Physics question has divided my friends

[DrHook]

I bought the Honda when it was one year old with a bad motor, I wanted a perfect body to start with. Terribly impractical for the street, I was a weight nut and the plexiglass windows didn' even roll down as everything inside the door panel was gutted. Although it was very loud inside I still loved the sound. Probably about an eight inch long driveshaft, my back was a few inches from the tires and the engine was right in front of me. The engine was set back so far that the front injection stack almost cleared the hood, with only about a 1/2" notch in the hood. The tranny was a C6 with a manual clutch in front of it instead of a torque converter. In the picture from behind I had a rear end that was shortened so much that top fuel tires were inside the body lines. There was less space between the tires than the width of one tire. In the wheelie pic that was the more practical racing rear end. I could switch to methanol pretty fast with the hilborn injection. I got the car down to 2350 lbs. and never took it to the strip for a time ET. At high speed it got light in the front and drifted back and forth so I built a spoiler in the fall and by spring my interests moved away fron cars but I still have it although it is in pieces. I have two 427 Ford side oiler high riser engines, one with inj. the other with a blower. If you look close in the picture from the front with the front end off, to the right of the pulleys, there is a power window reversible motor that slacks the fan belt for 1/4 mile runs. The pulleys I made all have extremely deep grooves to keep the belt on when it is loose. A real benifit is in doing this I changed the ratios to run the large fan and water pump twice as fast to keep it cool on the street with the small radiator that I used. It was the first project I did when I bought a new Atlas lathe (can I say Atlas?) Keeping it extreme I went in other directions just as far out there but for fear of being accused of showing off I won't post pics unless someone asks.

That's awesome! I had dreams of stuffing a BB Mopar in a MG midget when I was younger, but spent all my time building other people's toys and never got "around to it"...

 

[Bluechipx]

That's awesome! I had dreams of stuffing a BB Mopar in a MG midget when I was younger, but spent all my time building other people's toys and never got "around to it"...

When you say big block mopar if you are referring to the 440, I raced several 440's on our back road quarter miles. I would beat of the line, pull somewhat, then hold my own thinking I've got this guy put away, but every race seemed to go the same way with the 440 coming back pretty strong at the end where it would be anybodys game. Must be the 440 came with a high gear from the factory and nobody offered any other options? I ran a 5:13 or a 4:86. Do you happen to know the ratio that came stock in the 440's?

 

[GregSY]

I never worried about off the line when I ran a 440...I'd let them run out in front of me then by the top of the track I'd be ahead. That was always the difference between a big block and small block...the small blocks would fade out at the top end. These were all stock or fairly close to stock (cam carb headers) cars.

 

[DrHook]

When you say big block mopar if you are referring to the 440, I raced several 440's on our back road quarter miles. I would beat of the line, pull somewhat, then hold my own thinking I've got this guy put away, but every race seemed to go the same way with the 440 coming back pretty strong at the end where it would be anybodys game. Must be the 440 came with a high gear from the factory and nobody offered any other options? I ran a 5:13 or a 4:86. Do you happen to know the ratio that came stock in the 440's?

I have no idea what the factory ones came with- all the ones I built were modified with whatever fit the HP/torque curve/tire size, etc.

 

[ratbldr427]

Most of the cars with Dana 60's in them from the factory that I have ran across seems like 4,10 was the most common low gear. Of course you could put any thing you want in them.
One friend ordered a 64 Sport Fury with the Stage3 426 package(he claimed it was only the 2ed ever built like that). It had a 4.10 in it. Don't remember if it was a Dana 60 or not.

 

[CarbideBob]

I never worried about off the line when I ran a 440...I'd let them run out in front of me then by the top of the track I'd be ahead. That was always the difference between a big block and small block...the small blocks would fade out at the top end. These were all stock or fairly close to stock (cam carb headers) cars.

Known as the "Big Block Boggie"

 

[metal-ica]

Who else read the original post and thought who the hell is going to put 2,000psi through a 2" tube?

....then the video on post 36 holy shit!

