Calculating top speed on ice...

[Johansson]

I measured the kick yesterday and found out that it is possible to support the engine from below instead of from the handlebar mounted mounts I drew earlier, would this help in any way? The engine could rest in a U-shaped mount which is slotted for a bolt welded to the engine to slide in and keep the engine from moving around, the drawing might explain this better:

If it weren´t for the ejectors this wouldn´t be a problem since I then could weld a pair of bolts to either side of the super cone just like the rear mount is made for the test frame, but now it is a bit more difficult.

[milisavljevic]

Hej!

I measured the kick yesterday and found out that it is possible to support the engine from below.

If at all possible, please go this way. The ejectors do not reach to the bottom of the super cone;
it should be easy enough to position a rest under the super cone (note: not the exit cone please).

Cheers,
M.

[milisavljevic]

Anders,

If it weren't for the ejectors this wouldn't be a problem since I then could weld a pair of bolts
to either side of the super cone just like the rear mount is made for the test frame...

You are thinking too small. Take the mounting rail idea, make it much shorter and relocate it
to the bottom of the super cone (eg., half way down its length, or close to the exit cone join).
A bolt can be welded to this rail, or conversely, stick with the slot then run the bolt through it.

I think you can handle it from here!

Cheers,
M.

[Eric]

Having the cradle mount like you drew will certainly help.

With the cradle style you could then have a longer support, since it wont be welded to the engine the thermal expansion will be independent of the engine and wont damage it in any way.

A good place to center the cradle would be at the 2/3 point on the engine, with the cradle extending several inches outward in each direction.

Might seem like a pain but taking the time to design the mounts properly is well worth it.

Eric

[Eric]

Here's a sketch of the method I typically go with.

I typically put the hard mount near the engines center of mass so any vertical and side to side movement is well supported, with cradle mounts extending to the front and back.

I usually go with mounting the cradles on the smaller tube diameters, and the cone sections. The expansion of the cone length and width will still conform to the relatively non expanding angled cradle on the cone section.

If the cradles were put on the combustion chamber and expansion section, the net expansion would cause the front and back of the engine to bow upwards.

Also when mounting external parts to an engine, I use fairly long rods. They are plenty strong but any thermal expansion generated will easily flex the rod with non permanant deformation, so they can just spring back to original shape once cooled.

With an augmenter mounted to a hot section of the engine I once again use rods, but calculate the projected temperature of section I am mounting it to, and the temperature of the augmenter, calculate the ratio of expansion between the two, and then mount the rods at the proper angle so the expansion between top and bottom come out to roughly the same. The same method applies for making mounts from one section of a J bend engine to another.

For example:

Augmenter section temperature: 1thermal unit
Engine Section temperature: 2 thermal units

Engine expansion = 2x augmenter expansion

Expansion over 5" of engine tube = Expansion over 10" of augmenter tube

So if we weld 2 rods on each side of the augmenter 10" apart, tapering down to 5" apart as mounted on the engine, the expansion between the top and bottom will be the same, resulting in no warping stress on the system.

Eric

[Johansson]

Great input Eric, a cradle like the one in the picture you posted would be nice if it weren´t practically difficult to fit on the kick. I will still try to make the engine rest on the rear mount, testing will tell if the tail has to be fixed further to avoid having it shaking around to much.

A thing that might prevent this is to move the front mount "up" a bit on the CC top so the engine thrust push the tail down into the mount.

[Johansson]

Please proceed as was discussed. If you cannot do this, then ignore what I post here.

Que?

[milisavljevic]

.

Que?

इसके बारे में भूल जाओ!
Забудьте об этом!
Vergessen Sie es!
Strunta i det!
Glem det!
잊어버려!
Olvídalo!

Forget about it!

Cheers,
M.

[Johansson]

The thrust mount is in place now, the CC needs to be that high from the ground so the engine can be level without risking that the exit cone hit bumps or pieces of ice on the track.

Next week I´ll start on the rear mount, but now it is time to start celebrating the Swedish midsummer!

[milisavljevic]

Hejsan Anders!

The thrust mount is in place now.

Your project is coming together in a most excellent way! Woot!

Cheers,
M.

[Johansson]

I´ve been busy with other things lately but the weather forcast promises heavy rain next week: perfect workshop weather!

My plan is to finish the rear engine mount and set the engine up for propane, next weekend we´ll have time to test run the engine and see how well the mounts and welds hold up. It will be interesting to find out how this baby runs.

Do a 11kg propane bottle produce enough gas at 15C to get the engine running any higher than idle?

[milisavljevic]

Hejsan Anders!

Do[es] a[n] 11kg propane bottle produce enough gas at 15C to get the engine running any higher than idle?

I suggest feeding from two (2) such bottles; this is adequate to sustain a high thrust level for a time.

And yes, this configuration has been tested (ie., it is a known good configuration for Thunderchine).

Cheers,
M.

[Johansson]

Do[es] a[n]11kg propane bottle produce enough gas at 15C to get the engine running any higher than idle?

Damn. Believe it or not, I actually hesitated on the spelling on that one before I posted it.

I suggest feeding from two (2) such bottles; this is adequate to sustain a high thrust level for a time.

That sounds like a plan, thanks!

[Johansson]

I spent a couple of hours on the rear mount today, left to do is to fit two turnbuckles to the upper mounts for tail angle adjustments.

[milisavljevic]

Hejsan Anders!

I spent a couple of hours on the rear mount today.

Very sweet. I do have one question: what restrains the engine from chattering on top of its cradle?
I see a potential for mischief in the lack of positive control, but perhaps I am missing some detail?

Btw., I will have the requested email (with the good stuff!) out to you within 12 hours of this post.

Cheers,
M.