10/23 Raptor Video

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Rataplan

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thanks God he is ok. Imho this plane has a lot of skeletons in the cupboard ..load it on a truck and desiggn a new with in aviation common practice. next time a bolt of the steering can block something...
 

Andy_RR

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After investigation it turns out that the stake washer that locks the stake nut on the prop shaft failed. 40 hours of flying time ago I reassembled that using unused tabs on the washer and it had no play. I'm guessing it was just a poor design and as I said we're not using it going forward. Once the nut came loose the play in the shaft allowed the belts to jump on the pulleys and that was game over.

I'm guessing its poor design !!!!! mild understatement????
To be fair, I doubt anyone here would have predicted this failure mode prior to its actual occurrance. While I agree the design is something that even Heath Robinson would reject out of hand, it demonstrates how difficult developing a reliable reduction drive can be. Doing it in the air is a bit stupid, really, but still somewhat unavoidable at some stage in the development cycle.
 

lelievre12

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To be fair, I doubt anyone here would have predicted this failure mode prior to its actual occurrance. While I agree the design is something that even Heath Robinson would reject out of hand, it demonstrates how difficult developing a reliable reduction drive can be. Doing it in the air is a bit stupid, really, but still somewhat unavoidable at some stage in the development cycle.
Usually spline fretting precedes a lock tab failure as it takes motion against the nut to set up the metal fatigue in the tab. Many PSRU designs have suffered from it. It is premature to simply blame the tab without investigating deeper. The obvious conclusion is that Diesel torque pulses are difficult to engineer away. Something readily apparent when the original harmonic coupling failed. A larger coupling simply moved the issue farther downstream.
 

wsimpso1

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After investigation it turns out that the stake washer that locks the stake nut on the prop shaft failed. 40 hours of flying time ago I reassembled that using unused tabs on the washer and it had no play. I'm guessing it was just a poor design and as I said we're not using it going forward. Once the nut came loose the play in the shaft allowed the belts to jump on the pulleys and that was game over.

I'm guessing its poor design !!!!! mild understatement????
Lock tabs on nuts usually rely upon the nut not moving at all. If the joint being secured shifts back and forth, the joint will fail. This can happen for a variety of reasons: inadequate assembly torque, underestimated loads, undersized components, etc. Evidence will include fretting on splines, threads, washer and nut faces, etc, and then as the joint further loosens, impact damage on splines, bearing damage, etc.

If fretting is found, the joint was “working” and failure was imminent once that started. That it ran as long as it did might mean that the joint was only barely inadequate at this power level or it might mean that the nut had been under torqued before being locked. By extension, if the engine was making intended power instead of the low power apparent from performance, the joint was then either badly undersized or badly undertorqued, and this failure would have occured much more quickly. Perhaps other failure modes would have surfaced as well.

While this design may not be intended going forward, all of the failures seen can provide very valuable lessons learned for future designs.

Billski
 

dwalker

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Lock tabs on nuts usually rely upon the nut not moving at all. If the joint being secured shifts back and forth, the joint will fail. This can happen for a variety of reasons: inadequate assembly torque, underestimated loads, undersized components, etc. Evidence will include fretting on splines, threads, washer and nut faces, etc, and then as the joint further loosens, impact damage on splines, bearing damage, etc.

If fretting is found, the joint was “working” and failure was imminent once that started. That it ran as long as it did might mean that the joint was only barely inadequate at this power level or it might mean that the nut had been under torqued before being locked. By extension, if the engine was making intended power instead of the low power apparent from performance, the joint was then either badly undersized or badly undertorqued, and this failure would have occured much more quickly. Perhaps other failure modes would have surfaced as well.

While this design may not be intended going forward, all of the failures seen can provide very valuable lessons learned for future designs.

Billski

I think we all need to remember this is a prototype and like most prototypes is only a vague indication of the final form. I am not sure if the "not the redrive we will use" statement is accurate, but there were obvious problems with it.
Much like the weight, some of the control issues, lack of performance, never surprised me or were any indication of what the final product would be. Having been around automotive development and prototyping for a few decades you just cannot put much into the original version/test mules. I could point to several cars that the prototype/pre-production cars had massive issues and required serious reworks, even with teams of engineers and massive budgets behind them. My only problem really with what Pete has done is he was very, very public about the program in ways which most developers tend to avoid.
I am quite puzzled by the issues he is having with the powerplant, as there are many examples of diesel engines converted for aviation, and all of the issues he seems to be having should have been anticipated and planed around. In one aspect it is easy to speculate that maybe they were anticipated and like many concept cars, pushed ahead anyway along the mentality that it is "more important to show up with a product that looks good and kinda works that not show up with anything at all". Kinda like the Toyota Supra concept car back a few years ago that could barely back off the trailer and when it came time to do the press rides they were not allowed to take it above 2nd gear in the parking lot, and even then it still barely ran and overheated.

