10/23 Raptor Video

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BoKu

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I'm still wondering what place in California is both qualified and willing to take Raptor in its current state and develop it into a marketable product. I for sure don't know all the composite aircraft development firms in the state, but I know a lot of them. And none of the ones I know seem like this is the kind of thing they'd want to get wrapped up in. So it will be interesting to see who he has in mind.
 

malte

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I'd like to hear from some of the torsional vibration experts on here...
I am not an expert, but I'll give it a try anyway. So please correct me, if I am wrong.

when he hits full power he says the violent shaking is the prop wash hitting the camera on a gimbal - and that he can't feel that sitting in the cabin...
No way this is due to propwash or any other aerodynamic "shocks" to set the camera in motion this way. Take a look at the streamlines of propellers:
You do not have a radial aerodynamic component significant enough to set the camera in motion. The vibration we see in the video is purely based on base excitation of the camera mount.

If the system hits the (vicinity of the) resonance frequency of the camera plus mount (essentially only a simple spring-mass system), you will have as much vibration energy transferred into the camera as possible. Vibration absorbers work that way, they only connect a spring and mass without damper to transfer vibration energy. So if the vibration on the camera is having high amplitudes, this must not necessarily conclude that the amplitude of the wing is extreme, it might be a resonance of the camera plus mount.

This is one of the reasons he might not feel significant vibrations in the cockpit (or around the fuselage).

The second reason is, that he sits pretty much between two dampers (the landing gears with shock absorbers and tires). You will not see a significant amplitude of any vibration there, whereas the camera is mounted at a free end of the structure that can vibrate freely and thus will always see higher amplitudes.

I have done a FFT analysis on the video sound.
Screenshot_20210408-165112 (2).png

He claims to run the engine at 3600RPM and the Prop at 2400RPM.

The engine is a six cylinder Diesel, so I assume that we have one combustion every 120° crankshaft rotation, or three combustion each revolution. 3600 RPM equate to 60 revolutions per second or 180 combustions per second. And sure enough we see a peak at around 190 Hz.

He has a 5 blade MT prop mounted that the claims runs at 2400 RPM or 40 revolutions per second. One blade passes the exhaust pipe two times per revolution, equating to 5 passes per revolution. So we expect to see 200 passes per second.

The FFT shows peaks at around 193 Hz, 296 Hz, 394 Hz, 480Hz, 586 Hz, 680 Hz, 773 Hz, 867 Hz, 973 Hz (the dominant frequency peak), 1066 Hz, 1172 Hz.

196 Hz and the multiples (394 Hz, 586 Hz, 773 Hz, 973 Hz and 1172 Hz) can be attributed to the Engine, Prop/Exhaust and the corresponding harmonics, where 393 Hz, 773 Hz and 1172 Hz being the octaves of the basic frequency.

I do not know exactly where the 296 Hz Peak originates, but it is roughly 5 times Engine RPM. The harmonics add to the 586 Hz Peak and seem to be responsible for the 867Hz peak.

The 480 Hz peak could be prop or engine, but it adds to the dominant 973Hz peak.

If I have counted correctly, the camera swings with around 10 to 12 Hz. However, I think I have noticed that the wing swings with around 2.5-3 Hz, what is what we would expect as a basic frequency for a carbon fibre wing of this span (for reference, the DG-200 swings with a natural frequency of 2 to 2.6 Hz depending on 15/17 meter configuration or carbon/glass spar).

So basically it is very possible that the engine/prop combo excites the wing in its resonance frequency. As I understand the system, the prop is mounted directly to the airframe (for whatever reason) and thus the prop excitations also transmit directly into the structure.

I agree with the notion of further investigation with a couple of accelerometers (even some cellphone-readouts would be better than nothing). However, I still think this would only serve engineering class because the list of issues with this airframe is too long to be addressed economically.
 

rv6ejguy

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Nice analysis.

The engine is mounted through typical rubber mounts.

I've dealt with many instances of TV and excitation of various airframe parts on several different airplanes. This is a classic example IMO. You can hear a period right near idle and that has always been there. This one near max rpm is a new one after the engine change.
 
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Dead on Time

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The engine is a six cylinder Diesel, so I assume that we have one combustion every 120° crankshaft rotation, or three combustion each revolution. 3600 RPM equate to 60 revolutions per second or 180 combustions per second. And sure enough we see a peak at around 190 Hz.

Pretty sure the TDI 3.0L V6 engine is a 90 degree engine 'odd fire' so 90 degree and 150 degree combustion events.

