Bluebird Archive Photos & Films

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klingon
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Joined: Fri Feb 27, 2009 8:22 pm
Location: Paisley Scotland

Re: A Picture paints a thousand words....

Post by klingon »

Just a wee thought in reply to the previous post-"a half empty tank"-any thoughts on that effecting K7's COG especially as the tank being half empty,(or half full if your an optimist) suffering from fuel sloshing around and spoiling the trim? eg making K7 tail heavy and liable to lift her hooter easier? :?
"I hate two faced people-don't know which face to punch first!"

Ernie Lazenby

Re: A Picture paints a thousand words....

Post by Ernie Lazenby »

Read Keiths post and thinking about it. I am on Grandson duties for most of the day so it will be this evening before I get around to replying in full.

In the interim= Keith has not yet explained why 20 MPH makes such a vast difference. First run at almost 300 mph no problems at all second run ---------

At those speeds any slight increase would have little effect.

The sponson lifting as per the photograph is due to 'tramping' No evidence of it during the first run. Flat calm.

Regarding the COG the 1/6th model runs equally well on a full tank or near empty - no sign of the front wanting to lift maybe at higher speeds it would h'mm.

I read nothing that convinces me thatbthe damage had anything to do with the accident but will ponder on Keiths interesting thoughts during the day.

Bills comment are in tune with my probable response. I love this forum.

BTW watch Ken Norris being interviewed about the accident and his thoughts about the water brake- rather telling I think.

KW Mitchell
Posts: 195
Joined: Sun Jan 18, 2009 11:37 am

Re: A Picture paints a thousand words....

Post by KW Mitchell »

Renegadenemo wrote:'the front spar is an aerofoil, albeit a poor one. It has a very rounded leading edge, short tapering chord, square trailing edge and span of 3-4 feet. If I assume the mean chord to be about 1 ft...'

Keith,

Well, you asked to be shot down so I thought I'd take a pop. In actual fact the chord is not tapering at all being of a square section throughout its entire length and as the spar reaches a max dimension of 9 inches square where it's buried under the foredeck, even adding the aerodynamic fairing, the chord length never attains a foot. The front spar is actually quite a slender design. The centre of the damaged region lies approximately 36 inches outboard of the vessel centreline and at this point the spar is only about 6 inches square. The distance between the root fairings is only 24 inches so there's not a lot to go at aerodynamically. But here's where I think your theory needs a rework.
Your numbers work if you treat the damaged spar in isolation but look forward of it and consider the aero of the nose. We only have to look at last year's F1 cars to appreciate how aerodynamic devices at the front can influence others further back. Assuming the nose didn't generate airflow that completely masked the disrupted spar fairing the resulting drag would favour the right-hand side of the nose being presented to the airflow and soon mask the spar fairing anyway. But that would hand the aerodynamic forces on the right-hand extent of the spar an advantage...

PS - For those who can't be bothered with the techie-babble please feel free to admire the tinwork. Proud of that, we are.
I'm not sure I should have started this - my wife's not seen me for days!

Bill - I didn't have any accurate drawings and was 'guesstimating' from pic's and little sketches in The BBY's.
So reduce my estimate of Reynold's No. by half, it's still 1.25x10^6 ------------!

And as for the span reduction fair enough. However, Bill, let me take you back to WWII. Remember the Vergeltungswaffe 1 (not a bit of Geordie speak Friday night on the Quayside --------). Yes, the German V1 flying bomb. Tiny wings of only a few feet span, weight 4750 lb, airspeed 350mph - this is beginning to sound a bit familiar ---------!!

As to the effect of the nose on airflow at the damaged spar surely that would require a yaw angle way above our considerations here - or are my perspectives not quite right again?

However, let's assume that it did. The airflow would become even more highly disturbed over the damaged spar than it was. The airflow over the right spar would be enhanced increasing lift. This is precisely what happens in my example of the twin engined aircraft with the left engine out - the right wing begins to produce more lift which induces an additional rolling motion to the left.

As I said in my first post on this issue - a roll-yaw couple develops.

Oooh and that photo' of the left spar - looks like a super-sexy aerofoil to me! Could build a flying model based on that ---------------!!

Heh - anyway - when are you going to introduce your ideas on engine gyroscopics on the final run, in this debate? The physics were sound enough ----------!

Keith - I'll lift you wellie-plodgers into that beautiful world of the air above - Mitchell

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Renegadenemo
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Re: A Picture paints a thousand words....

Post by Renegadenemo »

I'm not doing my gyroscopics in here - the physics will get completely out of hand!

Good fun throwing this stuff about though.
I'm only a plumber from Cannock...

"As to reward, my profession is its own reward;" Sherlock Holmes.

'Sometimes you gotta be an S.O.B if you wanna make a dream reality' Mark Knopfler

Ernie Lazenby

Re: A Picture paints a thousand words....

Post by Ernie Lazenby »

Grandsons now gone home- love him to bits but 2 yr olds can be trying!

The following is for benefit of all readers and offered in any easy to understand way.

To comply with the requirements for the world water speed record a vessel must start form the displaced mode and move to the planing mode while remaining in contact with the water.

In the displaced mode ie in the water hydrodynamics are the predominant forces and as the vessel moves to planing aerodynamics become predominant. That said one cannot be considered in isolation to the other.

One often overlooked point is that Hydroplanes are referred to as three point vessels when in reality theres a fourth point of suspension; the air under the hull. Remember Ken Warby talking about how he got his boat to tramp thus bleeding that air out removing a possible backwards flip factor.

