methods, but with a wet hull I like to trim the parts separately, so I'll get the module/wtc balanced out of the hull, and you can use a bit of cord in the middle as a sling to see which end is heavy. With that right, mark off where the centre of the tank is in the hull (this is likely to be decided for you with a kit) and then get the balance right on the hull too, you'll probably find it's stern heavy with the metalwork up the arse end. Alternatively you can do it all in one hit if you wish, it just gets heavier and a bit more cumbersome.

I like to do the balancing over something soft so if the parts slide off the cord/sling it doesn't get damaged. If you're accustomed to aeroplanes you'll be familiar with balancing your c.g. to within a certain point on the wing.

[RCSubGuy]

If it helps, my last Skipjack refurb had an R&R. Detailed video overview here:

[g2tiger]

RCSubGuy,

Thanks for the input. This is the video that got me moving on my skipjack after I was giving consideration to just a surface runner. I will review the video again to glean more info. I have to fixe what appears to be a small leak at the aft end of the ballast tank on the low side. Ill also run my antenna into the air intake. that is something I forgot to make happen on my boat. I am running a 75 MHz radio and my need a newer radio since I am getting interference. I also was running her on the surface at the lake today with a few other club members and found that the rudders would not set. I need to pull them and see what is going on. I am fairly sure I put a flat spot on the shafts. I spoke with Lyle Price an old sub guy from a few years ago and he suggested I cut up my weights into smaller amounts. he thought I may be adding too much and that was why it is difficult to balance submerged.

Worst case is I will see the experts at Sub-Fest and have them help me out.

Charlie

[g2tiger]

Subculture,

Thanks again. Good information. Ill work on your input and RCSubGuy's info. I just finished checking the ballast tank for leaks by blowing and pressurizing the tank and applying soapy water. No leaks. I will check my servo bellows. I probably should change the bellows for seals. I will see what I hvae in the parts boxes.

Charlie

[Subculture]

I like bellows, they're low in friction especially when you're running rotary to linear motion. Should be easy to find any leak if it's in that area, always make sure the end of any control rods are free from sharp edges and burrs.

[DrSchmidt]

Found the Revell kit for 60 Euros online and couldn't hesitate. Making it RC is very tempting.

[He Who Shall Not Be Named]

Found the Revell kit for 60 Euros online and couldn't hesitate. Making it RC is very tempting.

Wellll... talk'n parts done!

Get to it.

I have it on good authority that there's at least one idiot on this forum who can give guidance, if any is needed.

David

[DrSchmidt]

I's in the backlog .... U1 first

[g2tiger]

He Who Shall Not Be Named, I agree. I have many, many spare parts, boats and such that can attest to the fact that any idiot can and will do anything up and including provide advice. You gonna make a showing at the Subfest?

DrSchmidt, go for it. While it’s very frustrating it is also rewarding. I can attest to that.

Plus, I need all the advice I can get. When left ot my own devices disaster is not far off.

Update on my boat. got her back to level surfaced. WTc leak check is good. I put ty wraps around the bellows at the end where it is on the rod. I think it was glued and it became un sealed at that point. Next step is to cut down the weights from 1/2 Oz to smaller for submerged trim. Well see. Also, I got the rudder secured, it was perpetually loose at the control arm.

Thanks everyone. I'm making progress. I appreciate your input.

[He Who Shall Not Be Named]

He Who Shall Not Be Named, I agree. I have many, many spare parts, boats and such that can attest to the fact that any idiot can and will do anything up and including provide advice. You gonna make a showing at the Subfest?

DrSchmidt, go for it. While it’s very frustrating it is also rewarding. I can attest to that.

Plus, I need all the advice I can get. When left ot my own devices disaster is not far off.

Update on my boat. got her back to level surfaced. WTc leak check is good. I put ty wraps around the bellows at the end where it is on the rod. I think it was glued and it became un sealed at that point. Next step is to cut down the weights from 1/2 Oz to smaller for submerged trim. Well see. Also, I got the rudder secured, it was perpetually loose at the control arm.

Thanks everyone. I'm making progress. I appreciate your input.

I'll be there.

[g2tiger]

He who shall not be named,

Excellent!

[g2tiger]

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.