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turn fins?

Old 08-28-2007, 09:34 PM
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terry kelly
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Default turn fins?

does anyone know that if a turn fin has a twist to it or if it is not inline correctly "straight" will it make the boat "hydro" track funny? i mean my miss bud since i changed turn fins seems to track kinda weird i have to put right trim into it and when i looked at the bottom of the hull the rear of the fin was crooked and pointing into the center of the boat a bit.. the rear of the the fin was facing toward the inside of the hull. i am going to test tomorrow with any hope but just wondering if anyone has a comment to help out on this. also i rolled the turn fin and put curve into it do you think i should have done that? i have seen alot of riggers with this design "just testing" thanks
Old 08-28-2007, 09:36 PM
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Sean Bowf
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Default RE: turn fins?

Yes it will, especially at 45 MPH. You need to put a straight edge on it, and compare that to the bottom of the hull, and they should be pretty close to parallel.

Sean
Old 08-28-2007, 09:42 PM
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terry kelly
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Default RE: turn fins?

what about the curve do you think i am wasting my time ? i mean all riggers use that design and i understand it helps hold in the corner , i guess i am trying to keep the right sponson down as i also have been having some cav problems in the corners or tipping the sponsons and you can hear the engine race a bit, waddya think sean?
Old 08-28-2007, 10:10 PM
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Sean Bowf
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Default RE: turn fins?

I don't know what turn fin you installed...but when I first tried a straight turn fin on my rigger, and tried to make a left correction at full speed, the boat stood up on its sponson (turned on its side). This is when I realized the problems folks were talking about having with the version 1 MV turn fin. So yes, a slight curve at the bottom can help. Another advantage I see with it, is if the boat starts to lift, you can do a very slight turn to the right, and it will suck the boat back down to the water. Some folks, instead of curving the bottom in, will bend the whole blade inward at an angle. I have done no testing with this setup, so can't give advice as to which is better.

As to props...my personal experience is mainly with 2 blade props. With a 2 blade prop on a MV, it will pick up RPM in the corners, and then sound like it shifted down a gear in the straights. This is normal. Even though the RPM is lower in the straights, the boat is moving faster. This is where the 2 blade prop has its advantage when compared to a 3 blade prop. The 3 blade prop will carry more speed through the corners, and may not have this RPM increase. So its advantage over the 2 blade is its ability to carry speed through a turn. But...with the mod MVs I have seen, you better come out of the turn ahead, and on the inside lane...or the 2 blade is going to pass you in the following straight.

Just my 2 cents.

Sean

EDIT: I wanted to add...that it may be that a stock MV will have higher speeds with a 3 blade prop. I know Kelly Miller was having good success with it on his Son's stock MV.

I have zero personal experience with proboats, so can't comment on what works with them. The proboat that beat me this last weekend (formula with a CVRM) was running a 2 blade prop.
Old 08-28-2007, 10:17 PM
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Sean Bowf
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Default RE: turn fins?

Here is a pic of the 2 fins (MV versions 1 and 2) next to each other.

Not sure if this is helping or not...

Sean
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Old 08-28-2007, 10:31 PM
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terry kelly
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Default RE: turn fins?

yes well it seems i am on the right track to getting this handling problem fixed, thank you alot.. my turn fin i have put a slow curve in the whole thing , i will post some pics tomorrow it has a nice slow curve top to bottom, as far as props i heard of some guys trying some x440 props on their vegas and it is working? i ordered some to try on my vegas when it arrives "when that is" . and btw the turn fin is from the guys that alot of people do not care for on here "just trying to stay correct on here" it is fairly thick looking but i think alot of my problem was sorta like binding the hull up with the turn fin alignment and the rudder fighting for action it should clean it up a bit. also thickness of the rudder mine is another brand x one and is about 1/8 in thick at the back i am thinking about thinning it down in my mill but what about suggestions? thick , thin ? waddya think sean..?
Old 08-28-2007, 10:50 PM
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Sean Bowf
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Default RE: turn fins?

I have never tried his new turn fin. Someone asked me to try it, as a comparison...and I have no problem with giving an honest answer one way or the other if I do try it. I take it you have the second version?? I think the first version was grabbing too well, and causing some spinout problems. I think the second version was one that had a bend at the top of it, but had a straight blade. So the whole blade is supposed to be bent in toward the center of the boat.

