Sailrocket 2 set to launch

Problems-mods to foil don't feel right and the flap came off the horizontal wing
and too much wind.... http://www.sailrocket.com/

click on image-you can see the flap in mid air! :

 

Sailrocket

Fairly good runs today-just over 50 knots-got the "B" class record. But there is a problem with the main foil. In three different configurations* Sailrocket still hits a barrier close to 51 knots. But they got a lot of data today and I'll bet they'll figure this out. They have two weeks left in the official timing window...

*1) "normal" foil
-2) "normal" foil with fences
-3) wedge shape ventilated foil



pictures today--click on image:

 

Time for the cockpit canopy, with a nice headrest it will be safer too.

 

I made a FOILED AGAIN post on the VSR blog. I have copied it below for more exposure.

Pardon the length below, but I be will building up to a point.

As is frequently done, I will refer to he apparent inability to exceed a specific speed even as wind speed increases as "hitting the wall" or just the "wall".

Hitting the wall has been observed by many displacement craft that are limited by a specific "hull speed". This is not applicable VSR, VSR 2 or other foiling / planing craft. Foiling craft have a different but very hard to penetrate wall. This was noted long ago by the Trifoiler / Longshot team.

The Trifoiler platform relied on foils for lift, automatic roll control and lateral forces (as needed for the sail/wing to provide forward thrust). Both VSR efforts use a foil to provide lateral forces primarily with a small vertical component (for vector balancing in pursuit of inherent roll stability). I was not surprised when the first VSR effort found their wall at a higher speed (10% - 15% or so) given the reduced reliance on foils.

VSR 2 did a good job of fixing most of the things that made VSR 1 risky to operate (Yea !!!!!!). VSR 2 adopted an easy change foil with two foils. One is a supercavitating version to try to penetrate the wall noted during runs of the original VSR. VSR 2 has hit the wall at about the same speed as the original with multiple foil configurations (Oh! - wailing and gnashing of teeth).

On the surface, the new results would seem to say that either the VSR 2 supercavitating foil just happens to have some new flaw that keeps the same wall (max speed) in place, or that there is more to the story than we think.

Gosh it would be great if some interested party following VSR 2 could have an epiphany, figure out the real reason and help the VSR 2 team beat this incredibly frustrating problem. They certainly have the tool (VSR 2) that would allow a simple foil change to confirm victory. They certainly have paid their dues (use of true innovation, diligent pushing forward, Paul putting his arse on the line riding the monster and just plain pain and agony) and deserve a break about now.

Ok, so now lets get real. No one is likely to just "figure out the problem". What we can do is really put on our thinking caps on and share any potentially useful results so that the VSR team can try some stuff that may ferret out this sneaky gremlin.


Here is my go at something.

Hitting the same wall with a traditional foil section and a wedge foil section was very unexpected. Highly unexpected results frequently tell us we are just plain doing something wrong. This begs the question:

"What single error or wrong assumption could cause both foil designs to produce the same speed limit"

That leads us to think about any SIMILARITIES in how the foils were designed. Were the required surface areas calculated using the same inputs and assumptions. Was the plan-form (shape) selected using the same process. Was the aspect ratio determinedusing the same criteria.

Even though I can make an argument that it would be great to have a foil with more surface area to try, I really just want to spur everyone to stop and see if they have any unique knowledge, experience or innovative ideas that could help all speed sailors (and wannabe speed sailors) make some real progress in blasting that darn wall into a pile of rubble.

 

Sailrocket

The main foil holds the boat down, so the low-pressure side is underneath the foil. What I'm thinking -and Paul alluded to this- is that the sideways movement of the foil is screwing up the lift on the foil by having an untoward impact on the low-pressure side of the main foil. For instance if the mainfoil is angled down from the transition outboard it may be possible that the low pressure side is being affected by the leeway. Ketterman discussed how leeway can have a negative effect on a lifting foil if the leeway impacts the low-pressure side of a foil.
Just took another look at the main foil(from way back) and I think I'm probably wrong in this assesment


This is one of the only things all three configurations would be dealing with...
Be nice if Tom Speer could take a look at this...

 

They both have similar drag from the spray/aerated/sliced water...less should give more eh? Spats against splats.....the new slogan of speed.....

