Calculating top speed on ice...

[Johansson]

M: I found those pics on the web but every kick looks just the same. With thin-walled steel tubing instead of wood it should make a lightweight and solid frame for the engine.

Engine mounts by the way, what is your opinion about them? Should the engine be fixed to the frame or would a spring mounted engine survive the vibrations and bumps better?

Even grandma would wear a varm knä filt whenever grandpa squired her around!

Perhaps I should go all the way and get an inflatable love doll dressed up for the occation and use as a passenger/symmetrical fairing?

PyroJoe: Thanks for the advice, I will have to give the braking some real thought so I won´t do something stupid. One good thing is that the track is long enough for the kick to slow down enough from air resistance so I can brake it with my feet once the engine is shut down, I´d rather slide a kilometer before it stops than hitting the brakes at 150+ km/h and risk that it goes into a spin/tips over.

[Jutte]

"There is something impressionable about a vehicle disappearing from beneath you, leading to a full body glide to terra firma and a beloved ritual of extracting gravel lodged under the skin. Something often laughed about, but not forgotten."
HAHAHAHA...the story of my youth.Honda XR 500 at great speed and from great heights - " Who cut away the hill?-wahhh!"
"I hit that jump/ramp/hill real fast this time...wahhh!"" I can make this...wahhh!" - always followed by the
full body glide to terra firma...LOL! Great memories..LOL, but as you say not forgotten!
However - never had to extract gravel just spit out heaps of dust, lots of small twigs to the admiring
gales of laughter from my friends.
Never got a trip to the hospital - although it's a wonder.
So you take care Joe!

[milisavljevic]

Hello Anders,

Should the engine be fixed to the frame
or would a spring mounted engine survive the vibrations and bumps better?

If you follow Joe's lead ("GRIM"), I suggest that you should rigidly mount the front of the combustor*
to the frame, and then attach moving linkages on either side of the tailpipe (use the "super cone").
Moving linkages permit thermal expansion (springs are an option). Look at this image and this one.

Note: In the second image, I am referring only to the linkage at the far left, beneath the "exit cone".
You will need two (2) linkages (for each side of the duct), then not place them as far back as shown.

Perhaps I should go all the way and get an inflatable love doll...

LOL! It sounds more like a bisymmetric fair-lay-ing, if you ask me!

One good thing is that the track is long enough for the kick to slow down...

Ah! That reminds me (hopefully my last question...sigh): Once you reach your maximum safe speed,
and if this occurs long before you have traversed 2000 m (eg., after only 1000 m), can you back off
the throttle? Or is the point how fast you are going once you make 2000 m? I assume it's the former.

Thanks,
M.

*The combustor mount may be sprung (eg., hinge spring), but keep in mind this is the thrust mount.

[PyroJoe]

It is good to hear there is plenty of track.

As your coming off top speed and starting deceleration try to throttle down slowly, as much as the engine will allow, it is somewhat of a delicate balancing act between drag and thrust.

If the thrust is suddenly terminated, power quickly shifts to the drag forces and can have some unexpected results. IMO it is best to have some power on the deceleration, slowly adjusting down the throttle, down to a reasonable speed before powering off.

Joe

[Johansson]

Ah! That reminds me (hopefully my last question...sigh): Once you reach your maximum safe speed,
and if this occurs long before you have traversed 2000 m (eg., after only 1000 m), can you back off
the throttle? Or is the point how fast you are going once you make 2000 m? I assume it's the former.

Yup, when I feel that I´ve reached the highest safe speed I´ll back off the throttle and cruise to the finish line. The speed track is constructed so you have 1000m to accelerate, during the next 1000m your speed is measured at constant intervals and then there is 1200m to slow down the vehicle. I believe that the final speed reading you get is your average speed over the second kilometer so in order to get a decent reading you have to run the entire track.

Good point again there, PyroJoe, my first idea was to build the fuel system with only two settings, idle and full throttle, but I should perhaps reconsider and make an adjustable "medium" thrust setting for slowing down. The full thrust throttle will be a dead mans grip design so when I let go of it the engine should back down to the lower thrust setting, I´ll try to keep it as simple as possible so I can concentrate on keeping the kick on track and won´t have to adjust any throttle settings at speed.

[milisavljevic]

Hejsan Anders!

Thank you for the new information: now I clearly imagine the entire speed run in my mind.

Stealing a (kinda-sorta) march from fighter pilots, you may implement two (2) dead man's
controls: one hand grips the (suggested) two-position high-thrust/low-thrust throttle* and
your other hand grips a kill switch - alternate implementation: a jet ski style wrist lanyard.**

Cheers,
M.

*I suggest that you implement a ramp between the power levels (ie., not instantaneous)

**or use an ankle lanyard, whichever is more appropriate

[tufty]

a jet ski style wrist lanyard

This. A manual kill switch is useless, if you're gonna have one it must be a "dead man's handle". As for the idea of an emergency chute, I'd tend to attach it to the pilot, not the vehicle.

Simon

[milisavljevic]

.

As for the idea of an emergency chute, I'd tend to attach it to the pilot, not the vehicle.