As to their rudders...I don't really know. I have had good luck with a modifed stock MV rudder and have not seen a need to change. Their rudder is thinner, so should have less drag, but then you have that 1/8th inch tube hanging down in front of it. I would think this would create A LOT of drag. Again, no personal experience or testing, just thinking out loud, but I would think that tube would cause more drag than what was saved by having a thinner blade. My understanding is that the bottom of this tube is supposed to be even with the middle of the strut barrel. I run my strut pretty deep compared to most folks...so my thinking is in respect to my setup.

As to making it thinner, I read an article once about rudder shapes. It said that a wedge shaped rudder gives more control when heat racing...but a rudder that is sharp on the front and back (parabolic?) has less drag. The article mentioned this being a good rudder for a SAW event. I have no idea how old the article was, or if the information was correct or current. If it is current/correct, I don't know how thin a blade can get before it loses the control advantage a wedged shaped blade is supposed to have over a parabolic one.

I am going to do some testing on a rudder blade I received from a guy in NC...that was going to be marketed under the name "Speed Freak RC"...but I think that name is taken. Anyhow, attached are a couple pics of the blade. It would be a bolt on replacement to the MV rudder blade. You can see that it has a thinner blade to it...there are also some other differences, that I won't mention. I have not got it wet yet, so can't comment on if it gives an improved speed without sacrificing control or not.

Sean
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Old 08-29-2007, 12:27 AM
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TIA
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Default RE: turn fins?

FYI, with riggers we usually move the turn fin back to keep the right sponson down.

If the cg is behind the turn-fin it tends to lift the sponson when turning.

FWIW
Old 08-29-2007, 06:55 AM
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terry kelly
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Default RE: turn fins?

sean i think we agree on alot of stuf , i thank you for you input .. as far as the pickup tube hanging down i modded mina already, if you look across the rear shoes it is barley sticking down from therejust enough i belive to pick up the cooling the engine needs , when i do a half throttle pass water is reallly shooting from the outlet.. i am not sure how much drag i am geting but i will bet it is a whole lot better thanb when the tube hung halfway down the rudder "i moved it like a inch up" .. have you tried any x440 props on your vegas yet? i am going to keep up on my pro boat deal "even though i think the vegas has way more potential " even after my vegas arrives and i have a second coming for testing and eventually a .21 conversion using the cmb from my sport hydro.[>:] that thing should haul ass..lol let me know the props you have tried if you can pm me and their outcome , it would be useful info.. and i think i will put my rudders in the mill for a visit to the fat farm..lol , also if you can pm me the name of the guy that you got the rudder from i like the water pickup in the rudder better than the tube.. like to covert that to my bud boats thanks alot
Old 08-29-2007, 07:47 AM
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Default RE: turn fins?

ORIGINAL: Sean Bowf
I am going to do some testing on a rudder blade I received from a guy in NC...that was going to be marketed under the name "Speed Freak RC"...but I think that name is taken. Anyhow, attached are a couple pics of the blade. It would be a bolt on replacement to the MV rudder blade. You can see that it has a thinner blade to it...there are also some other differences, that I won't mention. I have not got it wet yet, so can't comment on if it gives an improved speed without sacrificing control or not.
If it's from the "guy in NC" that I think it's from, he does good work. I do wonder about the location of the water pickup in the partial picture you posted. It looks kind of high on the rudder blade.
Old 08-29-2007, 07:50 AM
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Default RE: turn fins?

ORIGINAL: terry kelly
...also if you can pm me the name of the guy that you got the rudder from i like the water pickup in the rudder better than the tube.. like to covert that to my bud boats thanks alot
Speedmaster http://www.rossisales.com has .21 size rudders with water pickups.
Old 08-29-2007, 07:11 PM
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Default RE: turn fins?

The turn fin from the "guys that alot of people do not care for on here" seems to work pretty good on my boat. I have a spinning out issue that is related to my rudder, but since I put that fin on my boat the spinning out problem has been reduced greatly, not to mention about .2 or .3 mph increase in speed. I am setting up a new boat and will be running a modified MV rudder with that turn fin. I'm hoping that the spiining out issue will go away so I can actually win all the heats, not just the only one I finish ! ( To date, I have won every heat I have finished with my mod RTR ! )
Old 08-29-2007, 10:35 PM
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Default RE: turn fins?

ORIGINAL: terry kelly

.. have you tried any x440 props on your vegas yet?
I did try an x440. I took some of the tongues off, back cut it a little, rounded the back corners, I think I even made the diameter a little smaller, and still could not get it to turn decent (pic attached). Best speeds I got were 39-40MPH. I am sure I still have A LOT to learn when it comes to modifying props.