What I would like to see going forward is either a complete rebuild of the existing aircraft or a second aircraft incorporating actual solutions to the issues in the existing aircraft, including flight safety envelope, performance, weight, etc. Apparently they have the molds for the airframe, so hopefully with a little work to lighten the layup schedule, make the needed changes for control and cooling issues, they will be able to produce what is needed. At the same time I hope the powerplant will go through a proper revision with a critical eye on weight reduction, proper turbo sizing, and of course, a revamped and improved redrive.

Bill covers the locktab failure pretty well, cannot really add much to it, only give my opinion that if there was a nut that provided a single point of failure that would allow the belts on the redrive to come off, it would be something checked very often. Locktabs or not.
 

rv6ejguy

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At the higher weights being flown on the last 2 flights, higher power levels were probably being maintained for longer in the climb so this was a new realm as far as component stress went. This is why you beat on stuff on the test phase on the ground and over the airport. Testing at the highest weights ever, heading out over mountainous terrain, simply not a good decision. This should have been done over Valdosta along with full flight envelope expansion using experienced test pilots.

Babying engines and redrives hoping they will be reliable at higher power levels down the road isn't sound testing procedure.

I don't feel PM appreciated what a leap it would be from flying around at very low power settings at low altitudes, temperatures and weights compared to an airplane at gross, on a hot day, climbing directly to FL250 at 80%+ HP. Not even close to being the same. I discussed the turbocharging, cooling and intercooling requirements for diesels up at these altitudes before. This stuff is not trivial and virtually impossible for someone with PMs experience to accomplish with reliability. There are no passenger carrying turbo diesels certified for flight at 25,000.

The engine/ PSRU testing only nibbled at true durability testing, mirroring his flight testing procedures. Little, past proving it would fly, was accomplished.

That PM got this far through trial and error without serious injury is testament to his determination, drive and exceptionally good luck. I'm just glad he's still around to continue the project, hopefully under professional oversight.

As I mentioned way back in the original Raptor thread, PM would get a good education on this project and find out as many of us do, that we are not as smart as we think we are when we start out.
 
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Vigilant1

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Apparently they have the molds for the airframe, so hopefully with a little work to lighten the layup schedule, make the needed changes for control and cooling issues, they will be able to produce what is needed.
If the fuselage and flying surface molds are to be used in a production airplane, presumably the aerodynamics of that plane would strongly resemble this prototype (if the CG is the same). As the plane exists and can be made to fly, I would assume somebody will want to explore the aerodynamic envelope to see if there are any surprises before committing to this airfoil, incidence, shape, etc.
 

Turd Ferguson

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with all due respect, a the final version of a prototype should accurately define the form, function and performance of the production version. The plane should have been subjected to a complete test program, stability and control, performance, systems, etc. If there are operational kinks or the performance falls significantly short of goal, it's not ready for production. All this "prototype" has show is there is a lot of problems that need to be addressed. None of the faults have been resolved; instead they were covered with band-aids so the project could advance to the next failure.

Imagine building a production version of this plane right away (which was suggested by the builder).
What would you advertise? What has been verified by testing?
Takeoff distance: "Pretty dang long"
Landing distance: "Even longer than takeoff"
Climb rate: "300 fpm until engine overheats, then 50 fpm to max altitude"
Max altitude: "4986 ft on days when there are a lot of thermals" (Will require optional 'skyhook' to join mile high club)
Stalling speed: "Are you nuts?"
Top speed: "155 mph" (achieved during third emergency landing)
Pressurized: "Yes, but it does't work and besides, nobody will see how cool you look flying this plane if you are in the flight levels"
Air conditioned: "Yes, but can't turn it on because the heater has to be ON all the time for engine cooling - again it's about looking cool, not actually being cool"
 
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dwalker

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with all due respect, a the final version of a prototype should accurately define the form, function and performance of the production version. The plane should have been subjected to a complete test program, stability and control, performance, systems, etc. If there are operational kinks or the performance falls significantly short of goal, it's not ready for production. All this "prototype" has show is there is a lot of problems that need to be addressed. None of the faults have been resolved; instead they were covered with band-aids so the project could advance to the next failure.

