Calculating top speed on ice...

[Fricke]

That could work, but the transition between the external tank and the on board fuel cell might kill the engine. Easier just to top it off from a bottle.

Might be so... But if you feed the external fuel to the suction line from the fuel cell and keep the external fuel container above the fuel cell then there shouldn't be any problems. A quick disconnect hydraulic coupling and a ball valve should be sufficient. Any way it's your "kick"

If I weren´t hung like a horse I might have saved 5kg, but one can only dream...

Haha... The young boys of Sweden...

[milisavljevic]

A special "Chunky Bacon Hello!" to Simon (and Ruby fans everywhere)

Hejsan Anders!

97km/h was [is] a bit slower than I had expected...

No worries with respect to top speed, Anders: you will easily exceed 100 kph, IF you have the balls for it!

I do not have the time to get into this now (as I politely mentioned before), but I will make some points:

[1] the acceleration run is only 1000 meters, unless you change your mind about a braking chute
[2] as Simon noted, the ejectors add thrust, but this is a variable quantity (function of velocity)
[3] pulsejet core thrust is a variable quantity that increases significantly (a function of velocity)
[4] net acceleration (summing all thrust and drag forces) will increase over the acceleration run

I modeled your speed run before, but not exhaustively (also politely mentioned way back in this thread),
which is why I invite all readers to go back and read through the early posts. I stopped modeling after it
became obvious that Anders would back off the throttle long before the kick reached terminal velocity.

I will finish this "task" when I have more time; we can all compare notes then. It should be a real "hoot"!

Cheers,
M.

[Eric]

I'm not sure what position you will be in while racing, but unless you have an aerodynamic cowl around yourself and the kik the ultimate speed will be lower than most would think, mainly because people are very draggy.

Standing vertically, with 55lbs thrust the top speed would be just about 40 mph.

Crouched down a bit would increase it closer to 48 mph.

If you were practically sitting on the engine you could probably get to 100kph but I would not expect anything over that.

You could also squeeze a bit of speed out of it by wearing a spandex ski racers suit, and an aerodynamic helmet.

Unfortunately in this speed range there isnt a considerable boost in output, as your terminal speed is going to be a fraction of what the engine could do on a plane.

If you made a nice aerodynamic cowl you would hit very high speeds, as you would have about 5-6 times less drag, and you would probably top off at around 110-120 mph.

If you did want the engine to really pick up more at this speed range you would need an intake shroud to convert some of that drag into extra mass flow through the intake.

Personally I think 40-50 mph would be more than enough when standing on skinny little runners half an inch off the ice

Calculating an exact terminal velocity with a vehicle and rider that dont have a fixed coefficient of drag or frontal area, an unknown dynamic thrust profile, and a slew of other variable conditions is a bit meaningless and overly idealized.

Eric

[milisavljevic]

.

People are very draggy.

Calculating an exact terminal velocity...is a bit meaningless and overly idealized.

Puh-leeze! I need to stitch up my sides...back in three weeks.

. . . LOL-M.
.

[Johansson]

As Eric wrote there is no way of telling how much drag the kick with me on it will produce, so any calculation will have to be considered as a qualified guess really. The reason why I want to hear some guesses is so I have a clue of what to expect, any top speed (not average speed over the distance) below 100km/h would be a great disappointment.

One thing I can do to cut the drag down a bit is to fit a plexi screen from the handlebar down to the front of the kick, it won´t ruin the look of the kick and it is easy to fit so I can do a first run without it and then another with the screen to see if it helps.

[milisavljevic]

Hejsan Anders!

Ummm... If you won't leave for your vacation, then how I am ever going to have mine? Sigh.

There is no way of telling how much drag the kick with me on it will produce.

This statement is entirely false. This is a real world problem, and not subject to conjecture.

You may recall from far back in this thread, I asked you to conduct a tow test with the kick:

A series of timed runs over a measured course, where you coast to a stop after being pulled
to a known speed (eg., by a snowmobile) will provide quantitatively accurate measurements
of the drag forces acting on an inert kick. This is not rocket science; it does requires effort.

. . . . . . . "You can lead a horse to water, but you cannot make it drink.".

Any calculation will have to be considered as a qualified guess really.

Some "guesses" are more "qualified" than others. Maybe we can have a pool and bet on this?

Any top speed below 100km/h would [will] be a great disappointment.

You will not be disappointed in the kick; you will be the limiting factor in how fast you move.

And I will go one step further: if it appears (after testing) that your top speed is not what is
desired, I will tell you how to modify Thunderchine to increase its thrust to a suitable level.

There you have it, mate. A guarantee of success from someone with your interests at heart.

This is my last post on this question; the rest of you are welcome to flog the horse to death.*

Cheers,
M.

* For at least three weeks, at any rate!

[tufty]

Hey m.

As a matter of interest, do you have an estimate of the thrust curves for the raw jet and the jet + ejectors as a function of velocity? And, assuming it's not too much to ask, the method you might use to arrive at such figures.

you will be the limiting factor in how fast you move

Indeed. As I was reminiscing with Forrest earlier regarding motorcycles, here's another anecdote. On my FZR400, at speeds above 180kph*, going from "full tuck" over the tank to "sitting upright and desperately trying to hold onto the bars" would slow me down faster than "giving the brakes a fistfull" - even with twin disks and 4 pot calipers up front. Bad aerodynamics hurt your top speed.