Good stuff bluechip ... I wish we were neighbors (not next door neighbors, but like down the street neighbors)

Google Photos

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[Firstram]

Who else read the original post and thought who the hell is going to put 2,000psi through a 2" tube?

....then the video on post 36 holy shit!

Good stuff bluechip ... I wish we were neighbors (not next door neighbors, but like down the street neighbors)

Google Photos

photos.google.com

I do special effects in the film industry. We often use air mortars to blow things up instead of pyro, it's generally safer and no permits needed. Our largest mortar is a 60 gallon tank with a 3" ball valve and we run pressures up to 325 psi, depending on the gag. We start low and test our way up, the destructive power of compressed air is shocking.

I would enjoy living next door to the OP!

 

[Bluechipx]

I paid a tidy sum for the hydro, it was new and never been in the water so I will be careful not to destroy it. I plan on putting sand bags or something like that equaling my weight in the drivers seat and starting out real low on the thrust. I made a set of tapered bore nozzles that will reduce nozzle size down to 1/2". That, coupled with infinitely adjustable pressure should be extra safe for starting out. Asphalt rocket cars tip the rocket up in the back to hold it down to the track (3 degrees?) but I am troubled by doing that. If the angled thrust holds it down, what happens at 100+ when the thrust fades away? I am thinking about an airfoil wing on the front set at "0". As I slowly increase speed if the front starts to rise I can adjust the airfoil slightly to compensate. The first trial will probably be 2-3 hundred psi and the hydro may only go fifty feet, but I feel small increments will be the way to go. The tanks will be mounted with a lot of chromemoly tubes with r/l heim joint ends to possibly twenty places and be pre-loaded for length. Because the land speed record is so high and the water speed record is so low (314?) and the boat was destroyed during the run, I'll go for a hundred to one fifty mph in as fast time as possible. An asphalt rocket car WITH a driver went 247 mph in 1.6 seconds in 500 feet! I suppose these figures are just as possible on water, my hydro only weighs 240 lbs and the tanks weigh around 330 lbs. I did some checking and carbon fiber tanks are available with a minimum burst pressure of 15,000 psi but the outlets are smaller than I want.

 

[metal-ica]

Is the boat a shell or does it have something in it now?

 

[???]

This is getting better and better. Having been involved in a world record sailing attempt in the initial stages I can assure you that when it goes wrong on the water at speed it goes spectacularly wrong.

Please keep us posted as an ex soldier I love seeing shit blow up.

 

[Bluechipx]

Is the boat a shell or does it have something in it now?

Pretty much a shell. In fact to even get into the cockpit you need a screwdriver to remove the lexan cover. As far as steering I've been told from a asphalt guys that if you are pointed correctly you don't have to do much. Standing on the starting line of a dragstrip quarter mile and looking at the finish line, it looks pretty tiny, like threading a needle. On a deserted lake the craft could vary a hundred yds either way and it wouldn't be an issue. At first I'll try only a fin and see how it works out. I'll have to add controls I guess if I ever get the courage to remove the ballast and hop in and give it a try. I would think that after many tests if everything went smooth at say 2,000 psi, I could back it down to around 1,600 psi and give it a try. I'm thinking about making some changes to the trailer so when it launches it will be guided for the first 8 or 10 feet by carpeted guides. Almost all boats sit low in the back when at rest in the water due to the engine is near the back or with an outboard, off the back. With the tanks near the CG, the boat should sit very close to the attitude it will be at at speed eliminating it becoming airborne at firing.

 

[Bluechipx]

Here is a short video about a model rocket with a hydro similiar to my design (coincidently), Incredible acceleration!

 

[???]

Have you heard of or do you even grasp the concept of inertia. You can't compare a model boat to something full sized with regards to mass and acceleration. The only time you use models as a comparison is drag.

 

[Bluechipx]

Have you heard of or do you even grasp the concept of inertia. You can't compare a model boat to something full sized with regards to mass and acceleration. The only time you use models as a comparison is drag.