DoT
 

flywheel1935

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As Malte says> As I understand the system, the prop is mounted directly to the airframe (for whatever reason) and thus the prop excitations also transmit directly into the structure.

Correct, the prop ,via the PRU is "hard Bolted" to the engine mount, whilst the engine is "Soft Mounted" via compliance bushings to said engine frame. with 'cush-drive' to the PRU cambelts.
The Cush-Drive itself was giving some issues a few YT videos back, but, as per usual, this has now been parked in "I,m fine with that" vault. 🙃
 

MechEngr32

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I'm still wondering what place in California is both qualified and willing to take Raptor in its current state and develop it into a marketable product. I for sure don't know all the composite aircraft development firms in the state, but I know a lot of them. And none of the ones I know seem like this is the kind of thing they'd want to get wrapped up in. So it will be interesting to see who he has in mind.
My best guess would be ICON Aircraft . They are good at convincing non-pilots to buy the A5 (40 units/year?). They would get an instant customer base of position holders and they have experience with composite manufacturing. Not sure how many position holders are left but to ICON it could be 50 years worth of A5 buyers. Time will tell I guess.
 

flywheel1935

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Will two foundering projects be better together?
Interesting point, both projects are 'vanity projects' that appeal to people who want to bask in the reflected glory by association. ICON promote the lifestyle we all dream off but rarely will get the chance to enjoy. Raptors flying SUV appeals to the family guy who wants weekends away 2-3000 miles from home, again a dream 99.999999999 % of people will never be doing.
Neither will gain mass sales, so it's not even worth thinking about, only Cirrus got the GA world to listen, and their product actually does 'what it says on the tin', but at significant cost !!!!
 

rv6ejguy

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Not to worry about production. That's years away, if ever, given the current state of the design...

So many companies fall into this same old trap:

1. Promise the moon without even having built or flown the airplane.

2. Somehow come up with a kit price before step 1 is complete.

Peter was talking about training, air taxis and certification way back in 2013. Completely naive.

Though I like what the guys at Dark Aero are doing, they are following this same path with step 1 and 2. No way this plane will meet the cruise speed specs they are forecasting IMO either.

Why can't folks designing new aircraft just wait until the prototype is built, flown and tested before they open their mouths? Usually they are forced to eat their words or revise their overly optimistic predictions- performance downwards, weight and cost upwards...
 
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BJC

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They are good at convincing non-pilots to buy the A5 (40 units/year?).
Given ICON’s capitalization, 40 aircraft sold per year is abysmal.

Not sure how many position holders are left but to ICON it could be 50 years worth of A5 buyers.
I don’t believe that there would be more than a handful of Raptor buyers, and those will be ignorant dreamers who never will fly one.


BJC
 

BJC

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Neither will gain mass sales, so it's not even worth thinking about, only Cirrus got the GA world to listen, and their product actually does 'what it says on the tin', but at significant cost !!!!
Yes, it is costly, but there is a market for it. Over 8,000 produced and sold to date.


BJC
 

Hephaestus

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Yes, it is costly, but there is a market for it. Over 8,000 produced and sold to date.
Market for fork tailed doctor killers is probably bigger now than ever... Between security arrive 2 hours ahead + close contact risks during covid and reduced schedules...
 

BBerson

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Neither will gain mass sales, so it's not even worth thinking about, only Cirrus got the GA world to listen, and their product actually does 'what it says on the tin', but at significant cost !!!!
Cirrus floundered at the beginning with a pusher. Pusher has never seen a mass certified market, as far as I know.
Cirrus abandoned the pusher.
 

231TC

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I'm still wondering what place in California is both qualified and willing to take Raptor in its current state and develop it into a marketable product. I for sure don't know all the composite aircraft development firms in the state, but I know a lot of them. And none of the ones I know seem like this is the kind of thing they'd want to get wrapped up in. So it will be interesting to see who he has in mind.
I'm guessing it isn't an existing qualified composite aircraft development firm. That's not the way he operates. He thinks he's smarter than everyone already in the business, so he's not going to use an established company to carry out his "revolution" in GA. Probably just some software guys with money to blow, who intend to build production from scratch.

I don't know any more than anyone else about his production plans, but I learned that a guy named Kevin Halverson is part of "the team on the west coast." He's involved in several startups, mostly unrelated to aviation. But he is also CTO of a company called RPR Aero. Almost nothing about the company online and nobody I know in aviation or venture capital has ever heard of it, but he/they have a patent application involving wing spars with "integrated power cells." I didn't look too closely at that, but at first glance it looks like investor bait. Anyway, that invention is unrelated to Raptor, but the guy is part of the team so I'd guess his company is involved, too.
 
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