Quicksilver

[KW Mitchell]

Back to technical matters relating to Quicksilver ...

I didn't get chance to address a point made by Keith Mitchell about tailplanes - specifically, the need for a tailplane (to have or not to have) on a speed-record boat or car.

I don't want to challenge any of the designers who have equipped their boats - or cars, for that matter - with a horizontal stabiliser. They clearly knew their machines better than anyone else and were the best placed to decide whether this would aid them in terms of pitch stability.

But what I will say is that it is not necessarily an open-and-shut case that the addition of a tailplane is essential to pitch stability. I am not about to give away the secrets of what we have learned in windtunnel and other studies on Quicksilver, but if you look at the original design concept for BloodhoundSSC, it did not have a horizontal stabiliser. Now, of course, it's true that the Bloodhound design team subsequently revised their concept and there is a tailplane clear for all to see today, but the very fact that they were initially entertaining the idea of not using one attests to the fact that it isn't - or shouldn't be - an automatic assumption to have one.

When I worked with Ken Norris on the various earlier Quicksilver designs, Ken was open to the idea of dispensing with the tailplane. That is not to say he would have finally opted to go that route, only that he was entertaining the idea of dispensing with a tailplane. A tailplane can contribute to pitch instability if you're not careful. It's not an open-and-shut case.

In most cases, yes - but not all.

Each case, I guess, is different. We don't have a tailplane on Quicksilver's design, but our boat is modular and we can change it, so we could add one if we have to.

We would prefer to do without it. It's more weight, more work. It will be interesting for everybody - us included - to see how the test-runs go, sans tailplane.

Nigel - thanks for the response on the tailplane issue. I appreciate it's not straightforward and the design of such obviously requires great care. If K7 had ever 'grown' one it would in my view required such a mod' to have been applied to the 1/9th scale model used in the initial wind tunnel measurements made in Stollery's lab..

Indeed, regardless of the tailplane issue, I have always felt grave concern that through K7's extended development with spar position, sponson, fin, powerplant etc., all being altered at some stage, the original wind-tunnel data were not reworked with a modified scale model. There is not a little risk in taking data derived at 250 mph and then applying such to describe how a machine will behave in modified form at speeds in excess of 300 mph.

Another, perhaps rhetorical question (which perhaps you may wish not to comment on as far as QS is concerned) is that I would have thought that if aerodynamic control surfaces were adopted (which I still firmly believe a priori that they should be) then the inclusion of moveable elevators or canards operated as active stabilising devices using feedback from pitching data input, would be such as to improve the boat's stability significantly. This, of course - as I am sure you will appreciate - would be fully automatic under computer control. The degree of feedback would be dependent on airspeed and could be designed to 'govern' engine power i.e. outside pilot control, so that the craft could not exceed it's safe operating envelope - akin to that in modern aircraft control systems.
But perhaps you're way ahead of an old speculator like me poking about in the dark!

Keith

[quicksilver-wsr]

Thanks for your feedback, Keith.

I will answer your second question in a separate post later, as it's a whole subject unto itself and gets me into the potentially hot water of what is - and is not - a boat. With active aerodynamic control, you start to get into the realm where the craft perhaps isn't a boat anymore - it's potentially an aeroplane. We have chosen with Quicksilver not to cross that line. As I say, another subject for another day, but I'll be happy to answer your question as best I can.

Moving to your other - easier! - point about Bluebird K7. Personally, I do not know either way whether Ken and Donald re-tested a scale model of the boat at some later stage in its development. It would certainly have been better to have tested a reconfigured model, if at all possible, embodying the external modifications made to the craft over time (and the revised all-up weight and CG position that came with the upgrade from the Beryl to the Orpheus, of course).

I can't comment beyond that, because I don't know. Ken never mentioned it, and I never asked, because my interest in Bluebird - and Ken's, too, at that stage - was more in the form it was in at the end of its development life, because obviously that was the final expression of the design and the one that went the fastest - as well, of course, as being the configuration in which it flipped over onto its back, and we didn't want that happening with Quicksilver.

