I think that I can fly.

[Clive Everest]

As many of you will be aware we have been planning to fit foils to our boat following the nationals.
Watching Graham and Eddie over the last year this looks like a lot of fun in a very Cherub way.
It probably also offers the biggest potential jump in performance of any obvious development.
It seems that the press cannot get enough of foiling developments it could really raise the profile of the class. Every magazine and online publication seems to be full of it since the last AC. Most of this is happening in new one design cat classes. By been one design they are snookered as they cannot make themselves better once the limitations of their design have been established.
The A class cats are foiling as a development class but with rules that were written to stop foiling and as a consequence they make it harder and more expensive than it could be.

The Cherub is one of the very few proper development classes left and offers the opportunity to lead the fundamental development of future sail boats in a real competitive environment.

It would appear to me that the biggest challenges with putting a Cherub on foils will be light wind take off and staying on-board. Speed will probably not be an issue. The Kiwi R classes have already shown that it can be done.

Clearly the Moth is the benchmark foiler. Compared to them we have similar sail area to weight (without spinnaker). We have plenty of righting moment – more than they do for the rig and weight.
However our hulls are only one foot longer and three times the width carrying twice the weight so getting to take off speed will be hard.

We therefore need a very wide foil that will carry the weight at relatively low speed with low induced drag. I also hope that a large foil will also stop the top end speeds being too mental which I like.

To stay on board we are going to need very good height control. Last year at QM we all saw Riot Vans potential but the crashes need to be eliminated. We do not have graham and Eddies bounce.

The solution that we are about to try on A + E has a large lift foil mounted between 2 parallel centerboards. The foil is 1.45m span and 0.23m^2 area. We were going to make it even wider but this width allows us to roll the boat on the trolley.
By having the lift foil span the 2 parallel centerboards we avoid all the structural issues of the T joint.
The wand control is able to adjust the angle of the entire foil not just the flap. I am hoping that this will give good height control. I chose this arrangement for these reasons.
Dan and Roger have done a superb job this week of making a main foil in MDF moulds that Paul Croote machined for me. Their main comment has been that the main foil was massively easier and quicker (cheaper) to build than the flapped Moth foils. They now want to convert their Moths to a similar system.
Pictures attached.
The centerboards are very lightly forward of the old ones. This extends the wheel base improving pitch stability but hopefully will not upset the balance.
The centerboard cases are oversized to make it easy to drop the centerboards. They were made by laying up a sheet of carbon with a return that can be set into the foam of the hull.
Each case weight 300g. I have not re weighed the boat but the total additional weight added to the hull is between one and two kg.
We have used the remains of Roland's broken Demon rudder to extend ours to close to the length it was before we drastically cut it down.
Weather permitting we will launch tomorrow. I don’t think that we are going to try and race Bart’s Bash thought.

[Clive Everest]

more pics

[Clive Everest]

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[Clive Everest]

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[roland_trim]

Good luck tomorrow,
R

[Phil Alderson]

Clive,

I like the plan, good luck tomorow.

I have always liked the idea of the main foil rotating, and using the twin boards does solve the problem of the centre axle. I have always thaught that with the moth flap foils in full lift config it must be quite high drag, and moving the main foil as a whole shoudl be able to give a greater range of lift adjustment.

Does the wand drive the main foil directly, or does it use the secondary foil like a servo tab?

Do you expect much latteral movement of the center of pressure of the main foil with a change in alpha?
 

[Clive Everest]

Hi Phil,
The wand drives the foil directly.
The center of lift on the cambered foil does move aft as the speed increases and the Cl goes down.
The tail plane is there to control / neutralise this.
without it the theoretical push rod forces would increase from 100N at 8kts to 800N at 18kts.
The pitch of foil on the tail plane can be adjusted ashore.
There may be some advantage from allowing the push rod force to increase a bit with speed. It will mean that the wand stays very attached to the water and any elasticity will make the boat fly lower at speed which is attractive.

The intention is that the center of lift is always aft of the pivot so there is  direct force through the control linkages and backlash is not an issue.

I would love to use the wand to directly control the tail plane / servo tab.
It would mean that the foil would trim to a constant Cl as you flew through chop with no input from the wand / control system. The control gain could then be set much lower giving a smoother ride.
At the moment I can not see how to route the control through to the trim tab and do not have faith in it then having enough authority to dominate friction in the main foil bearings. One step at a time.

The wand and the control tubes through the fore deck are carbon golf sticks brought from the scrapie for a pound. As a sailor there is something very satisfying about cutting the head off a golf stick.

 
live

[Neil C.]

As a sailor there is something very satisfying about cutting the head off a golf stick.

Brilliant

[ade white]

how dit go? how dit go?
debs is going to be really pissed as she was hoping for some housework doing... do you realise this may mean me getting out the jig saw again!!! Clive this is not very helpful, how dit go?

[Clive Everest]

Sorry to be slow replying. Helen had organised an evening of culture. I could have spent the evening in a dark quiet room.

We got to fly. The control system is no where near good enough. lots of big crashes.
Upwind was easier than downwind. Had some moments showing promise and plenty that will give food for thought.
Thanks to Harriet of harbour Chandlers for having a camera to hand.

[Clive Everest]

It's much better than house work Ade.

[Clive Everest]

Why am I getting warning message:

Warning: topic is currently/will be locked!
Only admins and moderators can reply.

[Tim Noyce]

Too much awesome content perhaps. Nice Helmets!

[BenR]

Great work Clive, hopefully Diana and i will be down to Hayling soon to see you in action. Helmets look like a sensible idea!

just unlocked the topic (according to the log, it was you who locked it!)

[Neil C.]

Impressive stuff Clive.
Quick question for you. Can you explain the purpose / function of the extra winglet, trim tab thingy behind the main foil for me? I couldn't quite work it out from your original posts.