10/23 Raptor Video

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wsimpso1

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For those more knowledgeable than me, what is the likely scenario should the PSRU haul in flight? Just prop stoppage! Prop loss? If he sheds the prop and maybe a bit more hardware, will Raptor be controllable with a sudden CG shift?
There a bunch of modes, so what would happen depends upon the failure that occurs. I do not feel like going through all of them, so let's get to consequences on this rear engine canard airplane:
  • If the prop stops, it drags;
  • If the prop windmills, it drags;
  • If the prop departs the airplane, drag is low, and CG shifts forward slightly - ship is still stable, might have issue with lifting the nose for flare and landing;
  • If the prop pieces hit anything, it can cause controllability problems;
  • If the prop and prop bearing system and/or engine or all come loose but do not leave the airplane, the CG will shift slightly aft, potentially rendering the airplane unstable in pitch and/or yaw;
  • If the prop and prop bearing system and/or engine or all come loose and leave the airplane, the CG aft will shift forward, the airplane will become very stable in pitch and yaw, may not be able to hold the nose up, may have compromised maneuverability and may not be able to slow down then flare for landing;
  • If equipment carrying oil and/or fuel is damaged during any of these events, a fire becomes possible.
Then there are a bunch that, if they happen slowly enough, you catch them before anything catastrophic occurs.

In short, just about all failure modes lead to a forced landing, some may adversely affect stability and/or control, some may force that landing to higher speeds and/or prevent flare for landing, and the plane may burn.

As to likely modes, the most likely is in several types. I can imagine:
  • Isolator failing with a loss of drive to the prop;
  • Belts failing in sequence with a loss of drive to the prop;
  • Propshaft or crankshaft extension bending or breaking, stopping the prop;
  • Propshaft or its bearing sets failing and the prop departing the airplane;
  • Parts from disintegrating drive and or damaged systems make for oil and/or fuel spill and fire;
  • Prop sheds a blade, then prop imbalance tears either the prop mount or the entire engine mount from the airplane;
  • Loss of drive to the prop results in immediate engine over rev and broken crankcase, oil and fuel spill, and fire.
Can you tell I was writing Failure Modes and Effects Analysis of systems since 1980? There are so many things that can go wrong in a system, and ALL of the failures that can produce them have to be put out of reach for a safe system to result. This is why I get freaked out about inventing a new PSRU.

Billski
 

wsimpso1

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Is there a way to reduce TVs ?
Start here: Torsional Vibration and Resonance - Basic Theory and Issues

The fact that a piston engine is running pretty much defines what we call the "forcing function". Firing pulses, pistons accelerating back and forth in the bores, the crank and connecting rod system do their own thing, then there are differences between banks, between cylinders, etc. More cylinders reduce all of the amplitudes while raising the range of frequencies. You can attach a torsional pendulum to the flywheel end of the engine - they are very effective at taking off whatever order of engine rotation you tune them for.

Once you have a set of vibrations making up your forcing function, you can deal with it by effectively isolating the engine from the rest of the system. Soft systems are nice, putting resonance below the lowest forcing frequencies you are worried over, and hopefully the rest are way above the highest frequencies.

Stiff systems are what we have in direct drive airplane engines with the prop hub bolted to the crankshaft flange. Stiff systems must put the lowest big resonance safely above the highest forcing vibration. Being successful on this can be elusive.

We have been doing this since the advent of rotating machinery and turbo machinery, so it is fairly well understood in some circles, and is traditionally taught in Engineering schools. Trouble is how many students never use it after graduation, and good luck after that.

Billski
 

wsimpso1

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I think he'd be better off if it was driving the engine. It would spin more slowly, and possibly stall. Letting it spin up would be bad, I think. I relate this to helicopter autorotations. Faster blade rotation produces more lift (drag in that world) than a slow rotation.
I keep hearing this, but have you ever played with a pinwheel? A freewheeled prop will run to a speed based upon its airspeed and pitch, and has no or little torque reaction, so can not generate much drag. Now if it is freewheeling and dragging the engine with it, yeah, it sucks up energy then.

Ideally, you could stop the prop, and this is usually done by feathering the prop when the engine fails.

The big danger I would worry over with a freewheeling prop is if it can overspeed the bearings and either lose the prop and shaft or start a fire. So, while doing FMEA of the thing, you identify the max freewheel rotation speed and make sure the bearings and shafts that might be spun with the prop are safe to the highest rpm you can freewheel the prop to.

Billski
 

BBerson

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Certified airplanes sometimes have rpm avoid zones.
Marc's prop came off with some airframe damage but the landing was a success.
 

BJC

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I keep hearing this, but have you ever played with a pinwheel? A freewheeled prop will run to a speed based upon its airspeed and pitch, and has no or little torque reaction, so can not generate much drag. Now if it is freewheeling and dragging the engine with it, yeah, it sucks up energy then.
Dirt simple demo here


BJC
 

rv6ejguy

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Is there a way to reduce TVs ?
@rv6ejguy @Malish You are talking about restricting the RPM range. How common is this when designing a new aircraft ?
I have hundreds of customers flying auto conversions with PSRUs and almost every one has some rpm band that is best avoided. Hopefully it's narrow and out of the normal flight rpm range. I have one at 1050-1250 rpm so I generally either idle at 1000 or above 1300. I added some flywheel mass a few years back and this drastically reduced the TV in that range though it's still detectable.

steel.jpg

Sometimes a small change in inertia somewhere in the system can have drastic effects. One customer with an LS powered Velocity had tremendous TV issues (cannot even run the engine at the resonant rpm it shakes so bad) using the same drive as another customer with an LS. The difference was the propeller used- he had a prop weighing about 45 pounds, the other setup used a prop weighing around 20 pounds and had no such issue.
 
