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Author Topic: Bmprs class D build 60" Deep V  (Read 6312 times)

Brigadair

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Re: Bmprs class D build 60" Deep V
« Reply #25 on: April 11, 2013, 08:31:42 PM »

Looks good on Youtube, I bet there is a lot more to come from the performance of this boat!
Look forward to seeing it on Sunday.

Garry
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Tug-Kenny

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Re: Bmprs class D build 60" Deep V
« Reply #26 on: April 12, 2013, 10:15:12 AM »


Welcome to the forum Brigadair.

Ken

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F1 madness

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Re: Bmprs class D build 60" Deep V
« Reply #27 on: April 13, 2013, 08:40:38 AM »

Hi garry
welcome bud
Hopefully find out sunday still need to do some setting up so will be doing this there and need to finish running in the engine so will see how it goes from there :-)) 
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F1 madness

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Re: Bmprs class D build 60" Deep V
« Reply #28 on: May 17, 2013, 08:27:01 AM »

UPDATE
After sunday race at telford and some issues so work was needed to be done
The problems the boat itself was too light and flighty and the other problem was pulling too the right,i was having to almost full left to try and keep the boat in a straight line ,when actually making a turn i would need to correct with some left the boat would spin out,due to these issues i decided not too run in the 2nd heat
Heres what iv done,iv added a layer of CF right up past the seams this has added some extra weight and reinforced the hull aswell
Added left turn fin ,2ltr fuel bag,after talking to the designer of the hull iv shortened the stinger 35mm to bring the prop closer to transom
all thats left now is repair the hatch after a flip,hoping to run it this weekend and see if the changes have helped and reset up the trims




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derekwarner

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Re: Bmprs class D build 60" Deep V
« Reply #29 on: May 17, 2013, 09:57:45 AM »

Hi F1M..........knowing little  :o  about these fast machines........ {:-{ but do I see......
1. the propeller is anti clockwise rotation
2. the blade rudder is to the right hand side of the axis of the propeller
Thinking about this....the pressure on each of the three propeller blades is on the leading edge, the lower pressure is then also on the trailing edge of each blade
From this ......should the vessel not have the tendency to turn to Port or the left?......... :o  ....Derek
 
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black magic racing

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Re: Bmprs class D build 60" Deep V
« Reply #30 on: May 17, 2013, 11:33:48 AM »

the boats pull to the right, to stop this from happening we off set the drive to the right of the boat by about 4 mm which helps keep the boat on the straight, %%  sometimes because of the power this is still not enough and the use of a different prop can over come this,also another way to to angle the rudder slightly over so that it forces the boat to run straight, :-))
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ids987

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Re: Bmprs class D build 60" Deep V
« Reply #31 on: May 17, 2013, 12:15:18 PM »

Hi F1M..........knowing little  :o  about these fast machines........ {:-{ but do I see......
1. the propeller is anti clockwise rotation
2. the blade rudder is to the right hand side of the axis of the propeller
Thinking about this....the pressure on each of the three propeller blades is on the leading edge, the lower pressure is then also on the trailing edge of each blade
From this ......should the vessel not have the tendency to turn to Port or the left?......... :o  ....Derek


Hi Derek, the anti-clockwise rotation of the prop (as viewed from the rear), means that the torque transmitted up the shaft to the engine, tries to rotate the boat clockwise (again, as viewed from the rear), causing it to tend to list right, and veer right. Additionally, the paddle wheel effect of the prop in the water, will tend to try and pull the rear end of the boat leftwards - again, causing a tendency to veer right.
Our main friend here is the rudder. The main reason that a right side rudder offset is conventionally used, is because the lift from the rudder helps to lift the right side of the boat, and counteract the natural tendency to list and veer right. Having the trailing edge of the prop roughly level (equidistant respective to the transom), as the leading edge of the rudder, is said to help. I suspect that shortening the transom to prop distance should also help (prop has less leverage on the boat). Having the rudder equidistant, I believe, is meant to help in the sense of the rudder kind of catching the wash thrown off the prop, and re-directing it straight back.


