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Size Constraint


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PAV X Dec. 11, 2017, 7:23 a.m. PST
@Ave Zoid
https://www.youtube.com/watch?v=QSdwNl-9mPU
Attachments

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PAV X Dec. 11, 2017, 5:52 a.m. PST
@Ave Zoid
https://www.youtube.com/watch?v=lcs0dMcTv9I

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PAV X Dec. 11, 2017, 5:52 a.m. PST
@Ave Zoid
https://www.youtube.com/watch?v=Qv3k49QVzLM

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PAV X Dec. 11, 2017, 5:49 a.m. PST
@Ave Zoid
Yes, its a really bad idea...

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Ave Zoid Dec. 11, 2017, 12:28 a.m. PST
@PAV X
I am sure you all have seen the other "deathchair" prototype.

https://youtu.be/ALYECvs06XI

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ExpAir Dec. 10, 2017, 11:25 p.m. PST
what exactly is single string design

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Ken Burner Dec. 10, 2017, 8:14 p.m. PST
@ExpAir
With that known (possible spin on single engine loss) I'd say you might consider some redundancy planning.

Ironic, as I'm typing this I'm watching the series "Air Disasters."

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Ken Burner Dec. 10, 2017, 8:09 p.m. PST
@ExpAir
I think the main spar would be a primary structure subject to the 1.5 load rule. As to a single fuel line feeding 4 engines on a plane, I believe the single fuel line would be considered a single point failure BUT since one could normally glide a plane to a safe landing, it would mean you that met the "systems or components which, in the event of their failure, permit safe landing of the operator, may be of single string design."

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ExpAir Dec. 10, 2017, 7:58 p.m. PST
well - considering i have at least 12 motors - im safe on the motors - but lest say for argument I didnt, lets say i only had a large left fan and a large right fan, and I loose 1 of them, i will go down like a ton of iron ore - as I cannot glide on 8foot wingspan, or more accurately, I can glide, but not in a way that causes a safe arrival with the operator back on the planet :)

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Ken Burner Dec. 10, 2017, 7:55 p.m. PST
On a bi-plane, loss of a motor/prop would not be a single point failure as loss of any one motor/prop would not result in loss or "limb or life."

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Ken Burner Dec. 10, 2017, 7:52 p.m. PST
The primary structure (as it means to me) in the case of the quad chair, means the chair and motor/prop arms (the fuselage.) That has to be documented to be stress-able to 1.5 times expected load. Each of the 4 motors and props would be subject to the single failure point rule.

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ExpAir Dec. 10, 2017, 7:48 p.m. PST
so yes i see now - unless the chair could sustain a motor failure and survive, it would not class as human ratable. The most suspicious point of failure by my observation on that design is the mounting bracket - obviously designed for light loads only. anyway - yes I will need to analyse my design carefully for single point failures - which i would assume could even mean a fuel line running to all motors - or even main spar strength

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ExpAir Dec. 10, 2017, 7:44 p.m. PST
ok - found it
I will reproduce the relevant section here so we can look at it

Safety
Human-ratable

The intent of this competition is to develop technologies that can be rated for people to safely fly in the future. Consequently, the competition requires that all device architectures are, at the fundamental concept level, "human-ratable." The organizers define "human-ratable" as follows:

A device that has no systems or components, except for primary structure, in which a single point failure results in loss of an operator's life or limb.

Systems or components which, in the event of their failure, permit safe landing of the operator, may be of single string design.

Structure and component suitability

The primary structure may be a single point of failure if:

adequate proof testing is performed, or
it is designed to loads significantly higher than expected loads (safety factor ≥ 1.5) and its structural integrity is regularly inspected.
Adequate quality, performance, and service life of all components must meet appropriate requirements for the intended application.

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Ken Burner Dec. 10, 2017, 7:40 p.m. PST
So in the case of the quad prop chair video, I think the rules would require two motors and two props on each corner for that type configuration unless the remaining three motor/props could handle the load. At least that is how I interpret the rules. And a beefier chair!

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Ken Burner Dec. 10, 2017, 7:36 p.m. PST
As I read it it is pretty clear, no single point failures are acceptable.

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ExpAir Dec. 10, 2017, 7:31 p.m. PST
Would be interesting to get some official clarification on safety and when a craft would be deemed unsafe

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Ken Burner Dec. 10, 2017, 7:26 p.m. PST
@ExpAir
Or of course a parachute or wings or something else could bring it down safety.

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Ken Burner Dec. 10, 2017, 7:24 p.m. PST
@ExpAir
I think that they do disqualify it. If the right front motor/prop failed, the whole craft would fail and descend tumbling. That is, unless the left rear motor/prop would reverse (providing down thrust instead of up thrust to balance the craft) and the left front and the right rear had enough thrust to maintain lift.

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ExpAir Dec. 10, 2017, 7:16 p.m. PST
@Ken Burner
oh ok yes I see what you mean. although I would add that the rules don't technically disqualify the craft as you describe - or did I miss something

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Ken Burner Dec. 10, 2017, 7:10 p.m. PST
@ExpAir
In this case I wasn't writing about preexisting work. The craft would't quality because it has no "back ups." A single point failure can occur on any of the 4 motor/props. So 8 motor/props would be needed and even at that, any one prop has to provide enough lift that two normally provided. Plus the primary structure, that being the chair and each prop "arm bracket" has to be sized to 1.5 times expected load. Looks like a standard chair to me, not one that would hold a 1.5 safety factor that the rules require (doesn't appear to handle 300 lbs. (136 kg.)