 

The aft foil should probably be mounted so it is in clear water too. Looks like it is operating in the firehose from the forward nozzle.

 

Good discussion.

If the problem is the angle of the foil, the fix is EASY. Get rid of the angle, scale up the size of the rear main pod a little and add the ability to take on water ballast to maintain roll stability.

The main foil is off to the windward side of the hull quite a bit. The forward pod is a planing surface and it may mess the surface a little bit, but I really do not think that the main foil is seeing churned up water to the extent that would mess up performance.

They seem to use onboard cameras a lot to make sure they can review stuff like this.

 

Planing surfaces do have merits. One of these days someone will build a machine with a long travel suspension to handle the bumps....I think the foil drag will prove the limiting factor. An aero down force wing might be interesting to explore as an alternative. Getting things out of the water reduces the major source of drag. Any one try the Newick new moon shape on a stepped hull for leeway resistance?

 

Sailrocket

From Paul Larsen today:

There is just an immense amount of info in these two shots. They are taken in very similar conditions at very similar speeds... with two totally different main foils plugged in. The top one(right, below) is the with the cavitating, wedge shaped foil and you can see how close the foil is tracking to the bubbly, ventilated wake of the rudder. It's almost in it. The lower(left, below) photo is with a conventional foil and it is travelling well clear of the wake. The rear pod is flying in both and the fixed angle (but self retracting) rear skeg in the back float is just kissing the crests. You can see the wave impacts of the front float as it jumps across the crests. The fact is that the Cav foil is built with 3 degrees of angle in it as it was always assumed it would be travelling in a fully ventilated/cavitating mode. these shots show that it clearly is not. The flow is most likely fully attached back to the base of the foil and... it's performing quite nicely. The trouble is that it's now subject to the standard foil issues and that won't give us that glorious sonic 'boom' that we crave. All good evidence.
The rudder loads were similar for the two runs with low loads around 5-30 kg. This would suggest that loss of grip at the front/rudder was unlikely. What is interesting is how submerged the main foil is in both instances. VESTAS Sailrocket 2 should be riding on her transition. This is the curved section of the foil. Instead she is sitting much lower with a large part of the 'first foil' (the upper more horizontal foil) submerged. This suggests that the foil is pulling down too hard... or we have stood the rig up too much to stop the leeward pod from flying and thus reduced the net up lift... blah blah blah. I could go on... really I could. I hate to cut it short for you technoheads out there who are no doubt getting right into this... but that's how it goes when the wind starts to blow and you have to drop everything, make a quick call on what changes will be best to try out and then get out there.

click on image-

 

I was right about the cameras.

I was not so right thinking that the main foil was assured of being in clean water. When they are using their new cavitating foil, it looks uncomfortably close to the disturbed stuff from the front of the boat.

Note that the track from the front is really mostly the wake from the front steer rudder.

The seem to think that they may be on to the problem with the main foil pulling down to hard. Lets hope that a simple adjustment will confirm that they are on the right track.

 

Sailrocket

Running out of time. They may cut the supercavitating foil down in the hopes that that would allow it to break free........
UPDATE: Simon Fishwics comment is good. Cutting the board down increases the foil loading so instead--take Helena for a ride first!

Wrong! see my next post...

 

Might be a catch 22 with the cavitating foil. If it breaks loose and cavitates might it not also reduce the downforce significantly and/or suddenly? It might be helpful to have the flap/wing on the foil side of things.

 

Sailrocket

-------------
As I understand it, unless the foil thats designed to cavitate cavitates it is causing a lot of drag and would have a similar "boundary" speed-wise as the normal foil. That prevents them from going much faster than they have already. Fishwics solution was borne out in a previous test when Larsen sailed with a crew and went faster than ever before-seems to show that the cavitating foil may work better under more load? But the problem is the foil is pulling down so extra weight lessens the load! So if it works better it does so
because the load is less.....

 

I wonder if they reduce the angle of attack with the extra person on board, the blog doesn't say. It would be interesting to try the other approach- 1-2 up in lighter wind conditions without the foil at all. The lesson may be that after a certain speed foils shouldn't be in the water...Give them something to do while waiting for big wind.