Marvins Creations

[MarvinMan]

I had noticed the graphs were broken when I uploaded them. I had hoped that google docs would make the spreadsheets more accessible than uploading them to dropbox.

When I started I wasn't particularly planning on publishing the data, so the labelling reflects my aversion to unnecessary typing. On the static results W is rotational speed of the prop, T is torque, and F is forward thrust (because T was already taken by torque). F/T gives a sort of measure of efficiency. On the second sheet, V is airspeed.

As torque and rotational speed are pretty constant at all airspeeds using variable pitch to control speed is probably better, but would need more work to characterise the pitch needed for peak thrust and zero thrust across the full speed range, especially if you did want to increase prop speed once in the air to take advantage of the improved airflow over the wings.

It appears that most of the energy input goes into just rotating the fins for no gain, so larger props allow more thrust/speed from a given rotational speed. The large props I tested using a cross piece as the hub were the best of the non-offset designs tested. Assuming it had enough thrust to get off the ground when retracted, a prop with pistons to increase its diameter might work well for efficient cruising or maximising top speed. I imagine such a design would make the handling of the plane awful, but it would be very fast.

Airspeed test rig.


Static thrust rig.

[z26]

Thanks, its much clearer now.  I'll still need a bit of time to process the data, but I really like your test rigs

about the piston thing... I just did a reconfiguring continuum to test a concept and it seems to work (but only for anchored application because of phantom forces ).  Have two continuum each attached to to a solid attach point.  Then, attach both of these to a third part (can be a fin if you hack map files, must have at least two attach points otherwise) but do so in a way that the two arcs conflict with each other on what the position of the third part should be.  Now, by setting one of the continuums's mass to 0, you can weaken one of the connection and give near complete authority to another, thus changing the position of the third part.  This seems more rigid than pistons, but again phantom forces...

This might not be useful for prop planes, but there might be some applications nonetheless.


UPDATE: the technique itself seems useful, but a big problem is that when saving, any stress in the voltaic arcs is relieved, which stops anything from functioning.  My bigger worry is about how map files works: I'm not sure its possible to create a feature like that even using manual file editing.  Even just being swallowed by an hypercube then spit back cancels the effect

[MarvinMan]

Interesting idea. I've not come across any obvious mechanical integrity problems with the props I've been testing, but I assume offsetting the fins is beneficial because it counters some of the stretch in the arcs, letting them effectively move to their optimal position under load/at speed.

Can hypercubes be used for de-stressing any structure? For example a string of continuums bent into a loop being turned into a stable structure that won't spring back when broken.

[z26]

just checked, and not always. a line of 5 continuums tied by long voltaic arcs, with one end fixed with a hook and the other end bent, then fixed with another hook keeps its tension if its hypercubed or if the game is saved.

I tried the same setup, but while also connecting the two extremities with a second line of continuums.  hypercubing or loading displaced the position of the second line.  the assembly was still under tension overall, but there no stress BETWEEN line one and line two.


I guess that the internal stress of a stucture is relieved, but not the stress that comes from external forces bending the structure.