Hi Daz,


Some other things of note (you probably know most of this already, delete as appropriate):


1) Different props react differently. Generally, bigger props, and especially more pitch, cause more problems, but other prop characteristics also have a bearing. Might be worth trying two blade instead of three.
2) Prop again, the sharper the prop, the less likely to give issues.
3) Strut / stinger offset towards the right (a few mm), tends to help (because the strut or stinger also creates lift), but generally not too quick or easy to implement if not already built in. Strut / stinger depth and angle (respective to keel line), can also have a bearing.
4) More rudder blade in the water means more lift on the right of the boat. If you can get the rudder a bit deeper, it should help. More offset too, but the greater the offset, the more it affects left turns, and the longer the rudder needs to be to get the same rudder depth. Can't really see how far your rudder is offset at the moment. General consensus normally suggests an offset in the region of 60ish - 70ish mm.
5) Check carefully for any play or flex in the rudder linkage. A deep vee won't naturally go straight. The rudder is constantly holding it.
6) Similar to above, rudder servo power needs to be adequate; both to hold the boat in a straight line, and pull it back after a right hand turn.
7) I'm still - to some extent, battling this with my C Class, but getting there. My AA boat started to do the same after I raised the rudder to install bigger trim tabs. I fixed it by taking means to get the rudder depth back, and now tends to slightly lean left at speed (due to the rudder lift), but doesn't seem to steer left, presumably because the other factors are counteracting.


Good Luck. Keep us posted.
Ian
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ids987

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Re: Bmprs class D build 60" Deep V
« Reply #32 on: May 17, 2013, 12:54:57 PM »

the boats pull to the right, to stop this from happening we off set the drive to the right of the boat by about 4 mm which helps keep the boat on the straight, %%  sometimes because of the power this is still not enough and the use of a different prop can over come this,also another way to to angle the rudder slightly over so that it forces the boat to run straight, :-))


Sorry bud, posted my novel before I saw your post.
Could I pick your brains on rudder angle too please.
Which way do you go with the rudder angle; Is that the left to right angle from the vertical you're adjusting ?
Do you think the front to back angle makes a difference too; I think (in theory), if the rudder is tucked in at the bottom, it should tend to make it drag right (by pulling the right side of the transom down), and angling the bottom further out should help by creating more lift on the right side. I've never quite proved how it works in straight line handling (although I've used rudder angle to adjust turn attitude before).
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black magic racing

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Re: Bmprs class D build 60" Deep V
« Reply #33 on: May 17, 2013, 01:19:49 PM »

no probs mate,by angling the rudder so that the bottom is towards the prop i find straightens the boat up and stops it leaning over to the right,the rudder when at speed pulls the boat upright ,i have found this to work very well indeed on troublesome boats,we all come across one sooner or later lol,
by pushing the bottom of the rudder forwards tends to give the boat abit more drag but also will make the front of the boat dip down at speed and in turning,sometimes this can help in setting up a boat if the boat is abit nose high and also if the boat is abit unstable in corners,
pulling the rudder back is less drag and can raise the nose of the boat but be careful when corning at speed as it can also make the boat twitchy with the nose not wanting to dip in.
A ll the best   kurt
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ids987

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Re: Bmprs class D build 60" Deep V
« Reply #34 on: May 17, 2013, 05:37:29 PM »

no probs mate,by angling the rudder so that the bottom is towards the prop i find straightens the boat up and stops it leaning over to the right,the rudder when at speed pulls the boat upright ,i have found this to work very well indeed on troublesome boats,we all come across one sooner or later lol,
by pushing the bottom of the rudder forwards tends to give the boat abit more drag but also will make the front of the boat dip down at speed and in turning,sometimes this can help in setting up a boat if the boat is abit nose high and also if the boat is abit unstable in corners,
pulling the rudder back is less drag and can raise the nose of the boat but be careful when corning at speed as it can also make the boat twitchy with the nose not wanting to dip in.
A ll the best   kurt
[/quote


Thanks Kurt, Yeah. I've used rudder bottom more forward a few times, to hold the back end down a bit, to control spinouts. Not experimented much with rudder for straight line running though - apart from recently, with rudder depth.

Cheers: Ian
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F1 madness

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Re: Bmprs class D build 60" Deep V
« Reply #35 on: May 17, 2013, 06:20:30 PM »

Hi Ian
its all setup to the instructions off danny the designer of the hull
The only thing i done different is run a stinger instead of 80mm strut thats why iv shortened it
The stinger is offset 4mm to the right (as you look at transom) offset and rudder depth set at the diagram and mearsurements he sent me
The prop is 7015/3 which has been sharpend and balanced iv only got a couple of props as unsure which props to buy till running then work out what i need,planning on ordering a couple more props next week and have 1 more i wanna try on it 1st
Theres a tiny amount of play (and is minimal) in the servo but not enough to make pull to the right as it does
servo is a 26kg 1/5 MG digital servo so should be strong enough for the application
Before i do anything else i will run it on sunday and see if it still doing it,im gonna try the other prop i got,i have got a 2 blade alloy prop but there no ID numbers on it so dont know what it is,other concern is it cavitates the 3 blade easily before it bite so a 2 blade will more than likely do the same
Trial and error and keep trying different things ill sort it 1 way or another  :-)) 
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