Actually they claimed it went 204 in four seconds, there are full size, with a driver, rocket cars going faster in less time than the model guys here claim, which I find a little hard to swallow. Somehow I can't visualize a full size rig with a driver pulling out ahead of the model if they left at the same time.

 

[jim rozen]

"You can't compare a model boat to something full sized ..."

Unless you understand the math of scaling relations. This is a complicated matter that can NOT be solved by hand-waving on the intenet. Start with a good book on fluid dynamics.

*( scaling relations are important. Two brothers once derived airfoil designs based on their own experimental data, accidentally doing the scaling correctly. All the other published data were simply wrong because they measured lift and drag separately against a spring scale. Orville and Wilber compared them directly using a null ballance technique, because they did not have fancy equipment. Yep, washtub, wood box, fan on an old flat-belt driven bench grinder arbor, and - genius happens: wire coat hanger null balance with tabs of sheet metal measuring drag, balanced directly against lift from the DUT - the airfoil model.

They're both in the same airstream so the scaling relation drops out of the math.)

 

[???]

Start with a good book on fluid dynamics.

I think the problem goes a lot deeper than reading a fluid dynamics book is going to solve
And I'm not talking about the physics problem.

 

[goldenfab]

Who else read the original post and thought who the hell is going to put 2,000psi through a 2" tube?

....then the video on post 36 holy shit!

Good stuff bluechip ... I wish we were neighbors (not next door neighbors, but like down the street neighbors)

Google Photos

photos.google.com

WOW I missed the video when I read through this thread at first.

For sure you're not going to get any useful engineering data from a model without getting deep into physics but general handling characteristics generally scale up well with aircraft so I doubt it will be much different for this missle on water. But even then if handling characteristics change at different speeds then you're back into a complex physics problem to know how the speed of the model relates to the full scale article.

As to the original question of getting fuel into the airstream for a look cool factor Bernoulli's principle pretty much ensures there is going to be a drawing effect and you don't even need them to be at a downstream angle, a right angle to the flow should suffice and why not start with ports through the 2" pipe's wall instead of tubes because tubes are going to disrupt the flow. This could all go sideways if you have supersonic flow but I've forgotten what little I knew.

Have you thought about a standalone flamethrower to achieve your effect?

 

[boslab]

Nominally the pipe will be fashioned as a Venturi a reduction then rapid increase then A1 V1 = A2 V2 or equation of continuity is used velocity increases pressure drops, fascinating stuff
A1 is cross section area, v1 is velocity , simplistic but cheap and cheerful, easy enough compared to the full Bernoulli equation as pressure, density and even the height of the orifice live in that.
Mark

 

[Bluechipx]

WOW I missed the video when I read through this thread at first.

For sure you're not going to get any useful engineering data from a model without getting deep into physics but general handling characteristics generally scale up well with aircraft so I doubt it will be much different for this missle on water. But even then if handling characteristics change at different speeds then you're back into a complex physics problem to know how the speed of the model relates to the full scale article.

As to the original question of getting fuel into the airstream for a look cool factor Bernoulli's principle pretty much ensures there is going to be a drawing effect and you don't even need them to be at a downstream angle, a right angle to the flow should suffice and why not start with ports through the 2" pipe's wall instead of tubes because tubes are going to disrupt the flow. This could all go sideways if you have supersonic flow but I've forgotten what little I knew.

Have you thought about a standalone flamethrower to achieve your effect?

I'm sure the only way I could achieve a fire for looks would be when I use just air in both tanks and no water. (obviously?) With just air, it is much, much louder and a sure way to get complaints. After an air only test my wife was at the supermarket 2-3 days later and a woman who lives two miles away asked her "did you hear that loud sound last monday around seven?" to which my wife replied it was just my husband messing with his rocket. Here's what I've learned, when using just air the nozzle and cone is covered in frost or ice and the air condition can make for some dramatic effects. If the humidity and dew point are just right there can be a giant cloud close to a hundred yards across that lasts until the wind disperses it. I really need a video of it on a perfect day. Although I have never tested it, I believe with water, the nozzle cone wouldn't have any effect on thrust.