Going back to the early K7 modifications, though, the mod to raise the front sponson-arms was one that was highly significant - because if a boat can't plane it will never get up to high speed in the first place. Also, I was interested to learn from Ken that - right from the off, when the boat was first built - there were alternative engine-mounting positions, fore and aft, and that seemed like a really clever touch.

We looked at that idea for Quicksilver and in the end we didn't go that route - we plumped for one position and will live with it - but having the facility to shift the position of the engine to alter the craft's CG was a great idea.

If they had tested a revised windtunnel model later in the development process, maybe the accident would never have happened. Hindsight again - a wonderful thing. If they didn't, I can only assume that they felt confident at the time that they didn't need to.

Ken believed that many factors could have contributed to the flip. Potential causes were still occurring to him years afterwards and it never really left his mind.

[rob565uk]

Nigel

According to "Into the Water Barrier" (page 189), in addition to adjustable engine mounting points, the sponsons of the early K7 (before the higher covers were added later) could also be adjusted fore and aft and in early attempts to make K7 plane, the engine was moved back and the sponsons moved forward as far as they could go. This seems a good option, but for QS would obviously be complicated by the fact that your sponsons contain the Pilot, plus associated systems..

[quicksilver-wsr]

Yes, Rob - all good stuff.

Building-in adaptability can really help matters. It's a smart way to go with a speed-record boat - maybe less-so with a car - and the Norris Brothers went that route with K7.

Of course - as with virtually everything in engineering - there is a down side: it is the weight penalty, because every time you design-in an extra mounting point for something (even if you end up never using it) you are adding what I call "scar weight."

I learned that phrase when I was closely involved in covering NASA's Space Shuttle programme, as a writer. The term "scar weight" was the term they applied (and I'm sure it's not a phrase unique to NASA, but that's where I picked it up) whenever a Shuttle Orbiter vehicle had to be modified to carry a special payload. NASA obviously kept such modifications to a minimum, because once the payload has been carried ... it's gone, it's launched ... job done ... but a certain amount of reinforcement, or whatever, built into the spacecraft structure, remained integral to it and couldn't be removed, and was there for the rest of the lifetime of the vehicle, reducing (however slightly) that vehicle's load-carrying capability in the future.

We have a lot of adaptability built-into Quicksilver. The whole boat is modular. No other machine in record-breaking history, on either land or water, has as much built-in adaptability as ours has. But we live with a certain weight penalty because of that.

On the front-sponsoned boat we have finally ended up with, you are right to point out that having so much kit - including people! - in the sponsons makes life a little more tricky and limits some of the things we can do in terms of adaptability.

In actual fact, though, even back at the time when we had our focus on the well-known rear-sponsoned version of Quicksilver - when I was intending to complete the design work started, but nowhere-near completed, by Ken Norris - the decision was made (by Glynne Bowsher and I) to have just one engine-mounting position. The reason was that the way Glynne designed the spaceframe - which was a totally different way to how Ken wanted to do it - did not lend itself to moving the engine.

It was all to do with the way the lines of spaceframe tubing were triangulated. The load-paths through the structure would all have been compromised to an unacceptable degree if we changed the position of the engine within the spaceframe, so we stuck it in one spot and now we have to live with it.

And that's the other thing. You have to make some firm decisions and some draw hard lines that you can't cross. You can't make a speed-record boat design absolutely adaptable. Because if you did, you wouldn't have a boat ... you'd have a piece of Plasticine!

[quicksilver-wsr]

Following the earlier discussions about tailplanes on WWSR craft - i.e. a horizontal stabilising surface; to have or not to have - it's worth considering the role of the vertical fin, or tailfin ...

I mentioned that it is not our intention to fit a tailplane to Quicksilver. We are, however, going to have a tailfin.

Sharp-eyed viewers of our website will have noticed that the windtunnel model in the "Testing" section of the site - found under the generic heading "The Craft" - has no tailfin. That is not because we won't be using one on the full-size boat, it's simply because it is a standard technique in a proper windtunnel test programme to compare "with" and "without" - so that the contribution of the component under scrutiny can be quantified - and when that particular photograph was taken, the test then under way involved assessing the model without its tailfin. At other stages in the test programme, the tailfin had been in place.