Simon

* 180kph was where the speedo hit the stop - as this was a jap import machine and as stock** was capable of at least 220kph***, I can only assume the Japanese don't know how to speed.
** i.e. 400cc with a stock exhaust, as opposed to 520cc, "aggressive" cams, and a "modified to look stock at first inspection" exhaust.
*** The speed at which I was pulled over by the police along the Windsor Road (limit - 50mph), and given a "mild caution" before the policeman then asked what machine it was, and could he have a go, please.

[Eric]

I like how you paraphrased out the important part of that quote.

I am pretty sure he means there is no way of telling how much drag the kick will actually produce with him on it, without doing a bunch of completely unnecessary towed drag tests to find the actual drag coefficient so that you can enter it into an equation that a monkey could do. None of which can be done until winter. And dont tell me that he can go to a wind tunnel laboratory with the same result.

I mean really, hes going to wait until winter and then tow it up to speed without the engine running so that you can calculate the supposed exact top speed? Calculating a range of speeds is not only easier, but its more useful information than one speed at one exact posture. A simple shift of him arcing his back an inch more or less, or moving his elbows in or out an inch, will throw off both the cd and the frontal area significantly, making an exact speed you calculate a nice, but otherwise useless piece of info.

And what kind of top speed do you think he would hit if he had a much longer track? From what little I have seen of your posts here you make it sound like 100 kph is but a fraction of the speed he could reach. 55lbs thrust sounds nice but its actually not a whole lot. Per pound thrust the kick wont go a lot faster than a bike or gokart, and hes not going to hit anything significantly over 100 kph without an aerodynamic cowl, or much more thrust than that engine can muster.

I dont visit the forum a lot lately, but every time I do I see something you post that I cant help but comment on. I cringe at the idea of actually reading through this entire thread.

Ha, some guesses are more qualified than others... While that may be true, talking like a pirate and posting cartoons, and cliche's in response to any opposition, does not count as qualification.

If you actually want to have a useful conversation, why not explain how you are calculating the top speed or just come right out and post what equation you are using so we can all enter the data and see for ourselves.


Johansson,
If you can get some lexan, you should be able to make a very nice cowl for it, that can form around the kick and be quite aerodynamic, lexan bends very nicely and holds the shape, and can also be thermally formed with a heat gun to make compound curves. Its also stronger than plexi and almost impossible to shatter. A racing snowmobile front / wind screen would be a good shape to emulate.

Eric

[milisavljevic]

.

Hey m.

Hey Simon!

You have a PM.
.

[milisavljevic]

Hejsan Anders!

There are times when Eric does know what he's talking about, and the following is close enough to one of them:

Johansson,
If you can get some lexan, you should be able to make a very nice cowl for it, that can form around the kick
and be quite aerodynamic, lexan bends very nicely and holds the shape, and can also be thermally formed
with a heat gun to make compound curves. Its also stronger than plexi and almost impossible to shatter.

As to the rest...well, no need to make him cringe more than he normally would. Even he deserves some respect.

Cheers,
M.

PS: And we all know that there was still plenty of snow and ice about when you first opened this thread. Right?

PPS: Tomorrow will be exactly 100 days from when I first advanced the tow test idea. Reading is fundamental.

[Eric]

Ah if only all of us had the free time to spend pedaling pathological bullshit by the truckload and reading 20+ page threads in their entirety so we could be more like everybody's favorite forum troll.

Hows nudis and uflow going by the way? Seems like you really worked out the kinks you were having.

Go out in the real world and actually do some of the things you pontificate about, then we'll talk about who knows what they are talking about, and who makes up bullshit because it sounds good at the time.

Please by all means if I am so horribly wrong show us the proof, I'm dying to find out what magic equations, i mean mathematical equations, you are using.

[ace_fedde]

I also would like to complain about M. and his pirate!

M.,
You said:

Cap'n M. drank all my rum while watching this movie on DVD, then passed out on the fo'c'sle ( peace at last! ).

Evidence now points out that it wasn’t Cap’n M. drinkin’ yours, but you drinkin’ Cap’n M.’s!!

Evidence:

Evidence 0001a

The whole story already stinked to me because if it was Cap’n M. drinking yours, he would have been drinking all of
your Rakija!

Confess!!

Fedde

[Johansson]

I got some more work done on the kick today, if everything goes as planned I can do a liquid test run later this week.

This is the Y-connection for the propane and liquid fuel, the propane hose connects with a compressed air coupling so it can be easily removed once the engine is running on liquid. A non-return valve with a restrictor plate is fitted for the liquid fuel line, at the moment the restrictor has a 2mm hole drilled in it but I will find the right size once I start testing the engine.

I also made a new vapour coil with one more turn of tubing since the old one couldn´t heat the liquid propane enough.

[Eric]

Try putting a thin reflective stainless ring / tube around the heat coil section, they have a very tiny surface contact area for their volume, a stainless 'insulator' ring would reflect IR back onto the tubes, and keep the localized area hotter so that more heat can be transferred by contact, without risk of that section melting.

2 mm should be more than enough for the restrictor, in fact I would probably start with 1 mm, when converted to vapor the liquid flow through 2 mm would be equivalent to a 32 mm tube flowing vapor. If it does need that much fuel, then holy crap.

If the restrictor is too big its going to slowly fill the coils with liquid and then the engine will go nuts.

For best results the fuel system should be made so that each stage presents the fuel with a significant expansion, which means your injector effective area will have to be pretty big so that you arent injecting ice cold partially expanded fuel.

[milisavljevic]

Hejsan Anders!

I got some more work done on the kick today.

Better and better!

Cheers,
M.

PS: You have a PM.