Stability Problem Quastion....

[LiPo Power]

I am very new to the RC boating and I love it so fare.
This time I would like to ask you PRO boaters to help me out with a little issue I have with my Formula Fastech.
This problem was not there when the boat was out of the box.
I noticed that my rudder mount is not very solid and it has a little play right where is connected to the strut. What would happen if the rudder mount is a little bit too loose? How will the boat react to it?
My boat right now likes to bounce left to right when high speed and it is hard to get full speed for more than few seconds on flat water. It was very stable until the moment when expending foam was add it to the nose of the boat for better floating in case of dive. Prop was changed to X642 but even if the original stock prop is installed the same problem is still there.
Could you please suggest few ideas I can try to see if I can resolve this problem?
Thank You
Robert

[HappyOne]

As for the rudder, do you mean at the point where it pivots?

If the only change that you made was to add foam to the bow section, I would suggest that you check two things:

1) Has the hull deformed at all by the expanding foam?
2) Where is the balance point from the transom? Maybe it is nose heavy.

[Doby]

The foam adds next to no weight. I looked at the hull last weekend and there were no deformations. What LiPo is experiencing now is that the hull no longer rides severley "wet" (bow heavy) as when he first brought it out. Now due to proper strut angle alignments and an upgraded prop that all combined basically added about 8 Mph to the performance of the boat the handeling characteristics have changed. Thats one heck of a difference !!!!!!!

It now rides on top of the water at greater speeds and is more suseptible to wind and wave inputs. This combined with the relativly flat ride surface can make it a bit squirrley in the handeling department, especially in the turns.

This is a classic case of having to find the right balance of speed/ handeling for the user.

How much speed does LiPo want?
How good of a handeling boat does LiPo want?
Can LiPo live with a bit less speed?
Can LiPo live with less handeling?

Only LiPo can determine that. Every adjustment has its trade off.

I think we'll try a bit less of a prop angle this weekend and see how that goes.

Also, the rudder movement is just about what every stock RTR boat has.

[HappyOne]

Ah....speed induced squirrely.

Lipo, think of it more as a test of one's driving abilities. It will improve your game

[Darin Jordan]

Could you please suggest few ideas I can try to see if I can resolve this problem?
Thank You
Robert

Robert... All of the symptoms you are experiencing are a matter of setup and the general design of the hull.

Here is what you need to do to get things tracking correctly.

1) Make sure all your hardware is tight

2) On your turn fins, make a mark to indicate where the chine is, then take them off and bend them outwards at this line until they are perpendicular to the hull bottom.

3) Make sure your trim tabs are flat, or even a tad up... this boat does NOT like the nose being pushed down... It has a deep keel in the front and will hook badly in the turns if you try to trim down too much.

4) Bend the inside corner of each trim tab down at about a 30-45-degree angle. Go in maybe 1/4 to 3/16" with a pair of pliers and bend the inside tips downward. This will eliminate about 90% of your chine-walking problem. See the attached pic. Bend down the red areas.

5) Trim your strut to neutral... flat with the keel, as a starting point.

6) Because this is a sub-surface drive, it's going to be sensitive to prop choice and how the prop is prepped. Going bigger in diameter isn't going to be the best choice. The boat will try to climb up the prop, so the larger the diameter, the more the boat will be lifted out of the water in the back. This will make the issues worse. I found good handling on mine with a smaller prop that has more pitch... Try a Y537/3 or X440/3 or similiar prop. You'll want low to or even NO lift in the prop, so backcutting would help. You also don't need a lot of blade area in the water, so detounging and other measures to reduce blade surface area would help.


If you don't understand how to achieve #6, then DO 1 thru 5, and then try your X642 prop and see how it goes... I think you'll find a world of improvement with these adjustments.

This boat has some definate limits, due to the sub-surface drive layout, so doing what works on an SV27 as far as prop goes will NOT likely work. Need to think a little differently. The boat will want to rise out of the water in relation to the center of the prop, so, as I've said previously, prop choice is going to be a little tough.