Looks like JD has a sponson mod that will get a stock engine to run these kinds of speeds (40sh MPH) with an M440 (detongued X440). The places I have raced, this mod would put the boat into the mod RTR class, even though it has a stock engine. But 40 MPH would beat most Mod RTRs I have seen run.

ORIGINAL: terry kelly

also if you can pm me the name of the guy that you got the rudder from i like the water pickup in the rudder better than the tube.. like to covert that to my bud boats thanks alot
The rudder I have is a prototype. He cut 2, and ruined one in the process. Not sure if it will go into production...will know more after I do some testing with it. Pretty sure this is NOT the guy piper is thinking of. This guy deals with full size stock cars for his bread and butter.

ORIGINAL: RcBoatman59

The turn fin from the "guys that alot of people do not care for on here" seems to work pretty good on my boat. I have a spinning out issue that is related to my rudder, but since I put that fin on my boat the spinning out problem has been reduced greatly, not to mention about .2 or .3 mph increase in speed. I am setting up a new boat and will be running a modified MV rudder with that turn fin. I'm hoping that the spiining out issue will go away so I can actually win all the heats, not just the only one I finish ! ( To date, I have won every heat I have finished with my mod RTR ! )
Norm, I think he listed the blade as .5 inch thick. Pretty sure he meant .05. Anyhow, this is the same thickness as the grim fin. After spinning out twice in the straights at Chanute, Kelly's setup has me rethinking my use of the grim fin. I am wondering if it has too much of a bite to it. I am pretty sure that during my second spinout I was making a minor left correction...not really sure on the first one. Anyhow, this has me thinking about trying out the stock fin again...or modifying the version 1 fin I have to see if I can make it have a little more grab than the Version 2, but less than the grim fin. The speed increase you mention, is it over the stock fin, the grim fin, or over the original fin James put out?? if I remember right, the first version fin he put out was .2 MPH faster than the grim fin out of the package (neither sharpened beyond the way they came).

Sean
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Old 08-29-2007, 11:33 PM
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Default RE: turn fins?

It was above the grim and the other one. My boat never performed well with the stock fin, kept wanting to flip over in the straights.
I think you are correct on the thickness ! 1/2 " would maybe add a wee bit to much wieght !
When are you gonna be ready to see the BLACK BEAST run ?
Old 08-29-2007, 11:36 PM
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Sean Bowf
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Default RE: turn fins?

I have family in town this weekend. I am not sure what my wife has planned for me next weekend...but we can look at running then if you will have your boat ready. Kelly had asked that I let him know next time I am going up to Del...I think he might want to come test and tune too.

Sean
Old 08-30-2007, 04:27 AM
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terry kelly
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Default RE: turn fins?



I did try an x440. I took some of the tongues off, back cut it a little, rounded the back corners, I think I even made the diameter a little smaller, and still could not get it to turn decent (pic attached). Best speeds I got were 39-40MPH. I am sure I still have A LOT to learn when it comes to modifying props.

Looks like JD has a sponson mod that will get a stock engine to run these kinds of speeds (40sh MPH) with an M440 (detongued X440). The places I have raced, this mod would put the boat into the mod RTR class, even though it has a stock engine. But 40 MPH would beat most Mod RTRs I have seen run.


this thread is getting intresting.. i never thought of using a m440... and he is getting those speeds out of a aquacraft engine? what are the differences between the aq engine and the os.. just cheaper quality or second technology? remember i have not recieved mine yet "my vegas's" , also what are we talking as far as a sponson mod? do you have any pics of the sort? or possibly a link, well anyway guys have a grat one and keep the good info coming along. see ya
Old 08-30-2007, 07:17 AM
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Sean Bowf
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Default RE: turn fins?

I have never seen official numbers posted for the Aquacraft engine. My personal opinion is that it has about 60% of the power of the CVRM. When I switched from the Aquacraft engine to the OS, I realized about a 10 MPH increase in speed while using the same prop. That is why, in the other thread, I was surprised they only reported a speed about 2-3 MPH higher with the CVRM after that sponson mod. I would like to know how the CVRM does after it on the 3.5 pipe and dialed in.

Externally, the CVRM has A LOT bigger carb than the aquacraft engine.

The sponson mod is in the original MV thread. You can find it here: http://www.rcuniverse.com/forum/m_43...11/key_/tm.htm . It is the fourth post from the bottom.

Sean

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