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MechEngr32

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If ICON builds 40 aircraft per year with 200+ people and has one LSA "certified. Alexander Schleicher builds 100 aircraft with 100 people per year and has a current choice of 15 Models/Versions with 10 powered gliders among them, two of which are electric and 4 of the models having their first flight in the past 10 years. I think if I were in need of a manufacturer who has experience in efficient production of complex composite aircraft with a high quality standard, I'd talk to Schleicher (or Schempp-Hirt, HpH, Jonkers...). ICON doesn't spring to mind directly.



I agree completely with your assessment. I offered up ICON as a possibility not as a “good logical” choice but one that fits the Raptor story line. Lots of hype, lots of marketing, lots of not much reality. The ICON CEO certainly seems to be able to attract investors and get media attention. Apparently there is a “California Company” interested. The unveiling video, if it comes to pass, will certainly be interesting.
 

Vigilant1

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Apparently there is a “California Company” interested. The unveiling video, if it comes to pass, will certainly be interesting.
If there is an announcement, and if the "California company" is a publicly traded company, it might be tempting to become one of those short-selling vultures that Elon is always complaining about.
 
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TarDevil

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There a bunch of modes, so what would happen depends upon the failure that occurs. I do not feel like going through all of them, so let's get to consequences on this rear engine canard airplane:
  • If the prop stops, it drags;
  • If the prop windmills, it drags;
  • If the prop departs the airplane, drag is low, and CG shifts forward slightly - ship is still stable, might have issue with lifting the nose for flare and landing;
  • If the prop pieces hit anything, it can cause controllability problems;
  • If the prop and prop bearing system and/or engine or all come loose but do not leave the airplane, the CG will shift slightly aft, potentially rendering the airplane unstable in pitch and/or yaw;
  • If the prop and prop bearing system and/or engine or all come loose and leave the airplane, the CG aft will shift forward, the airplane will become very stable in pitch and yaw, may not be able to hold the nose up, may have compromised maneuverability and may not be able to slow down then flare for landing;
  • If equipment carrying oil and/or fuel is damaged during any of these events, a fire becomes possible.
Then there are a bunch that, if they happen slowly enough, you catch them before anything catastrophic occurs.

In short, just about all failure modes lead to a forced landing, some may adversely affect stability and/or control, some may force that landing to higher speeds and/or prevent flare for landing, and the plane may burn.

As to likely modes, the most likely is in several types. I can imagine:
  • Isolator failing with a loss of drive to the prop;
  • Belts failing in sequence with a loss of drive to the prop;
  • Propshaft or crankshaft extension bending or breaking, stopping the prop;
  • Propshaft or its bearing sets failing and the prop departing the airplane;
  • Parts from disintegrating drive and or damaged systems make for oil and/or fuel spill and fire;
  • Prop sheds a blade, then prop imbalance tears either the prop mount or the entire engine mount from the airplane;
  • Loss of drive to the prop results in immediate engine over rev and broken crankcase, oil and fuel spill, and fire.
Can you tell I was writing Failure Modes and Effects Analysis of systems since 1980? There are so many things that can go wrong in a system, and ALL of the failures that can produce them have to be put out of reach for a safe system to result. This is why I get freaked out about inventing a new PSRU.

Billski
Thanks!

And he doesn't wear a chute!
 

rbarnes

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I have hundreds of customers flying auto conversions with PSRUs and almost every one has some rpm band that is best avoided.
Many airplanes have this. My Grumman Tiger had a big plaque glued to the instrument panel "Do not operate at 1850 to 2200 rpm" due to the prop harmonics in that particular install and engine combo. Whole point in TV testing is to find those rpms, but some people think they can TLAR it... 🤦‍♂️
 

BBerson

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Dirt simple demo here


BJC
That is a bit too simple. In his test he has the fan blowing the flat backside of the prop. In flight the wind hits the curved frontside. I did it with my fan and my prop, big difference. It barely rotates in the correct orientation and doesn't hurt when sticking my finger in it.
 

PPLOnly

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Who know how this system will work in this aircraft with pusher prop in the back?
If the propeller falls off or seizes, it shouldn’t be an issue. Otherwise I’d imagine the lines will tangle in the propeller if there is forward speed. Go look at some YouTube videos of these deployments in flight and the chute goes up and back as it catches the wind.

In the second video shown in this clip you can see the lines go straight back for a period of time. He should have a method of shearing the prop first sequenced with the BRS system.

 

Hephaestus

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In the second video shown in this clip you can see the lines go straight back for a period of time. He should have a method of shearing the prop first sequenced with the BRS system.
Shearing prop isn't necessary. The lines are made with the theory that attitude/failure may cause propeller entanglement.

There's no reason to complicate unnecessarily. BRS, GRS and the smaller makers already account for this in the base design.
 

TFF

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I think the loss of prop is more likely the need for the BRS, but anyway it was discussed plenty in the previous zillion page thread. Nothing new under the sun here except watching.
 

henryk

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Who know how this system will work in this aircraft with pusher prop in the back?

=with GRS,

which was tested in real sytuation (unrecoverable spin of AEROMOBIL-3 !)



 
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ImperfectSense

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=with GRS,

which was tested in real sytuation (unrecoverable spin of AEROMOBIL-3 !)



Wow. First off, hard landing! Glad the pilot was ok. I do not see a full parachute in that image, just something that looks like a drogue? It's possible the full chute was removed by rescue crews before the photos were taken, but it's also possible that it failed in some way and that failure led to the hard (apparently nose-first) landing? But also, in terms of applicability to Raptor, that flying car has a much smaller diameter prop, presumably less horsepower, and more distance between the parachute deployment location and the prop...
 
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