Imagine building a production version of this plane right away (which was suggested by the builder).
What would you advertise? What has been verified by testing?
Takeoff distance: "Pretty dang long"
Landing distance: "Even longer than takeoff"
Climb rate: "300 fpm until engine overheats, then 50 fpm to max altitude"
Max altitude: "4986 ft on days when there are a lot of thermals" (Will require optional 'skyhook' to join mile high club)
Stalling speed: "Are you nuts?"
Top speed: "155 mph" (achieved during third emergency landing)
Pressurized: "Yes, but it does't work and besides, nobody will see how cool you look flying this plane if you are in the flight levels"
Air conditioned: "Yes, but can't turn it on because the heater has to be ON all the time for engine cooling - again it's about looking cool, not actually being cool"
I would agree with you if I felt like Peter was approaching this project like an aircraft, but it's obvious he's not. Everything he has done echos what I've seen in software, marine, and automotive prototype development.

I've felt for a while reading this and other threads that comparing anything Peter has done to anything in a typical aircraft manner is a waste of time. It's very obvious he doesn't even know what that is.
 

cheapracer

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You all knew it was "When", not "If", and yet you all suddenly go soft.

The guy is a danger to himself, others on the ground, and the homebuilder/kit industry.

I don't want to see him dead, or seriously hurt, none of us do, but he is putting others, who were lucky this time, in danger, and I have zero sympathy for him.

Re: An old Australian saying: "I hope he banged his head and knocked some sense into it".
 

lelievre12

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There are no passenger carrying turbo diesels certified for flight at 25,000
The Thielert/Continental CD155 was EASA certificated up to 25K. Intercooling was not that tricky and a single turbo only used.

F378D60F-3640-4198-919C-9BFEC5BC62E1.jpeg

However newer CD155 are no longer certificated that high. So it is true that none, including the CD300 powered DA50RG, can go that high anymore if certified. However for experimental the engine will do it as the specs show.

The advice was and remains that PM’s life would be so much simpler had he fitted just a single turbo.
 

231TC

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I would agree with you if I felt like Peter was approaching this project like an aircraft, but it's obvious he's not. Everything he has done echos what I've seen in software, marine, and automotive prototype development.

I've felt for a while reading this and other threads that comparing anything Peter has done to anything in a typical aircraft manner is a waste of time. It's very obvious he doesn't even know what that is.
True, but that's kind of been the point in criticizing his approach. We know it's different and coming from a different perspective and skillsets, but that's WHY it's so bad. Aircraft are extremely different than software, boats, and cars.

Marine is probably the closest comparison in terms of supporting life, but even that unforgiving environment is much less demanding than flying. You can be rescued from a ship experiencing catastrophic failures, even long after it has sunk. In the air, you are physically on your own until you get back on the surface. And things happen so much faster in the air.
 
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Toobuilder

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OK - reality check: how could you possibly fit the molds of the airplane "into" the airplane? By definition, the molds are larger than the part they create, and "should" be significantly heavier
 

Turd Ferguson

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Apparently there was little damage from this emergency landing
I can't believe nobody in Nebraska has a camera. I'd like to see if there was any apparent damage. Did he land gear up or gear down? I guess if it didn't flip on it's back, it was only because the engine was heavy enough to counteract that force.
I did see in a news clip that the FAA was called to investigate. I wonder if they will actually go and how deep will they dig?
cornfield.jpg
 
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bmcj

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If the fuselage and flying surface molds are to be used in a production airplane, presumably the aerodynamics of that plane would strongly resemble this prototype (if the CG is the same). As the plane exists and can be made to fly,
Yeah, but now when you make the new molds, the final product will have corn cob shaped depressions in it… kind of like dimpling a golf ball, but on a much larger scale.
 

231TC

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OK - reality check: how could you possibly fit the molds of the airplane "into" the airplane? By definition, the molds are larger than the part they create, and "should" be significantly heavier
I assumed he meant a lot of the smaller ones and not all of them. But now that you say that, I'm questioning whether I understood him correctly at all. I'm going to remove that part of the post.
 
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