Hate to say it kids, but these quad-rotors are gonna be outlawed for civvies in short-order. All I see is an anonymous weapons platform waiting to happen. Better play with'em with yer kids before some new brand of terrorist mods one....

That could have easily killed them all if the chute got caught in either of the rotors. What an asshole.

Something very odd happens at the 9 second mark where the bird seems to 'jump' towards the rotors.

I'm really not sure what to make of this video.

NASA aerospace engineer Mark Moore says a key objective with Samarai is to achieve propulsion redundancy all the way out to the tips of the prop-rotors. One way this is achieved is by using short-range laser scanners at each corner of the vehicle to watch for potential blade strikes and quickly stop the affected prop-rotor before impact.

He says a test rig was built that showed electric motors can be stopped in any position "incredibly quickly", especially given each single-blade rotor's small size and low weight. The result is a compact configuration, although there is some wasted rotor thrust from download on the wings, Moore says.

My understanding is that a correct autorotation is NOT accompanied by a hard landing. However, it IS very difficult to pull off (hard---what a pun!), the closest personally analogy I can think of, being docking a boat by chopping the throttle while still tens of yards away from the dock, casting it up alongside just So---with all the kinetic energy elegantly spent before kissing the dock side.

The helicopter analogy, again, to my knowledge, is that once engine failure is clearly happening, you flatten the pitch, give up the lift the blades were generating, start falling and preserve main rotor RPM as much as possible---and you get exactly one chance and one chance only to pull pitch (make the rotor blades bite the air) at just the right distance above the ground to decelerate the helicopter just as all the rotational energy of the blades finishes spending itself in generating that last, final iota of lift--and then you kiss the ground.
Or not.

YouTube description:

According to the pilot-in-command (PIC), he was performing autorotations at the lower part of the main rotor rpm green arc in part due to weight considerations. Upon entering the accident autorotation, he maintained an airspeed between 85-90 knots in the hope that extra speed would allow a more aggressive deceleration flare prior to touchdown, which should in turn further slow the rate of descent and forward speed. The helicopter's rate of descent was high, and as the PIC turned the helicopter onto the runway heading it was apparent to him that the rate of descent was excessive and that he was too low to execute either a proper deceleration flare or perform a power recovery. He attempted to level the helicopter as much as possible prior to impact to minimize the damage to the helicopter and prevent injury. The helicopter landed hard with the left skid contacting the runway first. The left skid collapsed, damaging the outboard landing gear damper attachment structure. The helicopter slid about 100 yards before coming to a stop. According to the manufacturer, the main rotor rpm range is 90 percent to 106.4 percent. At the helicopter's weight and the density altitude on the day of the accident, the main rotor rpm during the autorotation should have been above the 106.4 percent limit (red line), requiring the pilot to increase collective pitch to maintain the rotor rpm within limits. Performing autorotations at the lower part of the green arc provides less availability of rotor energy to perform an autorotation landing. The pilot should have recognized that he was not achieving the required main rotor rpm for the autorotations and terminated the maneuvers. The helicopter was within weight and balance limits.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

The pilot's failure to maintain adequate main rotor rpm during an autorotation, which resulted in a hard landing.

That had to be like an RC helicopter strapped with explosive or something. Military helicopters don't just vaporize when they are hit. There should have been large chunks of debris; like identifiable pieces of the tail, rotor, or cockpit.

You can hit a helicopter with a guided missile and it won't blow up like that.

I wonder why this is necessary. It seems all the planets we want to land on-and can land on b/c they're not made of gas or are on fire-have at least a little bit of atmosphere. It makes more sense to use parachutes and giant electric ducted fans or even heli rotors to land. Stop with the rocket fuel. And launch from the edge of space if possible.

And that makes ten votes. Had a rotor failure on one of our race cars a few years back and it was a frightening crash. I can't imagine a dragster going out of control

Edit: Oh boy, wall of text crits for 10k.

His explanation was rather short and somewhat misleading. Maybe they thought a proper explanation would have been too dry or too lengthy to be of any interest for a sufficient number of their viewers.

tl:dr

If all rotor settings are indicated to be correct, a feedback loop within the circuit indicated a subset of correct connections on the plugboard, even if the initially assumed connection turned out to be wrong. It didn't show all connections, but enough to run it through a modified Enigma to determine if it's a false positive or in fact the correct setting. If it was correct, the rest could be done by hand.

----------------------- Long version -----------------------

Apologies in advance. We had to recreate parts of the Bombe as a simulation, but a) it's been a while and b) it was in German. I'll try to explain the concept behind it, hopefully without screwing it up entirely.

The combination of clear message and code snippet (2:25) is called a crib. This can be used to create a graph, wherein letters are the vertices and connections together with their numerical positions are the edges.

For example, at position 1, "A" corresponds to "W". So you'd create an edge between "A" and "W" and mark that edge as "1". At position 4, "B" corresponds to "T", so there's the edge marked as "4". All edges are bidirectional, the transformation at a specific position can go either way.

Once your graph is finished, you check for loops. These are essential. Without loops, you're boned. In this case, one loop can be found at positions 2,3,5 in form of "T->E->Q->T".

