Offset Drivelines in 1/8 Hydroplanes

[John Finch]

excellent post,.. thank you for your input. A quick question,. specifically on a sport 21,.. why would I not want to use a lifting prop such as the 14 series? There are no rear sponsons to lift the hull from the water,.. does the wide hull do the lifting with air? Some set up a sport boat with the strut deeper, to get the hull to actually run level. Would it not be effective to set the hull up as designed to run, level, and use a lifting prop to keep the tail out of the water?

key to this is how much prop is in the water and how it affects speed. Example............If a prop is riding with the hub out of the water and the whole blade in the water it will travel further each revolution in the water than if only two thirds of the blade were in the water. So if you lift the blade out of the water to raise the transom you turn great rpm but don't go very fast. Example......two weeks ago at the pond i ran a prop that ran high out of the water 88 mph top speed, engine screaming. Settled the transom down into the water by Kicking the strut back and moving the front sponsons forward to put more weight on the prop. Result was more blade in the water.....98 mph. The 14 series props don't lift much but they also don't have as much pitch angle as the 16 series lifting prop. The 14 series front of the blade can act as a governor at high speed but they are sometimes a good choice just the same. I run an x457 three blade on my circus circus but a 62x88, I think that is right, on my roundnose Bardahl. Both 1/8 scale boats. I don't have any experience with the 21 size boats and very little with the 40 size boats in the last 30 years so someone else might be able to help out on prop selection.

 

[anthony_marquart]

well the good news is that the props will have the tongue cut back and be back cut.. reducing the lift even more.. we will see soon..

Just for peoples notes,.. I'll be running

GP310 sport hydro hull, probably just under 5lbs,. saddle tanks on both sides of the engine.

NR 5P, .17 cc head button, clearance 0.008

AB Parabolic pipe

Unfortunately this week only 55% byrons fuel

Testing initial set ups for lifting and non lifting props.. and I will put the results in the build thread for that boat. as not to steal this one anymore.

 

[Charles Perdue]

I'm about to start setting up a sport40 boat. So,.. if I understand all this correctly,.. a good recommendation would be to,

-center the engine in the hull

-use battery weight to keep the left sponson down, (lifted from torque)

-maybe add a shim to the strut to keep the boat from pulling into the course. This helps with SAW speed reducing rudder input to keep it straight.

Anthony,

Everyone has there opinion as you know. What works for one might not work for another. I would ask the manufacturer or someone who has your particular hull. Not just anyone, but someone who's boat works really well. Seeing is believing, not what someone says on line. I have seen boats that worked really well on line but sucked big time at the lake. It is all relative. With that said.......i would start out with it set up just like you said if you don't have other input. Then, if you have to hold a lot of left rudder to keep the boat straight I would start changing things ONE THING AT A TIME. Keep in mind.........the sponon that hits the water the hardest will make the boat veer in that direction. I am sure that is part of what Doug is doing with shifting the strut to the left of centerline. I would rather add a couple of ounces of lead on the left sponson if needed.

The rudder mounted on the right of centerline will help push down the left sponson. It will also make left hand corrections easier without blowing the boat off the water. If the rudder is kicked back even the slightest it will lift the transom and the prop will walk the boat to the center of the course. So the rudder as well as the strut depth plays a lot in controlling prop walk. Etc. Etc. As you already know. There are so so many variables and so many ways to counter issues that I think it best to start simple and take the issues one at a time. I like to add a bit of a wedge to the right sponson sometimes to counter torque. Maybe 1/2 degree more than the left sponson AOA. Of course unsharpened props and oversized props cause prop walk but we are talking hull set up right now. Too small a rudder will let the boat walk to the right because as you said.....the rudder is what keeps the boat from walking right. I have found that setting the rudder with the right side parallel to the center line of the hull with the left side of the wedge hitting the oncoming water to be the best rudder centering. I would set the rudder in that manner and then start adjusting other things ONE AT A TIME to pull the boat into harmony with the rudder. Make the boat go straight and not crab.