It is worth considering whether a tailfin is or is not necessary on a WWSR craft. Immediate logical says, "Of course!". But then you consider the fact that the hydrodynamic forces on the parts of the boat that are in the water vastly exceed the aerodynamic forces on the parts of the boat that aren't - water being 800 times the density of air, and drag increasing as the square of the speed - and the effectiveness of (and, therefore, the need for) the tailfin starts to come into question.

And, if you could get rid of the tailfin, you'd reduce both the craft's weight and its aerodynamic drag, so that's an attractive proposition.

However, just when you think you have made a breakthrough and discovered that you don't need a tailfin, you analyse the role of the tailfin in maintaining the craft's stability in a turn, and then you go back the other way and decide that you do need a tailfin after all.

We have a principle fundamental to the design of Quicksilver called "The Balanced Boat". I can't give away the numbers but I can vouch for the fact that, having looking into whether we could do without a tailfin, we have decided that we can't - or, rather, that it's better to have one than not.

[polo]

Nigel, why did you drop the Canard configuration and the Adour engines?

[quicksilver-wsr]

Happy to help you, Polo, but let me know what you mean by "canard" configuration. Do you mean the rear-sponsoned design that we showed when the Quicksilver project was first revealed to the public? The one we actually started building for real, but later abandoned?

I just want to clarify what you're referring to, because we tested Ken's "flying wing boat" - which, of course, was a totally different concept altogether - with little canard surfaces fitted (the canards are just visible in the photo of Ken and I with the windtunnel model of that design, in the "News" section of our website).

[polo]

Nigel, The reverse 3 pointer, one at the front and 2 at the back planing surfaces and why dump the Adours? they would have made your boat a bit smaller and lighter.
Ta

[quicksilver-wsr]

It wasn't a three-pointer, Polo. It was a four-pointer, and that was a fundamental feature of every single one of the Quicksilver design concepts that Ken Norris came up with. It fact, it was pretty much the one single thread of consistency that ran through the whole lengthy process as one idea succeeded another.

People get confused by the fact that the two planing shoes at the front of the boat appear to be joined together by a V-shaped planing surface in between them, but in actual fact this central feature is only in contact with the water when the boat is in either the static-buoyancy or low-speed conditions. As soon as the boat starts fully planing this central surface lifts out of the water totally, leaving the boat planing solely on the two shoes at the front and the two shoes at the rear of the boat.

Terms such as "three-pointer", "four-pointer" - or "50-pointer" - refer to the number of planing surfaces a craft has in contact with the water when fully planing. Every Quicksilver concept has been a four-pointer. We stuck with it because we think it's a good idea. More stable - like a car having four wheels, one in each corner.

The decision to drop the Adour was Ken's, not mine. I was highly put-out, because Ken - after lengthy deliberation - finally decided he wanted to power Quicksilver with an Adour, so I purchased one for £4,500 in the early 1990s and the dealer who got me that engine also got a second one - for use as a spare - for us. Volunteers drove up from Bournemouth to collect the first Adour from Bruntingthorpe, near Leicester, during the Easter Bank-Holiday weekend, sacrificing time with their young families - and the moment Ken set eyes on it when he returned to the office, after his Easter break, he said he didn't think the Adour was a suitable engine, after all, because the big cluster of intricate pipework that all Adours have on their underside would mean that, to create adequate clearance between the bottom of the engine and the inside of the hull, the engine would have to sit too high in the boat, thus creating an unacceptably high thrust-line.

I was not amused, but as was usual in those days, I said nothing. A great deal of time and effort - not to mention £4,500 - was wasted on a whim. Ken already had the Rolls-Royce brochure on the Adour, which showed scale drawings of the engine with its pipework cluster, as well as detailed dimensions, so he had no excuse for not knowing about the tangle of pipework underneath.

There you have it. Not one of my happiest times working on Quicksilver. The Adour was a waste of time from the outset because of the fact that its use would have dictated a high-thrust line, and this would threaten pitch stability when throttling back at very high speeds.

Ken should never have been considering it in the first place.

[polo]

Nigel, thanks for that.
Why did you drop the reverse boat though. I know Ken thought highly of this type of configuration even though it was contrary to the Warby,Taylor[Hustler] and BB layout. What was the thought process in starting with it? sorry lots of questions. Ta