Bluebird K7, the "New" tail fin & Balance point query

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thunderer
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Bluebird K7, the "New" tail fin & Balance point query

Post by thunderer » Wed Jun 24, 2009 4:37 am

Please excuse me if this has been asked and answered before, but since I am new to this forum and the fact that I have looked through the topic titles I could not actually see a specific mention of the wing and centre of gravity (balance point) mentioned together.

If there is one thing I have being trying to gauge, it is at what point in the bluebirds structure the craft will balance if hung by one, singular, harness . Having seen the photographs taken so far and some of the footage shot (both old and new) actually brought this question to the fore tonight.

Taking into consideration Donald Campbell's weight (anybody know this at all ??) in the nose of the craft and considering the weight of the jet engine and the "new" tailfin being added, at what point of the craft is the balance point? To get an idea of the point I strive to make, take a 300mm (30cm) rule, and add 3 two pence pieces to one end, then place a pen under the rule and slide it towards the coins until a balance is reached. Notice how close it has to be to the coins to effect that balance and how fine a point that balance line actual is ? That is what I am talking about in relation to "balance point".

This is the point I am trying to make. IF, and it is a big IF, as the new tail fin added more rear weight, was it counteracted at the nose end of the craft in any way with ballast ? we may never know the answer to that, but it does pose that question of where the actual balance point is. If the balance were more aft than fore, then I am sure this would have contributed to the situation that arose from the last and final run that Donald ever made. yet perversely we may never know the balance point unless a way can be devised to calculate it, taking into consideration Donald's weight, with said weight distributed nominally in the cockpit of the vessel. Short of finding someone of the approximately the right height and weight, wearing a matching helmet and oxygen mask and similar clothing there will never be an "accurate" way to learn this. If it were known, then more could be learned of the conditions that arose during those last, fateful, moments of Donald's life. .

I in no way intend to sounds disrespectful to either Donald or his memory I have every respect for him, nor in any way shape or form do I wish to upset Donald's family members.

I merely ask a question to help solve a riddle that has now taken hold of my mind in relation to bluebird K7.
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lsrdatabase

Re: Bluebird K7, the "New" tail fin & Balance point query

Post by lsrdatabase » Wed Jun 24, 2009 10:03 am

Hi Thunderer,

Good Point, but surely Leo's sand bags that were used to effect a balance would have countered that.

Regards, Fred

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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by f1steveuk » Wed Jun 24, 2009 7:19 pm

Having seen the reams of Calc's done by Norris Bros, I'm sure it was taken into account!
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by thunderer » Wed Jun 24, 2009 10:06 pm

Hi guys,

I'm sure that it may have been looked at but as to the ingots of lead, that merely goes to strengthen the query. so much lead up the A--e end with the engine, a lighter fore end and a tendency to raise the bows is unavoidable as far as I can tell. Balance is about the perfect distribution of weight along the length and breadth of the vehicle (something learnt form R/C, but that is feasible and proven in 1:1 scale) which also goes to the query. If lead was placed top keep the A--e down and raise the front up, would that not cause a serious fore to aft imbalance of weight ?

I also think, and notice i stated "think", that had the craft been balanced form fore to aft, it should in theory have planed more easily. Now, having raised this question, I have since read the 19 page thread that contains all sorts of calculations on aerodynamics and aerodynamic drag in relation to the "duck strike" incident. Whilst I understand that point I see the a--e end the craft being heavier as more of an indicative force than the aerodynamic disturbances caused by the "duck strike", yet together and in conjunction with the wake of the last run before the attempt ? who knows, all three maybe contributed. The biggest suspect to me however is that maybe too much weight was added in the a--e. And as to calculations, there is nothing that calculations can tell you any better, than finding the "balance point" by aide of lifting strops and harnessess, or a balanced cradle laid over beam in a workshop to find the fore/aft balance point. Calculations are mainly theory, VISUAL conformation is a FACT.

NOW, using an r/c vehicle as an aide hear and it is merely to make my point more easily understood, a Traxxas revo 2.5 4WD monster truck has most of the weight at the rear end, what with the engine, exhaust, fuel tank and servo battery all gathered behind the centreline. Under accelleration, it squats, HARD. At terminal velocity, it still remains squatted at the a--e end and, if hitting a small obstacle it will lift the front end up to get over it with a tendency to want to "nose up". Under hard deceleration (braking) it gains a serious "Nose Down" attitude. Imagine that Traxxas revo to be K7 and then try to balance that truck. perversely, the addition of a little extra length in the front end of the revo chassis (33mm) all but killed that tendency off. Yet it is still apparent. HOWEVER, add a little counter weight to the rear and it behaves just like the shorter 2.5 variant with shorter chassis. Consider this aspect of balance, then consider K7.

Thought provoking ?

Now hopefully, you should see where I am going with this part.

Considering the overall length of the craft, the added weight in the tail, the element of "suck it and see" in relation to that additional aft end weight, mixed in with unsettled and disturbed port side aerodynamics, the water wake,high speed and what you get is a huge dirty great big unknown. Even in the face of the "so called" successful first run.