Do 1 thru 5 then report back... I think you'll like what you discover.

[LiPo Power]

I went to pond last night to play with the prop settings and swich back to stock. She was still "squirrley" as you saying Doby. Batteries on the stock spot, stock prop and same issue was there. VERY strange! Yes I took the turn fins out and back but did not change anything to them. That is why I have this concern about the rudder mounting on its hinges. I understand that in way higher speeds she will change characteristics but going back to stock set up should bring her back to nice flat stable straight flight on the water, right?
Well it is not. Call me weird but she is different. And that is my little problem....
Doby, I will be at the pond on Saturday, will show you the stock set up handeling.
Thanks guys, you are the best!! I wish I can upload pictures....

[LiPo Power]

Sorry, my respond should be ahead of Darin's.
Thank you Guys, will do....
Robert

[Darin Jordan]

That is why I have this concern about the rudder mounting on its hinges.

My rudder is not "tight" either... under way, however, the forces on the rudder pretty much pin it back and hold it straight, unless you turn it...

I've had some pretty loose rudders and they've never been this kind of an issue.

The instability you are experiencing is being caused by the hull lifting out of the water and not having enough control surface remaining in to keep it stable. Again, this is due to the flat bottom at the back half of the hull, and the sub-surface prop design. It's NOT really a "deep V" hull... it starts that way, but then quickly turns into a flat bottom. The combination can be a tuning challenge.

Also, I think getting a longer rudder would help in left-hand turns. As it is, when the boat rolls into the left turn, the rudder is almost lifted out of the water. It can be made to work, but you have to drive it correctly. It won't do it well at higher speeds, so you have to back off, set the nose down into the turn, then ease back into it. It's still touchy that way, but it works. A longer rudder... maybe another 1/2" or so, would help a lot.

The stock rudder can be made to work fine, however. That's what mine still has. I WAS thinking of maybe remounting down lower on the hull.

Bending out the turn-fins will help IMMENSELY in the turns. It'll stop fighting them. As they come stock, they try to force the boat back upright in the turn and it "jacks" on them. VERY unstable. Bend them out so they are 90-degrees with the bottom on each side, and you'll find the cornering much improved.

[LiPo Power]

Got it all done! Saturday will be my next test, will see.
Darin, thank you for all your suggestions. I like it. At the pond Doby is my hero, very helpfull PRO RC person on the spot.
Will let you know the findings.
BDW, it says that you are Team Horizon, could you please expand a little more for me please what it means? If you are close with Horizon I would like to ask you another quastion next time.
Thank You for now
Robert

[Darin Jordan]

BDW, it says that you are Team Horizon, could you please expand a little more for me please what it means? If you are close with Horizon I would like to ask you another quastion next time.
Thank You for now
Robert

I'm being sponsored this season by Horizon Hobby, Spektrum Radios, and ProBoat... I'm a VERY lucky racer at the moment!

Ask away... I'll answer if I can...

[LiPo Power]

Is this it as for the turn fins?

[Darin Jordan]

Looks pretty good... Here are some pics of mine. I think my turn-fins are bent out a bit further. Otherwise, the rest looks good from what I could tell of the pics...

Test it and let us know how it works out.

[LiPo Power]

After the test run I would like to say I LOVE IT !!! I have done all the little tweeks as per suggestions and this boat ROCK's !!! I had to give up a little bit of speed but I tell you now I am in controll of the boat. Speed was arround 35-37 MPH and that is very good for this boat. Thank You guys, Doby and Darin and all the guys at the pond Kitchener. It was fantastic run and I will post the pictures very soon as my album here at OSE..... Untill the next time.....

[AKS]

So LiPo, would you recommend the Formula Fastech to a fellow Newbie?

[LiPo Power]

I would, for sure.
Out of the box over 30 MPH!
If you looking for faster boat it will be LITTLE more money