Sam's DT Project for GCSE

[Torchy]

This is Sam not dad because registration is disabled (forum problem?):

We are planning to make a T foil to add to Loco's spare rudder. This will also cover my DT GCSE so there will be market research related questions.

What do I need to check to know the rudder will take a T foil?

How will we attach the T foil to the rudder?

My DT project also needs to involve a business case, so i need to think about that too.

What type of foam is in a T foil and how do we shape it? Nigel says Clive Everest had an idea about this and we're looking at that thread.

What T foil section shape should I use?

Could it be mass produced, say in a factory?

[ade white]

Hi Sam, (FOR YOUR GCSE FOLDER)
As cherub user I am planning on a similar upgrade. (therefore here is evidence of 'Identifying the Need' and 'meeting user needs' and using 'existing products' to place in your Section 1 Assessment Criteria). Also in Section 2: Research; you can add evidence of other people making similar items in different ways and means. Hopefully for your Market research you can include Clive's idea of using windsurfing fins.
 
MY upgrade is going to be a retro 'bodge' affair (Big thanks to Clive for the idea and in typical Cherub fashion!) and this is my initial plan to make my T-Foil...
I am finding 2 windsurfing fins approx 40 cm each.
Then I will grind down one profile side. 1 for left and 1 for the right side. Finally giving an assymetric lifting foil shape. ( IE flat on underside and an aero-foil profile section on the topside) (you can do the diagrams)
Then I will cut the power-box casing sections so that they meet together (I have not yet thought of the 'marrying' shape but it will need to add strength as the joint will be the weakest link).
I will then add a carbon cloth layup onto a prepped release agent flat mould. (Polycarbonate sheet) and press the 'ground flat' profile surfaces of the 'married' fins onto the layup.
If I think the profiles are too thin I can thicken the layup or add a complete top surface layup as well, but I have to consider the weight issue.
I will add carbon layup onto the top of the mid joined section area of the fins to add strength for the center section.
I will then Slide it all into sealed end plastic bag, seal the open end and carefully placing in a vacuum tube to suck out the air to help produce the bond when curing.
I will also add a weight onto the top of the mould whilst curing to improve the bond.
This will, hopefully, make my flat section to join onto the rudder blade.

To fit the section to the blade I will cut a slot halfway into the back section of the rudder leaving the front half intact.
I will grind a section of the cut half of blade to allow for more carbon overlay cloth to strengthen the area, but aiming to keep the rudder profile as thin as possible.
There are lots of bodging methods I could use here but keeping minimal resin to cloth is the strongest way and looking at the cloth weave is vital for strength over weight and bulk.
Then probably a test... then... either a repair or BUYING a new blade!!!
After that it is a lot of fairing, sweat and toil and finishing... or waiting for a new blade from a good manufacturer and not an idiot like me. having said that "how hard can it be" (is it a ! or a ?). Food for thought... now go for it!
bfn ade. cu at the inlands!

[Phil Alderson]

Have you read:
http://www.uk-cherub.org/doku.php/tech/t-foil_rudder
http://www.uk-cherub.org/doku.php/tech/foils  (I have a part written update for this so check back later)

For your questions:

What do I need to check to know the rudder will take a T foil?

You can't know if it will be strong enough till it breaks and you know it wasn't! If you sand through the laminate very carefully you can count the layers, and work out what was used to construct the foil but only in the area you have cut, and you now have a hole in the foil.

How will we attach the T foil to the rudder?

You need to add the fibres in a way that they will take the loads.  the strength of laminate is direction dependant, if you have some UD fibers they have 100% of the strength along the length and 0% at 90 degrees to the direction.

What type of foam is in a T foil and how do we shape it? Nigel says Clive Everest had an idea about this and we're looking at that thread.

You need a high density foam, low density foam will crush, and the foil will break. You need to cut the foam away to make the shape, and some way of knowing you are close to your template.

What T foil section shape should I use?

You could probably write a PHD on this and still have more work to do

Could it be mass produced, say in a factory?

Shaping a core is time consuming, there is a much better way if you want to make more than one thing the same shape.

[Torchy]

Thanks everyone for all the help and support. Ive got some really good ideas to think about,
Sam.

[phil_kirk]

The business case argument for mass production could be countered by identifying the required no of foils to the same design and considering the investment required for mas production. Then compare this against the cost of making the same no. by manual time consuming methods.   

Consider that foils are developed quite regularly and that the need for one design may not be high. 

I agree high density foam core.  I have succesfully used layups of 2 unis + 1 weave and 3 unis tapered (thickest at the top of the foil thinnest at the bottom) +1 weave successfully. Consider calculating the bending moment on the foil and identifying the correct no. of layers required as evidence.
Good workmanship is key so anything that improves quality of workmanship (eg. vacum baging)is worth considering within reason.

[MK]

From my recent(isn) experience of GCSE RM i think you will really struggle to hit the marking criteria with a T foil, it is heavily weighted to looking for standard woodworking and metalworking techniques, and a finished product with mechanisms and moving parts

[roland_trim]

I agree high density foam core.

There have been several T-rudders made and not broken out of less.

Simon  had an interesting response when asked about Born Slippy's magic foils which are so light they get blown along the beach. His quote was along the lines of "Yes they were light, but most of the rest of that batch broke".

[Neil C.]

Indeed. Born Slippy's original daggerboard let go at the Weymouth Nationals in 2001. But I think the rudder is still the original. What I can't work out is why the ultralight rudder stock has never failed. No end plates to the slot or anything. 

[ade white]

Initially I thought the same about the T foil not being adequate for a GCSE RM project However there is a lot of perrpheral evidence I think you could include that would be relevant to gain marks. (Just be careful reading through the assessment criteria).
(I'm thinking you could show the adjustment mechanisms etc and the different moving parts and mechs needed for the T to work. especially if you built some simple card models along with diagrams and also show your understanding of the ergonomic considerations needed for it to work...

[Torchy]

This is Nigel...the principle of this project was discussed with the DT teacher in June. I will check he understood that we weren't talking about the mechanism but just the foil addition to the existing (spare) rudder. We had quite a long chat, so I think it was clear.

[ade white]

that good then. its all about hitting the assessment marks!!!

[Banshee Ambulance]

From my recent(isn) experience of GCSE RM i think you will really struggle to hit the marking criteria with a T foil, it is heavily weighted to looking for standard woodworking and metalworking techniques, and a finished product with mechanisms and moving parts

All very true. I would have thought that you would need to extend the project to include adjustment systems to meet the scope expected. Standard woodworking/metalworking may well come into it too could be achieved using cedar for a core perhaps? Mass production as such should not be an issue, you just need to demonstrate that you could produce more than one economically and think about an existing need for the product. Unfortunately, I just wanted one for my boat wont cut it.