The hard thing about a scale boat, unlike the versitility of your rigger, is getting the weight enough forward so that the boat does not blow off the water yet have enough weight on the prop that it doesn't get high out of the water and walk the boat into the course. Don pinckert told me one time a long time ago, and it is so true............if the tail is higher than the nose the boat will not blow off the water. Do it by making the strut deeper rather than letting the prop ride high out of the water. Also keep in mind the higher the tail is off the water the less AOA on the front sponsons. I am rambling now.....got to get back to work.

Hello John, while we see the same on a lot of settings, this is one that I have questions about. Setting the right side of the rudder blade so that it is inline with the center line of the hull is adding a lot of left trim into the rudder. In my experience, this makes a boat flighty. I know that you have ran very fast using this setting. Maybe the flighty boat is quicker in record trials.

I like to have the center line of the rudder blade parallel to the centerline of the hull with other settings, turn fin, strut set for the boat to pull just slightly to the left (8 to 10 feet for the length of the straightaway) when the rudder blade is neutral. Then when the rudder is trimmed to make the boat go straight it settles the boat down on the water. This is what I like for heat racing anyway.

Charles

 

[anthony_marquart]

On this .21 boat the rudder is mounted on the right side, next to the strut which is centered on the boat.. I will be bringing my shims..

 

[RobertWurster]

Yes i tried lots of set ups with my boat.It is the one in my aviator pick.It seemed to realy like the x440 3,ran really well with a x442.I got the props done exept for being bar cut i dont know what else was done but they are very sharp.Engine and strut centered in boat.

 

[John Finch]

I'm about to start setting up a sport40 boat. So,.. if I understand all this correctly,.. a good recommendation would be to,

-center the engine in the hull

-use battery weight to keep the left sponson down, (lifted from torque)

-maybe add a shim to the strut to keep the boat from pulling into the course. This helps with SAW speed reducing rudder input to keep it straight.

Anthony,

Everyone has there opinion as you know. What works for one might not work for another. I would ask the manufacturer or someone who has your particular hull. Not just anyone, but someone who's boat works really well. Seeing is believing, not what someone says on line. I have seen boats that worked really well on line but sucked big time at the lake. It is all relative. With that said.......i would start out with it set up just like you said if you don't have other input. Then, if you have to hold a lot of left rudder to keep the boat straight I would start changing things ONE THING AT A TIME. Keep in mind.........the sponon that hits the water the hardest will make the boat veer in that direction. I am sure that is part of what Doug is doing with shifting the strut to the left of centerline. I would rather add a couple of ounces of lead on the left sponson if needed.

The rudder mounted on the right of centerline will help push down the left sponson. It will also make left hand corrections easier without blowing the boat off the water. If the rudder is kicked back even the slightest it will lift the transom and the prop will walk the boat to the center of the course. So the rudder as well as the strut depth plays a lot in controlling prop walk. Etc. Etc. As you already know. There are so so many variables and so many ways to counter issues that I think it best to start simple and take the issues one at a time. I like to add a bit of a wedge to the right sponson sometimes to counter torque. Maybe 1/2 degree more than the left sponson AOA. Of course unsharpened props and oversized props cause prop walk but we are talking hull set up right now. Too small a rudder will let the boat walk to the right because as you said.....the rudder is what keeps the boat from walking right. I have found that setting the rudder with the right side parallel to the center line of the hull with the left side of the wedge hitting the oncoming water to be the best rudder centering. I would set the rudder in that manner and then start adjusting other things ONE AT A TIME to pull the boat into harmony with the rudder. Make the boat go straight and not crab.

The hard thing about a scale boat, unlike the versitility of your rigger, is getting the weight enough forward so that the boat does not blow off the water yet have enough weight on the prop that it doesn't get high out of the water and walk the boat into the course. Don pinckert told me one time a long time ago, and it is so true............if the tail is higher than the nose the boat will not blow off the water. Do it by making the strut deeper rather than letting the prop ride high out of the water. Also keep in mind the higher the tail is off the water the less AOA on the front sponsons. I am rambling now.....got to get back to work.

