Hmmmm. More 50's... but...
Sat, 15 Oct 11 22:28
Hmmmmm...
Well it looks like ventilated foils aren’t going to give up all their secrets that easily. We went out today in what I would call ‘top-end’ conditions with gusts up to 31 knots. The first run wasn’t in winds this strong. It was pretty much a repeat of yesterdays 50 knot run. The boat felt great and I managed to use the whole of the course. We are still downloading data but we know it was another run between 47-48 knots with peaks over 50.
SMOKING. GREAT CONDITIONS, WING IN, SITTING LOW... BUT...
Hmmmmm.
What’s going on here? I was sheeted in further and it was ‘solid’ wind. We really should be seeing continual solid progression, especially in these winds. I went again as the wind was hitting the 30’s. When the wind is gusting 30 it represents average winds more around 26-27. Helena sounded nervous as she called out the gusts. VESTAS Sailrocket 2 is made to sail in winds to 30 knots. I am only worried if it represents an ‘over speeding’ situation with crazy build ups of apparent wind. The apparent is what the boat feels and hence what will pull it apart. We aren’t there yet so I made the call to go for it and see what happens. I can always just ease the wing. I reckon on being pretty damned aware that I’m doing over 60! I discussed it with Alex as he is good at repeating my earlier plans and reasoning to me. The main reason for taking a bold step was to know for sure that we were over optimum design wind speeds of 26 knots average. If we still had a ‘glass-ceiling’ around 50 knots then we would know beyond all doubt that there was something we were missing. Raising the wing and launching the boat all went pretty well which is always encouraging. The comm.’s went down for the 87th time. VESTAS Sailrocket 2 accelerated like a scalded cat. I hit the course at pace and the acceleration came in brilliant bursts. I’m really starting to get comfortable with this boat... then BAM... she kicked and slowed. I figured either the wing or part of it had blown out. I pulled in arm fulls of mainsheet and there was nothing there. Obviously something in the new purchase system had failed for some reason. The middle section of the wing spun out to 90 degrees using its full-feathering range.
I put the rudder hard to windward to turn the rapidly slowing boat under the wing. Next I kicked up the main foil to allow the tail of the boat to skid around under the wing. The RIB was quickly up to me. As soon as they had me hooked up by the bow I went below decks to chase the culprit. It was nothing major. Simply a small string had failed as VESTAS Sailrocket 2 accelerated hard in the strongest conditions she had sailed in. I had replaced a single spliced string with a doubled up string of the same diameter but with two bowlines in it. It failed at the bowline. Typical, I should know better although I didn’t think it was that critical. Annoyingly it had happened at the peak wind of the day just as we were hitting 48.77 knots coming onto the course. I’m pretty sure we would have seen some higher big 'fun' numbers... but have no idea how high. It was set to be our biggest run. Once fixed we went straight back up to the top of the course and did another run. The wind was down to 22-25 knots. It was a real nice, clean run. I sheeted the wing in fully and the leeward pod leapt into the air. Not only does closing the wing-gaps in the wing increase the efficiency of the main wing, but it also increases the efficiency of the ‘wing-extension’ that sticks out the side. This purely gives vertical lift.
NOW THIS IS A GREAT LOOK. IT'S MY NEW SCREENSAVER. THIS IS VSR2 FULLY IN THE GROOVE. BEAUTIFUL. I'M STARTING TO FALL FOR THIS BOAT!
WE ARE FLYING BOTH THE LEEWARD AND AFT FLOATS. THERE IS SPRAY... BUT IT'S HARDLY HITTING THE BOAT AS THE FUSELAGE IS ALIGNED WITH THE APPARENT WIND.
OK... THAT'S FLYING THE LEEWARD POD A BIT TOO HIGH NOW!
The leeward pod flew high for the whole run. This is a sign that we can stand the wing more vertical. The leeward pod should only be flying at 50 knots with full flap deflection. There was no flap deflection here.
Overall it was our best run. I noted on the tell-tale on the bow that the apparent wind was around 10 degrees off being aligned with the fuselage. We did an average over 500 meters of better than our old ‘B’ class record but less than our best VSR1 run (which the WSSRC were too old to ratify) i.e. around 47.5 knots. We hit another peak just shy of 50. Something is definitely going on here.