I agree with Simon.

Supporting arguments:

[1] There is no easy or obvious place to attach a braking 'chute - a kick lacks a rear deck or transom.
.. . Down low, there is a screaming, red hot Thunderchine; safe to say this is not a suitable location.*

[2] Anders' safety is more important than braking his kick. A second 'chute may then be mounted in
front of him, and only deployed if and when Anders has "left the building". This is not an "either/or".

Additional points, not necessarily related to the above:

[3] It is trivial to rig a braking 'chute to keep it near the ground (prevents unintentional parasailing).

[4] I suggest that Anders mount his Thunderchine inverted relative to the plans (ie., ejectors down).

Cheers,
M.

*I realise a heat shield is between Anders and Thunderchine; however, to be suitable for mounting
.a braking 'chute, it would have to be constructed as a structural element. Even so, it is not ideal.

[PyroJoe]

"[3] It is trivial to rig a braking 'chute to keep it near the ground (prevents unintentional parasailing)."



http://www.motorcycle.com/events/inside ... 87792.html

"Equally important is the location of the lanyard attachment. If the attachment is connected too high, it can cause downward force at the rear when the chute opens, making the front end light and unstable. If the attachment is too low, the rear of the bike can literally lift off the ground upon deployment. Great lengths were taken to insure that the Ack Attack’s lanyard attachment was in a neutral position. Mike had the bike hoisted into the air, dangling from its tail with the rider on board. The machine hung from the lanyard attachment positioned so that the bike was perpendicular to the ground. All guesswork was removed."

"So what if it goes 150 in first gear and can light the tire in any of its six gears with just a twist of the wrist? I’ve heard it said many times - It’s not what you ride that matters. It’s that you ride."


Just for grins
Johansson appears to have a good grip on the task at hand, so I will have nothing more to add.



Joe

[milisavljevic]

.
I had missed out on the "Ack Attack" story: most appropriate for Ander's project. Thanks for sharing.

(quoted at the end of the article) "It’s not what you ride that matters. It’s that you ride."

A good and truthful quote...all the more so for the double meaning hidden within.

Cheers,
M.

[Johansson]

That´s one long bike!

There are no obvious attachment points for a parachute on a kick so the easiest route would be to skip the chute-route (he he) and let the air resistance do most of the braking instead, it seemed to work for the guy at this years event that was towed after a car on a snowracer up to 160km/h. Next year he says he will go 200km/h.

[milisavljevic]

Hmmm...

Let the air resistance do most of the braking.

I have everything I need (I think) to run some numbers for the acceleration and deceleration profiles.
I will check this option for you. To decelerate from 200 kph to a dead stop in under 1200 m, requires
a minimum average deceleration of 0,131 gee. Not that your deceleration profile will be neatly linear.

If you are curious, the initial instantaneous braking power (at 0,131 gee) is 11-12 HP, depending on
the max. weight of the kick at engine shutoff, and again assuming a fictitious constant deceleration.

I'll be back. Meanwhile...enjoy the weekend, everybody!

Cheers,
M.

[milisavljevic]

.
You know, Anders, you could do the following:

[1] load up a similar kick to simulate your entry
[2] pull on your flame-resistant togs (blowup doll?)
[3] have someone tow you up to your desired speed
[4] coast to a stop and measure the distance covered

You need not reach 200 kph, any speed will do, as long as you measure it and the distance required to stop.
It is a trivial matter to extrapolate required stopping distances for any / all speeds. And what is more, this
provides the means to determine your maximum attainable speed over the first 1000 m, with good fidelity.

Why screw around with maths*, when you can experiment? .M. is always here to help with extrapolating.

Just thinking out loud here...

Evil M.

*that's what the blowup doll is for, right?

[larry cottrill]

You're getting some really good advice on braking and such. One thing to remember is that you will probably be the heaviest (i.e. most massive) accelerated element. You will also be the draggiest, unless you have a highly protective fairing that routes the airflow clear around you.

Don't just rely on being able to "ease your way out" of high speed -- remember that there COULD be a total power failure at any time, for a number of reasons. At high speed, this means a SUDDEN, DRAMATIC change in the thrust/drag balance. This will be mitigated somewhat if you have a very effective speed fairing, but it will still be significant. If the vehicle drag were fairly high and you were well-shielded from wind drag, you would feel "thrown forward" when this hits. If you are a significant part of the drag, you might just feel a sudden lessening of the "pulling" of the kick. These are forces you need to be prepared for. The "drag chute on the pilot" idea is interesting and, in this case, not without merit.

For the pilot, an emergency situation in this vehicle is a LOT different than the more usual case of being strapped into a seat (in which case you are practically part of the vehicle mass). I am probably just re-stating what you already know / what's already been said. Good luck! Man, what an exciting run that's going to be!

L Cottrill

[Johansson]

I agree, great input from you guys!

Before any jet powered runs I will try to get someone to tow me after a snowmobile so I can get used to handling the kick at speed, but that is 8-9 months away so I will concentrate on the engine at this point.

M, how long do you think that an engine made from 1mm sheet metal (non SS) would survive?