Hello John, while we see the same on a lot of settings, this is one that I have questions about. Setting the right side of the rudder blade so that it is inline with the center line of the hull is adding a lot of left trim into the rudder. In my experience, this makes a boat flighty. I know that you have ran very fast using this setting. Maybe the flighty boat is quicker in record trials.

I like to have the center line of the rudder blade parallel to the centerline of the hull with other settings, turn fin, strut set for the boat to pull just slightly to the left (8 to 10 feet for the length of the straightaway) when the rudder blade is neutral. Then when the rudder is trimmed to make the boat go straight it settles the boat down on the water. This is what I like for heat racing anyway.

Charles

Charles.

You are right about the SAW setup. I use that setup all the time as there is no turnfin and very little if any boat touching the water. The tad of left keeps the boat perfectly straight. It works for my heat racing stuff too. I do have a perfectly centered rudder on my circus circus as I modified the running surfaces to make the boat track straight. I would say either way is a good starting point but I would NEVER use more than that much left rudder. Something I forgot to mention........I thin all my rudders, so there is very little wedge on the left side to cause drag.

Mike,

Your boat drove great the other weekend. Handled the corners very well too. Shortening the rudder a half inch got rid of the hop. Just one of those small changes that makes a big difference. If I get into electric racing It will be with one of your boats! It was the first electric I have driven that gave me a bit of a rush! You could thin that rudder a bit too.

 

[Mike Luszcz]

Thanks John, I am very glad you enjoyed the boat. I can not believe what a difference the rudder length made! Changed the whole boat! I hope to put a gas sport hydro in your hands someday soon as I think you can do good things with it! Mike

 

[Samuel Hagan JR]

Since rudder placement came up. What's the pros and con of having the rudder on the left or right,

 

[anthony_marquart]

I'm totally new to sports or scales,.. but I can see that the rudder on the right would help push the left sponson down,, as it is lifted by torque,.. I personally think that getting the rudder closer to the TF makes for less rudder through, which is always good. I'm sure there is a reason there are so many on the left side.. I don't know those reasons,.. I'm also wondering about flat or round bottom struts. I like flat bottom struts,.. maybe the ticket is a flat bottom strut with the low lift prop.. I'm starting with a round bottom strut.. I need to get a flat one to try back to back with..

 

[RobertWurster]

Not shure but i thinck with the rudder on the right you will get lift on that side whitch in turn you will be fighting with the turn fin and get more drag.With the sp 20s i have built i have always put it on the left.

 

[anthony_marquart]

well i hope i didn;t mess up putting it on the right. It would be a major rebuild to move it to the other side. If I have trouble ill thin the blade as far as possible, run it as short as i can and hope for the best..

 

[Samuel Hagan JR]

I'm totally new to sports or scales,.. but I can see that the rudder on the right would help push the left sponson down,, as it is lifted by torque,.. I personally think that getting the rudder closer to the TF makes for less rudder through, which is always good. I'm sure there is a reason there are so many on the left side.. I don't know those reasons,.. I'm also wondering about flat or round bottom struts. I like flat bottom struts,.. maybe the ticket is a flat bottom strut with the low lift prop.. I'm starting with a round bottom strut.. I need to get a flat one to try back to back with..

I'm new also. I'm getting a flat bottom strut for my new sport 40 and scale. The way I see it is if it doesn't work I can always round it. But I would like to know more about which side of the boat to put the rudder. On my old DPS hull it's on the right. Everyone else I see is on the left. I was told that putting it on the left makes turning easier.

 

[RobertWurster]

Dont go buy me Anthony,I was just told to always put it on the left.so that what i do.Im no great racer.I havent raced yet.LOl,Just been running for fun for about 4 years.I will be doing some racing in 2013.On my sp20s i limmit the amount of rudder travle and then turn real good.I cant waite to se your 310 run and hope it is all good for you.I have a new 5p sitting here getting ready to send to Steave Wood.

 

[John Finch]

44 years of racing experience tells me put it on the right. Here is the history.............Back in the seventies we put the rudders on the left to hold down the right sponson in the turns. Rudder on the left puts down pressure on the right sponson, but it also aids torque in lifting the left sponson, so left turn corrections blew the boats off the water very easily. Turn fins were straight and small as servo strength was about 54 inch ounces of torque max! see the delema.