Here the Bombe comes into play. It uses scramblers, each combining all three rotors plus reflector of an enigma into one segment. This way, one Enigma setting is functionally equal to a single scrambler.

Now you can use those scramblers to create an electrical circuit that corresponds to your graph -- scrambler = edge. All scramblers are set to the same initial configuration. The first scramber remains at in the inital configuration, while the second and third get configurations in relation to their edge's numerical value. Configuration in this case means the value of their internal three rotors, so there are 26*26*26 possible settings within each scrambler.

It's basically a sequence of three encryptions.

Example: in our little TEQ triangle, the first scrambler (TE, 2) gets a random starting position. The second scrambler (QE, 5) gets turned three notches, the third scrambler (QT, 3) gets turned one notch. The initial configuration might be wrong, but only the relation between the scramblers matters. A wrong result simply tells you to turn all scramblers another notch, until you get it right.

You have a possibly correct setting when the output matches the input. Specifically, a voltage is applied to the wire of letter "T", leading into the first scrambler. And on a test register attached to the last scrambler, the wire of letter "T" should have a voltage on it as well. If the setting is incorrect, a different letter will light up. Similarly, all incorrect inputs for this particular setup will always light up a different letter at the the end, never the same (thanks to the reflector). If output equals input, you're golden. And if several loops are used, all with the same input/output letter, each of their outputs must equal the input.

To reduce the number of false positives, you need as many connected loops within the crib as possible.

So far, that's an Enigma without a plugboard. To account for that, they introduced feedback loops into the circuit. In our small scale case, the output of the third scrambler would be coupled back into the input of the first scrambler. The number of loops determines the number of possible outcomes with each specific setting. All of these are fed back into the first scrambler of each loop.

The plugboard, however, changed the input into the system of rotors. Instead of a "T" in our example, it might be a "Z", if those two letters were connected on the board.

A random hypothesis is made and fed into the machine. If the scramblers are set incorrectly, a different letter comes out at the end of each loop and is in return fed back into the first scramblers. Result: (almost) everything lights up. If you start with a good graph, everything will light up.

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A key element for this was the "diagonal board", which represented a) all possible connections on the plugboard and b) the bidirectional nature of those connections (AB = BA). Maybe it can be explained without pictures, but I sure as hell can't, so "a grid of all possible connections between scramblers and letters + forced reciprocity" will have to suffice.
-----

If, however, the setting was correct, a wrong hypothesis for the input connection merely meant that everything except the right connections was lit up.

Let's say the fix point of the loops in our graph is the letter "T". We assume that it's connected to the letter "Z" on the plugboard. A voltage is applied to "Z" on the test register, and thereby inserted into the circuit at the first scrambler. Loop #1 applies voltage to the letter "A" on the test register, #2 lights up "B", #3 lights up "F". These three outputs are now fed back into the first scrambler, so now the scrambler has voltage on ZABF, which in return lights up ZABF+GEK on the test register.
This goes on until everything except "U" is lit up on the test register. That means three things: a) the settings are correct, b) the hypothesis is wrong, c) "T" is connected to "U".

Reasons:
a) if the settings were incorrect, the entire register would be alive
b) if the hypothesis was correct, only the letter "Z" would be alive on the register
c) due to the feedback loop, the only way for the output to be "U" is if the input was also "U", and the reciprocity within the system makes it impossible for any other input to generate the output "U". Since "T" was the fix point for our loops, "T" is connected to "U".

Similarly, if the initial hypothesis is correct, everything on the test register except "U" stays dead.

The diagonal board provides registers for every single letter and allows the user to pick one as a test register. During operation, all the other registers serve as visual representations of the deductions based on the initial hypothesis. So you actually get to see more than just the initial connection, all based on the same concept.

Well, they wanted to use a single machine for both encoding and decoding of messages, so the use of a reflector to channel the signal right back through the rotors strikes me as rather pragmatic.

What bothers me is that they relied on "security through obscurity".

The sheer number of possible settings with 3 (4) rotors of a random configuration, each with adjustable rings, plus a plugboard with a variable number of connections -- that's a metric fuck-ton of permutations. But the rotors had fixed wiring and were limited in number. As soon as the Allies got their hands on a set of rotors, the possible number of settings was reduced radically. And the number of connections on the plugboard was standardized to 10 in '41.

Now, what if they had replaced one of the fixed-wiring rotors with a sort of pluggable rotor disc, a rotor that could be reconfigured on site within a minute? That would have screwed the boys at Bletchley Park, wouldn't it? Instead of 60 combinations for 3 out of 5, you'd have 20*26! (2 out of 5 and one random). Have it reconfigured daily, just like the starting positions, and brute force would have required much more effort.

It would still have been vulnerable, given the reflector issues, the nonsensical guidelines for the plugboard, the need to transmit settings, the vast numbers of codebooks, etc. But the numbers would have been more to their favor.

The rotor blades are blown off before they eject.

Look soon to RC hobbyists to be up in arms over proposed legislation (paranoid/agendabots) calling for sweeping bans after some douche straps something bad to a quad rotor.

The rotors are soo big they're moving a TON of air and that could provide enough lift. However my problem is with the camera angle...I can barely tell it's up, put the camera lower down idiots!