As the wind had dropped we called it a day. We need to digest this position and focus on problem areas. I can only guess that it has to be something funky relating to the ventilated foil. If we are truly ventilated then the speed should just keep climbing. So I figure that we are not fully ventilated. So what are we? That’s the question. I already had some theories from a few days ago that I figured the 50 knot run dispelled yesterday. They are back in the forefront of my mind now.
Overall the day was very successful. VESTAS Sailrocket 2 really behaved herself in some pretty full on conditions and saved her own bacon when the mainsheet blew out. VSR1 would have rained down in that situation. VSR2 is proving to be very good at doing what she is designed to do and that is to be a tough, reliable and stable testing platform for dragging these experimental foils down the course in the real world.
I’m annoyed about the events of the second run. I think I may just have to commit to the WSSRC and book a record attempt (time to play that game). This means hoping that we can find a real breakthrough between now and then. We have to do it really otherwise we have to come down all over again. New team, new visas, more flights, extended carnet etc. So the pressures on to get it done now. We still aren’t at record breaking speeds... but every day we are closer. I’m more confident in all aspects of the boat. The new mainsheet is better, weaknesses were found and VSR2 has one again proved that she’s tough and wants to live. Yeah, I’m happy with that.
Cheers, Paul
p.s. sorry for the late blog at the end of the day. Sometimes the internet here just goes haywire. it's not for lack of trying on our part. TIA as they say!
Speed / practice
Submitted by orca99 on Mon, 10/17/2011 - 05:47.First - Thanks for the regular blogs now - I always appreciate reading about the teams progress.
I note that all the focus related to the 50 knots "wall" is on the foils.
After only 2 days of sailing at speeds around 50 knots, I feel this conclusion may be a bit premature.
It may be worth to just simply get more practice runs; There may be many more knots to gain in that way.
Paul - do you feel that you have had enough time in the boat to find the optimal trim angles for the wing? If the rig is standing more vertical, can you trim the wing harder for a given wind speed?
Have you tried the canopies yet?
Orca99
Sunday
Submitted by Mike Ewart on Sun, 10/16/2011 - 20:12.Hi Paul great runs today dont let it grind you down you seem to be doing the right things and the results will come. The idea of using the second seat for foil checking is interesting. I have been drifting around our lake in my IC today and was looking forward to coming home and checking what you had been doing in some wind.
Keep it up some great pics as well
Foil Drag
Submitted by Matt Higginson on Sun, 10/16/2011 - 15:56.Hello Paul; Congrats to the whole team on the rapid progress. The new boat is a marvel.
I believe you wrote that the new foil is a basic "axe-head" wedge shape, as is typical of supercavitating foils. I was wondering what the angle of the wedge is? As the speed increases, the angle of attack of the foil would probably be decreasing (unless the sailforce is also rising as the square of the speed)..? If so, there may be a point when the angle of attack of the foil is less than the angle of the wedge; this could mean the suction face makes contact again and the drag shoots up. Maybe at about 50 knots..?
If this was the case, you might be able to get a bit more speed by blunting or filing the leading edge to give the water on the suction side a bit of a kick away from the suction face. Ultimately you'd probably need to make a smaller wedge angle (thinner and weaker) or a shorter wedge which would run at a higher angle of attack (also weaker).
Hopefully this is not the problem at all, but it seems strange how the speed seems to have hit a wall at 50.x knots.
In any event, I know you've got a great team working on it. All the best,
Matt
Measuring ventilation
Submitted by Chris Sutcliffe on Sun, 10/16/2011 - 11:42.Just thinking about the ventilation issue you may/may not be having. I'm guessing the only way to progress is to measure if the foil is ventilating or not. This could be done in a number of ways.
1. measuring the presence of water or air at the surface of the foil this could be done with either a resistance or capacitance set up go here http://www.rbr-global.com/products/wg-55?lang= or here http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-097-chemical-investigations-of-boston-harbor-january-iap-2006/lecture-notes/waveprobe.pdf. In both cases wires would have to be bonded to the low pressure side of the foil and subsequently calibrated.
2. Measuring the presence of water by pressure. In this case sensors and wires would have to be embedded in the foil by drilling holes and milling channels.