As the years passed the servos got stronger and the turn fins got larger and then there was the curved turn fin that holds the right sponson down in a corner. Tilted turnfins do the same, but the servos could not handle the job of turning a boat with a large turnfin until the mid 80s or so. Since the turnfin could now hold the right sponson down in a turn now the rudder can be moved to the right to fight torque. Now with the rudder on the right we can make small adjustments to the left at full speed on a lot of boats while heat racing. Before, you had to chop the throttle before making left turn adjustments.

So, if you are not using the curved turn fin the rudder on the left makes sense. If you have a curved turn fin that holds the right sponson down in the corner the rudder on the right allows easier and safer heat racing characteristics.

If you think the rudder on the right is going to cause drag and make the boat turn right I can tell you unless you have a huge thick rudder it aint happenning. Every scale boat I have run........EVERY one......has worked better with the rudder on the right after 1990 because of turnfin and servo advancements.

Credentials........Two years in a row impba 1/8 scale national champion, 2010 hobart 1/8 scale winner, and tons of district wins to back it up. Bardahl round nose, circus circus, 7 elevin, lobster boat,budweiser, etc etc. Had a bunch. Not just a SAW modeler. I have been heat racing for a long time and scale is still my favorite class.

 

[anthony_marquart]

Nothing like advice with history to back it up!!! Thanks!@!1

 

[RobertWurster]

Goog info,Mr,Finch.

 

[Dasboatman]

Hey John,

Guess we should add Historian to our resumes also - Har, Har !!!

First radio I bought for boats in 1970 was a Kraft 3 channel using KPS-11 servos. The last update to Kraft servos I recall was the KPS-20H. I believe I was still running this radio when I left Norfolk in 1970. In 1987 I was running Futaba

S-29 and S-131 for throttle and rudder.

These old servos may have been in the 47 oz/in torque range - down hill and down wind.

I was curious as to the torque used in a Friend's helo the other day - he said for me to grab an output arm and he would show me. I think those servos are in the 200 oz/in range and digital. Servo power is no longer an issue.

Here's a pic of the rudder assembly we had available back then. And a pre radio hydro that belinged to a Friend.

My Scale and Sport 40 rudders are on the right also. Shafts down the hull centerline. CHEERS !! Bob

 

[Tim Kish]

Earlier this year I purchased a tired Bud T5 boat with the intentions of trying all the different things you just can't do after the boat is finished.

After trying a number of things I got the boat dialed in pretty good but it still wanted to lift the left sponson and turning at any real speed resulted in a blow off or spinning out

.

So I decided to move the rudder from the left as the manufacturer suggested to the right , it was night and day , now I can turn left if need be and testing into a strong wind the left only lifted slightly , nothing a little weight wouldn't cure.

My only problem with the rudder on the right was the fin I was using was not the proper fin , so the next time out it will have a turnfin with a lot more curve in it.

Funny thing is when I first started testing this boat I thought there was no way I was going to waste the time or money to repaint it , but after the last couple runs I think it may just be worth it.

Tim

 

[RobertWurster]

Was that u32 a hand cranck like a model A LOL

 

[John Finch]

Earlier this year I purchased a tired Bud T5 boat with the intentions of trying all the different things you just can't do after the boat is finished.

After trying a number of things I got the boat dialed in pretty good but it still wanted to lift the left sponson and turning at any real speed resulted in a blow off or spinning out

.

So I decided to move the rudder from the left as the manufacturer suggested to the right , it was night and day , now I can turn left if need be and testing into a strong wind the left only lifted slightly , nothing a little weight wouldn't cure.

My only problem with the rudder on the right was the fin I was using was not the proper fin , so the next time out it will have a turnfin with a lot more curve in it.

Funny thing is when I first started testing this boat I thought there was no way I was going to waste the time or money to repaint it , but after the last couple runs I think it may just be worth it.

Tim

Good to hear Tim.