After all, has it not already been written that there was a certain level of "suck it and see" in relation to the added weights after the sandbag tests ?
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by klingon » Wed Jun 24, 2009 11:02 pm

Check my posting 3 days ago re tail-theres another factor to add as well-turbulent downforce from the increased tailheight from the Gnat tailfin added to K7-albeit in a shortened form.Originally as we all know K7 was constructed with absolutely no tail at all-and over time sprouted all sorts of increasingly bigger fins on the rear to try and stabilise the craft,Without the benefit of CAD or the like I think it was a matter of "suck it and see" with these mods-It would be so interesting using modern methods to discover what exactly happened to the airflow over the tail of K7 at speeds well in excess of her original design remit-personally I have a gut feeling that a pressure wave in front of the fin could have exerted a significant downforce on the tail and -to return to school physics-using the sponsons as a fulcrum point the only way for the nose of K7 to go was up-not much at 300mph to achieve laminar airflow and lift-the rest was tragically obvious,---or on the other hand she just might have hit a big bump on the water---
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by thunderer » Thu Jun 25, 2009 7:39 am

I understand what you are saying but no one, singular, act or fact can categorically define the final, fatal, incident.

lets look at the facts.

These are just "some" of the facts that I have managed to glean over the years.

1) Increased rear end weight (lead ingots)
2) Addition of a modified Gnat Tailfin (with theories over air flow dynamics and pressure waves)
3) Orpheous jet engine boosted 10% over Max (and the oscilation debate)
4) Disrupted Airflow on the port side due to a prior duck strike (another discussed theory)
5) Hitting the water disturbance from the first leg of the record attempt run. (the wake the craft created)
6) A modified craft operating way outside the original design remit and varying considerably from original design and design concept (Evolution I believe that's called).
7) "A lot of bloody Row" during the final run as reported by donald, leading to the questioning of when the engine mount breaking (discovered to have broken under tension rather than compression) actually happened and igniting (scuse the pun) the ensuing "Thrust Vector" theory.
8) The front sponsons lifting clear of the water on the first leg of the run (study the footage, it is plain to see where this happens), indicating fore end lift tendency with the same thing then happening again for 1 or 2 seconds before the final, fatal, incident) questioning the overall balance, aerodynamics and planing dynamics instability at that point in time.
9) The relative unknown of the CofG (balance point) of the craft. (another contentious issue if there ever was one)

Only when we can truly understand each singular instance of the above, within the correct context and understand each event/fact to its fullest, can anybody truly state what the final series of events were that played their part in the unfolding of the tragedy.

In discussion with a friend last night over bluebird K7, he made the following statement:
Ok so it was a big blue boat with a jet engine strapped in with two floats at the front, going over 300 and made unstable by the wake of it's previous run it then lifted the front end and did roughly a 330 degree backflip before hitting the water. what else is there to understand, it happens a lot these days in racing
A valid question, which was swiftly answered by stating the facts laid out above, with the following reply
So basically, the theorists are saying that on the final run the guys speed, the boats aerodynamics (disturbed or otherwise), the tail fin being fitted and the guy hitting his own wake and the broken engine mount contributed to the crash all by themselves as a single series of events?? B--ls--t !. it takes a BIGGER series of PROVEN and provable events to link together to culminate in the end result and those events mentioned in the final run are a small part of a much bigger picture than has been looked at by the sounds of it. Even AFTER i have looked at the footage of the crash.
This was from a guy who has no interest in bluebird K7, nor an inclination to involve himself in such matters.

Do I really need to say anymore on what an "average" member of the public may think about that short space of time and the events that unfolded therein? if the guy can say what he did, especially having had no prior awareness of the incident until i started gassing about the website and the footage, then surely it can be repeated in infinate incarnations by the remainder of the public at large.

All i will say is this.

We need to pin down the full chain of events of that led into that fateful day, from the moment K7's Orpheous was fitted, through the stationary testing, the time that she entered the waters of coniston, to the second the waters enveloped both her and Donald campbell. Only THEN can we start even thinking of trying to resolve the series of events that became that fateful day of history never to be forgotten.
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by thunderer » Thu Jun 25, 2009 9:18 am

Cheers mike, that made me smile !!! you happen to have a time machine I could borrow ? hehe

And wheres bill with the diary updates ? i'm getting bored with nothing to read!! lol
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by thunderer » Thu Jun 25, 2009 9:43 am

I wouldn't call you numpties, especially with the meaning I know for that term, but i can understand the workload part...............although that said, I unofficially "retired" when I was 19 (!!!!).

Pic of the day is an EXCELLENT idea! and a "library" of previous "picture of the day" entries would be nice as well, but thats another workload for another time.

I've had another idea too..........it involves the team and two huge boxes, one involves biscuits, tea and coffee, the other involves spirits and beer.

Seriously though, the work you guys are doing is EXCELLENT, world class even, and i say that from the standpoint of having restored a vintage MG with my father. Not the easiest thing in the world to do and the "emptiness" of it all when work is complete is a big void to deal with. what you are doing is about 2 million times harder in a totally different world.

If only they would let you rebuild that WWII Mosquito they dropped all those years ago..............that sure would be a sight for sore eyes.


BTW, how's the BBP mugs ? I just ordered one today, it's coming down to the "smoke" (london).
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by Renegadenemo » Thu Jun 25, 2009 10:18 am

Mike Bull wrote:Despite physical appearances, Bill is just one man you know! :lol:
Not for long - took the baby to the doctor's yesterday. Nothing wrong with her but I blagged a go on the blood pressure machine while I was there and it appears those numpties are taking their toll! Time to stop the biscuits, methinks.
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Re: Bluebird K7, the "New" tail fin & Balance point query

Post by Renegadenemo » Thu Jun 25, 2009 11:16 am

Mike Bull wrote:Have I got to start bringing in salad bowls for tea break time instead then?! :o

Certainly wouldn't do you any harm...
I'm only a plumber from Cannock...

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