3. Measuring the presence of water by measuring skin friction by use of a hot film anemometer or some such
None of the above techniques are easy to achieve but I think the most robust is the resistance wire which would also be the simplest to implement in the field...particularly as the second web link gives instructions...
Thinking about it some more do you artificially trip the ventilation by metering air into the foil low pressure side this might ensure you get ventilation all the way down the foil.
Best of luck all the record isn't that far away now
Measuring ventilation - backing into the number
Submitted by Tim on Sun, 10/16/2011 - 22:33.Chris S., Paul - Your ideas about detecting measuring the amount of ventilation are a potentially sound way to understand what is happening with the foil. Assuming that Saturday's winds should have generated higher speeds than oberved during the runs, assuming that hidden gremlins within the foil are robbing the boat of speed, there must be an observable/measurable amount of stress/strain on the foil.
Along this line, I wonder if there is an easier way that the VSR2 team can back into a good calculation of the amount of drag on the foil by placing strain gauges on both sides of the foil in two axis to get a handle on the loads generated by and upon the foil. Knowing the power and the loads on the wing, and the loads on the front rudder, in addition to what is measured on the rear foil would allow a good understanding of the drag generated by the rear foil. This, in turn, would allow an understanding of the ventilation a/o cavitation on the foil.
Of course, I look forward to the analysis and conclusions of team VSR2.
All the best,
Tim, Vermont
Well done..
Submitted by monomuncher on Sun, 10/16/2011 - 02:45.Hi Paul,
Can you alter the angle of your foil in relation to being set at 90 degrees to the wing, the kite boarders sail is a little infront of their board, you could achieve this by turning the leading edge of the foil towards the wing just slightly, easier said than done..
Foil angle...
Submitted by Paul on Sun, 10/16/2011 - 06:05.Hi MM... the yaw of the foil is fixed although we can swing the whole beam/rig fore and aft. We can also change the pitch and roll/inclination of the main foil. We will have a look at all options in the next couple of days.
Cheers, Paul.
Speed demons-
Submitted by Tim on Sat, 10/15/2011 - 23:25.Informative blog. Many thanks for that....sounds like an interesting day out there.
Just out of curiousity, are you convinced that the the speed limitations you felt that you observed today are related to the foil? I ask because - viewed from my armachair vantage - I wonder whether there might be an issue with the wing...specifically whether you are bleeding too much high-pressure air through the wing section pieces to the low pressure side? Reduced lift or increased drag?
Looking forward to your thoughts!
Pressure bleed...
Submitted by Paul on Sun, 10/16/2011 - 06:12.Hi Tim,
For sure we can improve the details on the wing and will start this morning when we take the wing off and do a full clean up/service. There will be some gains here so we might as well take them. I feel the issue is bigger than that though. I'm annoyed that we didn't see what results sailing in top-end conditions would yield. If we still only topped out at 50 then it would have been a no-brainer foil issue. The following run showed that we could still hit 50 in less wind. We'll just keep plugging away at the details, collecting the info... and we'll see what comes of it all.
Cheers, Paul.
Great reports keep them
Submitted by hummmming on Sat, 10/15/2011 - 23:18.Great reports keep them comming
Do you have any way of monitoring the flow over the foil?
Also have you tried the 2 pilot concept yet and why is that important what will an extra set of hands let you do?
Foil flow and 2 hands...
Submitted by Paul on Sun, 10/16/2011 - 06:18.Hi Hummmmming,
We have tried filming the foil from directly above but it gets difficult as the part of the foil we want to see is the surface that is inclined 30 degrees downwards i.e. tucked under the water. The best way to see it is from the side looking at its span. Obviously we will have to try a bit harder on this front. We figured we were through any flow issues when we got over 45 knots.
we didn't know what the cockpit workload would be like on this boat when we designed it. We still thought we may need to swing the beam fore and aft to get the boat started but this hasn't been the case. It actually appears to have a relatively simple cockpit workload so I don't feel the need for an extra set of hands. This free's up the back seat for joy riders. Might be a good way for the right person to actually check out the foil come to think of it.
Cheers, Paul.
Second chair...
Submitted by Tim on Sun, 10/16/2011 - 22:35.Where do I sign up for the second seat?!