Author Topic: Myths of supersonic cars, part 1: Bud Rocket  (Read 2931 times)

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Blue

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Myths of supersonic cars, part 1: Bud Rocket
« on: September 02, 2014, 02:30:59 AM »
This is the first of a series of posts/blogs we are starting to dispel some of the myths surrounding supersonic ALSR records and attempts.  We welcome anyone posting or messaging me directly with unanswered questions about the ALSR, the contenders, or the designs currently proposed.  We'll start separate threads for separate technical subjects.

The following is in response to a recent question sent to us that there had never been a definitive explanation of why the Budweiser car momentarily lifted in back as it fired the sidewinder motor and accelerated approaching Mach 1.  The car returned to a flat attitude with all three wheels on the ground at its top speed and before engine shut down.  Clearly, the lifting force was not present between 700 and 730 mph.  Explanation follows:
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On the Budweiser car, every engineer we have consulted on the subject from Boeing, to Lockheed, to Stanford agrees that it was simply the high initial impulse from the sidewinder motor combined with its high thrust line that caused the car to momentarily wheelbarrow.  AAR’s and SAR’s (air-to-air and surface-to-air misilles) use a star port in their motors to create a very high initial thrust that then reduces over the first few seconds of flight.  This high initial thrust is 2X to 4X the sustaining thrust and is used to “get the missile off the rail” and up to closing speed.

The high thrust line of the motor and its high initial thrust combined to create a thrust vector that was above the sum of the earth’s G and the vehicle’s vertical CG vs.the front wheel contact patch.  So it simply got pushed onto its nose.  If the rocket had sustained that thrust, the car would have gone over forward.  Luckily, the AIM-9 initial thrust decays rapidly.  This is why the car was off the ground behind at 650 mph, yet on the ground at 730.  Be wary of quotes of “SHOCK WAVES” from anyone outside of the top of the industry.  There simply wasn’t enough surface area on the rear of the car for the transonic effects to even be considered since the car was flat from 700 mph on.

Flat bottom cars are another matter.

Offline Malcolm UK

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Re: Myths of supersonic cars, part 1: Bud Rocket
« Reply #1 on: September 02, 2014, 06:31:28 AM »
I take it Blue that you have been able to review the data record by 'Project Speed of Sound'.  I was always told that none of the claimed speeds were picked up by the insitu 52.8 feet timing traps set out on the desert.

Can it be concluded that the struts for holding the rear 'uprights' as used on Blue Flame, SMI Motivator and the Budweiser would not be a "poor design" feature?

[Great thread to get away from the speculation written down regarding this 'car'].

Thanks, Malcolm 
Malcolm UK, Derby, England.

velocity

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Re: Myths of supersonic cars, part 1: Bud Rocket
« Reply #2 on: September 21, 2014, 01:27:23 PM »
Please know that there was extensive scientific work put into the the design of the Blue Flame by Professor Paul Torda who taught at the Illinois Institute of Technology. This included testing in the now defunct Ohio State University supersonic wind tunnel where he determined that the car would theoretically remain stable to 1,000MPH. Blue Flame fabricator Pete Farnsworth still has the all-brass model used by Torda including the optional wheel pants (shown in the photo) which were found to be more destructive than helpful.

Of course, once Reaction Dynamics ceded control of the car to its sponsors, this fabulous, record-setting American design was never fully vetted at Bonneville -- just like the Breedlove/FossettLSR.

The University library holds all the documentation to this day. I have several of the pertinent doctoral thesis used to the build that magnificent machine. I became friends with the Professor when he caught me sneaking into his classes when I was still in high school; he was a brilliant, gentle and engaging man who would often hold open discussions at his home for speed crazies.  Would that we could extract the Blue Flame from its German "prison" , Ok, museum, I dare say, dare dream, that it may still have some useful life.
« Last Edit: September 21, 2014, 01:30:51 PM by velocity »

Offline DaveL

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Re: Myths of supersonic cars, part 1: Bud Rocket
« Reply #3 on: September 30, 2014, 08:55:59 AM »
Concerning the Bud Rocket lifting its back wheels off the ground, the photo I’ve seen not only shows the wheels off the deck but also appears to show the car in the middle of one of Earl Flanders’ short timing traps. I believe three of these were set up in an effort to capture the vehicles top speed. To me, this suggests the ‘wheelbarrowing’ event was at or near top speed. Firing of the Sidewinder was 4-5 seconds earlier and would be approximately 5000’ before the expected top speed of the vehicle. Surely nowhere near the traps. Also, video footage shows the exhaust plumes flare to be at its most intense upon Sidewinder ignition, this then decays over its burn time. To my eyes, the ‘wheelbarrowing’ photo shows the exhaust plume more consistent with the rocket near flame out.
« Last Edit: September 30, 2014, 09:02:17 AM by DaveL »

Offline Graham

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Re: Myths of supersonic cars, part 1: Bud Rocket
« Reply #4 on: September 30, 2014, 09:58:57 PM »
I take it Blue that you have been able to review the data record by 'Project Speed of Sound'.  I was always told that none of the claimed speeds were picked up by the insitu 52.8 feet timing traps set out on the desert.

Can it be concluded that the struts for holding the rear 'uprights' as used on Blue Flame, SMI Motivator and the Budweiser would not be a "poor design" feature?

[Great thread to get away from the speculation written down regarding this 'car'].

Thanks, Malcolm 

A student of mine ran what I would consider to be good quality simulations on a high-fidelity recreation of the Blue Flame, we reckon that for the record speed achieved, the struts were producing about 30% of the total drag. The exposed wheels another 45% of the total on top of that. Fairing the struts and wheel a little may have helped to considerably reduce that, and indeed that's what the original design called for -  the one that was most extensively tunnel tested and that you can see if you google for images (the one Louise refers to). However, enclosing struts in a large wing makes the wing very prone to sudden and unwanted changes in force (or indeed force reversal) when a shock forms on the upper or lower surface or both, as the Bloodhound team has been seemingly very careful to characterize. The main public Blue Flame reports hint at some of this without going into explicit detail, but I haven't seen all the work that was done (e.g. all the theses Louise mentions).

The Blue Flame tunnel tests were a useful tool at the time but the way they approximated the ground would have led to drag and lift forces being compromised, I think my student ran some simulations on that too, I can probably estimate a quantification as to how far off the numbers may have been if I can dig it all out.
Graham Doig
Fluids Laboratory for Interdisciplinary Projects - www.thinkflip.net
Aerospace Engineering Department
California Polytechnic State University