Lets look at the forces acting on K7 to keep it on the water

Mass (weight)
Thrust from the jet engine
Stability relevant to its speed.
Angle of attack to the water surface
ground effect
COG relevant to its speed

Forces tending to flip it backwards

Air flow acting on the surface area of the vessel relevant to the speed
Instability leading to increased surface area being pushed into the air foward of the boat
Lack of jet thrust relevant to the speed and angle of attack.
Altered COG due to reduced mass (ie much reduced fuel)
Excessive tramping


Okay so K7 ran very well without any problem on the first runs damaged spar and all. She managed 297 mph and its difficult to conclude that the extra 20 mph or so she achieved on the second run would bring the damaged sponson into play.

Its very clear that the water on the second run was very disturbed something DC mentioned very early into the run and this resulted in excessive tramping.By now the COG had moved aft (I am not clever enough to work out by how much) An unstable vessel increasing the forces acting on the areas of the boat already under direct attack by the air ie the Sponson ramps and the angled area under the nose plus the 26 ft long surface area under the hull. Add in a engine that may have stopped running or throttled back and you have hydroplane blowover with or without any damage to the sponson arm cosmetics.

Looking at direction stability: hydrodynamics are the predominant forces. Two fins on the sponsons, a rudder and the stabalising fin on the rear offside
These appendages would in my opinion create forces much greater than any forces created by the damaged area of the sponson.

Referring back to not dealing with forces in isolation. Aeroplanes operate in a medium very much less denser than water and aerodynamics are the only consideration. I can see how damage to a wing with its inbuilt cord could cause yaw but we are dealing with a boat which has no cord introduced by design. I dont think its reasonable to conclude that the damage caused directional instability or was any factor in the crash.

Just an opinion from a retired aged plod. Feel free to forensically pull that lot apart if you wish.

BTW I think we forget that the greatest expert on K7 was DC himself; he understood the boat better than anyone and not withstanding any pressures he may have been under to get a new record one cannot conclude he would have carried on with the attempt if he had even an inkling that the damage would cause problems. Well meaning amatuers at the time may have expressed concerns but DC and Leo Villa were the two people qualified to assess any risk.


Now wears my tin hat as I make for the air raid shelter! :lol:

KW Mitchell
Posts: 195
Joined: Sun Jan 18, 2009 11:37 am

Re: A Picture paints a thousand words....

Post by KW Mitchell »

Gyroscopics - the physics is easy; it's the math's that's damned hard (never understood it)!

So how can we explain it:

My first amorous advancements to my wife made her dodge to one side,
then, wilting at my passion, she was spent into a spin,
and fell into my arms!


There you are, gyroscopic precession a la MitchSpeare.

Now the serious bit that His Smithship seems reluctant to post:

After the first run on Jan 4th, DC performed a wide 180 which took him close to Peel Island. He then accelerated in a long curving arc to the right to get 'on track' for the measure km.

The rotating component is the Orpheus' bowels, 10% boosted over max. normal rating, 10,000rpm. The other important factor; the engine's direction of rotation - clockwise looking at the front.

All these elements are such as to produce gyroscopic precession which acts in a direction to lift the right sponson. How significant was the force, we just don't know - but again another possible factor to add to the mix!

There is a weakness in this argument that I posed to Bill; once the boat was tracking straight the gyro' force would disappear. And we will never know whether the photo' on that last run was when it was curving, or, running straight. Pity.

K.

Ernie Lazenby

Re: A Picture paints a thousand words....

Post by Ernie Lazenby »

Looks like Keith and I hit the send button at the same time !

tas
Posts: 68
Joined: Tue Dec 02, 2008 1:26 pm
Location: Sarf East London

Re: A Picture paints a thousand words....

Post by tas »

With the spars (before bird interruption) having rounded leading edges and equally flat tops and bottoms, surely air would have passed over both surfaces at an equal rate? If they did have any aerofoil effect, surely it would be purely due to anomalies in the roundness of the leading edge meaning that it could have just as easily have been downforce produced instead of lift?

I may not be an aerodynamicist but I cant see how something 'D' shaped can produce definate lift.
"He who goes to bed with an itchy bum, wakes up with a smelly finger"

KW Mitchell
Posts: 195
Joined: Sun Jan 18, 2009 11:37 am

Re: A Picture paints a thousand words....

Post by KW Mitchell »

Ernie Lazenby wrote: Now wears my tin hat as I make for the air raid shelter! :lol:
No need, Ernie, I think we agree to disagree - in the nicest possible way!

Anyway, I think many will be getting 'Forum Fatigue' at our musings ----------.

Keith
PS please let me know when and where your South Shield's bash is on - I'd like to get down and see you and your creations.

Ernie Lazenby

Re: A Picture paints a thousand words....

Post by Ernie Lazenby »

KW Mitchell wrote:
Ernie Lazenby wrote: Now wears my tin hat as I make for the air raid shelter! :lol:
No need, Ernie, I think we agree to disagree - in the nicest possible way!

Anyway, I think many will be getting 'Forum Fatigue' at our musings ----------.

Keith
PS please let me know when and where your South Shield's bash is on - I'd like to get down and see you and your creations.
I am sure if anyone is getting forum fatigue they will soon speak up :D Its all interesting stuff even if those who contribute disagree. :D

Regarding South Shileds I will post something nearer the time. I have just found out that the organisers dont have any insurance to cover the models and the building is left unattended during the night! I have to work out the logistics of getting everything up and back again twice! I am not happy at leaving unattended models that have taken me years to make.

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