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Author Topic: One from the 'to-do list' RAF launch build  (Read 1107 times)

John W E

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One from the 'to-do list' RAF launch build
« on: June 10, 2023, 06:46:50 pm »

hi there - being going through my 'old' books and I came across Marine Modelling (July 2015) with a free plan for the RAF Rescue Launch.   Basically stuck to the hull design of the plan, but, I have added one or two bits and pieces - still not finished it yet though.  Here are couple of pics and progress so far.


John



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raflaunches

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Re: One from the 'to-do list' RAF launch build
« Reply #1 on: June 10, 2023, 09:23:30 pm »

Hi John


Fantastic build so far, nice to see the ‘simple’ design being updated and being finished to higher standard. These vessels look beautiful on the water.
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Nick B

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John W E

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Re: One from the 'to-do list' RAF launch build
« Reply #2 on: June 25, 2023, 03:40:18 pm »

hi there, well got her bottom wet this morning - she ran well on 7.2 batteries and 2 JP motors running on 30 mm 3 bladed props.   I managed to get about 15 to 20 minutes run time out of a set of batteries.


John
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gra2

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Re: One from the 'to-do list' RAF launch build
« Reply #3 on: October 06, 2023, 09:14:13 am »

Very nice.
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derekwarner

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Re: One from the 'to-do list' RAF launch build
« Reply #4 on: October 06, 2023, 01:07:01 pm »

John....that double redundancy built into the steering linkages system is  :-)) .....


Derek
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John W E

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Re: One from the 'to-do list' RAF launch build
« Reply #5 on: October 06, 2023, 06:39:14 pm »

Derek


I have witnessed one or two rudder linkages fail when they have only been a single arm connect.   Especially, when you get a load of feathers from the lake around the rudder and propeller and it overstretches the linkage.    The little nylon bits pop off and in one case I have seen the metal connecting bar bend.


So, belts and braces - as they say - better safe than sorry.


John
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Shipmate60

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Re: One from the 'to-do list' RAF launch build
« Reply #6 on: October 06, 2023, 07:00:56 pm »

Nice one John.


Bob
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JimG

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Re: One from the 'to-do list' RAF launch build
« Reply #7 on: October 06, 2023, 08:22:47 pm »

Derek


  The little nylon bits pop off and in one case I have seen the metal connecting bar bend.


So, belts and braces - as they say - better safe than sorry.


John
Use heat shrink tubing over the nylon clevises to keep them closed or better use metal clevices and heatshrink. If the metal rod is liable to bend use a thicker one, 3mm instead of 2mm connections will resist much larger forces than you are liable to get on a boat rudder. The only time I use a pull pull linkage is on large aircraft rudders where there is a large area to move under load. Even turbine powered jets use a single rod linkage although normally 3mm with 2mm only on smaller ones.

Jim
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John W E

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Re: One from the 'to-do list' RAF launch build
« Reply #8 on: October 07, 2023, 11:04:41 am »

hi I am still working out how you put heat shrink over the nylon clevices - as it interferes with the movement  of the servo arm.


I don't know about your idea of the tork and pressure on a rudder of an aeroplane being more than on a boat - because some of these IC boats the rudders are under some extreme pressures.    I know when I designed the linkage for Bluebird - I had to use a nylon snake with a metal clevice to take the strain.   Even though Bluebird's rudder only moves when you are slow manoeuvring but at high speed the rudder movement is reduced to 2% as to try and use the rudder when she is at high speed 30 mph + is 'seat of the pants' stuff and clean underwear  %%  .


When I download the video of when I was running Bluebird and I clipped something in the water, you will see how she jumps and when I retrieved the model, I found the rudder was slightly bent.


https://www.youtube.com/watch?v=Cm4mhoYShWg


John
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JimG

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Re: One from the 'to-do list' RAF launch build
« Reply #9 on: October 07, 2023, 12:46:09 pm »

hi I am still working out how you put heat shrink over the nylon clevices - as it interferes with the movement  of the servo arm.


I don't know about your idea of the tork and pressure on a rudder of an aeroplane being more than on a boat - because some of these IC boats the rudders are under some extreme pressures.    I know when I designed the linkage for Bluebird - I had to use a nylon snake with a metal clevice to take the strain.   Even though Bluebird's rudder only moves when you are slow manoeuvring but at high speed the rudder movement is reduced to 2% as to try and use the rudder when she is at high speed 30 mph + is 'seat of the pants' stuff and clean underwear  %%  .


When I download the video of when I was running Bluebird and I clipped something in the water, you will see how she jumps and when I retrieved the model, I found the rudder was slightly bent.


https://www.youtube.com/watch?v=Cm4mhoYShWg


John
The heat shrink covers most of the clevis leaving just enough space at the end for the control horn to move, I have control surfaces with an area of at least 20 to 30 times your rudders, enough that high torque digital servos are needed to stop blowback at speed. I have measured the speed of one of my turbine jets using  GPS telemetry and it reached 130 mph groundspeed into wind so airspeed would be higher. This is slow compared to many sports jets which are reaching speeds of 200 mph and control must be rigid at these speeds, control surface areas are again much more than a boats rudder. We do at least have a considerably lower risk of hitting objects in mid air.
Jim
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Re: One from the 'to-do list' RAF launch build
« Reply #10 on: October 08, 2023, 02:34:42 pm »

And don't forget, closed loop is far superior to snakes.


 Regards  Ian.
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